Medical Response to Effects of Ionizing Radiation

MEDICAL RESPONSE TO EFFECTS OF IONISING RADIATION

Proceedings of a conference on Medical Response to Effects of Ionising Radiation held at Queen Elizabeth II Conference Centre, London, 28–30 June 1989.

MEDICAL RESPONSE TO EFFECTS OF IONISING RADIATION

Edited by

W.A.CROSBIE Authority Chief Medical Officer, UKAEA

and J.H.GITTUS Director, Communication & Information, UKAEA

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Preface

In 1987 an incident occurred in Goiânia (Brazil) which spotlighted the role which the medical community needs to play in coping with the effects of ionising radiation. A medical radioactive source was accidentally exposed and many people received varying doses, some fatal, of radiation. This accident, like the Chernobyl reactor accident, placed unprecedented demands on the local medical and emergency services, and it is with the response to such demands that this conference is concerned. The conference sets out various scenarios and then considers laboratory and clinical aspects of medical effects upon the individual. Then the responsibilities, plans and resources for coping with an event are covered. Finally the long-term effects of radiation, including epidemiological studies, are presented. Some prominent authors signalled their intention to use the conference as a platform for presenting new findings, and the speakers and chairmen were chosen for the authority which they bring to bear on these important topics. The conference is aimed at a general audience, and the papers are presented in a readily understood manner. It will be of interest to general medical practitioners, accident and emergency personnel, environmental health officers, environmental planning officers, community physicians, safety engineers, environmental scientists, epidemiologists and officials from both government and industry. It will also be of particular value to news and media personnel. W.A.CROSBIE J.H.GITTUS

Contents

Preface List of Contributors

v ix

The medical implications of nuclear power plant accidents J.G.Tyror

1

Setting the scenario—potential hazards of the nuclear fuel cycle R.J.Berry and N.McPhail

37

The medical management of radiation casualties A.W.Lawson

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Medical management of the patient immunosuppressed by ionising radiation J.C.Cawley The Goiânia accident J.R.Croft

75 83

Current radiation risk estimates and implications for the health consequences of Windscale, TMI and Chernobyl accidents 102 R.H.Clarke The role of biological dosimetry in a radiological accident in the UK D.Lloyd

119

Some priorities in experimental radiobiology G.E.Adams

132

Arrangements for dealing with emergencies at civil nuclear installations M.J.Turner and I.F.Robinson

151

The National Response Plan and Radioactive Incident Monitoring Network(RIMNET) M.W.Jones

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181

viii

The role of MAFF following a nuclear accident M.G.Segal Medical response to effects of ionising radiation: resources for coping with an event, the role of the Community Physician J.D.Terrell Local emergency arrangements for radiation accidents A.Jones Monitoring and assessment of radiation exposure from routine radioactive discharges, and its relevance to the question of disease clusters S.R.Jones

195

224 230

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Studies of leukaemia incidence in Scotland (Abstract) J.Urquhart

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The relevance of population mixing to the aetiology of childhood leukaemia L.J.Kinlen

272

The role of ionising radiation in the aetiology of the leukaemias R.A.Cartwright

279

A method of detecting spatial clustering of disease S.Openshaw, D.Wilkie, K.Binks, R.Wakeford, M.H.Gerrard and M.R.Croasdale

295

Prediction of the effect of small doses: inconsistencies in the epidemiological evidence (Abstract) 309

R.Doll

List of Contributors

G.E.Adams, Medical Research Council Radiobiology Unit, Chilton, Didcot, Oxon OX11 0RD. R.J.Berry, Health and Safety Directorate, British Nuclear Fuels plc, Risley, Warrington, Cheshire WA3 6AS. K.Binks, British Nuclear Fuels plc, Risley, Warrington, Cheshire WA3 6AS. R.A.Cartwright, Leukaemia Research Fund Centre for Clinical Epidemiology, University of Leeds, Department of Pathology, 17 Springfield Mount, Leeds LS2 9NG. J.C.Cawley, University Department of Haematology, Royal Liverpool Hospital, Prescot Street, PO Box 147, Liverpool L69 3BX. R.H.Clarke, National Radiological Protection Board, Chilton, Didcot, Oxon OX11 0RQ. M.R.Croasdale, Central Electricity Generating Board, Sudbury House, 15 Newgate Street, London EC1A 7AU. J.R.Croft, National Radiological Protection Board, Northern Centre, Hospital Lane, Cookridge, Leeds LS16 6RW. R.Doll, Cancer Epidemiology and Clinical Trials Unit, University of Oxford, Gibson Building, The Radcliffe Infirmary, Oxford OX2 6HE. M.H.Gerrard, Tessella Support Services, 104 Oak Street, Abingdon, Oxon OX14 5DH. A.Jones, County Emergency Planning Officer, Somerset County Council, County Hall, Taunton, Somerset TA1 4DY. M.W.Jones, Radioactive Substances Division, HM Inspectorate of Pollution, Department of the Environment, 43 Marsham Street, London SW1P 3PY. S.R.Jones, Environmental Protection Group, British Nuclear Fuels plc, Sellafield, Seascale, Cumbria CA20 1PG. L.J.Kinlen, CRC Cancer Epidemiology Unit, University of Edinburgh, 15 George Square, Edinburgh EH8 9JZ. A.W.Lawson, Company Chief Medical Officer, British Nuclear Fuels plc, Sellafield, Seascale, Cumbria CA20 1PG. D.Lloyd, National Radiological Protection Board, Chilton, Didcot, Oxon OX11 0RQ. N.McPhail, Health and Safety Directorate, British Nuclear Fuels plc, Risley, Warrington, Cheshire WA3 6AS. S.Openshaw, Centre for Regional Development Studies, University of Newcastle upon Tyne, Claremont Building, Newcastle upon Tyne NE1 7RU. I.F.Robinson, HM Nuclear Installations Inspectorate, Health and Safety Executive, St Peters House, Bootle, Merseyside L20 3LZ. M.G.Segal, Food Science Division, Ministry of Agriculture, Fisheries and Food, Ergon House, c/o Nobel House, 17 Smith Square, London SW1P 3HX. J.D.Terrell, District Medical Officer, West Cumbria Health Authority, West Cumberland Hospital, Hensingham, Whitehaven, Cumbria CA28 8JG.

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M.J.Turner, HM Nuclear Installations Inspectorate, Health and Safety Executive, St Peters House, Bootle, Merseyside L20 3LZ. J.G.Tyror, Director, Safety and Reliability Directorate, United Kingdom Atomic Energy Authority, Wigshaw Lane, Culcheth, Warrington, Cheshire WA3 4NE. J.Urquhart, Information and Statistics Division, Scottish Health Service, Common Services Agency, Trinity Park House, Edinburgh EH5 3SQ. R.Wakeford, British Nuclear Fuels plc, Risley, Warrington, Cheshire WA3 6AS. D.Wilkie, Windscale Laboratory, UKAEA, Sellafield, Seascale, Cumbria CA20 1PF.

THE MEDICAL IMPLICATIONS OF NUCLEAR POWER PLANT ACCIDENTS

J G TYROR Director, Safety and Reliability Directorate United Kingdom Atomic Energy Authority

ABSTRACT This paper examines the UK position regarding the potential for an accident at a nuclear power plant, the safeguards in place to prevent such an accident occurring and the emergency procedures designed to cope with the consequences should one occur. It focuses on the role of the medical services and examines previous accidents to suggest the nature and likely scale of response that may need to be provided. It is apparent that designs of UK nuclear power stations are robust and that the likelihood of a significant accident occurring is extremely remote. Emergency arrangements are, however, in place to deal with the eventuality should it arise and these incorporate sufficient flexibility to accommodate a wide range of accidents. Analysis of previous nuclear accidents at Windscale, Three Mile Island and Chernobyl provide a limited but valuable insight into the diversity and potential scale of response that may be required. It is concluded that above all, the response must be flexible to enable medical services to deal with the wide range of effects that may arise.

INTRODUCTION Recent accidents including those at Goiania and Chernobyl have highlighted the importance of an effective medical response in dealing with accidents involving radioactive materials. Although the chance of such accidents is extremely small, they have the potential to give rise to a number of unique features including radiation exposures, contamination and psychological stress. These features justify detailed consideration and the preparation of procedures to mitigate their consequences. The first section of the paper examines the philosophy and procedures behind the design and operation of nuclear power plant for ensuring that the likelihood of an accident is kept as low as reasonably practicable. This theme is developed in the second section which reviews the emergency procedures which are nevertheless available in case a

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severe accident actually develops. Section 3 examines experience gained from major accidents at Windscale, Three Mile Island and Chernobyl and considers the medical effects and the load placed on medical services. The final section builds on this experience and speculates on the likelihood of such a demand being made in the UK, the magnitude of the consequences and the scale of response that might be required. Although the paper is primarily concerned with the position in the UK, and in particular with that concerning nuclear power reactors, it is necessary to examine the international arena for experience of nuclear incidents and their medical response.

NUCLEAR POWER PLANT SAFETY Commercial nuclear power was born out of the wartime development of the atomic bomb and from the outset the potential hazards involved in working with significant quantities of radioactive material were well recognised. Safety and the need to prevent accidental release of radioactive material has therefore been of prime concern at all stages of the design and operation of nuclear plant. The responsibility for this lies clearly with the operator, who works within a strict regulatory framework. It is this combination of operator responsibility and regulatory control that provides the basis for nuclear safety within the UK.

Legislative Framework The primary legislation governing Health and Safety standards at civil nuclear installations in the UK is the Health and Safety at Work, etc, Act 1974 plus the associated provisions made under the Nuclear Installations Acts of 1965 and 1969. National legislation is, however, subject to guidance from the international arena. The International Commission for Radiological Protection (ICRP) made a number of recommendations in their Publication 26 in 1977 and some of these formed the basis for a Euratom directive. As signatories of the Euratom Treaty, the UK is bound to introduce legislation to at least the standard of the directive, which it did by the introduction of the Ionising Radiations Regulations in 1985. Commercial nuclear facilities including power reactors must not be constructed or operated without a nuclear site licence granted by the Health and Safety Executive (HSE). The HSE delegates its licensing and regulatory functions to the Nuclear Installations Inspectorate (NII) and they in turn ensure that all necessary arrangements for monitoring safety are made by the licensees. In addition to the HSE/NII, the nuclear industry is also subject to regulation by the Department of the Environment (DoE) and the Ministry of Agriculture, Fisheries and Food (MAFF). The DoE is responsible for granting authorisations for the storage and disposal of solid radioactive waste and also for the discharge of materials to atmosphere. Whilst MAFF are also involved in these activities, their main interests are in the authorisation of liquid discharges to rivers or sea and the impact of all discharges on the environment.

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The Nuclear Site Licence The issue of a nuclear site licence is dependent upon the satisfactory outcome of an NII review of proposals made by a prospective licensee. These proposals set out the safety principles on which the design of the nuclear plant is based and demonstrates how they can be met by the reference design. The NII must be satisfied from its examination of these proposals that the facility can be built and operated to the required standard of safety before recommending that a nuclear site licence be granted by the HSE (Ref 1). A nuclear site licence is generally accompanied by a series of licence conditions attached by the HSE as considered necessary in the interests of safety. The conditions are far-reaching and influence many areas including design, construction, operation, modification and maintenance of the facility in addition to the radiological protection of personnel both on and off site. They may be added to, amended or revoked at any time during the period when a licence is in force and this provides a very flexible regime of safety control.

The NII Safety Assessment Principles The fundamental principle applied in the UK to the regulation of industrial risks is the so-called As Low As Reasonably Practicable (ALARP) principle (Ref 2). This requires that operators take all reasonably practicable steps to reduce risks bearing in mind the cost of further reductions. Detailed guidance on how this principle is to be implemented for nuclear facilities is provided by both regulators and designers. In order to guide its assessors, the NII have developed a set of Safety Assessment Principles (Ref 3) to ensure consistency in the assessment of nuclear power plants of different designs. They include both limits and assessment levels which provide guidance as to whether all reasonably practicable steps have been taken to prevent accidents and, should they occur, to minimise their radiological consequences. The principles can be broadly divided into 3 categories; the first category provides a set of fundamental principles for radiological protection. The second category lays down basic principles for the limitation of the radiological consequences of operation for both normal and accident conditions and the third category is mainly concerned with engineering features of the plant. The semi-quantitative guidance provided by the NII, detailing the relationship between radiation dose to the public and accident frequency, is illustrated in Figure 1.

Safety by Design The primary objective of nuclear plant designers is to establish a good, safe design which fulfils the general plant performance specification. This specification includes details of the duty of the plant and, importantly, the requirement to meet the safety objectives and safety principles discussed previously. To this end, reactors tend to be conservatively designed with wide margins of safety and based on proven technology backed up by extensive testing and experience.

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Figure 1. NII safety assessment principles Defence in Depth—Multi-Barrier Principles One of the most important techniques employed by designers to ensure a satisfactory standard of safety is that of providing defence in depth. This provides the basic framework for most nuclear power plant safety and has been refined and strengthened through many years of application. The defence in depth concept compensates for both human and mechanical vulnerability and is centred on several levels of protection preventing the release of radioactive material to the environment. This multilayer principle is based primarily on a series of barriers which would need to be breached in turn before harm could occur to people or the environment. These are physical barriers providing containment of radioactive material at successive levels. They may serve both operational and safety purposes, or safety purposes only. The reliability of physical barriers is enhanced by applying the defence in depth methodology to each of them in turn and by protecting each of them by a series of measures. Each physical barrier is designed conservatively, its quality is checked to ensure that the margins against failure are acceptable and all plant processes capable of affecting it are controlled and monitored in operation.

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ERL: An Emergency Reference Level (ERL) is the radiation dose below which countermeasures to protect the public are unlikely to be justified. The National Radiological Protection Board (NRPB) is the UK body with responsibility for advising on this level, which is presently set at, for example, 100 mSv whole body dose equivalent for evacuation. See Section 2.

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A number of human aspects of defence in depth are also used to protect the integrity of the barriers. These include quality assurance, control procedures, safety reviews and other administrative areas within the general safety culture. Engineered Safety Features Wherever practicable passive safety features are incorporated into the design of nuclear power plant. In addition, engineered systems are provided to shut down the reactor, maintain cooling and limit any release of fission products that may occur should there be a fuel failure. Both the initiation and operation of these engineered safety features are highly reliable. This is achieved by the appropriate use of fail-safe design and by independence between safety systems and plant process systems. Systems are designed to ensure that failure of a single component does not cause the entire safety feature to fail (the single failure criterion). To guard against this, redundancy is built into systems to ensure that sufficient back-up is available in the event of a component failure. In addition, diversity is built into the design to ensure that safety mechanisms can be operated by alternative means should the primary means fail. Diversity is also important in ensuring that safety systems are not disabled by common mode failure conditions. Design Guidelines To assist in the practical application of these principles, the Central Electricity Generating Board (CEGB) publish design safety criteria (Ref 4) which apply to the design of all their nuclear power reactors. These are accompanied by a set of Design Safety Guidelines (Ref 5) which expand and interpret these criteria for the new generation of Pressurised Water Reactors (PWR) to be introduced in the 1990’s. They are similar to the NII Safety Assessment Principles but in some cases they are more stringent. Thus the CEGB state that accidents giving rise to doses of 1/10 ERL should not exceed 10-4 per reactor year compared with the NII figure of 1 in 3000 reactor years. The CEGB’s design guidance is illustrated in Figure 2. Accidents which would give rise to high off-site doses are covered by a target total frequency of 10–6 per year for all accidents giving a ‘large uncontrolled release’, with a maximum contribution of 10-7 from any single accident sequence. Some latitude is allowed for ‘uncontrolled releases’ at levels between 1 ERL and 10 ERL to have probabilities somewhat higher than 10-6.

Safety in Operation The way in which a plant is operated is dictated by the conditions attached to the nuclear site licence. These conditions ensure that all steps are taken by the licensees to protect both workers and members of the public from risks associated with the operation of nuclear reactors. These plants are regularly inspected by the NII to ensure that the conditions of the site licence are being complied with.

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Nuclear plant operating staff are of a high professional standing and are well qualified by both experience and training. Automatic systems ensure that plants operate within well defined safe limits and are designed such that any breach of these limits results in the plant shutting down. Reactor shutdown and other immediate emergency actions, are fully automatic on modern reactors and no input is required from the operator for about half an hour after they have shut down. This avoids the need for rushed decisions and enables the operator to take advantage of a pre-arranged formal system of technical advice. The training and re-training of operators on simulators to deal with such situations is required by the NII and is a standard part of operational procedure.

