United Nations Scientific Committee on the Effects of Atomic Radiation

S O U R C E S , E F F E C T S A N D R I S K S O F I O N I Z I N G R A D I AT I O N

UNSCEAR 2020/2021 Report

Volume IV
SCIENTIFIC ANNEX D:
Evaluation of occupational exposure to ionizing radiation

SOURCES, EFFECTS AND RISKSOF IONIZING RADIATION
United Nations Scientific Committee on the
Effects of Atomic Radiation
UNSCEAR 2020/2021
Report to the General Assembly,
with Scientific Annexes

VOLUME IV
Scientific Annex D

UNITED NATIONSNew York, 2022

NOTE
The report of the Committee without its annexes appears as Official Records of the General
Assembly, Seventy-sixth Session, Supplement No. 46 (A/76/46).
The designations employed and the presentation of material in this publication do not imply theexpression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning the legal status of any country, territory, city or area, or of its authorities, or concerning
the delimitation of its frontiers or boundaries.
The country names used in this document are, in most cases, those that were in use at the time thedata were collected or the text prepared. In other cases, however, the names have been updated,
where this was possible and appropriate, to reflect political changes.
The attachments cited in this annex are electronically available for download fromhttp://www.unscear.org/unscear/en/publications/2020_2021_4_Attachment.html

UNITED NATIONS PUBLICATION
Sales No. E.22.IX.4
ISBN: 978-92-1-139209-8
eISBN: 978-92-1-001006-1© United Nations, September 2022. All rights reserved, worldwide.
This publication has not been formally edited.
Information on uniform resource locators and links to Internet sites contained in the present
publication are provided for the convenience of the reader and are correct at the time of issue.
The United Nations takes no responsibility for the continued accuracy of that information or forthe content of any external website.

ANNEX DEVALUATION OF OCCUPATIONAL EXPOSURE TOIONIZING RADIATIONCONTENTS
LIST OF ABBREVIATIONS ................................................................................................................................................ 3
I.

INTRODUCTION......................................................................................................................................................... 5
A. Scope and objectives of analysis ............................................................................................................... 7
B.

II.

Sources of occupational exposure to radiation................................................................................... 7

METHODOLOGY AND SOURCES OF DATA ..................................................................................................... 8
A. Dose assessment methodology for occupational exposure .......................................................... 8
B.

Dose recording ............................................................................................................................................... 13

C.

Dose distribution ........................................................................................................................................... 14

D. Sources of data ............................................................................................................................................... 15
E.

Estimation of worldwide levels of exposure ....................................................................................... 16

III. LEVELS AND TRENDS OF EXPOSURE TO NATURAL SOURCES OF RADIATION................................ 25
A. Cosmic ray exposure of aircrew and space crew .............................................................................. 26
B.

Exposure in extractive and processing industries ............................................................................ 35C.

Oil and gas extraction .................................................................................................................................. 41

D. Radon exposure in workplaces other than mines ............................................................................ 42
E.

Conclusions on occupational exposure to natural sources of radiation ................................. 45

IV. LEVELS AND TRENDS OF EXPOSURE TO HUMAN-MADE SOURCES OF RADIATION ..................... 48
A. Nuclear fuel cycle .......................................................................................................................................... 48
B.

Medical uses of radiation ........................................................................................................................... 82

C.

Industrial uses of radiation ..................................................................................................................... 104

D. Military uses .................................................................................................................................................. 118
E.

Miscellaneous uses of radiation............................................................................................................ 121

F.

Conclusions on occupational exposure to human-made sources.......................................... 125

12 UNSCEAR 2020/2021 REPORT

V. ASSESSMENT OF GLOBAL PRACTICES ......................................................................................................... 127
A. Trends in occupational exposure ......................................................................................................... 131
B.

Dose to lens of eye ..................................................................................................................................... 132

VI. IMPLICATIONS FOR FUTURE EVALUATIONS ............................................................................................. 133
VII. SUMMARY AND CONCLUSIONS .................................................................................................................... 135
ACKNOWLEDGEMENTS ............................................................................................................................................. 138
Members of Expert Group ............................................................................................................................... 138
List of national contact persons and national experts contributors to UNSCEAR Global
Survey on Occupational Exposure ........................................................................................................... 139
REFERENCES................................................................................................................................................................... 141

The attachment cited in this annex includes 23 tables with supplementary information and iselectronically available for download from the UNSCEAR website
http://www.unscear.org/unscear/en/publications/2020_2021_4_Attachment.html

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 3

LIST OF ABBREVIATIONS
AFAN

African Alara Network

AGR

Advanced gas-cooled reactor

BSS

Basic safety standards

BWR

Boiling water reactor

CARI

Computer and Automation Research Institute

EPCARD

European Program Package for the Calculation of Aviation Route Doses

FBR

Fast-breeder reactor

FDG

Fluorodeoxyglucose

GCR

Gas-cooled reactor

GDP

Gross domestic product

GNI

Gross national income

GSD

Geometric standard deviation

HTGR

High-temperature graphite reactor

HWR

Heavy water reactor

IAEA

International Atomic Energy Agency

IARC

International Agency for Research on Cancer

ICAO

International Civil Aviation Organization

ICRP

International Commission on Radiological Protection

ICRU

International Commission on Radiation Units and Measurements

ILO

International Labour Organization

ISEMIR

Information System on Occupational Exposure in Medicine, Industry and Research

ISL

In situ leaching

ISO

International Organization for Standardization

ISOE

Information System on Occupational Exposure

ISR

In situ recovery

ISS

International Space Station

JISCARD

Japanese internet system for calculation of aviation route doses

LET

Linear energy transfer

LLRD

Long-lived radionuclide dust

LWGR

Light-water-cooled, graphite-moderated reactor

MDL

Minimum detectable level

NASA

National Aeronautics and Space Administration

NORM

Naturally occurring radioactive material

4 UNSCEAR 2020/2021 REPORT

OECD/NEA

Organization for Economic Co-operation and Development/Nuclear Energy Agency

PCAIRE

Predictive code for aircrew radiation exposure

PRIS

Power Reactor Information System

PWR

Pressurized water reactor

RnP

Radon and its progeny

SPECT

Single-photon emission computed tomography

SI units

International System of units

UMEX

Information System on Uranium Mining Exposure

UNSCEAR

United Nations Scientific Committee on the Effects of Atomic Radiation

WHO

World Health Organization

WLM

Working level month

WNA

World Nuclear Association

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 5

I. INTRODUCTION
1.
Radiation exposure can occur as a result of occupational activities utilizing sources of ionizing
radiation. It is incurred by workers using radiation or radioactive substances in industry, medicine,
education and research. Occupational exposure can also occur from natural sources of radiation, e.g.,crews exposed to cosmic radiation during air travel and space flights or workers in coal, uranium or othermineral mining exposed to radon and other natural radioactive substances. The average level ofoccupational exposure is generally similar to the global average level of natural radiation exposure, butsome workers can receive exposure several times higher than this [U10].
2.
The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reviews
the sources of occupational exposure and estimated distributions of individual annual effective doses andannual collective effective doses from occupational exposure in various industry sectors in accordancewith the source types. It is of particular interest to examine the changes that have taken place over timewith the introduction of improved practices, new technology, and revised regulations. Radiation sourcesand exposure estimates are, therefore, periodically reviewed and updated by the Committee to evaluate
prevailing trends in occupational exposure and to identify new worker groups receiving significant
radiation doses.
3.
This annex supplements and updates previous UNSCEAR publications on occupational exposure[U2, U3, U4, U6, U8, U10]. Differences exist between countries in the procedures for monitoring andreporting occupational exposure; reflecting, for example, differences in regulatory requirements andpractices. As a result, comparisons of data on doses are not always straightforward and may be somewhat
limited in scope.
4.
The outcome of the Committee’s assessments is the scientific basis for national and internationalorganizations to evaluate the necessity for developing radiation protection standards, recommendations
or guidance. The Committee’s assessments are used also by the relevant agencies of the United Nations
system in formulating international safety standards for protection of the public and of workers against
ionizing radiation; those standards, in turn, are linked to important legal and regulatory instruments in
Member States. Governments and organizations throughout the world rely on the Committee’s
assessments of the sources and effects of radiation as the scientific basis for estimating radiation risk,
establishing radiation protection and safety standards and regulating radiation sources.
5.
The analysis of worldwide occupational exposure presented in this annex is based primarily on datasubmitted by the United Nations Member States in response to the UNSCEAR Occupational Exposure
Survey for the period 2003–2014. The survey is supplemented by data from peer-reviewed literature andreports from national competent authorities. Where appropriate, reference is made to summaries of earlier
evaluations by the Committee for completeness and comparison.
6.
In the current annex, the Committee has updated its evaluations of occupational exposure fromnatural and human-made sources of radiation. The annex is subdivided into sectors according to the typesof exposure and sources. The subsectors associated with occupational exposure to natural sources ofradiation included in the evaluation are: (a) radiation exposure of aircrew and space crew; (b) exposurein extractive and processing industries (mining of coal, of minerals other than coal and of uranium);(c) exposure from oil and natural gas extraction industry; and (d) radon exposure in workplaces otherthan mineral extraction industries. The subsectors associated with occupational exposure to human-madesources of radiation are: (a) exposure within the nuclear fuel cycle; (b) exposure due to medical uses of6 UNSCEAR 2020/2021 REPORT

radiation; (c) exposure due to industrial uses of radiation; (d) exposure for military purposes; and(e) exposure from miscellaneous uses of radiation, consisting of groups of exposed workers not includedin the subsectors described previously. The current annex addresses veterinary medicine in the subsector
on medical uses of radiation; previously, it was included in miscellaneous uses of radiation.
7.
The Committee began collecting data on occupational exposure due to natural radiation sources inconnection with the preparation of the UNSCEAR 2000 Report [U7, U8]. Until the implementation of
the former International Basic Safety Standards (BSS) [I1] in the 1990s, most countries had not been
particularly concerned with assessing occupational exposure to natural sources of radiation. Over the past
two decades, exposure to enhanced levels of natural radiation has become a focus of attention forradiation protection. The European BSS [E2] and related guidance [E3] established requirements toevaluate the levels of occupational exposure to natural sources of radiation. The current internationalsafety standards on radiation protection, such as the BSS [I12] and the European BSS [E8] further develop
such recommendations and requirements and may influence the content and data collection for future
UNSCEAR assessments of occupational exposure. Regarding data collection and compared to earlier
evaluations, the Committee had expected and hoped for a greater response rate to the UNSCEAR
Occupational Exposure Survey from United Nations Member States for periods evaluated in this annex.
8.
The Committee’s assessment of occupational exposure due to human-made sources of radiation
includes exposure within the subsectors of nuclear fuel cycle, medical uses of radiation, industrial usesof radiation, uses of radiation sources for military purposes, and miscellaneous uses of radiation. The
following information regarding the collection of data for the Committee’s assessment of occupational
exposure due to human-made sources of radiation should be noted:−

For the nuclear fuel cycle sector, the Committee requested data on occupational exposure forthe same work activities evaluated in its previous reports: uranium mining and milling, uranium
conversion and enrichment, fuel fabrication, reactor operation (permanent staff and contractors),
spent fuel reprocessing, and research in the nuclear fuel cycle. In addition, data were also
requested for the subsectors on decommissioning, management of radioactive waste and spent
nuclear fuel, safety and safeguards inspections, and transport within the nuclear fuel cycle;−

For the medical sector, the identified work activities and division into subsectors are similar to
those used in the previous evaluation [U10]. The Committee requested data on occupational
exposure in diagnostic radiology (and separately for conventional and interventional diagnostic
radiology), nuclear medicine, radiation therapy, dental practice, and veterinary medicine. The
Committee also requested data for different work categories (physicians, nurses, technicians,
and others) in most work subsectors in medical use of radiation;−

For the industrial sector, the Committee collected data and evaluated the level of occupational
exposure in industrial irradiation, industrial radiography, luminizing, radioisotope production
and distribution, well logging, accelerator operation, use of industrial gauges, and all otherindustrial uses of radiation. These are the same subsectors that were previously used;−

For the sector on military use of radiation sources, the Committee assessed available data on
occupational exposure due to manufacture of weapons, the use of nuclear ships and their support
facilities, and other relevant military activities (e.g., research, transport and non-destructive testing);−

For the miscellaneous sector, the Committee included use of radioactive material in educational
establishments and research applications, management of disused radioactive sources fromindustrial activities, transport of radiation sources outside the nuclear fuel cycle, and other nonspecified occupational groups.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 7

A. Scope and objectives of analysis
9.
The principal scope and objectives of this evaluation of occupational exposure remain, largely, as
in the previous assessments of the Committee, as follows:−

To assess average annual effective doses to workers (both the average dose and the distributionof doses within the workforce) for each of the major work sectors and subsectors involving theuse of ionizing radiation;−

To assess the average annual collective effective doses to workers for each of the major work
sectors and subsectors involving the use of ionizing radiation;−

To estimate the worldwide level of occupational exposure for different sectors involving
exposure to natural sources and to human-made sources of radiation;−

To identify and analyse temporal trends in occupational exposure in order to evaluate the effects
of changes in regulatory standards or requirements, e.g., changes in dose limits, newtechnological developments and modified work practices;−

To identify possible new groups of workers receiving higher doses due to implementation of
new techniques in applying radiation sources;−

To address the level of exposure to the lens of the eye;−

To identify research needs, and implications for future analysis of occupational exposure.

10. This analysis does not address occupational exposure due to radiological accidents (e.g., Chornobyl
and Fukushima) as the Committee published dedicated evaluations on this topic, including occupational
exposure aspects [U9, U11, U16].

B. Sources of occupational exposure to radiation
11. According to the International Labour Organization (ILO), the definition of occupational exposure
to any hazardous agent includes all exposure incurred at work, regardless of source [I47]. The term
occupational exposure is used in this annex to denote all radiation exposure incurred by workers in thecourse of their work, with the exception of: (a) exposure to the normal local natural background radiation;(b) exposure from exempt activities involving radiation or exempt sources; and (c) any medical exposureof patients [I29]. Occupational exposure is usually measured by individual monitoring; when this is not
feasible, data from monitoring of the workplace are used to assign individual doses. The doses are usuallyassessed and recorded for radiation protection purposes by licensees and competent authorities. Thisannex uses two different categories of workers: (a) monitored workers, which refers to all workers subject
to individual or workplace monitoring; and (b) measurably exposed workers, which refers to the workers
who have received doses equal to or above the administratively established recording level used in themonitoring programme.
12. The International Commission on Radiological Protection (ICRP) and the International Atomic
Energy Agency (IAEA) have previously distinguished between “practices”, human activities that
increase exposure or likelihood of exposure, and “interventions”, actions that reduce exposure or
likelihood of exposure [I1, I25]. However, since its Publication 103 [I29] published in 2007, ICRP has
used a situation-based approach to characterize the circumstances where radiation exposure may occur
as “planned”, “emergency”, and “existing” exposure situations. ICRP considers that it is appropriate to8 UNSCEAR 2020/2021 REPORT

limit the use of the term “intervention” to describe protective actions that reduce exposure, while theterms “emergency” and “existing” exposure situations should be used to describe radiological situations,where such protective actions to reduce exposure are needed [I29]. Although the term “practice” can still
be and is used, especially in regulatory text and in the International BSS [I12] and European BSS [E2],to describe regulated sources within planned exposure situations, the Committee decided to avoid theterm “practice” and replace it in this evaluation by work sectors. Occupational exposure occurs in theworkplace as a result of exposure to external sources of radiation only, or as a result of a combination of
exposure to external sources and of intake of radioactive substances (radionuclides) to the body byinhalation, ingestion or skin absorption. Some workplaces have a potential risk for external exposure
only, others have potential risk for both types of exposure (internal and external).
13. Occupationally exposed workers, who have recognized rights and duties in relation to occupationalradiation protection, are subject to controls established by the national regulatory authorities. To enable
an assessment of their exposure, they are mostly monitored individually through a routine and continuingmeasurement programme, the alternative being workplace monitoring. A substantial number of workers,
mostly those exposed to ionizing radiation, are not individually monitored. The exposure situations forthese workers differ considerably with regard to such influences as the type of industry, conditions in theworkplace, radionuclides involved and their physical and chemical forms. There are also workers who
are not classified as occupationally exposed and are not subject to regulatory control; nonetheless, they
are monitored for reassurance purposes. However, obtaining a comprehensive set of exposure data forsuch workers is difficult.
14. The criteria for selecting the workers to be monitored and for exposure to be recorded differ
considerably between countries. Some regulatory authorities or operators/employers monitor only
exposed workers while others, for various reasons, include non-exposed workers in their individual
monitoring programmes. Also, countries use different approaches for recording doses and related
exposure data. As demonstrated in table A.1 in the electronic attachment, some countries report that
calculated radiation doses below the established minimum detectable level (MDL) are recorded, whileothers state that only doses above a certain defined level of exposure are registered. This may lead to bias
and additional uncertainties in the results when comparing levels of exposure between different countries
and sectors.

II. METHODOLOGY AND SOURCES OF DATA

A. Dose assessment methodology for occupational exposure
15. The principal dosimetric quantities in radiation protection as defined by the International
Commission on Radiation Units and Measurements (ICRU) in its Report 51 are the following [I44]:−

Absorbed dose in a tissue or organ T, DT, is defined as the mean energy absorbed per unit mass
averaged over the entire tissue or organ. The International System of units (SI unit) for absorbed
dose is joule per kilogram (J/kg) and its distinctive name is Gray (Gy);−

Equivalent dose in a tissue or organ T, HT, is defined as the sum of the absorbed doses in thattissue or organ, weighted by the relevant radiation weighting factor, wR, for each radiation type

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 9

R, DT,R×wR. The radiation weighting factors reflect the higher biological effectiveness of charged
particle radiation with high linear energy transfer (LET) per unit length as compared with lowLET radiation. Since wR is dimensionless, the SI unit for the equivalent dose is the same as forthe absorbed dose, J/kg, and its distinctive name is Sievert (Sv);−

Effective dose, E, is the tissue-weighted sum of the equivalent doses (HT×wT) in all specified
tissues and organs, T, of the body. The tissue weighting factor, wT, is selected to represent therelative contribution of that tissue or organ to the health detriment in a reference population
resulting from uniform irradiation of the body. The sum of the tissue weighting factors is 1. The
unit for the effective dose is the same as for absorbed dose, J/kg, and its symbol is also Sv;−

Committed equivalent dose, HT (τ), is the time integral of the equivalent dose rate in a particular
tissue or organ that will be received by an individual following intake of radioactive material
into the body by a reference person, where τ is the integration time in years. The committed
period is taken to be 50 years for adults;−

Committed effective dose, E(τ), is the sum of the products of the committed organ or tissue
equivalent doses and the appropriate weighting factors, wT, that will be received by an individual
following intake of radioactive material into the body by a reference person, where τ is theintegration time in years, which is 50 years for adults.

16. The reference person referred to here is a hypothetical person for whom the organ or tissue
equivalent doses are calculated by averaging the corresponding doses of the reference male and reference
female. The equivalent doses of the reference person are used for the calculation of the effective dose bymultiplying these doses by the corresponding tissue weighting factors [E11].
17. Operational quantities are used in practical application for monitoring and investigating situations
involving external exposure. For area monitoring, two quantities: namely, the ambient dose equivalent,
H*(d), and the directional dose equivalent, H’(d, Ω), are used to assess the exposure to external radiation.
The ambient dose equivalent, H*(d), at a point in a radiation field is the dose equivalent that would be
produced by the corresponding expanded field in the “ICRU sphere” at a depth, d, on the radius opposing
the direction of the aligned field. The directional dose equivalent, H’(d, Ω), at a point in a radiation fieldis the dose equivalent that would be produced by the corresponding expanded and aligned field in the“ICRU sphere” at a depth, d, on the radius in a specified direction Ω. The personal dose equivalent Hp(d)is the dose equivalent in soft tissue (commonly) interpreted as the sphere of 300 mm in diameter; at an
appropriate depth, d, below a specific point on the human body. This point is usually given by the position
where the individual’s dosimeters are worn. The depth for H*(10) or Hp(10), for monitoring of effective
dose is 10 mm depth in soft tissue. The depth for H’(0.07, Ω) or Hp(0.07), for monitoring of equivalentdose to local skin is 0.07 mm. The depth for H’(3, Ω) or Hp(3), equivalent dose to the lens of the eye is
3 mm. The unit of ambient, directional dose equivalent and personal dose equivalent is J/kg, and its
distinctive name is Sievert (Sv) [I44].
18. The basic quantity used herein to express radiation exposure is the effective dose. This derived
quantity is developed for radiation protection purposes but cannot be directly measured. The Committee
uses it to compare radiation doses in different work activities and exposure scenarios. An estimate of theeffective dose, E, needs to take the contribution from external and also from internal exposure into
account, as appropriate. E is usually reported in millisievert (mSv). It can be calculated from an annual
dose using the following expression:
𝐸𝐸 = 𝐸𝐸external + Σ𝑒𝑒𝑗𝑗,inh (50). 𝐼𝐼𝑗𝑗,inh + Σ𝑒𝑒𝑗𝑗,ing (50). 𝐼𝐼𝑗𝑗,ing(1)

10 UNSCEAR 2020/2021 REPORT

where Eexternal is the effective dose due to external exposure received during a year (often the period ofstudy), which is calculated on the basis of the operational quantity Hp(10); ej,inh(50) — the committed
effective dose per unit activity intake by inhalation of radionuclide j, integrated over 50 years; Ij,inh is theactivity intake of radionuclide j by inhalation during the year; ej,ing(50) is the committed effective dose
per unit activity intake by ingestion of radionuclide j, integrated over 50 years; and Ij,ing is the activity
intake of radionuclide j by ingestion during the year. For most forms of intake, the dose coefficientsprovided by ICRP are for intakes by inhalation and ingestion and do not take account of uptakes throughthe skin although it is well known that such may occur. The ICRP occupational intake of radionuclides
series has provided dose coefficients for injection of some radionuclides which could be used as asurrogate for rapid absorption through skin [I35] using a specific ICRP Data Viewer [I42]. However,these coefficients were published after the period selected for this evaluation.

1. Assessment of effective dose from exposure to external sources ofradiation
19. For dose assessment of exposure to external sources of radiation, three operational quantities areused: (a) the ambient dose equivalent H*(10); (b) the directional dose equivalent H’(d, Ω); and (c) the
personal dose equivalent Hp(d) [I44]. Both the ambient and directional dose equivalent are applied to area
monitoring, while the personal dose equivalent is reserved for individual monitoring of workers (viapersonal dosimeters worn on the body). The effective dose cannot be measured because of thecomputational values needed for each organ dose and the personal dose equivalent is used for estimationof the effective dose. For assessment of the radiation protection quantity effective dose, a depth d=10 mm
is selected, and for assessment of the equivalent dose to the skin, hands, wrists, and feet, a depth
d=0.07 mm is used. In special cases of monitoring, such as the dose to the lens of the eye, a depth d=3 mm
is used. The SI unit for these three operational quantities are J/kg and the corresponding distinctive nameis Sievert (Sv).
20. A factor that contributes to the uncertainty in the external dose assessment is the placement of thepersonal dosimeters. Most often, the dosimeter is placed on the front of the body, which is satisfactory
provided that the dosimeters have been designed to measure Hp(10). In radiology, where lead aprons are
frequently used, various approaches have been adopted. In some cases, the assessment of effective doses
to workers is carried out by means of a dosimeter worn on the trunk, under the apron. Where exposure is
likely to be greater, for example in interventional radiology, two dosimeters are sometimes used, oneplaced under the apron and a second outside. The purpose of the second dosimeter is to assess thecontribution to the effective dose due to the irradiation of unshielded parts of the body [N3]. Whenmonitoring is intended to give only an upper estimate of an exposure, a single dosimeter is worn outside
the apron. Understanding the placement of dosimeters, particularly with regard to protective aprons, isimportant to properly characterize the dose received and to minimize the uncertainties.
21. The IAEA conducted a survey covering cardiologists from 56 countries, which found that 76% of
the studied interventional cardiologists stated that they always used their personal dosimeter (77% indeveloped countries and 70% in developing countries); and 45% of the interventional cardiologists statedthat they always used two dosimeters (50% in developed countries and 24% in developing countries)[C12, I9]. The comparison of doses between countries is complex due to the lack of harmonization in
how personal dosimeters should be used. Another study with cardiologists from 11 countries in Latin
America showed that only 64% of the cardiologists used their personal dosimeters regularly, only 36% were
aware of their personal dose values, only 41% used protective ceiling-suspended screens, only 14% had
detailed knowledge of the X-ray system they were using and only 27% knew the quality control results[C13, V3, V4].

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 11

22. ICRU recommendations on the acceptable levels for total uncertainty in measured radiation doses
in Reports 47 and 66 [I43, I45] are broadly consistent with similar statements made by ICRP. ICRU
recommends that, for single measurements of the operational quantities, “in most cases, an overall
uncertainty of one standard deviation of 30% should be acceptable”. The error of instruments may
substantially exceed this limit at some energies and for certain angles of incidence but conform to it when
they occur in a radiation field with a broad energy spectrum and broad angular distribution [I43, I45].
23. A distinction should be recognized between the accuracy of a measurement with a dosimeter underlaboratory conditions in a well-known radiation field and that of a measurement in the workplace [A14,V1, V2]. The EC Radiation Protection 160 report [E7] recommends that, for a measurement of theoperational quantity Hp(10) for a single field component and for a quantity value equal to or greater than
1 mSv (equals the recommended annual effective dose (E) limit for the members of the public) inproportion to the wear period, the combined uncertainty should be less than 30% for photon/electron
workplace fields and less than 50% for neutron fields. From considerations of the response characteristicsof neutron personal dosimeters currently used, and from the results of intercomparisons, there are
difficulties meeting a 30% combined uncertainty criterion for whole body doses from neutrons. Even
with a relaxation of the criterion to 50%, it is not possible with any current design of neutron dosimeters
to meet the criterion over the full range of neutron energies possibly present in the workplace [E7].

2.

Assessment of effective dose from cosmic radiation

24. Aircrew personnel are exposed to primary and secondary fields of cosmic radiation in theatmosphere, which are very complex in terms of particle composition and energies. The various
components of the cosmic radiation field have been thoroughly discussed in the UNSCEAR 2008 Report[U10]. Individual monitoring by measurement is impractical, as instruments that can assess the entire
spectrum of the radiation field considerably exceed the size and weight of ordinary personal dosimeters.
As a consequence, aircrew dose, in terms of effective dose, E, is calculated by means of computer
programs, thus following the recommendations of ICRP Publication 132 [I37]. This approach is feasible,
since the radiation field at aircraft locations is accurately calculated, except in extremely rare cases ofsudden increases of intensity and energy due to solar particle events, which can lead to much higher
doses. Solar particle events and the associated doses are of concern to space crews operating outside theearth’s protecting atmosphere. Individual monitoring of aircrew personnel based on computer programs
relies on knowledge of geographic location (latitude/longitude), flight altitude, solar cycle phase, andpilot and aircrew information. Software codes are generally validated by comparing the calculated valuesof E with the measured values of the operational quantity ambient dose equivalent H*(10). The agreement
between calculated and measured values should be within ±30% at a 95% confidence level, as
recommended by ICRU [I43, I45].

3.

Assessment of effective dose for radionuclide intake

25. In its UNSCEAR 2008 Report [U10], the Committee provided a detailed overview of effective dose
assessment for intakes of radionuclides, on which the most recent ICRP recommendations were publishedin ICRP Publication 103 [I29]. However, the release of a set of companion publications for occupational
intakes of radionuclides are started in ICRP Publications 130, 134, 137 and 141 [I35, I36, I38, I40]. The
revised dose coefficients were calculated using the human alimentary tract model [I28] and a revision of
the human respiratory tract model that takes account of more recent physiological data [I35]. In addition,
information is provided on absorption into blood following inhalation and ingestion of different chemical

12 UNSCEAR 2020/2021 REPORT

forms of elements and their radioisotopes [I33, I35, I36]. The most recent ICRP recommendations were,
however, not applied in 2003–2014, the period of data collection for the current assessment. The reported
effective doses provided in the current evaluation were calculated on the basis of earlier methodologies
for calculating doses due to intakes of radionuclides as provided in ICRP Publications 26 and 60 and the
publications under their umbrella [I24, I25].

4.

Assessment of effective dose for radon inhalation

26. As early as 1988, the International Agency for Research on Cancer (IARC) classified radon as aproven human carcinogen because studies of miners occupationally exposed to radon were noted toprovide a direct basis for assessing lung cancer risk to miners [I22]. The Committee also concluded that
inhaled radon and its progeny have been established as carcinogens for the lung in several comprehensive
evaluations [U7, U9, U14].
27. In line with the International BSS recommendations [I12], employers are required to ensure that theactivity concentrations of radon in workplaces are below a suitable reference level, and that protection is
optimized. This reference level should not be set higher than 1,000 Bq/m3. It is, therefore, often the casethat annual effective dose data for exposure to radon are available only if at workplaces the radon
concentrations in air exceed 1,000 Bq/m3 for 2,000 working hours in a year.
28. The health risk due to exposure to radon comes mainly from the inhalation of its short-lived decay
products and the resulting alpha particle irradiation of the bronchial airways. The radiation dose delivered
to the respiratory system and the resulting potential health detriment are a complex function of the radon
decay products’ aerosol characteristics and the physiological parameters of the exposed individual [H4,I27, I35, I46, U7, U9, W4]. Quantities and units used for the assessment of effective dose resulting frominhalation of radon and its progeny are given in UNSCEAR reports [U9, U10, U14].
29. There are several workplaces where doses from radon can be high enough to justify monitoring orprotective action (e.g., in mining, mineral processing) and in some underground and above-groundworkplaces (e.g., show caves, spas, underground laboratories or stores, water treatment plants, storage
facilities or even some office buildings and schools).
30. For workers in mining (especially uranium mining) and mineral processing, radiation exposure isnormally under regulatory control. Most regulatory bodies follow the radiation protection
recommendations of ICRP. For radon exposure, ICRP Publication 65 adopted the dose conversion factorof 5 mSv per working level month (WLM) (1 WLM = 6.38 × 105 h Bq/m3 EEC) [I26]. ICRP recently
revised the dose conversion factor to 12 mSv per WLM for mines, 20 mSv per WLM for an indoor
workplace and 24 mSv per WLM for a tourist cave [I38]. However, these new conversion factors were
not implemented for the review period analysed in this assessment.
31. For workplaces other than mines, most workers exposed to radon are not monitored. In theliterature, many radon measurements taken in these workplaces are reported. The majority of the studies
have measured radon gas concentrations in units of Bq/m3, and subsequently assessed radon doses toworkers by using the UNSCEAR dose conversion factor of 9 nSv per (h Bq/m3), assuming the total annual
working hours (≤2,000 hours) and a radon equilibrium factor (typically F=0.4). Because several different
dose conversion factors are available, the UNSCEAR Occupational Exposure Survey has requested theparticipating Member States to specify the dose conversion factor used in their calculations (adopted intheir country).

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 13

32. For the purpose of evaluating average effective doses from radon inhalation by public and worker,
the Committee adopted a dose conversion coefficient of 9 nSv per (h Bq/m3) in 1982 [U4]. This value
was retained by the Committee in its assessments [U8, U9, U10]. Recently, the Committee reviewed
epidemiological studies of lung cancer risk from radon exposure published since 2006 [U14]. The
evidence reviewed by the Committee is compatible with its previous dose assessments of lung cancer
risk due to radon exposure and it concluded that there was no reason to change the established doseconversion factor for its dose assessments.

5.

Assessment of doses to lens of eye

33. In the past couple of decades, new and relevant information has appeared regarding theunderstanding of the radiation risk of cataract formation. As a result, in its Publication 118 [I32], ICRP
revised the former threshold for tissue reactions of the lens of the eye and reduced it from 1.5 to 0.5 Gy.
The recommended annual equivalent dose limit for the lens of the eye for occupational exposure inplanned exposure situations was reduced from 150 to 20 mSv averaged over five consecutive years and
50 mSv in any single year. The development of sensitive methods for monitoring eye exposure has thus
become increasingly important. To assist in computational assessments of radiation dose to the lens of
the eye for exposed persons, ICRP Publication 116 [I30] provides approved reference data on conversion
coefficients for the lens of the eye for estimating the absorbed dose to the lens. These new ICRP
conversion coefficients were, however, not applied in 2003–2014, the period of data collection for theCommittee’s assessment presented in this annex.
34. ICRP, in Publication 139 [I39], describes the challenges in monitoring the exposure of the lens of
the eye. The difficulties in placing a device to which the dosimeter can be attached near the eyes are themain challenge. While the quantity Hp(3) has been used or proposed for control and evaluating the doseto the lens of the eye in relation to the ICRP dose limits, few physical dosimeters have been constructed/
calibrated to assess these operational quantities properly for d=3 mm. In principle, the reading of adosimeter over the apron at collar level is a reasonable indicator of the dose to the lens of the eye when
protective glasses are not worn, but when protective glasses are used, the collar dosimeter may grossly
overestimate the dose to the lens of the eye [D7, I10, R3, S5, V5]. In addition, with the significant
uncertainties involved in the dosimetry of the lens of the eye and the fact that actual doses to the lens of theeye may be of the same order as the annual equivalent dose limit to the lens of the eye, the important taskof assessing compliance with the annual equivalent dose limit has become a challenge [I30, I34, I39, N5].
35. An intercomparison exercise dedicated to lens of the eye dosimeters used in medical practice gave
an overview of the different dosimetric systems currently available in Europe for lens of the eye dosemonitoring [C13]. The observed results were satisfactory overall since, among the 20 participant
countries, 17 were able to provide 90% of their responses in accordance with the standard requirementsof the International Organization for Standardization (ISO) [I50]. For a minority of participants, somediscrepancies compared with the reference doses were observed for irradiation set-ups characterized bylarge angles and/or low energies. Some improvements could be achieved by applying calibration of thedevices used [C13].

