Exposure of the U.S. Population from Occupational Radiation: Recommendations of the National Council on Radiation Protection and Measurements (N C R P Report)

NCRP REPORT No. 101

EXPOSURE OF THE U.S. POPULATION FROM OCCUPATIONAL RADIATION Recommendations of the NATIONAL COUNCIL O N RADIATION PROTECTION AND MEASUREMENTS

Issued )une 1 , 7 989

National Council on Radiation Protection and Measurements 7910 WOODMONT AVENUE / BETHESDA, MD 20814

LEGAL NOTICE This report was prepared by the National Council on Radiation Protection and Measurements (NCRP). The Council strives to provide accurate, complete and useful information in its reports. However, neither t h e NCRP, the members of NCRP, other persons contributing to or assisting in the preparation of this report, nor any person acting on the behalf of any of these parties (a) makes any warranty or representation, express or implied, with respect to the accuracy, completeness or usefulness of the information contained in this report, or t h a t the use of any information, method or process hsclosed in this report may not infringe on privately owned rights; or (b) assumes any liability with respect to the use of, or for damages resulting from the use of any information, method or process disclosed in this report, under the Civil R:ghts Act of 1964, Section 701 et seq. as ametrded 4 2 V.S.C. Section 2000e et seq. (Title VII) or any other statutory or common law theory gouerniw liability.

Library of Congress Cataloging-in-Publication Data Exposure of the U.S. population from occupational radiation: recommendations of the National Council on Radiation Protection and Measurements. cm.-(NCRP report ; no. 101) p. lssued J u n e 1989 Bibliography: p. Includes index. ISBN 0-929600-05-3 1. Ionizing radiation-Dosage-United States. 2. Radiation workersDiseases-United States. 3. Radiation dosimetry. 4. Radiation-Safety measures-United States. I. National Council on Radiation Protection and Measurements. 11. Title: Exposure of the US population from occupational radiation. In. Series. RA569.E98 1989 363.1'79-dc19 89-3141 CIP

Copyright O National Council on Radiation Protection and Measurements 1989 All rights reserved. This publication is protected by copyright. No part of this publication may be reproduced in any form or by any means, including photocopying, or utilized by any information storage and retrieval system without written permission from the copyright owner, except for brief quotation in critical articles or reviews.

Preface The NCRP has long recognized the need for a clear assessment of the magnitude of doses from various sources of radiation to which the population of the U.S. is exposed. In anticipation of the need to gather data for input into this process, five assessment committees, each addressing a different source category, were established. NCRP reports assessing exposures from natural background, consumer products, nuclear power generation, and diagnostic medical radiation have been published (NCRP, 1987a,b,c,d, NCRP, 1989). This Report is concerned with the assessment of the dose to the population from occupational radiation. The Report outlines reasons for personnel monitoring, personnel dosimetry methods, and uncertainties associated with personnel dosimetry. Occupationally exposed populations are reviewed and annual effective dose equivalents are provided. One highlight of the report is the inclusion of neutron dose equivalents. Conclusions and recommendations for the area of occupational exposures a r e given and a glossary is presented. This Report represents one source of information for the overall summary of exposure of the population from all sources which was presented in NCRP Report No. 93, Ionizing Radiation Exposure of'the Population of the United States (NCRP, 1987d). The International System of Units (SI) is used in this Report. Numerical values followed by the value in conventional units in parentheses, in accordance with the procedure set forth in NCRP Report No. 82, SZ Units in Radiation Protection and Measurements. This report was prepared by the Council's Scientific Committee 45, on Radiation Received by Radiation Employees. Serving on the Committee for preparation of this report were:

Donald E. Barber, Chairman School of Public Health University of Minnesota Minneapolis, Minnesota Barbara G. Brooks Lawrence H. Lanzl Office of Nuclear Regulatory Department of Medical Research Physics U.S. Nuclear Regulatory Rush-Presbyterian-St. Commission Luke's Medical Center Washington, D.C. Chicago, Illinois

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PREFACE

Roy E. Shore

Paul S. Stansbury

Institute of Environmental Medicine New York University Medical Center New York, New York

General Electric Company Wilmington, North Carolina

Robert A. Wynveen Environmental Safety and Health Department Argonne National Lab Argonne, Illinois

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NClZP Secretariat: Thomas M . Koval The Council wishes to express its appreciation to the Committee members for the time and effort devoted to the preparation of this Report.

Warren K. Sinclair President Bethesda, Maryland March 15,1989

Contents 1. Introduction .................................................. 1.1 Purpose and Objectives ............................... 1.2 Scope and Limitations ................................ 1.2.1 Problems In Making Comparisons .......... 1.2.2 Quantities Examined ......................... 1.2.3 Exposure Categories .......................... Need to Stratify Data within Occupational 1.3 Categories ........................................... 2. Personnel Dosimetry ....................................... 2.1 Reasons for Personnel Monitoring ................... Review of Personnel Dosimetry Methods ........... 2.2 2.3 Uncertainties Associated with Personnel Dosimetry ............................................ 2.3.1 External Dose Equivalent .................... 2.3.2 Internal Effective Dose Equivalent ......... 2.3.3 Uncertainties in Estimating Population Dose Equivalents ........................... 2.4 Deriving Population Dose Equivalents from Measured Doses ....................................... 3 . Review of Occupationally Exposed Populations ...... 3.1 Neutron Dose Equivalents ............................ Environmental Protection Agency (EPA) Report 3.2 Overview ............................................. 3.3 Nuclear Power Production ............................ 3.3.1 Introduction ................................... 3.3.2 Uranium Mines ............................... 3.3.3 Uranium Mills ................................ 3.3.4 Uranium Fuel Fabrication ................... 3.3.5 Commercial Light Water Nuclear Power Plants ........................................ 3.3.5.1 Collective Dose Equivalent by Work Function and Personnel Type ............................... 3.3.5.2 Task Specific Information .......... 3.3.5.3 Transient or Short-term Workers ...........................

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CONTENTS

Nuclear Powered Ships and Support Facilities .................................... 3.3.7 General Conclusions Related to Nuclear Power Plants ................................ 3.4 Medical Occupational Exposure ...................... 3.5 U.S. Public Health Service (PHs) .................... 3.6 Industrial Workers (other than Nuclear Fuel Cycle) ................................................. 3.7 U.S. Department of Energy (DOE) Laboratories ... 3.7.1 Introduction ................................... 3.7.2 Annual Average Dose Equivalent ........... 3.7.3 Annual Collective Dose Equivalent ......... 3.8 Commercial Aviation .................................. 4. Summary ...................................................... 4.1 Data Summary ........................................ 4.2 Worker Census ......................................... 4.3 Mean Annual Effective Dose Equivalents Compared to Limits ................................. 4.4 Cumulative Effective Dose Equivalents ............. 4.5 High Effective Dose Equivalents ..................... 4.6 Data Management ..................................... 5. Conclusions and Recommendations ..................... Appendix A: Glossary .............................................. References ........................................................... The NCRP ........................................................... NCRP Publications ................................................. Index ................................................................. 3.3.6

1. Introduction 1.1 Purpose and Objectives Numerous investigators have examined occupational exposure to ionizing radiation as a function of occupation (Klement et al., 1972; Cook and Nelson, 1980; Fujimoto et al., 1985; Kumazawa et al., 1984). The National Council on Radiation Protection and Measurements (NCRP) has reviewed the literature on the subject of occupational exposure to ionizing radiation to assemble, in a single document, the effective dose equivalents and the collective effective dose equivalents (see Glossary in Appendix A) for the U.S. work force. Although achieving this goal involved the difficulties described in Section 1.2.1, the current Report provides evidence that occupational exposures are responsible for only a small fraction of the total collective effective dose equivalent for the entire U.S. population. The current Report is intended primarily for the information of the radiation protection community, but i t should also be of interest to the layperson for the perspective it provides on the contribution of occupational exposures to the total population exposure. The objectives of this review were a s follows: 1. Determine whether a reliable, quantitative statement of effective dose equivalent is possible based on studies already reported. 2. Document the best available estimate of effective dose equivalent received by radiation employees a s a function of occupation. 3. Contribute to improvement in the estimation of effective dose equivalent a s a function of occupation. 4. Determine whether it is possible to establish trends in effective dose equivalent with existing data. 5. Identify occupations in which workers receive the largest individual and collective effective dose equivalents, especially those occupations in which there is a potential for reduction of effective dose equivalent with changes in radiation protection practices. 6. Identify needs for additional information, studies and monitoring. 7. Recommend improvements in monitoring methods, data recovery, and analyses for future studies.

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1. INTRODUCTION

Although improvements in the recording of personnel dosimetry data are possible and desirable, a separate NCRP report addresses the issue of record keeping and only a few observations related to this issue are included in the current Report. Data from a report by the U.S. Environmental Protection Agency (Kumazawa et al., 1984) have been included in a separate section of this Report because of the wealth of information that report contains on many occupational categories, including medical staff. The present Report expands on that report and breaks new ground on what is known about the effective dose equivalent and the collective effective dose equivalent as a function of occupation. The radiation exposure data from several specific organizations and segments of the occupationally exposed population have been included in some detail in this Report, either because of the comprehensive nature of their exposure records or the substantial size of the occupationally exposed population they represent; e.g., the U.S. Department of Energy (DOE) and the population exposed in the nuclear power industry. The review of the data clearly indicated the need to include some discussion of the reasons for and the uncertainties associated with personnel dosimetry. There was also a specific interest in stratifying the data with respect to high-LET radiation, low-LET radiation, and effective dose equivalent from internal depositions of radioactive materials. This stratification is extremely difficult to achieve because of the limited information available from data reported in the literature, but a t least some indication of the importance of stratifying occupational exposures was possible.

1.2 Scope and Limitations There are limitations on the use of personnel dosimetry data for the accurate determination of effective dose equivalent to individual radiation workers. These limitations are based on three factors, the importance of which depend upon the type of radiation field being measured: 1. orientation of the dosimeter and employee with respect to the radiation field, 2. accuracy of exposure evaluation of the dosimeter under both carefully controlled laboratory conditions and variable field conditions, and 3. relationship of dosimeter measurements to the effective dose equivalent.

1.2 SCOPE ANDLIMITATIONS

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Personnel dosimeters are designed and used primarily to assure that adequate protection is provided to the wearer and to comply with regulations. Although dosimeters, in varying degrees of sophistication, measure doses which can be converted to dose at various depths in tissue, they are not intended to provide an exclusive measure of organ dose or an accurate measurement of the effective dose equivalent. Additional data concerning the source and exposure conditions are usually required to permit the calculation of the effective dose equivalent. The International Commission on Radiation Units and Measurements carefully defines effective dose equivalent and the relationship of this quantity to the quantities measured by personnel dosimeters worn on the surface of the body (ICRU, 1985). Ideally, personnel dosimetry data should include information sufficient to enable reasonable estimation (within 2 30%)of the average and collective effective dose equivalents; however, published exposure data rarely are sufficiently detailed to enable this to be done. Usually, the reported dose equivalents are the result of conversion of a dosimeter dose to a surface dose equivalent a t the point of measurement by simple multiplication by a quality andlor calibration factor. Even if it were possible to convert reported exposures and doses to precise effective dose equivalents, it is highly unlikely that the biases introduced by this assumption would significantly alter the results and conclusions of this Report. Consequently, in this Report, personnel exposures reported in units of dose equivalent, dose, or exposure for low-LET radiation, are assumed to represent effective dose equivalents.

1.2.1 Problems Zn Making Comparisons When one attempts to summarize and compare average doses reported in the literature, a number of difficulties are encountered. 1. Some reported average doses are based on the total population monitored. Others are based on that fraction of the population exposed to doses above some minimum detectable level (measurably exposed workers). 2. Minimum detectable levels vary as a function of type of dosimeter used and are often chosen arbitrarily. 3. ,The statistical errors associated with the data are rarely documented. 4. Job classifications often differ from one report to another. When they are the same, cross-over of workers from one job classification to another and activities involving multiple job classifications confound the observations. For example, teleth-

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1. INTRODUCTION

erapy personnel often are responsible for brachytherapy as well. 5. Extraordinary circumstances (e.g., major, non-routine changes in operations or maintenance) in an industry in any given year distort the averages (e.g., the closing of Public Health Hospitals in 1982 resulted in loss of personnel from exposure situations that might otherwise have continued). 6. The actual types of radiation sources and radioactive materials used can differ within a job classification and function. 7. Administrative changes in record keeping occur, such as changing from recording minimum detectable doses as zero to recording the numerical value of the minimum detectable dose. 8. Different conversion factors are used by different organizations to convert beta, gamma and neutron exposures to dose equivalents. 9. The use of different monitoring frequencies (dosimeter exchange periods) can produce different average and total exposures even if similar actual exposures exist. 10. Exposure data are frequently not given for the same years for different occupational categories. Comparative analyses between data reported by different authors would be facilitated if radiation exposure data reported in the literature included: 1. the minimum detectable level (MDL)for the dosimeter and how data a t or below the MDL were recorded (i.e., as zero or the dose equivalent corresponding to the MDL), 2. the standard deviations associated with the means of observations, 3. a statement concerning administrative changes, if any, that would affect the reported average dose equivalent, 4. a description of how the dosimeter data was converted to dose equivalent, and 5. the monitoring period used for each personnel dosimeter measurement.