Figure 2. CEGB design safety criteria

Operational safety is also improved by incorporating lessons learned from incidents and experiences at other plants. Guidance on these matters will come from within the industry, from the HSE/NII, who must be informed of all incidents or potential incidents at nuclear installations in the UK, or from one of the internationally established agencies. These include: The International Atomic Energy Agency (IAEA) who investigate all serious radiological accidents and produce a detailed account from which all States may learn and hence avoid similar consequences (Ref 6). The International Nuclear Safety Advisory Group (INSAG) who advise on the safety of nuclear power plants. This body (established by the IAEA) serves as an international forum for the exchange of information on nuclear safety issues, and assists in the formulation of common safety concepts where appropriate (Ref 7).

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The Organisation for Economic Co-operation and Development, Nuclear Energy Agency (OECD/NEA). This organisation maintains an Incident Recording System (IRS) which can be used to provide information on particular operational experiences and incident events. The World Association of Nuclear Operators (WANO) which is also being established to disseminate information and to enable experience to be made more widely available to nuclear operators throughout the world.

EMERGENCY PROCEDURES Despite all reasonably practicable steps taken to design and operate nuclear plant to the highest levels of safety, there can be no absolute guarantee that accidents will never happen. It is therefore necessary to have emergency arrangements to deal with any accident that might occur. We are all too aware of the demands made on emergency services in recent years in responding to major non-nuclear accidents at Bradford City Football Club, Manchester Airport, Kings Cross Station, Clapham Junction, Lockerbie and Kegworth. The responses to these accidents have demonstrated that civil Emergency Plans exist and that the emergency and medical response capabilities are in place to deal with large scale accidents. The response to such accidents is planned at Local Authority level and is based on arrangements involving the Police and other emergency services. These plans need to be sufficiently flexible to cope with a wide variety of potential incidents. Despite the fact that nuclear accidents could give rise to a number of unique characteristics, the response required to protect the public is not vastly dissimilar to that required for other civil emergencies. Consequently, nuclear plant emergency arrangements are integrated with existing County Emergency Plans to ensure that, where possible, there is commonality in the response required by organisations which have a role to play.

Nuclear Emergency Planning It is a requirement of a nuclear site licence that the operator must have an emergency plan approved by the NII. Such a plan will provide a general framework with detailed arrangements focused on a reference accident. These plans are published and are available for public scrutiny. They are regularly exercised in the presence of the NII, to ensure their continued effectiveness in providing the necessary action, both on and off site, to protect members of the public. There is no single emergency plan which provides a universal optimum solution; each site will develop its own which will be subject to scrutiny by the NII. If the plant is new, emergency plans will have to be in place before the plant is commissioned. They are generally based on a tiered structure of alert: Building Emergency: Where the effects of an incident are confined within building. Site Emergency: Where there are no off-site effects.

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District Emergency: Where the incident gives rise to effects off site. The plans must be able to cope with a wide variety of accidents, ranging from those with potential for a release of little more than the routine radioactive discharge to those with potentially far reaching off-site consequences, possibly involving fire and injury to operating staff. The operator is at all times responsible for the on-site control of the incident irrespective of whether it has off-site consequences or not. The emergency plan for the affected site should contain a wide range of response capabilities which could be drawn upon to assist in the control of an incident. Off-site action involves the local emergency services and other authorities which may be called upon to implement measures to protect the public. As with any other type of civil emergency, the main responsibility for interaction with the public lies with the Police. The importance of the Police role and their experience in dealing with a variety of emergency situations cannot be too strongly emphasised.

Accident Consequences The consequences of an accident for operating staff and other workers at the plant could be severe, dependent upon its detailed nature and speed of development. If a serious accident did occur, it is likely to result in the release of volatile radioactive species including caesium, radioactive noble gases, and the radio-odines both in gaseous and particulate forms. This radioactive material would be transported by the wind from the affected plant and behave similarly to a plume of smoke, dispersing into the atmosphere and depositing some of its contents on the ground. The activity contained within the plume could give rise to radiation exposures to the public in a number of ways. The first consideration is the external dose from the airborne plume itself, material deposited on the ground and possibly on the skin and clothing of people in its path. The second, and possibly most significant route of exposure, is via the inhalation of material suspended in the plume. Finally and on a longer timescale, there are exposures arising from the consumption of contaminated food and water. The release of radioactivity resulting from a serious reactor accident should not cause any immediate health effects to the public but there are a number of countermeasures which could be appropriately taken to minimise longer term effects. These include: (a) Sheltering—The normal constructional materials used in houses and other buildings provide some protection from the effects of radioactive materials released to the atmosphere, up to a factor of ten dose reduction being obtained in favourable circumstances. (b) Potassium Iodate Tablets—If taken early enough, the thyroid can be blocked with stable iodine and this limits the absorption of radioactive iodine which may be present in the radioactive plume.

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(c) Evacuation—If it is practicable to evacuate personnel from the effected areas, doses arising from exposure to the plume itself and from activity deposited on the ground could be reduced. Furthermore, following the incident, checks would be made on foodstuffs and MAFF may consider it necessary to introduce restrictions on agricultural produce and dairy products. These countermeasures should reduce exposures and help ensure that the public are not exposed to significant risks to health. The Police, the Local Authority, MAFF and the Local Health Authority would all be involved in the emergency response. It is the responsibility of the Local Health Authority to ensure that the health of the public is considered at all times during the control of the incident particularly with regard to countermeasures. Upon being informed of the incident, representatives from all organisations with a role to play would proceed to the local Operational Support Centre (OSC). Once established, the OSC becomes the focal point for liaison activities and the co-ordination of advice to all outside organisations. Upon declaration of an emergency a Government representative would be dispatched to the OSC to act as Government Technical Adviser (GTA). His principal task is to preside over all off-site developments and to ensure that consistent advice is given to all interested and involved parties including Government departments and the media.

Medical Aspects There are many important aspects which must be considered for an emergency plan to work effectively. The arrangements must include procedures for clarifying responsibilities, ensuring that effective teams can be readily mobilised, providing robust communications facilities, manning of control, support and media briefing centres, etc, etc. We are primarily concerned, however, with the medical implications of accidents and therefore attention is focused on these.

The Medical Response for On-Site Personnel Nuclear establishments are generally well drilled in their response to accidents/ emergencies. Each establishment will have its own emergency instructions, exercised on a scheduled basis and personnel working in affected areas should follow these instructions. Dependent on the type of emergency these may require staff to stay indoors (shelter) or possibly to evacuate to a local assembly point. Any monitoring and decontamination of personnel that may be required can be arranged on site since facilities are available for showering, change of clothes and health physics monitoring. In the event of a major accident it is possible that workers or personnel involved with bringing the incident under control may require medical treatment. Most nuclear establishments have on-site medical services which are geared to deal with emergencies including those requiring decontamination procedures. Medical staff are on call at every site and if conventional injuries allow, the medical centres would be used to receive, decontaminate and sort casualties prior to transfer to hospital.

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The fact that a nuclear accident could result in demands being made on NHS hospitals and on the Health Service generally has long been recognised. Operators are therefore responsible for ensuring, in consultation with Local Health Authorities (in Scotland the Health Boards), that arrangements exist with particular hospitals for emergency treatment of personnel injured on a nuclear site (Ref 8). It is unlikely that patients would be able to be segregated at the scene of the incident and it is upon arrival at the main co-ordinating hospital that initial sorting of patients would be performed. Personnel who have neither been irradiated or contaminated could, if not in danger from conventional injury, be transferred to outlying hospitals without facilities for handling contaminated patients. Subject to any immediate life-saving and rescue measures, special care should be given to the handling of persons who have been contaminated by radioactive material or who may have been exposed to very high levels of radiation. Whilst there are a considerable number of hospitals able to deal with contaminated casualties, there are very few with the facilities required for the care of patients who have received high external doses. Contaminated Casualties It is possible that personnel directly involved in the accident or involved in actions to mitigate the consequences may have become contaminated with radioactive material. Whilst there may be more immediate life-threatening symptoms associated with their injuries, care must be taken to reduce spread of contamination. This would limit internal exposure of both the patient and the people dealing with his injuries, ie ambulance men, medical staff, nurses, etc. It would also reduce the risk of contaminating ambulances, hospital wards, treatment rooms and corridors. This is an area of continuing consideration. Thus, for example, workers at the UKAEA’s Dounreay establishment are developing a plastic envelope for preventing the spread of contamination from accident victims. This consists of a PVC base with heavy-duty “ding-film” sides. The envelope is opened out and placed on the stretcher and the casualty is laid on top. The sides are then wrapped round the person as required. These can be partially rolled back to allow access to local wounds or even cut and then re-sealed. As far as possible contaminated patients would be treated at hospitals having suitable facilities, ie a medical health physics team. Dependent upon the scale-of the incident it may be necessary to establish temporary contaminated patient facilities within the smaller hospitals but arrangements for this would have to be formulated at the County emergency planning level and outline arrangements included in the emergency plan. Irradiated Casualties Irradiated casualties present a different problem. As with contaminated patients the first priority is the treatment of any life-threatening conventional injuries. This should be followed by decontamination processes and collection of blood samples which, together with analysis of personal dosemeters, would allow an assessment to be made of the extent of the radiation injury. Only those who have received doses of between 1 and 10–12 Gy (Gray)2 will benefit from supportive care (Ref 9). Very few hospitals have the

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sophisticated protective isolation facilities required for such care and it is likely that they would already be fully occupied. Arrangements are in place for the Royal Marsden Hospital to receive any irradiated casualites from CEGB sites.

The Medical Response for the Public Off Site It is important to stress that there would be few, if any, clinical effects manifested amongst the general public. Consequently it is only on-site personnel who are likely to require early hospital treatment. It is possible that in a major accident some members of the public close to the plant would become contaminated to an extent requiring decontamination and receive radiation doses considerably greater than those arising from natural background radiation. Whilst this should not result in any early health effects, medical counseling may be necessary for re-assurance purposes. Guidance for the Imposition of Countermeasures—ERLs The Local Health Authority would be involved in any decisions involving the issue of potassium iodate tablets to the public and they would also be consulted regarding other countermeasures under consideration. Guidance on the circumstances under which countermeasures might be taken is provided in the UK by Emergency Reference Levels (ERLs). These were initially recommended by the Medical Research Council in 1975 and subsequently revised by the National Radiological Protection Board (NRPB) in 1981 (Ref 10). The ERLs provide an aid to decision-making in the early stages following an accidental release of radioactive material into the environment, or in anticipation of such an event. Following this initial period it is expected that a team able to advise on continued protection measures would be assembled and the ERLs may not then be appropriate. The NRPB recognise the different risks and social costs associated with the various countermeasures and have recommended a lower and upper level of estimated dose for each. If the lower level is exceeded the countermeasure should be actively considered and taken, unless circumstances dictate otherwise. If predicted doses are higher than the upper level, the Board then considers the countermeasure to be essential. Figure 3 presents a summary of the Board’s recommendations. ERLs can be regarded as “primary limits” but in order to provide guidance in the aftermath of an incident it is necessary to compare measured data with Derived Emergency Reference Levels (DERLs). These are practical quantities which can be directly compared with environmental measurements to assess the seriousness of the release and help form judgements on the need for protective countermeasures. These intervention levels are determined in advance and agreed with theappropriate regulatory

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For an explanation of health physics units and terms please refer to Appendix 1.

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appropriate regulatory bodies. It is important, however, that they should always be seen as providing guidance rather than specifying a level at which action must be taken. Figure 3 An illustrative summary of the emergency reference levels recommended by the NRPB

Source: ERL2 (NRPB) 1977

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Distribution of Stable Iodate Tablets Administration of stable iodate can reduce the uptake of radio-iodine which would otherwise concentrate in the thyroid gland. It has been shown experimentally that a dose of 100 mg of potassium iodide is virtually 100% effective if taken immediately or at the time of exposure to radio-iodine, 75% effective if taken 1.5 hours afterwards, and 50% effective if taken 5.5 hours later (Ref 11). For most populations evidence shows that risks to individuals of sideeffects caused by taking stable iodine are generally very low, but there is little guidance on the quantities which should be administered. Populations living close by UK nuclear facilities know of the existence of stable iodine tablets and are aware of predetermined plans to distribute them.

Brief Comparison of the Emergency Planning Practices of Major Nuclear Countries The nuclear emergency planning practices for countries with a significant nuclear power programme were reviewed following Chernobyl. There are differences related to the tiered organisation of Government and to the type of power reactor or nuclear facility being operated. Most countries, including the UK, place the responsibility for off-site emergency response with Local Government and rely on Central Government Departments to provide operational support. In the UK these would include The Department of Energy, DoE, MAFF, etc. In general, the emergency plans vary in their sophistication between countries but they are broadly similar because the radiological aspects are based on the recommendations of the ICRP. The differences lie mainly in the allocation of responsibilities and there are no areas where the UK plans appear to be significantly less stringent.

MAJOR ACCIDENT EXPERIENCE As the previous sections have shown, UK nuclear facilities are designed to be robust and they are operated within a strict regulatory framework. The limited number of nuclear accidents both in the UK and abroad is testimony to the high level of safety adopted in the operation of nuclear facilities world-wide. It is important, however, to analyse accidents which have occurred to see if lessons can be learned and to examine the implications for medical services. CRITICALITY INCIDENTS WITHIN THE NUCLEAR INDUSTRY An example of where previous experience and analysis of accidents has heavily influenced the evolution of present-day policy is in the field of nuclear criticality safety. These involve accidents in plants intended for operation with sub-critical quantities of fissile material or in experimental facilities where criticality was achieved unintentionally. There have been 37 reported criticality accidents since the mid–1940’s but they now occur less frequently (3 within the last 23 years). Analysis of these accidents has provided valuable guidance regarding principles of criticality control and an insight into the biological effects of high doses of gamma and neutron

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radiations Of these 37 accidents, seven gave rise to a total of 9 deaths. The types of incident are summarised in Table 1 below:

TABLE 1 Summary of criticality incident types (ref 12)

Amongst these accidents there have been 8 well documented criticality excursions in chemical processing plant, all occurring with aqueous solutions of highly enriched uranium or plutonium. These 8 accidents resulted in 2 deaths and 19 workers being significantly over-exposed to radiation, but the general public was not endangered by any of these excursions. The accidents were not caused by misleading criticality information or errors in its interpretation, but by difficulties with equipment, procedural inadequacies and violations, or a combination thereof. Full details of the 8 chemical processing plant criticality accidents can be found in Reference 13, but the general features are summarised in the Table 2 below. In a number of instances the radiological consequences of incidents in unshielded facilities have been limited by evacuation of personnel alerted by alarms. Especially for prolonged and multiple excursions, alarms and subsequent evacuation must be credited with saving lives. It is important therefore that high integrity alarm systems are fitted in areas where there is potential for an accidental criticality excursion. The 2 fatalities amongst this group of accidents were suffered by personnel within 1m of an excursion and significant exposures were received by personnel standing up to a distance of 15m away. By normalising data from a number of criticality incidents it is possible to make broad deductions as to the fall-off of dose with distance and it is concluded that within approximately 3m of an excursion, lethal exposures can be expected. At a distance of 20 m the exposure is approximately 0.25 Gy, a level at which effects are generally not medically detectable. These distances are quite comparable to those considered dangerous for plant subject to moderate chemical explosions.

*From Ref 14

TABLE 2 Criticality accidents in processing plants*

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The concentration of criticality accidents in chemical plants, 5 in the period 1958 to 1962, can be partly attributed to increased production of highly enriched uranium and plutonium without corresponding growth and sophistication of the facilities. As a result of this cluster of accidents, however, techniques for criticality control were refined and a number of facilities were modernised resulting in an improvement of the accident record. In terms of a medical response, acute effects arising from criticality accidents generally involve a limited number of on-site personnel. For accidents which occur outside shielding, external exposures to both gamma and neutron radiations are the principal concern and these can vary from a fraction of a Gy up to 10’s of Gy. Consequently there is a corresponding range of health effects, ranging from small exposures with no medically detectable effects through to fatalities resulting from high doses. The LD50/30, ie the dose expected to be lethal to 50% of those people exposed within 30 days of exposure is in the region of 4–5 Gy. Symptoms differ, however, dependent on dose but for lethal doses the time before death decreases with increasing dose, eg: An operator exposed in an Argentinian accident in 1983 received approximately 20.6 Gy/gamma and 17 Gy/neutron. He was coherent following the incident but 20 minutes later he began vomiting. He remained lucid until 4–5 hours before his death which occurred 2 days later.