B. Dose recording
36. In order to ensure the reliability of dose assessments, some countries have implemented systems toauthorize monitoring services based on a set of requirements established by the national regulatory

14 UNSCEAR 2020/2021 REPORT

authority, while others apply criteria based on the quality management system for accrediting individual
monitoring services. In most countries, dose reporting and recording are regulated by national laws ornorms and may differ for various categories of workers depending on their exposure. The IAEA, in its
publications [I2, I3, I4] and more recently [I15], has provided guidelines for how monitoring data andresults are to be reported, which dose levels are to be recorded, and which documents and records ofradiation exposure are to be maintained.
37. Despite guidelines for dose recording, variations from country to country may significantly affectthe reported values of average annual collective effective dose. This will increase the uncertainty incomparisons between data compiled in different countries. The approaches used in measuring andreporting occupational exposure in each country for which data were reported are summarized intable A.1 in the electronic attachment. If major differences in used approaches are obvious, caution should
be exercised when directly comparing data. The main differences arise because of the following factors:−

The protocol for determining whom in the workforce should be monitored and for whom doses
should be recorded in specific categories;−

The recording level used;−

The recording of dose values less than recording level or the minimum detection limit (MDL);−

The techniques used for measurement of external radiation exposure (e.g., thermoluminescence
dosimeter or optically stimulated luminescence dosimeter);−

The approach adopted to fill missing monitoring periods in the records;−

The evaluation of anomalous results, such as unexpectedly high dose values;−

Whether or not internal exposure is included or treated separately;−

Whether natural background is subtracted from the recorded dose;−

The reliability of the individual monitoring data.

C. Dose distribution
38. The dose distributions presented in this annex follow the same approach as the ones used in previous
UNSCEAR reports [U8, U10]. For the purpose of comparing dose distributions and of evaluating trends,
three characteristics of dose distributions were identified as being particularly useful: (a) the averageannual effective dose (E); (b) the average annual collective effective dose (S); and (c) the average annual
collective effective dose distribution ratio for certain doses (SRE) [U10], which is given by:
𝑆𝑆𝑆𝑆E =

𝑆𝑆(>𝐸𝐸)𝑆𝑆(2)

where S(>E) is the average annual collective effective dose delivered at annual individual doses thatexceed E (mSv).
Similarly, the distribution ratio for the number of exposed workers for certain doses (NRE) is given by:
𝑁𝑁𝑁𝑁E =

𝑁𝑁(> 𝐸𝐸)
𝑁𝑁(3)

where N is the total number of workers, N(>E) is the number of workers receiving annual doses exceeding
E (mSv).

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 15

D. Sources of data
1.

Literature review

39. A comprehensive database search of published literature related to occupational exposure wasconducted, covering the period 2003–2017, with inclusion of additional relevant recent articles andreports. Pre-screening sought to identify publications that might demonstrate changes of trends andupdates in work sectors since the UNSCEAR 2008 Report [U10]. Publications were deemed suitable forpre-screening if there was a match on one or more of the following search terms: “ionizing radiation andoccupational exposure or radiation exposure”; “radiation worker” and “occupational exposure”. A moredetailed search was conducted for six broad sectors identified for occupational exposure (natural sources,
nuclear fuel cycle, medical uses, industrial uses, military activities and miscellaneous use of ionizing
radiation). This process was followed by screening and evaluation of the relevant literature from 2003
onwards through the PubMed and ScienceDirect databases, including studies and reports provided byinternational or governmental organizations. About 700 articles and reports were identified for review,of which about 50% were assessed as meeting the selection criteria following the UNSCEAR 2017
Report, annex A [U13].

2.

UNSCEAR Occupational Exposure Survey

40. The purpose of the Committee’s current evaluation of worldwide occupational exposure is toprovide more detailed and updated information on exposure to ionizing radiation related to different work
activities, e.g., to identify job functions and categories of work within each practice that lead to more
relevant exposure, to identify the contributions of external versus internal exposure to the total effective
dose, and to obtain information about the reliability of measurements associated with the accreditation or
authorization of monitoring services.
41. The current evaluation is based on data from the UNSCEAR Occupational Exposure Survey,
launched in 2016 and completed in 2019. The evaluation follows the same procedure as that for former
evaluations: a formal request to all Member States of the United Nations for data to be submitted via the
UNSCEAR online platform. Two questionnaires were prepared for the survey, a simplified and a detailed
questionnaire. In the simplified questionnaire, essential data on the number of workers and the averageannual effective dose for each work sector, subsector, work category and subcategory were requested.
The detailed questionnaire requested data on the number of monitored workers, average annual effective
dose for all monitored workers, average annual collective effective dose and dose distribution for theperiod 2003–2014. In order to be able to perform a more detailed analysis of the data, some additional
information was also requested. The data obtained by the questionnaires were supplemented by data fromthe literature review and also data obtained from other international organizations. By September 2019,a total of 57 Member States had responded to the simplified questionnaire, providing data on numbers ofworkers in different work sectors. Forty-four countries responded to the detailed questionnaire, providing
data on numbers of workers along with average annual effective doses and/or average annual collective
effective doses. The list of countries responded to the UNSCEAR Occupational Exposure Survey is presented
in table A.2 in the electronic attachment and the list of national contact persons in the acknowledgement.
42. The detailed questionnaire was designed in such a way that it could be answered by countries witheither a limited national database or with a comprehensive national database. It comprises:

16 UNSCEAR 2020/2021 REPORT−

Basic questions: value of MDL, value of recording level, information about accreditation/authorization of dosimetry services; number of monitored workers; number of measurably
exposed workers; average annual effective dose for all monitored workers; average annual
effective dose for measurably exposed workers; dose distribution for the effective dose intervals:
E<MDL; MDL–1; 1–5; 5–10; 10–15; 15–20; 20–30; 30–50; E>50 in mSv; average annual
collective effective dose for each subsector or worker category;−

Detailed questions: for work sectors, subsectors and work categories and subcategories, thecontribution made by internal (inhalation of radon and its progeny and intakes of otherradionuclides) and external dose to the total effective dose and also the factor used to convert
radon exposure to effective dose; percentage of females in the workforce; and doses to the lensof the eye and hands, when appropriate. Also, where possible, occupational data by work
category were requested for some medical subsectors.

43. The simplified questionnaire was designed to obtain essential data from countries not prepared torespond to the detailed questionnaire. The questionnaire also asked for data on average annual effective
dose and its standard deviation, and the uncertainty in the number of workers expressed as a percentage.
Additional data were requested about the availability of the national dose register database for radiationdose records; the annual dose limit for effective dose adopted by the country; the recording dose; thevalue of MDL in mSv per measurement interval and the recorded dose quantity (E or Hp(10)). The
mandatory requested data were the number of workers involved in each subsector.
44. The 44 countries that responded to the detailed UNSCEAR Occupational Exposure Survey andprovided additional methodology information had external dose monitoring services available. About
68% of these had internal monitoring in operation. About 80% of the countries had a central occupationaldose register.

E. Estimation of worldwide levels of exposure
45. The worldwide annual number of monitored workers, the worldwide average annual collective
effective dose and the worldwide average annual effective dose were estimated for most of the sectors ofoccupational exposure, including natural and human-made sources of radiation. The determination of thenumber of monitored workers and the average annual effective dose per worker in all sectors could not
be derived directly from data obtained from the UNSCEAR Occupational Exposure Survey because oflacking information. Moreover, not all State members of the Committee provided data for the current
assessment. Where collected data were not sufficient to derive quantitative estimates, regression-basedmodels were derived for the association between the annual number of workers or average annual
effective dose and available predictor variables. These models were then used to estimate (extrapolate)
the number of workers or the average annual effective dose for countries where no reported data except
for predictor variables were available. Table 1 presents a list of predictor variables used in this assessment.
46. The quality of the Committee’s global evaluations of occupational exposure depended on theavailability of samples of representative data and on the quality of the data collected from the countries
surveyed. In addition, the use of extrapolation models necessarily introduced uncertainty and potential
bias to the estimates because the methods were limited to statistically derived predictions using only theavailable data, but with limited knowledge of their adequacy, precision, and representativeness. The
overriding limitation was the low rate of participation by United Nations Member States in providing
occupational exposure monitoring data.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 17

Table 1. Predictor variables by sector and subsector used in the UNSCEAR extrapolation models
SectorSubsector

Job category

Predictor variables

NATURAL SOURCES OF RADIATION
Coal extraction andprocessing

Average total primary coal production foreach period

Mineral other than fuelmineral extraction
and processing

Average annual total mineral other than fuelmineral production for each period

Oil and gas extraction

Average total petroleum production foreach period, annual GDP for each period
HUMAN-MADE SOURCES OF RADIATION
Uranium mining andmilling

Nuclear fuel cycle

Average total of extracted ore for eachperiodReactor operation

Average energy generated per type ofreactor for each period

Fuel fabrication
Other subsectors

No predictor parameter used
Physicians
NursesDiagnostic radiology

Technicians
Other jobs
Combined job
categories

Annual GDP, physician density, computer
tomograph density, and gamma camera or
nuclear medicine unit density within aperiod. Other medical parameters should
be used (i.e., interventional radiology
systems density), but data not available
worldwide

Physicians
NursesConventional
radiology

Technicians
Other jobs

Same predictor variables as applied indiagnostic radiology

Combined job
categories
MedicalPhysicians
NursesInterventional
radiology

Technicians
Other jobs

Same predictor variables as applied indiagnostic radiology

Combined job
categories
Physicians
NursesNuclear medicine

Technicians
Other jobs
Combined job
categories

Same predictor variables as applied indiagnostic radiology

18 UNSCEAR 2020/2021 REPORT

SectorSubsector

Job category

Predictor variables

Physicians
NursesRadiation therapy

Technicians
Other jobs

Same predictor variables as applied indiagnostic radiology

Combined job
categories
Dental radiology
Veterinary medicine
Other medical uses

Industrial

Same predictor variables as applied indiagnostic radiology
Same predictor variables as applied indiagnostic radiology

Industrial irradiation

Annual GDP for each period and number ofirradiators or sterilization facilities forindustrial irradiation

Industrial
radiography

Annual GDP for each period and averageannual petroleum production

Luminizing

Annual GDP for each period

Radioisotope
production anddistribution

Annual GDP for each period and number of
research reactors

Well logging

Annual GDP for each period and averageannual petroleum production

Accelerator
operation

Annual GDP for each period

Industrial gauges

Annual GDP for each period and averageannual petroleum coal and other mineralproduction

Other industrial uses

Annual GDP for each period

Educational
establishments

Annual GDP for each period and number of
research reactors

Disused radioactive
sources
MiscellaneousTransport ofradiation sources
outside the nuclear
fuel cycle

Annual GDP for each period

Other occupationalgroups

47. Ideally, information on national practices and the sophistication of local radiation protection could
be used to predict unknown values for the number of monitored workers and the average annual effective
dose (or, alternatively, the national average annual collective effective dose). However, for occupational
exposure to radiation from sectors other than the nuclear fuel cycle, summaries of the national practices
were not readily available. A variety of approaches were possible for extrapolation (e.g., scaling by
population size, by employment rates in industrial or medical sectors). Until now, the Committee hasbased its approach on presumed proportionality to the average gross domestic product (GDP) over a

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 19

specified time interval [U6, U8, U10]. Several considerations have influenced the choice of this quantity
in preference to others, notably the availability of reliable worldwide statistics on GDPs and theirpotential for general application; the latter because a GDP can be reasonably correlated with a country’slevel of industrial activity and of medical care, characteristics unlikely to be reflected in any other single
quantity. To make the extrapolation more reliable, it should be applied not globally but separately bycountry or within geographic regions, economic regions or economic classes, followed by summation
over those groups. Such a strategy would result in extrapolations of available data within groups ofcountries with broadly similar levels of economic activity and would allow for general geographicalcomparisons. However, the poor participation of many countries—in particular, those in low economic
classes—in the UNSCEAR Occupational Exposure Survey, necessitated extrapolations to be madeglobally rather than within economic classes, which might have afforded better precision.
48. Notwithstanding the problems of sparse data encountered in this evaluation, some improvement in
extrapolation has been expected due to the use of multiple predictors (table 1). For example, for the medical
sector, the predictors used were the GDP per capita (GDP at current prices in USD [U1]) in each year withineach period and other likely correlated variables (when available), e.g., the physician density (number ofphysicians per 1,000 persons), computed tomographs (number of computer tomographs per million
persons), and gamma camera or nuclear medicine unit density (number of nuclear medicine machines per
million persons). As discussed below, some improvements are also expected as a result of using statisticalmodelling techniques in which the best fit model was selected from a range of alternative models.

1.

Methodology of extrapolation and uncertainty assessment

49. The intermediate goals for estimating the total number of workers worldwide in all sectors and theworldwide average annual effective dose over all sectors were to estimate the number of monitored
workers in each subsector in each country and the average annual effective dose within each occupational
subsector in each country. However, estimates of the average annual effective dose and the number ofworkers were available only from a small fraction of the world’s countries, particularly those of higher
economic status. Because estimates were not available from many countries, strategies were devised to
extrapolate the data from those countries providing data to those not providing data, so that a worldwide
estimate of the average annual effective dose (within a subsector), and a worldwide estimate of the total
number of workers (in the same subsector) could be derived. Because extrapolation was involved, astrategy for assessing the uncertainty was also developed so as to give approximate confidence boundsof the estimates.
50. For the present evaluation, a number of assumptions were made in order to develop a strategy that
could be applied systematically within and across the occupational work subsectors. First, it was assumed
that the reported values from the countries were average values, but not absolutely precise, i.e., the true
value was uncertain. Second, it was assumed that the values submitted by each country reporting data
were equally likely to be greater or smaller than the true average value. This assumption implied that thevalues provided by each country were approximately the 50th percentile of a distribution of theuncertainty on the true average value. Third, the distribution of uncertainty around the reported averagevalue was assumed to be a right-skewed so that the lower bound of the uncertainty distribution would not
be less than zero. For convenience, the distribution of uncertainty around the estimate was assumed as
log-normal implying that the reported average value was also approximately equal to the median orgeometric mean of the uncertainty distribution.
51. Because the data sets that were used in each country to derive their reported values were notavailable, there was no means to estimate the precision of each reported value. Hence, a decision was20 UNSCEAR 2020/2021 REPORT

made to subjectively characterize the uncertainty of the reported values to be within 15% of the true value(at the one-sigma confidence level). For a log-normal distribution, this level of uncertainty translates toa geometric standard deviation (GSD) of the uncertainty distribution of about 1.15.
52. For those countries not reporting any data, a strategy was necessary to estimate, i.e., extrapolate, avalue from data reported from countries with data, and to estimate the uncertainty of the extrapolated
values. To extrapolate values for countries not reporting data, a strategy based on regression models that
could be used for predictive purposes was developed. Because of computational difficulties in using theresults of individual model fittings to estimate the uncertainty of each extrapolated value, a decision wasmade to subjectively estimate the uncertainty of each extrapolated value to be ±40% of the true value (atthe one-sigma confidence level). For a log-normal distribution, this level of uncertainty translates to a
GSD of the uncertainty distribution of about 1.4.
53. In summary, an uncertainty of each country’s estimate of average annual effective dose and thenumber of workers, in the form of a GSD, was subjectively assigned to be 1.15 for countries that reported
data, and to be 1.4 for the estimates from countries for which an extrapolation model to make estimates
was used.
54. The extrapolation models to estimate the average annual effective dose and the number of workers
for countries not reporting data were derived using the reported data for model development. The
modelling approach was to use available covariate data such as GDP and other variables presented intable 1 for the countries that reported values to develop multivariate regression equations that could be
used for predictive purposes. Using the derived model and the covariate data from each country notreporting data, values of the average annual effective dose and the number of workers could be estimatedfor those countries not reporting.
55.

The form of the multivariate extrapolation model was:𝑌𝑌 = 𝛽𝛽0 + 𝛽𝛽1 𝑧𝑧1 + 𝛽𝛽2 𝑧𝑧2 + 𝛽𝛽3 𝑧𝑧3 + 𝛽𝛽4 𝑧𝑧4 + 𝜖𝜖

(4)where Y was either the number of monitored workers in a specific country or the average annual effective
dose in that country, β0 was the intercept and β1 the fitted regression coefficients, and 𝜖𝜖 was the error
vector for the four predictor variables. The z1 values were the parameters for fitting, e.g., GDP in a specificyear as presented in table 1 for a listing of predictor variables for each occupational subsector.
56. In this work, stepwise multivariate linear regression was used to fit predictive models with various
combinations of covariates. To prevent over-fitting, the maximum number of predictor variables allowed
was four but could also be fewer, depending on the data available (table 1). Although other statisticaltechniques besides linear regression, e.g., Poisson regression, could theoretically be used and might bepreferred, linear regression of the reported values was used for reasons of simplicity and transparency.
To ensure consistent results with Poisson regression models, predicted values from the linear regression
models, when negative (i.e., physically impossible values), were set equal to zero.
57. The extrapolation models were applied to each country not providing data as a means for predicting
the number of workers and the average annual effective dose for that country. While the model
development process resulted in several possible models, each was based on slightly different
combinations of the available covariate data. The model chosen for use was the one with the largest
adjusted coefficient of correlation (R2) where the “adjustment” was the standard statisticalimplementation to account for the number of predictor variables.
58. While development of extrapolation models was originally intended for both (a) the number ofworkers and (b) the average annual effective dose, model derivation efforts indicated that the available

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 21

covariate data were unsatisfactory for predicting the average annual effective dose, i.e., the adjusted R2
values of the prediction models for average annual effective dose were too low for the models to bereliable. Hence, the regression-based extrapolation models were used only for estimating the number ofworkers in countries that did not report data, but not for the average annual effective dose, which requireda different strategy, as described in the paragraphs below.
59. Extensive fitting models for the number of workers showed that models for individual occupational
subsectors either fit relatively well (adjusted R2>0.7) or very poorly (adjusted R2<0.1). For this reason,
the extrapolation of the number of workers was conducted only for those subsectors for which the derived
extrapolation models had adjusted R2≥0.7. Fortunately, those subsectors for which adequate models could
not be developed are known to be relatively small contributors to the worldwide workforce. The
occupational subsectors where the extrapolation models were not deemed to be reliable included oil andgas extraction, radioactive waste management, transport within the nuclear fuel cycle, safety andsafeguards inspections, the “other categories” of the nuclear fuel sector, veterinary medicine, military
uses, disused radioactive sources, transport of radiation sources outside nuclear fuel cycle, and otheroccupational groups.
60. While the worldwide total number of workers is probably underestimated because extrapolation
models for some subsectors could not be developed, the underestimation does not appear to be large
because those subsectors are known to have far fewer workers. The derived uncertainty interval,
described in a later section, attempts to account for any underestimation.
61. The regression-based modelling procedure allowed for an estimation of the number of workers foreach country within each participating occupational subsector. To achieve the goal of estimating theworldwide total number of workers in each subsector, the country-specific estimates of the number ofworkers (determined either as a reported value or an extrapolated value) were simply summed:𝑛𝑛

𝑁𝑁T = � 𝑁𝑁𝑖𝑖
𝑖𝑖=1

(5)

where NT is the worldwide total number of workers in a single occupational sector, Ni is the reported or
extrapolated number in country i, and n is the number of countries worldwide that conducted theparticular occupational subsector.
62. The total uncertainty on the worldwide number of workers, expressed as a GSD, was determined
as a weighted average of the country-specific GSD values over all countries participating in the subsector:𝑛𝑛

𝐺𝐺𝐺𝐺𝐺𝐺NT = exp ���[𝑙𝑙𝑙𝑙(𝐺𝐺𝐺𝐺𝐺𝐺𝑖𝑖 )2 × 𝑤𝑤𝑖𝑖 ] �
𝑖𝑖=1

(6)

where GSDNT is the total GSD for the estimated number of workers for all countries participating in thesubsector, n is the number of countries with workers in the particular subsector, and the weighting factor
wi for each country i, was determined as the fraction of the total worldwide number of workers (NT) in
the subsector contributed by country i, i.e., wi = Ni/NT. As noted, the GSD values used in the summation
were assumed as 1.15 for countries providing data, and 1.4 for the countries for which, in assigning avalue, model extrapolation was necessary.
63. Extrapolation models for the average annual effective dose required a different strategy because theregression-based models were found not to be satisfactory due to an absence of correlations between
available covariate data and the reported average annual effective doses. Hence, for this purpose, the22 UNSCEAR 2020/2021 REPORT

average annual effective dose was based solely on a weighted average of the estimates from the subset
of countries providing data on dose per worker (within each occupational subsector) with weighting
factors equal to the fraction of the workers from each country participating in the subsector:
𝑛𝑛

𝐷𝐷w = � 𝐷𝐷𝑤𝑤,𝑖𝑖 × 𝑤𝑤𝐸𝐸,𝑖𝑖
𝑖𝑖=1

(7)

where Dw is the estimate of the worldwide average annual effective dose (for a given subsector), n is thenumber of countries responding to the UNSCEAR Occupational Exposure Survey for the subsector, Dw,iis the reported average annual effective dose in country i, and wE,i is the weighting factor for each countryi, determined as the fraction of the total number of workers from countries providing values of averageannual effective dose (NTE) contributed by country i, i.e., wE,i = Ni/NTE.
64. One acknowledged weakness of this method is that some countries were not represented in theweighted average because they had not reported an average annual effective dose for workers and because
no suitable extrapolation model for the dose per worker could be derived. However, as described below,
the derived uncertainty interval attempts to allow for that possible underestimation.
65. Here, the overall GSD of the average annual effective dose was derived as a weighted average ofthe GSD for all countries, including those countries for which no estimates could be made, i.e.:𝑛𝑛

𝐺𝐺𝐺𝐺𝐺𝐺E = exp ���[𝑙𝑙𝑙𝑙(𝐺𝐺𝐺𝐺𝐺𝐺𝑖𝑖 )2 × 𝑤𝑤𝑖𝑖 ] �
𝑖𝑖=1

(8)

where GSDE is the uncertainty for the average annual effective dose considering for all the world’s
countries participating in the subsector, and n is the total number of countries with workers in theparticular subsector regardless if extrapolation estimates were possible for the country. As describedabove, for the estimation of average annual effective dose, the GSD-value for countries providing data wasassumed as 1.15, and 1.4 for the countries for which no extrapolation could be made. The weighting factor
wi for each country i, was determined as the fraction of the total worldwide number of workers (NT)contributed by country i, i.e., wi = Ni/NT.
66. While the described strategy to estimate the uncertainty on the worldwide total number of workers
is only an approximation, it is worthy to note that the method attempts to derive a subjective confidence
interval to account for the possible underestimation of the number of workers. While the estimate of theworldwide average annual effective dose was based on a weighted average of data from countries
reporting data, the uncertainty (expressed as a GSD) was based on a weighted average of all countries.
The GSD derived by considering all countries, including those for which no extrapolation could be made,contributed to a more realistic uncertainty estimate that attempts to account for any underestimation.
67. To interpret the derived uncertainty for the worldwide estimates for number of workers and for
average annual effective dose, the overall (worldwide) GSD for each of the two estimated quantities wasused to derive an interval or range in which the true value was expected to lie — on the basis of theavailable information and the extrapolation strategy described. The interval, consistent with log-normal
theory, was derived with the lower bound equal to the ratio of the estimate and the squared GSD (estimate
divided by GSD2) and an upper bound equal to the product of the estimate and the squared GSD (estimate
times the GSD2). Under the assumption that the uncertainty distribution is log-normal, this interval would
encompass approximately 95% of the range in which the true value would be expected to lie. Here we
refer to this interval as a “subjective confidence interval”.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 23

68. The worldwide number of workers was estimated as a sum of the number of workers in all
subsectors:
𝑠𝑠

𝑁𝑁WN = � 𝑁𝑁𝑖𝑖
𝑖𝑖=1

(9)

where NWN is the worldwide number of workers, Ni is the number of workers in subsector i, and s is thenumber of subsectors.
69. The uncertainty on the worldwide number of workers across all subsectors, expressed as a GSD,
was determined as a weighted average of the subsector-specific GSD values:𝑠𝑠

𝐺𝐺𝐺𝐺𝐺𝐺WN = exp ���[𝑙𝑙𝑙𝑙(𝐺𝐺𝐺𝐺𝐺𝐺𝑖𝑖 )2 × 𝑤𝑤𝑖𝑖 ] �
𝑖𝑖=1

(10)

where GSDWN is the worldwide GSD for the estimated number of workers over all countries and all
subsectors, s is the number of subsectors, and the weighting factor wi for each subsector i, was determinedas the fraction of the total worldwide number of workers (NWN) in the subsector i.
70. The worldwide average annual effective dose over all countries and all subsectors was estimated as
the average value weighted by the number of workers in each subsector:
𝐷𝐷WE = ∑𝑠𝑠𝑖𝑖=1 𝐷𝐷𝑤𝑤𝑤𝑤,𝑖𝑖 × 𝑤𝑤𝑆𝑆,𝑖𝑖(11)

where DWE is the estimate of the worldwide average annual effective dose over all countries and all
subsectors, s is the number of countries responding to the UNSCEAR Occupational Exposure Survey forthe subsector, DWS,i is the average annual effective dose in subsector i, and wS,i is the weighting factor foreach subsector i, determined as the fraction of the total number of workers in each subsector.
71. The uncertainty on the worldwide average annual effective dose across all subsectors, expressed asa GSD, was determined as a weighted average of the subsector-specific GSD values:
𝐺𝐺𝐺𝐺𝐺𝐺𝐷𝐷𝑊𝑊 = exp ��∑𝑠𝑠𝑖𝑖=1[ln (𝐺𝐺𝐺𝐺𝐺𝐺𝑖𝑖 )2 × 𝑤𝑤𝑖𝑖 ]�(12)where GSDDw is the GSD for the worldwide average annual effective dose across all countries and all
subsectors, s is the number of subsectors, and the weighting factor wi for each subsector i, was determinedas the fraction of the total worldwide number of workers (NWN) in the subsector i.

2.

Practical implementation of model and uncertainty estimation

72. The worldwide level of occupational exposure from natural sources was estimated for civilian
aviation, coal extraction and processing, and minerals other than fuel minerals. For civilian aviation, theextrapolation was not needed for number of workers since the International Civil Aviation Organization(ICAO) provided the data for the countries that did not respond to the UNSCEAR Occupational Exposure
Survey; the average annual effective dose is weighted by the number of workers. For coal extraction andprocessing, the extrapolation of number of workers was based on the linear regression model applying
the average annual total primary coal production for each period as an independent variable; the average

24 UNSCEAR 2020/2021 REPORT

annual effective dose is weighted by the number of workers. For mineral other than fuel mineral
extraction and processing, the extrapolation of number of workers was based on the linear regression
model applying the average annual mineral other than fuel mineral production for each period as anindependent variable; the average annual effective dose is weighted by the number of workers. However,
the worldwide level of occupational exposure for gas and oil extraction could not be derived because oflack of correlation between dependent variables and the independent variables applied in the linear
regression model, which are GDP and petroleum production. The same was true for radon exposure in
workplaces other than mines; the complexity of the subject along with the lack of data did not allow an
extrapolation for this work sector.
73. Five sectors are associated with human-made sources of radiation: (a) nuclear fuel cycle;(b) medical; (c) industrial; (d) military; and (e) miscellaneous groups of workers not included in the
sectors described previously. The predictor variables used to extrapolate the dependent variables arepresented in table 1. An updated evaluation for exposure to human-made sources of radiation for militaryuses was not conducted because of lack of data.
74.

Limitations of methodology as implemented are summarized below:–

The representativeness of the countries was evaluated on the basis of the World Bank
classification of the world’s economies. There are four income groups: high, upper-middle,
lower-middle and low income used in this evaluation. The assignment of each country is basedon gross national income (GNI) per capita (currency: USD). The updated threshold for each (inJuly 2020) is: GNI below or equal to 1,045 USD for low income, GNI in a range from 1,046 to
4,125 USD for lower-middle income, GNI in a range from 4,126 to 12,745 USD for uppermiddle income, and GNI above 12,745 USD for high income. For the period 2010–2014,
76 countries were classified as high income, 55 countries as upper-middle income, 48 countries
as lower-middle income and 36 countries as low income. The data were obtained from the WorldBank database for 2014 [W15];−

For this assessment, the proposed extrapolation procedure was found not to be viable for eachof the conventionally defined income groups because of inadequate participation by United
Nations Member States and the resulting lack of data for several classes that allowed to derive
the 49 mathematical models to determine the number of workers for sectors, subsectors and job
categories. As shown directly below, there were no data on the number of workers in low income
and lower-middle income countries and few data from upper-middle income countries. Only thehigh income countries provided adequate data for extrapolation of the number of workers:–

Zero of 49 subsectors and job categories (0%) in the low income group;–

Zero of 49 subsectors and job categories (0%) in the lower-middle income group;–

Eight of 49 subsectors and job categories (16%) in the upper-middle income group;–

Thirty of 49 subsectors and job categories (61%) in the high income group.

75. The same problem of lack of data existed for estimating the average annual effective dose per
worker by economic class, as is shown below. Only the high income countries provided adequate data:–

Zero of 49 subsectors and job categories (0%) in the low income group;–

Zero of 49 subsectors and job categories (0%) in the lower-middle income group;–

One of 49 subsectors and job categories (2%) in the upper-middle income group;–

Twenty-two of 49 subsectors and job categories (45%) in the high income group.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 25

76. The analysis indicated that extrapolation by economic class was not possible and, for that reason,
extrapolation using data of all Member States with data pooled together was the only alternative. The
preventing analysis by economic classes significantly restricts the ability of the extrapolated values to be
tailored to any specific economic class. Technical limitations imposed by sparse data also included
limiting the ability to check and satisfy statistical assumptions on linearity, equality of variance acrosspredictor variables (homoscedasticity), and normality.
77. Lack of knowledge about which countries were carrying out the activities of the subsectors inmedical, industrial and miscellaneous sectors was also a challenging problem. Both the number ofworkers and the average annual collective effective dose per country could potentially be exaggerated in
the extrapolation if a given country did not conduct such activities.
78. To assist in disregarding countries from extrapolation that did not have each subsector, a survey
was conducted with the assistance of the IAEA in 2019 (table A.3 in the electronic attachment). Thissurvey was a simple (yes or no) questionnaire asking if the country had conducted studies of thesubsectors listed in those three sectors. The IAEA survey also had inadequate participation by countries,
which prevented a systematic use of the survey results. A total of 31 countries responded to the survey,
14 countries from Africa, 12 countries from Asia, one from South America, and four from Europe. For
the current analysis, the critical data are those from Africa since there was no contribution from thisregion to the UNSCEAR Occupational Exposure Survey. On the basis of the data obtained in the IAEA
survey, it was assumed that all countries used diagnostic radiology (conventional radiology andinterventional radiology), dental practices, and radiation therapy. However, only countries with per capita
GDP higher than 500 USD were assumed to practice nuclear medicine and veterinary medicine using
ionizing radiation.

III. LEVELS AND TRENDS OF EXPOSURE TO NATURAL SOURCES
OF RADIATION
79. Exposure of workers to enhanced natural background related radiation is encountered in manyoccupational settings. Until implementation of the International BSS [I1, I12], most countries had notbeen particularly concerned with assessing occupational exposure to natural sources of radiation. Overthe past years, this has become a focus of attention in radiation protection. The European Union has
established safety standards for the protection of workers exposed to radiation from natural sources [E1,E8]. Since 2002, 19 European Union countries and three additional associated countries (Iceland, Norway
and Switzerland) have regularly recorded the associated doses in an occupational exposure database [P6].
80. Besides the European Union countries, some countries have already implemented radiation
protection legislation for workers to natural sources of radiation. The great majority of workers exposed
to such sources are not individually monitored. They include aircrew, workers involved in mineral sandand processing industries (e.g., mining and milling of ore, physical mineral separation processes andthermal processes for extraction, processing and combustion of minerals) and in the oil and gas industry,
and workers exposed to radon in various workplaces.