1.2.2 Quantities Examined

In this report, we assess the average dose equivalent and the collective dose equivalent for people exposed in various occupations. For some purposes, it may be more meaningful to consider quantities other than dose equivalent. For example, for risktbenefit considerations or intercomparisons where large differences in produc-

1.2 SCOPE AND LIMITATIONS

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tion of power arise, it may be useful to examine dose equivalent per unit of power produced rather than individual or average dose equivalent. Similarly, in medical radiology, the dose equivalent per projection or per diagnostic procedure would be preferable to simple average and collective dose equivalents for risktbenefit considerations. Although risk benefit considerations apply primarily to patient exposure when one is concerned with medical exposures, the occupational exposure of medical staff is proportional to both patient workload and patient exposure. However, in this Report the average or collective dose equivalent is given to enable the reader to assess the potential health impact on the population a s a whole for numerous occupational categories. These quantities can be used to examine trends, establish priorities and provide information for ALARA analyses for major occupational groups. No attempt has been made to weight or correct the data (for comparative purposes) for variables such as the following: number of facilities or sources. amount of radioactive material. megawatt years of power produced by a nuclear power plant. dose per x-ray projection. frequency of inspection violations. number of overexposures. highest individual dose. An occupationally exposed population monitored with personnel dosimeters is composed of two major segments. Usually the larger segment of the population includes those who are monitored but receive doses below some minimum detectable level (MDL). The smaller segment includes those who are monitored and receive doses equal to or greater than the MDL. This latter segment is referred to a s the "measurably exposed" population. When a n average dose equivalent is based on these two segments combined, it is much smaller than the average dose equivalent based on the measurably exposed segment alone, X,, if a major fraction of the population is exposed to less than the MDL. Under such circumstances, the ratio of and X,provides a n indication of the dose distribution among the personnel monitored. This ratio is especially high in those occupations where most of the exposures are below the MDL, as in the case of dental hygienists or dentists. Conversely, when most of the exposures are equal to or greater than the MDL, the ratio is small, as in the case of reactor maintenance workers. Therefore, the ratio can be used a s a n indicator of those occupations in which doses might be reduced. If people with neither exposure nor exposure potential were monitored in a deliberate effort to decrease the average exposure, this ratio would

x,,

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1. INTRODUCTION

be large and caution must be used in interpreting its significance. Nevertheless, the ratio can be used as a rough indicator of those occupations in which seemingly more than enough attention is given to personnel monitoring, as apparently is the case for many occupational categories. Another ratio, the Collective Dose Ratio (CR) is the ratio of annual collective dose equivalent determined from doses exceeding 15 mSv (1.5 rem) per year to total collective dose equivalent. This is equivalent to the collective absorbed dose ratio (MR) used by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 1982).This ratio also provides an indication of the shape of dose distributions. The NCRP uses CR as the symbol for this ratio to avoid confusing MR with exposure and to facilitate recall of the meaning of the symbol. UNSCEAR (1982) found CR values from 0 to 0.8 but regarded a range of 0.05 to 0.5 as normal for most categories of occupational exposure. The NCRP, in this Report, finds CR to range from to 0.6. This ratio is, of course, a strong function of both the number of observations and the dose distributions above and below 15 mSv (1.5 rem).

1.2.3 Exposure Categories

The following types of personnel categories are considered in either this Report or in the references. The present Report emphasizes those categories which contribute most significantly to the collective dose equivalent. Accelerator personnel Administrative personnel Department of Energy (DOE) personnel Contractor employees Visitors Reactor facility employees Fuel fabrication employees Fuel fabrication, processing and reprocessing personnel Uranium enrichment process employees Weapons fabrication and testing employees Office workers Accelerator workers General research workers Others Education Industrial

1.3 DATA STRATIFICATION

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Radiographic Manufacturing Distribution Well logging Medical Dental Hospital Private practice Veterinary Chiropractic Podiatry Nuclear power plant Commercial Naval Fleet Shipyard Transportation Airline crews Trucking and other shipping Uranium fuel cycle Miners Millers Fuel fabricators Fuel processors Uranium enrichment Research Other The list of specific tasks that involve actual or potential exposure to ionizing radiation is long. The length of the list is a function of how finely occupational activities are divided and the specific terms used to describe those tasks. Most of the data in this report are for U.S.populations but some data from Canada and other countries are included for comparison. When international comparisons and temporal trends are examined, the reader should consider sociopolitical and economic factors that influence the observations such as the termination of commercial fuel reprocessing in the United States in the late nineteen seventies.

1.3 Need to Stratify Data within Occupational Categories

When a relatively small number of people within a particular occupational category receive much higher doses than those received

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1. INTRODUCTION

by others, the mean dose equivalent for all people within the category is still useful for calculating collective dose equivalent; but, this mean may obscure the presence of the high exposure group in the category and is artificially high with respect to the remainder. For example, Hughes et al. (1983) found the average annual dose equivalent for five nurses to be 23 mSv (2.3 rem) and the average annual dose equivalent for five laboratory personnel involved in brachytherapy to be 15 mSv (1.5 rem). These averages a r e well above the average dose equivalent for all 437 personnel in the radiotherapy occupational category, which was 2.57 mSv (0.26 rem). This example illustrates that persons within a single, broad job classification can experience widely different doses. Unfortunately, stratification of types of exposures within general occupational categories is often impossible without personal communication with the people exposed and those maintaining the records. Baker (1988) reported annual dose equivalents of 5.5 mSv (0.55 rem) for cardiologists in general practice, 18 mSv (1.8 rem) for cardiologists who perform catheterizations, and 16 mSv (1.6 rem) for radiologists who perform special procedures. These mean dose equivalents are significantly larger than the mean dose equivalents reported by Kumazawa et al. (1984) for medical personnel. This again illustrates the need for detailed stratification of occupationally exposed groups if the personnel who experience the higher dose equivalents a r e to be identified.

2. Personnel Dosimetry 2.1 Reasons for Personnel Monitoring There are many reasons for using personnel dosimeters. They are used to: 1. assess the exposure of both individuals and groups of people, primarily for radiation protection purposes, 2. document exposure (or the absence thereof) for regulatory or legal purposes (Wachsmann, 1961 and Forgotson, 19631, 3. detect unsafe working practices, 4. detect changes in exposure conditions (including accidental exposures), 5. aid administration of ALARA (See Glossary) programs, 6. satisfy union or employee concerns, and 7. help satisfy society in general that radiation industries are concerned about the doses people receive. Certain types of operations require that employers file reports on personnel exposure and monitoring with various federal andlor state agencies. The U.S. Nuclear Regulatory Commission requires exposure reports for persons who are licensed by the Commission to operate a nuclear reactor designed to produce electrical energy, to manufacture or distribute certain quantities of by-product material, to possess radioactive material for industrial radiography, or to possess or use certain special nuclear materials, such as 235Uor plutonium, in fuel fabrication or fuel reprocessing. The U.S. Department of Energy requires: an annual report from all of its contractors. Many state governmental agencies require employers to maintain exposure records.

2.2 Review of Personnel Dosimetry Methods

Federal regulations related to radiation exposure define dose limits which must not be exceeded in a stated period of time. In order to gauge whether the worker is being subjected to doses greater than the limits, the regulations call for the recording of radiation doses of individual radiation workers. Occupational dose equivalents are

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PERSONNELDOSIMETRY

estimated from personnel dosimeter measurements. The film badge has been relied on for quantitative estimates of personnel exposure for many years. Since about the mid-1970's, greater reliance has been placed on thermoluminescent dosimeters (TLD) because of certain superior characteristics for personnel dosimetry and their lower detection thresholds for some types of radiation. Swaja (1984) conducted a survey in 1983 to determine the status of external gamma and neutron dosimetry with personnel dosimeters. A total of 102 organizations participated in his mail survey. Those surveyed included military, regulatory, university, hospital, laboratory and utility facilities. Respondents to his survey reported use of a number of different types of personnel dosimeters; but, the predominant types were thermoluminescent (LiF and CaSOJ and film badge dosimeters for gamma and x radiation, and albedo or track etch type detectors for neutrons. There is clearly no standard method for radiation monitoring among a variety of types of organizations that employ radiation workers.

2.3 Uncertainties Associated with Personnel Dosimetry

2.3.1 External Dose Equivalent

Under the simplest field circumstances, such a s the measurement of energetic gamma radiation exposure with a dosimeter badge such as a film badge or a thermoluminescent dosimeter, numerous variables introduce uncertainties into the assessment of exposure and dose delivered to the wearer of the dosimeter. These variables include: 1. location of the dosimeter on the person, 2. orientation of the person with respect to the radiation field, 3. directional dependence of the dosimeter response, 4. corrections required with control dosimeters, 5. representativeness of the location of the background dosimeter, 6. extreme temperature and humidity differences between dosimeter locations, 7. calibration accuracy of reference dosimeters used to evaluate exposure of personnel dosimeters, 8. dosimeter processing (or readout) accuracy, 9. suspected spurious doses (usually relatively high) which cannot be readily explained or discounted,

2.3 DOSIMETRY UNCERTAINTIES

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10. errors introduced as a result of lost or damaged dosimeters which require dose assumptions to be made in lieu of data, 11. energy dependence and lack of specificity with respect to the type of radiation, and 12. failure to wear the dosimeter. It is understandable that a n effective dose equivalent assessment for an individual based on a single personnel dosimeter measurement can have a large uncertainty associated with it. Careful attention to the dosimetry of the individual is assumed to be given by the radiation protection people responsible for administration of any dosimetry program so that the errors associated with the measurement are minimized. For gamma radiation, body absorption alone can introduce large errors into the evaluation of the dose delivered (Brodsky et al., 1965; ICRU, 1985). If a person wears a dosimeter on the chest and is frequently positioned so that the body is between the dosimeter and the source of radiation, a large error between the dose equivalent and the dose delivered to the dosimeter occurs. For =OCogamma rays, the error can be as high as 100 percent under usual exposure circumstances. For low-energy gamma or x radiations, such as those encountered in departments of diagnostic radiology and nuclear medicine, the error could be much larger. Most personnel do not remain in constant geometry with respect to the radiation sources they use. Consequently, the dosimeter measurements can be taken to be representative of the wearer's average exposure. Under unusual geometry conditions, the responsibility for acquiring measurements appropriate for the estimation of the effective dose equivalent rests with the person responsible for the monitoring program. Field studies in nuclear energy operations of various kinds indicate that during the period of employment, average cumulative doses are received from penetrating gamma radiation that is incident on the body from many directions. In these cases, the average dose is close to the maximum tissue dose, and a dosimeter badge, worn regularly and correctly, and processed and interpreted properly, is potentially capable of assessing an individual's annual dose to within 10 to 20 percent over the dose range of 1 to 50 mGy (100 to 5000 mrad) (Brodsky et al., 1964). If the radiation field is multidirectional or the worker orientation toward it is random, then the sum (or mean) of many measured exposures over time will tend to be a good approximation of cumulative (or mean) exposure for a person. One survey showed that workers reported 50 to 100 percent of their radiation exposure to be multidirectional, depending on type of work (Maruyama etal., 1981). When all variables are considered, one could envision an accuracy

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of about a factor of two associated with the ability of any personnel dosimeter to measure the effective dose equivalent. Throughout this Report, reasons are given for the large uncertainties associated with data from personnel dosimetry records. However, it should be noted that a large uncertainty in a small effective dose equivalent is not only tolerable but acceptable. Furthermore, because the number of observations is very large in some occupational groups, the errors on the means of the observations are very small. When one has a large number of measurements over a long period.of time there need be little concern about the representativeness of the sample. This probably explains the absence of error limits in many of the reports on occupational exposure to radiation. This shortcoming notwithstanding, the data clearly indicate that the work force in the United States receives a collective effective dose equivalent well below that which would be associated with current effective dose equivalent limits. Compared with other hazards in the workplace, radiation is probably the best characterized and measured. Existing dosimetry technology for external exposure situations is more than adequate to protect the health of the work force.