WINDSCALE FIRE: 1957 Brief Description of Incident The Windscale Piles were, in effect, a very early, simple type of nuclear reactor whose main use was the production of material for the weapons programme. In essence they were large blocks of graphite, honeycombed with horizontal channels in which natural uranium fuel, canned in aluminium was made critical. Cooling was achieved by passing air over the fuel on a once through basis. This was then discharged to atmosphere through the distinctively shaped chimneys which housed filters to remove particulate material. It must be stressed, that these reactors were rather crude by modern standards and bear little resemblance to the sophisticated commercial reactors used for the generation of electrical power today. The accident occurred during the routine, controlled release of stored Wigner energy from the graphite of one of the piles. This operation started on 7 October 1957 and initially followed a normal course. On 9 October, however, it was noted that some of the recorded temperatures in the Pile seemed to be abnormal, and at noon on 10 October an air sample taken in the open showed radioactivity levels to be significantly higher than normal. Operating staff initially thought that a fuel cartridge had burst but at 1630 a visual inspection revealed glowing fuel cartridges in over 100 channels. Shortly after midnight the Police were warned of the possibility of an emergency and during the 11th and 12th October 1957 water was used to cool the Pile and extinguish the fire (Ref 15).

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Measures Taken to Protect the Workers Once it was established that air contamination levels in open areas on site were higher than normal, contractors working on the construction of the Calder Hall reactors were sent home and workers elsewhere on the Windscale site were given instructions to stay indoors and to wear respiratory protection. The aluminium cladding in many of the fuel cartridges failed and fission products were released into cooling channels. Much of the radioactivity was retained on the filters but there was clearly some release from the chimney stack. The most radiologically significant elements released in the fire were Iodine–131, which following either ingestion or inhalation concentrates in the thyroid, and Caesium–137, a longer lived nuclide which irradiates the whole body both when ingested or inhaled, and via external radiation. Radiation doses received by workers at the plant as a result of the accident were not excessively high. During the 13 week period including the incident, 14 workers exceeded the maximum permissible quarterly dose level of 3 rem (30 mSv (milli-Sieverts)). The highest figure recorded for the same period was 4.66 rem (47 mSv). It is important to note that a number of these doses were received knowingly by personnel directly involved with controlling the incident. There was also some hair and hand contamination but this was successfully removed by routine procedures. The principal health hazard both to workers and members of the public arose from radioactive iodine and in order to assess the effects, thyroid iodine surveys were performed. The highest activity was found in the thyroid of an AEA employee. The value was 0.5 µCi (micro-curies) and this compares with the ICRP level for safe continuous activity of 0.1 µCi. Surveys were also carried out amongst workers for Strontium activity (Sr-89 and Sr-90), but levels found were at most, one-tenth of the maximum permissible body burden. Biological samples for radioactive Caesium were also found to be satisfactory (Ref 16). The staff most exposed during the incident received the regular medical examinations given to UKAEA workers throughout their subsequent employment. They have also been included in epidemiological studies of UKAEA and BNF Pic workers performed by independent experts (Refs 17, 18 and 19). These studies showed mortality rates below those of the general population and consistent with those expected in a normal healthy workforce.

Measures Taken to Protect the Public Following the accident the hazard to the public arose from inhalation, ingestion and external radiation arising from fission products released from the uranium fuel. It was possible at an early stage to reject the need for emergency measures based on inhalation or external radiation, but measurements of the Iodine content of milk produced locally made it necessary to restrict the collection and distribution of milk from areas around the site. Milk forms an important part of the diet of young children and there was particular concern that radioactive Iodine in the milk would be concentrated in the infant’s

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thyroid. Calculations indicated that it than 0.1 µCi 1-1. Initially, collection of milk from farms within 2 miles would be unwise to permit consumption of milk with activity levels greater of the site was restricted and ultimately this was extended to 200 square miles, including the coastal strip south of Windscale to a distance of 30 miles. Iodine–131 has a physical half-life of approximately 8 days and based on this fact alone, disregarding the cleansing action of rain, etc, it was anticipated that levels would soon fall below 0.1 µCi 1-1. This proved to be the case but the final relaxation of the milk restrictions were delayed to make sure that Strontium levels were also within safe limits. Other foods including eggs, vegetables, etc, were investigated but all proved to be within safe limits. It was reported at the time that the Cumberland population took the accident remarkably calmly. The AEA stated that it would pay compensation for milk that was disposed of and curiously, during the period of the ban, there was a noticeable rise in the milk yield from local herds (Ref 20).

Lessons Learned from the Windscale Fire It is important to note that there were no rapid catastrophic failures associated with this incident since it developed over a period of days (7th–12th October 1957). It did not give rise to any seriously high doses or non-stochastic effects and consequently no immediate medical response was required. The recommendations and conclusions arising from the final report of the Committee appointed by the Prime Minister to make a technical evaluation of the fire in the Windscale Piles, centre on the methods used for the release of stored Wigner energy (Ref 21). In addition, there was a certain mistrust of instrumentation during the course of the incident and the Committee recommended a substantial increase in the number of instruments required, particularly for temperature measurement and fuel element failure. The committee of the inquiry were satisfied that it was in the “highest degree unlikely” that any harm was done to the health of people in the area, workers at the Windscale plant, or members of the general public. A number of weaknesses were identified, however, notably the delay between recognition of the existence of an accident with potential for the emission of radioactive substances and the institution of an extensive and rapid milk sampling programme throughout the area at risk. Once countermeasures had been agreed and brought into play, however, the committee considered them to be adequate to prevent ill effects. At the time of the accident there was practically no information published regarding safe levels of Iodine–131 in milk. It was considered important to err widely on the safe side and to ban the consumption of milk from farms in the area. The first area restricted was a coastal strip approximately 2 miles wide but this was later to be extended to an area of approximately 200 sq miles. Following the incident there was some criticism for not making the area pessimistically large at the beginning and then shrinking it, since this was considered to be psychologically more acceptable.

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Application of the data in the Medical Research Council (1975) report (Ref 22) to the circumstances of the Windscale fire confirmed Iodine–131 to be the most important radio-nuclide concerned. The recommended ERL of dose to the thyroid from I–131 was 30 rem (300 mSv). This corresponds to a derived ERL of peak activity in milk for adults in the MRC (1975) report of 3.8 µCi 1-1 (based on an assumed milk consumption of 0.5 litres per day). Since the highest measured concentration of I–131 in milk produced close to Windscale was 1.4 µCi 1-1 the dose to the thyroid, had this been consumed as normal, would have been in the order of 11 rem (110 mSv) for an adult and possibly up to twice that for a child (Ref 23). The controls instituted to prevent milk being consumed with I–131 levels greater than 0.1 µCi 1-1 ensured, however, that actual doses to the thyroid were far less than this figure. (Maximum of 9 mSv to a child). The collective effective dose equivalent commitment to the population of the UK and Northern Europe is estimated as 2×103 person Sieverts (Ref 24). If the Windscale fire had happened today the response would be unlikely to differ significantly from the actions taken in 1957. Stable iodate would probably be issued once the incident had been recognised and a programme of monitoring instituted at an early stage to check for radio-iodine build-up in milk. As in 1957, evacuation would not be considered appropriate for an incident of this magnitude. THREE MILE ISLAND: 1979 A Brief Description of the Incident Two Pressurised Water Reactors (PWR’s) each of approximately 900 MW(e) and designed by the US company Babcock and Wilcox are situated on the Three Mile Island site in the Susquehanna River, Pennsylvania. The nearest sizeable town is Harrisburg which has a population of approximately 68,000 people (1979 figure). Unit No 1 came into commercial operation in 1974 and was shutdown for re-fuelling at the time of the accident. Unit No 2 entered commercial service on 30 December 1978 and suffered a serious accident just 3 months later on 28 March 1979. The accident at Three-Mile Island developed in a manner determined by equipment malfunction, some design weakness and operator error. The loss of feedwater to the steam generators should have been dealt with by the installed safety systems, but escalated into a more serious event because vital equipment had been disconnected during maintenance. Decisions made by the operators during the subsequent course of the event have also been shown to have exacerbated the situation. The initial accident sequence at Three Mile Island (TMI) occurred over a period of minutes. A feedwater pump trip led to an absence of an effective heat sink and the primary system pressure began to rise. After approximately 15 minutes a pressure relief valve opened (correctly) but then failed to re-shut properly when the coolant pressure dropped. The operators did not realise this failure for about 2 hours and as a result, large amounts of active water were discharged into the containment sump. Since the sump pumps were running at this time, some of this water was transferred to an auxiliary building outside the containment building. Faulty decisions made during the water loss resulted in about half the fuel lacking coolant. This gave rise to substantial fuel damage and a release of fission products into the containment building.

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Despite a considerable release of radioactivity from the damaged fuel only nominal exposures were suffered by the general public since the containment proved to be effective. For a period of about 7 days following the accident there was, however, considerable anxiety regarding the safety of the plant and whether the containment would continue to hold.

Actual Hazard (Radiological) During the early stages of the accident some coolant was released into auxiliary buildings. Since this area was at a slightly lower pressure than the containment building and because the water was cooling down, dissolved fission product gases came out of solution and escaped from the building. This was the source of a plume of radioactive gas which naturally gave rise to public concern. The plume contained mainly radioactive noble gases and some traces of radio-iodine. The radioactive water was subsequently pumped back into the containment and the release terminated.

Health Effects Although there was a fairly swift and catastrophic failure of the core, this accident did not give rise to any casualties at the site. Radiation doses received by workers did not give rise to any non-stochastic effects and consequently there was no requirement for an immediate medical response. During the period from 28 March to 30 June 1979, 3 Three Mile Island workers received doses between 30–40 mSv (3–4 rems), which exceed the Nuclear Regulatory Commission (NRC) maximum permissible quarterly dose of 30 mSv (3 rems). The President’s Commission estimate that between 28 March and 15 April 1979 the collective dose to the population living within a 50 mile radius of the plant resulting from activity released was approximately 20 person-Sieverts (2000 person-rems). This figure can be compared with the estimated annual collective dose from background radiation for the same group of 2400 person-Sieverts (2.4×105 personrein). The incremental increase due to the accident at Three Mile Island to persons living within a 50 mile radius, was therefore approximately 1% of the annual background level. The same figure for people living within a 5 mile radius was calculated to be approximately 10%. The maximum estimated dose received by a member of the public during the accident was 0.7 mSv (70 milli-rems). The major health effect of the accident appears to have been the psychological stress imposed on people living in the region of Three Mile Island. There was immediate distress produced by the accident among many groups of the general population living within 30 miles of the plant. The highest levels of distress were found amongst people living within 5 miles of the reactor, those with pre-school children, and amongst workers from the plant itself. One of the major factors contributing to this heightened level of stress was the uncertainty caused by the lack of reliable information and guidance via the media. The actual radiation levels outside the plant were low but for several days there was uncertainty about the possibility of serious releases from the containment building. Federal and state officials disagreed regarding the information on which to base

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decisions regarding counter-measures. Some officials based their decisions on actual radiation levels outside the plant whilst others based their decisions on the potential for a major release from the containment building (Ref 25).

Countermeasures On 30 March the Governor advised pregnant women and those with pre-school children to leave the area within a 5 mile radius of the plant until further notice, but this was in direct contrast to advice from the Pennsylvania Bureau which stated that no protective action of any kind was required. As a precautionary measure most pregnant women and young children were evacuated from the area surrounding the plant and a more general voluntary exodus also occurred (the advice to pregnant women and pre-school children was formally lifted on 9 April 1979). The President’s Commission concluded (Ref 25) that whilst the extent of the media coverage was justified, a combination of confusion and weakness in the source of information and lack of understanding on the part of the media resulted in the public being poorly served. The effectiveness of Potassium-Iodide for thyroid gland protection in the event of a release of radio-iodine was well recognised and the food and drug administration had authorised use of Potassium-Iodide as a thyroid blocking agent for the general public in December 1978. At the time of the Three Mile Island accident, however, PotassiumIodide for this use was not commercially available in the United States in sufficient quantities. No supplies of Potassium-Iodide were held on site but major efforts by the Federal Government resulted in delivery of substantial supplies to Pennsylvania within 2 days. There was conjecture as to whether the drug should or should not be issued. The Department of Health strongly opposed distributing the drug to the public stating that radio-iodine levels were far below those laid down for protective action and the fact that by then the likelihood of a high level release was diminishing. It was also considered that distributing the drug would increase public anxiety and that the possibility of adverse side-effects presented a potential public health problem in itself. Consequently, the Potassium-Iodide remained in a warehouse under armed guard throughout the emergency.

Positive Aspects of the Three Mile Island Accident The accident at Three Mile Island is as yet the only case of a severe core damage accident in a commercial PWR and there has been extensive examination of equipment and procedures that went wrong. It is important to note, however, that in many respects the plant and its operators performed well. The containment also survived an hydrogen burn (explosion) although it was not specifically designed for such an event. There is no doubt that if the containment had not held, the consequences of this incident would have been on a far larger scale. It can be concluded that although the Three Mile Island accident was the most serious prior to Chernobyl, the health consequences which arose were in the event relatively trivial.

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Lessons Learned from the Three Mile Island Accident In addition to the President’s Commission, the US Nuclear Regulatory Commission constituted a Special Review Group (SRG) to review the lessons learned from the Three Mile Island accident (Ref 26). This study was highly critical of the overall safety culture at the plant. It highlighted the requirement for increased technical competence, for improved training, for a more effective inspection and enforcement programme and for marked improvements to emergency plans. As a direct result of the accident at Three Mile Island all nuclear operators instituted a major review of their emergency schemes. A number of changes were introduced in the UK covering: The establishment of an Operational Support Centre (OSC) during an emergency to act as the focal point for liaison between the operator, emergency services, Government departments and other agencies such as DoE and MAFF. The establishment of media briefing centres. The installation of fixed gamma monitors around the perimeter of each power station to provide a time profile of any release of airborne activity (Ref 27). The accident did not give rise to any immediate casualties at the plant and the effectiveness of the containment building ensured that the public were not significantly affected. Consequently, very little was required in the way of a medical response. The lack of Potassium-Iodide was soon remedied with approximately a quarter of a million one-ounce bottles of the drug being provided within 2 days of the request. Although the requirement for a medical response is questionable, this accident highlights the unseen health effects arising from a nuclear emergency. The 20 years which had elapsed since the Windscale fire had seen the development of a more widespread apprehension about the safety of nuclear power. In the event this was exacerbated by poor communications, conflicting guidance, and media coverage with an insufficient technical basis which all served to heighten public anxiety leading to high levels of psychological stress amongst many groups. In responding to a nuclear emergency we should be prepared for the widespread anxiety that would undoubtedly arise. CHERNOBYL: 1986 General Description of the Incident In the early morning of 26 April 1986, what is probably the worst accident in the history of commercial nuclear power generation occurred at the Chernobyl Nuclear Power Station approximately 60 miles north of Kiev in the Ukraine. The plant involved was a 1000 MW(e) reactor of the RBMK type which is peculiar to the Soviet Union. In 1986 there were 14 RBMK reactors in service and a further 8 under construction. The accident resulted in the destruction of the Unit 4 reactor core and much of the building which

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housed it. Large amounts of radioactive fission products were released into the atmosphere, contaminating land around the station and requiring the evacuation of approximately 135,000 people. The accident occurred during a test being carried out on a turbo generator at the time of a normal scheduled shutdown of the reactor. It was intended to test the ability of the turbo generator to supply electrical energy, following loss of external electricity connections, for the short period of time until standby diesel generators could supply emergency power. Improper test procedures and serious violations of basic operating rules placed the reactor at low power in cooling conditions which could not be stabilised by manual control. Subsequent events led to the generation of steam voids which introduced positive reactivity and resulted in an increasingly rapid rise of power. Attempts were made to stop the chain reaction but a rapid shutdown was not possible since most of the control rods had been completely withdrawn from the core. The rapid energy release ruptured the fuel causing an explosion of sufficient energy to disrupt the 1000 tonne reactor cover plate. This was followed by a second explosion after 2–3 seconds which resulted in hot pieces of the reactor core and fuel being ejected from the building causing fires in surrounding areas and an ingress of air to feed the burning graphite core (Ref 28). Radioactive releases from the plant continued for several days and were not stopped until 10 May 1986.