26 UNSCEAR 2020/2021 REPORT

A. Cosmic ray exposure of aircrew and space crew
1.

Civilian aviation

81. The exposure of aircrew has already been presented in previous UNSCEAR reports [U6, U8, U10].
Aircrew are exposed to cosmic radiation, which is composed of primary and secondary radiation. The
former consists of high-energy particles of galactic and solar origin, whereas the latter consists of scatterproducts resulting from interaction processes in the atmosphere and in the aircraft structure. The intensityof the dose rate during a flight predominantly depends on three physical factors: (a) it increases with thealtitude above sea level; (b) the geomagnetic shielding reduces the dose rates by deflecting parts of thecharged cosmic and solar particles, particularly in the region ±30º around the equator. However, between
60° latitude and the geomagnetic poles, increasingly more charged particles intrude along thegeomagnetic field lines into the atmosphere and cause a rise in the ambient dose equivalent rate. An
exception is the South Atlantic Anomaly, a geographic region that extents from about −50° to 0° latitudeand from −90° to 40° longitude, where—due to the asymmetry between the magnetic and rotation axesof the earth—the flux of energetic particles is increased; and (c) in phases of high solar activity the fluxof galactic particles towards the earth is scattered, leading to a reduction of the ambient dose equivalent
rate in the atmosphere. In times of low solar activity, the protecting effect of the solar wind is weak, andthe ambient dose equivalent rates are higher. The solar activity changes more or less periodically in acycle of 11 years. The route dose of a flight thus depends physically on the altitude profile, the latitude,
the date and the duration of the flight. The individual annual dose of an aircrew member also depends onthe flown route mix and on the number of block hours, both of which are influenced by a number of work
arrangement factors.
82. In the past decades, extended experimental studies of the monitoring methodology for estimating
the low- and high-LET components have been performed and continuously advanced [B22, B23, F10,
H9, L6, V10, V11, V12]. Since the radiation field at aviation altitudes is very complex, different types of
dosimeters and spectrometers have to be used in order to assess every component. The most common
detectors delivering a comprehensive picture of the radiation field at flight altitudes are tissue equivalent
proportional counters and semiconductor dosimeters and spectrometers. Other typical detection devices
for measurements of the different field components are, for instance, thermoluminiscent dosimeters forthe non-neutron component, bubble dosimeters for low-energy neutrons and etched track detectors forcharged particles. Also, electronic personal dosimeters, delivering real-time doses, are occasionally usedand have proved to be in satisfying agreement with the above-mentioned passive detectors [B23, F10].
83. The period which was analysed regarding occupational exposure in the present annex covers thedecreasing phase of solar cycle 23 from its maximum in the year 2000 to its minimum in 2009, followedby the increasing phase of solar cycle 24 to its maximum in 2014. The measured ambient equivalent dose
rates during minimum solar activity are larger than those measured during maximum solar activity. Also,
high altitudes and latitudes are associated with higher dose values. The comparison of the effective routedoses between the middle of the decreasing phase of solar cycle 23 (January 2004) and its minimum(January 2009) showed an increase from 25 to 30 µSv on the trans-equatorial route Frankfurt–
Johannesburg, and from 50 to 78 µSv on the polar route Frankfurt–New York [F9]. Earlier experiments
performed during maximum solar activity (1991–1992) measured an average dose rate of 3.0 μSv/h on aflight from Paris to Buenos Aires at an average flight altitude of 10,070 m [B22]. In contrast, the average
dose rate measured during the solar minimum phase (1996–1998) and a higher latitude (Paris–Tokyo)
was 6.6 μSv/h at an average flight altitude of 10,700 m. The influence of flight altitude on the dose rateis demonstrated by a Concorde-flight from Paris to New York during the solar maximum and minimum
and at an average flight altitude of 15,400 m (maximum flight altitude: 18,000 m). During the solar

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 27

maximum and minimum, the average dose rates were 8.5 and 9.5 μSv/h, respectively, which aresignificantly higher values than those measured at lower altitudes.
84. Established experimental monitoring systems have been successfully used in order to measure thedifferences in the ambient dose equivalent, H*(10), in different positions within the aircraft. The ambient
dose equivalent rate in the front and back of the cabin has been found to be up to 19% higher than in the
middle part [K12]. Moreover, the measured ambient dose equivalent rate is higher with a full tank (up to25%), in particular in the middle part of the cabin, which is due to an increased contribution of moderated
neutrons produced within the full tank.
85. The detector response of a tissue equivalent proportional counters has been simulated and thefindings concerning detector characteristics have been used to simulate the radiation field outside theaircraft. Thus, conclusions concerning the shielding effect of the aircraft could be drawn. The measured
ambient dose equivalent rate within the aircraft is reduced by up to 25% when compared with calculationsin free atmosphere [B7].
86. A particular subject of research interest is the investigation of the radiation exposure at highaltitudes during solar storm periods and solar particle events, which are indirectly measured as groundlevel enhancements by ground-based neutron monitors and registered an increase of the number of highenergy charged particles striking the earth’s atmosphere. In-flight measurements during solar storm
periods have been evaluated and indicated an increase of up to about 80% of the total dose for flights
crossing the polar region [B11]. Another study estimated a maximum dose rate of 1.7 mSv/h during asingle flight [C17]. In the context of dose increase, the equator region is less affected by ground level
enhancements. A variety of models aiming to predict the increase of radiation exposure due to solar
particle events has been developed on the basis of very limited experimental data on ground level
enhancements. The comparison of calculations and measurements of the ambient dose equivalent rates
showed good agreement with a discrepancy between the model and measurements of typically less than
±25% [A7, A8]. However, some investigated models disagreed with each other by an order of magnitude,
which might be due to the fact that the analysis of ground level enhancements during geomagnetically
disturbed conditions is quite complex [B10].
87. Dose assessment based on measurement is a complex task due to the aforementioned complexityof the radiation field at aviation altitudes. Therefore, effective doses, E, for aircrew are not derived byindividual monitoring using dosimeters; instead, they are routinely calculated using special computer
programs that take flight parameters such as altitude, geographic position, and solar activity into account.
The average annual effective dose is, therefore, usually estimated using codes that are validated byexperimental data of the ambient dose equivalent H*(10) [B24, E5].
88. Several computer programs 1 have been developed in different countries for route dose calculation.
Some of these have been approved by civil aviation authorities and serve as official national monitoring
tools and some have purely scientific purposes. Comparisons for periods close to the solar minimum andmaximum and for selected flights covering major commercial routes show an overall agreement between
the codes within ±20% from the median [B24, B25, M3]. Furthermore, most of the mentioned codes havepreviously been validated by measurements showing an agreement between calculated and measured
values better than ±20% [E4].
89. For the purpose of official dose monitoring of aircrew personnel, typically the calculated values ofeffective dose E are periodically verified by measurements of ambient dose equivalent H*(10), which is1

For example: CARI, EPCARD, JISCARD, and PCAIRE.

28 UNSCEAR 2020/2021 REPORT

generally used as a surrogate for E. Various studies evaluating actual flight profiles concluded that,
depending on the measuring method and calculation technique of the used program code, the deviation
between experimental data and calculated values of H*(10) ranges between 10% and 30% [B8, B9, B28,
G3, H9, L4, L6, W6].
90. For the purpose of continuous code validation with experimental data, an open access database wasbuilt up from records of the mixed field dosimetry device LIULIN placed on board Czech Airlines aircraft
since 2001. For the monitoring period 2001–2011, calculated results by computer codes used for routine
dosimetry of aircrew were compared with long-term measurement results from the database [P9]. It
comprises records of energy deposition spectra, absorbed dose rates, and ambient dose equivalent rates.
Moreover, it offers calculated values for effective dose and ambient dose equivalent [B24, O1]. The
relative differences between measured and calculated values were mostly within ±30%. In contrast toother sources of measured dose values, this database presents relatively recent values of long-term
measurements that are publicly available.
91. Data from the UNSCEAR Occupational Exposure Survey for aircrew are presented in table A.4 inthe electronic attachment. The table includes values for the periods 2000–2004, 2005–2009 and2010–2014, which were subject of the survey, whereas values for the periods 1990–1994 and 1995–1999,
have been presented in former UNSCEAR reports [U6, U8]. For the period 2000–2004, the data for three
countries, Czechia, Lithuania and the Netherlands, were used from the UNSCEAR 2008 Report [U10],
as for these countries no updated values were provided via the UNSCEAR Occupational Exposure
Survey. For the civilian aviation subsector, 22 countries replied to the survey, of which 12 countries
provided only their most recent information regarding the number of aircrew (not included in table A.4
in the electronic attachment). More detailed responses on the number of workers, the average annual
collective effective dose, and the average annual effective dose, regarding the periods of interest, were
provided by 10 countries: Denmark, Finland, France, Germany, Greece, Iceland, Japan, Slovenia, United
Kingdom and United States.
92. According to the responses to the UNSCEAR Occupational Exposure Survey, the average annual
collective effective doses of monitored workers in civilian aviation reported in the periods 2000–2004,
2005–2009 and 2010–2014 were 734, 773 and 738 man Sv, respectively. The respective reported averageannual effective dose was 2.7, 2.8 and 2.7 mSv, ranging from 1.3 to 3.1 mSv for the period 2000–2004,
from 2.1 to 3.1 mSv for the period 2005–2009, and from 1.0 to 3.1 mSv for the period 2010–2014. The
average annual effective dose weighted by the total numbers of monitored workers for 2000–2014 was
2.7 mSv. Due to a lack of data, dose data could not be evaluated separately for cockpit and cabin crew. It
must be stressed that these numbers were derived on the basis of information provided by the 10 countries
that replied to the survey in varied detail. For a worldwide estimate, additional sources of data wereconsidered. The uncertainty interval for the average annual effective dose ranges from 1.5 to 4.6 mSv.
93. An estimate for the worldwide numbers of aircrew personnel was derived on the basis of numbers
provided by ICAO [I23]. ICAO forecasts future traffic and capacity using panel regression andeconometric modelling. Then, for this forecast, the needed fleet was estimated, and the number of aircraft
determined. Given the worldwide number of aircraft, the number of pilots and cabin crew members wasderived. Since no personnel data for the years earlier than 2015 were available from ICAO, an estimate
was made on the basis of the total number of monitored workers as presented in the UNSCEAR 2000
Report [U8] for 1995–1999, and of the total number of workers for the years 2015–2019 as provided by
ICAO, who estimated an average total number of 898,200 workers. Assuming linear growth for all
periods since 1995–1999, the number of aircrew personnel was estimated to be 400,000–500,000 for theperiod 2000–2004, 550,000–650,000 for the period 2005–2009, and 700,000–800,000 for the period
2010–2014. As for the numbers of cockpit and cabin crew, the data provided by ICAO for the years

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 29

2015–2019 show a constant ratio of 38% (cockpit) vs. 62% (cabin), which–due to their consistency–isassumed to be about the same for earlier periods.
94. ICAO also provided information concerning worldwide aircraft traffic for the period 2010–2014[I23]. A differentiation between long-, medium- and short-haul flights has become challenging in recent
decades, since cabin crew personnel, in particular, are increasingly distributed to all categories of flights.
Due partly to very large inter-country heterogeneity with regard to different categorizations, retrospective
estimations based on worldwide volume of traffic alone are insufficient for the derivation of reliablevalues. However, it can be stated that, on average, 4% of worldwide flights have flight durations of more thansix hours, 13% have flight durations of one–six hours, and 83% have flight durations of less than one hour.
95. The worldwide information about number and radiation exposure of aircrew personnel as collected
and derived from the sources mentioned above is presented in table 2 and in table A.4 in the electronic
attachment. If a linear increase is assumed, the number of aircrew personnel has steadily grown by afactor of about 2.5 from 300,000 (1995–1999) to ~750,000 workers (2010–2014). Due to the lack ofsufficient information, the average annual collective effective dose was estimated roughly for the three
periods under investigation using the average annual effective dose from the survey data and the numberof aircrew provided by ICAO. Noticeable effects on the average annual effective dose due to solar activity
are not to be expected, since the periods under consideration comprise solar minimum and maximum
phases and should therefore even out (for 2000–2014, the only solar minimum occurred in 2009 and twosolar maxima in 2001 and 2014). The uncertainty interval for the worldwide number of workers, for2010–2014, ranges from 570,000 to 990,000.
Table 2. Estimates of worldwide levels of annual occupational exposure for civilian aviation workers
Number of workers(103)

Average annual
collective effective dose(man Sv)

1990–1994a

1995–1999

PeriodAverage annual effective dose (mSv)
All flights

Short-haul
flights

Long-haul
flights

800b

a

1–2b

3–5b

300b

900b

3b

2b

3b

2000–2004450c

1 220d2.7e

2005–2009600c

1 680d2.8e

2010–2014

750c

2 030d2.7e

aNot enough data to estimate the worldwide level of exposure.

b

Values taken from earlier UNSCEAR reports [U6, U8].

c

Estimates values based on data provided by ICAO [I23].

d

Estimated from data referred to in footnotes c and e.

e

Average dose values as provided by 10 countries via the UNSCEAR Occupational Exposure Survey.

96. Deriving the worldwide exposure of aircrew personnel on the basis of the dose information of only
10 countries is subject to uncertainties for three main reasons: internationally different limits on working
hours, heterogeneous definitions of short/medium/long haul, and location of operation, i.e., latitude. All
except one of the countries that reported dose values to the UNSCEAR Occupational Exposure Survey
were European countries, which are legally regulated by the European Union. According to theseregulations, crew members should not exceed 900 block hours in a calendar year [E6]. For the UnitedStates, the only non-European country reporting on dose, the number of annual block hours for pilots islimited by the Federal Aviation Administration to 1,000 hours, whereas for cabin crew members nolimitations are defined, yielding an imbalance in average dose values between cockpit and cabin crew

30 UNSCEAR 2020/2021 REPORT

members [N4]. Given these discrepancies, a worldwide extrapolation considering regulations of all
countries requires more information of the respective countries in order to reduce the uncertainties.
Another source of uncertainty is introduced via the varying definitions of short-, medium- and long-haul
flights, which differ from country to country and airline to airline. The classifications can be based onflight distance, flight time, or whether a flight is intercontinental, international or domestic. Especiallythe latter classification strongly depends on country location and size and, therefore, cannot be used forinternational comparisons. The latitude where the airlines operate also influences the national averageannual effective dose values. Aircrew on domestic flights in equatorial countries receive a lower dosethan aircrew flying on polar routes. Additional uncertainties which cannot be easily assessed on aworldwide basis are airline specific agreements in order to compensate for stress factors (flight duration,
number of crossed time zones) and agreements concerning individual route preferences due to factors
such as gender, age, family status, and other social ties.
97. Regarding the number of female personnel working in the aviation sector, Germany and Greece inthe UNSCEAR Occupational Exposure Survey reported that the proportion of female workers was about
60%. Even though the number of female pilots had increased, the majority of female workers were cabincrew [F9]. Another source reporting on female workers in the period 1992–1996 found that in the UnitedStates, about 84% of flight attendants were female [G2]. According to an ILO report, the gender ratio in
the civil aviation has, on average, remained relatively unchanged [S8]. It identifies a multitude of reasonsfor a prevailing gender imbalance, from differing career paths due to maternity to national legislation
preventing women from entering the transport sector.
98. The European Union has established standards for the protection of workers exposed to naturalradiation [E1]. Since 2002, several Member States of the European Union calculate and record aircrew
doses as occupational exposure in their national dose registers. In addition, thanks to continuous research
regarding the radiation exposure of civilian aircrew personnel, many peer-reviewed studies provide
comprehensive dose information from many countries, also outside the European Union. In the following,
dose estimates for aircrew for various countries, as published in these studies, are presented.
99. In Canada, a year-long study of the cosmic radiation exposure of Air Canada pilots during the solar
minimum phase in 2009 was carried out. It showed that the estimated annual effective doses received bypilots were higher than the annual general public limit of 1 mSv, with the majority receiving about 3 mSv,
although none exceeded the recommended intervention level of 6 mSv [B14]. Another study focusing on
the cosmic radiation exposure for crew members of a transport squadron in the Canadian Air Force withina period of 30 months (2007–2009) found that more than half of the aircrew received higher annual
effective doses than the general public limit of 1 mSv per year, with some crew members receiving aneffective dose of almost 4 mSv. The dose distribution over all crew members exhibits two maxima, one
at 0.5 mSv and the other at 2.5 mSv [B13]. Both studies were based on the dose calculation code PCAireand the calculations were supported by on-board measurements.
100. In Czechia, individual dosimetric monitoring of aircrew has been required by law since 1998. A
study presents the effective dose values of Czech aircrew covering 20 years of dose collection [K13]. All
dose values were calculated using the computer code Computer and Automation Research Institute(CARI). In the years 1998–2017, the average annual effective doses ranged from 1.3 to 2.1 mSv; thecollective effective doses ranged from 1.3 to 5.1 man Sv, depending on the solar activity. The overallmean value of the average annual effective dose over the investigated 20 years was 1.6 mSv. Table 3
summarizes the mean, median, minimum and maximum values for the average annual effective dose of
the Czech study [K13].

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 31

Table 3. Exposure of Czech civilian aircrew members for the period 1998–2017 [K13]Year

Number ofworkers

Mean (mSv)

Median (mSv)

Minimum value(mSv)

Maximum value
(mSv)

1998

857

1.5

1.7

~0.01

2.8

1999

1 055

1.5

1.6

~0.01

2.5

2000

1 042

1.5

1.7

~0.01

2.5

2001

1 245

1.4

1.5

~0.01

2.9

2002

1 202

1.5

1.6

~0.01

3.2

2003

1 309

1.7

1.8

~0.01

3.0

2004

1 484

2.0

2.1

~0.01

3.4

2005

1 765

2.0

2.1

~0.01

3.4

2006

1 865

2.0

2.2

~0.01

3.8

2007

1 902

2.1

2.3

~0.01

4.4

2008

2 158

1.9

2.2

~0.01

3.8

2009

2 111

1.8

2.1

~0.01

3.9

2010

2 044

1.6

1.8

~0.01

3.3

2011

1 865

1.6

1.8

~0.01

3.7

2012

2 065

1.5

1.6

~0.01

4.1

2013

2 353

1.4

1.2

~0.01

3.7

2014

2 208

1.4

1.2

~0.01

5.3

2015

1 815

1.4

1.2

~0.01

5.4

2016

1 922

1.4

1.3

~0.01

5.7

2017

1 881

1.4

1.2

~0.01

4.9

101. In an investigation in Finland of the radiation dose to Finnish aircraft cabin attendants, the averagecosmic radiation dose was calculated (CARI-6) as 3.2 mSv (range: 0.0–9.5 mSv) per active work year[K7]. The analysis was based on questionnaire data obtained from 544 flight attendants. Another study
examining the dose to cabin crew in Finland made use of individual flight timetables and calculated theannual dose with the European Program Package for the Calculation of Aviation Route Doses (EPCARD)
software. The annual effective radiation dose of cabin crew members increased linearly from 0.7 mSv in
1960 to 2.1 mSv in 1995 [K8]. Since these values are lower than the 3.2 mSv of the previous study, theauthors assume that the result of the previous study was overestimated. A more recent study examined
the annual dose values of cabin and cockpit crew members by means of the dose estimation programs
CARI-6 and EPCARD. In total, 1,535 cockpit crew members (5% female) and 3,487 cabin crew members(87% female) of Finnish airline personnel were included in the study. The average age of the study
participants was 44 years and over 60% were between 30 and 50 years [T1].

32 UNSCEAR 2020/2021 REPORT102. In Germany, a cohort study covering 6,000 male pilots from 1960 until 2004 was performed by
Hammer et al. [H2]. The study was based on a job-exposure matrix and calculations for individual flight
profiles using CARI-6. In the group of subjects still active by the end of 2004, the median cumulative
effective dose over the occupational lifetime per person was 29.4 mSv and the first and third quartile andthe maximum value were 23.0, 40.5 and 71.4 mSv, respectively. For persons no longer employed, thevalues for the median, first and third quartiles and the maximum cumulative effective dose were 31.3,
12.3, 45.3 and 73.9 mSv, respectively. The cumulative effective dose was strongly correlated withduration of employment and flight hours. In a more recent work by Wollschläger et al. [W14], the samecohort was investigated, using a job-exposure matrix and EPCARD for individual dose calculations.
According to this analysis, the average annual effective dose was 2.25 mSv (range 0.01–6.39 mSv). Malecabin crew had a higher average annual effective dose (2.63 mSv) than female cabin crew (2.15 mSv).
Similarly, male cockpit crew showed a higher average annual effective dose (2.29 mSv) than female
cockpit crew (1.85 mSv). Radiation exposure of all German aircrew was also investigated on the basis ofdata from the national dose register from 2004–2009 by Frasch et al. [F9]. The respective dose values forpilots, cabin crew, female, and male workers are summarized in table 4. The category “Other” consists
mainly of loadmasters and special air force staff. In 2004, at the middle of the decreasing phase of solar
activity, the average annual effective dose was 1.9 mSv and increased until the solar minimum in 2009
to 2.3 mSv. With the decreasing protection by solar activity the frequency distributions of annual doses
stretch towards higher dose values. These accounts in particular for doses above the median. Also, theannual doses of pilots and flight attendants vary significantly with age and gender due to age-dependent
phases of professional career and family status.
Table 4. Doses of all monitored aircraft crew personnel in Germany [F9]Number ofworkers

Collective dose(man Sv)

Mean
(mSv)

Median(mSv)

Maximum
value
(mSv)

Standard
deviation
(mSv)

2004

29 852

58.21

1.9

1.9

6.1

1.0

2009

36 596

85.88

2.3

2.4

7.0

1.3

2004

313

0.49

1.6

1.4

5.6

1.1

2009

609

1.09

1.8

1.6

6.8

1.3

2004

7 982

15.58

2.0

1.7

5.7

1.0

2009

9 853

21.81

2.2

2.0

6.7

1.3

2004

16 626

32.29

1.9

2.0

6.1

1.0

2009

20 426

48.35

2.4

2.3

6.9

1.2

Job category
year
All aircraft crew

Cockpit, female

Cockpit, male

Cabin, female

Cabin, male
2004

4 098

9.21

2.2

2.4

5.3

0.9

2009

4 822

13.84

2.9

3.0

7.0

1.2

2004

871

0.65

0.7

0.8

2.8

0.4

2009

953

0.78

0.8

0.8

3.0

0.5

Other

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 33

103. In Ireland, during the years 2002–2005, there was a 75% increase in the number of aircraft personnel
receiving doses >1 mSv, due to an increase of the total number of flights flown per year [C16]. The
percentage of aircrew receiving doses in the range 4.0–6.0 mSv increased from 0.2% (2002) to 4.5%
(2005). In 2004 and 2005, the average annual effective doses received by Irish aircrew were 1.8 and2.0 mSv, respectively. Route doses were calculated with CARI-6 and validated with EPCARD.
104. A study from Japan calculated the effective doses for the round-trip flights from Tokyo Narita
International Airport to 12 cities (Auckland, Bangkok, Frankfurt, Hong Kong, Honolulu, London,
Madrid, Moscow, New York, San Francisco, Singapore and Sydney) using the CARI-6 code underconservative conditions. The highest estimated dose for the round trip was that to New York with 210 μSv
and the lowest estimated dose was to Hong Kong with 26 μSv [Y2]. Another study obtained the annual
effective doses for pilots and cabin crew of Japanese Airlines in 2007 using JISCARD [Y3]. According
to this study, the annual crew doses were 1.7 mSv on average, and 3.8 mSv at maximum for pilots,
whereas for cabin crew the average annual effective doses were 2.2 mSv, and 4.2 mSv at maximum.
105. The aim of a study in Lithuania from 2003 was to evaluate potential doses that could be received
by aircrew of Lithuanian Airlines. Measurements and calculations (CARI-6) were performed in the periodof modest solar activity. Therefore, and despite the fact that only short-haul flights are operated by
Lithuanian Airlines, the study concludes that the annual dose of 1 mSv may be exceeded under somecircumstances [M7].
106. In Portugal, the annual effective dose for aircrew in military transport missions has been estimatedat 1.5–1.8 mSv [A13]. Assuming a six-month period of pregnancy in which female crew members arestill working, the dose equivalent to the fetus may vary between 0.8 and 1.0 mSv. Another assessment ofoccupational cosmic radiation exposure of Portuguese airline pilots showed that all investigated pilots
received more than 1 mSv per year of service [S12]. The authors analysed medium-haul flights, whichwere defined as flights within Europe, and long-haul flights, which were defined as flights between
Europe and other continents. The average dose rates estimated for medium-haul pilots (3.29 ± 0.24 µSv/h)were larger than those for long-haul pilots (2.66 ± 0.33 µSv/h).
107. In Saudi Arabia, aircrew are not considered to be radiation workers and, hence, are notoccupationally monitored. In a one-year study, the radiation exposure of Saudi Aramco aircrew wasmeasured or estimated using CARI-7 program and thermoluminiscent dosimeters [S9]. Of all monitored
aircrew, the minimum annual effective dose was about 0.4 mSv and the maximum annual value was
0.8 mSv. However, from a total number of 2,767 investigated flights, only 11 flights were “out-ofkingdom” flights, i.e., flights of relatively long duration and high altitudes. With 1,595 flights, themajority of flights were domestic flights of short duration (≤1 hour) and low altitude. The study showed,
depending on flight duration and altitude, pregnant aircrew may reach the annual pregnancy radiationdose limit of 1 mSv.
108. In Spain, an investigation of the radiation exposure of aircrew working for Iberia performed in 2001
yielded an average annual effective dose of 1.4 mSv, ranging between 0.4 and 2.7 mSv [S1]. The averagevalue for short-haul flights was considerably lower (1.7 mSv) than the value for long-haul flights(2.2 mSv). However, the average annual effective doses can increase by 5–20% since the values presented
in this study were obtained when solar activity had reached a maximum value, which is associated withlow dose values.
109. In Taiwan, China, occupational exposure of aircrew to cosmic radiation is currently neither
regulated nor monitored. A recent study, based on publicly accessible civilian aviation statistical reports,
proposes a comprehensive approach for estimating the average annual collective and the average annual

34 UNSCEAR 2020/2021 REPORT

effective dose received by Taiwanese pilots [Y1]. For the period 2006–2018, the average annual effective
doses varied between 1.7 and about 3.0 mSv, with a mean value of 2.2 mSv.
110. In Turkey, cosmic radiation doses for aircrew of Turkish Airlines were estimated using CARI-6
software on board 137 flights (60 domestic and 77 international) [P3]. The doses for each flight varied
from 1.2 to 83 µSv. Annual effective doses for short-haul flights from Istanbul to domestic airports
covering 800 hours on each route were calculated to range from 1.0 to 1.7 mSv. In contrast, annual
effective doses of international flight routes for 800 hours were calculated to range from 1.8 to 4.8 mSv.
111. In the United States, using the methodology for the retrospective exposure assessment for flightcrew of the former Pan American World Airways company, the average annual flight attendant effective
dose was estimated to 2.4 mSv (career dose range 0.33–100 mSv) [W2]. Another study by Anderson
et al. [A16] analysed radiation exposure of female crew members of the Pan American company bymeans of questionnaire data. Completed work history questionnaires were received from 5,898 living
cohort members. Mean employment time as flight attendant was 7.4 years at the Pan American company
and 12 years in total. The estimated average annual effective dose of occupational cosmic radiation
exposure was 2.5 ± 1.0 mSv, with a mean career dose of 30 mSv [A16].
112. Assessing the contribution to radiation dose from exposure to solar particle events, a computermodel was developed by the National Aeronautics and Space Administration (NASA) and solar storm
data were provided by the National Oceanic and Atmospheric Administration Space Weather Prediction
Center from two study periods (1992–1996 and 1999–2001) [A17]. As a result, seven solar particle eventswere identified to have the potential to significantly increase the radiation exposure for US flightpersonnel on commercial routes. For a flight of a couple of hours during a solar particle event, the authors
estimated a maximum effective dose of 1.2 mSv for aircrew personnel. That means that during solar
particle events, pregnant crew members could potentially exceed the ICRP recommended dose limit of
1 mSv during pregnancy.
113. Using the same cohort as in Waters et al. [W2], Yong et al. [Y4] estimated the cosmic radiation
exposure of 5,964 former United States commercial cockpit crew members. The average annual effective
dose was calculated to be 1.4 mSv (median = 1.4; range 0.0042–2.8) but varied from 0.081 mSv (range
0.00072–0.14) in 1940 to 1.6 mSv (range 0.059–1.8) in 1980 [Y4]. The career dose was strongly
correlated with the duration of employment (Spearman correlation coefficient: 0.90). The average career
dose was 28 mSv (median = 31; range 0.0047–71). Exposure to cosmic ionizing radiation and circadianrhythm disruption was estimated for a time range between 1963 and 2003 for 83 male pilots from a major
United States airline by Grajewski et al. [G1]. Pilots flew a median of 7,126 flight segments and 14,959
block hours for 27.8 years. The median of the annual radiation exposure from cosmic radiation was
estimated to be 1.92 mSv. Another study by Grajewski et al. [G2] evaluated data of 764 female flightattendants resulting in an annual average effective dose of 0.36 mSv within the period 1992–1996.

2.

Space crew

114. The naturally occurring radiation environment in space differs substantially from that experienced
on earth, in both type and intensity. Three main sources generally affect exposure to ionizing radiation
while in the space environment: (a) galactic cosmic rays; (b) solar particle events; and (c) radiation fromparticles trapped in the earth’s magnetic field. Both galactic cosmic rays and radiation from particles
trapped in the magnetic field are fairly constant sources of exposure while solar particle events are
sporadic and transient events. All these sources are composed of accelerated particles with velocities near
the speed of light [B1, B16, B17, T4].

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 35

115. The majority of crewed spaceflight missions have been conducted in low-earth orbit where
exposure to galactic cosmic rays and solar particles from solar particle events are limited to trajectories
that cross regions of polar latitudes and exposure to radiation from particles trapped in earth’s magnetic
field is limited to trajectories that traverse the South Atlantic Anomaly. These range in duration from a
few hours to the current record for consecutive time in space – 438 days [B16, B17, M2]. Historically,
the only missions to go beyond the protection of the earth’s magnetic field were the Apollo missions
conducted in the 1960s and 1970s. Crews on these missions were exposed to galactic cosmic rays as wellas varying contributions of radiation from particles trapped in earth’s magnetic field due to different
trajectories through the Van Allen belts. Total absorbed radiation doses experienced during these shortduration missions (1–13 days) were relatively low (1.6 to 11.4 mGy) [B16, B17]. In space, humans arealways surrounded by different material which can act as shielding. Due to the nature of high-energy
particle interactions with matter, the amount of available shielding alters the radiation environment
experienced by humans in space, which impacts the ultimate radiation dose [N9]. To date, a total of
336 NASA astronauts have flown in space and have had their cumulative dose recorded using
thermoluminescent dosimeters. The mean total badge dose (estimated absorbed dose) for these astronauts
was 16.8 mGy with a standard deviation of 23.6 mGy [N12].
116. Radiation monitoring during long-term space missions aboard the Mir space station andInternational Space Station (ISS) demonstrates that the crew member’s effective dose can be as high as
100–300 mSv after a one year space mission, i.e., 0.4–0.8 mSv per day [B15, P11].
117. In order to better understand radiation doses to sensitive organs inside the human body, Sihver et al.
[S10] reported various phantom experiments performed in space. The results from the measurements inthese phantoms have shown that the crew member effective dose on the ISS is in the order of 0.4–0.8 mSv
per day, depending on solar cycle, shielding and the orbit.
118. Biodosimetry of astronaut lymphocyte samples, taken prior to- and post-flight (two samples),provides an important in vivo measurement of radiation-induced damage incurred during space flight,
which can be included in the astronauts’ medical records. Between 2007 and 2015, Health Canada
analysed samples from seven astronauts who had stayed on the ISS for approximately six months [B6].
The estimates of the incurred absorbed dose for the astronauts were all less than 0.25 Gy.
119. Biological doses determined by chromosome aberration frequency from pre- and post-flight blood
sample analysis and physical doses measured in flight using thermoluminescent dosimeters worn by ISS
crew members were analysed by Cucinotta et al. [C20]. Physical and biological doses for 19 ISS crew
members yielded an average effective dose for the approximately six-month missions of 72 mSv.
Analyses showed that 80% or more of organ dose equivalents incurred on the ISS are from galactic
cosmic rays and only a small contribution is from trapped protons and that the galactic cosmic ray dose
contribution decreased due to the high level of solar activity in recent years [C20, Z1].

B. Exposure in extractive and processing industries
120. The extraction and processing of natural resources from soil or rocks is common across the world
for the production of a variety of products. As radioactive substances are found in variable quantities inall natural material, extraction and processing can result in significant exposure to workers. Protection
can be optimized through raising awareness and applying controls. Mining and processing industries
employ a predominantly male workforce. Although more women are now working in mining in somecountries, any increase in female employment is generally very low.

36 UNSCEAR 2020/2021 REPORT121. All rocks, soil and water on earth contain varying concentrations of the radioactive nuclides 40K,
238
U and 232Th and radioactive daughter nuclides in their decay series. Disturbance of any material (e.g.,
mining) and its processing to extract specific target material (e.g., smelting) or the modification of natural
distributions (e.g., mineral sand separation) can result in exposure to ionizing radiation. Radiation
exposure of workers is usually dependent on the radionuclide concentration, extraction and processing
method, and exposure duration. For mining operations, the main source of exposure is typically radon inunderground operations. In mineral processing activities, mineral dust and accumulation of gamma
radiation emitting radionuclides can contribute to significant exposure. A number of new assessments inthese areas have been made since the UNSCEAR 2008 Report [U10].

1.