2.3.2 Internal Effective Dose Equivalent

Radioactive materials can enter the body by inhalation, ingestion, injection, or absorption through the skin. Internal dosimetry is the estimation of the dose to individual organs and the effective dose equivalent from radioactive materials taken into the body. It is impossible to measure directly the internal dose received by an individual. However, the dose can be calculated based on the quantity of radioactive material in the body, the distribution of the radioactive material within the body, the type and energy of radiation emitted by the radioactive material, the fraction of the emitted energy that is absorbed by the tissue, the mass of tissue involved and the value of the fractions which are used to convert the dose to effective dose equivalent. The values of some of these parameters can be estimated from data obtained by in vivo measurements made on the exposed workers. The magnitude of the uncertainty associated with the estimation of the internal dose and the effective dose equivalent is much larger than that associated with external dosimetry. The uncertainty is also a strong function of the nuclide in question and the technique used to estimate the dose. Traub and Robinson (1987) and Booth, et al. (1985)have investigated these uncertainties and have estimated the magnitude of them. Booth et al. (1985) suggest that the uncer-

2.3 DOSIMETRY UNCERTAINTIES

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tainty in calculating dose equivalents from lung counting can be a s large a s a factor of 3 a t a level corresponding to 30 percent of permissible lung burdens. Booth et al. (1985) reviewed sixty thousand in vivo measurements made on personnel a t four nuclear power plants (including both pressurized and boiling water types) operating under various conditions and four thousand in vivo measurements made on personnel from a single fuel fabrication facility over a period of three years. They used the data from 1978 to 1983 to estimate the average annual effective dose equivalent and found it to be trivial, 0.08 mSv (8 mrem). A study in 1977 (Wilkinson, 1984) reported that internal doses could be a concern for U.S.Department of Energy (DOE) workers exposed to 2 3 8 Pand ~ 239P~ but , only one percent or less of all DOE workers employed since DOE sites began operations, had intakes equal to or greater than 10 percent of the limits. Also, for the year 1983, Traub et al. (1985) reported that 97 percent of 15,134 DOE workers had either no internal uptakes of radioactive material or had uptakes less than 10 percent of the limits. There is potential for internal exposure in the uranium fuel fabrication industry (Thein et al., 1982). One study based on 4000 in vivo determinations over a three-year period a t one plant estimated a mean lung content of 47 pg of 235U.For this lung burden they estimated an average effective dose equivalent of 2.75 mSv (275 mrem). This effective dose equivalent is of the same order a s that estimated for the population of the U.S. from the decay products of naturally occurring 222Rn(NCRP, 1987d). Caution should be used in interpreting these results because of the large uncertainties associated with the assessment of effective dose equivalent from internal uptakes of radioactive materials. In most occupational categories, the average annual effective dose equivalent and the annual collective effective dose equivalent from internally deposited radioactive materials are likely to be trivial compared to the magnitude of these quantities attributable to external radiation.

2.3.3 Uncertainties in Estimating Population Dose Equivalents Distributions of annual occupational radiation exposure data typically are skewed because of the comparatively high number of low exposures. Because of the high degree of skewness, means and standard deviations taken arithmetically are unstable summary measures and inefficient estimates as well. These measures can be affected

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greatly by a few high values if the size of the population being characterized is small to moderate. Usually, if a series of dose distributions are being compared, a lognormal distribution is assumed and sample geometric means and standard deviations are calculated as summary statistics. Kumazawa and Numakunai (1981) suggested that a more complex distribution, which they called a "hybrid lognormal" model, provides a better fit to occupational radiation exposure data. However, a simple lognormal distribution is probably adequate for most comparisons of distributions and is easier to work with. Although the lognormal model is useful for comparing dose distributions, the arithmetic mean, rather than the geometric mean, is the statistic of choice for projecting risks for an exposed population (at least for the linear model for biological response to radiation). There are several important segments of the total population monitored with personnel dosimeters. There are those who are monitored but receive exposure below the minimum detectable level (MDL) for the dosimeter, those who are monitored and receive exposures above the MDL and, those who receive exceptionally high exposures. In this Report, the "monitored population" refers to the entire population wearing personnel dosimeters. Those exposed to greater than the MDL are referred to as, "measurably exposed" and those exposed a t or below the MDL are referred to as "not measurably exposed." If the average dose equivalents of different populations are to be compared, information is required as to the size and management of the population segment not measurably exposed, because this will affect appreciably the means and variances (Hutchison, 1982). This information rarely appears in published articles on personnel dosimetry. The treatment of the not measurably exposed segment will be critical to an accurate estimate of the mean when this segment is large relative to the monitored population. The magnitude of the change in the mean dose equivalent attributable to including or excluding a low-exposure group may be appreciated by the following example. Suppose that about 30 percent ofnuclear power plant workers receive measurable dose equivalents less than 1 mSv (0.1 rem), but that this same group incurs only about 3 percent of the collective dose in this occupational category. If these low-exposure workers were excluded, the average dose equivalent for nuclear power plant workers would increase by 43 percent, 1/(1-0.3) = 1.43. Obviously, the magnitude of the differences in means with and without selected segments of a population will depend upon the distribution of dose equivalents within that population. The data in Table 2.1 were reported by Cohen et al. (1976) in a study which included 50 percent of the industrial x-ray facilities, 45

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TABLE2.1-Summary of t k number of industrial radiation doses by annual dose ranges in 10 states for the years 1970-75" (After C o k n et al., 1976) Annual '@pe of x-ray unit dose range ( ~ S V ) ~ ' . ~ Radiographic Analytical Mixed others

Accelerators

Radium source

Not measurable 0-1 1-2.5 2.5-5 5-7.5 7.5-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 100-110 110-120 120 + Yrotal number of individuals for all six years, 6,935. Total number of workers with measurable exposures, 2,148. bAnnual doses compiled over the six-year period. "Limitsin force at the time of these measurement. were higher than 50 mSv/y, d lmSv = 100 mrem.

percent of the accelerators (medical and non-medical), and 90 percent of the industrial radium facilities in the U.S. a t that time. The study encompassed about 34 percent of all U.S. workers exposed to industrial x-rays, 13 percent of all U.S. workers exposed a t accelerators and 23 percent of all U.S. workers exposed to radium sources. In this study, the dose equivalents for workers not measurably exposed were taken to be zero. If they had been taken to be 0.1 mSv (10 mrem) (the approximate MDL for personnel dosimeters exposed to penetrating radiation) instead of zero, the mean annual dose equivalent and collective dose equivalent would have increased by only about 5 percent. This would suggest that reasonable assumptions one might make about the mean dose equivalent for the not measurably exposed segment little affect the overall mean dose equivalent or the collective dose equivalent. However, if those not measurably exposed are excluded from the mean, then the mean dose equivalent becomes about 3.3 times the mean calculated with the dose equivalent for the not measurably exposed taken to be zero. The way the dose equivalent below the MDL is handled is not consistent and may introduce bias into the data. The collective dose

16

!

2.

PERSONNELDOSIMETRY

equivalent is little affected by the method of treating the not measurably exposed; but, the mean dose equivalent can be affected appreciably. The dosimeter renewal period can also affect the recorded dose equivalent because the MDL is a function of the length of the renewal period. If this period is constant, neither the mean dose equivalent nor the collective dose equivalent for the monitored population is much affected by the MDL unless the mean dose is close to the MDL. If one is interested in the collective effective dose equivalent, it can be shown that the value determined for most occupationally exposed populations is little affected by the way the not measurably exposed segment of the population is treated (i.e.,assuming the dose equivalent for the population with no measurable exposure to be either zero or the MDL, will usually have little effect on the collective dose for the population). Another problem, that of the segment of individuals exposed to doses close to or greater than the occupational limits is generally not severe, since the category includes less than 1in 1,000 in most large occupational series (Kumazawa et al., 1984). A number of procedures may be employed for assigning a dose equivalent to this segment. The choice of procedure will rarely have an appreciable effect on the mean and variance of the population (Hutchison, 1982). Although individuals with exceptionally high exposure are the individuals of greatest concern relative to risk and radiation protection practices, their exposures usually do not greatly affect the mean for the population because they represent such a small fraction of the population. Using the x-ray data in the first three columns of Table 2.1 as an example, the effect of deleting all the dose equivalents over 50 mSv (5 rem) is to reduce the estimated mean and the estimated collective dose equivalent by about 25 percent. It is also important to be aware that the distribution of the doses for a whole occupational category cannot be assumed to be representative of the dose distribution over time for an individual in the occupational category. Johnston et al. (1986) have shown that the distribution of doses to all individuals in a particular monitoring period is not necessarily the same as the distribution of doses to a particular individual in all monitoring periods.

2.4 Deriving Population Dose Equivalents from Measured Doses Because of the uncertainties introduced as a consequence of the handling of dose equivalents below the MDL, one might reasonably

2.4 DERIVING DOSE EQUIVALENTS

1

17

consider the possibility of predicting the mean dose equivalent for a monitored population from the mean dose equivalent for the measurably exposed segment of that population. The data suggest that in the United States, the mean dose equivalent for the monitored population is about one-half the mean dose equivalent for the measurably exposed segment. However, the collective dose equivalent for the monitored population will nearly equal the collective dose for the measurably exposed segment. Collective and mean dose equivalent can be estimated for the monitored population using data from the measurably exposed segment only, if the ratio of the number of those monitored to those measurably exposed is known and provided the population is large. This ratio is about two when the MDL is taken to be 0.2 mSv (20 mrem) for a single measurement and is reasonably constant over time for the work force as a whole. Brooks (1981b) reported the number of individuals monitored and the number measurably exposed for different lengths of employment ranging from less than 90 days to 20 years. The data apply to nuclear power plant personnel who terminated their employment during the period 1969 to 1977. The ratio of the number monitored to the number measurably exposed varied from 1.1to 1.7 and is somewhat higher in the early and later years of employment as opposed to the intermediate years. For the years 1973 to 1983, data reported by Brooks et al. (1985) and Schmitt and Brice (1984) yield a ratio of 1.5 to 2.3 for nuclear power plant and fuel fabrication personnel in the U.S. Kumazawa et al. (1984) also reported a value of 2 for the ratio of mean measured dose equivalents to the mean of dose equivalents for those monitored. A ratio of 2 in these means implies that nearly half the population was below the MDL; i.e, that the ratio of the number monitored to the number measurably exposed approached two. Hutchison (1982) observed ratios of the number monitored to the number measurably exposed to be 2 for personnel in nuclear industry, but for medical personnel the ratio was 4. He used 0.1 mSv (10 mrem) as the MDL for a single measurement. Data obtained from R.S. Landauer Jr. and Co. (1975) from 1859 customers involving 25,746 monitored individuals show that the ratio of persons monitored to persons measurably exposed is a function of occupational category. When all the categories are combined the ratio is 2.6. Kumazawa et al. (1984) found this ratio ranged from 1.3 for Navy personnel to 9.6 for Public Health Service personnel, with an overall ratio of 1.8 for all federal government workers. This ratio is more variable and somewhat higher in Canada than in the U.S. (Fujimoto et al., 1985a). The average ratio for all worker classifications was 3.2. The greater variability is a t least partially

18

/

2. PERSONNELDOSIMETRY

attributable to the more detailed occupational categories, and resulting smaller numbers of workers per category, in the Canadian data. The ratio of number of personnel monitored to those measurably exposed in Canada in 1983 ranged from 1.1 for reactor fuel handlers to 44.4 for dental hygienists (Fujimoto et al., 1985a). This clearly demonstrates the impossibility of accurately predicting the mean dose equivalent for the population monitored from that of the measurably exposed segment of the population in an individual worker classification.