The Soviet Emergency Response The emergency response to the accident can be conveniently split into a number of phases:

1st Phase 2nd Phase 3rd Phase 4th Phase

: The initial catastrophic failure of the core (seconds). : The immediate response required to bring the accident under control (hours). : The secondary response involving evacuation and measures taken to limit further release of fission products from the burning core (days). : The long-term measures required to make the site safe. Cleanup and entombment of the damaged reactor (months).

Fire Immediately following the accident the first priority was fighting a number of fires which had broken out in some 30 places including the roof of the reactor building (height 71m). Within 7 minutes firemen from the nearby towns of Chernobyl and Pripyat set out for the plant and within 1 hour the worst of the fires were under control. After 31/2 hours the fires were extinguished leaving only the graphite core burning within the reactor. The firemen who initially dealt with the fires were exposed to high doses of radiation arising from fuel and core materials ejected from the reactor by the explosion. Six of these men fell ill very quickly and subsequently died within days. As a result of the continuing graphite fire and on-going significant release of fission products, the decision was taken to cover the exposed core with boron

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compounds, dolomite, sand, clay and lead. The boron was to stop any re-criticality; the dolomite gave off C02 as it heated up which starved the fire of oxygen; the lead absorbed heat and melted into the gaps to act as shielding, whilst the sand acted as a filter against the release of radioactive particles. Over the period 27 April to 10 May approximately 5,000 tonnes of material was dropped by Military helicopters covering the core and effectively filtering out the fine aerosol fission products (Ref 29). Evacuation The largest concentration of population near to the plant was approximately 10 km away at the town of Pripyat (45,000 people). During the accident itself these people were effectively sheltering since the majority of them were inside asleep. In addition, the initial plume missed the town but on the following day (27 April) the wind direction changed and the plume moved towards Pripyat. The decision to evacuate Pripyat was made at 2.00 pm on 27 April and within 21/2; hours the entire population had been removed. Later, when the control zone of 30 km was established the remainder of the 135,000 people in that zone were evacuated within days. Some tens of thousands of cattle were also evacuated. The Russians adopt a system of emergency reference levels similar to those used in the UK. For a predicted whole body dose of 250 mSv (25 rem) evacuation would only be considered but if predicted doses approached 750 mSv (75 rem) the decision to evacuate would be certain. Organisation Moscow was informed of the accident within 5 hours and according to information given in Vienna a single Emergency Control Centre was established in the town of Chernobyl, 16 km from the site. The Emergency Controller was a senior official of the State Committee for Atomic Energy and he headed a support team of approximately 1,000 technicians. Thousands of troops were also deployed to the area to carry out a number of support activities. The central emergency organisation directed the remainder of the emergency response, including decisions regarding evacuation, food and water bans and the mitigating actions taking place at the plant. Medical Response The medical response got underway swiftly with 2 teams of medical staff leaving the neighbouring town of Pripyat for the site within 20 minutes of the accident. Iodate tablets were issued on site within 11/2 hours and house to house in Pripyat within 19 hours. The initial medical response was provided by the Chernobyl regional hospitals and institutes which served the plant. Very early on, broad clinical criteria were established to determine those who were very sick, requiring immediate hospitalisation (Group 1), those who were not very sick (Group 2) and those with no symptoms of radiation syndrome (Group 3). One hundred and thirty persons were assigned to Group 1 and these were all hospitalised locally by the end of the first day with 129 later being sent to specialist hospitals in Moscow and Kiev. Eventually 203 people were found to have acute radiation syndrome of either second, third or fourth (the most severe) degrees (see Table 3) but these cases were confined to firemen and plant workers and there were none amongst the general public.

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TABLE 3 Degree of radiation syndrome

In addition to a number of the firemen, some of the plant emergency personnel received high doses (greater than 1 Gy). Five persons received significant thermal burns, but there were many more cases of beta radiation burns3. By 0600 hours on 26 April (5 hours after the initial explosion) one plant worker had died from severe thermal burns, one was never found and 108 people had been hospitalised. A further 24 were admitted later (Ref 30). Once the patients suffering from acute radiation syndrome had been hospitalised, additional investigations of blood and bone marrow were performed and radiation dose assessments made using chromosome aberration analysis techniques. Bone marrow transplants were undertaken for the worst affected victims, but in addition to the 2 deaths reported to have occurred immediately following the accident, a further 29 fatalities were subsequently reported amongst those hospitalised and diagnosed as suffering from acute radiation syndrome. The medical care which was made available on a short timescale including blood transfusion, chemotherapy, antibiotics, and techniques to prevent infection did, however, appear to have been effective in limiting the number of fatalities. Within a few days over 400 medical teams of doctors, nurses, assistants and medical students (5,000 total) had been assembled to assist in hospitals and to carry out checks amongst evacuees. By 10 May several hundred thousand people had been medically examined.

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Fifty-six people received burns to greater than 1% of their body and the majority of these were due to beta radiation burns. They were mainly due to highly beta active contaminants being entrained on wet clothing and hence in close contact with the skin. This gave rise to high localised doses of beta radiation and nonstochastic effects similar to thermal skin burns. The time at which the symptoms manifest themselves is not well determined, however, and can range from a few hours to a number of weeks.

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There is no doubt that a detailed analysis of medical effects and treatments arising from exposures received during the Chernobyl accident would greatly increase the knowledge of radiation-related injuries. In addition, long-term follow-up will be required not only of patients suffering acute effects but of the 135,000 people evacuated from the 30 km radius exclusion zone. Although such checks can be considered as a continuing burden or legacy resulting from the Chernobyl incident, the study may help provide much needed information relating to the biological effects of low doses of ionising radiation. Initial assessments suggest, however, that over the next 70 years the spontaneous incidence of all cancers, amongst the 135,000 evacuees, is not likely to increase by greater than approximately 0.6% (Ref 28). On a wider scale, approximately 70 MCi (Megacuries) of activity (excluding noble gases) were released during the course of the accident, some of which was spread over much of western Europe. In Britain restrictions were imposed on the slaughter of lambs grazing on Caesium-contaminated grass in parts of Wales, Cumbria and Scotland. The additional average dose in Britain during the year following the accident, is estimated to have been in the order of 3.5% of the annual dose due to natural background radiation (70 µSv compared to approximately 2000 µSv). This is similar to the magnitude of the increase caused by atomic weapons testing in the early 1960’s.

Lessons Learned from the Accident at Chernobyl The Chernobyl accident was so unique to the Soviet RBMK reactor design that there are very few lessons for the United Kingdom to learn from it in terms of plant design and safety features. The main effect has been to reinforce and reiterate the importance and validity of UK safety standards and procedures. It is considered that a reactor accident of the type that occurred at Chernobyl could not happen in the United Kingdom (Ref 31). There is no doubt that the accident resulted in a tragic loss of life and whilst there may not be a lot to be learned in the fields of reactor design and operation, the accident should provide valuable information for medical and other emergency services. Experience in the treatment of acute radiation syndrome and of beta radiation skin burns has been greatly increased and should become widely available once the final analysis has been completed. The results will help optimise therapeutic schemes and the experience gained will be valuable for the successful handling of any similar major emergency, should this ever be required. A SUMMARY OF EXPERIENCE GAINED FROM THE MAJOR NUCLEAR ACCIDENTS Table 4 summarises the main characteristics of each of the 3 major accidents referred to above. They differ from each other in many respects and provide no definitive guidance relating to any future emergencies. Perhaps the main feature to note is that in all cases, the emergency lasted for several days. In other respects the experience gained can be summarised under three major headings: (1) Treatment of Radiation Injury/Acute Radiation Syndrome There is no well defined, systematic route which all of these nuclear accidents took and consequently no consistent medical response. They varied widely in their severity,

TABLE 4 A summary of the main characteristics of the three reactor accidents

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in the number of people affected and in the type of injuries they received. The Chernobyl accident, however, clearly demonstrated the potential for a wide range of effects amongst plant workers and emergency personnel including: Conventional Injuries Thermal Burns Beta Radiation Burns Contaminated Casualties Casualties Exposed to High Doses of Radiation The incident at Chernobyl resulted in personnel receiving radiation exposures sufficiently high for them to experience acute radiation syndrome. Whilst the accident resulted in a tragic loss of life, the experience gained in treating these patients and the techniques used to mitigate the consequences of their injuries will be of medical value. Similarly, knowledge has been improved in the area of radiation-induced skin burns. The Chernobyl accident in particular highlighted the limitations of the protective clothing which was available for emergency use. (2) Development of Techniques to Control the Emergency Each of the nuclear accidents considered has contributed to the development of control techniques for major nuclear emergencies. The 1957 Windscale fire highlighted the importance of the radio-iodines and in the course of time this led to the development of Emergency Reference Levels. In 1979 the Three Mile Island accident highlighted the inadequacies of local emergency plans but did however show the importance of good robust engineering design which enabled the reactor containment vessel to withstand the accident. In 1986 the Chernobyl incident provided insight into the potential scale of consequences that can arise from a major nuclear accident. The scale and range of the emergency response required at Chernobyl prompted a review of the UK emergency arrangements. The Prime Minister in December 1988 in a written Parliamentary answer “confirmed the availability of contingency plans which would permit an effective response to be made to any nuclear accident, including those with more widespread effects than the specific site and off-site plans are designed to cater for.” (ie the ‘reference’ accident). On a wider scale Chernobyl also introduced the world to the concept of nuclear transfrontier pollution. (3) Effects On, and Response of, the Public At the time of the Windscale accident in 1957 reports suggest that the public’s reaction in the neighbourhood of the plant was fairly low key. This was in marked contrast to the accident at Three Mile Island 20 years later which, whilst it did not give rise to significant releases of activity to the environment, did nevertheless produce a significant problem of psychological stress and anxiety amongst people living nearby. This accident also highlighted the inadequacies of controllers and of the media in providing the public with clear and consistent advice regarding their best interests.

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The accident at Chernobyl served to underline these inadequacies in communications with the public. The number of phone calls received by the National Radiological Protection Board and other similar agencies provided an indication of the perceived risk which people in the UK considered themselves to be exposed to. Quite often fears were disproportionate to the actual technical or statistical likelihood of harm. This phenomenon was perhaps best demonstrated by the Goiania incident (discussed later in the proceedings by Mr J R Croft of the NRPB) which, apart from the direct effects of the accident, gave rise to far reaching socio-economic consequences. Goiania provided a unique opportunity to examine the effects of perceived risk and stigma under actual conditions.

FUTURE IMPLICATIONS The location of commercial nuclear power reactors in the UK and others operated by the UKAEA and BNF Plc, are shown in Figure 4 and their characteristics are summarised in Table 5. The general principles which determine the safety of nuclear plant in the UK were discussed in Section 1 and these principles are applied to the plant listed in the Table. The inquiry into the CEGB’s application to build the Sizewell ‘B’ plant provides a recent detailed illustration of how these principles are applied in practise. The Public Inquiry opened on 11 January 1983 and ran for 340 days. The Inspector produced a report to the Secretary of State which contained 109 chapters of which 44 dealt with various safety matters (Ref 32). The main emphasis in the Sizewell ‘B’ safety case was on those incidents arising from relatively frequent faults which the plant is designed to deal with following the principles outlined in Section 1. It is shown that the severity and frequency of these satisfy the criteria illustrated in Figures 1 and 2 and are such as to be unlikely to require any public countermeasures. A preliminary analysis of the likelihood and consequences of more severe accidents was, however, also presented to the Inquiry (Ref 32). This showed that the estimated frequency of an accident arising from internal faults and involving major fuel damage was about 10-6 per year. Containment failure and a subsequent large release of radioactivity into the environment was predicted for a small proportion of these cases. Consideration of external events (such as earthquakes, aeroplane crashes) and human error would increase these values somewhat but in general, it may be claimed that the risk of an accident leading to an uncontrolled release is in the region between 10-5 and 10-6 per annum. The HSE has recently examined the tolerability of risk (Ref 33). It suggests that individual risks of death of 10-6 per year due to stochastic doses received following a nuclear accident might be broadly tolerable and that plant designed to the Principles and Criteria described above comfortably satisfy such a criterion. In societal terms the HSE suggest that a major accident (involving doses of 100 mSv out to 3 km) anywhere in the UK might be accepted as just tolerable at a frequency of 10-4 per year.

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Figure 4. Britain’s Nuclear Power Stations In very broad terms we may therefore conclude that the chance of an accident occurring at a UK nuclear power plant is distributed as follows Class I

Serious accident but with on-site implications only

:

Around 1 in a few thousand per year

Class II

Accident with off-site consequences requiring public counter-measures

:

Around 1 in a few tens of thousands per year

Class III

Major accident with severe off-site consequences

:

Around 1 in a million per year

31 TABLE 5 Britain’s nuclear power stations—1989

NOTES: *Design Output Number of People Involved The number of plant personnel likely to be affected by an accident depends not only on the class of accident, but also the numbers present on site. The number of people working on a reactor site depends somewhat upon the reactor type, its operational state and, more importantly, upon the time of day/week. During normal day shift there may be

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up to a few hundred people present on a modern reactor site. This number falls during other hours and at the weekend, to a level which may be less than 100 dependent upon shift maintenance staffing levels, etc. The number of people involved in any on-site emergency response depends upon the scale of the incident. Twenty-eight people fought the fire at the Chernobyl reactor (Ref 30), but it is likely that the response in the UK would be greater. They would also be accompanied by a similar number of medical/ambulance staff. It is important to note that emergency response crews would be monitored and relief crews organised so as to ensure that doses received by individuals do not exceed non-stochastic limits. This subject is currently being addressed and it has been suggested (Ref 34) that substantial efforts should be made to keep doses to workers and emergency services persons on site, to levels below those at which non-stochastic effects may occur, ie 0.5 Gy to the whole body, or 5 Gy to any organ or tissue which may be preferentially exposed. The number of people living in the vicinity of a nuclear power plant varies in detail from site to site. It is somewhat dependent upon the age of the station and the siting criteria used at the time that the station was built. All Magnox stations were built on relatively remote sites, but some of the later AGR stations, which were considered safer due to increased pressure vessel integrity, were built nearer to urban areas than had previously been permitted. Assessments of the radiological consequences of a release of radioactivity from a given site are undertaken using complex computer models. These models represent the atmospheric dispersion and deposition of radioactivity for any weather sequence and evaluate the implications for the particular local population distribution. Clearly the magnitude of any effects are dependent on the size of the release. In general we estimate that up to a few thousand might be affected by Class II accidents rising to a few tens of thousands for Class III. It is important to note, however, that no early health effects occurred amongst members of the public at Chernobyl and the chance of any occurring in the UK is remote.

Requirements for an Effective Medical Response As recent non-nuclear incidents have shown, there is no shortage of excellent people able to respond to major accidents at short notice and under adverse conditions. Studies of the nuclear accidents to date, however, demonstrate the wide diversity and scale that these accidents can take. It is essential, therefore, that any response must be flexible so as to accommodate the wide range of potential accidents and the diversity of patients’ injuries that could arise. The response may conceivably require the treatment of contaminated casualties, those who have received high external doses of radiation and those with conventional injury. In addition, there would be many in the area who, although not acutely affected by the incident, may suffer stress-related effects for some time after the incident.

CONCLUSIONS 1. As discussed in Section 1 nuclear facilities are designed, built and operated to extremely high levels of safety. This, together with the strict application of

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regulatory controls, ensure that major accidents in nuclear plants can occur only with a very low probability. The UK has enjoyed hundreds of reactor years of commercial nuclear power generation without serious accident. 2. As the response to recent non-nuclear incidents has demonstrated effective emergency plans are in place to deal with large-scale emergencies. Emergency plans in place at nuclear establishments can be seen as an extension of those already in existence at Local Authority level for civil emergencies. Arrangements must, however, be made for dealing with injuries peculiar to accidents involving radioactivity, ie for contaminated patients and those exposed to high doses of radiation. 3. Examination of previous nuclear incidents shows no pattern. There is a marked difference in scale and number of persons affected and a great diversity in the range of effects. Similarly the timescale over which the accidents develop can vary. There may be a catastrophic initial event as occurred at Chernobyl or the accident may develop over a period of days as occurred at Windscale and Three Mile Island. Protracted accidents such as these invariably lead to a build-up of tension amongst people in the vicinity. 4. The medical emergency response to nuclear accidents in the UK needs to be based on flexibility. There is potential for a wide range of effects amongst plant workers or Emergency Response Teams including: Conventional Injuries Thermal Burns Beta Radiation Burns Contaminated Casualties Casualties Exposed to High Doses of Radiation The number of personnel exposed in this group will vary but it may be as high as about a hundred. 5. As with the Chernobyl incident, it is important that facilities are available for the treatment of patients who have received high external doses of radiation. This was one of the main lessons learned from Chernobyl and it is important that these facilities are available in the UK. 6. Rapid evaluation of high doses received by operators and emergency personnel are required to assist in rapid decisions regarding treatment procedures. 7. It in unlikely that any immediate radiological health effects will occur amongst members of the public. Countermeasures for public protection may be required however, and medical staff would be expected to participate in such considerations. In particular the decision to issue potassium iodate tablets to the public would need to be made in conjunction with the Local Health Authority.