Coal mining

122. The main potential sources of occupational exposure in the extractive industries are the naturalradionuclides arising from the radioactive decay of the 238U and 232Th series. Exposure may occur via
three main routes: (a) inhalation of radon and its progeny; (b) inhalation and ingestion of ore dust; and(c) external irradiation with gamma rays.
123. Between 2000 and 2014, the coal production industry was concentrated primarily in 12 countries(Australia, China, Colombia, Germany, India, Indonesia, Kazakhstan, Poland, Russian Federation, South
Africa, Turkey, and United States). These 12 countries contributed 90–94% to worldwide coalproduction. In the period 2010–2014, China contributed up to 48%, and the United States contributed
about 12% to the worldwide production. The average annual total coal production for each period (2000–
2004, 2005–2009 and 2010–2014) is shown in table 5 for those 12 major producers along with four othercountries (Islamic Republic of Iran, Japan, Philippines and United Kingdom) that are not major producers
but have responded to the UNSCEAR Occupational Exposure Survey, submitting data on number ofworkers. The worldwide total primary coal production increased by a factor of 1.6 (from 5.07×103 million
metric tonnes in the period 2000–2004 to 7.88×103 in the period 2010–2014). The worldwide increase isdriven by production in China, which increased by a factor of 2.3 (from 1.67×103 million metric tonnes
in the period 2000–2004 to 3.80×103 in the period 2010–2014).
124. Data from the UNSCEAR Occupational Exposure Survey on coal mining are included in table A.4
in the electronic attachment. For coal mines, three countries provided data for the periods 2000–2004 and2005–2009 (Poland, United Kingdom and United States). Data from China [L7, U10] and Turkey [F7]were added for the extrapolation analysis. For the latter period (2010–2014), only two countries
responded to the detailed questionnaire (Poland and United Kingdom) providing data for the number ofworkers and average annual effective dose. Four countries responded to the simplified questionnaire(Islamic Republic of Iran, Japan, Philippines, and the United States), providing data on workforce only.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 37

Table 5. Average annual amount of total primary coal production [U17]Country

Average annual of total primary coal production (million metric tonnes)
2000–2004

2005–20092010–2014

Australia

334

387

447

China

1 673

2 744

3 796

Colombia

46

67

85

Germany

208

198

190

India

364

471

547

Indonesia

116

226

389

Iran (Islamic Republic of)

1.1

1.3

1.1

Japan

1.9

1.3

1.2

Kazakhstan

77

95

116

Philippines

1.8

3.5

7.1

Poland

162

147

139

Russian Federation

248

288

326

South Africa

231

248

257

Turkey55

71

70

United Kingdom

29

18

16

United States

994

1 031

940

World

5 075

6 548

7 881

125. The predictor variable used to extrapolate the coal mining workforce was the average total primarycoal production given in table 5 and the number of workers were obtained from the survey (table A.4).
The average total primary coal production accounted for by the countries that responded to the survey
corresponded to 56, 60 and 62% for 2000–2004, 2005–2009 and 2010–2014, respectively. The worldwide
number of workers was calculated on the basis of the relationship of the number of workers per productionof total primary coal. According to the reported data, the number of workers per production of one million
metric tonnes decreased over time: 2,138 (2000–2004), 1,350 (2005–2009) and 995 (2010–2014). The
estimated worldwide number of workers are presented in table 6 and table A.4 in the electronic attachment
for each period and were about 10.9, 8.8 and 8.0 million in the three periods, respectively.
Table 6. Number of workers for total primary coal production reported to UNSCEAR SurveyCountriesa

Number of workers (103)
2000–2004

2005–20092010–2014

China

6 005

5 100

4 700

Poland

103

92

84

United Kingdom

6.0

6.0

5.2

United States

101

120

125

Total reported

6 215

5 318

4 914

Worldwide

10 900

8 800

8 000

a

Value from UNSCEAR 2008 Report [U10].

38 UNSCEAR 2020/2021 REPORT126. The worldwide average annual effective dose represents the average annual effective dose weighted
by the number of workers for each country that provided data through the detailed questionnaire of
UNSCEAR Occupational Exposure Survey and additional data obtained from the literature review. The
estimated worldwide average annual effective doses are 2.3, 2.1 and 1.6 mSv for the periods 2000–2004,
2005–2009 and 2010–2014, respectively. The uncertainty interval for the number of workers for 2010–2014 ranges from 4.9 to 13 million and the uncertainty interval for the worldwide average annual effective
dose from 1.0 to 2.6 mSv. The estimated worldwide average annual collective effective doses are 25,070,
18,480, and 12,800 man Sv for the periods, respectively. These data are presented in table 7 and table A.4
in the electronic attachment. All worldwide estimates should be used with caution, since they wereprimarily derived from data for the single country that accounts for 95% or more of the reported numberof workers and collective effective dose, as shown in table 8. However, this country represents about 33,
42, and 48% of the average worldwide total primary coal production for the periods, respectively.
Table 7. Estimates of worldwide levels of annual occupational exposure for coal mining
Average total primarycoal production(million metrictonnes)Number of workers(103)

Average annual
collective effective
dose (man Sv)

Average annual
effective dose (mSv)

1990–1994a

3 910

2 737

0.7

1995–1999a

6 900

16 5602.4

Perioda

2000–2004

5 072

10 90025 070

2.3

2005–2009

6 544

8 800

18 480

2.1

2010–2014

7 934

8 000

12 800

1.6

Values from earlier UNSCEAR reports [U6, U8].

127. Occupational exposure data for coal mining workers obtained from the literature review have beenused to supplement the data obtained from the UNSCEAR Occupational Exposure Survey. Three
countries have published data related to national surveys: China, Poland and Turkey (table 8). The
Chinese data for the average annual effective dose for coal mining, obtained through the literature review,
have been used in estimating the worldwide average annual effective dose for coal mining.
Table 8. Occupational exposure data for coal mining workers obtained from literature review
CountryYear

Number ofworkers(103)

Average annual
effective dose(mSv)

Average annual
collective effective
dose (man Sv)

China

2002–2004

6 005

2.4

14 412[U10]

2005–2009

5 100

2.2

11 335[L7]

2010–2014

4 700

1.7

7 982

[L7]

PolandTurkey2000–2004

Notes

Reference

2.0

Nose
breather

[S13]

2.7

Mouth
breather

[S13]

4.9

[F7]

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 39

2.

Mineral mining and processing

128. The sources of radiation exposure for mineral extraction discussed in this section are basically as
described in the coal mining section above. The evaluation of occupational exposure in mineral mining
and processing comprises the following group of commodities: iron/steel-alloys, non-ferrous metals,
precious metals and industrial minerals. The extraction and processing industries of these commodities
account for about 14% of the total extraction industry in the period 2010–2014. Mineral fuel (coal,petroleum, natural gas and uranium), which is not included in this subsector, accounts for about 86% of
the total mineral extraction in the period 2010–2014 [R7]. Of the group of commodities studied here,
iron/steel-alloys comprise about 63% of commodities production in the period 2010–2014. It is followed
by industrial minerals, which comprise about 32% of the production during this period. The productionof these commodities worldwide was concentrated primarily in six countries: China (about 28%),
Australia (17%), Brazil (11%), India (7%), the United States (5%) and the Russian Federation (4%). The
data are presented in table 9.
Table 9. Average annual total mineral production other than mineral mining per country in the
period 2010–2014 [R4, R5, R6, R7]
Values reported to the UNSCEAR Occupational Exposure Survey are given in bold
Average annual total production (million metric tonnes)
Country
Australia

Iron, steelalloys a

Non-ferrous
metals b

Precious
metals c

Industrial
minerals d

Total

Total
production
(%)

338

5.0

0.0021

19.1

362

16

1.5

1.5

<0.1

Bangladesh
Brazil222

1.8

0.0001

18

242

11

Canada25

4.1

0.0008

31.6

61

2.7

China

432

30

0.0038

184

647

28

Germany

0.05

0.5

33.3

34

1.5

India

109

2.7

0.0003

38.5

150

6.5

Iran (Islamic Republic
of)

21.1

0.7

0.0001

27.3

49

2.1

0.2

0.2

<0.1

4.5

24

1.0

Iraq
Kazakhstan

18.7

Kenya

0.1

0.1

0.2

<0.1

Madagascar

0.4

0.1

0.5

<0.1

Mexico9.5

1.3

0.0053

22.6

33

1.4

Philippines

0.7

0.1

0.0001

0.9

1.7

<0.1

0.6

0.0012

6.6

7.2

0.3

Poland1.1

0.0009Russian Federation

59

4.9

0.0018

29

91

4.0

South Africa

55

0.9

0.0005

3.1

59

2.6

Sweden17

0.5

0.0003

0.05

18

0.7

9.7

9.8

0.4

United Kingdom

0.1

40 UNSCEAR 2020/2021 REPORT

Average annual total production (million metric tonnes)
Iron, steelalloys a

Non-ferrous
metals b

Precious
metals c

Industrial
minerals d

Total

Total
production
(%)

34

4.2

0.0014

88.8

127

5.5

All countries above

1 339

53.9

0.0185

519

1 917

83

Survey countries

862

45

0.011

407

1 215

53

1 460

83

0.028

760

2 300

100

Country
United States

WorldwideaeIncludes iron, chromium, cobalt, manganese, molybdenum, nickel, niobium, tantalum, titanium, tungsten and vanadium.

Includes aluminium, antimony, arsenic, beryllium, bismuth, cadmium, copper, gallium, germanium, indium, lead, lithium,
mercury, rare earth minerals, rhenium, selenium, tellurium, tin and zinc. Bauxite is not included.
bcIncludes gold, palladium, platinum, rhodium and silver.

Includes asbestos, baryte, bentonite, boron minerals, diamonds (gem/industrial), diatomite, feldspar, fluorspar, graphite, gypsum
and anhydrite, kaolin (China clay), magnesite, perite, phosphates, potash, salt (rock salt, brines, marine salt), sulphur (elemental/
industrial), talc (including steatite and pyrophyllite), vermiculite.
d

From the UNSCEAR Survey, data on workers involved in other mineral extraction and processing are included in table A.4 inthe electronic attachment. For the period 2003–2004, two countries responded to the detailed survey (United Kingdom and UnitedStates). For the period 2005–2009, three countries responded to the detailed survey (Slovenia, United Kingdom and United States).
For the period 2010–2014, seven countries replied to the simplified questionnaire, providing data on number of workers for thelatest period (Bangladesh, Brazil, China, India, Sweden, United Kingdom and United States). Three of those countries also replied
to the detailed questionnaire (Brazil, India and United Kingdom).

e129. The predictor variable used to extrapolate the workforce was based on the total mineral production
other than fuel minerals given in table 9, and the number of workers obtained in the UNSCEAR
Occupational Exposure Survey, given in table A.4 in the electronic attachment. The worldwide average
production of these minerals increased by a factor of 1.8 from 2000–2004 to 2010–2014. The countries
responding to the survey for the period 2010–2014 are responsible for about 52% of the total productionof the minerals grouped as iron/steel-alloys, non-ferrous metals, precious metals, and industrial metals.
There is a statistically significant correlation between the production of the minerals and the number ofworkers. The worldwide number of workers was calculated on the basis of the relationship of the numberof workers per production of those four groups of minerals. According to the reported data for 2010–2014, the number of workers per production of one million tonnes during that period was 1,628. Becauseof the lack of data for the two previous periods (2000–2004 and 2005–2009), the number of workers per
production could not be derived reliably. The estimated worldwide number of workers for 2010–2014 is
3.8 million. This value may be underestimated because the production of bauxite was not considered in
the calculation, which represents about 10% of the total production of non-ferrous metals. Only three
countries provided average annual effective dose for the period 2010–2014. The weighted average annual
effective dose is 2.5 mSv. This value is a rough global estimate because of the small sample size and thethree countries reporting average annual effective dose data account for only 17% of the total production.
Average annual effective dose data for different types of mines, available from the literature (2003–
2014), are presented in table 10. A large variation (range of values) in the reported values for averageannual effective dose can be observed. The average annual collective effective dose is estimated as
9,500 man Sv. As described in section II.E.2, the uncertainty interval calculated for the worldwide
number of workers is from 2.3 to 6.2 million and the uncertainty interval for the worldwide averageannual effective dose is from 1.3 to 4.9 mSv.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 41

Table 10. Summary of average annual effective dose for mineral production other than fuel mineral
Average annual effective dose(mSv)

Reference

Granite industry

0.0003–0.2[E13]

Sandblasters

1.2–16.5[E13]

Columbite-tantalite

12 (0.008–18)[M10]

Phosphate (radon daughters)

27 (0.69–80.99)[K3]

Phosphate (external exposure)

12 (6–56)[K3]

0.7 (0.22–1.9)[D6]Gold (open pit mines)

0.2–0.3[D1]Gold (underground mines)

1.7–2.0[D1]

Hungary

Manganese

2.6–3.6[K1]

Iran (Islamic Republic of)

Twelve different types of mines<0.1–31[F2]

Nigeria

Granite

0.25

[A1]

Country
BrazilDemocratic Republic of
Congo
Egypt

Type of mining

Gold
Ghana

C. Oil and gas extraction
130. Naturally occurring radioactive material (NORM) found in the earth’s crust, largely in the form of226
Ra and 228Ra and their associated radionuclides, is brought to the surface during gas and oil production
processes. NORM represents a potential internal radiation exposure hazard to workers from the inhalationand ingestion of natural radionuclides (238U, 228Th and 232Th progenies), particularly during maintenance,transport of waste and contaminated equipment, decontamination of equipment and processing of waste.
The short-lived progeny of the radium isotopes, in particular of 226Ra, emit gamma radiation capable ofpenetrating the walls of internally contaminated pipes and vessels. Therefore, the deposition ofcontaminated scales and sludge in these components produces enhanced dose rates outside thesecomponents. The values depend on the amount and activity concentrations of radionuclides present inside
and the degree of shielding provided by pipe or vessel walls.
131. The average annual effective dose was estimated as 3.2 mSv for workers in an oil refinery in Egypt,
assuming exposure to external gamma radiation sources, inhalation of particulates, and skin exposure due
to beta radiation. The assessment was derived from activity concentration measurements of samples taken
throughout the plant [B2]. The average annual effective dose for workers at the oil and gas facilities inArgentina was estimated to be in a range from 0.02 to 1.6 mSv. Only the external radiation exposure
pathway was considered in the dose estimate [C5].
132. The average annual effective dose for workers exposed to radium in natural gas extraction fromshale rocks in the United States was estimated to range from 0.002 to 0.36 mSv. Exposure to external
gamma radiation and inhalation of radon and particles were considered in the dose assessment [Z2].
133. The exposure of maintenance personnel who perform pipe scale rattling operations has beenreported by Hamilton et al. [H1] in a comprehensive study on that specific task. Under controlled
conditions using personal air samplers and dosimeters on operators, coupled with a significant numberof area samplers, the external, inhalation and ingestion exposure was determined. On the basis of an42 UNSCEAR 2020/2021 REPORT

assessment of cleaning 20 pipes per day for 250 days per year, the average annual effective doses for theoperator and helper were assessed to be 3.3 and 4.9 mSv, respectively [H1].
134. Data from the UNSCEAR Occupational Exposure Survey on gas and oil extraction are included intable A.4 in the electronic attachment. For the period 2000–2004, only the United States responded to thesimplified survey, providing number of workers. For the period 2005–2009, only the United Kingdom
responded to the detailed questionnaire and the United States responded to the simplified questionnaire.
For the period 2010–2014, three countries—Brazil, United Kingdom and United States—replied to thedetailed survey. Another five countries responded to the simplified survey through 2017, providing
number of workers (China, Islamic Republic of Iran, Iraq, Kenya, and the Philippines).
135. An estimation of the global oil and gas extraction workforce was not possible by extrapolation due
to the lack of statistically significant correlation between number of workers and oil production. The lackof correlation may be due to differences in data provided, such as submission of total number of workers
in the oil extraction industry or submission number of workers involved in tasks such as maintenance.
For future analysis, the requested data should be specific for the workforce involved in maintenance. The
total number of workers reported by the countries responding to the UNSCEAR Occupational Exposure
Survey for the period 2010–2014 is around one million; the average annual effective dose is 0.2 mSv andthe average annual collective effective dose is about 200 man Sv.

D. Radon exposure in workplaces other than mines
136. The levels of radon in workplaces are exceptionally variable, and high radon doses to workers canoccur also in places other than underground mines. In the UNSCEAR 1993 Report [U6], the exposure toradon progeny was considered only in underground mines. The UNSCEAR 2000 Report [U8], in addition
to mines and below-ground workplaces, included radon spas, subways, show caves and tourist mines,
and also underground water treatment plants and underground stores. Above-ground workplaces such as
factories, shops, offices and schools were also considered in the UNSCEAR 2000 Report [U8]. Exposure
to radon in these workplaces was, therefore, usually regarded as essentially unamenable to control.
However, there has been increasing interest in some workplaces, including underground ones, whereradon levels are expected to be high and there is some scope for reducing the radon levels.
137. Before 2000, there were very few data on which to base an estimate of worldwide exposure to radon
in workplaces. In the United Kingdom, radon concentrations were measured in 4,800 workplaces in areasof the country where levels were expected to be above average radon concentration of 210 Bq/m3, and in
710 cases the concentration exceeded 400 Bq/m3. Of the estimated 1.7 million workplaces in the United
Kingdom, 5,000 with about 50,000 workers are expected to exceed 400 Bq/m3. Their collective effective
doses and average individual doses were 270 man Sv and 5.3 mSv in a year [U7, U8]. On the basis of theUnited Kingdom data and with extrapolation on the basis of GDP, a crude estimate was that theworldwide average annual collective effective dose would be about 6,000 man Sv and the average annual
effective dose 4.8 mSv for workplaces exceeding 400 Bq/m3 [U10].
138. In workplaces other than mines, radon concentration is measured in Bq/m3 instead of WLM as inmines. To evaluate the average annual effective dose from radon inhalation in those workplaces, theCommittee’s radon dose conversion factor of 9 nSv per (h Bq/m3) of radon equilibrium equivalentconcentration is used [U14].
139. The assessment of average annual effective dose due to exposure to radon depends not only onradon concentration in workplaces but also on the location-specific radon equilibrium factor, F, and actual

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 43

working hours per year. In indoor workplaces, F=0.4 is commonly used. However, due to different
ventilation rates and variation in solid particle concentrations, F values vary widely, from as low as 0.15
to as high as 0.89, with a mean of 0.44 [C8]. In underground show caves and tourist mines, the F values
can also vary from 0.10 to 0.85 with an overall average value of 0.40 [C11]. The average F values inthermal spas vary from 0.10 to 0.45 with an overall average of 0.30, somewhat lower than the overall
average F value for show caves and tourist mines [C11].
140. Any scientific work referenced in this annex and used to perform a dose assessment will respect the
local F value where reported. For example, site-specific F values were used to assess occupational
exposure to radon in Australian tourist mines and caves [G4, S14], where the F values varied from 0.19
to 0.75 with an average of 0.39. The F value of 0.57 was used to assess radon exposure for workers in
Spanish and Romanian show caves [A12, C21]. In thermal spas, the average local F values were reported
to be 0.1 in Hungary [K2], 0.15 in China [L8], and 0.2 in Greece [N6]. If no local F value is reported, adefault value of 0.4 is used to obtain a dose from radon exposure.
141. For average annual effective dose assessment, normal time spent in workplaces is commonly
assumed to be 2,000 hours per year. However, in many underground workplaces or in some storage rooms
or water treatment plants where radon concentrations are significantly elevated, this is not the case. For
example, annual working hours for seasonal tour guides in Australian tourist mines and caves varied from
650 to 1,500 hours [G4, S14], significantly lower than commonly assumed 2,000 working hours per year.
For different rooms in a thermal spa resort in South Africa, Botha et al. [B20] applied different occupancy
hours (varying from 414 to 1,932 hours per year) to assess workers’ annual effective doses from exposure
to radon in the air. Some underground workplaces are used by workers as offices or storage rooms withno regular occupancy. For example, bank staff spent less than 130 hours per year in underground safe
deposit rooms in Italy where radon concentrations were significantly elevated [T5]. In three fish culture
stations in Pennsylvania, United States, radon concentration varied from 44 to 600 Bq/m3 [L5]. Working
hours in the hatch houses were limited due to the overall process of maintaining fish cultures; theoccupancy time for workers varied from 4 to 629 hours per year. If location specific working hours are
not given in an article, the typical 2,000 hours per year is conventionally used in the dose assessment.
142. The spectrum of workplaces other than mines where radon can present a hazard is wide.
Underground workplaces can accumulate high radon levels in the same way as underground mines. Suchworkplaces include subways, tunnels, underground parking, caves, spas, close-out mines open to visitorsand some underground stores/offices. Results of the literature review are summarized in table 11. The
average values for workplace categories in this table are simple averages of reported values fromliterature review without population weighting (due to lack of information on numbers of workers in
different workplaces). Table 11 shows the occupational radon exposure in different workplaces, which
all have a wide range of average annual effective dose varying from 0.2 to 5.1 mSv. Radon exposure is
generally higher in underground than in above-ground workplaces. The table also shows the complexityof the matter, with several factors influencing the occupational radon exposure.
143. Workers in the category of above-ground workplaces are the second largest group identified inannex B of the UNSCEAR 2000 Report [U8]. As shown in table 11, except in some storage rooms andcertain parts of water treatment plants, radon concentrations in above-ground workplaces are generally
low, and the resulting average annual effective dose is generally less than 1 mSv.

44 UNSCEAR 2020/2021 REPORT

Table 11. Summary of radon exposure in workplaces other than mines
Practice

Average Rn(Bq/m3)(range)Average annual
effective dose(mSv), (range)

References

Show-cave/tourist-mine

3 090(20–>30 000)

5.1
(0.01–50)[A12, A15, C21, F6, F8, G4,
L2, L8, S2, S14, T3, W1]

Thermal spa/hot spring250(30–2 810)

3.4
(0.2–18)[B20, C2, K2, L8, N6, N7, N10,
S4, V8]28(5–85)

0.2(0.04–0.6)[F8, H10, H11]

Laboratory/storage/
winery/office400(20–8 660)

2.7
(0.1–8.4)[C6, F5, L8, R10, T5, V7]

School/university/
hospital

180(10–1 360)

1.3
(0.1–9.8)[A10, A18, B3, C7, C9, C15,
I51, K11, M1, O10, S18, V8,
V9, Z3]

Office/business building74(23–273)

0.5(0.2–2.0)[A3, B3, B26, C6, C9, C14,
C15, C18, E12, I51, O10, T5,
W3, W5]

Factory66(10–220)

0.43(0.1–1.3)[A6, I51, I52, M5, O10]

Storage/wine cellar

190(10–860)

1.4(01–6.2)[A10, B21, D3, S4]

Water plant/fish hatchery793(20–2 720)

1.4
(0.01–4.7)[A5, J2, R9, L5]

SourceUnderground

Above-ground

Subway/tunnel/
parking garage

144. Even though information on numbers of workers in different above-ground workplaces is generally
not available, one can expect that most workers are in factories or office/business buildings where averageradon concentrations are generally below 100 Bq/m3 and the associated annual effective doses below
1 mSv. From 2007 to 2017, more than 7,600 federally owned indoor workplaces in Canada were tested
for radon [W5]. For a total of 255,557 public servants, the average radon concentration in federal
workplaces was 34.3 Bq/m3; the corresponding annual radon effective dose was 0.25 mSv (with F=0.4
and 2,000 working hours). A study by Whicker and McNaughton [W3] reported radon concentrations in
the offices of Los Alamos National Laboratory with a mean value of 24.3 Bq/m3 and an annual effective
dose from radon exposure of 0.3 mSv (based on 2,000 working hours and F=0.4). In a national radon
survey of bank companies in Italy, Trevisi et al. [T5] reported on more than 342,000 employees working
in 311 bank workplaces. The radon levels in underground workplaces ranged from 27 to 4,851 Bq/m3
with an overall mean value of 153 Bq/m3.
145. With labour statistics in 2017, time statistics and more than 7,600 long-term radon measurements
in various workplaces, occupational radon exposure in workplaces other than mines was assessed byChen [C10] for a total of 18,709,820 workers in Canada. The assessment showed that the average annual
effective dose due to radon exposure in workplaces other than mines was 0.21 mSv in Canada,significantly lower than the earlier, crude global estimate of 4.8 mSv, which was based on experiencefrom the United Kingdom for workplaces exceeding 400 Bq/m3 [U8, U10].
146. The available data from the current UNSCEAR Occupational Exposure Survey for radon in
workplaces other than mines are given in table A.4 in the electronic attachment. Four countries have

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 45

reported data for the period 2003–2014. Even with these very limited data, the responses demonstrateconsiderable variation for the average annual effective dose, from 1.0 to 6.0 mSv.
147. Clearly, elevated levels of radon have been found in a number of countries, but the levels of
exposure vary considerably according to the workplace. So far, owing to lack of information, theCommittee has performed only crude estimates of the worldwide levels of exposure. Although thequantity of data available for the last two periods has increased, the sample sizes are still very small, andthe levels of exposure depend on factors that vary from country to country, such as geology, building
material, working conditions and regulatory regimes.
148. Although the data received by the UNSCEAR Occupational Exposure Survey are very limited,
extensive new data have been reviewed from the literature as summarized in table 11. These data showthat the average annual effective doses vary from 0.2 to 5.1 mSv for underground workplaces and from
0.4 to 1.4 mSv for above-ground workplaces. For workplaces other than mines, the majority (likely morethan 99% according to Canadian labour statistics [C10]) are above ground. In view of this (i.e., aboveground factories and business buildings for the majority of workers), the average annual effective dosefrom radon exposure in workplaces other than mines is estimated to be 1.0 ± 0.5 mSv.

E. Conclusions on occupational exposure to natural sources ofradiation
149. Because of the limited data available, the evaluation of the worldwide level of radiation exposure
to natural sources has been possible for only some sectors. Civilian aviation, coal mineral extraction andprocessing, and mineral other than fuel minerals are the sectors for which the worldwide evaluation was
conducted for the period 2010–2014. No evaluation for the gas and oil extraction sectors nor for radon
exposure in workplaces other than mines was conducted.
150. The evaluation of occupational exposure due to cosmic radiation for civilian aviation is based ondata from the UNSCEAR Occupational Exposure Survey and supplemented by data provided by ICAO.
The additional personnel data have improved the evaluation compared to previous UNSCEAR reports[U8, U10]. For the periods 2000–2004, 2005–2009 and 2010–2014, the worldwide number of civilian
aviation personnel is estimated to be ~450,000, ~600,000 and ~750,000, respectively. It has, thus,increased by a factor of about 2.5 compared to the period 1995–1999 [U10]. The average annual effective
dose for workers is estimated to be 2.7, 2.8 and 2.7 mSv for the mentioned periods, respectively. This isin the same order of magnitude as previously estimated by the Committee [U8, U10]. The estimatedglobal average annual collective effective dose for civilian aviation is 1,220, 1,680 and 2,030 man Sv forthe periods 2000–2004, 2005–2009 and 2010–2014, respectively. The uncertainty interval for theworldwide number of workers ranges from 567,000 to 990,000 and the uncertainty interval for theworldwide average annual effective dose from 1.5 to 4.6 mSv.
151. Mining is an extensive industry. Employment in the mining industry is changing for a variety ofinterrelated reasons: commercial, political, technological, demographic and social. The net effect,
however, has been a steady fall in the number of people employed in mining. According to the ILO, since
the early 1990s, when about 25 million people were estimated to be employed in mining (including some
10 million in coal mining), the decline in employment has ranged from steady to more rapid at different
times in different regions [I48]. Mining is still a male-dominated industry. Although more women are now
working in all aspects of mining in some countries, any increase in female employment is generally very low.

46 UNSCEAR 2020/2021 REPORT152. The level of exposure in mines depends on a number of factors, including type of mine, geology,
working conditions, technology and engineered controls such as ventilation systems. For coal mining,
the UNSCEAR 1988 Report [U5] estimated the global average annual collective effective dose for mining
as 2,000 man Sv. The UNSCEAR 2000 Report [U8] estimated worldwide average annual collective
effective dose for coal mining as 2,700 man Sv, which is about 16% of the estimate value of
16,560 man Sv in the UNSCEAR 2008 Report [U10].
153. The estimated worldwide average annual collective effective dose is about 12,800 man Sv for theperiod 2010–2014. For coal extraction and processing, the estimated number of workers is about
10.9 million for 2000–2004, 8.8 million for 2005–2009 and 8.0 million for 2010–2014. The extrapolationof the workforce data is based on data for countries responsible for 56, 60 and 62% of the average total
primary coal production for the periods 2000–2004, 2005–2009 and 2010–2014, respectively. For coal
extraction and processing, the estimated average annual effective dose is about 2.3 mSv for 2000–2004,
2.1 mSv for 2005–2009 and 1.6 mSv for 2010–2014. There is gradual decrease in the average annual
effective dose, from 2.4 mSv (1990–1995) [U10] to 1.6 mSv (2010–2014). The uncertainty interval for
the worldwide number of workers for coal extraction and processing for the period 2010–2014 ranges
from 4.9 to 13 million and the uncertainty interval for the worldwide average annual effective dose from
1.0 to 2.6 mSv. For extraction and processing industries other than fuel extraction industries, theestimated number of workers is about 3.8 million for 2010–2014. The estimated average annual effective
dose is about 2.5 mSv and the estimated average annual collective effective dose is about 9,500 man Sv.
The uncertainty interval for the worldwide number of workers for extraction and processing industries
other than fuel extraction industries for the period 2010–2014 ranges from 2.3 to 6.2 million and theuncertainty interval for the worldwide average annual effective dose from 1.3 to 4.9 mSv. The current
worldwide estimate of the workforce for mining and processing industries seems to be more solid thanthe previous ones since it is based on data of countries responsible for about 60% of the average annual
total primary coal production and total mineral production other than uranium and oil. The level ofradiation exposure in coal mining has declined compared to the UNSCEAR 2008 Report [U10], which ismainly due to decreasing levels of radiation exposure in China. It is probably due to the improvement ofventilation in government owned mines and the closing of smaller township and private mines. Despite
the improvement in the data provided, there are still limitations regarding their representativeness.
154. The worldwide number of workers exposed to natural sources of radiation for the period 2010–2014
is estimated at a minimum of 12.6 million workers; 24,300 man Sv for the average annual collective
effective dose; and about 1.9 mSv for the average annual effective dose weighted by the number ofworkers. The uncertainty interval for the worldwide number of workers for all three sectors of natural
sources of radiation for the period 2010–2014 ranges from 7.8 to 20 million and the uncertainty interval
for the worldwide average annual effective dose from 1.1 to 3.3 mSv. This is a rough estimate of the levelof exposure to natural sources of radiation. Since the contributions of radiation exposure to oil and gas
extraction and radon exposure in workplaces other than mines have not been estimated in the current
analysis, the estimated values presented in table 12 are certainly an underestimate. The level of radiation
exposure has decreased over time. This may reflect the radiation protection measures implemented in theconcerned countries. A vast majority of workers exposed to natural sources of radiation are notindividually monitored. In order to compare exposure estimations in table 12, the values for the period
1995–1999, were taken from table 91 of the UNSCEAR 2008 Report [U10], on total number of monitored
workers, total average annual collective effective dose and total average annual effective dose, excluding
the contribution from radon at workplaces other than mines.
155. Although the data received by the UNSCEAR Occupational Exposure Survey are very limited forradon exposure in workplaces other than mines, new data have been reviewed from the literature, assummarized in table 11. Extensive reviewed data from literature showed that the average annual effective
doses vary from 0.2 to 5.1 mSv for underground workplaces and from 0.4 to 1.4 mSv for above-groundANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 47

workplaces. For workplaces other than mines, the majority (likely more than 99% according to Canadianlabour statistics [C10]) are above-ground workplaces, such as factories and business buildings. In viewof this fact, the average annual effective dose from radon exposure in workplaces other than mines is
estimated to be 1.0 ± 0.5 mSv.
156. The worldwide level of occupational exposure for oil and gas extraction was not estimated due tothe limited available data. Although an increasing number of countries responded to the simplified
UNSCEAR Occupational Exposure Survey, no statistically significant correlation was found between the
independent variables (GDP and oil production) and the dependent variable (workforce). The lack ofcorrelation may be due to discrepancies in data provided by the countries, such as submission of total
number of workers in the oil extraction industry or submission of data for the number of workers involvedin tasks, e.g., maintenance. For future analysis, such data should be included.
Table 12. Summary of estimates of worldwide levels of annual occupational exposure for workers
exposed to natural radiation sources, excluding oil and gas extraction, and radon exposure in
workplaces other than mines
Categories

1995–1999

2000–2004

2005–20092010–2014

NUMBER OF MONITORED WORKERS (103)
Civilian aviation

300

450

600

750

Coal extraction/processing

6 900

10 900

8 800

8 000

Mineral extraction/processing

4 600

a

a

3 800

Total

11 800aa

12 600b

AVERAGE ANNUAL COLLECTIVE EFFECTIVE DOSE (man Sv)
Civilian aviation

900

1 220

1 680

2 030

Coal extraction/processing

16 56025 07018 48012 800Mineral extraction/processing

13 800

a

a

9 500

Total

31 260aa

24 300b

AVERAGE ANNUAL EFFECTIVE DOSE (mSv)aCivilian aviation

3.0

2.7

2.8

2.7

Coal extraction/processing

2.4

2.3

2.1

1.6

Mineral extraction/processing

3.0

a

a

2.5

Total

2.7

a

a

1.9

b

No worldwide estimation was possible because of limited data or no reliable data.