3. Review of Occupationally Exposed Populations

3.1 Neutron Dose Equivalents

The minimum detectable dose equivalent for nuclear track emulsion type A (NTA) film under ideal conditions is about 0.20 mSv (20 mrem) for neutrons with energies greater than 1MeV (Baum, 1984). This minimum detectable dose equivalent rises proportionately with photon exposure. At the Brookhaven National Laboratory (BNL), significant neutron dose equivalents arise only a t accelerators, and neutrons contribute only about 15 percent ofthe total dose equivalent (Baum, 1984). Of course, the comparative importance of neutron dose equivalents is a function of the quality factor used and the depth a t which the dose equivalent is determined. In this section, dose equivalent is taken to be entrance or surface dose equivalent. Neutron dose equivalents appear to be trivial compared to photon doses around either betatrons or linear accelerators in medical use. The ratio of neutron dose equivalent (Sv or rem) to photon absorbed dose (Gy or rad) within a meter or less of the isocenter (see Glossary) of either type of accelerator ranges from 0.025 to 4.1 mSv per Gy (2.5 to 410 mrem per rad) even when the photon energy mode is as high as 45 MeV (NCRP, 1984). Fleischer et al. (1984) observed that the standard deviation associated with individual measurements of neutron dose equivalent using the very best methods under ideal conditions is about 30 to 40 percent. The study involved track-etching techniques using ally1 diglycol carbonate (CR39) and polycarbonate films. Under field conditions uncertainties as large as a factor of two could easily occur as suggested by the range of minimum detectable levels reported a t U.S. Department of Energy (DOE) facilities (Murphy et al., 1981). The number of personnel monitored for neutrons in a survey of 24 DOE facilities in 1979 was 24,787, of whom only 336 (1.4 percent) received neutron dose equivalents greater then 5 mSv (greater than 0.5 rem) (Murphy et al., 1981). The distribution of neutron dose equivalents a t DOE facilities is given in Table 3.1. Almost 80 percent

20

1

3. REVIEW O F OCCUPATIONALLY EXPOSED POPULATIONS

TABLE3.1-Neutron Dose (Sv)^

dose equivalents i n the year 1979 at 24 DOE facilities (After Murphy et al., 1981) Collective Doseb person-Sv' Number of personnel

0 - 0.005 24,451 61.1 0.005 - 0.010 259 1.9 0.010 - 0.020 68 1.0 5 0.1 0.020 - 0.030 4 0.1 0.030 - 0.040 0.040 - 0.050 3 0 Totals 24,787 64.2 "1 Sv = 100 rem. T h e product of the dose mid-range times the number of personnel. Kumazawa (1986)estimated total collective dose equivalents to be 10 to 19 person-Sv (1,000 and 1,900 person rem). ' 1 person-Sv = 100 person-rem, Q assumed to be 10.

of the personnel monitored a t these facilities performed defenserelated work. For non-thermal neutrons, the MDL is about 10 to 30 percent of occupational dose equivalent limits a t DOE facilities irrespective of the type of monitoring device used. The types used are given in Table 3.2. There are large uncertainties associated with these estimates, because the quality factor (Q) for neutrons is a function of neutron energy, and the energies to which personnel are exposed may not be known. Small amounts of hydrogenous material near or around the employee readily alter high energy neutron spectra. It would be a monumental task to take into account the variation of Q with neutron energies in evaluating the dose equivalent from neutrons. Consequently, conservatism is the order of the day, and dose equivalent TABLE3.2-Personnel

Dosimeter Type TLD - Albedo NTA Film TLD-Albedo + NTA Film TLD + Track Etch NTA Film + Polycarbonate

neutron dosimeters used i n the year 1979 at 24 DOE facilities (After Murphy et al., 1981) Minimum Detectable Number of Level" Facilities Personnel (~SV)~ 16 21,033 0.1-0.5 3 2,667 0.3-0.5 3 1

218 144

0.1-0.5 0.4-0.5

1

725

0.4-0.5

"For fast neutrons. For a n occupational environment over a 4-week period; 0.5 mSv (50 mrem) corresponds to a n average rate of 0.31 m r e m h or 12 percent of the average, occupational limit. Quality factors used ranged from 3 to 10 depending on neutron energy. bl mSv = 100 mrem.

3.1 NEUTRON DOSE EQUIVALENTS

1

21

TABLE 3.3-Neutron dose equivalent to Navy personnel, calendar year 1984 (After Green. 1986) Neutron dose equivalent ranae (mSv)'

All totals

lbtal individuals monitored

lbtal Person-Svhc

15,414

2.94

Average annual neutron exposure for all persons monitored is 0.19 mSv (0.019 rern). For those exoosed the averaee is 0.24 mSv (0.024rem). "1 mSv = 100 mrem = 0.1 rem. blperson-Sv = 100 person-rem. 'Q taken to be 10.

rates are probably overestimated by a t least a factor of two (unless Q is taken to be 20 instead of 10). Nash et al. (1985) determined the response per rem of an albedo dosimeter (see Glossary) for 56 neutron spectra which were generated by moderating 241Am-Beand 252Cfneutron sources with various combinations of lucite, polyethylene and steel. The response per Sv of the albedo dosimeter, a %iF - 'LiF detector pair behind a cadmium shield encased in a plastic badge, varied by more than a factor of seven for spectra having average energies ranging from 0.4 to 4.5 MeV. It is possible to correct for this energy dependence and reduce the root mean square error in TLD response per Sv to less than 10 percent using measurements made with moderated BF3counters and rem meters. Table 3.3 summarizes the neutron dose equivalents for monitored personnel in the U.S. Navy. The population monitored for neutrons in the U.S. Navy is second in size only to the population in the U.S. Department of Energy (DOE) monitored for neutrons. Data provided in Table 3.3 are the results of measurements with LiF albedo dosimeters. The results were adjusted, where appropriate, for correct spectral response using techniques similar to those described above. Therefore, the results are considered a reliable reflection of neutron dose equivalents for U.S. Navy personnel. Tables 3.4 and 3.5 summarize data from selected nuclear power plants (Kindley, 1985). Inspection of the 1984 data for those measurably exposed indicates: 1. Average neutron dose equivalents ranged from 0.03 to 1.3 mSv (0.003 to 0.130 rern). 2. Average gamma dose equivalents ranged from 0.9 to 13.0 mSv (0.090 to 1.30 rern).

TABLE 3.4-Neutron and gamma radiation dose equivalents for the year 1984 at selected nuclear power plants (AfterKindley, 1985) NEUTRON Plant and

Number of personnel exposed

Dose equivalent (rnSvP Highest Average

Number of personnel

(mSv)'

0 PenonSV~.~

Highest

Average

2,827 2,369 1,872

30 45 49

0.9 8.4 13.0

2.55 19.90 24.62

0.23

0.024

7,068

-

6.7

47.07

0.22

0.0060

1,767

-

6.7

11.77

0.05 0.03 0.60 0.05 0.25 0.50 0.85 1.30

0.0025 0.0030 0.014 0.0075 0.0075 0.10 0.22 0.17

1,120 3,062 1,393 1,395 539 2,373 2,090 1,369

29 45 29 40 21 34 37 25

2.6 6.4 3.6 6.8 2.7 4.7 5.7 3.0

2.95 19.45 9.41 ,.05 1.47 11.17 11.95 4.14

5.6

0.53

13,341

-

4.9

65.59

953 5.6 0.038 68 AVG. (14) d v = 100 mrem = 0.1 rem. '1 person-Sv = LOO person-rem 'Q taken to be 10. dAveragesare for BWRs which have neutron exposures. A number of BWRs have no neutron exposures. 'No data available. Totals are the sum ofthe data for the plants listed.

4.9

4.69

28 68 10

6.0 0.3 d

106

-

AVG. (4)

27

-

PWR, D

51 100 23 150 30 203 258 134

0.4 e 1.6 0.3 1.0 2.1 16.4 7.9

949

-

B C TOTALr(4)

E (2) F G (2)

H (2) I (2) J (2) K (2) TOTALr(14)

"

0.58 0.05 0.40

Pers~n-Sv~.~

D m equivalent

0.016 0.0034 0.0040

(units)

BWRd,A(2)

L

GAMMA

elrposed

g

3< 8 d

53 25 0

TI

2: m

8

i 3 0

$

3.1 NEUTRON DOSE EQUIVALENTS

1

23

TABLE 3.5-Gamma to neutron dose ratios al selected nudearpowerplants, 1984 (Afler Kindley, 1985)

Plant

Boiling Water Reactor (BWR) A B C All BWRs

Personnel exposed

Average dose equivalent' GammaRieutron

Collective dose equivalent Gammd Neutron

100 34 187 67

2 158 33 29

156 5,853 6,155 1,961

21 30 60 8 17 11 7 9 14

53 212 6 135 11 9 7 2 8

1,180 6,483 361 1,255 196 110 54 24 123

Pressurized Water Reactor (PWR)

D E F G H I

J K All PWRs "Q for neutrons taken to be 10.

3. Average gamma to average neutron dose equivalent ratios ranged from 2 to 212. 4. Ratios (gamma to neutron) ofcollective dose equivalents ranged from 24 to 6,500. The highest neutron dose equivalent in Table 3.4 for site J is probably high by a factor of about 10 because interpretation of the dosimeter response was based on LiF calibrated with high energy neutrons only (Kindley, 1985). The comparatively high dose equivalent for site K was attributed primarily to a shielding design problem which has since been corrected. Consequently, the average and ranges in Table 3.4 overestimate the exposures in 1984. The data in Table 3.6 also show that although fast neutron dose equivalents a t nuclear power plants occasionally are measurable, average annual fast neutron dose equivalents to personnel are small compared with dose equivalents from gamma radiation. Further, for the nuclear power plants included in Table 3.6 there was no significant difference in neutron dose equivalents a t boiling water and pressurized water nuclear power plants. On the basis of this sample several conclusions are possible. Among them are: 1. Neutron and gamma radiation dose equivalents are highly variable from one nuclear power station to another. 2. The collective dose equivalent from neutron radiation is trivial compared to the collective dose equivalent from gamma radia-

24

/

3. REVIEW OF OCCUPATIONALLY EXPOSED POPULATIONS

TABLE3.6-Average annual fast neutron dose equivalents, measured andlor calculated, above MDLs for nuclear power plant personnel (After Kovach and Pavlich, 1985) Dose equivalents, mSv, at different nuclear power plants Pressurized water plants Boiling water plants B C D E

Year

A

1976 1977 1978 1979 1980 1981 1982 1983 1984 1985d

---

NDb ND

-ND

0.20(1)'

--0.35(15) 0.81(19) 0.33(47) 0.49(14)

ND ND ND ND 0.42(6) 0.34(25) 0.33(10)

ND ND ND ND ND -ND ND 0.20(3)

ND

--

ND ND ND ND

--

-----ND 0.30(2) 0.4384)

1.80(2)

ND ND ND 0.28(6) 0.28(6)

8--meansno data. bND means PO single dose greater than 0.2 mSv (20 mrem); therefore, an annual dose which is not detectable. 'Numbers in parentheses are the numbers of people with measurable doses. *The"year"1985 is through 9 December only because these were the latest available data at the time.

tion in the nuclear power plant population even if Q were doubled, in most situations. 3. Only about 8 percent of all nuclear power plant workers are measurably exposed to neutrons. 4. Although neutrons might be expected to coiltribute more to total dose equivalent at pressurized water than a t boiling water nuclear power plants, the data summarized here do not support such an expectation.

3.2 Environmental Protection Agency (EPA)Report

Overview (Kumazawa et al., 1984) Kumazawa et al. (1984) have prepared for the EPA a review of occupational exposure in the U.S. Their work is included in this Report because of its comprehensiveness for several occupational categories including medical practice, dentistry, industrial radiography and occupations associated with the nuclear fuel cycle. The occupational categories and data bases included in their work are summarized in Tables 3.7, 3.8 and 3.9. The mean and collective dose equivalents given in Tables 3.8 and 3.9 assume the MDL to be between 0.05 and 0.2 mSv (5 and 20 mrem) depending upon the year

:3.7--8ee~ipationsand their data bases examined by Kumazawa et al. (1984) DOSE DATA BASE I -_BASIS FOR POPULATION . _ -.-. ES _- PIMATE - - -

-

- -

--

MEDICINE: Dentistry Private practice (excluding radiologists) Hospital Veterinary and chiropractic Podiatry

INDUSTRY: Industrial radiography and manufacturing and dstribution

Dose distributions in each subcategory of medicine Estimate taken from the total number of dental in 1960,1965 and 1970 were constructed from con- workers. sideration of the dose distributions for 1975and 1980, Estimate taken from the number of x-ray machines in physicians' offices and in clinics. and trends of mean annual dose data for the period 1960-1980. The dose distributions used for each sub- Estimate of workers in hospitals relied on the number of non-federal radiologists based in the hospicategory in 1975 and 1980were constructed entirely tal. From commercial dosimetry data. Estimated from the number of x-ray machines in each type of medical practice Estimates taken from the number of podiatrists. Estimate taken from the corresponding numbers Dose distribution for industrial radiography was con- of by-product material licensees of the NRC and NRC agreement States. structed from NRC reports. Dose distribution for Manufacturing and Distribution was based on NRC reports and commercial dosimetry data.

OTHER INDUSTRIAL USERS The dose distribution for other industrial users was Estimate taken from the numbers of by-product estimated from the sum of the dose distributions in licensees, facilities using non-medical x-ray machines eighteen industrial workers groups of commercial and particle accelerator users. data. MISCELLANEOUS: Education

Transportation

Early dose distributions in education and transportation for the years 1960,1965and 1970 were based on academic and transportation licensee data in the AEC 1966-1971 film badge studies. Dose distributions in 1975 and 1980 were estimated from commercial dosimetry data.

Estimates of exposed faculty and staff were based on rough estimates of program offerings to students, that involved radiation courses. Estimates based on NRC studies.

BASIS FOR POPULATION ESTIMATE

DOSE DATA BASE

NUCLEAR FUEL CYCLE:

I

ci'

Dose distribution for nuclear power reactors in 1970 Estimates obtained from NRC reports. was obtained from a n NRC report. Distributions for all subcategories for 1960, 1965 and 1970 (except reactors) were constructed from the 1966-1971 film badge report for AEC and agreement states licensees Estimates obtained from a n NRC special study t h a t was updated by more recent information. and the trend of the dose distributions in each category. The 1975 and 1980 dose distributions in each subcategory were obtained from NRC reports, except for data on uranium enrichment workers which was obtained from ERDA/DOE reports.