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8. In general the numbers of people directly affected by countermeasures could range from a few hundred to several thousand. Public concern about radioactivity and radiation can give rise to psychological concerns and medical counseling of this group— as well as many others not directly involved—may be required. 9. It is essential that in the event of a nuclear accident, arrangements are in place for both the control organisation and the media to provide the public with reliable information concerning their best interests. Medical counsellors must also be provided with appropriate details of the accident and its consequences. 10. The programme of public education must be continued to enable the public to appreciate the risks associated with nuclear plant accidents. This should go some way to avoiding unnecessary alarm and anxiety. As the incidents at Three Mile Island, Chernobyl and Goiania have shown, the public see risks from nuclear accidents as being far reaching and quite often their reaction to the perceived risk is greater than the actual risk would warrant.

REFERENCES 1. Gronow, W.S., HM Nuclear Installations Inspectorate. Safety and Siting of Nuclear Power Plants in the United Kingdom. National Radiological Protection Board— Advanced Radiological Protection Course. NRPB–LN141, 1987. 2. Tyror, J.G., Garnsey, R., Hicks, D. Severe Accident Research in the United Kingdom. Paper presented at the 16th Water Reactor Safety Meeting, Gaithersburg, October 1988. 3. Nuclear Installations Inspectorate. Safety Assessment Principles for Nuclear Power Reactors, HMSO, London (1979). 4. Central Electricity Generating Board. Design Safety Criteria for CEGB Nuclear Power Stations. Rep HS/R 167/81, Revised, CEGB, London (1982). 5. Central Electricity Generating Board. PWR Design Safety Guidelines. Rep DSG2, Issue A, CEGB, London (1982). 6. International Atomic Energy Agency. The Radiological Accident in Goiania, September 1988. Vienna, 1988. 7. International Atomic Energy Agency. Safety Series No 75—INSAG 3: A Report by the International Nuclear Safety Advisory Group—Basic Principles for Nuclear Power Plants. Vienna, 1988. 8. Health and Safety Executive. Emergency Plans for Civil Nuclear Installations. HMSO, London, 1982. 9. Professor A Barrett, Glasgow Institute of Radiotherapeutics and Oncology. Treatment of Severe Radiation Injury (September 1984). National Radiological Protection Board—Advanced Radiological Protection Course. NRPB–LN123, 1987. 10. National Radiological Protection Board. Emergency Reference Levels: Criteria for Limiting Dose to the Public in the Event of Accident Exposure to Radiation. NRPB– ERL2, 1981.

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11. Ramsden, D., Passant, F.H., Peabody, C.P., and Speight, R.G. Radioiodine Uptakes in the Thyroid: Studies of the Blocking and Subsequent Recovery of the Gland following Administration of Stable Iodine. Health Physics 13, 633–46, 1967. 12. Stratton, W.R., Los Alamos Scientific Laboratory of the University of California. A Review of Criticality Accidents. LA 3611, 1967. 13. Knief, R.A. Nuclear Criticality Safety, Theory and Practice 1985. 14. Paxton, H.C. Historical Perspective of Nuclear Criticality Safety in the United States, Proc. ANS TOPL. Mtg. Nuclear Criticality Safety, EL. Passo, Texas. 8–10 April 1980. SAND80–1675, p. 21, Sandia National Laboratories. 15. Quinten, A., Dunster, H.J., UKAEA, Risley. Report on the Health and Safety of Employees of the UKAEA, 1957. IGS–R/R–4. 16. HMSO, London. Accident at Windscale No 1 Pile on 10 October 1957. November 1957. 17. Fraser, P., Booth, M., Beral, V., Inskip, H., Firstat. S., and Speak, S. Collection and Validation of Data in the United Kingdom Atomic Energy Authority Mortality Study. British Medical Journal, Vol 291, pp 435–439, 1985. 18. Beral, V., Inskip, H., Fraser, P., Booth, M., Coleman, D., Rose, G. Mortality of Employees of the United Kingdom Atomic Energy Authority, 1946–1979. British Medical Journal, Vol 291, pp 440–447, 1985. 19. Smith, P.G., and Douglas, A.J. Mortality of Workers at the Sellafield Plant of British Nuclear Fuels. British Medical Journal, Vol 239, 845–854, 1986. 20. Herbert, R. The Day the Reactor Caught Fire. New Scientist, pp 84–87, 14 October 1982. 21. HMSO, London. Final Report of the Committee Appointed by the Prime Minister to Make a Technical Evaluation of Information Relating to the Design and Operation of the Windscale Piles and to Review the Factors Involved in the Controlled Release of Wigner Energy, July 1958. 22. Medical Research Council (MRC), 1975. Criteria for Controlling Radiation Doses to the Public After Accidental Escape of Radioactive Material. HMSO, London. 23. Baverstock, K.F. and Wenart, J. Medical Research Council (MRC). Emergency Reference Levels for Reactor Accidents: A Re-Examination of the Windscale Reactor Accident. Health Physics, Pergamon Press, 1976. Vol 30 (April), pp 339–344. 24. Crich, M.J., Linsley, G.S., National Radiological Protection Board. An Assessment of the Radiological Impact of the Windscale Reactor Fire. October 1957. R135. Chilton, Oxon, 1983. 25. Kemeny, J.G. (Chairman). The President’s Commission on the Accident at Three Mile Island, the Need for Change: The Legacy of Three Mile Island. Washington DC, October 1979.

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26. US Nuclear Regulatory Commission, Office of Inspection and Enforcement. Report of Special Review Group, Office of Inspection and Enforcement on Lessons Learned from Three Mile Island. NUREG– 0616. 27. International Atomic Energy Agency. Proceedings of a Symposium, Rome, 4–8 November 1985. Emergency Planning and Preparedness for Nuclear Facilities. (Vienna, 1986). 28. International Nuclear Safety Advisory Group. Summary Report on the Post-Accident Review Meeting on the Chernobyl Incident. International Atomic Energy Agency, Vienna, 1986. 29

Collier, J.G., Myrvddin-Davies, L. Chernobyl. Central Electricity Generating Board, October 1986.

30. Mould, R.F. Chernobyl—The Real Story. Pergamon Press 1988. 31. United Kingdom Atomic Energy Authority. The Chernobyl Accident and its Consequences. NOR4200, Second Edition, London, April 1988. 32. Sizewell ‘B’ Public Inquiry Report: Report by Sir Frank Layfield, HSMO, ISBN O 11 411576 1 (1987). 33. Health and Safety Executive. The Tolerability of Risk from Nuclear Power Stations, London. HMSO, 1988. 34. Hill, M.D., Wrixon, A.D., Webb, G.A.M. Protection of the Public and Workers in the Event of Accidental Releases of Radioactive Materials into the Environment. Journal of Radiological Protection, Volume 8, Number 4, December 1988.

APPENDIX 1 Gray (Gy) - Unit of absorbed dose of radiation=1 J/kg=100 rads Sievert (Sv) - Unit of radiation dose equivalent=100 rems Stochastic - Describes effects for whom the probability of occurrence in an exposed population (rather than severity in an affected individual) is a direct function of dose: these effects are commonly regarded as having no threshold; hereditary effects are regarded as being stochastic; some somatic effects, especially carcinogenesis, are regarded as being stochastic. Non-Stochastic - Describes effects whose severity is a function of dose; for these, a threshold may occur; non-stochastic somatic effects—include cataract induction, nonmalignant damage to skin, haematological deficiencies and impairment of fertility.

SETTING THE SCENARIO—POTENTIAL HAZARDS OF THE NUCLEAR FUEL CYCLE by R J BERRY and N McPHAIL Health and Safety Directorate British Nuclear Fuels plc Risley Warrington Cheshire WA3 6AS

The previous paper has outlined the hazards of the operation of nuclear reactors as sources of electrical power; in the UK the majority of these are operated by the Central Electricity Generating Board and the South of Scotland Electricity Board. British Nuclear Fuels plc, which was created in 1971 from the former production division of the United Kingdom Atomic Energy Authority, is with its French opposite number, COGEMA, one of the Western world’s only two suppliers of the full range of nuclear fuel cycle services. In addition, BNFL also own and operate two nuclear power stations, Calder Hall on the Sellafield Site and Chapelcross in Southern Scotland. The geographical location of BNFL’s plants in North West England and Southern Scotland are shown in Figure 1 and the elements of the nuclear fuel cycle are shown in Figure 2. The “front end” of the fuel cycle activities are carried out at BNFL’s plants at Springfields and Capenhurst. Uranium arrives at Springfields as ore which has been mined overseas. It is purified and undergoes various chemical and mechanical processes to make the fuel which is used in nuclear reactors.

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Figure 1

Figure 2

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Magnox reactors, which have now been operating successfully for more than 30 years in the UK and overseas, use natural uranium which has been cast and machined into metal fuel rods encased in magnesium-aluminium alloy (magnox) cans. The more modern and more efficient Advanced Gas Cooled Reactors and Pressurised Water Reactors require uranium fuel which has been “enriched” by increasing the proportion of the fissile isotope Uranium– 235. Uranium enrichment is carried out at BNFL’s Capenhurst site using a cascade of gas centrifuges which separate the lighter Uranium–235 (less than 1% of natural uranium) from the heavier and more prevalent Uranium–238. The enriched uranium is returned to Springfields where it is manufactured into ceramic uranium oxide pellets which are then encased in stainless steel cans and these individual fuel “pins” are further put together into complete fuel assemblies for use in nuclear power stations throughout the UK.

The potential hazards associated with operations at the Capenhurst and Springfields plants are mainly of a chemical nature, due to toxic chemicals handled in various parts of the process, including hydrogen fluorides and uranium hexafluoride, which decompose in the atmosphere yielding hydrogen fluoride and uranyl fluoride. Whilst there is an associated radiological risk, it is of a very much lower magnitude and comes from the low levels of radiation naturally emitted in the spontaneous radioactive decay of uranium in uranyl fluoride. The only significant potential radiological hazard at these sites which could lead to major doses to the workforce, is from the inadvertent bringing together of a critical mass of uranium such that fission can take place (a criticality incident/accident). As discussed later in the paper, the plants are designed to minimise this possibility and operating rules further reduce the chance of such untoward occurrences. A criticality accident would be extremely unlikely to have any off-site consequences for the general public, but is the major radiological hazard to the workforce.

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After several years in a nuclear reactor, the nuclear fuel becomes depleted in the fissile isotope Uranium–235 and needs to be replaced. When removed from the reactor, the fuel is both heat generating and intensely radioactive and is normally stored underwater. An initial cooling period allows some of the short-lived radioactivity to decay and the fuel is then transported to BNFL’s reprocessing complex at Sellafield in extremely robust transport containers known as transport flasks. On arrival, the spent fuel is stored for a further period underwater prior to reprocessing, to allow further decay of some of the shorter lived radioactive products of nuclear fission.

Reprocessing consists of a series of chemical separation processes in which the uranium fuel rods are stripped of their encasing cans and treated to separate residual uranium (at least 96% by weight of the total) from the by-product Plutonium (about 1% of the total mass) and highly radioactive but non-useful waste (less than 3% of the total). The highly active waste is retained in safe storage while the reclaimed uranium is recycled for use again as fuel. Of the existing fuel in Britain’s AGR power stations, some two thirds has come from material recycled from the earlier magnox reactors. Current reprocessing plant started operating in 1964 and is designed to reprocess fuel from magnox reactors. The Thermal Oxide Reprocessing Plant (THORP), a massive new complex to reprocess fuel from AGR and PWR both in the UK and overseas, is now being constructed at Sellafield and is expected to be operating in the early 1990’s. High level (heat generating) and Intermediate level radioactive waste separated during reprocessing are at present stored on the Sellafield site. Plants currently under construction will convert liquid high level and intermediate wastes into glass blocks and cement monoliths respectively. Low level radioactive waste is disposed of safely in near-surface trenches at the nearby Drigg site and liquid waste via the sea pipeline. Both disposal routes are strictly controlled by a system of authorisations from Government Departments.

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In contrast to the nature of the hazards at the “front-end” of the nuclear fuel cycle, those associated with reprocessing are mainly of a radiological nature and arise from the possibility of an aerial release of radioactivity into the atmosphere, which is then carried off-site. An accidental release of radioactive material in liquid form is unlikely to be a major short term health risk to either the workforce or the general public. As discussed for the “front-end” plants, however, the storage of nuclear materials is always associated with a risk of criticality accident which could be of consequence to workers, although unlikely to have any consequences off-site to the general public.

Restricting the discussion, for the balance of this paper to Sellafield as the site which has the greatest potential for radiological hazard, it is important to understand the system of safeguards designed to prevent radiological accidents. BNFL as operators would wish, and the general public have every right to demand, that the possibility of an accident leading to the release of sufficient radioactive material to cause interference with the normal activities of the public, or to require special arrangements to be made to protect the workforce, should be extremely remote. The “safety cycle” designed to ensure this high level of safety is shown in Figure 3. During the design of plant, safety aspects are treated as of great importance and all credible combinations of foreseeable events which could lead to an accident are taken into account. Appraisals of safety are carried out at all stages from the initial design concept through to plant start-up and are continued during operation of all plant. All such safety appraisals and safety procedures are kept under review by a nuclear safety committee which includes independent members and the whole safety system is subject to corporate audit. In addition, the design, construction and operation of all such plant are assessed independently by the Nuclear Installations Inspectors of the Health and Safety Executive. Their permission is required to commence construction, and subsequently to operate any plant handling nuclear material.

Figure 3

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As with any industrial process, there will always remain a risk, no matter how small, for releases of radioactive materials from the Sellafield plants, these include the fuel cooling ponds, the highly active waste storage tanks and the Plutonium stores. Each of these has extensive and reduplicated safety features to prevent radiological accidents. For example, the highly active waste storage tanks contain concentrated, highly radioactive, liquid waste from reprocessing. Because of the intense radioactivity, the liquid is self-heating and therefore has to be kept cool. If all cooling was lost and the design of the tank allowed boiling of the liquid to occur, amounts up to hundreds of TBqs of radioactivity could be released into the atmosphere in a single event. The highly active waste storage tanks are designed so that the probability of such a release is exceedingly small. Each tank has ample spare cooling capacity to cope with the heat generated by the radioactive waste; there are four separate sources of cooling water available and three separate sources of electricity to operate the cooling water pumps. In addition, spare tanks are always kept empty on site into which liquid might be transferred if significant failures occurred in coiling coils in a particular tank. Even in the event of all the cooling mechanisms failing, it would take several hours for the contents to reach boiling point, and days before boil-away, and hence release to the atmosphere of the radionuclides, was complete. This would allow time for measures to be taken to prevent any release of these materials to the environment.

Plutonium which has been separated from the spent fuel during reprocessing is also a potentially valuable fissile material which can be used when mixed with uranium as fuel in modern thermal nuclear reactors, but which would be far more efficiently used as a fuel for future generations of fast reactors to ensure long term availability of economic supplies of electricity after easily obtainable new sources of uranium ore have been worked out. The plutonium, in the form of

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plutonium oxide powder packaged in stainless steel cans, is stored on the Sellafield site in an impressively sturdy monolithic building. The potential hazards from the stored plutonium are the release of this material to the atmosphere via a failure of one or more of the stainless steel cans, or a criticality event resulting from the accidental bringing together of a mass of plutonium sufficient to sustain the nuclear chain reaction. The store and the packaging are both designed so that this kind of criticality event cannot occur, because of the geometry of the packages and the way in which they are positioned. In the very unlikely event of a criticality, the potential hazard would be direct radiation exposure to the workers in the store, leading in the almost unimaginable worst case, to doses large enough to cause the acute radiation syndrome to workers thus exposed. A potential hazard to the general public exists only if either plutonium dust (or fission products in the event of a criticality event) escape to the atmosphere following an accident in which the stainless steel can packaging the plutonium oxide powder was broached. The possible effects on both groups are also reduced by countermeasures, including automatic criticality and airborne radioactivity detection devices within the store and a filtered ventilation system to prevent egress of radioactive material to the environment. There is redundancy and diversity in the engineering design provisions and in the air filtration systems, and administrative arrangements are designed also to minimise the chance of accident. In the unlikely event of a major accident, the impact on the workforce and general public would be ameliorated by invoking emergency arrangements involving the local and national authorities. These arrangements include consideration of evacuation, sheltering, food bans etc.