These data, taken from table 91 of UNSCEAR 2008 Report [U10], exclude the contribution from radon at workplaces other thanmines for reason of comparison.
b

48 UNSCEAR 2020/2021 REPORT

IV. LEVELS AND TRENDS OF EXPOSURE TO HUMAN-MADE
SOURCES OF RADIATION

A. Nuclear fuel cycle
157. A major source of occupational exposure is the operation of nuclear reactors to generate electricalenergy. This involves a complex cycle of activities, including uranium mining and milling, uranium
conversion and enrichment, fuel fabrication, reactor operation, decommissioning, spent fuel reprocessing,research and development activities, radioactive waste management, safeguards inspections, andtransport. Occupational exposure arising from this sector was discussed and quantified in previous
UNSCEAR reports: 1972 [U2], 1977 [U3], 1982 [U4], 1988 [U5], 1993 [U6], 2000 [U8], and 2008 [U10],
with comprehensive evaluation in the UNSCEAR 1977, 1982, 2000 and 2008 Reports. In comparison
with many other sources of exposure, the activities in the nuclear fuel cycle are well documented, andconsiderable quantities of data on occupational dose distributions are available, in particular for reactor
operation. This annex considers occupational exposure arising at each main stage of the fuel cycle.
158. Each stage in the fuel cycle involves different types of workers and work activities. In some cases,
e.g., for reactor operation, the data are well segregated while, in others, the available data span several
activities, e.g., for uranium mining and milling. The data on occupational exposure for each activity isderived primarily from the UNSCEAR Occupational Exposure Survey [U3, U4, U5, U6, U8, U10]. Other
sources exist, particularly the joint Organization for Economic Co-operation and Development’s Nuclear
Energy Agency (OECD/NEA) and IAEA Information System on Occupational Exposure (ISOE) [O3],which serves as a key source of occupational exposure data for reactor operation in the period 2000–
2014, as do the Joint Reports by OECD/NEA and IAEA [O4, O5, O6, O7, O8].
159. For each stage of the fuel cycle, this annex provides estimates of the magnitude of and temporal
trends in the average annual collective effective dose and per capita effective doses, and the numbers ofmonitored workers. The average annual collective effective doses are also expressed in normalized terms,
i.e., per unit practice relevant to the particular stage of the cycle. For uranium mining and milling, uranium
conversion and enrichment, fuel fabrication and spent fuel reprocessing, the normalization is initiallypresented in terms of unit mass of uranium or fuel produced or processed. An alternative way to normalize
is in terms of the equivalent amount of energy that can be (or has been) generated by the fabricated (orenriched) fuel. The basis for the normalizations, i.e., the amount of mined uranium, the separation work
during enrichment and the amount of fuel required to generate a unit of electrical energy in various reactor
types, that were given in UNSCEAR 2008 Report, annex B [U10]. For reactors, the data may benormalized in several ways, depending on how they are to be used. In this annex, normalized averageannual collective effective doses are given for each reactor type and per unit electrical energy generated.

1.

Uranium mining

160. Previously, the mining of uranium generally involved underground or open-pit techniques toremove uranium ore from the ground followed by ore processing. The milling process involves thecrushing and grinding of raw ores followed by chemical leaching, separation of uranium from the leachate
and precipitation of yellowcake [K5], and drying and packaging of the final product for shipment.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 49

161. Uranium ore can be extracted by physically removing it through conventional surface orunderground mining methods or by chemically dissolving the uranium out of the rock ore through either
heap leaching or in situ leaching (ISL) or in situ recovery (ISR) [U18]. Surface mining (also referred toas opencast, open pit, or strip mining) techniques are applied to ore bodies that are close to the surface
and are generally a cost-effective method for extracting large volumes of lower-grade ore. These
techniques may then be combined with other bulk extraction techniques (such as conventional milling,leaching and extraction, or alternative techniques such as heap leaching) that would be uneconomical forunderground operations. Underground mining involves extracting rock through a tunnel or opening inthe side of a hill or mountain and is generally applied for the extraction of higher-grade ores. ISL isgenerally applied to shallow deposits that exist in non-porous shale or mudstone, or in situations where
uranium can be recovered from otherwise inaccessible or uneconomical formations [O9, U10, U18].
162. ISL for uranium has expanded rapidly since the 1990s, and is now the predominant method formining uranium, accounting for 45% of the uranium mined worldwide in 2012. ISL extraction, also
known as solution mining, or ISR in North America, involves leaving the ore where it is in the ground,and recovering the minerals from it by dissolving them and pumping the solution to the surface. A suitableleach solution (acidic or alkaline) is injected into the ore zone below the water table; thereby oxidizing,
complexing, and mobilizing the uranium. Subsequently, the uranium bearing solution is brought to thesurface through extraction or recovery wells for further processing [I13, I16].
163. Workers in the mining and milling of uranium ores are exposed to both external sources of radiationand intake of radionuclides. Mining operations such as drilling, blasting, loose-dressing, mucking,crushing, boulder-breaking, loading and dumping generate ore dust of different particle sizes, whichbecome dispersed in the mine environment and give rise to an inhalation hazard. Concentrations of theore dust are quite variable with time and location. Extremely high values can be reached during blastingand ore dumping. In general, these workplaces are very dusty and, consequently, there is a potential riskof inhalation of aerosol particles containing radionuclides from the 238U decay chain. Doses due to intakeof radionuclides depend on workplace conditions, which vary considerably according to the type of mine
(underground or above ground), the ore grade, the airborne concentrations of radioactive particles (whichvary depending on the type of mining operation and the quality of ventilation) and the particle size
distribution. In underground mines, the main source of doses due to intake of radionuclides is radon andits decay products. Because of the confined space underground and practical limitations to the degree ofventilation that can be provided, the total committed dose is of greater consequence in underground mines
than in open-pit mines. In open-pit mines, the inhalation of radioactive ore dust is generally the largest
source of committed dose, although the doses tend to be low. Higher doses resulting from this source
would be expected in ore milling and in the production of yellowcake. Intake of radionuclides makes thegreatest contribution to the total effective dose resulting from underground mining.
164. Most natural uranium is mined for electrical energy production in fission reactors, but it is also usedin nuclear research reactors and in military activities. Commercial uranium use is determined primarily
by the fuel consumption requirements of power reactors and continues to increase steadily, while therequirements for research reactors remain modest by comparison.
165. Between 2000 and 2014, uranium production was concentrated in 22 countries. Global uranium
production increased by a factor of 1.6 between 2000 and 2014, mainly as the result of rising productionin Kazakhstan and Namibia. The five-year average of annual uranium production in the world increased
from 37 kt (in 2000–2004) to 57 kt (in 2010–2014) [O4, O5, O6, O7, O8, O9]. The average of annual
uranium production is shown in table 13 for each country included in the subsector. The 10 countries
with the largest production (Kazakhstan (37%), Canada (16%), Australia (11%), Niger (8%), Namibia(7%), Russian Federation (5%), Uzbekistan (5%), China (3%), United States (3%) and Ukraine (2%))
account for 96% of the world production in 2010–2014.

50 UNSCEAR 2020/2021 REPORT

Table 13. Average worldwide uranium production [O9, U10]
OP: Open pit; ISL: In situ leach; CoP: Co-product/by-product; UG: Underground

Countries

Types of mining

Average annual uranium production for eachperiod (tonnes U)
2000–2004

2005–20092010–2014

OP, ISL, CoP

7 742

8 415

6 062

Brazil

OP

146

257

197

CanadaOP, UG

11 373

10 028

9 277

China

UG, ISL

718

836

1 450

Czechia

UG, ISL

458

325

216

France

CoP

103

4

5

101

40

34

Australia

Germany
Hungary

CoP

7

2

3

India

UG

225

250

391

Iran (Islamic Republic of)

OP

5

12

Kazakhstan

ISL

7 758

20 757

Malawi

OP

18

825

Namibia

OP

2 472

3 607

4 066

Niger

OP, UG

3 051

3 239

4 407

Pakistan

37

43

45

Romania

88

84

80

2 771

Russian Federation

ISL, UG

3 013

3 395

3 109

South Africa

CoP

803

575

540

Spain
Ukraine62
OP, UG

791

817

920

United States

OP, ISL, UG

1 030

1 562

1 712

Uzbekistan

ISL

1 904

2 354

2 575

~36 900~43 600~56 700

Total

166. uranium mining workforce may be exposed externally to gamma rays emitted from ore, processmaterial, products, and tailings, and exposed internally from the inhalation of long-lived radionuclide
dust, radon and radon progeny, and through ingestion and wound contamination. A detailed dose
assessment was conducted for each type of uranium mining through the Information System on Uranium
Mining Exposure (UMEX). The survey contains official data provided by 36 countries and 5 national
reports prepared by the IAEA. The average annual effective dose for each type of mining and processing
method and for the components of each pathway of exposure derived from the UMEX survey arepresented in table 14. Extraction by ISL results in higher average annual effective dose (3.9 mSv)
followed by underground mining (1.8 mSv), open-pit (open cut) mining (1.5 mSv), open pit (open cut)processing (1.4 mSv), underground processing (0.5 mSv) and other techniques (0.9 mSv) [I16].

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 51

The exposure from external gamma radiation for the ISL technique is not corrected for natural
background exposure, and the annual effective dose may be overestimated by some 0.5 to 1 mSv.
167. The ISL extraction technique has become the dominant uranium mining and processing method,
increasing from 17% (2000–2004) to 46% (2010–2014). Underground mining has decreased over time:
42% (2000–2004) to 28% (2010–2014). Open-pit mining has also decreased over time: 28% (2000–2004)
to 19% (2010–2014), as presented in table 15. Most uranium mining in Kazakhstan, Uzbekistan and theUnited States uses ISL extraction methods, also used in Australia, China and the Russian Federation[O4, O5, O6, O7, O9].
Table 14. Average annual effective dose components of each pathway of exposure in different typesof mining and processing derived from the UMEX survey [I16]
LLRD: Long-lived radionuclide dust; RnP: Radon and its progeny
Average annual effective doses (mSv)
Types of miningaExternal gamma
irradiation

LLRD

RnP

Total

Underground mining

0.85

0.18

0.80

1.83

Underground milling

0.24

0.18

0.12

0.54

Open pit mining

0.74

0.45

0.28

1.47

Open pit milling

0.52

0.54

0.38

1.44

In situ leaching (extraction andprocessing)

2.50a

0.36

1.07

3.93

Other

0.49

0.23

0.21

0.93

Not corrected for background exposure, which could lead to an overestimation of 0.5–1 mSv per year.

Table 15. Distribution of worldwide uranium production [O4, O5, O6, O7, O8, O9]
Type of miningaPercentage distribution of world uranium production (%)
2000–2004

2005–20092010–2014

Open pit

28

26

19

Underground

42

36

28

In situ leaching

17

27

46

Heap leaching (stope or block)

2

2

0.6

In-place leaching

<0.1

<0.1

0.0

Co-product/by-product

10

9

7

Other methods a

0.5

0.1

0.5

Includes mine water treatment and environmental restoration.

168. Occupational exposure data from the current UNSCEAR Occupational Exposure Survey for
uranium mining in the nuclear fuel cycle are given in table A.5 in the electronic attachment. For uranium
mining, three countries provided occupational exposure data for 2000–2004 (Australia, Canada andCzechia), which account for 53% of the total average annual uranium production for 2000–2004.
Additional workforce data for countries responsible for 45% of the world uranium production were52 UNSCEAR 2020/2021 REPORT

obtained from the Joint Reports by OECD/NEA and IAEA [O4, O5]. For the period (2005–2009), fivecountries responded to the UNSCEAR Occupational Exposure Survey (Australia, Canada, China,
Czechia and France). These countries account for 45% of the total average annual uranium production
for the period 2005–2009. The workforce data for countries responsible for another 46% of uranium
production were obtained from the Joint Reports by OECD/NEA and IAEA [O6, O7]. For the period
2010–2014, seven countries responded to the UNSCEAR Occupational Exposure Survey (Australia,
Canada, China, Czechia, France, India and Russian Federation). These countries are responsible for 36%
of the total average annual uranium production for the period 2010–2014. The workforce data forcountries which account for 56% of uranium production were obtained from the Joint Report by NEA
and IAEA [O9]. The number of workers obtained from this Joint Report includes the workforce from themining and processing industries. Therefore, the current evaluation of occupational exposure in uranium
production industry does not separate the uranium mining and uranium milling subsectors.
169. The workforce data obtained from the UNSCEAR Occupational Exposure Survey and from the
Joint Reports by OECD/NEA and IAEA cover 99% of the worldwide average uranium production forthe period 2000–2004, 91% of the uranium production for the period 2005–2009 and 95% of the uranium
production for the period 2010–2014. Therefore, no extrapolation was needed. The number of workers
from the countries that reported occupational exposure data in the period 2000–2004 represents 12% of
the global workforce and for the period 2010–2014 even 46%. On the basis of a trend of greater global
workforce representation in the survey, the average annual effective dose for monitored workers obtained
from the survey was applied to the entire global workforce. The analysis is complicated by a shift in themineral extraction process (from open pit and underground mining to a greater use of ISL technique)between the periods 2000–2004 and 2010–2014 (table 15). As illustrated in table 14, mining using ISL
technique may result in significantly greater individual exposure than open pit or underground mining,
however an accurate background correction was not performed for these data. While production andworkforce data are considered to have acceptable representativeness, there may be no correlation with
monitored worker exposure and the global estimate.
170. The estimation of worldwide exposure in uranium mining activities is based on the average annual
effective dose reported by countries in the UNSCEAR Occupational Exposure Survey: 2.7 mSv for
2000–2004, 2.5 mSv for 2005–2009 and 2.8 mSv for 2010–2014, with the assumption that the values are
representative averages for all such activities, and using data on the size of workforce also from the Joint
Report by NEA and IAEA [O8].
171. Trends of exposure in mining are presented in table 16 and figure I. Uranium production has gone
through three cycles over the past 40 years, which includes an initial period (1975–1989) of moderate
growth followed by a period of significant reduction of about 40% (2000–2004). Recently (2010–2014),
uranium production again increased to 57 kt, similar to the levels experienced in the 1970s and 1980s.
During the same 40-year period, the estimated annual number of monitored workers substantiallydecreased (from 240,000 in 1975–1979 to a low of 22,000 in 1995–1999); in the three latest five-year
periods (2000–2014), the estimated annual number of workers increased again to 44,000. Over the initial
25 years of evaluation (1975–1999), the average annual effective dose was around 4 to 5 mSv. During
the past three periods, the average annual effective dose is estimated to have been fairly constant at alevel somewhat less than 3 mSv. The average annual collective effective dose coupled with mining
followed the same pattern of number of workers, decreasing from 1,300 man Sv (1975–1979) to around80 man Sv (2000–2004) and then increasing again to around 120 man Sv (2010–2014). Over the 40 yearsof evaluation, the average annual collective effective dose per unit uranium produced significantly
decreased from 26 to 2 man Sv/kt U, (table 16 and figure I). Further, the average annual collective
effective dose per unit energy generated significantly decreased from 5.9 to 0.5 man Sv/GWa (table A.5
in the electronic attachment).

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 53

Table 16. Estimates of worldwide levels of annual exposure in uranium mining
Annual amountof U production(kt U)

Average annual
collective
effective dose
per unit mass(man Sv/kt U)

Number ofmonitored
workers(103)

Average annual
collective
effective dose(man Sv)

Average annual
effective dose(mSv)

1975–1979a

52

26

240

1 300

5.5

1980–1984a

64

23

310

1 600

5.1

1985–1989a

59

20

260

1 100

4.4

1990–1994a

39

8

69

310

4.5

a

1995–1999

34

2.5

22

85

3.9

2000–2004

37

2.1

28

77

2.7

2005–2009

44

1.9

33

82

2.5

2010–2014

57

2.2

44

123

2.8

Perioda

Values from earlier UNSCEAR reports [U3, U4, U6, U8, U10].

172. According to the UMEX survey, during most of the milling process the material is wet so usually
gamma exposure will dominate. However, during final product drying and packaging, the material is dry
and inhalation of long-lived radionuclide dust is likely to dominate the dose. Generally, it is in the final
product area that the highest occupational doses are recorded in a processing facility. Table 14 presents
the average annual effective doses obtained from the UMEX survey: 3.93 mSv for ISL (extraction andprocessing), 1.44 mSv for open-pit milling and 0.54 mSv for underground milling [I16].
173. Occupational exposure data from the current UNSCEAR Occupational Exposure Survey for
uranium milling in the nuclear fuel cycle are given in table A.6 in the electronic attachment. Five countries
reported exposure data within the period 2000–2014. The average annual effective dose for monitored
workers ranges from 0.41 mSv (India, 2010–2014), to 3.8 mSv (Czechia, 2010–2014). In the survey,
Australia and Canada reported that for uranium milling, the contribution to the total effective dose frominternal exposure (inhalation of dust and radon) was larger than the contribution from external exposure.
One country, Canada, reported that 6% of monitored workers were female in uranium milling. The total
average annual collective effective dose for the countries that responded to the survey for the period
2010–2014 was 4.2 man Sv (table A.6 in the electronic attachment).

54 UNSCEAR 2020/2021 REPORT

Figure I. Estimated worldwide trends in occupational exposure due to uranium mining

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 55

2.

Uranium conversion and enrichment

174. Uranium conversion and enrichment is the process by which the final product from the milling
process (e.g., U3O8, UO4, UO2 or (NH4)2U2O7) is converted to a gaseous form before the concentrationof 235U is enriched. Most light water reactors (LWRs) use fuel slightly enriched in 235U (generally about
3–5%). In contrast, gas-cooled reactors (GCRs) and heavy water reactors (HWRs) use natural(unenriched) uranium, which contains about 0.7% of 235U. Some older research reactors use highenriched uranium (up to 98% of 235U). For example, the U3O8 from the milling process is converted to
UO2 by a reduction reaction with an acid. The UO2 is converted to uranium tetrafluoride (UF4) by theaddition of hydrofluoric acid and then to uranium hexafluoride (UF6) using fluorine gas (F2). The
enrichment process requires the uranium to be in a gaseous form, since most enrichment is performed bygas centrifugation techniques which use thousands of rapidly spinning vertical tubes that separate 235U
from the slightly heavier 238U isotope. The global uranium conversion capacity summarized in table 17
are based on data from the World Nuclear Association (WNA) [W7, W8, W9, W10, W11, W12].
Table 17. Global conversion capacity for the period 2005 to 2015 [W7, W8, W9, W10, W11, W12]Country

BrazilLocation

Sao Paulo

CanadaPort Hope

China

Lanzhou &Hengyang

FranceRussian Federation

United Kingdom

United States

Total

Pierrelatte
Angarsk
Seversk
Springfields

MetropolisYear

Nameplatecapacity (tU)

Capacity
utilization (%)

Capacity
utilization (tU)

2005–2011

90

2013

40

70

28

2015

100

70

70

2005–2015

12 50070

8 750–14 000

2005

1 000

2007–2011

3 000

3 650

2013–2015

3 650–4 000

4 000

2005–2014

14 000–15 000

70

14 00055

12 000–18 000

2005–2007

15 0002009–2013

25 0002015

12 50012 5002005–2013

6 000

5 000

2005

14 0002007

17 6002009–2013

15 00070

2015

15 00070

2005

62 5902007

68 69064 5902009

76 09064 5902011

75 59055 531201376 19068

51 4782015

59 10078

46 320

13 00010 500175. Uranium conversion plants are operating commercially in Canada, China, France, the RussianFederation, and the United States (table 17). As a result of low demand for commercial nuclear power
plant fuel and excess inventories of uranium, four primary producers have either reduced (Cameco) or56 UNSCEAR 2020/2021 REPORT

suspended production at their conversion facilities (ConverDyn) or closed permanently (Springfields
Fuels, United Kingdom) and two out of three Rosatom facilities (Russian Federation), while only one
new conversion plant (Orano’s Philippe Coste) has started operation to replace equivalent shutteredcapacity at the same site. Large commercial enrichment plants are in operation in France, Germany, theNetherlands, the Russian Federation, the United Kingdom, and the United States, and a few smaller plants
are operating elsewhere (e.g., Argentina, Brazil, India, Islamic Republic of Iran and Pakistan).
176. Exposure data for uranium enrichment are given in table A.7 in the electronic attachment. For 2003–
2014, the reported data represent merely 20–40% of the world enrichment activities and cannot be said
to be globally representative. Consequently, the Committee was unable to estimate worldwide numbers
due to a lack of data. According to the reported data, the average annual effective dose to monitored
workers was low and remained at a level of about 0.1 mSv between 1990 and 2014. The total average
number of reported monitored workers and the resulting total collective dose were somewhat lower
during 2003–2014 than during 1995–2002, about 10,000 monitored workers and about 1 man Sv.
However, as stated in table A.7, since data are missing from some major enrichment facilities, care should
be taken in drawing global conclusions or comparisons. Nevertheless, it can be concluded that theindividual and collective doses arising from uranium conversion and enrichment remain relatively low.
177. Occupational exposure (external and internal) occurs during the conversion and enrichment stagesof the fuel cycle. Inhalation of yellowcake, UF4, uranium dioxide (UO2), uranium trioxide (UO3), uranyl
fluoride (UO2F2), and UF6 gases may occur at different stages of the uranium conversion process. The
activities with the greatest potential for inhalation exposure are yellowcake sampling, removal of ash
waste following purification, and maintenance activities. Inadvertent release of UF6 may occur during
sampling, UF6 cylinder loading and unloading, and maintenance activities [S16]. External radiation
exposure generally contributes more to occupational worker exposure than internal radiation exposure
does for these stages. Limited worker exposure data was obtained for the conversion stage. Averageannual collective effective dose for the Honeywell International facility (United States) varied between
1.5 and 1.6 man Sv between the 2006–2009 and 2010–2014 periods. The average annual effective dose
to monitored workers decreased from 1.95 to 1.33 mSv for the 2006–2009 and 2010–2014 periods. The
average annual effective dose for measurably exposed workers decreased from 2.11 to 1.42 mSv for thesesame periods. The Cameco facility in Port Hope, Canada, is both a conversion and fabrication facility.
As such, occupational exposure for the conversion stage at Port Hope is reported under the fuelfabrication stage in table A.8 in the electronic attachment.

3.

Fuel fabrication

178. Fuel fabrication facilities convert natural or enriched uranium into fuel for nuclear reactors. Fuelfabrication for LWRs typically begins with the receipt of low-enriched uranium (UF6) from an enrichment
plant. The UF6 is heated to form a gas, and then the UF6 gas is chemically processed to form uranium
dioxide (UO2) powder. This powder is then pressed into pellets, sintered into ceramic form, loaded into
zircaloy tubes, and constructed into fuel assemblies. In the case of HWRs that use natural uranium as
fuel, the fabrication process does not entail the handling of enriched 235U (e.g., UF6 or uranyl nitratesolutions). Following the conversion of the final product from the milling process into UO3, further
processing converts this into ammonium diuranate ((NH4)2U2O7), or ammonium uranyl carbonate(UO2CO3·2(NH4)2CO3), which is then reduced to form reactor grade (high purity) UO2. Dry natural UO2
powder is pressed into pellets, sintered, and loaded into zircaloy tubes. The global fuel fabrication
capacity is summarized in table 18 for LWRs and table 19 for HWRs.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 57

179. The major process safety concerns at nuclear fuel fabrication facilities are those of fluoride
handling. Workers may be exposed to ammonium diuranate, ((NH4)2U2O7), UO2F2, and UO2 powder.
The primary inhalation hazard is from uranium dioxide powder during packaging and unpackaging,powder handling and pellet production, and maintenance activities. The risk of exposure is managed
through the rigorous control of material.
Table 18. World fuel fabrication capacity of light water reactors [W13]tHM: tonnes of heavy metal
Country

Location

Fuel fabrication capacity (tonnes per year)
Conversion

Pelletizing

Rod/assembly

Resende

160

120

400

Yibin

800

800

800

Baotou a

200

200

600

FranceRomans

1 800

1 400

1 400

Germany

Lingen

800

650

650

India

Hyderabad

48

48

48

Kumatori

0

383

284

Tokai-Mura a

450

690

690

Kurihama

0

620

630

Kazakhstan

Oskemen0

108

0

Republic of Korea

DaejeonRussianFederation

Elektrostal

Brazil
China

Japan

700

700

700

b

1 500

1 500

1 560

Novosibirsk

450

1 200

1 200

Spain

Juzbado

0

500

500

SwedenVästeras

787

600

600

United Kingdom

Springfields c

950

600

860

Richland

1 200

1 200

1 200

Wilmington

1 200

1 000

1 000

Columbia

1 600

1 594

2 154

12 645

13 91315 276

United States

Total
a

Includes fuel fabrication capacities of two companies.

b

Includes approximately 220 tHM for high-power channel reactors.

cIncludes approximately 200 tHM for advanced gas-cooled reactors.

58 UNSCEAR 2020/2021 REPORT

Table 19. World fuel fabrication capacity of pressurized heavy water reactors [W13]Country

Rod/assembly(tonnes per year)

Location

Argentina

Cordoba and Eizeiza

160

Port Hope

1 500

Peterborough

1 500

China

Baotou246

India

Hyderabad

1 000

Pakistan

Chashma20

Republic of Korea

Taejon400

Romania

Pitesti

250

Canada

Total

5 076

180. The estimated exposure data for fuel fabrication are given in table 20 and table A.8 in the electronic
attachment. This information was provided by countries that responded to the UNSCEAR Occupational
Exposure Survey and represents approximately 80% of the fuel fabrication workforce. Exposure data
were not obtained from several countries, but the information submitted is considered representative of
the entire subsector and a global estimate was made with relatively good confidence on the basis of theamount of reactor fuel produced and that this fuel was fabricated for LWRs and HWRs. The averageannual number of monitored workers has been reasonably constant for all five-year periods since 1975 at
about 20,000 but with a small peak of 28,000 in the 1985–1989 period. The worldwide average annual
number of measurably exposed workers in the periods 1990–1994 and 1995–1999 was estimated to beapproximately 10,000—about half the number of monitored workers. On the basis of the current survey,
this estimation remains valid. The estimated average annual collective dose showed a decline, from 36 to
21 man Sv, between the first two five-year periods, and little change over the next two periods, with thevalue for 1990–1994 being approximately 22 man Sv, and then increased to about 30 man Sv for 1995–
1999. It then gradually decreased during the last three periods, to a value below 20 man Sv. The averageannual effective dose to monitored workers showed an initial decline, from 1.8 to 1.0 mSv, during thefirst 5-year periods, increased to 1.4 mSv at the end of the 1990s, and then finally decreased again toabout 0.9 mSv.
Table 20. Estimated worldwide levels of annual occupational exposure due to fuel fabrication
Number of monitored
workers (103)Annual collective effective
dose (man Sv)

Average annual effective dose tomonitored workers (mSv)

1975–1979a

20

36

1.8

a

1980–1984

21

21

1.0

a

1985–1989

28

22

0.8

1990–1994a

21

22

1.0

1995–1999a

22

30

1.4

2000–2004

23

26

1.2

2005–2009

21

19

0.9

2010–2014

20

17

0.9

Perioda

Values from earlier UNSCEAR reports [U6, U8].

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 59

181. The increase in the average annual effective dose for measurably exposed workers in the
1995–1999 period could have been because some countries began to include the dose due to internal
exposure in their dose records. There are two main sources of exposure in the fabrication of nuclear fuel:external exposure to gamma radiation and internal exposure resulting from the inhalation of airborne
material. Beginning in 1994, the United States combined internal and external radiation exposure data intheir national reporting for nuclear fuel cycle workers. According to the report of the United States
Nuclear Regulatory Commission [U19], the annual collective dose increased threefold due to theinclusion of internal dose from the inhalation of uranium. This change in national reporting accounted
for 80% of the increase in average annual collective effective dose for the 1995–1999 period. In Sweden,
the monitoring method for internal exposure to uranium was improved in 2008, which then revealed
significantly higher effective doses to specific workers, and a higher annual collective effective dose forrelated five-year periods.
182. The internal dose component depends also on the type of nuclear fuel. Occupational exposure in
the production of nuclear fuel is expected to be lower for fuel involving only natural uranium than forthat involving enriched uranium. The type of dose recorded in the national database can be a source of
discrepancy between countries. Some countries record only doses due to external exposure and others
record doses due to both internal and external exposure. Moreover, some countries include workers who
do not work in controlled areas in their individual monitoring programme. The variation in types ofnuclear fuel also influences the comparison of doses between countries.
183. In summary, the average annual collective effective dose and effective dose for monitored andmeasurably exposed workers related to fuel fabrication in the nuclear sector has decreased since the
1995–1999 period. The countries included in table A.8 in the electronic attachment account for 75–80%of the annual global production capacity for uranium pelleting and fuel rod assembly [W13].

4.

Nuclear power reactor operation

184. Reactors used for electrical energy generation are characterized by their coolant system andmoderator: light-water-moderated and cooled pressurized water reactors (PWRs); light-water-moderated
and cooled, boiling water reactors (BWRs); pressurized heavy-water-moderated and –cooled reactors(HWRs); gas-cooled graphite-moderated reactors (GCRs), in which the gas coolant, either carbon dioxideor helium, flows through a solid graphite moderator; and light-water-cooled, graphite-moderated reactors(LWGRs). These are all thermal reactors, in which the moderator material is used to slow down fast
fission neutrons to thermal energies. Fast-breeder reactors (FBRs) at present make a minor contribution
to electrical energy production.
185. Occupational exposure can vary significantly from reactor to reactor and is influenced by suchfactors as reactor size, age and type. Several broad categories for commercial nuclear power reactors
currently in operation include PWRs, BWRs, GCRs (which include older Magnox reactors) and also
newer generation reactors, advanced gas-cooled reactors (AGRs), HWRs and LWGRs. Within eachcategory, much diversity of design and diversity in the refuelling schedule can be seen, which may
contribute to differences in occupational exposure. In addition, changes in operating circumstances canalter the exposure at the same reactor from one year to the next. Some of these variations will be discussed
in this section.
186. Thirteen countries responded to the UNSCEAR Occupational Exposure Survey and provided
occupational exposure data for operating commercial nuclear power reactors (2000–2014). In addition,
data on exposure of workers at operating nuclear power reactors are available from ISOE. These data

60 UNSCEAR 2020/2021 REPORT

have been published annually as ISOE reports from the OECD/NEA since 1992. The ISOE report [O3]contains information on average annual collective effective dose trends for the nuclear power industry in
the OECD Member States. These trends include those related to occupational exposure from operating
reactors and from definitely shutdown reactors. They also include occupational exposure data (e.g.,
average annual collective effective dose, average annual effective doses and number of workers per
reactor by country and type of reactor). The ISOE report [O3] also contains occupational exposure datafrom 76 participating utilities from 29 Member States. This includes data from the database for a total of
377 operating reactor units and 57 shutdown reactors, covering about 90% of the world’s operating
commercial reactors. The data provided in response to the UNSCEAR Occupational Exposure Survey
and ISOE data are presented in table A.9 in the electronic attachment.
187. The average number of operating reactors over the evaluated period is 440 for 2000–2004, 439 for
2005–2009 and 451 for 2010–2014. The average number of PWRs increased from 263 to 274 from 2000–
2004 to 2010–2014. The average number of BWRs increased from 91 (2000–2004) to 94 (2005–2009)
and then decreased to 87 (2010–2014). The average number of HWRs progressively increased from 37(2000–2004) to 59 (2010–2014). However, the number of GCRs and LWGRs has decreased from 31 to
17 and from 19 to 15 over the past three periods, respectively. The average number of nuclear powerreactors in operation and the average electrical energy generated per country and type of reactor for eachperiod (2000–2004, 2005–2009 and 2010–2014) are presented in table A.9 in the electronic attachment.
The average annual electrical energy generated during 2000–2004 was 288 GWa; during 2005–2009
297 GWa, and during 2010–2014 279 GWa.
188. Data on occupational exposure for reactors of each type and a worldwide summary by reactor typeand generated energy are given by country in table A.9 in the electronic attachment. Worldwide levels of
exposure have been estimated from the data obtained from the UNSCEAR Occupational Exposure
Survey and from ISOE. The extrapolations are based on the generated electrical energy per type of reactor
in operation. Very little extrapolation was needed, as the data on annual collective effective dose were
substantially complete; close to 100% for PWRs and GCRs, about 94% for BWRs, and 88% for HWRs.
However, for LWGRs, exposure data were provided from only 6% of the operating reactors. Previous
UNSCEAR evaluations treated FBRs and high-temperature graphite reactors (HTGRs) separately. No
data were provided on these either in the ISOE database or in response to the UNSCEAR Occupational
Exposure Survey, and only two FBRs (Beloyarsk-3 and -4) were in operation between 2000 and 2014.
The UNSCEAR 1993 and 1988 Reports [U5, U6] concluded that they made a negligible contribution to
occupational exposure and, hence, would not be considered further.
189. The procedures for the recording and inclusion of doses incurred by workers who regularly carryout their work on the premises or site of another employer and who may be exposed due to the site
operator’s use of radiation or who may take onto a site their own source of radiation (such workers,
referred to as itinerant or outside workers, are often employed by contractors) may differ from utility toutility and country to country [I15]. This may influence the respective statistics in different ways. In somecases, itinerant/outside workers may appear in the annual statistics for a given reactor several times in
one year (whereas they should rather appear, with the summed dose recorded, once only). If appropriate
corrections are not made, then statistics so compiled will inevitably overestimate the size of the exposed
workforce and underestimate the average individual dose and also the fractions of the workforce and theaverage annual collective effective dose arising from individual doses above the prescribed levels. This
will be important only where transient itinerant workers are used extensively and where no central point
for the collection and maintenance of dose records (e.g., national dose registry) is used. For example, thismay be important for reactor operations when itinerant workers are hired to assist with reactor refuellingand maintenance (i.e., outages). Many hundreds of itinerant workers will augment the permanent
workforce at an operating reactor for several weeks or months until the maintenance and refuelling
activities are completed.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 61

190. Countries differ in how they present information on the exposure of workers at nuclear installations.
The majority present statistics for the whole workforce, i.e., employees of the utility and itinerant
workers, often with separate data for each category; some provide data for utility employees only,
whereas others present the average annual collective effective dose for the total workforce but individual
doses for the utility workers only.
191. The type of reactor is just one factor influencing the doses received by workers. Other basic featuresof the reactor play a role, including the piping and shielding configuration, fuel failure history, reactor
water chemistry, and work procedures and conditions at the reactor. All of these can differ from site tosite, even between reactors of the same type, contributing to the differences seen in occupational
exposure. At all reactors, external irradiation by gamma rays is the most significant contributor to
occupational exposure. The exposure occurs mostly during scheduled maintenance/refuelling outages.
For the most part, such exposure is due to activation products (60Co, 58Co, 110mAg, 124Sb); however, whenfuel failures occur, fission products (95Zr, 137Cs) may also contribute to external exposure. At BWRs,
workers in the turbine hall incur some additional external exposure due to 16N, an activation product withenergetic gamma radiation (6.13 and 7.11 MeV), carried by the primary circulating water through theturbines. In HWRs, heavy water is used as both coolant and moderator. Neutron activation of deuterium
produces a significant amount of tritium in these reactors so, in addition to the usual external exposure,workers receive internal exposure due to tritium, which is a pure beta-emitter with low electron energy,
on average only 5.7 keV.
192. The estimation of workforce exposure worldwide in reactor operation is based on the average
generated energy, per type of reactor, per country, and on reported data on average annual collective dose.
The average annual effective dose for monitored workers is calculated for countries with a reported
number of workers and is assumed to be representative for all the workforce for each reactor type andperiod. The total number of workers is estimated using collective dose and average annual effective dosefor each reactor type. The data are presented in table A.9 in the electronic attachment.
193. PWRs constitute the majority of installed nuclear generating capacity for the period 2000–2014,
followed by BWRs (table A.9 in the electronic attachment). Averaged over the whole period, 89% of thetotal energy was generated in LWRs (of this 68% was from PWRs and 21% from BWRs), with
contributions of 5.7% for HWRs, 2.3% for GCRs and 2.9% for LWGRs. FBRs contribute only about
0.1% of the total energy generated. There are significant differences between occupational exposure at
PWRs and that at BWRs, therefore, each type of reactor is considered separately.