2 E:fi

Department of Defense (DOD) The dose distributions for the years of 1960,1965 and Estimates were taken h m the Department ofDefense government records. 1970, for all government subcategories, were obtained Department of Energy (DOE) from government exposure data. Distributions for Estimates were taken from the Department of Energy government records. 1975and 1980 were determined from Federal Agency Other Federal Government data, except for the Veterans Administration where Estimates were taken from Federal Government Records. the dose distributions were estimated from commercia1 dosimetry data.

B

Nuclear power reactors and fuel fabrication and reprocessing Nuclear waste management and uranium mills Uranium enrichment

GOVERNMENT:

s>

Z

F

=:

g

g a 'u

S5 0

2

TABLE 3.8--Summary of mean annul dose equivalent to monitored workers, 1960-1985 (After Kumazawa et al.. 1984) Mean annual dose equivalent (rnSv). Occupation

Medicine Dentistry Private practice Hospital OtheP Industry Radiography Manufacturing and distribution Other users Nuclear Fuel Cycle Power plants Fuel fabrication and reprocessing Othe~ Government Dept. of Energy Dept. of Defense Other agenciesd

2.10 3.20 3.00

2.10 3.00 2.90

2.00 3.20 4.00

1.20 3.20 3.80

1.10 3.60 3.90

1.00 3.80 4.00

3.80 2.00 1.50 2.00 0.80 0.30 0.70 0.90 0.30 1.80

3.70 2.10 2.10 1.80 2.60 0.30 0.70 0.90 0.40 1.80

3.10 2.10 1.60 1.60 1.80 0.30 0.80 1.10 0.40 1.50

2.80 1.00 1.10 1.40 1.00 0.30 0.70 0.70 0.70 1.20

1.00 1.40 0.60 0.80 0.50 0.20 0.70 0.60 0.70 1.10

0.90 1.50

Miscellaneous Education Transportation All workers "1mSV = 100 mrem. bVeterinarians,chiropractors, and podiatrists. 'Uranium enrichment, nuclear waste management, and uranium mills. *PublicHealth Service (PHS) (workers in various agencies and facilities covered by the PHs Personnel Monitoring Program). 'Projected.

E 2

of exposure and all dose equivalents less than the MDL were taken to be zero. The dose equivalent distributions published in their report imply that 0.1 mSv (10 mrem) was a commonly used MDL. Except for nuclear power plant and transportation personnel the mean annual dose equivalent to monitored workers either declined or remained stable from 1960 to 1985. The mean annual dose equivalent for some occupational categories declined during this 15-year period by a s much a s a factor of 10 (e.g., dentistry) but for most occupations, the decrease was closer to a factor of 2 or 3. Occupational categories with the three highest mean dose equivalents projected for 1985 were: nuclear power plants (4 mSv or 400 mrem), industrial radiography (3 mSv or 300 mrem), and portions of the uranium fuel cycle (1.5 mSv or 150 mrem). The average doses in all other categories in Table 3.8 were projected to be 1 mSv (100 mrem) or less in 1985. Table 3.9 summarizes the collective dose equivalents for the same period and occupational categories given in Table 3.8. This table shows collective doses increasing for all industry, nuclear power plant and transportation personnel. The three categories with the highest projected collective doses were nuclear power plants (730 person-Sv), industrial "other" users (340 person-Sv) and hospitals (160 person-Sv). When one considers that background radiation delivers a n annual effective dose equivalent of 30 mSv (300 mrem), a collective effective dose equivalent of about 690,000 person-Sv (69,000,000 person-rem) to the U.S. population (NCRP, 1987d1,these occupational collective dose equivalents seem trivial by comparison. When all categories in Table 3.9 are combined, the collective dose equivalent projected for 1985 was about twice that found for 1960. The average exposure per worker decreased, but the number of workers increased. More recent data for nuclear power plant workers show that the projected values for these workers for the year 1985 was too high (see Section 3.3.5).

3.3 Nuclear Power Production

3.3.1

Introduction

Several studies and surveys (Kumazawa et al., 1984, and Brooks et al., 1982) demonstrate that although many more workers are potentially exposed to radiation in other occupations, the collective and average dose equivalents for workers a t commercial nuclear

TABLE3.9-Sum-

of annual collective dose equivalent to monitored workers 1960-1985 (After Kumazawa et al., 1984) Annual collective dose eauivalent (lo3 . - wrson-Sv)'

. ~ ~ ~ -

Occupation Medicine Dentistry Private practice Hospital OtheP Subtotal Industry Radiography Manufacturing and distributing Other users Subtotal Nuclear fuel cycle Power plants Fuel fabricators and reprocessors Other ' Subtotal Government Dept. of Energy Dept. of Defense Other agenciesd Subtotal Miscellaneous Education Transportation Subtotal TOTAL "1person-SV = 100 person-rem.

1960

1965

0.15 0.31 0.11 0.01 0.58

0.12 0.26 0.15 0.01 0.54

0.10 0.22 0.17 0.01 0.50

0.08 0.18 0.18 0.02 0.46

0.06 0.16 0.17 0.02 0.41

0.03 0.14 0.16 0.03 0.36

0.007

0.03

0.04

0.05

0.08

0.10

0.006 0.10 0.11

0.02 0.13 0.18

0.03 0.20 0.27

0.04 0.20 0.29

0.03 0.27 0.38

0.03 0.34 0.47

0.001

0.002

0.03

0.20

0.52

0.73

0.009 0.003 0.01

0.018 0.007 0.03

0.026 0.008 0.06

0.03 0.01 0.24

0.01 0.01 0.54

0.01 0.01 0.76

0.16 0.04 0.001 0.20

0.24 0.24 0.002 0.48

0.15 0.17 0.002 0.32

0.11 0.09 0.003 0.20

0.06 0.06 0.003 0.12

0.05 0.05 0.002 0.10

0.009 0.002 0.01 0.91

0.015 0.004 0.02 1.25

0.025 0.009 0.03 1.18

0.018 0.02 0.04 1.23

0.015 0.035 0.05 1.50

0.012 0.053 0.06 1.75

1970

1975

1980

1985O

z

sE *

8

2

., w U

bVeterinary medicine, chiropractic medicine, and podiatry. 'Uranium enrichment, nuclear waste management and uranium mills. dPHS (workers in various agenciea and facilities covered by the PHS Personnel Monitoring Program). 'Projected.

3 0 z \

h3

LD

30

/

3. REVIEW OF OCCUPATIONALLY EXPOSED POPULATIONS

power plants are second only to those of workers in underground uranium mines. The possibility of significant exposure was recognized early in the development of the industry, and there are considerable data on occupational doses of workers in this field. One of the major sources of these data is the annual exposure report that each licensed commercial nuclear power facility is required to submit to the U.S. Nuclear Regulatory Commission (NRC). These reports provide the dose distribution in 18 dose increments ranging from no measurable dose to 0.12 Sv (12 rem) or greater of all individuals (including visitors, contractor personnel, etc.) monitored a t each nuclear power plant site each year. Such reports have been collected, summarized and published by the NRC since 1972 so that industrywide trends in certain parameters, such as number of individuals monitored, average dose equivalents, etc., can be examined. Summarized below are exposures in the various stages of the nuclear fuel cycle ranging from uranium mines to the power plants themselves.

3.3.2

Uranium Mines

Miller (1977) estimated external and internal radiation exposure to several occupational categories in open-pit uranium mines by measuring gamma radiation from external sources, radon and its decay products, airborne uranium aerosols and body burdens of uranium. The occupational categories included excavation equipment operators, truck drivers, equipment maintenance personnel, ore control personnel and engineering staff. The average external exposure rate was observed to be of the order of 0.13 pC/(kgh) (0.5 mR/h); but, rates up to 2.6 &/(kgh) (10 mlUh) were observed near ore bodies containing a few percent uranium. Typical ore analysis in this mine was 0.44 percent U,Os, 0.05 percent UO, and 0.01 percent thorium, with some nodules exceeding 5 percent U308 These external exposure rates are somewhat higher than the average estimated by Kumazawa et al. (1984). Based on a mean annual dose equivalent of 3.5 mSv (350 mrem) in 1980 in underground uranium mines and assuming 1,600 workhours per year for measurably exposed miners, they estimated the average exposure rate to be 52 pC/(kgh) (0.2 mWh). The average external exposure rate in nonuranium metal mines they estimated to be 26 pC/(kgh) (0.1 mWh) based on a mean annual dose equivalent of 2.2 mSv (220 mrem) for measurably exposed miners in 1980. It appears likely that the external dose equivalent rates in open pit and underground uranium mines and underground nonuranium mines differ only by a factor of about 2. Dose equivalents from both external and internal sources are

3.3 NUCLEAR POWER PRODUCTION

/

31

delivered to miners as a result of the presence of radon, radon decay products and uranium aerosols. Miller (1977) reports annual dose equivalents from external sources ranging from 0.7 to 1.6 mSv (70 to 160 mrem) for 47 open-pit miners based on film badge measurements for the period July 1975 to February 1976. The internal depositions calculated from the concentrations of uranium in urine ranged from 4 to 8 percent of occupational limits for uranium during the period September 1975 to October 1975 (Miller, 1977). In spite of significant, removable radioactive material on equipment (4,000-20,000 alpha dpm per 100 cm2)and clothing, very little makes its way into miners. Miller (1977) also notes that the hazards from exposure to radiation and radioactive materials in this openpit mine are about the same as those encountered in underground uranium mining with the primary difference being attributable to lower concentrations of radon daughters in the open-pit mine. Table 3.10 summarizes exposures to radon and radon decay products in U.S. underground uranium mines from 1967 to 1972. The dose per working level month (WLM, see Glossary) to the bronchial epithelial cells depends upon both the physical assumptions made about the radon decay products and the biological assumptions made concerning the inhalation and deposition of the decay products. Depending upon the assumptions made, the calculated dose conversion factor ranges from 200 m G ~ / J h r n -to~ 40 G ~ l J h m (0.07 - ~ to 14 rad/WLM) (DOE, 1987). In this Report we have used 1.5 Gy/Jhm-3 (0.53 rad/WLM). If the quality factor for the energy de~ositedby the radon decay products is taken to be 20 and a weighting factor (wT) of 0.08 (ICRP, 1981) is applied, a factor of 2.4 S V / ~ T(0.85 ~ ~ rend/ - ~ WLM is obtained to convert WLM to effective dose equivalent. This is the same factor used by UNSCEAR (1982)to convert Jhm-3 (WLM) in mines to effective dose equivalent. In 1973, there were 115 operating underground uranium mines in the U.S. These mines employed approximately 1,430 miners (Goodman, 1973). The results of radon decay product measurements in 67 of these mines are given in Table 3.11. For comparison, the concentrations in six non-uranium underground mines are also given in Table 3.11. Although the sample size is small, the comparison shows similar ranges of exposures in both types of mines but lower concentrations occur in non-uranium mines more frequently than in uranium mines. Table 3.12 summarizes exposures to radon decay products in 62 underground uranium mines in the U.S. in 1977 (AIF, 1978). In this table, "production" includes production and development personnel. "Maintenance" includes mechanics and electricians. "Service" includes motormen, haulage crews, drift repairmen, station tenders, skip ten-

TABLE3.10-Average, full-shifl radon decay product concentrations in U.S. underground uranium mines, 1967-72 (Afler Archer, 1973) Year and number of workers

Exposure

WL

.

dm-*

1967

1968

1969

1970

1971

1972

Total workers Average exposure, WL

, Average exposure, WLM

,J h ~ n - ~ Average effective dose equivalent, Svb U

Collective effective dose equivalentb, person-Sv

E u 410

200

120

75

99

34

=Theconversion of WL to SI units (Jm-3) and rounding results in gaps in the ranges expressed in SI ( J m - 9 units. blSv = 100 rem. 1 person-Sv = 100 person-rem. Conversion factor taken to be 2.4 SvIJt~rn-~ (0.85 rernlWLM) for continuous exposure and WT = 0.08 (ICRP, 1981).