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EMERGENCY PLANNING Notwithstanding the complex and effective safety systems in place to prevent accidents, an emergency scheme has been drawn up to ensure that the necessary organisation is available should an accident lead to the escape of sufficient radioactive material, or there be a sufficiently high radiation dose rate on site to cause interference with the normal activities of the site or the general public. Safety studies have been carried out for those plants at Sellafield with the greatest potential for creating an off-site hazard in order to determine the size of an incident for which detailed emergency planning is required. Emergency arrangements based upon these assessments are drawn up with the relevant local organisations such as the Police, taking accounts of such factors as local geography and demography. The overall off-site emergency scheme is then designed with sufficient flexibility to be capable of extension. Planning for immediate actions such as sheltering or evacuation of the general public (and the issue of stable potassium iodate tablets should a reactor accident occur and radioactive iodine be a major potential source of public exposure) are based on the Emergency Reference Levels (ERL) promulgated by the National Radiological Protection Board (NRPB).

For foreseeable accidents on site, the likely off-site consequences at Sellafield are restricted to evacuation of persons from the site and out to two kilometres, involving only some tens of persons other than the site workforce. Evacuation would be considered if the whole body dose saving to the general public was in excess of 100 mSv and definitely be implemented if the dose saving exceeded 500 mSv, being the lower and upper ERLs currently specified by NRPB. The actual dose saving at which action would be implemented would depend on the circumstances on the day. Even in the worst case involving release of radioactive material, this would be expected to take place over a significant time period (hours), further reducing the total radiation dose and its effect once counter measures are taken.

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Beyond two kilometres, sheltering indoors would be recommended for members of the general public up to a few kilometres from the site; this countermeasure would be considered if the predicted dose saving from the countermeasure was likely to exceed 5 mSv to the whole body, and would definitely be implemented if the dose exceeded 25 mSv. These levels of radiation are incapable of producing clinically detectable radiation injury.

A recent discussion paper circulated by NRPB staff gives a review of radiological protection in relation to accidents, in the light of experience gained following the Chernobyl accident and the possible revisions of risk factors. These ideas if subsequently adopted would lead to a reduction in the dose for which countermeasures would be implemented.

CONSEQUENCES OF A MAJOR ACCIDENT As we have seen, the mechanisms by which the activities of the workforce or the general public would be affected following a major accident at the Sellafield complex, would be the release of radioactive material to the atmosphere or as a result of a criticality accident. For an aerial release, potential deleterious effect would be mainly from the inhalation of the emitted radioactive gases. Effects of direct radiation and of material ingested on food would be much smaller. The risks to the workforce from an aerial release are that the initial incident occurs before protective countermeasures can take place, such as evacuation, sheltering or donning protective equipment, and that additional exposure will be received by recovery teams of workers who are attempting to bring the incident under control. For the former, risks are limited by design of the plant and ready availability of countermeasures, and for the latter by careful monitoring, use of appropriate protective equipment, restriction of exposure time, etc. The risk to the general public following a release to the atmosphere of

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radioactive materials is limited by the imposition of countermeasures such as sheltering and evacuation in the short term, and by control of availability of contaminated foodstuffs, when this occurs, in the longer term. Even for the most serious accidents, the maximum dose which any individual on or off site is likely to receive as a result of an aerial release of radioactive material is of the order of a few hundred mSv allowing for the effective implementation of the emergency scheme. At this dose level, no member of the general public will have reason to show any evidence of the acute radiation syndrome; no-one should require hospitalisation or even medical treatment as a result of radiation injury from such a release. The possible increased radiation exposure to recovery teams on site should be limited by control procedures, and thus acute radiation injuries should not form part of the initial clinical problem. As in any industrial accident, mechanical injury, trauma of various sorts, thermal burns etc, may well form part of the casualty pattern following a major accident. Members of the recovery team may have received in the worst case localised skin doses which might result in minor radiation burns—but these will not be apparent in the short term.

The possibility that casualties will be contaminated with radioactive material does have to be considered however, and hospital services which receive such casualties must have facilities and training for the reception and handling of contaminated casualties. For a criticality accident, the hazard is from intense local neutron and gamma radiation in the area concerned, which pose an acute radiation syndrome risk to the workforce in the immediate vicinity. Because dose rates from direct radiation fall rapidly with increase in distance away from their source, and because they are reduced by shielding with concrete and other materials, this hazard really is applicable only to personnel in the immediate vicinity. A severe unshielded criticality incident, of which a small number

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of workers could receive sufficient radiation doses to cause death from the acute radiation syndrome or very severe injury is prevented by operational control and by the design of the plant. The effects of a criticality event on the workforce are alleviated by the inclusion of shielding which is built into it, the continuous operation of criticality detection alarms and the training in appropriate countermeasures such as rapid building evacuation.

MEDICAL ARRANGEMENTS This paper has detailed the attention which is given to safety on the Sellafield site so that the probability of a major accident leading to the release of radioactive material sufficient to cause interference with the normal activities of the plant, or of the general public, or requiring special arrangements to be made to protect the workforce, is very low. Even in the worst case, it is not anticipated that persons off-site will require medical treatment due to the radiation effects of the most severe foreseeable accident. However, persons within the immediate vicinity of the Sellafield works affected by any countermeasures such as evacuation/sheltering will be monitored as a reassurance measure. On site, trained medical and nursing staff are available to deal immediately with injuries to the workforce. Extensive medical facilities range from local surgeries within the plant staffed by a nurse, to the main medical building, which could be described as a mini-hospital. The on-site staff consist of 1 Senior Medical Officer, 3 Medical Officers, 18 Nurses, 6 Surgery Assistants, 2 Radiographers and 3 Medical Laboratory Technicians. All of BNFL’s Medical Officers have been trained in aspects of radiation medicine at the US’s Oak Ridge Associated University.

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For accidents involving the workforce, or others within the perimeter of the works, and where there is no radiation hazard, on-site services will deal with those casualties for which they have full capability. However, as with any industrial accident, the assistance of NHS specialist services will be available should injuries be sufficiently serious (eg trapped casualties or persons too severely injured to be moved any distance). In such cases, a request would be made to the Duty Consultant Surgeon at the West Cumberland Hospital to consider despatch of a mobile team. In the event of large numbers of casualties, the medical staff at Sellafield will decide whether it is necessary to seek activation of the Major Accident Procedure of the West Cumbria Health Authority. West Cumberland Hospital staff have been trained by the BNFL medical staff in the handling of contaminated casualties. Where members of the workforce or others within the perimeter of the works have been exposed to significant radiation doses, the Senior Medical Officer at Sellafield will decide whether the casualties so affected can be treated at the West Cumberland Hospital, or whether to transfer them to the Royal Victoria Infirmary, Newcastle, where the full panoply of support services are available in a centre with major radiotherapy and haematology/oncology departments.

In summary, for foreseeable accidents, the likelihood of genuine radiation casualties from accidents at Sellafield is very small, but like any industrial site, there could be a requirement to deal with a wide range of injuries following a major accident. The only special problem likely to occur is the necessity to deal with casualties who have been contaminated with radioactive material, so that the receiving hospital staff understand the problems this involves and the avoidance of any hazard to themselves.

THE MEDICAL MANAGEMENT OF RADIATION CASUALTIES DR. A.W. LAWSON Company Chief Medical Officer, British Nuclear Fuels plc Sellafield, Cumbria ABSTRACT

This paper reviews the key aspects of the medical management of radiological over-exposures and contamination incidents involving radioactive materials. The presentation is based on a simple but practical system of medical classification of radiation accidents. Emphasis is placed on the importance of the team approach in particular the role played by the medical physicist in ensuring the safe handling of these casualties. INTRODUCTION A radiological accident may be defined as “An unforeseen occurrence, either actual or suspected, involving an exposure of, or contamination on or within human beings and the environment by ionising radiations”. For many years the Radiation Emergency Assistance Centre/Training Site at Oak Ridge, Tennessee has maintained a retrospective and ongoing register of significant radiological accidents based on criteria laid down by the U.S. Department of Energy. The Registry was primarily established to ascertain all the relevant facts about radiological accidents with a view to (i) teaching and communicating the lessons to be learned and (ii) following up survivors in order to determine and document the incidence of late effects. In a recent review of the Registry database Lushbaugh [1] set out the number of individuals involved and the number of fatalities reported as a result of major radiological accidents between 1944 and March 1988 (Table 1). He also showed that radiological accidents could be conveniently classified under three main headings, viz- Criticality Excursions, Radiation Devices and those due to Radioisotopes (Table 2). One significant observation as a result of this project is well illustrated in Figure 1 where the frequency of reported accidents due to the mishandling of radiation devices can be seen to have risen considerably in comparison to

51

52

the incidence of accidents arising from accidental criticality excursions or from contamination by radioisotopes. TABLE 1

Table 1 —

Major Radiation Accidents—Worldwide Types of Injuries 1944—March 1988 TABLE 2

Table 2 —

Details the specific device or the radioisotope involved in the REAC/TS Register of Radiological Accidents.

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Figure 1

Figure 1 — Frequency Distribution of Major Radiation Accidents—Worldwide 1940—March 1988

THE MEDICAL CLASSIFICATION OF RADIOLOGICAL ACCIDENTS The nature and severity of any illness which may follow exposure to ionising radiations is dependent on:- (i) The dose received. (ii) The dose rate. (iii) The part of the body and the volume of tissue irradiated and (iv) The quality and type of radiations. For example, a single dose of 4 Gray to the whole body, delivered as an instantaneous exposure, would result in a serious illness with the probability of 50% of those exposed dying within 30 days. However, if the same dose of 4 Gray was delivered in four separate exposures of 1 Gray, with an interval of a few days between, it is likely that no deaths would occur and the subsequent illness would be much less severe. If however, the dose of 4 Gray was received over a working life time, no acute illness would develop, although populations exposed to this level of radiation would be expected to show an increased incidence of late effects, such as leukaemia and other malignancies. The clinical picture however is entirely different if the dose of 4 Gray is delivered to a limb in an instantaneous exposure. There would be no immediate symptoms or signs but after a latent period of three weeks or more, erythema and epilation may occur depending on the area affected (the thin skin of the flexor surfaces being more radio-sensitive) and by the type and energy of the radiations involved.

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For descriptive and treatment purposes it is convenient to designate radiation accidents as those due to:– (i)

EXTERNAL RADIATION,

–

(ii) CONTAMINATION INCIDENTS,

–

(iii) COMBINED RADIATION INJURY, –

either whole body or partial body (local) exposure. either external or internal, but both may co-exist. when the whole body exposure is associated with conventional injuries, e.g. wounds or thermal burns.

Although this system of accident classification tends to be an oversimplification it has nevertheless proved of value in practice. In respect of combined radiation injuries Hirsch [2] in a recent presentation made reference to the very narrow ‘time envelope’ in which surgical procedures could be carried out. He considered that surgery was precluded between the 2nd and 12th days following whole body radiation exposure and that urgent surgical procedures had of necessity to be carried out early as mortality increased the longer the delay. MEDICAL MANAGEMENT In order to respond effectively in the event of a radiological incident the physician in charge must have a basic understanding of the type of injury which may be expected to follow certain levels of exposure. The doctor must also have the specialist assistance of a medical physicist (Radiological Protection Adviser) to conduct the essential contamination and dosimetry assessments. In direct contrast to the conventional accident or illness, immediate danger to life is not usually the presenting feature in accidents involving over-exposure to ionising radiations unless there are associated physical injuries. It will be readily appreciated therefore that the physician’s initial responsibility in the accident situation must be to ensure that the airway is maintained and haemorrhage controlled before dealing with the radiological aspects of the incident. In the initial management of the heavily contaminated and incapacitated casualty, and depending on the local circumstances, spread of contamination can be limited by cutting off the clothing and covering the casualty with a blanket before transfer to the medical facility.

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TABLE 3

Tables 3 and 4 set out the types of accident, possible location and the ionising radiations which may be involved in external radiation and contamination incidents [3]. TABLE 4

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In general the initial management will be largely dictated by the circumstances in which the accident occurred but the following guidelines, summarised in Figure 2, set out the basic functions of the medical response in the emergency situation. 1 To render immediate first aid to any persons who may be injured, irradiated and/or contaminated during the incident. N.B. It is imperative that the medical team are adequately briefed and wear protective equipment before entering contaminated areas. 2 To liaise with the Radiological Protection Adviser and obtain the best possible estimate of doses received by individual personnel. 3 To carry out a detailed clinical assessment including biological investigations where indicated on the personnel involved. 4 To maintain detailed clinical records particularly with regard to the time of onset and the nature of any symptoms and signs as they develop. 5 To determine the subsequent management of radiation exposed personnel based on: (a) History of the accident. (b) The clinical condition of the patients. (c) Initial dosimetry assessments. (d) The number of casualties. If there are several casualties it may be necessary to establish a system of priorities. A simple form of triage advocated by the French [4] is to place over-exposed personnel into one of 3 categories. Category 1 Casualties who have received over-exposures to radiation but who also have combined injuries such as wounds, burns and/or contamination. Category 2 Casualties who are judged to have received whole body exposures at such levels that they will require treatment in a specialised haematological unit. Category 3 Casualties who are asymptomatic; are estimated to have received relatively low levels of whole or partial body exposure and who are free from any other form of injury.

FIGURE 2

Figure 2 —

The initial emergency response; the evaluation of casualties and the procedures followed after a radiological accident.

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The de-tailed management of the potential biological effects of the ionising radiations are now considered in more detail. LOCAL EXTERNAL RADIATION (RADIATION BURNS) The skin is very vulnerable to external radiation exposure and damage in varying degree is relatively common following radiotherapy and minor accidents involving X and ray sources. Skin reaction is related to the absorbed radiation dose which is in turn dependent on the energy of the radiation and whether this is electromagnetic or particulate. In the case of electromagnetic radiation the effect on the skin is inversely proportional to the energy of the radiation and thus for a given external dose gamma—radiation is less likely to cause damage than X-rays. Beta-particles on the other hand give up their energy rapidly in the skin and subcutaneous tissues and emissions of this nature constitute a particular skin hazard. With so many variables therefore it may prove difficult to relate the observed skin damage to a specific radiation dose unless the type of radiation and its energy is known. As with all types of exposure the dose rate is important and skin effects are likely to be reduced if a given exposure is spread over a longer period of time. A transient erythema may appear within 2–3 hours after a moderate exposure at a high dose rate, to be followed after a variable latent period by fixed erythema which may progress to vesiculation. The development of the burn however is much slower in comparison to that produced by a thermal injury. Another important point of distinction between thermal and radiation burns is that the radiation injury often proves to be more severe than first thought. This is due to the fact that the energy deposition associated with electromagnetic radiation does not fall off as rapidly as that following thermal injuries and as a consequence tissue damage to a varying degree may occur at depth. The most important injury is to the endothelium of the blood vessels which may result in an obliterating endarteritis causing ischaemia and necrosis of overlying or peripheral tissues. Other organs which may be affected include the hair follicles and sweat glands. Loss of body hair usually follows exposures in excess of 3–4 Gray and irrespective of the size of the dose usually takes place about 2–3 weeks after the exposure. With doses in excess of 7 Gray the hair follicles are destroyed and the epilation is permanent. Following exposures in excess of 20–30 Gray the end result is a lesion which is slow to heal and which may subsequently become the seat of malignant change.

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Management of Radiation Burns The occupational group now most at risk from experiencing radiation burns is that of industrial radiographer. In the majority of cases the patient only attends for consultation after the radiation burn has become manifest, although in a few cases they may have been examined earlier because of a reported over-exposure on their film badge. In these cases the diagnosis is fairly straightforward. On the other hand it is infinitely more difficult if no history of exposure to ionising radiations can be elicited. In the initial assessment of a patient suspected of having sustained a radiation burn the following factors should be taken into account:1 2 3 4

The time of exposure if known; the nature of the incident; in particular the type of radiations involved. The possibility of co-existing whole body exposure to penetrating radiation. The possibility of contamination by radioactive dusts or liquids. Whether there was any evidence of transient erythema, and the time of appearance of fixed erythema or other evidence of radiation burns.