(a) Light water reactors
Pressurized water reactors
194. External exposure due to gamma radiation is the main source of occupational exposure at PWRs.
Since, in general, only a small contribution comes from internal exposure, it is rarely monitored. The
contribution of neutrons to the overall level of external exposure is insignificant. Most occupational
exposure occurs during scheduled plant shutdowns, when planned maintenance and other tasks areundertaken, and during unplanned maintenance and safety modifications. Activation products and, to alesser extent, fission products within the primary circuit and coolant, are the main source of external
exposure. The material used in the primary circuit, the primary coolant chemistry, the reactor’s design,and operational features, and the extent of unplanned maintenance all influence the magnitude of the
exposure resulting from this source. Significant changes over time in many of these areas have affected
the levels of exposure. One of the main non-standard maintenance operations associated with significant
dose is the replacement of steam generators [U8]. By far the largest numbers of operating PWRs are62 UNSCEAR 2020/2021 REPORT

located in the United States, France and Japan. These three countries operate about 55% of the operating
PWRs. In general, more than half of the energy (55%) generated by PWRs in the 2010–2014 period was
produced in the United States and France. Another 30% was generated in the Republic of Korea (7%),
China (6%), the Russian Federation (5%), Ukraine (5%) and Germany (5%). Electricity generation by
PWRs in Japan decreased to 5.8 GWa during the 2010–2014 period due in part to the shutdown of their
PWR fleet in 2011.
195. The average worldwide number of PWRs increased from 78 in 1975–1979 to 274 in 2010–2014.
The corresponding average annual electrical energy generated increased much more, from 27 to 195 GWa.
The number of monitored workers at PWRs increased from about 63,000 to 230,000 in 1985–1989.
Between the periods 1985–1989 and 2005–2009, the numbers ranged from 230,000 to 310,000. In the
recent period 2010–2014, the number of monitored workers increased to 370,000 (figures II and III,
table 21 and table A.9 in the electronic attachment) [U10]. Overall, the number of measurably exposed
workers is about 40% of that for monitored workers during 2010–2014. Between the first two periods,
the average annual collective effective dose increased by a factor of about two, from 220 to 450 man Sv.
Between 1985 and 1999, the estimated average annual collective effective dose fluctuated in a range from
400 to 500 man Sv. In the last three periods, it decreased by a factor of three: 227 man Sv in 2000–2004,
192 in 2005–2009 and 146 in 2010–2014. Over the past three decades, annual collective effective dose
has been decreasing at PWRs. This decrease in collective dose is best demonstrated by examining averageannual collective effective dose per operating reactor and per electrical energy generated in a year
(table 21). The gradual decrease in the average annual collective effective dose per reactor and averageannual collective effective dose per energy generated is most likely the result of continual improvementof protection measures with improved reactor design and operational procedures, and of measures toreduce the source term in the reactor primary cooling system.
196. The five- to tenfold reduction in the normalized average annual collective effective dose during thepast three decades is associated with the substantial decrease in the average annual effective dose tomonitored workers. The average annual effective dose decreased by a factor of 10 between the periods
1975–1979 and 2010–2014, from 3.5 to 0.4 mSv, respectively. The worldwide average annual effective
dose to measurably exposed workers, 0.91 mSv in 2010–2014, is about twofold higher than that for all
monitored workers. The occupational exposure data for PWR workers submitted in response to the
UNSCEAR Occupational Exposure Survey, when supplemented with exposure information from theISOE database, is almost 100% complete for the period 2000–2014. While one country did not provide
average annual effective dose data for their individual workers, average annual collective effective dose
data for these workers was obtained. The distribution ratios of number of monitored workers, NRE, andof average annual collective effective dose, SRE, have not been evaluated because of a lack of data.

Boiling water reactors
197. External exposure due to gamma radiation is also a main source of occupational exposure in BWRs,
with most exposure occurring during scheduled shutdowns, when planned maintenance is undertaken,
and during unplanned maintenance and safety modifications. At BWRs, workers engaged in maintenancein the turbine hall incur some additional external exposure due to the decay of 16N. In the period 2010–2014, the largest numbers of BWRs were located in the United States (35) and Japan (24). Overall, 60%of the electrical energy generated by BWRs in the 2010–2014 period occurred in the United States.
Electricity generation by BWRs in Japan decreased from 16.0 to 3.74 GWa between the periods 2005–2009
and 2010–2014 in part due to the shutdown of their BWR fleet in 2011.
198. The average worldwide number of BWRs consistently increased from 51 in 1975–1979 to 94 in
2005–2009; and decreased to 87 reactors in 2010–2014 [U10]. The corresponding increase in the averageannual electrical energy generated worldwide was somewhat greater, from about 15 GWa in 1975–1979 to

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 63

64 GWa in 2005–2009, decreasing to 52 GWa in 2010–2014. The number of monitored workers at BWRs
worldwide increased from about 59,000 to about 160,000 between the 1975–1979 and 1990–1994 periods
and has remained between 130,000 and 150,000 since 1994 as presented in figures II and III as well as
in table 21 and table A.9 in the electronic attachment. Overall, the number of measurably exposed
workers has been 40–65% of the number of monitored workers for the past 20 years. The average annual
collective effective dose has decreased from about 450 man Sv during the 1980–1984 period to about
85 man Sv during the 2010–2014 period. Over this same time interval, there has been a twofold increasein the energy generated. The normalized average annual collective effective dose per reactor and theaverage annual collective effective dose per GWa electricity produced have both consistently decreased
during every five-year period since 1984. Both sets of values indicate significant reductions over the past
30 years, indicating that the efficiency of protection measures from design and operational procedures,and measures to reduce the source term (e.g., 60Co at cooling system surfaces) has improved over time.
199. Eight countries responded to the UNSCEAR Occupational Exposure Survey. These data were
supplemented by those obtained from the IAEA Power Reactor Information System (PRIS) and the
NEA/IAEA ISOE databases. The combined data represent over 90% of the BWRs in global operation
between 2000 and 2014. The global estimate of occupational exposure due to BWR reactor operation isbased on average annual collective effective dose for measurably exposed workers and annual energy
generated. The data are presented in table A.9 in the electronic attachment.
200. The substantial reduction of the average annual collective effective dose over time is associatedwith an eightfold decrease in the average annual effective dose to monitored workers over the past
40 years (table 21). The worldwide average annual effective dose to measurably exposed workers,
1.2 mSv in 2010–2014, is about twofold higher than that for monitored workers. The distribution ratiosof the number of monitored workers, NRE, and of the average annual collective effective dose, SRE, havenot been evaluated because of a lack of data. Occupational exposure data for BWRs submitted in responseto the UNSCEAR Occupational Exposure Survey and supplemented with information from the IAEA
PRIS [I7] and the NEA/IAEA ISOE databases are representative of all operational BWRs.

(b) Heavy water reactors
201. The worldwide average number of HWRs increased from 12 in 1975–1979 to 59 in 2010–2014[U10]. The corresponding increase in the average annual energy generated worldwide was somewhat
greater, from about 3 to 19 GWa. The number of monitored workers in HWRs worldwide increased fromabout 7,000 to about 58,000 over the 40 years of evaluation, as shown in figures II and III, table 21 andtable A.9 in the electronic attachment. Overall, the number of measurably exposed workers was about
40% of the number of monitored workers. The average annual collective effective dose varied between
30 and 60 man Sv in the periods between 1975 and 1999, and increased from 40 to 60 man Sv during thelast three periods. The normalized average annual collective effective dose per reactor was around
2.4 man Sv in the first three periods, but then dropped to 1.1 man Sv and has remained relatively constantover the past 25 years. The corresponding values normalized to the electrical energy generated have fallen
by a factor of more than three, from 11 to 3 man Sv per GWa, over the past 40 years. Both sets of values
suggest significant improvement in the efficiency of radiation protection measures for both design andoperational procedures.
202. The average annual effective dose to monitored workers has constantly decreased over the past
40 years. There has been about a fivefold reduction overall. The worldwide average annual effective doseto measurably exposed HWR workers, 2.2 mSv in 2010–2014, is about twofold higher than that tomonitored workers. The doses due to the intake of tritium (as tritiated water) may have provided an major
contribution, around 20%, to the total effective dose [H6] The occupational exposure data for HWR

64 UNSCEAR 2020/2021 REPORT

workers submitted in response to the UNSCEAR Occupational Exposure Survey, when supplemented
with exposure information from the ISOE database, is representative of up to 96% of the operational
HWRs reporting, annual electricity generated, and average annual collective effective dose. The
distribution ratios of the number of monitored workers, NRE, and of average annual collective effective
dose, SRE, have not been evaluated because of a lack of data.

(c) Gas-cooled reactors
203. There are two main types of GCRs: Magnox reactors, including those with steel pressure vessels
and those with pre-stressed concrete pressure vessels, and AGRs. Another type, HTGRs, reported
previously [U5], is no longer in operation. Most of the experience with GCRs has been gained in the
United Kingdom, where they have been installed and operated for many years. Initially, the GCRs wereof the Magnox type, but throughout the 1980s, the contribution of AGRs, both in terms of their installedcapacity and energy generated, increased. The contribution from AGRs to occupational exposure will
increase as Magnox reactors are decommissioned.
204. In its UNSCEAR 1993 Report [U6], the Committee investigated the differences in occupational
exposure between the Magnox reactors and AGRs. These arise mainly from the use of concrete (asopposed to steel) pressure vessels in the AGRs (and the later generation of Magnox reactors) and theincreased shielding they provide against external radiation, the dominant source of occupational
exposure. That report identified significant differences between the various types, with the average annual
effective dose in first-generation Magnox steel-pressure-vessel reactors remaining uniform at about
8 mSv, whereas the corresponding values for Magnox reactors with concrete pressure vessels and for
AGRs were less than 0.2 mSv. During the 1990–1994 period, significant dose reductions were achievedat the Magnox reactors, with further reductions during the next two periods. More detailed information
can be found in the reviews of radiation exposure in the United Kingdom [U10]. In this annex, nodistinction has been made between the various types of GCRs.
205. The worldwide number of GCRs averaged over five-year periods decreased significantly from 40
in the period 1975–1979 to 17 in the latest period (2010–2014) [U10]. Several Magnox reactors havebeen shut down. With the permanent shutdown of Tokai-1 (Japan) in 1998, the only operating GCRs arein the United Kingdom. There has been a corresponding decrease in both the average annual energy
generated worldwide and the number of monitored workers, as shown in figures II and III, table 21 andtable A.9 in the electronic attachment. Over eight five-year periods, the average annual collective effective
dose decreased from 36 to 1 man Sv. The normalized average annual collective effective dose per reactor
decreased from 0.9 to 0.05 man Sv, while the corresponding values per amount of generated energy also
decreased, from 6.6 to 0.14 man Sv per GWa. Both sets of values indicate significant reductions over theeight periods, showing that the efficiency of protection measures from both design and operational
procedures has improved over time.
206. The average annual effective dose to monitored workers worldwide, averaged over five-year
periods, fell progressively from 2.8 to 0.06 mSv over time. The global occupational exposure data for
operational GCRs is complete since the only operational ones for 2000 to 2014 are in the United
Kingdom. The distribution ratios of the number of monitored workers, NRE, and of average annual
collective effective dose, SRE, have not been evaluated because of a lack of data.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 65(d) Light-water-cooled graphite-moderate reactors
207. LWGRs were developed in the former Union of Soviet Socialist Republics and installed only inwhat is now the Russian Federation, Ukraine and Lithuania. Data equivalent to only 11% of the totalenergy generated by LWGRs were available from the ISOE database and from the UNSCEAR
Occupational Exposure Survey, provided by Lithuania. The Russian Federation has provided data
through the UNSCEAR Survey; however, these data were not specific to LWGRs.
208. The overall number of operating LWGRs increased from 12 in the first period to 20 in 1985–1994.
Since then, it has slowly decreased to 15 in 2010–2014 [U10]. The corresponding average annual energy
generation increased from 4.4 to 10 GWa in the period 1985–1999, and has since then been fairly
constant, around 8–9 GWa. In the UNSCEAR 2008 Report [U10] the estimate of the number of monitored
workers showed an increase from about 5,000 (1978–1979) to 13,000 (1985–1989), but with no data
available for the periods from 1990–1994. The estimated average annual collective effective dose
increased significantly over the periods, from 36 to 62 to 173 to 190 man Sv for the four periods from1978 and 1994. Over these periods, the normalized average annual collective effective dose per reactor
increased from 3 man Sv in 1978–1979 to 9 man Sv in 1985–1994. The corresponding normalized values
per electricity energy generation also increased from 8 man Sv per GWa in 1978–1979 to 20 man Sv per
GWa in 1985–1994.
209. In its UNSCEAR 1993 Report [U6], the Committee suggested that the large increase in averageannual collective effective dose between the second and third periods (62 to 170 man Sv) was artificial
in that the data included a major component from the after-effects of temporary work at Chornobyl.
However, the data for 1990–1994 showed a continued high exposure (190 man Sv).
210. The estimated worldwide exposure is uncertain due to uncertainties in the estimates for the periods
up to 1994, the lack of data in the period 1995–1999, and the limited exposure data for the three recent
periods (2000–2014). Exposure data were obtained from only two reactors in Lithuania in operation up
to 2009, but no exposure data were available for the 15 operational LWGRs in the Russian Federation.
Therefore, the estimate is based on expert judgement by the Committee, using the available reported
exposure data. The assumption was to use an average annual effective dose of 1 mSv and 2,500 workers
per reactor as representative for all LWGRs, together with the information from the IAEA PRIS database[I7] on the number of operating reactors and generated energy. This global estimate should be treatedwith caution since it is based on very few exposure data.

(e) Radiation exposure according to job category211. Information on doses according to job category has been provided through ISOE (table A.10). To
account for some non-homogeneity in the statistical recording systems, these data have been aggregatedinto five broad categories: refuelling, maintenance, inspection, servicing, and all other tasks.
212. In general, the doses associated with most annual jobs, regardless of reactor type, have decreased
from the 2000–2004 period to the 2010–2014 period. For PWRs, the average annual collective effective
dose per reactor showed a 37% decrease for refuelling jobs, a 35% decrease for inspection jobs, a 27%
decrease for servicing jobs and a 49% decrease for other jobs. For maintenance jobs, the averagecollective dose per reactor remained stable. For BWRs, the average annual collective effective dose perreactor associated with annual inspection and servicing remained stable from the 2000–2004 period to
the 2010–2014 period. However, the average annual collective effective dose per BWR increased forrefuelling and maintenance operations by 40 and 80%, respectively, between these same periods.

66 UNSCEAR 2020/2021 REPORT(f) Summary for nuclear power reactors
213. Data on occupational exposure at reactors worldwide are summarized in table 21 and table A.9 inthe electronic attachment. The worldwide number of power reactors averaged over the eight five-year
periods increased from 193 in the first period to 451 in the 2010–2014 period. A corresponding increasein average annual energy generation also occurred, from 55 to 279 GWa. Averaged over the whole period,
about 89% of the total energy was generated in LWRs (of this about 68% was from PWRs and 21% from
BWRs), with contributions of about 5.7% for HWRs, 2.3% for GCRs, and 2.9% LWGRs.
214. The summary below on estimates of worker exposure in the three recent periods include information
received from the UNSCEAR Occupational Exposure Survey and from the ISOE database. The
information is at least 90% complete for BWRs and HWRs and essentially 100% complete for PWRs
and GCRs. The number of monitored workers increased from about 150,000 to 630,000 during the studied
periods. The 1990–1994 period is the first for which there is a reasonably robust estimate of the numberof measurably exposed workers, some 260,000, which represents about 50% of the number of monitored
workers. The percentage of monitored workers with measurable effective doses has varied between
40 and 50% over time.
215. The average annual collective effective dose averaged over five-year periods has decreased fourfold
over the last three decades (1985 to 2014). The trends in annual values are shown in table 21, table A.9
in the electronic attachment and figures II and III. Averaged over the three recent periods, about 77% of
the average annual collective effective dose was received by workers at LWRs. The estimatedcontribution from workers at HWRs was 12%, at GCRs 0.5% and at LWGRs 10%.
216. The normalized average annual collective effective dose per reactor averaged over all reactors
decreased by about a factor of five from 3.7 man Sv per operating reactor to 0.7 man Sv per operating
reactor between the periods 1980–1984 and 2010–2014. The normalized average annual collective
effective dose per unit of electrical energy generated (man Sv per GWa) decreased tenfold over the same
timeframe. A generally decreasing trend is apparent for normalized figures for most reactor types.
217. The average annual effective dose to monitored workers averaged over all reactors fell steadily
between the periods 1975–1979 and 2010–2014, from 4.1 to 0.5 mSv. This downward trend in annual
dose to monitored workers is evident for each operating reactor type, although there are some differences
between reactor types in the magnitude of the doses and in their rate of decline.
Table 21. Summary of worldwide estimates of occupational exposure due to reactor operation
PWR: Pressurized water reactor; BWR: Boiling water reactors; HWR: Heavy water reactor; GCR: Gas-cooled
reactors; LWGR: Light-water-cooled, graphite-moderated reactor
Period

PWR

BWR

HWR

GCR

LWGR aAll reactors

AVERAGE NUMBER OF MONITORED WORKERS (10 )3b1975–1979

63

59

7

13

5

147

b

1980–1984

140

102

14

25

10

291

b

1985–1989

230

139

18

31

13

431

b

1990–1994

310

160

20

30

520

b

1995–1999

265

144

18

21

448

2000–2004

278

132

34

11

47

501

2005–2009

309

149

43

14

40

555

2010–2014

370

148

58

14

38

627

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 67

Period

PWR

BWR

HWR

GCR

LWGR aAll reactors

AVERAGE ANNUAL EFFECTIVE DOSE TO MONITORED WORKERS (mSv)b

1975–1979

3.5

4.7

4.8

2.8

6.6

4.1

1980–1984b

3.1

4.5

3.2

1.4

6.4

3.5

1985–1989b

2.2

2.4

3.4

0.8

13.2

2.5

b

1990–1994

1.3

1.6

1.7

0.5

1.4

b

1995–1999

1.9

1.6

1.6

0.3

1.7

2000–2004

0.8

1.1

1.2

0.3

1.0

0.9

2005–2009

0.6

0.9

1.1

0.1

1.0

0.7

2010–2014

0.4

0.6

1.0

0.06

1.0

0.5

1975–1979b

220

279

32

36

36

603

1980–1984b

450

454

46

34

62

1 046

1985–1989b

500

331

60

24

173

1 088

b

1990–1994

415

240

35

16

190

896

b

1995–1999

504

237

29

7

2000–2004

227

143

41

3

47

461

2005–2009

192

127

48

2

40

409

2010–2014

146

86

58

1

38

328

AVERAGE ANNUAL COLLECTIVE EFFECTIVE DOSE (man Sv)

777

NORMALIZED AVERAGE ANNUAL COLLECTIVE EFFECTIVE DOSE PER UNIT ELECTRICAL ENERGY GENERATED(man Sv/(GWa)
1975–1979b

8.1

18.3

11.0

6.6

8.2

10.9

b

1980–1984

8.0

18.0

8.0

5.8

8.3

10.4

b

1985–1989

4.3

7.9

6.2

3.2

16.7

5.7

1990–1994

2.8

4.8

3.0

2.0

20.3

3.9

b
b

1995–1999

3.0

3.8

2.4

0.71

2000–2004

1.2

2.2

2.9

0.4

5.3

1.6

3.1

2005–2009

1.0

2.0

2.8

0.3

4.8

1.4

2010–2014

0.75

1.7

3.1

0.1

4.8

1.2

NORMALIZED AVERAGE ANNUAL COLLECTIVE EFFECTIVE DOSE PER REACTOR (man Sv per reactor)
1975–1979b

2.8

5.5

2.6

0.90

3.0

3.1

b

1980–1984

3.3

7.0

2.4

0.84

3.8

3.7

b

1985–1989

2.3

4.0

2.3

0.54

8.7

2.4

b

1990–1994

1.7

2.7

1.1

0.44

9.4

b

1995–1999

2.0

2.6

1.2

0.21

2000–2004

0.86

1.6

1.1

0.09

2.5

1.0

2005–2009

0.72

1.4

1.1

0.10

2.5

0.9

2010–2014

0.53

1.0

1.0

0.05

2.5

0.7

1.9
1.9

The estimates in the periods (2000–2004, 2005–2009 and 2010–2014), are based on the number of operational reactors, energy
generated for each reactor and occupational exposure data for reactors in Lithuania up to 2009. The estimate is highly uncertain.

ab

Values from earlier UNSCEAR reports [U6, U8].

68 UNSCEAR 2020/2021 REPORT

Figure II. Worldwide trends in average annual collective effective dose due to reactor operation, andin normalized average annual collective effective dose per unit electrical energy and per reactor
PWR: Pressurized water reactor; BWR: Boiling water reactors; HWR: Heavy water reactor;
GCR: Gas-cooled reactors; LWGR: Light-water-cooled, graphite-moderated reactor

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 69

Figure III. Worldwide trends in occupational exposure from nuclear power reactors
PWR: Pressurized water reactor; BWR: Boiling water reactors; HWR: Heavy water reactor;
GCR: Gas-cooled reactors; LWGR: Light-water-cooled, graphite-moderated reactor

70 UNSCEAR 2020/2021 REPORT

5.

Decommissioning

218. When a nuclear facility is permanently closed, it must be decommissioned by safely removing itfrom service and reducing the residual content of radioactive material to a level that permits release of
the property and termination of the operating licence. During decommissioning, there is an increase inwork activities that involve occupational exposure. Such activities include decontamination of structuresand components, dismantling of components and demolition of buildings, remediation of any contaminatedground, and removal of the resulting waste.
219. Occupational exposure during decommissioning activities is influenced by several factors, such astype of facility, and operational history. The type of exposure differs from that during the operational phase.
In addition to external exposure, there may also be an increased risk of internal exposure due to radioactive
substances in dust (e.g., demolition). The choice of decommissioning strategy may affect occupational
exposure. Decommissioning of a nuclear facility involves one of three strategies: (a) immediate
dismantling; (b) deferred dismantling after a safe storage period; or (c) entombment of the facility.
220. The immediate dismantling strategy involves the initiation of decommissioning activities shortly
after the permanent cessation of reactor operations. This strategy implies prompt completion of thedecommissioning project (approximately 10 to 20 years) and involves the removal of all radioactive
material from the facility to another (new or existing) licensed facility. Under the deferred dismantling
strategy (sometimes called safe storage, safe store, or safe enclosure), reactor operation ceases, reactor
fuel is unloaded and placed in spent fuel storage pools and the nuclear facility is maintained andmonitored in a condition that allows the radioactivity to decay and with the potential to reduce
occupational exposure. Parts of a facility containing radioactive contaminants are safely stored andmaintained for upwards of 40 to 60 years until they can subsequently be decontaminated to levels that
permit parts of the facility to be dismantled and released for unrestricted use. Under the entombment
strategy, radioactive contaminants are encased in a structurally long-lived material such as concrete untilradioactivity decays to a level permitting the unrestricted release of the facility, or release with restrictions
imposed by the regulatory body.
221. Since decommissioning work activities are conducted, step by step, throughout several years,
exposure of workers may occur at different times during the whole process and will depend on the typeof work conducted. While most occupational exposure comes from external exposure, radioactive dust
may be generated when nuclear reactor facilities are dismantled. If this radioactive dust is inhaled, it will
result in an internal exposure.
222. Assessments presented in table 68 of UNSCEAR 2008 Report [U10], using data from 13 nuclear
power plants in the United States, showed that about 2,000 workers were involved in thedecommissioning process in the period 1995–2002, with an average annual effective dose for measurably
exposed workers of around 2 mSv and an average annual collective dose around 4 man Sv. The data were
not considered sufficient for evaluating the worldwide level of exposure.
223. In UNSCEAR 2016 Report [U12], an assessment of integrated exposure for a wholedecommissioning process for reactors that have been immediately decommissioned is presented. The
exposure was less than 10 man Sv per reactor. Exposure normalized to the total integrated electricity
supplied for each reactor was also assessed for eight of the reactors with an average of 1.8 man Sv per GWa,(table 24 in UNSCEAR 2016 Report, annex B [U12]). Using deferred dismantling or entombment
decommissioning strategies may result in some reduction in the total collective dose per reactor, but there
is insufficient data to support such a conclusion.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 71

224. In the present assessment on occupational exposure during decommissioning in the nuclear fuelcycle, available exposure data from the UNSCEAR Occupational Exposure Survey, the ISOE database,and the assessments in UNSCEAR 2016 Report [U12] conducted as part of radiation exposure fromelectricity generation are used. The data in the UNSCEAR Occupational Exposure Survey do not
distinguish between nuclear facility types whereas the ISOE database contains data fromdecommissioning of power reactors only. The ISOE database for decommissioning of power reactors forthe period 2000 to 2014 is not complete. Numerous annual reports for individual reactors undergoing
decommissioning activities were not submitted to ISOE, either by the utility or the Member State as partof their annual report. Gaps in annual occupational exposure reports cannot be bridged due to uniquedecommissioning tasks and scheduling for each reactor. Consequently, a global estimate of averageannual effective dose and collective effective dose is not projected.
225. Table 22 shows a summary of exposure data for the periods 2000–2004, 2005–2009 and 2010–2014
from both the UNSCEAR Occupational Exposure Survey and from ISOE. The average annual numberof monitored workers reported in the three periods vary between 18,000 and 24,000. The average annual
effective dose to monitored workers has decreased from 0.6 and 0.1 mSv during these periods. The totalcollective doses for the respective periods were 13.77, 3.37 and 3.43 man Sv, where decommissioning
activities in Ukraine in the period 2000–2004 account for 7.84 man Sv. The average annual collective
effective dose per reactor was 0.29 man Sv in the first period and decreased to 0.07 in the last period.
However, it is difficult to draw any conclusions because occupational exposure may differ depending on
the decommissioning activities at any given time for any given reactor. More specific data on
decommissioning of nuclear power reactors are presented in table A.11 in the electronic attachment.
Additional data on average annual collective effective dose for occupational exposure per unit for shut
down reactors by country and reactor type for 2008−2013 were presented in table 23 in annex B of the
UNSCEAR 2016 Report [U12]. While workforce data presented in table A.11 in the electronic attachment
may be representative of the type of activities and exposure for similar scheduled activities, there are nocorrelations between the number of workers, the type of plant being decommissioned, the specific task
undertaken in a particular year or the individual and collective effective exposure received.
226. In 2014, the Fukushima Daiichi nuclear power station entered into decommissioning phase. The
exposure data from this station are excluded from the average occupational exposure fordecommissioning due to the unique conditions compared to standard decommissioning strategies forplanned shutdown reactors.
Table 22. Estimated occupational exposure due to decommissioning from ISOE data
Period

PWR

BWR

HWR

GCR

LWGR

All reactors

Survey a

AVERAGE ANNUAL NUMBER OF MONITORED WORKERS (103)
2000–2004

6.54

4.70

0.79

10.85

22.88

11.3

2005–2009

11.02

3.12

0.18

3.76

18.08

12.0

2010–2014

18.30

6.93

0.56

4.59

23.45

20.7

AVERAGE ANNUAL EFFECTIVE DOSE TO MONITORED WORKERS (mSv)
2000–2004

0.53

0.34

0.17

0.72

0.57

0.45

2005–2009

0.15

0.26

0.23

0.07

0.15

0.35

2010–2014

0.08

0.09

0.06

0.12

0.09

0.39

72 UNSCEAR 2020/2021 REPORT

Period

PWR

BWR

HWR

GCR

LWGR

All reactors

Survey a

AVERAGE ANNUAL COLLECTIVE EFFECTIVE DOSE (man Sv)
2000–2004

3.47

1.78

0.68

7.84

13.77

5.1

2005–2009

1.71

0.84

0.56

0.25

3.37

4.2

2010–2014

1.91

0.84

0.09

0.57

3.43

8.0

0.03

NORMALIZED AVERAGE ANNUAL COLLECTIVE EFFECTIVE DOSE PER REACTOR (man Sv per reactor)a

2000–2004

0.19

0.19

0.04

4.36

0.29

2005–2009

0.07

0.08

0.03

0.25

0.06

2010–2014

0.08

0.05

0.01

0.28

0.07

0.02

Data reported from six countries to the UNSCEAR Occupational Exposure Survey and include the whole nuclear fuel cycle.

6.

Spent fuel reprocessing

227. The principal reason for reprocessing spent fuel from an LWR has been to recover unused uranium
and plutonium in the spent fuel elements. The practice is conducted in only a few countries: France andthe United Kingdom operate commercial-scale facilities, Japan and India have experimental facilities,
and the Russian Federation has been reprocessing spent fuel for reactors developed in that country [U8].
228. Spent fuel assemblies removed from a reactor are highly radioactive and produce heat. They are
therefore put into large spent fuel storage tanks or “ponds” of water, which cool them and, with three
metres of water over the assemblies, shield the radiation they emit. They remain in the spent fuel storage
tanks for a number of years either at the reactor site or at the reprocessing plant, and the level ofradioactivity decreases considerably with time. For most types of spent fuel, reprocessing occurs at any
time from 5 to 25 years after the fuel has been unloaded from the reactor.
229. The used fuel assemblies from LWRs can be dismantled and refabricated into fuel assemblies thatare compatible for use in an HWR reactor. In some instances, depleted uranium may be added to therecovered uranium to attain a natural uranium equivalent fuel with 0.71% 235U. For re-use in an LWR,
the uranium needs to be converted, enriched, and fabricated into new fuel pellets. A significant amountof plutonium recovered from used fuel is currently recycled into mixed oxide fuel. Reprocessing torecover uranium and plutonium avoids wasting a valuable resource, saving some 30% of the naturaluranium that would otherwise be required.
230. Several European countries and others, e.g., China, India, Japan, and the Russian Federation, havepolicies to reprocess used nuclear fuel. The exposure data for spent fuel reprocessing are given intable A.12 in the electronic attachment. Reprocessing in Japan did not restart after the closure of the Tokai
reprocessing plant in 2007 and China had not started any reprocessing during the studied periods. India
and the Russian Federation have not provided any information on the amount of used nuclear fuelreprocessed or the occupational exposure associated with this reprocessing in 25 to 30 years. The IAEA
estimates that the Russian Federation has reprocessed a total of 6,000 tonnes of spent nuclear fuel [I19].
While the United States has reprocessed some used nuclear fuel, none has been from civilian nuclear
power plants. The collected data are, therefore, not representative of worldwide reprocessing activities.
Since the period 1990–1994, the reported number of monitored workers and the average annual collective
dose generally decreased between the successive periods, as evidenced by the countries with complete
data in the UNSCEAR Occupational Exposure Survey. The increase observed for the 1990–1994 period

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 73

is explained by the fact that the information from the Russian Federation is available for only that period.
The average annual effective dose for monitored workers has, in general, decreased since 1980.
231. The estimate for the worldwide level of exposure between 1995 and 2002 in the UNSCEAR 2008
Report [U10] was based on the trends in the data from the reporting countries for earlier periods. The
Committee no longer believe that these extrapolations, leading to substantial increase in the number ofworkers and the average annual collective effective dose for the periods 1995–1999 and 2000–2002, arevalid and, therefore, these estimates have been removed from this annex. Although the reprocessing datafrom France and the United Kingdom, supplemented by data on naval propulsion fuel reprocessing fromthe United States, are believed to be representative for European countries, no attempts to estimate global
values were made. Nevertheless, “total values” for the three periods 2000–2004, 2005–2009 and 2010–2014
are assumed to be reliable enough for inclusion in the worldwide global values for all nuclear activities(table 27). It is clear, as evidenced from the reporting countries, that both incurred radiation doses andstaff numbers show decreasing trends during the studied periods. This is a natural and expected result
due to the closure of older reprocessing facilities, improved radiation protection measures, and a generaldecrease in reprocessing activities.