$

s

%=:

33

1

3.3 NUCLEAR POWER PRODUCTION

TABLE 3.11-Radon decay product concentrations in 67 U . S . underground uranium mines and 6 non-uranium mines in 1973 (After Goodman, 1973) No. of measurements Miners exposed to 2 6.2 (0.3 WL) (0.3 WL) Mines with 2 6.2

Percentages of measurements (0 - 0.3 WL) 0 - 6.2 >6.2 (0.3 WL)

U-mines

Other mines

267 767 67

539 703 6

53 47

84 16

ders, etc. "Salaried workers" include engineers, supervisors, geologists and ventilation personnel. In mines where production employees also perform maintenance, service and supervisory duties, such employees were classified as production workers. Kumazawa et al. (1984) noted that exposures reported by the Mine Safety and Health Administration for underground uranium mines in 1980 were lognormally distributed for exposures below about 3.5 x Jhm-3 (1 WLM). They estimated mean annual exposures of 2.1 x Jhm-3 (0.6 WLM) in 1975 and 1.8 x Jhm-3 (0.5 WLM) in 1980 for all underground uranium miners. For measurably exposed underground uranium miners the mean annual exposure Jhm-3 (1.1WLM) in 1975 and 3.2 x was estimated to be 3.9 x Jhm-3 (0.9 WLM) in 1980. They estimated the number of all underground uranium miners to be 6,000 in 1975 and 13,484 in 1980. These estimates are considerably higher than the 1430 miners in 1973 reported by Goodman (1973). The worldwide work force in non-uranium metal mines alone has been estimated to be between 90,000 and 100,000 (Kumazawa et al., 1984). Of these, about 4,200 were measurably exposed to concentrations in excess of 6.2 (0.3 WL) and received an annual exposure of approximately 1.1 x Jhm-3 (0.3 WLM) in 1980. I t therefore appears that the effective collective dose equivalent for all non-uranium underground mines would be a t least as large as the effective collective dose equivalent for underground uranium miners. Consequently miners, regardless of the type of mine in which they work, should be a high priority group for radiation exposure monitoring. In the late 1970s, the average exposure of uranium miners in the Jhm-3 (1WLM) per year. This U.S. was approximately 3.5 x is equivalent to an effective dose equivalent of about 8.5 mSv (0.85 rem). If the average effective dose equivalent is to be taken as the quantity of interest in establishing priorities with respect to radiation control and ALARA, the occupational exposures in underground uranium mines rank number 1. If the criterion for attention is the

.

TABLE3.12-Exposure of U.S.underground uranium miners to mdon decay products in 1977 as reported by 62 mine operators (After NF,1978)" Expasure

Jh~u-~

WLM

0-1.0 1.01-2.0 2.01-3.0 3.01-4.0 4.01-5.0b Total

0-0.0035 0.0035-0.0070 0.0070-0.011 0.011 -0.014 0.014 -0.018

Average exposure, WLM

,

Average effective dose equivalent, Svc

Production

l)rpe and number of workers Maintenance Service

?' Salaried

'mal

3,042 1,351 1,068 434

1,213 413 115 25

869 217 58 12

816 387 213 17

2

2

2

2

5,905

1,766

1,156

1,433

5,940 2,368 1,454 488 10 10,260

1.3 0.0046

0.91 0.0032

0.82 0.0029

1.1 0.0039

1.2 0.0042

0.011

0.008

0.007

0.009

Collective effective dose equivalenv (person-Sv) 65 14 8.1 13 100 There is a possibility that persons may have worked for more than one operator in 1977 and so have been reported more than once. The January 1,1978 issue of "Statistical Data of the Uranium Industry" (Grand Junction office of the U.S.Department of Energy) showed average employment in U.S.underground uranium mines in 1977 to be 5,425 persons. These DOE figures, however, did not include technical or supervisory persons wha work underground. ( 5 WLM). bNoexposures were greater than 0.018 SV = 100 rem. 1 personSv = 100 person-rem. Conversion factor taken to be 0.85 remMTLM for continuous exposure and w~ = 0.08 (ICRP, 1981).

3 m

$ v

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2 5

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Pu TI

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3.3 NUCLEAR POWER PRODUCTION

/

35

ratio of the average exposure level to the exposure limit then the underground uranium mines are still ranked number 1. They are ranked number 2 if collective effective dose equivalent is the concern. The combination of external exposure with the effective dose equivalent from radon decay products results in an average annual dose equivalent of the order of 10 to 20 mSv (1to 2 rem).

3.3.3

Uranium Mills

The primary radiological hazards in uranium mills are caused by 23eUand 234U(Fry, 1975). The 235Ufound in natural uranium is insignificant as a radiological hazard in mills because of its small isotopic abundance (Swaja and Sims, 1984). Natural uranium is also a heavy metal which is chemically toxic. Its renal toxicity is of primary concern to workers. Typical external dose equivalent rates encountered in uranium mills range from 0.2 pSvh (0.02 mrernlh) in non-process areas, such as offices, to several mSvh (several hundred mremlh) near radium concentrates (Swaja and Sims, 1984). Although dose rates exceed average occupational limits in some areas, typical doses to operating personnel range from about 0.3 to 1.5 mSv (30 to 150 mrem) per calendar quarter. External doses received by operating personnel from sealed sources contained in measuring and calibration devices (such as nuclear gauges and survey instrument calibration sources) can exceed external doses delivered from ore processing (Swaja and Sims, 1984). Although dose rates from sealed sources to some operators and maintenance personnel are less than 10 mSv (1 rem) per year, it is not unusual for some operations and maintenance personnel to receive more than 30 mSv (3 rem) per year. About 1000 workers a t uranium mills in the United States in 1975 and 1978 received average annual measurable dose equivalents of 4 mSv (400 mrem) and 2 mSv (200 mrem) respectively (UNSCEAR, 1982).These estimates were based on measurements with personnel dosimeters. Consequently, they do not include contributions to the effective does equivalent from inhaled radon or its decay products. The latter contribution to the effective dose equivalent is significant but smaller for this occupational group than for miners. Radon decay product concentrations in enclosed mill locations usually vary between (0.200 WL). However, concen0.10 (0.005 WZ) and 4.2 trations in excess of 21 (1.0 WL) have been measured in dead air spaces in mills (Swaja and Sims, 1984).

36 3.3.4

1

3. REVIEW OF OCCUPATIONALLY EXPOSED POPULATIONS

Uranium Fuel Fabrication

The radiological environment of the fuel fabrication stage of the fuel cycle is unique. Although there is no significant exposure to radon and its decay products in this occupational category, it is one in which the potential for internal exposure (see Section 4.2) is comparable to the potential for external exposure. External exposure estimates for the uranium fuel fabrication industry can be determined from monitoring results. Based on statistical reports to the NRC (Brooks, 1988), the average annual dose equivalent was found for 1985 to be 0.8 mSv (80 mrem) for all monitored workers and 1.3 mSv (130 mrem) for those measurably exposed. If the average external effective dose equivalent is summed with the effective dose equivalent from internal sources (see Section 4.21, the average overall effective dose equivalents to fuel fabrication workers is of the same magnitude as that of nuclear power plant personnel.

3.3.5 Commercial Light Water Nuclear Power Plants Dose equivalent data for nuclear power plant personnel have been reported to the NRC each year since 1972 (Brooks, 1988). These reports indicate that the total number of individuals monitored has increased nearly five-fold during these 13 years, while the number of individuals measurably exposed has increased nearly seven-fold. Data for all individuals (contractor personnel, utility personnel, etc.) for whom monitoring was provided during the year are reported. The large number reported not measurably exposed reflects the policy of some utilities to monitor everyone coming on site, including visitors. When dose equivalents are reported by more than one facility, a compilation of all reports from all facilities will not be exact with respect to either the average annual effective dose equivalent or the collective effective dose equivalent for the occupational category in question. For example, an individual who is monitored by five different facilities would be counted once in the report from each facility. However if the data and the reports from all of the facilities were summed, this person would be counted as five individuals rather than as one. Although correction of the data for this multiple counting does not significantly affect the values of the average annual dose equivalent per nuclear power plant, the correction could be important. Failure to apply a correction would provide an average dose to individuals that was biased in the low direction and would

3.3 NUCLEAR POWER PRODUCTION

/

37

cause the collective dose ratio, CR, (see Glossary) to be underestimated. This type of confounding of data can also occur in other occupational categories such as industrial radiography and medical practice. Where individual annual doses are not available for summation to obtain the annual collective dose, the collective dose is estimated from the dose distribution. The NRC estimated the collective dose incurred by individuals monitored a t each nuclear power plant site by summing the products obtained by multiplying the number of individuals reported in each of 18dose ranges by the midpoint of the corresponding range. In 1981, a few facilities began reporting the actual collective dose incurred by these individuals, and these values are now used for these facilities. Table 3.13 summarizes the occupational exposure data for all commercial light water nuclear power plants (LWRs) which operated for 1 year or longer for the years 1973 through 1985. The NRC data given here were used by Kumazawa et d.(1984) but in the latter review all nuclear power plants, irrespective of operating period, were included. The number of nuclear power plants included, the electrical energy generated, and the average related capacity are also given for each calendar year because general trends in occupational radiation exposures are best evaluated within the context of other pertinent information. The number of nuclear power plants included increased three-fold during the thirteen-year period, while the number of workers with measurable doses increased seven times. This resulted in the average number of such workers per nuclear power plant nearly doubling and a decrease in the average dose equivalent by about one third. The average dose equivalent per nuclear power plant worker in the U.S.in 1985 was lower than in any previous year since 1973. Figure 3.1 presents in graphical form some of the data in Table 3.13. Although there was an increase in the number of nuclear power plants during the period 1974 to 1985, the increase in the annual collective dose equivalent is much more impressive. The annual collective dose equivalent appears to have gone through a maximum and declined in both 1985and 1986 (Masse and Driscoll, 1988). There appears to be no correlation between the number of nuclear power plants and the annual collective dose equivalent. Light water nuclear power plants (LWRs) consist of two major types, BWRs and PWRs (see Glossary). Data similar to those shown in Table 3.13 have been compiled for each type in Tables 3.14 and 3.15. Table 3.14 shows that from 1973 to 1985 the number of BWRs increased from 12 to 28, and the average number of workers a t each of these plants increased from 445 to 1,366. The average collective

TABLE 3.13-Summwy

of annual information reported by cornmercinl light water cooled nuclear power plants, 1973-85 (AfterBrooks, 1986;

i*,

1988)

Year

Number of reactors included

Annual collective dose equivalents (Person-Sv)'

1973 24 140 1974 34 137 209 1975 44 1976 53 264 1977 57 325 64 318 1978 1979 67 400 1980 68 538 1981 70 541 1982 74 522 1983 75 565 1984 78 552 1985 82 430 "I pemn-Sv = 100 person-rem. blmSv = 100 mrem.

Number of workers with measurable dose equivalents

Average dose equivalent per worker (rnS~)~

14,780 18,466 25,491 35,447 42,266 45,998 64,122 80,331 82,183 84,382 85,646 98,092 92,871

9.4 7.4 8.2 7.5 7.7 6.9 6.2 6.7 6.6 6.2 6.6 5.6 4.6

-

0 M

Average Average number collective of personnel dose equiv. with measurable per reactor dose equivalents (Pers0n.S~)~ per reactor

5.82 4.04 4.75 4.99 5.70 4.97 5.97 7.91 7.73 7.05 7.53 7.08 5.25

616 543 579 669 742 719 956 1,181 1,174 1,139 1,142 1,258 1,132

Average collective dose equiv. (Person-Sv per MW-y)'

Average electnclty per reactor (MW-y)

Average rated capacity Net ( W e )

0.019 0.013 0.012 0.012 0.012 0.010 0.013 0.018 0.017 0.016 0.017 0.015 0.020

299 320 404 413 462 494 447 429 449 443 439 467 507

496 575 630 6 677 702 705 699 719 738 742 776 806

y - y

s

2

8

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2 M

$ 0

&

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59

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3.3 NUCLEAR POWER PRODUCTION

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39

Annual collective dose equiv. (person-Sv)

Number of power plants

Year

Fig. 3.1. Number of light water nuclear power plants and annual collective dose equivalent for the years 1974 through 1985 (After Brooks, 1988).

dose equivalent per plant varied between 4 and 11 person-Sv (400 and 1100 person-rem) until 1980, after which a decreasing trend began to appear. Table 3.15 presents similar information for PWRs, whose number increased from 12 to 54 during the same thirteen years. The average number of workers a t each of these plants remained a t about 600 from 1973 to 1979 and has been about 1,000 workers since that time. Some of the increases seen in the number ofworkers and collective dose equivalents in 1979 through 1982 resulted from safety-related (backfit) actions required by the NRC following the Three Mile Island accident. Figures 3.2 and 3.3 show the trends in annual average dose equivalent and collective dose equivalents for BWRs and PWRs for the years 1974 to 1985. The average dose equivalent per worker decreased from 1974 through 1985 for both pressurized and boiling water nuclear power plants (see Figure 3.2). So, the trend in annual collective dose equivalent observed in Figure 3.1 is attributable to an increase in the number of workers during these years. The decrease in the annual collective dose equivalent in 1985 was disproportionately large compared to the decrease in the number of nuclear power plant employees in 1985 and is attributable to efforts to reduce exposures, reduced modification work, and reduced major repair and replacement work (Driscoll, 1988). Figure 3.3 shows that boiling and pressurized water nuclear power plants contribute about equally to the annual collective dose equivalent.