In all cases a full physical examination should be conducted and a baseline blood screen, including chromosome aberrations, undertaken. The treatment of radiation burns is primarily directed to the prevention of infection and control of pain. In my limited experience of burns due to external radiation simple dry dressings, applications of merthiolate and judicious use of antibiotics proved more than adequate in the control of infection. However in the recent Goiania accident, in which 19 patients sustained radiationinduced skin lesions due to radioactive contamination the physicians in charge used a wide range of treatments including antiseptic and analgesic solutions, antibiotics and antiinflammatory agents. In addition, one group was given a series of injections to dilate and reduce capillary injury but without any obvious clinical benefit [5], Pain may be a late feature of radiation burns involving the extremities when it is usually due to ischaemia resulting from endarteritis. In those cases where amputation is contemplated various techniques have been developed such as thermographic imaging, to determine the demarcation between damaged and normal capillaries. The dilemma faced by the surgeon is deciding the optimum time to operate;

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if too early further necrosis may occur, if delayed unduly, the patients suffering is prolonged!

WHOLE BODY IRRADIATION—THE ACUTE RADIATION SYNDROME The salient clinical and laboratory features of this symptom complex were first described in proper sequence by Keller in 1946 [6]. It is now recognised that the acute radiation syndrome represents the radiosensitivity of the haematopoietic tissues, the lining of the small intestine and the central nervous system to a large acute dose of whole body penetrating radiation. The clinical effects following such exposures are again dependent on the dose rate, the dose absorbed and the nature of the ionising radiations. The acute radiation syndrome involves a series of clinical events that vary in timing and duration, depending on the degree of exposure and the extent of tissue injury. The greater the area of the trunk involved, the more severe will be the illness because of the location there of both the small intestine and a large portion of the haematopoietic tissues. In its classical form three clinical stages are recognised. A Prodromal Phase characterised by the onset of nausea and vomiting, associated with marked fatigue, lasting from a few hours to one or two days. This is followed by A Latent Stage of days to a few weeks duration when the patient is relatively symptom free but nevertheless significant changes will be seen in the peripheral blood count. The third stage or Manifest Illness usually begins with an abrupt onset and is associated with diarrhoea, vomiting, severe fluid and electrolyte loss, intestinal ulceration and haemorrhage. Depending on the absorbed dose three specific syndromes can be identified. (i)

The Haemopoietic Syndrome The haematopoietic tissues are among the most radiosensitive in the body with the main impact being on the stem cells in the bone marrow. As a consequence there is inhibition of mitosis of the precursors of the red cells, the white cells and the platelets and changes in the peripheral blood count may occur very rapidly. The earliest change detected is a fall in the absolute lymphocyte count, which commences in the first few hours and continues for several days to levels commensurate with the amount of radiation absorbed. There is often a concomitant increase in the leucocyte count in the first few days, following which the granulocyte count begins to fall with the maximum leucopenia developing in 2 to 5 weeks. The fall in the platelet count parallels that of the granulocytes but begins a few days later. (Figure 3)

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FIGURE 3

Figure 3 — Typical haematological response following a radiation dose of 4.5 Gray. Lymphocyte, neutrophil and platelet values should be multiplied by 1000. Haemoglobin values are in grams per 100 ml. As the changes in the blood picture become more marked clinical symptoms ensue usually commencing with malaise, headache, fatigue, chills or fever. At this stage the patient is prone to infections, particularly in the mouth and throat and fungal overgrowth in the gastro-intestinal tract may subsequently prove troublesome.

(ii) The Gastro-intestinal Syndrome This syndrome is primarily due to the loss of gastro-intestinal epithelium in association with the agranulocytosis. The symptoms of anorexia, nausea, vomiting, diarrhoea and fever may begin a few days or a few weeks after the prodromal phase depending on the degree of radiation exposure. The diarrhoea may persist when it is frequently associated with blood loss from the gut. Ultimately the patients condition may deteriorate further with abdominal distension, loss of

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peristalsis, dehydration, circulatory collapse and death. The major associated clinical problems are related to systemic infection with enteric organisms, electrolyte disturbances and hypovolaemic shock.

(iii) The Central Nervous Syndrome Overwhelming doses of radiation of the order of tens of Grays can cause direct damage to the brain. Although there is little evidence of this syndrome following human exposure, experimental evidence would appear to suggest that the central nervous system complications following such a level of absorbed dose are secondary to vascular lesions and that the syndrome is in fact neurovascular in origin. The clinical features are characterised by the rapid onset of apathy, lethargy and prostration frequently followed by seizures, grand mal convulsions and death. Management of the Acute Radiation Syndrome

The general principles for handling emergency and accidental overexposures to ionising radiations are well set out in Appendix 3 of ICRP 28 [7] and form the basis of many emergency medical services procedures. However it will be readily appreciated from the description of the clinical syndromes which may be experienced by heavily irradiated casualties, that the subsequent management of these patients must lie within the specialist field of haematology. This aspect of the management will therefore be considered in more detail by Professor Cawley in his presentation on ‘The Management of the Immunosuppressed Patient’. At the scene of the accident the initial priorities are related to the treatment of life-threatening injuries, and the monitoring for serious external contamination. Following transfer to the medical facility a detailed clinical assessment should be conducted while awaiting the preliminary dosimetry information. Baseline biological investigations should also be initiated at this stage with sufficient blood being taken for a full blood count including blood group, HLA typing, chromosome aberrations and general biochemistry. All urine samples should be examined and retained. It is imperative that detailed clinical records are maintained, particularly with regard to the exact time of onset of any symptoms and signs as they may have early prognostic significance. The earliest symptoms are likely to be nausea and vomiting which may be alleviated by Hydrocortisone Hemisuccinate 100mg 1M, 8–hourly or by the use of Chlorpromazine 25mg IM or Metochlopromide 10mg IM. If vomiting persists a saline drip should be set up followed after 3 hours by 5% Dextrose (or 4% Dextrose+1/5 Saline). In a large nuclear establishment where extensive medical and dosimetric services are immediately

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available, preliminary dosimetric data will be available within 1–2 hours after the exposure. This information coupled with the initial clinical assessment will enable the attendant physician to establish priorities. Patients confirmed or estimated as having experienced an over-exposure in excess of 1 Gray should be admitted to hospital. Personnel known to have received less than 1 Gray should be kept in the medical facility until preliminary investigations are complete. Those estimated to have received between 0.25–1 Gray may be allowed home on completion of the examination and assessment providing they are symptom free. They should be prescribed mouth washes and reviewed next day. In respect of the hospitalised casualties it is the moderate dose group of 2–6 Gray who are most likely to need and respond to treatment. The clinical problems likely to be experienced are those of fluid balance, haemopoietic dysfunction and infection. The following summary gives some indication of the procedures which may be adopted [8]. 1

The patient’s environment is of paramount importance and barrier nursing procedures must be instituted.

2

Diets should not contain uncooked food especially raw fruit or vegetables.

3

The patient’s personal hygiene should be supervised– nails should be trimmed and scrubbed and local neomycin (Naseptin) applied to the anterior nares.

4

Systemic antibiotics should be administered if fever persists above 38ºC for more than 2 hours or there are other signs of infection in an agranulopenic patient.

5

The gut should be sterilised if granulocytes fall to less than 1.5×109 L-1.

6

Irradiated packed red cells and platelet infusions should be administered to maintain haemoglobin and platelet levels or whenever bleeding occurs in a patient with a platelet count below 60×109 L-1.

7

Intravenous acyclovir (5mg/kg) three times a day should be commenced about three weeks after the radiation exposure to prevent the activation of the herpes simplex virus.

It is of interest to note that simple haematological evaluation by peripheral blood lymphocyte count appeared to be the best single laboratory tool for ‘triage’ in deciding where medical resources would require to be allocated in the recent Chernobyl accident. Further, the use of allogenous bone marrow transplants proved particularly disappointing in the management of these patients.

64

versus Host Disease’ in patients whose transplantation immunity had not been fully suppressed by the radiation overexposure.

TABLE 5

Table 5 The sequence of events, the haematological changes, and the clinical outcome of four groups of irradiated personnel who exhibited the Acute Radiation Syndrome following the Chernobyl accident.

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This was primarily due to the development of ‘Graft CONTAMINATION BY RADIOACTIVE MATERIALS

When radioactive material in the form of dusts, liquids or gases is accidentally released into the environment, contamination may occur externally on the skin or internally by inhalation, ingestion or absorption through the intact or abraded skin. In the nuclear energy industry external contamination does not usually constitute a serious medical problem as static air samplers continually monitor for atmospheric contaminants and personal monitoring at the end of each shift ensures that radioactive contamination is identified at an early stage. The outcome however may be entirely different if contamination occurs and is allowed to persist due to the person involved being unaware of the fact. The series of events at Goiania in September/October 1987 bear tragic witness to this fact. EXTERNAL CONTAMINATION

The effects on the skin of radioactive contaminants essentially depends on the type and energy of the emissions from the radioisotope involved. Due to their relative short range emissions from particles are unable to penetrate to the basal cell layer of healthy skin. As a consequence the major concern associated with such contamination relates to its possible transfer to internal organs. On the other hand the emissions from particles penetrate to the deeper layers of the skin and depending on their energy to the subcutaneous tissues, thereby constituting a potential skin hazard. The effects of X and -rays are also energy dependent, the lower the energy of the incident radiation the more radiation will be absorbed and the greater the likelihood of skin damage ensuing. Many radioisotopes emit more than one type of radiation but it will be obvious from the foregoing that those which emit a preponderance of -particles are the most hazardous to the skin and subcutaneous tissues. Radioactive substances usually rest on the thin film of oil which covers the outer layer of the skin and the openings of the glands and hair follicles. As a consequence the decontamination techniques usually employed are based on the removal of this oily film by means of soap and detergents. With ingrained contamination particularly on the hands it may be necessary to employ, stronger agents to remove the outer horny layer of the skin.

Decontamination Procedures It should be appreciated that the intact skin is an excellent barrier to the absorption of radioactive materials and that harsh cleaning methods should not be employed in attempts to decontaminate the skin. Experience

66

has shown that it is important to be gentle when conducting decontamination procedures. It is a mistake to scrub too hard as the contamination may simply be rubbed deeper into the skin or alternatively it may render the skin too tender to complete the decontamination [9]. This particularly applies to the softer skin of the face. The basic agents and materials required to effect decontamination of the skin are:1

Soap and water

2

1% and 4% Cetrimide

3

Saturated solution Potassium Permanganate

4

10% solution of sodium metabisulphite

5

4% Xylocaine solution (or equivalent local anaesthetic)

6

Surgical gloves, rubber boots, protective aprons, large polythene bags for contaminated clothing and dressings, cotton wool balls, cotton wool applicators, nail brushes, adhesive masking tape and paper towels.

FIGURE 4

Figure 4. Decontamination Body Chart

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It is essential to conduct a total body survey before commencing decontamination. The monitoring results can then be transposed on to a body chart (Figure 4) such as that used at Sellafield, which clearly demarcates the extent and degree of the contamination.

The following priorities and procedures should now be adopted:1

Breaks in the skin should be identified and covered.

2

Radioactive contaminants around body orifices, particularly the nose, should be removed first.

3

Decontamination should be carried out by starting at the periphery of the contaminated area then working gently towards the centre.

4

Soap and water should be used initially and if this fails to remove all the contaminant, 1% Cetrimide may then be tried.

5

If contamination persists the next step is to use a saturated solution of potassium permanganate which removes some of the horny layer of the skin, but care must be taken that any undissolved crystals do not come into contact with the skin. This substance must not be used near the eyes or on the hair and should only be used with great care on the softer areas of skin. The potassium permanganate solution should be left on for a few minutes only, until the skin is deeply discoloured. It is then washed and allowed to dry, the resulting pigmented area then being treated with the 10% solution of sodium metabisulphite to remove the coloration. If the contamination still persists these procedures may be repeated with the proviso that considerable care must, at all times, be given to the state of the skin.

If redness or tenderness develops decontamination procedures must be stopped and in such circumstances it is good practice to cover the area with a lanolin-containing cream followed by an impervious dressing. The patient can then be examined again the following day when the condition of the skin will usually allow further attempts at decontamination to be carried out. Decontamination procedures may have to be applied to other areas, e.g. hair, teeth and mouth, eyes, nostrils, ears, etc, and some ingenuity may be required to accomplish clearance of the contaminant. INTERNAL CONTAMINATION

The major hazard associated with the accidental intake of radionuclides is undoubtedly the risk of late stochastic effects and decorporation is primarily undertaken with this possibility in mind. It is nevertheless recognised that a very large intake could follow the maladministration of a therapeutic agent or by accidental inhalation, ingestion or from heavily

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contaminated multiple wounds and in such an event these patients would need to be immediately admitted to a specialised facility and treated as if they were suffering from the Acute Radiation Syndrome. Following a radiological incident internal contaminants tend to be selectively deposited in specific body organs and tissues depending on the nuclide involved. Radioisotopes of stable elements normally found in the body follow the stable isotope (e.g. radioiodine is taken up by the thyroid) while other radioisotopes adopt the metabolic pattern of stable elements to which they are chemically related (e.g. strontium follows the same pattern as calcium). On the other hand plutonium for no specific reason is preferentially deposited in bone and liver. It follows therefore that the organ retaining the highest concentration of the radionuclide is the one most likely to sustain immediate radiation effects and/or subsequent malignant change and is usually regarded as the target organ for that particular isotope. One of the major difficulties experienced in the early management of persons internally contaminated with radionuclides is that the extent and magnitude of the contamination is seldom immediately available to the attendant physician. It is recognised that the hazards posed by an accidental intake relate to the quantity, site of deposition and metabolism of the radionuclide in addition to its physical half-life and the radiosensitivity of the target organs. Nevertheless the decision whether or not to implement treatment must on occasion be based on only limited information. Fortunately, an accidental intake is unlikely to pose an immediate threat to a patient’s life and decorporation is therefore primarily undertaken to reduce the risk of late effects, such as cancer. This poses another problem in that the need for initiating treatment in a particular case has to be based on an assessment of the risk of late effects in the individual concerned. As Voelz [10] pointed out—‘If discomfort, side effects or risk accompany the therapy, it is especially important to understand the need and basis for treatment’. The general principles adopted in the management of persons accidentally contaminated with radionuclides are twofold [11], (i)

To reduce absorption and internal deposition, and

(ii) To enhance elimination or excretion of the absorbed nuclides. It must however be recognised that while there are a large number of radioisotopes which theoretically could prove to be hazardous most are seldom encountered or have short physical half lives and therefore do not represent a serious problem in medical management. I have therefore limited the contents of this section to a review of the therapeutic procedures utilised for some of the more common radionuclides.

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Iodine 131 This radionuclide may be released into the immediate environment following a reactor accident or any incident involving the release of fresh fission products e.g. following a nuclear weapons test. Most of the iodine released will be readily absorbed by inhalation, ingestion or through the skin. In the event of an incident, medical management is directed to the issue of stable iodine as a blocking agent to prevent uptake of the radioisotope by the thyroid gland. In a typical individual approximately 25% of a single intake of radioiodine will be retained in the thyroid after 12–24 hours. To be most effective therefore stable iodine should be administered as soon as possible after the incident. A recent report following experimental work in China [12] showed that stable iodine was 96.6% effective at the time of exposure but only 42.5% effective after four hours had elapsed. A convenient preparation for use in such emergencies is Potassium Iodate in tablet form and a consensus of opinion now suggests that one 170mg tablet daily (equivalent to 100mg iodide) provides adequate suppression of uptake of radioiodine in the adult [13]. In this country it is the practice to recommend half the adult dose for children under 12 years of age and a quarter of the adult dose for very young children. The frequency of reactions to iodide would appear to be very low. Based on American experience complications of iodide therapy in a presumably ill population represents a low order of risk of between 1×10-7 and 10×10-7 at a daily therapeutic level of administration [14]. Strontium and Radium Both these elements are absorbed from the intestine in competition with calcium. A number of treatment regimes have been advocated to reduce the gastro-intestinal absorption but in some cases the reports on the effectiveness of treatment varies quite markedly. In the case of strontium aluminium-containing antacids are recommended as being effective in reducing the intestinal uptake of radiostrontium by between 50 and 85% with aluminium phosphate appearing to be the most effective preparation. Alginates which are jelly-like substances obtained from brown seaweed will inhibit absorption of strontium if administered shortly after ingestion. However, their extreme viscosity makes them difficult to administer. Following ingestion, about 30% of radium is absorbed and subsequently most of this is excreted within a few days after the incident. The radium remaining is almost entirely deposited in the skeleton. Immediate stomach

70

lavage has been advocated for patients who have just ingested radium but little is known about the removal of radium once it is incorporated in the skeletal bones.