7.

Nuclear fuel cycle research232. Nuclear research and development are essential for maintaining the safe and efficient operation ofexisting nuclear power plants and fuel cycle facilities, and also for ensuring the emergence of new andinnovative nuclear energy systems. Global research and development efforts are striving to improveuranium resource utilization, maximize energy generation, minimize waste generation, improve safety,
and limit proliferation risk. There has been, however, a significant decline in nuclear research anddevelopment expenditures in recent years, which is reflected in a decrease in the number of monitored
workers conducting nuclear fuel cycle research (table 23).
233. For the Committee’s UNSCEAR 2008 Report [U10] it was difficult to estimate the levels ofoccupational exposure that could unequivocally be attributed to research and development related to thecommercial nuclear fuel cycle. Only few data were available separately for this category; even if this had
not been the case, uncertainties as to their proper interpretation exist. There was considerable variationin the levels of collective dose associated with research activities in each country, reflecting, inter alia,
the relative role of nuclear energy in the national energy supply and the extent to which nuclear
technology was developed domestically or imported. These difficulties remain also for this assessment.
Exposure data between 1975 and 2014 for research in the nuclear fuel sector are shown in tables 23 andA.13 of the electronic attachment. The response to the recent UNSCEAR Occupational Exposure Survey
was lower than in previous surveys.
234. The reported average annual number of monitored workers for the period 2000–2004 is about
33,000. A total of 22,000 workers reported by the United States for the period 2000–2002 and earlier
were conducting general research and most likely not nuclear fuel cycle research, so they are excluded in
the summary of 2000–2004. The reported annual average number of monitored workers is lower for thetwo recent periods compared to all previous periods and reflects a decrease in the number of reporting
countries. The average annual effective dose for monitored workers decreased between the periods
1975–1979 and 1995–1999, from 1.5 to 0.3 mSv. Since then, the average annual effective dose hasremained at the same level of 0.3 mSv per year.
235. The Committee estimated the worldwide level of exposure in its UNSCEAR 2008 Report [U10] on
the basis of the trends in data from reporting countries. The estimated number of monitored workers

74 UNSCEAR 2020/2021 REPORT

decreased by about 25%, from 120,000 in 1990–1994 to 90,000 in 2000–2002, and the estimated averageannual collective effective dose dropped by a factor of four over six periods, from 170 man Sv in
1975–1979 to 36 man Sv in 2000–2002 (table A.13 in the electronic attachment). This decrease was similar
to the reduction in the average annual effective dose from 1.4 to 0.4 mSv during the same periods.
236. An estimation of the worldwide level of exposure in nuclear fuel cycle research for 2003–2014
would not be reliable because of limited data and lack of an appropriate predictive parameter. The averageannual collective effective dose would be based on very few reporting countries. It is unclear whether thedecrease in the number of monitored workers is due to a decrease in activities in nuclear fuel cycle
research, a consequence of less data reporting, or both. From table A.13 in the electronic attachment, some
exposure trends for reporting countries can be identified. In Argentina and France, the average numbersof monitored workers have decreased over the past 40 years with the exception of 2010–2014, where thenumber of monitored workers increased in France. In China and India, the number has increased, while
for the Republic of Korea and Sweden, the number remains at the same level.
Table 23. Data on occupational exposure in nuclear fuel cycle research reported to UNSCEAR Survey
Number ofreportingcountries

Average annual
number of monitored
workers (103)

Average annual
collective effective
dose (man Sv)

Average annual effective
dose for monitored
workers (mSv)

1975–1979a

13

63.4

96.3

1.5

1980–1984a

15

75.5

89.4

1.2

1985–1989a

15

82.6

66.0

0.80

a

1990–1994

15

46.3

35.9

0.77

1995–1999a

13

48.3

14.6

0.30

2000–2004b

18

32.9

10.7

0.33

2005–2009

8

5.1

2.3

0.45

2010–2014

11

14.7

4.3

0.29

Years

a

Values from earlier UNSCEAR reports [U3, U4, U6, U8, U10].

b

Twelve countries reported data for 2000–2002, four countries for 2003–2004 and two countries for the whole period 2000–2004.

8.

Radioactive waste management237. Radioactive waste is produced at all stages of the nuclear fuel cycle. It is classified as low-,intermediate- and high-level waste [U10]:(a) Low-level waste includes paper, rags, tools, clothing, filters, which contain small amounts ofmostly short-lived radioactive material. In order to reduce its volume, it is often compacted orincinerated (in a closed system) before disposal. Worldwide it makes up 90% of the volume but only
1% of the radioactivity of all radioactive waste;(b) Intermediate-level waste contains larger amounts of radioactive material and handling may
require special shielding. It typically includes resins, chemical sludges and reactor components, andcontaminated material from reactor decommissioning. Worldwide it makes up 7% of the volume and
4% of the radioactivity of all radioactive waste;

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 75(c) High-level waste may be the spent fuel itself or the principal waste from its reprocessing. While
making up only 3% of the volume of all radioactive waste, it contains 95% of the radioactive
material. It includes highly radioactive fission products and some heavy elements with long-lived
radioactivity. It generates a considerable amount of decay heat and requires cooling and also special
shielding during storage, handling and transport. If the spent fuel is reprocessed, the separated waste
is vitrified by incorporating it into borosilicate glass which is sealed inside stainless-steel canisters
for eventual disposal deep underground. On the other hand, if spent reactor fuel is not reprocessed,
all the highly radioactive isotopes remain in it, and so the whole fuel assemblies are treated as highlevel waste. This spent fuel takes up about nine times the volume of the vitrified high-level wastethat would result from reprocessing and encapsulating an equivalent amount of spent fuel, which isthen ready for disposal.
238. The doses incurred by personnel managing radioactive waste depend on the scope of the activities
performed. The average annual effective dose for workers involved in the safe management of spent fuelis in the range 0.2–11 mSv. The level of exposure is lower for workers involved in radioactive waste
management (disposal), where the average annual effective dose is in the range 0.2–3 mSv [U10]. Elevencountries responded to the UNSCEAR Occupational Exposure Survey with information for waste
management workers monitored from 2003 to 2014. Summary data from the survey and the UNSCEAR
2008 Report [U10] is presented in table 24. The number of monitored waste management workers
increased from about 8,950 in the 2000–2004 period to 13,470 in the 2005–2009 period to 16,440 in the
2010–2014 period. The average annual collective effective dose also increased during each of these three
periods. The average annual effective dose associated with radioactive waste management for all
monitored workers decreased slightly from the 2000–2004 period to the 2010–2014 period. The averageannual effective dose for measurably exposed workers, however, increased slightly between the two
periods. The total reported values for radioactive waste management for the three periods 2000–2004,
2005–2009 and 2010–2014 are assumed to be reliable enough for inclusion in the worldwide global
values for all nuclear activities (table 27), but they are not regarded as either representative or inclusive(e.g., legacy sites, storage of spent nuclear fuel, or decommissioning waste) of all the activities associatedwith the nuclear fuel cycle sector.
Table 24. Data on occupational exposure due to nuclear fuel cycle radioactive waste management
reported to UNSCEAR SurveyCountry

China

Czechia

FranceMeasurably
exposedworkers(103)

Average annual effective
dose (mSv)

Average annual
collective
effective dose(man Sv)

Monitored
workers

Period a

Monitored
workers(103)

2003–2004

1 059

1 942

1.84

2005–2009

1 831

1 870

1.02

2010–2014

2 437

2 390

0.98

2003–2004

7

2.5

1

0.21

0.58

2005–2009

14

9.6

30

2.21

3.22

2010–2014

61

30

20

0.31

0.63

2010–2014

64

2.7

0

0.01

0.14

Measurably
exposedworkers

76 UNSCEAR 2020/2021 REPORTCountry

Germany

India

PolandSpain

SwedenSwitzerland

UnitedKingdom

United States

Total reported

Average annual effective
dose (mSv)

Period a

Monitored
workers(103)

Measurably
exposedworkers(103)

Average annual
collective
effective dose(man Sv)

Monitored
workers

Measurably
exposedworkers

2003–2004

613

132

86

0.14

0.66

2005–2009

621

84

110

0.17

1.26

2010–2014

998

94

130

0.13

1.43

2010–2014

1 493

638

680

0.45

1.07

2003–2004

48

44

27

0.56

0.61

2005–2009

46

24

20

0.33

0.62

2010–2014

49

23

10

0.25

0.53

2003–2004

252

34

16

0.07

0.48

2005–2009

215

28

10

0.04

0.30

2010–2014

220

14

4.4

0.02

0.31

2003–2004

526

100

95

0.18

0.95

2005–2009

723

104

110

0.15

1.06

2010–2014

1 194

123

200

0.17

1.64

2003–2004

51

15

3

0.05

0.17

2005–2009

91

27

20

0.21

0.70

2010–2014

141

30

20

0.12

0.55

2000–2004

460

160

0.35

2005–2009

1 660

860

0.52

2010–2014

1 966

690

0.35

2000–2004

5 930

1 940

1 220

0.20

0.63

2005–2009

8 272

2 634

1 660

0.20

0.63

2010–2014

7 819

2 367

1 900

0.24

0.80

2000–2004

8 950

2 270

3 550

0.40

0,64

2005–200913 470

2 910

4 690

0.35

0.67

2010–201416 440

3 320

6 040

0.37

0.89

The period 2000–2004 includes data from United Kingdom and United States for the period 2000–2002, taken from table 71,
UNSCEAR 2008 Report [U10] and reported data for the period 2003–2004. Data from all other countries for the period 2000–2004
contain reported data for the period 2003–2004 only.

aANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 77

9.

Transport within nuclear fuel cycle

239. The significant majority – about 95% – of radioactive consignments are not related to nuclear power
generation. As one example, Canada transports about one million packages of radioactive material eachyear [N11]. Transport is an integral part of the nuclear fuel cycle; from the transport of uranium ore to aconversion and enrichment facility to the disposal of spent fuel and components from a decommissioned
nuclear power plant. Most material used in nuclear fuel cycle is transported several times during its
progress through the cycle. Transport of radioactive sources outside the nuclear fuel cycle is discussed in
section IV.E.3.
240. Many countries have experience transporting nuclear fuel cycle material. In the United States,
nearly 3,000 shipments of commercially used fuel have been moved over 2.5 million kilometres in thepast 40 years, mostly over roads and some by rail. The United Kingdom and France transport a combined
average of 550 shipments of high-level radioactive waste every year, primarily by rail. Sweden makes
approximately 40 shipments per year, while Japan has made around 200 shipments per year [N11].
241. Workers who transport radioactive material include equipment operators and truck drivers. The
radiation exposure that these workers receive is generally very low (<1 mSv); hence, they are treated as
members of the public, i.e., with regard to the system regulating exposure to ionizing radiation. A French
report on occupational exposure found that the average annual effective dose to transportation workers
was 0.1 mSv for 1,002 monitored workers and 0.32 mSv for 310 measurably exposed workers [F4]. A
review of the annual occupational exposure reports published by the United States Department of Energy
found that monitored workers responsible for the movement and transportation of radioactive material
received average annual effective doses of less than 0.1 mSv (table 25). Approximately 10 to 15% of
these workers, however, received measurable exposure and their average annual effective doses gradually
increased from 0.4 mSv for the 2000–2004 period to 0.9 mSv for the 2015–2018 period [M8, M9].
242. Only few countries have provided occupational exposure information for transport in the nuclear
fuel sector in the UNSCEAR Occupational Exposure Survey. The average annual effective dose formeasurably exposed workers is in the range of 0.3–0.7 mSv, which is in agreement with the data reported
from the United States (table 25). While the data are informative, they are dominated by activities at theUnited States Department of Energy for the three periods in 2000–2014 and, thus, are not representativeof worldwide occupational exposure in transport within the nuclear fuel cycle. These data are not includedin the worldwide assessment of average annual exposure due to the nuclear fuel cycle.

78 UNSCEAR 2020/2021 REPORT

Table 25. Data on occupational exposure in transport within nuclear fuel cycle reported to UNSCEAR
SurveyCountry

China
FranceUnitedKingdom

UnitedStates aa

Averageannualcollective
dose(man Sv)

Average annual effective dose(mSv)

PeriodMonitored
workers(103)

2005–2009

44

32

0.7

2010–2014

84

38

0.4

2010–2014

896

234

94

0.1

0.4

2003–2004

7

7

3

0.4

0.4

2005–2009

18

18

5

0.3

0.3

2010–2012

24

24

10

0.4

0.4

2000–2004

1 323

200

85

0.06

0.4

2005–2009

1 823

254

140

0.08

0.5

2010–2014

1 514

179

147

0.1

0.8

2015–2018

1 038

124

90

0.09

0.9

Measurably
exposedworkers (103)

Monitored
workers

Measurably
exposedworkers

Data from annual reports of United States Department of Energy [M8, M9].

10. Safety and safeguards inspections
243. Occupational exposure also occurs for workers taking part in safety and safeguards inspections.
Such activities are conducted by regional and national authorities in Member States and by the IAEA.
Information on exposure within this subsector was introduced as part of the present UNSCEAR
Occupational Exposure Survey and just a few countries provided data. The number of monitored workers
in Germany was about 2,600, in the Republic of Korea 200–300, in Algeria 200–300, and in Czechia
20–30. About 10–20% of monitored workers were classified as measurably exposed. The average annual
effective dose for monitored workers was less than 0.3 mSv.

11. Other work categories in nuclear fuel sector
244. Exposure data for workers in the nuclear fuel sector not related to the above work categories andreported in the UNSCEAR Occupational Exposure Survey are summarized in table 26. The United
Kingdom reported an average annual collective dose between 4 and 6 man Sv, the United States about
2–3 man Sv and Czechia about 0.3 man Sv. India and China reported about 1 man Sv for the period
2010–2014. France reported an annual collective dose of about 16 man Sv for this category of workers.
With regard to the French data, reported by the Institute for Radiological Protection and Nuclear Safetyfor 2011, additional subsectors are used, e.g., logistics and maintenance (contractors), outfitting, nuclear
propulsion, and others [F4]. For the reported monitored workers in the period 2010–2014, about 54,000,
an average collective dose of 24.1 man Sv was reported, which gives an average annual effective dose of
0.4 mSv but with large variations between the reporting (0.1–1.9) countries.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 79

Table 26. Data on occupational exposure in work categories in nuclear fuel cycle not included in
specific subsectors and reported to UNSCEAR Survey
Averageannualcollective
dose(man Sv)

Average annual effective dose(mSv)

PeriodMonitored
workers(103)

2005–2009

0.44

0.32

0.72

2010–2014

0.66

0.83

1.26

2003–2004

0.14

0.12

0.30

2.12

2.54

2005–2009

0.15

0.12

0.29

2.02

2.39

2010–2014

0.14

0.11

0.27

1.93

2.50

2005–2009

30.3

9.55

16.0

0.53

1.67

2010–2014

31.3

10.15

15.5

0.50

1.53

India

2011–2014

0.97

0.69

1.30

1.33

1.89

Slovenia

2010–2014

0.023

0.023

0.04

1.54

1.54

2003–2004

8.24

8.18

5.81

0.71

0.71

2005–2009

7.25

7.24

5.67

0.78

0.78

2010–2014

6.46

6.46

4.24

0.66

0.66

2003–2004

17.0

3.16

3.01

0.18

0.95

2005–2009

13.6

2.29

1.74

0.13

0.76

2010–2014

14.5

2.48

1.92

0.13

0.78

Country

China

Czechia

FranceUnitedKingdom

UnitedStatesMeasurably
exposedworkers (103)

Monitored
workers

Measurably
exposedworkers

12. Summary
245. The trends in worldwide occupational exposure arising from each stage of the commercial nuclear
fuel cycle are summarized in table 27. The displayed data constitute annual averages over five-year
periods. For the period 2000–2004, averages are calculated on the basis of data (2000–2002) from the
UNSCEAR 2008 Report and data (2003–2004) in the recent UNSCEAR Occupational Exposure Survey.
Both uranium production and the related average annual collective effective dose increased during thethree studied periods. The uranium enrichment data include somewhat larger uncertainties. Occupational
exposure associated with fuel fabrication is little changed. Reactor operation is the main source of thenumber of workers and incurred radiation doses in the nuclear fuel cycle. Although the average numberof workers increased, both the average annual effective dose and the average annual collective effective
doses decreased over the three most recent periods. Decommissioning, spent fuel reprocessing, researchin nuclear fuel cycle, radioactive waste management, transport of fuel, and safety and safeguards
inspection all had a less impact on the overall exposure in the nuclear fuel cycle.

80 UNSCEAR 2020/2021 REPORT

Table 27. Estimated worldwide levels of annual exposure due to nuclear fuel cycle a

Practice/work sector

Monitored
workers (103)

Average annual
collective effective
dose (man Sv)

Average annual
collective effective
dose per unit energy
generated(man Sv/GWa)

Average annual
effective dose tomonitored
workers (mSv)

0.5

2.7

2000–2004
Mining

28

77

Enrichment

18

1.8

0.1

Fuel fabrication

23

26

0.1

1.2

Reactor operation b

501

461

1.6

0.9

Reprocessing c

16

7.9

0.5

23

14

0.6

c

33

11

0.3

Radioactive waste
management c

9

3.6

0.4

Total d,e

652

602

Decommissioning
Research

c

2.2

0.9

0.4

2.5

2005–2009
Mining

33

82

Enrichment

8

1.2

0.1

Fuel fabrication

21

19

0.1

0.9

Reactor operation b

555

409

1.4

0.7

Reprocessing c

6

1.9

0.3

18

3.4

0.2

c

5

2.3

0.4

Radioactive waste
management c

13

4.7

0.4

Total d,e

660

523

Decommissioning
Research

c

1.8

0.8

0.5

2.8

2010–2014
Mining

44

123

Enrichment

10

1.2

Fuel fabrication

20

17

0.1

0.9

Reactor operation b

627

328

1.2

0.5

Reprocessing c

6

1.4

0.2

23

3.4

0.1

c

15

4.3

0.3

Radioactive waste
management c

16

6.1

0.4

Total d,e

762

483

Decommissioning
Research

a
b
c
d
e

0.1

c

1.7

0.6

Data are annual values averaged over the indicated periods.
Does not include data for FBRs and HTGRs.
Numbers represent the total collected data.
Totals are presented to illustrate trends and do not reflect true values.
Data from IAEA PRIS database [I7] are used to estimate average annual collective effective dose per unit energy generated.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 81

246. The number of workers increased during the recent three periods, due to an increase in both nuclear
power reactor operation and uranium mining. Reactor operation is the dominant sector with regard to thenumber of monitored workers and accounts for about 627,000 in the recent period, which corresponds toabout 80% of the estimated total. Mining accounts for about 44,000 and fuel fabrication for about 20,000.
The estimated average annual number of workers is based on both collected good quality data (uranium
mining and milling, fuel fabrication and reactor operation) but also data that contain different levels of
uncertainty. Therefore, all total estimates should be treated with caution, and are best used to compare
trends within the different subsectors. National procedures for the recording and inclusion of doses
incurred by transient or contract workers during reactor refuelling and maintenance activities cansignificantly influence the annual statistics (e.g., number of monitored workers and average annual
effective dose) reported for operational reactors. Some, but not all, respondents to the UNSCEAR
Occupational Exposure Survey adjusted their annual statistics to account for itinerant workers and theiroccupational exposure.
247. The estimated worldwide number of monitored workers in the nuclear fuel cycle for the period
2010–2014 is 0.76 million, and the estimated average annual effective dose is 0.6 mSv. The averageannual collective effective dose is estimated at about 483 man Sv in the most recent period, which
represents a decrease of about 100 man Sv during the three reported periods. The main reason for thedecreasing trend is the decrease in exposure in reactor operation.
248. The average annual effective dose received by monitored workers in the nuclear fuel cycle, which
was estimated to 4.4 mSv in the first period (1975–1979), has since then continually decreased and isestimated as 0.9, 0.8 and 0.6 mSv, respectively during the three recent periods. However, there are large
variations in these averages depending on activity type in the nuclear fuel cycle, e.g., in reactor operation
the average annual effective dose decreased from 0.9 to 0.5 mSv during the three reported periods,
whereas in mining and milling operations the average annual effective dose varied between 2.5 and 2.8 mSv.
249. The UNSCEAR Occupational Exposure Survey also include exposure data (from 20 countries) for
the total nuclear fuel sector. The survey shows a 17% increase in average annual number of monitored
workers between the periods 2000–2004 and 2010–2014. Moreover, the average annual effective dose
estimated from the survey data shows a decrease from 0.9 to 0.6 mSv during the same periods.
250. The estimated worldwide levels of average annual collective effective dose are fairly certain formuch of the nuclear fuel cycle. Data for operating nuclear reactors are essentially complete for LWRs,
HWRs, and GCRs. Estimates for LWGRs are based on the number of operational reactors, the averageannual energy generated for each reactor, and historical data obtained for Lithuania’s operational
LWGRs. This later estimate is based on expert judgment and is highly uncertain. Nevertheless, thenumber of workers and the occupational exposure associated with operating reactors account for the vast
majority of data collected for the nuclear fuel cycle. Similarly, the data collected are essentially complete
for fuel enrichment, fuel fabrication, and reprocessing. Uncertainties associated with uranium mining will
improve with increased environmental monitoring, especially at ISL sites. While the underreporting anduncertainties associated with decommissioning, research activities, and radioactive waste management
may be considerable, the number of workers and their associated individual and collective doses are small
relative to the rest of the nuclear fuel cycle. The global number of nuclear fuel cycle workers, and theirindividual and collective doses, could be underestimated by as much as 10%.

82 UNSCEAR 2020/2021 REPORT

B. Medical uses of radiation
251. Radiation and radioactive sources are used in medicine for both diagnostic and therapeutic
purposes. Medical uses of radiation increase yearly as the benefits of procedures become more widely
disseminated. The wide range of applications, procedures and techniques used in the context of patient
exposure are described in the Committee’s recent evaluation of medical exposure from ionizing radiation[U15], which also discusses changes in practice and current trends. Usually, medical staff (physicians,
technicians, nurses, medical physicists, technologists and other personnel) constitute the largest group of
workers exposed to human-made sources of ionizing radiation. The exposure of those who support or
comfort patients undergoing radiation treatment or diagnostic procedure, often referred to as “carers andcomforters” [I12], is considered to be medical exposure and is not considered in this annex.
252. The Committee evaluated occupational exposure for each practice, using average values for all
workers over five-year periods without previously highlighting the influences of job function and medical
procedure on staff exposure. Providing relevant information on occupational exposure related to thedifferent practices by identifying job functions and categories of work within each practice was one of
the tasks the Committee was facing. It covered the estimation of effective doses and equivalent doses tohands and to the lens of the eye. However, the insufficient data provided by countries to the UNSCEAR
Occupational Exposure Survey burdened many of the estimated values with a large uncertainty. The
contribution of female workers in the medical sector was also assessed.
253. The estimate of worldwide average annual effective doses is based on data from the UNSCEAR
Occupational Exposure Survey and supplemented by data from the literature. For this analysis, it was
assumed that the dosimetry had used the right algorithm to calculate the effective dose. The design anduse of lead aprons were considered: i.e., dosimeter position, in particular whether the dosimeters were
worn outside the apron or under it, or whether one dosimeter was worn under the apron and a second
worn outside it. For the assessment of the doses to hands and to lens of the eye, it was assumed that thesewere estimated using the appropriate dosimeter and appropriate evaluation algorithms and procedures.
Data for the UNSCEAR Occupational Exposure Survey involved in the different subsectors of medical
uses of radiation are presented in tables A.14 to A.19 of the electronic attachment.

1.

Diagnostic radiology

254. Diagnostic radiology refers to the analysis of images obtained using predominately X-rays andincludes conventional diagnostic radiology and computed tomography. Diagnostic examinations with
X-rays have been used in medicine for over a century, with increasing sophistication and new techniques.
255. Exposure data from the UNSCEAR Occupational Exposure Survey (2003–2004, 2005–2009,2010–2014) in diagnostic radiology are given in table A.14 in the electronic attachment. Twenty-fourcountries responded to the survey within the period 2003–2014, which represents about 12% of theworldwide number of countries. The data provided in the UNSCEAR 2008 Report [U10] for 2000–2002
were added to the new survey data for the period 2003–2004 to form the broader period 2000–2004. On
the basis of the reported data, female workers constitute about 60% of the workforce (table A.15 in theelectronic attachment); however, the variation in this percentage between the few countries that reported
data is high.
256. In general, the Committee is evaluating diagnostic radiology, which includes conventional
diagnostic radiology and interventional radiology, as one pooled subsector. Although the UNSCEAR
Occupational Exposure Survey enabled data to be separately reported, most national databases still

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 83

combine data from conventional and interventional radiology. It is well known that occupational
exposure to conventional diagnostic radiology is significantly lower than to interventional radiology; thisis because interventions require the operator and assisting personnel to remain close to the patient andthus close to the primary beam of radiation. However, there are limitations in the analysis because very
few countries provided specific data for each one of these subsectors. Only 14 countries provided data
separately for conventional diagnostic radiology and 13 countries for interventional radiology. Becauseof the smaller sample of data compared to those 24 countries that provided pooled data, and also in orderto evaluate the worldwide trend of occupational exposure, the analysis of occupational exposure in
diagnostic radiology did not separate data from conventional and interventional radiology in thisevaluation. There is a wide variation in the average annual effective dose and percentage of measurably
exposed workers to monitored workers. These observed variations may be explained by many factors,
including the way data are recorded in national databases, the mixture of procedures performed by
medical staff, and differing protective measures implemented by each country.
257. Due to scattered radiation, the doses to the hands and lens of the eyes for interventional radiology
operators can potentially be very high. Only three countries provided data on equivalent doses for lens of
the eye, for which the recorded average annual equivalent doses were less than 4.4 mSv. Seven countries
provided data on equivalent doses to the hands; the recorded average annual equivalent doses vary
between 1 and 37 mSv. The detailed data provided are presented in table A.15 in the electronic attachment.
258. Occupational exposure data on diagnostic radiology obtained from the literature review were used
to supplement the data obtained from the UNSCEAR Occupational Exposure Survey. Three countries
have published data related to national surveys: Bosnia and Herzegovina, Ghana and Pakistan (table 28).
These data were also used in the estimation of the worldwide exposure.
Table 28. Occupational exposure data for diagnostic radiology obtained from the literature
Number ofmeasurably
exposedworkers(103)

Averageannualcollective
effectivedose(man Sv)Country

PeriodNumber ofmonitored
workers(103)

Bosnia andHerzegovina

1999–2003

0.824

0.484

2004–2008

1.156

0.721

Ghana

2008–2009

Pakistan

2003–2007

Average annual effective
dose (mSv)
Monitored
workers

Measurably
exposedworkers

Reference

1.3

1.6

2.4

[B4]

1.9

1.6

2.3

[B4]

0.278

0.12

0.42

[A2]

1.432

2.1

1.5

[J1]

259. The worldwide number of monitored workers is estimated on the basis of the methodology
described in section II.E.1. The number of workers involved in diagnostic radiology is estimated to beabout 8 million for the period 2010–2014. The total estimate is derived from the sum of estimatednumbers of workers in job categories of physicians, nurses, and technicians. Another job category called“others” consists of the job categories not mentioned above. The workforce of “others” was not includedin the sum due to its high uncertainty, which likely results in an underestimation of the number of workers
in diagnostic radiology. The worldwide estimate for the periods 2000–2004 and 2005–2009 were notderived because of limited data and lack of reliable correlation between the number of workers and thepredictor parameters used to derive the mathematical models. The worldwide occupational exposure data
in diagnostic radiology are presented in table 29. The estimate number of monitored workers has
increased over time, from 0.6 million (1975–1979) to more than 8 million (2010–2014). The uncertainty
interval for the worldwide number of workers ranges from 3.9 to 14 million. The UNSCEAR 2008 Report84 UNSCEAR 2020/2021 REPORT[U10] presented a workforce increase by a factor of seven from 1990–1994 to 1995–1999. The significant
increase of workforce is a result of a more reliable estimate based on data from the World HealthOrganization. Although the workforce for 2010–2014 is underestimated, the uncertainty interval accounts
for that underestimation. The worldwide estimated average annual effective dose for monitored workers
is the average annual effective dose weighted by the number of workers of each country that provided
average annual effective dose data (0.2 mSv), which is estimated as 0.4 mSv for the 2010–2014 period.
The uncertainty interval for the worldwide average annual effective dose ranges from 0.2 to 0.8 mSv.
There is a slight reduction to the average annual effective dose for monitored workers of 0.5 mSv(1994–1999) and an important decrease from 0.9 mSv (1975–1979). The estimated average annual
collective effective dose for the 2010–2014 period is 3,200 man Sv, which is slightly lower compared tothe period 1995–1999. The average annual collective effective dose increased substantially from 600 to
3,200 man Sv over the 40-years period of analysis.
Table 29. Estimated worldwide levels of occupational exposure in diagnostic radiology

PeriodMonitored
workers(103)

Measurably
exposedworkers(103)

Average annual effective dose(mSv)

Average annual
collective effective
dose(man Sv)

Monitored
workers

1975–1979a

630

600

0.9

a

1980–1984

1 060

720

0.7

1985–1989a

1 350

760

0.6

1990–1994a

950

470

0.5

a

1995–1999

6 670

3 335

0.5

2010–2014

8 000

3 200

0.4

350

b

a

Values from earlier UNSCEAR reports [U3, U4, U6, U8, U10].

b

No worldwide estimation was possible because of limited data or no reliable data.

Measurably
exposed workers

1.3

b260. The Committee has evaluated occupational exposure for various job categories within the field of
diagnostic radiology (for conventional and interventional radiology pooled together): physicians, nurses,
technicians, other job categories in this subsector. The limited data provided by the countries that
responded to the UNSCEAR Occupational Exposure Survey resulted in lack of statistically significant
correlation between the data and the predictor parameters. The majority of countries presented data for
the workforce in conventional and interventional radiology only. Out of the 33 countries which provided
occupational exposure data for different job categories, as presented in table A.16 in the electronic
attachment, 13 provided summarized data for all job categories. The size of the workforce for different
job categories were unfortunately the only reliable estimates that could be established. The data for theperiods 2000–2004 and 2005–2009 have not been used due to lack of reliable correlation between theavailable data and the predictor parameters used to derive the mathematical models. The numbers ofmonitored physicians and nurses for the period 2010–2014 are 0.5 and 0.6 million, respectively. The
number of monitored technicians for the same period is about 6 million. Physicians and nurses represent
about 10% of the estimated workforce each and technicians represent about 80% (“others” job category
is not included in the total estimate).

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 85(a) Conventional diagnostic radiology and computed tomography
261. Conventional X-ray examination involves static imaging; the various techniques applied(radiography, mammography and bone densitometry) and computer tomography are described in detailin UNSCEAR 2020/2021 Report, annex A [U15]. For radiography, which is the most widely used X-ray
application, the average doses depend on the equipment used. For computer tomography, occupationaldoses are generally very low, and the technique does not represent a significant source of occupational
exposure. For mammography, the doses are generally similar to those in computer tomography. In
general, the techniques used in conventional diagnostic radiography do not represent a major influenceon the level of occupational exposure.
262. Exposure data from the UNSCEAR Occupational Exposure Survey (2003–2004, 2005–2009,2010–2014) on occupational exposure in conventional diagnostic radiology are given in table A.14 in theelectronic attachment. Fourteen countries have responded to the survey for the period 2003–2014, which
represents about 7% of the worldwide number of countries. The data provided in the UNSCEAR 2008
Report [U10] for 2000–2002 were added to the survey for the period 2003–2004 to form the broader
period 2000–2004. Female workers represent about 65% of the workforce.
263. The equivalent doses to the lens of the eye and to the hands are evaluated for workers carrying out
conventional diagnostic radiology procedures. Only two countries have provided data on average annual
equivalent dose to the lens of the eye; the recorded doses vary from 1.7 to 1.9 mSv. Four countries
provided data on the average annual equivalent dose to the extremities (hands); the measurable dosesvary from 0.5 to 27 mSv. The data are presented in table A.15 in the electronic attachment. The fact thatvery few countries provided data on average annual equivalent doses to the lens of the eye and to thehands results in a poor reliability of any attempt at deriving global dose estimates. However, the available
literature data support the values of the UNSCEAR Occupational Exposure Survey [H7, O2, S19].
264. Occupational exposure data for conventional diagnostic radiology obtained from the literature
review have been used to supplement the data obtained from the UNSCEAR Occupational Exposure
Survey. Basić et al. [B4] published national survey data for Bosnia and Herzegovina on occupational
exposure for conventional diagnostic radiology (table 30). The data were also used in the estimation of
the worldwide occupational exposure.
265. The worldwide number of monitored workers is estimated on the basis of the methodology
described in section II.E.1. The worldwide estimates were performed only for the 2010–2014 forconventional diagnostic radiology, which was due to the limited data and also due to the lack ofcorrelation of the available data and the predictor parameters for the other periods (2000–2004 and 2005–2009). The number of workers involved in conventional diagnostic radiology is estimated to be about
8 million for the period 2010–2014. The uncertainty interval for the worldwide number of workers ranges
from 4.0 to 15 million. The average annual effective dose for monitored workers is the average annual
effective dose weighted by the number of workers of each country that responded to the UNSCEAR
Occupational Exposure Survey, which is estimated as 0.4 mSv. The uncertainty interval for theworldwide average annual effective dose ranges from 0.2 to 0.8 mSv.