TABLE 3.14-Summary of annual information reported by commercial boiling water nuclear power plants, 1973-85 (After Brooks, 1986;

w

1988)

'a

Year

Number of reactors included

Annual collective dose equivalents (Person-Sv)"

Number of workers with measurable dose equivalents

1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

12 14 18 23 23 25 25 26 26 26 26 27 28

46 71 126 126 190 151 183 295 255 244 275 27 1 206

5,340 8,769 14,607 17,859 21,388 20,278 25,245 34,094 34,832 32,235 33,473 41,105 38,237

Average Average collective dose equivalent dose equiv. per worker per reactor ( ~ S V ) ~ Person-Sv).

m

Average number ofpersonnel with measurable dose equivalents per reactor

Average collective dose equiv. (person-sv per MW-y)O

Average MW-y electricity per reactor (MW-y)

Average rated capacity Net (MWe)

445 626 812 776 930 81 1 1,010 1,311 1,340 1,240 1,287 1,522 1,366

0.013 0.017 0.022 0.015 0.021 0.013 0.016 0.027 0.023 0.023 0.028 0.027 0.018

283 290 321 373 396 47 1 467 418 419 410 374 369 409

459 513 611 647 645 668 669 664 674 674 675 722 766

5

2

d ?I h

"1 person-Sv = 100 person-rem. blm ~ =v 100 mrem.

8.5 8.1 8.6 7.1 8.9 7.4 7.3 8.7 7.3 7.6 8.2 6.6 5.4

3.80 5.07 7.01 5.49 8.28 6.04 7.33 11.36 9.80 9.40 10.56 10.03 7.35

X

sg 4

a

4

S

2

0

z

CA

TABLE3.15-Summary of annual information reported by commercial pressurized water nuclearpowerplants, 1 9 7 3 4 5 (After Brooks, 1986; 1988)

Year

Number of reactors included

Annual collective dose equivalents (Person-Sv)"

1973 12 94 1974 20 66 26 83 1975 30 138 1976 34 135 1977 1978 39 167 1979 42 217 1980 42 243 1981 44 287 48 278 1982 49 290 1983 1984 51 28 1 1985 54 225 ' I person-Sv = 100 person-rem. blI ~ S V = 100 mrem.

Number of workers with measurable dose equivalents

9,440 9,697 10,884 17,588 20,878 25,720 38,877 46,237 47,351 52,147 52,173 56,987 54,634

Average dose equivalent per worker (~SV)~

10.0 6.8 7.6 7.9 6.5 6.5 5.6 5.2 6.1 5.3 5.6 4.9 4.1

Average collective dose equiv. per reactor (PersonSv)'

Average number ofpersonnel with measurable dose equivalents per reactor

Average collective dose equiv. (Person-Sv per MW-y)'

Average MW.-y electnc~ty per reactor (MW-y)

Average rated capacity Net (MWe)

7.83 3.3 1 3.18 4.60 3.96 4.29 5.16 5.78 6.52 5.78 5.92 5.52 4.16

787 485 419 586 614 659 924 1,101 1,076 1,086 1,065 1.117 1,012

0.025 0.01 0.007 0.01 0.008 0.008 0.012 0.013 0.014 0.013 0.013 0.011 0.007

314 341 46 1 444 510 509 434 435 467 461 473 519 558

533 619 643 675 699 723 729 721 745 773 778 805 826

z o

$ g O

3 ?3

3

8 2

2

.

42

1

3. REVIEW OF OCCUPATIONALLY EXPOSED POPULATIONS

Average dose equivalent a

1 1 1 1

Year

Fig. 3.2. Annual average dose equivalent per worker for pressurized and boiling water nuclear power plant personnel for the years 1974 through 1985 ( A h r Brooks, 1988).

Annual collective dose equivalent (person-Sv)

500

300 200 100 0

1974 1975 1976 1977 1978 1979 lee0 1981 1982 1983 1984 1985

Year

Fig. 3.3. Annual collective dose equivalent from boiling and pressurized water nuclear power plants (After Brooks, 1988).

3.3 NUCLEAR POWER PRODUCTION

43

1

BOILING WATER REACTORS

a

O P E R A T l O l S AND SURVEILLANCE

S P E C I A L *AIWTEWAUCE

[&ql

R O U T I N E WAINTENANCE 1U.SERVlCE

1979

1980

INSPECTION

1981

UASTE PROCESSING REFUELIWG

1982

1983

1984

1985

YEAR

P

PLAYT PERSONNEL

C

-

CONTRACT PERSONUEL

Fig. 3.4. Collective dose equivalent by work function and personnel type at BWRs, 1979-1985 (After Brooks, 1988).

3.3.5.1 Collective Dose Equivalent by Work Function and Personnel Type. The NRC also collects data for several general categories of work and job functions and types of personnel. Figures 3.4 and 3.5 summarize the data reported separately for workers a t BWRs and PWRs for the years 1978 through 1985. At both BWRs and PWRs, contractor personnel have incurred almost two-thirds of the average collective dose equivalents for the last several years, most of which have occurred during special maintenance activities. These data also show that one of the major differences in collective dose equivalent between personnel a t BWRs and PWRs is attributable to differences in routine maintenance. Contractor employees at BWRs receive about 20 percent of the collective dose equivalent from routine maintenance. Such workers a t PWRs receive only about 12 percent of their collective dose equivalent from routine maintenance. Conversely, it appears that refueling activities a t BWRs contribute a smaller portion of the collective dose equivalent than a t PWRs. However, these differences are in part attributable to the fact that some facilities

44

1

3. REVIEW OF OCCUPATIONALLY EXPOSED POPULATIONS PRESSURIZED WATER REACTORS

35 OPERATIONS AN0 SURVEILLAWCE

a

ROUTINE MRINTENAYCE

P

= PLANT PERSONWEL

SPECIAL MAINTENANCE

(&ql

C

UASTE PROCESSING

CONTRACT PERSONNEL

Fig. 3.5. Collective dose equivalent by work function and personnel type at PWRs, 1979-1985 (After Brooks, 1988).

report maintenance dose equivalents in different occupational categories. Some are reported as "refueling doses." Lawrence et al. (1984) observed that collective dose equivalents for contractor and utility personnel were distributed in approximately the same proportions as the percentages of personnel in each of these two categories. Therefore, the average dose equivalents must have been about the same for these two categories ofpersonnel. Sixtysix percent of the collective dose equivalent was incurred by contractors, but contractor workers receiving greater than 1 mSv (0.1 rem) accounted for only 63 percent of the workforce. However, the problem of inadequate compilation of cumulative dose equivalents for transient workers may artificially lower the average annual dove equivalent for the contractor's temporary employees (see Section 3.3.5.3).

Task Specific Information. It would be desirable to know the specific tasks for which large collective dose equivalents and/or

3.3.5.2

3.3 NUCLEAR POWER PRODUCTION

1

45

higher than normal individual dose equivalents occur. Such information is not routinely reported a t any central location and may not be easily retrievable from individual plant records. However, some data, obtained from the computerized records maintained by a number of plants, have been published (Baum and Dionne, 1985 and Lawrence et al., 1984). The data in Table 3.16 show repetitive tasks a t BWRs and PWRs that were found to have an average collective dose equivalent greater than 0.3 person-Sv (30 person-rem) per outage a t ten sites (Baum and Dionne, 1985). There appear to be more tasks a t BWRs than a t PWRs which involve high dose equivalents. This is consistent with the fact that the annual collective dose equivalent per BWR unit has been higher than that per PWR unit for many years (Tables 3.14 and 3.15). The wide range between the maximum and minimum shown in Table 3.16 for tasks a t both BWRs and PWRs reflects differences in plant age and design, in the methods of performing a job and in assigning dose to that task, in the scope of the job, and in the number and type of items that were inspected, repaired or replaced. Lawrence et al. (1984) determined the collective dose equivalents incurred during several general tasks (steam generator repair and maintenance, control and drive repair and maintenance, decontamination and waste handling) by three types of personnel. The number of individuals and their average dose equivalents in these activities each year were also reported for some of the tasks. The average dose equivalent received by contractor workers is normally higher than that received by station and utility personnel, and contractor personnel usually incur a larger collective dose equivalent during steam generator repair and maintenance. Routine and special maintenance operations account for the largest collective dose equivalent and the largest average dose equivalent per worker (Brooks, 1979-1988 and Powers, 1985) as indicated in Figures 3.4 and 3.5. Also BWR personnel experience higher average and collective dose equivalents than PWR personnel (see Figure 3.2). The work of Imahori (1987) confirms a similar experience in Japan.

3.3.5.3. Transient or Short-term Workers. In an effort to examine the dose equivalents being received by transient or short-term workers, many of whom would be contractor personnel, the NRC has compiled data provided in termination reports. These reports are transmitted to the NRC when a monitored individual completes employment or a work assignment at a licensed nuclear power plant, and they contain personal identification and exposure information for each terminating person. This allows analyses to be done of the dose equivalents received by individuals who may be monitored by

TABLE 3.16-Repetitive, routine tasks with average collective doses greater than 0.3 person-Sv per outage for reactors during the period 19741984" (After Baum and Dionne, 1985) Type of facility and task

Boiling water reactors Snubber inspection & repair Torus repair, inspection & modifications In-service inspection CRUD (see Glossary) removal, rebuilding & replacement Scaffold installation & removal Primary valve maintenance & repair Jet pump inspection & repair Insulation removal & replacement Safety valve repair & inspection Plant decontamination Residual heat removal system repair and maintenance

Minimum

Collective dose equivalent per outage person-Svb Maximum

Average

0.026 1.O 0.32

14.0 6.0 3.8

2.9 2.8 1.5

0.063 0.24 0.07 0.099 0.006 0.093 0.094

2.3 1.2 1.5 1.4 1.7 0.8 0.7

0.6 0.6 0.6 0.5 0.4 0.4 0.4

0.11

0.5

0.3

3

m C

2 8

8

s5 0

3 Z

*

F 4

8 8a' U

%

9 %

3 z rn

Minimum Typ of Facility and 'Igsk

A

B

Maximum

C

A

B

C

A

Average B

C

Pressurized Wder Reactors Supplied by company A, B and C: Scrubber hanger & anchor bolt 0.003 0.009 c 5.80 2.20 c 1.10 0.34 c inspection & repair Steam generator eddy current testing 0.12 0.031 c 1.40 1.40 c 0.50 0.31 c Reactor disassembly & assembly 0.12 0.20 0.14 1.20 1.60 0.54 0.48 0.68 0.36 Steam generator tube plugging 0.034 0.045 c 1.80 5.80 c 0.47 1.20 c In-service inspection 0.001 c 0.076 1.30 c 0.64 0.46 c 0.31 Plant decontamination 0.005 c c 0.67 c c 0.45 c c Primary valve maintenance & repair 0.014 c c 1.20 c c 0.30 c c S d o l d installation/removal 0.005 c c 0.62 c c 0.30 c Snubber, hanger, and anchor bolt c c 0.048 c c 0.69 c c 0.33 inspection & repair "Years of available data varied from unit to unit. b s u l t s are indicative of nuclear power units sampled. Results are not necessarily representative of the entire nuclear industry. bl person-Sv = 100 person-rem. 'Less than 0.3person4v average.

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3. REVIEW OF OCCUPATIONALLY EXPOSED POPULATIONS

47 5 % $5 > M>%

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3.3 NUCLEAR POWER PRODUCTION

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49

several different power plants during the year. Table 3.17 (Brooks, 1985; 1988) shows that for the years 1977 to 1984 there have been between 3,100 and 7,400 individuals per yearwho have been reported as being terminated by two or more nuclear power facilities. The average annual dose equivalent for monitored transient workers is about 11mSv (1.1 rem), while the average dose equivalent of workers terminated by four or more facilities has ranged between 15 and 22 mSv (1.5 and 2.2 rem). This is a further indication that there are several thousand individuals, most of whom probably are contractor personnel, who are involved in tasks where there is potential for high exposure. But, until the U.S. establishes a way to collate individual dose equivalent data on a timely basis, determining workers' individual annual and cumulative dose equivalents will continue to be problematic.