Caesium Caesium is rapidly and almost completely absorbed from the gastro-intestinal and respiratory tracts. It is soluble in body fluids and follows the same metabolic pathways as potassium, tending to concentrate in soft tissues particularly muscles. In the management of a contamination incident the administration of the ion-exchange resin Ferric Ferrocyanide (Prussian Blue) is the treatment of choice. Prussian Blue is of low toxicity as it is not absorbed from the intestine. It binds the caesium ions that are enterically cycled into the gastro-intestinal tract so that the caesium is not reabsorbed. The biological half-life during treatment is reduced to about one-third of its usual value and the systemic uptake is likewise reduced. It proved to be of real value when combined with an exercise and sauna regime in the treatment of members of the public contaminated with caesium chloride in the incident at Goiania, Brazil in 1987. One of the attendant physicians confirmed, in a personal communication, that Prussian Blue was the most effective treatment used to remove the caesium. He indicated that 40 patients were treated with this compound in doses ranging from 1.5 to 10.0 grams per day, but daily doses above 10grams were not well tolerated. Nevertheless one patient with extremely high internal contamination received a total dose of approximately 1000 grams of Prussian Blue in just over a four month period with no harmful effects [15]. Diuretics were also introduced into the treatment regime but did not make any significant contribution to the elimination of the caesium. On the other hand forcing the intake of fluids to at least 3 lites per day proved to be useful and practical. The fact that the contaminant was caesium chloride, a highly soluble compound, undoubtedly contributed to the success of an exercise and sauna regime in accelerating the removal of the caesium by ‘sweating it out’.

Tritium Tritium is the only radioactive isotope of hydrogen and problems of contamination only arise when elemental tritium is oxidised to tritiated water. In this form it is rapidly and completely absorbed following inhalation or ingestion and it can also be absorbed through intact skin. It is distributed evenly throughout the body and effectively produces whole body irradiation. The medical management is usually comparatively straightforward consisting of forcing 3 to 4 litres of fluid by mouth per day coupled with

71

the administration of a diuretic. However in a recent incident involving two laboratory staff in Switzerland, Lloyd et al [16] reported that the physician in charge treated the most severely exposed individual with intravenous infusions of 7 litres per day. However this regime is not without risk and can only be employed in young fit persons.

The clearance half time of tritiated water is generally considered to be about 10 days but Lloyd also showed that even on an unsupervised forced fluid regime this was reduced to less than 6 days, thereby reducing the other subject’s predicted dose uptake to approximately 65% of the initial assessment.

Plutonium and other transuranic elements Inhalation incidents are the commonset form of occupational exposure and the initial medical concern is centred on whether or not to initiate treatment with a chelating agent. A number of chemical compounds enhance the elimination of metals from the body by a process whereby organic compounds exchange less firmly bonded ions for other inorganic ions to form a relatively stable non-ionised ring complex which can be readily excreted by the kidney.—Diethylene triaminepentaacetic acid (DTPA) is a powerful chelating agent which is effective in the removal of transuranic metals, the rare earths and some transitional metals from the body. It also binds trace metals such as zinc and manganese and this factor has to be taken into account if long term administration is deemed necessary. In inhalation incidents the decision whether to employ a chelating agent such as DTPA is largely dependent on the chemical properties of the compound involved and this is where a knowledge of the plant and processes is invaluable. Soluble compounds such as plutonium nitrate have a relatively rapid uptake from the lungs from where they are readily translocated via the blood stream to the skeleton and liver. It is during the period of translocation that chelation by the intravenous administration of DTPA has proved most effective and studies suggest that about 60–70% of the soluble plutonium uptake can be removed if the DTPA is administered on the first day after exposure. However intravenous DTPA has proved ineffective in the initial treatment of inhalation incidents involving insoluble compounds, such as plutonium oxide because of the relatively small amount of plutonium which translocates via the blood or intracellular fluids following this form of intake. Nevertheless in the event of a massive intake it would be prudent to use DTPA aerosols after collecting baseline urine samples. DTPA is available either as the calcium or the zinc salt. Animal experiments suggest that Ca DTPA is more effective than Zn DTPA when given promptly after exposure to Plutonium and americium. However no comparable

72

studies are available in humans. Clinical experience has shown that both salts of DTPA may be safely given by intravenous injection but only the calcium salt should be used if the treatment is by aerosol, as symptoms similar to metal fume fever have occurred following the aerosol administration of Zn DTPA. In the management of Plutonium contaminated wounds it is standard practice to give intravenous Ca DTPA before commencing elective surgical procedures such as wound excision. This ensures that any plutonium which may be released into the circulation can be readily chelated.

The Hanford Americium Accident in August 1976 in which a 64 year old chemical operator was injured and heavily contaminated following an explosion in an ion exchange column fully demonstrated the effectiveness and lack of toxicity after prolonged administration of DTPA. In the subsequent management of this patient a total of 584 grams was administered in just over 4 years [17]. In this accident an estimated 37GBq–185GBq (1–5Ci) of Americium was initially deposited on the operator and his clothing and this was reduced to 222MBq (6mCi) by on-site decontamination and to 37MBq (1mCi) after the first day post-exposure.

Figure 5 The effectiveness of DTPA in reducing liver and bone burdens In a report on the accident prepared by Heid et al in 1979 [18] they reviewed the effectiveness of DTPA in reducing the liver and bone burdens

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of Americium. They calculated the quantity available for deposition based on the amount excreted in the urine and faeces and the quantity estimated to remain in the bone, liver and facial skin to be about 40.7MBq (1100 Ci). Using models derived from animal experimentation they estimated that a total of 28.12MBq (760 Ci) would have been deposited in bone and liver if DTPA therapy had not been available. In effect they found only about 9.25MBq (250 Ci) was retained thereby confirming the effectiveness of DTPA in chelating and reducing the anticipated uptake of Americiam as a result of this accident. (Figure 5). REFERENCES

1. Lushbaugh, C.C., Ricks, R.C. Fry, S.A. A historical review of sealed sources acccidents. Radiation Protection in Nuclear Energy, Proceedings of a Conference in Sydney, April 18–22, 1988. pp. 401–408. 2. Hirsch, E.F. The Role of Surgery in the Management of Acute Local Radiation Injuries. The Medical Basis for Radiation Accident Preparedness, October 20–22 1988 Oak Ridge, Tennessee—To be published. 3. Schofield, G.B.—Procedures following Major Radioactive Contamination. Proceedings of the meeting at the University of Bristol, April 8th 1981, p. 11. 4. Nenot, J.C. Clinical Aspects of Accidents Resulting in Acute Total Body Irradiation. Oak Ridge Conference—to be published. 5. International Atomic Energy Agency, Vienna 1988—The Radiological Accident in Goiania p. 46. 6. Keller, P.D. A Clinical Syndrome following exposure to Atomic Bomb Explosions, J.A.M.A. Vol 131, No. 6, pp 504–506. 7. ICRP 28—The Principles and General Procedures for Handling Emergency and Accidental Exposures of Workers. Vol 1, 1978 p 17–21. 8. International Atomic Energy Agency, Vienna 1988—The Radiological Accident in Goiania, p. 45 9. Lawson, A.W.—Decontamination of the Skin. Proceedings of Symposium at Atomic Energy Establishment, Winfrith Nov 14th 1963, pp 69–76. 10. Voelz, G.L. Current Approaches to the Management of Internally Contaminated Persons. The Medical Basis for Radiation Accident Preparedness 18–20, October 1979 Oak Ridge, Tennessee. pp 311.

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11. N.C.R.P. Report No 65—Management of Persons Accidentally Contaminated wiht Radionuclides April 15, 1980, p 12. Traitement des Contaminations Internes, Experience chinoise. Copy received January 1988. 13. N.C.R.P. Report No 55. Protection of the Thyroid Gland in the Event of Releases of Radioiodine. August 1977, p 23. 14. N.C.R.P. Report 65—Management of Persons Accidentally Contaminated with Radinuclides. April 15, 1980, p 15. Oliveira, A.R. (1988) Personal communication. 16. Lloyd, D.C., Auf der Maur, A., Gossi, U. Accidental Intake of Tritiated Water: A Report of Two Cases. Radiation Protection Dosimetry Vol 15, No 3, pp 191–196 (1986). 17. Breitenstein, B.D., The 1976 Hanford Americium Exposure Incident: Medical Management and Chelation Therapy. Health Physics, Vol 45, No 4 pp 855–866 (1983r). 18. Heid, K.R. The 1976 Hanford Americium Accident Report prepared for the U.S. Department of Energy, January 1979, p 11.

MEDICAL MANAGEMENT OF THE PATIENT IMMUNOSUPPRESSED BY IONISING RADIATION

JOHN C.CAWLEY UNIVERSITY DEPARTMENT OF HAEMATOLOGY, ROYAL LIVERPOOL HOSPITAL, PRESCOT STREET, P.O. BOX 147, LIVERPOOL L69 3BX, UK

INTRODUCTION Since the immune system is distributed throughout the whole body and since its cellular and humoral constituents circulate, only irradiation to a large area will result in profound immunosuppression. All immunocompetent cells are ultimately derived from the bone marrow which is itself widely distributed throughout the skeleton. Doses in excess of 5Gy cause severe bone marrow suppression; doses greater than 15Gy will result in fatal damage to other organs such as the lung and gut. Experience and the consequence of lethal or near lethal whole-body irradiation is largely confined to two situations:1) Total body irradiation (TBI) for bone marrow transplantation 2) Nuclear accidents e.g. Chernobyl and Brazil. Most experience relates to the therapeutic use of TBI and I shall largely confine myself to this area, although I will later consider briefly the conclusions to be drawn from Chernobyl. 1) Therapeutic TBI for bone marrow transplantation The general aim of therapeutic irradiation is, of course, the ablation of tumour with minimisation of damage to other tissues including the bone marrow. The only exception to this general rule is the therapeutic supralethal external total body irradiation (TBI) used in treatment

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of widely disseminated radio-sensitive tumours such as acute leukaemia or lymphoma. At the doses employed ( 10–5 Gy), the limiting toxicity is bone marrow failure (and consequent immunosuppression etc) and some form of marrow rescue is necessary This may be done with the marrow of a donor (allogeneic [allo-] BMT) or with the patient’s own marrow (autologous [A] BMT) obtained before TBI (Nathan, 1983; Goldstone, 1986). Clinical BMT, therefore, provides a model for the medical management of the patient immunosuppressd by ionising irradiation. It must, of course, be immediately acknowledged that BMT patients constitute very imperfect models for subjects exposed to large doses of radiation during a nuclear accident. The accident patients will probably have received the irradiation over a much shorter period, will often have extensive burns and may well have ingested or inhaled radioactive substances. Bone marrow transplantion Both allogeneic and autologous BMT involve the basic sequence set out below:-

The essential difference between allogeneic and autologous transplantation is, of course, that the former involves the re-infusion of foreign marrow. This foreign donor marrow contains immunocompetent cells which potentially recognise the host as foreign and cause graftversus-host-disease. Both GVHD and manoeuvres (e.g. cyclosporin and Tcell depletion) designed to prevent GVHD cause profound immunosuppression. This type of immunosuppression is not a consequence of ionising irradiation per se and therefore allo-BMT seems a less appropriate model than auto-BMT for today’s meeting. The specific immunodeficiency of allo-BMT results in a number of late complications

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following initial marrow recovery (e.g. viral pneumonitis); these are not relevant to the present talk. Autologous BMT ABMT involves the following sequence of events:-

This period of immunosuppression following ABMT seems the best model we have for considering the management of the patient immunocompromised as a result of radiation following a nuclear incident. Immunosuppression following ABMT Infection after ABMT occurs in the first 3–4 weeks and is primarily due to profound neutropenia in association with breakdown of mucosal barriers (Prentice, 1984). After initial marrow recovery, late infections are uncommon although zoster and occasional pneumococcal septicaemias do occur. Irradiation per se does impair lymphocyte and NK function, but this seems to cause few, if any, clinical problems. Infections during the neutropenic period Early infections are due to two main groups of organisms—skin organisms associated with in-dwelling catheters (70%) and gutassociated bacteria (30%)—both cause septicaemia. Later, after prolonged neutropenia, fungal infection becomes significant, Candida and Aspergillus sp being particularly important. Oropharyngeal herpetic infection is common throughout the neutropenic period.

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Infection control strategies Table 1 sets out potential strategies for minimising infection in the neutropenic period. I shall consider each in turn in the context of ABMT/nuclear accidents. TABLE 1a) Possible infection-control strategies in patients severely immunocompromised as a result of ionising radiation

a) Modified from Hann and Prentice 1984. Laminar air flow rooms. In combination with other measures such as gastrointestinal decontamination, provision of pathogen-free air probably is beneficial and is probably, therefore, worthwhile for the patient exposed to large doses of radiation. Other protective measures. Simple attention to hygiene by staff is clearly important. Most units now recommend hand washing and treatment with antiseptic and the wearing of a clean gown/apron; elaborate theatre-style clothing has now been largely abandoned. Skin and hair bacterial decontamination with particular attention to the axillae, perineum and orifices is recommended. Long-term indwelling catheters (with protective skin tunnel) have

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reduced cannula-related local sepsis and made life easier for the patient. Their use has greatly increased the incidence of grampositive bacteraemias which are usually not life-threatening. Clean food is probably worthwhile. Gastrointestinal decontamination. Most studies suggest that some form of gastrointestinal decontamination reduces infections in severely neutropenic patients. Such decontamination may aim either for total gastrointestinal decontamination (using a combination of non-absorbable antibiotics) or for selective suppression of enterobacteriaceae. It is not clear which approach is preferable, but most Units use some form of gut prophylaxis. Systemic prophylaxis. Most centres do not use systemic antibiotics for prophylaxis, preferring to reserve them for treatment of actual or suspected infection. Imidazole derivatives and oral acyclovir probably protect against Candida and herpes simplex infections respectively, and are given as routine prophylaxis in most Units. Management of pyrexial episodes Broad-spectrum antibiotic combinations are given early and often without microbiological proof of infection. The initial choice of antibiotics will be influenced by the clinical circumstances; for example, gut symptoms will prompt the early introduction of metrionidazole. Subsequent microbiological evidence will determine later treatment. Most studies of therapeutic granulocyte transfusions have demonstrated a significant improvement in survival. However, the benefit is small and the continuous improvement of antibiotic regimes has meant that granulocyte transfusions are now rarely employed. Their use should be reserved for ill patients with severe neutropenia and for definite bacterial infection persisting in the face of maximum appropriate antibiotic therapy. Marrow Recovery Both GM- and G-CSF shorten the neutropenia following immunoradiotherapy (e.g Brandt et al, 1988) and very recently this approach has actually been pursued following accidental irradiation (Butturini et al, 1988). Which cytokine is better and whether the action of either might be potentiated by other cytokines such as

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IL–3 have not yet been determined. However, it now seems clear that cytokine treatment in some form or another is likely to be used in radiation victims in an attempt to minimise neutropenia and its attendant complications. Bone marrow transplantation If irradiation has caused irreversible damage to the most primitive haematopoietic progenitors, only bone marrow transplantation will aid bone marrow recovery. Autologous BMT would clearly be ideal in these circumstances, but this treatment would require the prophylactic harvesting of bone marrow from all radiation workers—hardly a reasonable option for the forseeable future. Allogeneic BMT also offers the prospect of rescuing the patient from irreversible progenitor damage (Gale & Reisner, 1988) However, this approach is fraught with difficulties. HLA-identical marrow from either a sib or a donor panel is required and this takes time and needs host leucocytes in substantial numbers. Also, the graft may cause serious GVHD in a patient who might have recovered spontaneously. Allo-BMT is not therefore an option unless the patient’s radiation exposure is known with some accuracy to be one that is almost certain to cause irreversible marrow damage without being inevitably fatal to other tissues. Even then, logistic difficulties mauy be insurmountable and Chernobyl (see later) has shown that allo-BMT is unlikely to be an important treatment option for radiation accidents in the immediate future. Allo-BMT from matched unrelated or from unmatched donors are currently high-risk procedures. Future immunological advances may, however, overcome these current difficulties and these forms of allo-BMT may become poosible treatment options at some future date. The lessons of Chernobyl 21/22 patients who received >6Gy died within 28 days. Mostly as a result of radiation burns rather than of immunosuppression. 7/23 patients who received 4–6Gy died and in all cases radiation burns were thought to be the cause of death. Only 1 death occurred among the more than 60 patients receiving doses