3.3.6 Nuclear Powered Ships and Support Facilities. The U.S. Department of the Navy operates nuclear powered ships of various types and therefore monitors associated personnel as they operate the nuclear propulsion plants aboard ship and repair the plants in shipyards. Table 3.18 summarizes the exposure information reported for these workers for the years 1970 through 1986. The average dose equivalent for workers, both on the ships and in the shipyards, peaked a t 2.7 mSv (0.27 rem) and 5.6 mSv (0.56 rem), respectively, in 1965. In 1967 the Navy Department adopted an annual limit of 0.05 Sv (5 rem), and the annual average dose equivalents generally declined until 1980 when they began to level off a t about 0.7 and 1.5 mSv (0.07 and 0.15 rem) for ships and shipyards, respectively. As expected, the average and collective dose equivalents remain higher for the shipyard personnel where maintenance activities are conducted, but Figure 3.6 shows that annual collective dose equivalents incurred by shipyard personnel have been reduced although the work has increased. It appears that average and collective dose ecluivalents in the U.S. nuclear navy stabilized after a period of decline during rapid expansion of the fleet (Schmitt and Brice, 1984). Figures 3.6 and 3.7 show the annual collective dose equivalent as a function of year for shipyard, civilian and military personnel. Table 3.18 shows that fleet personnel receive, on the average, lower dose equivalents than shipyard personnel. Comparison of the collective dose equivalent experienced by commercial nuclear power personnel (see Figure 3.1) with that experienced by personnel in the naval nuclear propulsion program (see

01 0

TABLE3.18-Radiation dose equivalents to shipyard and fleet personnel (A*

Schmitt and Brice, 1984 and Mangeno a n d l!von, 1987) Fleet

Year

Dose equivalent average (mSvP per person monitored

Fleet

Shipyard

Percent of personnel monitored who received greater than 10 mSvab

Fleet

Shipyard

'lbtal personnel

Total

monitored

person-SvL

Total personnel monitored

t

'Ma1 person-Sv'

w

Shipyard

1980 0.7 1.5 0.4 2.4 21,845 14.9 15,664 24.0 1981 0.6 1.3 0.1 1.7 23,808 14.2 17,718 23.1 1982 0.6 1.7 0.2 3.3 27,622 16.6 19,858 1983 0.7 1.7 0.2 3.4 27,645 18.3 21,121 1984 0.6 1.5 0.0 2.4 30,106 17.2 21,186 31.8 1985 0.5 1.3 0.1 1.9 31,465 15.5 21,352 28.0 1986 0.5 1.6 0.0 4.0 31,090 15.4 21,788 35.0 "1 mSv = 100 rnrem. bButless than 50 mSv. No one received 50 mSv or greater. 'Data obtained from summaries rather than directly from original medical records. Total person-Sv was determined by adding actual exposures for each individual monitored by each reporting command during the year. Total number monitored includes visitors to each reporting command. I t is expected that the large effort to compile comparable person-Sv data from original medical records would show differencesno greater than five percent. 1person-Sv = 100 person-rem.

:

;c m

$d

0u 8 2

F!.

=! 0 z

3.3 NUCLEAR POWER PRODUCTION Collaotlva

1

51

Numb., of

d o n qulv.

mhlm

-

-- ----.

Collective ddse equivolent (person-Sv)

Number of ships in oui\rhoul

Year

Fig. 3.6. Annual collective dose equivalent received by shipyard personnel from work associated with naval nuclear propulsion plants 1966-1984 (After Mangeno and Tryon, 1987). One Sv = 100 rem.

Collective dose

2w

equivalent (~rwn-sv)

200

Number of ships in

100

operotion

Ywr

Fig. 3.7. Annual collective dose equivalent received by military and civilian personnel in the naval nuclear propulsion program 1966-1984 (After Mangeno and Tryon, 1987). One Sv = 100 rem.

52

1

3. REVEW OF OCCUPATIONALLY EXPOSED POPULATIONS

Figures 3.6 and 3.7 and Table 3.18), shows that the collective dose equivalent in the nuclear navy in 1982 was about one-tenth that attributable to the commercial nuclear power industry. The ratio of monitored navy to monitored commercial power personnel in 1982 was about 0.6. So the difference is not solely attributable to the size of the populations monitored. Tables 3.14 and 3.15 show that the average dose equivalent for civilian nuclear power plant personnel has been about 6 mSv/y (0.6 rernly) for nearly a decade. In contrast, Table 3.18 shows navy-wide averages to be considerably smaller.

3.3.7 General Conclusions Related to Nuclear Power Plants More data on occupational dose equivalents are available and reported for commercial nuclear power plants than any other nuclear industry. Rapid growth in this field occurred during the years 1973 to 1978 when the number of light water reactors, the collective dose equivalent and the number of workers receiving measurable dose equivalents all increased by factors of 2 or 3. However, in 1979 and 1980, following the Three Mile Island accident, the collective dose equivalent and the number of workers receiving measurable dose equivalents increased by a factor of 1.7, while the number of nuclear power plants only increased from 64 to 68. For the period 1980 to 1984, the annual collective dose equivalent remained nearly constant, but declined in 1985 and 1986. The number of workers increased over the years and the average dose equivalent for measurably exposed workers decreased to about 6 mSv (0.6 rem) in 1984, and to less than 5 mSv (0.5rem) in 1986 (Brooks, 1988 and Driscoll, 1988).This could reflect efforts to reduce exposure levels. Similar general trends can be found in the data compiled separately for BWRs and PWRs; however, one would find that the values for the collective dose equivalent per plant, the number of workers per plant, and the average annual dose equivalent have been higher for BWRs than for PWRs since 1974. Data on the dose equivalents received by different occupational subgroups as they perform various specific tasks are not readily available for the nuclear power industry as a whole. Data collected for several broad categories of workers and tasks indicate that contract workers receive about 65 percent of the collective dose equivalent each year, most of which occurs during routine operations and maintenance activities. Presumably, once the nuclear power plant has been designed and built, dose equivalents incurred during routine operations and maintenance cannot be greatly affected. There-

3.4 MEDICAL OCCUPATIONAL EXPOSURE

/

53

fore, the sizable portion of the collective dose equivalent that continues to be attributable to special maintenance may indicate inadequate design of areas where such maintenance is done. Corrosion damage is generally considered to be the primary cause of high dose equivalents during special maintenance. Improved water chemistry and more resistive replacement materials are reducing this contribution to total dose equivalent. The data for nuclear propulsion plants indicate that the collective dose equivalent for the approximately 55,000 monitored ship and shipyard personnel has generally declined from its highest value of 223 person-Sv (22,300 person-rem) in 1966 to 50 person-Sv (5,000 person-rem) in 1984. This occurred in spite of the fact that during this time the numbers of ships in overhaul increased by a factor of 3. The average dose equivalent per monitored shipyard worker remains a t about 2 mSv (0.2 rem), which is about three times that of the personnel monitored on nuclear ships. These small values reflect the success of the Navy's efforts to keep doses as low as reasonably achievable (ALARA).

3.4 Medical Occupational Exposure

Much remains to be done in the United States to quantify in some detail the effective dose equivalents of medical staff in the private sector. The current Report relies heavily on the compilation of Kumazawa et al. (1984) for the characterization of exposures for medical personnel. The volume of medical diagnostic radiography is very large in the United States. Based on data from the Center for Devices and Radiological Health (FDA, DHHS) and other sources, Mettler (1987) estimated that in 1982 there were 127,000 medical and 204,000 dental diagnostic x-ray machines in use. About 890 million sheets of medical x-ray film were sold in that year (NCRP, 1989). Between 1970 and 1980 the number of medical x-ray examinations increased by 32 percent to 180 million, and the number of dental x-ray examinations increased by 50 percent to 101 million. The volume of diagnostic nuclear medicine examinations has also increased rapidly, essentially doubling in frequency from 1972 to 1982. In 1982 about 7.4-7.7 million nuclear medicine examinations were conducted (Mettler et al., 1985). Table 3.19 shows the estimates made for 1980 by Kumazawa et al. (1984) of the number of U.S. workers with potential exposures from dental, medical and veterinary x-ray machines. These numbers rep-

54

1

3. REVIEW OF OCCUPATIONALLY EXPOSED POPULATIONS

TABLE3.19-Estimated number ofpotentially exposed workers, mean dose equivalents and collective dose equivalents for monitored workers i n medicine and related fields, 1980 (After Kumazawa, et al., 1984) Mean dose Collective dose Number of workers equivalent equivalent Occupation (thousands) (mSv) (person-Sv) Dentistry 259 0.2 60 Private medical practice 155 1.0 160 Hospital 126 1.4 170 OtheP 44 0.5 20 Total 584 0.7 410 ""Other" includes chiropractic medicine with 15,000, podiatry with 8,000 and veterinary medicine with 21,000 potentially exposed workers.

resent a 46 percent increase since 1970 and a 93 percent increase since 1960. The table also presents the mean annual dose equivalents and collective dose equivalents for medical workers. The mean dose equivalents have decreased by 42 percent since 1970 and 63 percent since 1960, while the collective dose equivalents have decreased by 18 percent and 29 percent respectively.

3.5 U.S. Public Health Service (PHs)

The U.S. Public Health Service (PHs) provides radiation monitoring services for P H s personnel and for some other government agencies. The lithium fluoride dosimeters used have an MDL of about 0.1 mSv (10 mrem). Reported dose equivalents less than this MDL are recorded as zero by the PHs. Eighty-nine percent of persons monitored by the P H s were below the MDL for the years 1977 to 1985. More than 99 percent of the personnel monitored received less than 5 mSv (500 mrem) per year from 1977 to 1985 and no one exceeded 50 mSv (5 rem) for the years 1984 and 1985 (Lewis and Miller, 1985; 1987). The total collective dose equivalent for all personnel monitored was 0.15 person-Sv (15 person-rem) for the year 1985. The personnel monitored by the PHs are employees of the following organizations: Center for Devices and Radiological Health Indian Health Service Federal Bureau of Prisons U.S. Coast Guard Centers for Disease Control U.S. Capitol Police EPA laboratories

3.6 OTHER INDUSTRIAL WORKERS

/

55

U.S. Department of Labor, Occupational Safety and Health Administration (OSHA) Analytical Laboratory Federal Bureau of Investigation (FBI) Laboratory National Institute of Environmental Health Sciences (NIEHS) Gerontology Research Center, National Institutes of Health (NIH) U.S. Customs Service Immigration and Naturalization Service U.S. Postal Service St. Elizabeth's Hospital, Washington, D.C. U.S. Merchant Marine Academy Hospital U.S. Supreme Court Police Food and Drug Administration (FDA) Public Health Service Hospital, Camille, LA Table 3.20 summarizes the numbers of personnel monitored and the mean annual effective dose equivalents for some occupational categories from 1977 to 1985. The mean annual effective dose equivalents are based on all persons monitored.

3.6 Industrial Workers (other t h a n Nuclear Fuel Cycle) Partial information is available on several types of industrial radiation workers, including industrial radiographers, radionuclide manufacturers and distributors, low-level waste disposal workers and well loggers. The industrial radiographers work primarily with gamma sources (e.g., cobalt-60 or iridium-192) in testing pipeline welds, boilers, aircraft parts, etc. The second category manufactures and distributes medical andlor industrial radionuclides. The lowlevel waste disposal workers transport and dispose of radioactive wastes (e.g., from hospitals and laboratories) a t disposal facilities. The Nuclear Regulatory Commission (NRC) publishes annual reports summarizing occupational exposures in these categories. However, the reports do not include information from "Agreement States" (see Glossary) which maintain their own licensing and monitoring activities. Because these states do not submit annual exposure reports to the NRC, the latest NRC report includes only 21 states (Brooks, 1988). Table 3.21 shows for the NRC reporting states the numbers of monitored and measurably-exposed industrial radiographers, radionuclide manufacturers and distributors, and low-level waste disposal workers. I t also provides information on mean and collective dose equivalents and on CR. The mean dose equivalent to measurably exposed workers is highest among the industrial radiographers

56 1 3. REVIEW OF OCCUPATIONALLY EXPOSED POPULATIONS

/

3.6 OTHER INDUSTRIAL WORKERS

57

TABLE3.21-Annual dose equivalent data for selected categories of NRC licensees, 1985 (AfterBrooks, 1988)

Category

Mean dose Collective equivalent, Mean measurable No. of No. of No. with dose monitored dose licensees monitored measurable equivalent workers equivalent reporting workers doses (per~on-sv)~( ~ S V ) ~ (mSv) CR

Industrial 340 8,476 radiography Radionuclide rnfg. & dist'n. 33 3,958 Low-level waste disposal 2 1,240 "1 person-Sv = 100 person-rem. blmSv = 100 rnrem.

5,550

24

2.8

4.3

0.45

2,250

7.6

1.9

3.4

0.50

0.70

0.6

2.8

0.24

252

[4.3 mSv (0.43 rem)]. Over the last decade, the mean dose equivalent in the measurably exposed has decreased 26 percent among the radiographers and 45 percent among radionuclide manufacturers and distributors. For comparison with the numbers of workers in Table 3.21, Kumazawa et al. (1984) projected for 1985 that nationwide there would be about 32,000 industrial radiographers and 34,000 workers in radionuclide manufacturing and distributing. Table 3.22 summarizes the distributions of annual dose equivalents for the workers reported to the NRC. It is notable that among industrial radiographers, 0.14 percent of those monitored (or 0.22 percent of those with measurable doses) had annual dose equivalents of 50 mSv (5 rem) or more. The corresponding percents for the radionuclide manufacturers and distributors were 0.05 percent and 0.09 percent respectively. In 1979, for U.S. well loggers licensed by the NRC, the mean annual dose equivalents for measurably exposed personnel and for all monitored personnel were 4.2 mSv (420 mrem) and 3.5 mSv (350 mrem), respectively (Brooks, et al., 1982).The total number of workers monitored by NRC licensees in 1979 was 8723. Techniques used in well logging are similar regardless of where TABLE3.22-Annucrl dose-equivalent distributions (percents) for selected categories of NRC iicemees, 1985 (After Brooks, 1988) None