86 UNSCEAR 2020/2021 REPORT

Table 30. Occupational exposure data for conventional diagnostic radiology in Bosnia andHerzegovina [B4]
Number ofmonitored
workers (103)

Number ofmeasurably
exposed workers(103)

Average annual
collective effective
dose (man Sv)

1999–2003

0.773

0.447

2004–2008

1.070

0.667

PeriodAverage annual effective dose(mSv)
Monitored
workers

Measurably
exposed workers

1.1

1.5

2.3

1.7

1.6

2.3

(b) Interventional radiology
266. Interventional radiology is the use of X-ray imaging techniques to facilitate the introduction andguidance of devices in the body for diagnostic or treatment purposes [E8]. Such procedures may be
performed also by clinicians other than radiologists, such as cardiologists, orthopaedists,
gastroenterologists, urologists and vascular operators.
267. The radiation exposure of staff can be attributed to the type and complexity of procedure, radiation
protection barriers, staff experience, radiological equipment used, and workload. Knowledge of thesevarious parameters and their effect on scatter radiation levels can help to understand the fluctuation of
the average doses between countries, such as effect of the collimation of the beam, of detector distance,of height of table, of magnification, and of the position of the X-ray tube (above or below the table) [H3,
I39, P4, P5].
268. Currently, several radiation protection measures are implemented on a regular basis worldwide,e.g., radiation protection barriers, spectral filtration, pulsed fluoroscopy, low frame rates, and X-ray
systems with dose reduction post-processing algorithms [I31, I49, K6, K10, M6]. The implementation ofsuch radiation protection measures results in a reduction of exposure for operators at interventional
theatres. Also, it explains the trend of dose reduction and the large variation of doses between countries
or even between medical facilities in the same country.
269. A worldwide evaluation of radiological protection in interventional cardiology carried out by the
IAEA using the Information System on Occupational Exposure in Medicine, Industry and Research(ISEMIR) showed that there was a large difference in radiological protection policies between countries.
Of the 191 regulatory bodies contacted, only 81 replied. Some noteworthy results are: (a) just over 50%of the regulatory bodies mandate radiological protection training for personnel in order to be able toperform interventional cardiology procedures; (b) there is a spectrum of radiation protection licensing
systems in use throughout the world, ranging from the physician not needing a licence to use radiation ininterventional cardiology to the physician needing such a licence; (c) many regulatory bodies have limitedaccess to these data and, even if they do have access, the data are often not detailed enough to provide
the required information; and (d) a further complicating factor, namely that recorded doses may
underestimate true occupational exposure because compliance by interventional cardiology personnel
can be poor and because an individual’s exposure from different intervention cardiology facilities may
not be summed [I9, P1].
270. Exposure data from the UNSCEAR Occupational Exposure Survey (2003–2004, 2005–2009,2010–2014) on occupational exposure for interventional radiology are given in table A.14 in the electronic
attachment. Thirteen countries responded to the survey for the years 2003–2014. The data provided in the

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 87

UNSCEAR 2008 Report [U10] for 2000–2002 were added to the survey for the period 2003–2004 toform the broader period 2000–2004. Female workers represent about 55% of the workforce.
271. The equivalent doses to the lens of the eye and hands are evaluated for workers carrying out
interventional radiology procedures. Only one country provided data for the lens of the eye; the averageannual equivalent dose was 7 mSv. Four countries provided data on equivalent dose to extremities (skinof the hands) ranging between 0.7 and 37 mSv. The respective data are presented in table A.15 in theelectronic attachment. The available literature data support the survey’s values. An investigation in Poland
showed that for a three-month evaluation of equivalent doses to the hands and to the lens of the eye, 87%of these were lower than 0.1 mSv and only 0.03% of the recorded doses were higher than the annual dose
limit of 500 mSv. The same study showed that only 32% of the recorded equivalent doses to the lens ofeye were lower than 0.1 mSv and about 5% of the doses were higher than 5 mSv, which may indicatethat it is likely that a number of annual equivalent doses to the lens of eye may exceed the value of 20 mSv[S19]. Another study concluded that the annual median equivalent dose to the lens of eye in computer
tomography guided interventions did not exceed 20 mSv assuming 50 to 200 computer tomography
guided intervention procedures per year [H7]. These and additional data indicate that the equivalent doseto the lens of the eye has the potential to exceed 20 mSv per year in specific interventional procedures
and working conditions, in particular for interventional radiologists and cardiologists [O2].
272. Equivalent doses to the lens of the eye of urologists during interventional procedures have been
compared with values measured during interventional radiology, cardiology, and vascular surgery. The
measurements were taken in a surgical theatre using a mobile C-arm system and electronic personal
dosimeters (worn over the lead apron). Measurements were collected during 34 urology interventions(nephrolithotomies). The median values of the effective doses (in terms of Hp(10)) measured over theapron were 393 μSv/procedure for urologists and 21 μSv/procedure for nurses. The 3rd quartile of therecorded values was 848 μSv/procedure for urologists and 39 μSv/procedure for nurses. Median valuesof over-apron dose per procedure for urologists were 19 times higher than those measured for radiologists
and cardiologists working with proper protection (using ceiling suspended screens) in catheterization
departments [V6].
273. An evaluation of equivalent doses to the lens of the eye for staff in an interventional cardiology
department in Spain showed that doses for physicians ranged between 8 and 60 mSv, for a workload of
200 procedures per year. Lower doses were collected for nurses, with estimated annual equivalent doses
to the lens of the eye (in terms of Hp(3)) between 2 and 4 mSv [P10]. Effective doses from fiveinterventional cardiology centres in Spain were collected in the national registry programme of the
Spanish Society of Cardiology. Measurements were performed over the apron at a chest level using
electronic dosimeters. An average effective dose (in terms of Hp(10)) of 46 μSv/procedure was estimatedfor cardiologists. Lower doses were noted in other professionals such as assistant cardiologists, nurses,
or anaesthetists. Procedures for valvular and other structural heart diseases involved the highest
occupational doses, averaging over 100 μSv/procedure. The new limit for the occupational equivalentdose for the lens of the eye (20 mSv) is likely to be exceeded by those interventionalists who do not use
protection tools (e.g., ceiling suspended screen, goggles) even with standard workloads [S6].
274. The worldwide number of monitored workers is evaluated on the basis of the methodology
described in section II.E.1. The estimated number of monitored workers for interventional radiology is
about 0.8 million for 2010–2014, which is about 10% of the estimated number of workers involved inconventional diagnostic radiology. The uncertainty interval for the worldwide number of workers ranges
from 0.4 to 1.3 million.
275. The average annual effective dose for monitored workers is calculated as the reported averageannual effective dose weighted by the number of monitored workers for each country that responded to88 UNSCEAR 2020/2021 REPORTthe UNSCEAR Occupational Exposure Survey, which is estimated as 0.6 mSv. The uncertainty interval
for the worldwide average annual effective dose ranges from 0.3 to 1.2 mSv. Assuming that the weighted
average annual effective dose represents the worldwide value, the average collective effective dose isabout 500 man Sv.
276. Occupational exposure for staff performing interventional procedures in different institutions in
Bosnia and Herzegovina in 2009 showed that the highest average annual effective dose assessed was
1.6 mSv for the interventional operators at one institution. The study covers four out of five institutions
that perform interventional procedures. The results in table 31 present a large variation of doses between
the five hospitals [B5].
Table 31. Occupational exposure data for interventional procedures in different institutions in
Bosnia and Herzegovina in 2009 [B5]
Institution

Number ofmonitored workers

Average annual collective
effective dose (man Sv)

Average annual
effective dose (mSv)

INTERVENTIONAL OPERATORSClinical Centre of Sarajevo
University

16

0.021

1.4

University Clinical Centre of
Tuzla

10

0.004

0.52

Clinical Hospital Mostar

3

0.001

0.38

Special Heart Clinic of Bosnia
and Herzegovina

8

0.013

1.6

All institutions

37

0.039

1.1

NURSES
Clinical Centre of Sarajevo
University

11

0.009

0.98

University Clinical Centre of
Tuzla

16

0.006

0.39

Clinical Hospital Mostar

3

0.00080.28

Special Heart Clinic of Bosnia
and Herzegovina

11

0.006

0.55

All institutions

41

0.021

0.58

RADIOGRAPHERS
Clinical Centre of Sarajevo
University

4

0.003

0.79

University Clinical Centre of
Tuzla

3

0.00090.31

Clinical Hospital Mostar

20.00070.44

Special Heart Clinic of Bosnia
and Herzegovina

3

0.002

0.72

All institutions

12

0.007

0.59

Total

90

0.066

0.81

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 89

277. Interventional radiology specialists used to receive individual effective doses notably higher thanthose observed in conventional diagnostic radiology. An appreciable difference is not expected when new
radiological protection measures and techniques, such as the robotic catheter systems gaining favour inmany centres both for vascular intervention and cardiac electrophysiological ablation, have been
implemented. It is important to notice that the majority of the countries responding to the UNSCEAR
Occupational Exposure Survey are classified as high-income countries according to the World Bank
classification [B18, H3, H12, I31, I39, I49, K6, K10, M6, P4, P5].
278. The doses for the operators performing 25 fenestrated endovascular aortic repair or branched
endovascular aortic repair were assessed in a hospital in the United Kingdom. The results showed thatthe average annual doses to the head, to the thorax over-lead apron, and to the thorax under-lead apron
were 2.3, 3.0, and 0.4 mSv, respectively. The radiation doses associated with these procedures are likely
to be higher compared with standard, infrarenal aortic interventions [A9].
279. The average annual effective doses of the operators performing hip arthroscopy procedures,
femoroacetabular impingement procedures and soft-tissue pathology procedures in a hospital in the
United States was estimated at about 0.3 mSv. The dose assessment was based on data collected overfour months of performing hip arthroscopy procedures, and the operator was exposed to approximately
0.09 mSv. These data were extrapolated for 12 months (156 procedures) [C4].
280. The radiation exposure for a team of vascular operators was prospectively monitored in a 12-month
period in a hospital in China. The staff performed 30 endovascular aortic repairs, 58 arteriograms withand without embolization, and 61 percutaneous transluminal angioplasty and stent. The average annual
effective dose was estimated at 0.20 mSv (range, 0.13 to 0.27 mSv); the average annual equivalent doseto the lens of the eye was estimated at 0.19 mSv (range, 0.10 to 0.33 mSv) and the average annual
equivalent dose to the hand was estimated at 0.99 mSv (range, 0.29 to 1.84 mSv). These doses perprocedure for the chief operator were highest for endovascular aortic repairs. Significant differences wereobserved for the average hand dose per minute of fluoroscopy among different surgeons [H8].

(c) Dental practice281. Dental radiology is a part of diagnostic radiology; however, it has usually been presented separately
as occupational exposure is typically very low. Diagnostic X-ray machines are widely available and areused frequently in almost every dental practice or clinic. The total number of X-ray devices used in
dentistry is thus extremely large. Occupational exposure in dentistry is caused mainly by scatteredradiation from the patient and leakage from the tube head (although the latter should be insignificant withmodern equipment). The general trend over the past 30 or more years has been an increase in the numberof personnel involved in dental radiology, coupled with a steady decrease in average annual collective
effective dose. The majority of dental practitioners do not receive doses higher than the MDL and, indeed,some regulatory authorities do not require routine individual monitoring, except for high workload.
282. National data on occupational exposure arising from dental practice over the periods 2003–2004,
2005–2009 and 2010–2014 are provided in table A.14 in the electronic attachment. Only 28 countries
responded to the UNSCEAR Occupational Exposure Survey within the period 2003–2014. The data
provided in the UNSCEAR 2008 Report [U10] for 2000–2002 were added to the survey for the period
2003–2004 to form the broader period 2000–2004. The reported average annual effective doses range
between values below the MDL and 2.3 mSv. The high values of the average doses in some countries
may arise from the fact that dosimetry in these countries is implemented only for those workers for whom
received doses ≥MDL or higher than the recording level were expected (equal data for exposed andmonitored workers). Female workers represent about 75% of the workforce.

90 UNSCEAR 2020/2021 REPORT283. The worldwide number of monitored workers is estimated on the basis of the methodology
described in section II.E.1. The best estimates of the worldwide number of workers involved in dental
practice is about 350,000 for the period 2000–2004, 400,000 for the period 2005–2009 and 450,000
for the period 2010–2014. The uncertainty interval for the estimates of the worldwide number ofworkers ranges from 300,000 to 680,000.
284. The worldwide occupational average annual effective doses arising from dental practice over theperiods 2000–2004, 2005–2009 and 2010–2014 are estimated as the average annual effective dose formonitored workers weighted by the number of workers in each country that responded to the UNSCEAR
Occupational Exposure Survey. The estimated value is 0.2 mSv in each period. The uncertainty interval
for the worldwide average annual effective dose ranges from 0.1 to 0.3 mSv. Assuming that the weighted
average annual effective dose represents the worldwide values, the average annual collective effective
doses are about 70 man Sv for the period 2000–2004, 80 man Sv for the period 2005–2009 and 90 man Sv
for the period 2010–2014.
285. The trends for occupational exposure in dental practice from 1975 to 2014 are presented in table 32
and figure IV. The previous estimates of the number of workers were in the range of 260,000 to 500,000
within the period 1975–1999. In the current evaluation, the workforce in dental practice slightly increased
to 404,000 in the period 1995–1999 to 450,000 in the period 2010–2014. The average annual effective
dose decreased from 0.3 mSv (1975–1979) to 0.1 mSv (1990–1994, and 1995–1999), and then increased
to 0.2 mSv in three latter periods. The estimated average values are close to those reported by countries
as MDL over all the periods.
286. The estimated level of exposure is in agreement with the published data. Dose assessment for dental
personnel in different institutions in Bosnia and Herzegovina in 2009 showed that no personnel received
an annual effective dose higher than 1 mSv [B4]. Evaluation of the effective doses over three years(2011–2013) in 90 dental health professionals, 72 oral radiologists and 18 radiographic assistants(technicians or dental assistants), of 14 dental colleges in Karnataka state in India showed that theeffective doses are lower than 1.5 mSv per year [R2]. A total of 658 dentists were surveyed from April
2012 to May 2013 in the Republic of Korea. The results showed that the annual effective doses wereconsistently low, below 0.2 mSv [K4].
Table 32. Estimated worldwide levels of occupational exposure in dental practiceab

Average annual effective dose(mSv)

PeriodMonitored
workers(103)

1975–1979a

370

120

0.3

1980–1984a

500

93

0.2

a

1985–1989

480

25

0.05

1990–1994a

265

16

0.0.6

a

1995–1999404

2000–2004

Measurably
exposed workers
(103)

17

Average annual
collective effective
dose (man Sv)

Monitored
workers

Measurably
exposed workers

0.9

24

0.06

350

b

70

0.2

b

2005–2009

400

b

80

0.2

b

2010–2014

450

b

90

0.2

b

Values from earlier UNSCEAR reports [U3, U4, U6, U8, U10].
No worldwide estimation was possible because of limited data or no reliable data.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 91

Figure IV. Worldwide trends in occupational exposure at dental practices

92 UNSCEAR 2020/2021 REPORT

2.

Nuclear medicine

287. Nuclear medicine procedures involve the introduction of unsealed radioactive substances into thebody, most commonly to obtain images that provide information on either organ structure or function.
The radioactive substance may, in most instances, be administered intravenously, orally, by inhalation or
into a cavity (e.g., intrathecally or intra-articularly). A radionuclide is usually combined with a targetingchemical to form a radiopharmaceutical to be distributed in the body according to physical or chemical
characteristics (e.g., a radionuclide incorporated in a phosphate will localize in the bone, making a bonescan possible). The radiation emitted from the body is subsequently acquired to produce diagnostic
images. Less commonly, unsealed radionuclides are administered to treat certain diseases such as
hyperthyroidism and thyroid cancer, bone metastasis, primary or metastatic liver cancer, lymphomas, andneuroendocrine tumours. The use of radionuclide generators, particularly 99mTc generators, requires
handling substantial amounts of radioactive material during the elution process. The magnitude of
exposure while performing clinical nuclear medicine procedures depends on the precautions taken,
including the use of syringe shields when performing injections. When personnel are close to the patient
while giving injections and positioning the patient and camera, the imaging process makes the largest
contribution to their exposure. The use of automatic injectors and dispensers, in the case of positronemission tomography (PET), may reduce the occupational exposure [L1].
288. Tasks involving the preparation and assay of radiopharmaceuticals are associated with the highest
occupational exposure in nuclear medicine and can give annual doses of up to 5 mSv [N2]. There is apotential risk for intake of radiopharmaceuticals, especially for personnel involved in their preparation
and assay. Internal exposure of personnel is usually much lower than external exposure and is controlled
by monitoring work surfaces and airborne concentrations. However, the level of occupational exposure
will depend on the level of radiological protection measures applied in the workplace. There are studies
showing that annual effective dose can reach values up to 9 mSv, arising from the intake of 131I [K9].
289. National data on occupational exposure arising from nuclear medicine over the periods 2003–2004,
2005–2009 and 2010–2014 are provided in table A.14 in the electronic attachment. Twenty-five countries
responded to the UNSCEAR Occupational Exposure Survey for the years 2003–2014. The data provided
in the UNSCEAR 2008 Report for 2000–2002 were added to the survey for the period 2003–2004 toform the broader period 2000–2004. The sample does not separate workers involved in diagnostic ortherapeutic procedures only. There is a wide variation in the average annual effective dose, ranging from
0.2 to 1.8 mSv. Female workers represent about 70% of the workforce.
290. Nuclear medicine staff may receive high equivalent doses to the skin of the hands, especially to thefingers in contact with the syringe, if adequate radiological protection measures are not implemented.
Only eight countries have provided equivalent dose data for the hands (skin dose); the reported averageannual equivalent doses are 6 mSv (ranging from 1 to 11 mSv) in the period 2000–2004; average dose of
9 mSv (ranging from 1 to 18 mSv) in the period 2005–2009; and 14 mSv (ranging from 1 to 48 mSv) in
the period 2010–2014. Trend analysis suggests that extremity doses have increased over time. The
average annual equivalent doses to the lens of the eye were reported by only three countries. The
equivalent doses range from below the MDL to 7 mSv (table A.15 in the electronic attachment).
291. Data from six European countries (ORAMED Project) showed that if radiation protection standards
are low, the extremity (skin) doses can exceed the annual skin dose limit of 500 mSv for technicians,
physicians and nurses administering therapy with 90Y/Zevalin and 177Lu labelled peptides [R8]. The total
exposure of radiochemists or technicians during labelling procedures is almost threefold that received byphysicians or nurses when administering 90Y/Zevalin and involves more working steps and higher
activity. The non-dominant hand receives the highest doses. In the majority of cases, the tip of the index
finger or the thumb of the non-dominant hand was found to receive the maximum dose. The maximum

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 93

skin dose can be underestimated by a factor of about six if it is estimated using dosimeters worn on thewrist or on the ring finger [R8]. The high frequency of the preparation of radiopharmaceuticals fordiagnostic procedures may result in high extremity doses. Nevertheless, the specific dose rates for 99mTc
and 18F are comparatively lower and the measurements in glass vials exhibit only insignificant
contributions of beta and gamma mixed radiation fields [S17]. The highest doses for 90Y are in thefingertips. The doses estimated used ring dosimeters may be underestimated [B12]. The doses can be
reduced with implementation of optimized procedures [M4, O11, P2].
292. The European Good Manufacturing Practice guideline [E9] defines a number of quality control
tests that must be performed prior to the release of fluorodeoxyglucose (18FDG), among them measuring
the energy spectrum of the sample to detect other radionuclide impurities and measuring the half-life of
the radioisotopes in the sample. Significant differences in doses, depending on the hand and operator, canbe noticed. The difference in equivalent doses measured for each hand (average left-hand dose 1.5 mSv;
average right-hand dose 0.85 mSv) is probably due to the fact that all operators were predominately righthanded. If one operator was responsible for performing all quality control in a facility, the total annual
finger equivalent dose would be 392 mSv on the basis of the average dose received five times a week for
52 weeks of the year. However, this has the potential to be as high as 525 mSv annually, using the highest
individual operator average finger dose of 2.0 mSv per session. There is the potential for operators to exceed
the legal dose limits [F3]. Actually, any tasks that involve handling 18FDG result in finger doses that canreach the dose limit if radiological protection measures are not applied [L3].
293. The assessment of the equivalent doses to the fingers of workers conducting different tasks in
54 major institutions in India showed that the maximum equivalent doses were 0.35 mSv/GBq for elutionof 99mTc in radiopharmacy work; 1 mSv/GBq during injection of the radiopharmaceutical, and 0.95 mSv/GBq
for scintigraphy. Results are presented in table 33 [T2].
294. Results of a survey of occupational exposure over two years (2008 and 2009) in a nuclear medicine
department in Kuwait showed that the average annual effective dose (in terms of Hp(10)) and equivalentdose to skin (in terms of Hp(0.07)) are both about 1 mSv for physicians and technicians [A4]. Although
the authors have reported the operational quantities instead of effective dose and equivalent dose, thesedata were considered for comparison purposes.
Table 33. Maximum equivalent dose to fingers during different nuclear medicine procedures [T2]Procedure

Maximum equivalent dose to fingers (mSv/GBq)
NUCLEAR MEDICINE PROCEDURE USING 99mTc

Elution and radiopharmacy~0.35

Injection

1

Scintigraphy

0.95
NUCLEAR MEDICINE PROCEDURE USING 18FDG

Dispensing

0.097

Injection

0.324

Scintigraphy

0.56
NUCLEAR MEDICINE PROCEDURE USING 188/186Re and 153Sm

Angiosplasty due to 188/186Re

3.92

Preparation of

6.5

153

Sm for synovectomy

94 UNSCEAR 2020/2021 REPORT295. In Czechia, a survey of occupational exposure in a nuclear medicine department provided averageannual effective dose for physicians, technicians and radiopharmacists during the period 2001–2006. The
doses were significantly reduced over the six-year period for all three work categories, about twofold forphysicians and technicians and tenfold for radiopharmacists. Table 34 presents doses for staff working ina nuclear medicine department with a tendency of decreasing radiation exposure for all professional
categories, even though the administered activity of 131I increased during the six-year period [D4].
Table 34. Average annual effective dose of occupationally exposed staff in a nuclear medicine
department in Czechia [D4]Year

Average annual effective dose (mSv)
Physicians (n=5)

Technologists (n=9)

Radiochemists (n=2)

2001

1.9±0.6

1.9±0.8

3.2

2002

1.8±0.8

1.7±1.4

1.8

2003

1.2±0.8

1.0±1.0

0.6

2004

1.4±0.8

1.1±1.2

1.3

2005

1.3±0.6

0.9±0.4

0.6

2006

0.8±0.4

0.7±0.2

0.3

296. The use of high-efficiency cadmium zinc telluride detectors in single-photon emission computed
tomography (SPECT) cameras has demonstrated the ability to reduce the radiation exposure of staff andof patients undergoing myocardial perfusion imaging studies. An evaluation of occupational doses
conducted before and after the implementation of high-efficiency SPECT in a New York hospital in
2007–2008 was published by Duvall et al. [D8]. Table 35 presents the occupational doses by staff
category for a total of 3,539 patients tested before and 3,898 after the implementation of high-efficiency
SPECT. It is estimated that about 39% of the dose reduction was due to the new technology used, andrelated to the reduction of administered activity [D8].
Table 35. Average annual effective dose for staff of New York nuclear cardiology laboratory [D8]SPECT: Single-photon emission computed tomography
Average annual effective dose (mSv)
Staff category

Before the implementation ofhigh-efficiency SPECT a

After the implementation ofhigh-efficiency SPECT b

DEEP-DOSE EQUIVALENT
Nurse

4.9

2.9

Technologist

5.3

3.3

Administrative

0.43

0.27

SHALLOW-DOSE EQUIVALENT
Nurse

4.9

2.9

Technologist

5.6

3.3

Administrative

0.43

0.34

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 95

Average annual effective dose (mSv)
Staff category

Before the implementation ofhigh-efficiency SPECT a

After the implementation ofhigh-efficiency SPECT b

LENS-DOSE EQUIVALENT

a
b

Nurse

5.0

2.9

Technologist

5.5

3.3

Administrative

0.47

0.30

October 2007–September 2008.
October 2010–September 2011.

297. The worldwide number of monitored workers is estimated on the basis of the methodology
described in section II.E.1. The worldwide occupational exposure data in nuclear medicine are presented
in table 36 and figure V. The number of workers involved in nuclear medicine is estimated to be around
200,000 for the three latter periods: 2000–2004, 2005–2009 and 2010–2014. The uncertainty interval for
the worldwide number of workers ranges from 110,000 to 370,000.
298. The average annual effective doses arising from nuclear medicine over the periods 2000–2004,
2005–2009 and 2010–2014 are estimated as the average annual effective dose for monitored workers
weighted by the number of workers of each country that responded to the UNSCEAR Occupational
Exposure Survey. The estimated values are 1.1 mSv for 2000–2004, 0.7 mSv for 2005–2009 and 0.4 mSv
for 2010–2014. For the worldwide average annual effective dose, the uncertainty interval for the period
2010–2014 ranges from 0.2 to 0.8 mSv.
299. Assuming that the weighted average annual effective dose represents the worldwide values, theaverage annual collective effective doses are about 220 man Sv for the period 2000–2004, 140 man Sv
for the period 2005–2009 and 80 man Sv for the period 2010–2014.
300. The average annual effective dose was about 1.0 mSv during the first six five-year periods(1975–2004), then a decrease in the average annual effective doses was observed in the two latter periods
up to about 0.4 mSv. A similar trend was observed in a study involving more than 6,000 Chinese nuclear
medicine workers for whom the annual effective dose decreased from about 0.8 mSv in 2010 to 0.4 mSv
in 2016 [D2].
301. The Committee has attempted to evaluate the occupational exposure for various job categories
within the nuclear medicine subsector: physicians, nurses, technicians, and other job categories. The
worldwide level of exposure could not be derived because of limited available data and, therefore, theunacceptable high uncertainty of the predicted values. The data obtained from the UNSCEAR
Occupational Exposure Survey are presented in table 36 and table A.17 in the electronic attachment.
302. Although new SPECT radiopharmaceuticals are continually being developed, there is a major trend
to extend positron emission tomography procedures. Nowadays, 18FDG is the most used tracer but
research on other 18F-labelled molecules has resulted in several new radiopharmaceuticals, including 11C.
Furthermore, the search for new radionuclides introduced 62Cu, 68Ga, 86Y, 94Tc and 223Ra. Many of theseradionuclides emit positrons with relatively high energies combined with high-energy gamma emission.
The future number of procedures and the nature of these radionuclides can, consequently, increase wholebody exposure and exposure to the extremities [C19, S15].

96 UNSCEAR 2020/2021 REPORT

Table 36. Estimated worldwide levels of occupational exposure in nuclear medicine
Average annual effective dose(mSv)

Average annual
collective
effective dose(man Sv)

Monitored
workers

PeriodMonitored
workers(103)

1975–1979a

61

62

1.0

1980–1984a

81

85

1.0

a

1985–1989

90

85

1.0

1990–1994a

115

90

0.8

1995–1999a

117

89

0.8

2000–2004

200

b

220

1.1

b

2005–2009

200

b

140

0.7

b

2010–2014

200

b

80

0.4

b

Measurably
exposed workers
(103)

65

a

Values from earlier UNSCEAR reports [U3, U4, U6, U8, U10].

b

No worldwide estimation was possible because of limited data or no reliable data.

Measurably
exposed workers

1.4

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 97

Figure V. Worldwide trends in occupational exposure at nuclear medicine

98 UNSCEAR 2020/2021 REPORT

3.

Radiation therapy

303. Radiation therapy refers to the use of ionizing radiation produced by a sealed source or a radiation
generator to treat various diseases (usually cancer). Sometimes radiation therapy is referred to as radiation
oncology; however, selected benign diseases may also be treated. Radiation therapy is delivered throughexternal beams of radiation (teletherapy) or by placing sealed radioactive sources in or near the tumour
tissue (brachytherapy). External radiation beams may consist of high-energy X-rays or gamma rays,
electrons, protons, neutrons, or heavier charged particles. Gamma-ray beams are often produced by highactivity sources of 60Co while all other external radiation beams are produced by electrical equipment
such as X-ray machines and particle accelerators.
304. Brachytherapy, with a manual loading of the radioactive treatment sources, is usually the mostsignificant source of personnel exposure [I41, N2]. This may occur during the receipt and preparation of
the sources, during their loading and unloading, and during treatment. Treatments with an external beam
do not usually require personnel to be present in the treatment room when the beam is administered. The
possible exception may be made for low-energy (50 kV and less) X-ray contact therapy units, which aresometimes used for intracavitary treatment. Radiation therapy staff of medical accelerators operating withenergies of above about 10 MeV are also exposed to radiation due to activated material in the treatment
rooms. The activation arises primarily from photonuclear reactions and neutron capture. The assessmentsof an annual dose received by staff due to activated material during typical operations are in the range of
0.7–5 mSv. These numbers demonstrate that this dose is not negligible; however, they strongly dependon the chosen model and applied approach [A11, D5, P7, R1].
305. The evaluation of the average annual effective dose of a group of 20 radiation therapy workers in
Egypt showed that the average annual effective dose for the radiation therapy group (n=20) working on
a linear accelerator was 3.1 ± 1.5 mSv (range from 1.5 to 6 mSv/a) [E10].
306. Occupational exposure data for radiation therapy obtained via the literature review have been used
to supplement the data obtained from the UNSCEAR Occupational Exposure Survey. Two countries havepublished data related to national surveys, Bosnia and Herzegovina, and Pakistan (table 37). These data
were added to the data obtained from the UNSCEAR Occupational Exposure Survey to estimate theworldwide occupational exposure level.
Table 37. Data on occupational exposure for radiation therapy from literature review
Number ofmonitored
workers (103)

Average annual
collective effective
dose (man Sv)

Average annual
effective dose(mSv)

Reference

1999–2003

0.038

0.045

1.2

[B4]

2004–2008

0.045

0.071

1.6

[B4]

2003–2007

0.367

0.43

1.17

[J1]

Country

PeriodBosnia andHerzegovina
Pakistan

307. National data on occupational exposure arising from radiation therapy over the periods 2003–2004,
2005–2009 and 2010–2014 are provided in table A.14 in the electronic attachment. Twenty-six countries
have reported to the UNSCEAR Occupational Exposure Survey within the period 2003–2014. The data
provided in the UNSCEAR 2008 Report [U10] for 2000–2002 were added to the survey for the period
2003–2004 to form the broader period 2000–2004. The average annual effective dose ranges from below
MDL to 3.5 mSv. Female workers represent about 65% of the workforce.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 99

308. Staff carrying out brachytherapy procedures may receive high doses to the hands. Five countries
have provided data on average equivalent dose to hands (skin dose) and then for brachytherapy andteletherapy pooled together. The average equivalent dose was 1.2 mSv (ranging from 1 to 1.4 mSv) in
the period 2000–2004, 7.1 mSv (ranging from 0.2 to 37 mSv) in the period 2005–2009 and 1.6 mSv(ranging from 1 to 22 mSv) in the period 2010–2014. Germany provided a recorded value of 0.1 mSv forthe average annual equivalent dose to the lens of the eye (table A.15 in the electronic attachment).
309. The worldwide number of monitored workers is evaluated on the basis of the methodology
described in section II.E.1. The worldwide occupational exposure data in radiation therapy are presented
in table 38 and figure VI. The number of workers involved in radiation therapy is estimated to be about
200,000 for the periods 2000–2004 and 2005–2009 and about 300,000 for the period 2010–2014. The
data indicate a stable number of monitored workers involved in this practice since 1995. The uncertainty
interval for the period 2010–2014 of the worldwide number of workers ranges from 170,000 to 540,000.
310. The average annual effective doses arising from radiation therapy over the periods 2000–2004,
2005–2009 and 2010–2014 are estimated as the average annual effective dose for monitored workers
weighted by the number of workers of each country that responded to the UNSCEAR Occupational
Exposure Survey. The estimated values are 0.4 mSv for 2000–2004, and 0.3 mSv each for 2005–2009
and 2010–2014. The uncertainty interval for the period 2010–2014 on the average annual effective dose
ranges from 0.1 to 0.5 mSv. Assuming that the weighted average annual effective dose represents theworldwide values, the average annual collective effective doses are about 80 man Sv (2000–2004),
60 man Sv (2005–2009) and 90 man Sv (2010–2014). The average annual effective dose decreased from
2.2 mSv (1975–1979) to 0.3 mSv (2010–2014), which is close to reported MDLs by countries.
311. The Committee has attempted to evaluate the occupational exposure for various job categories
within the radiation therapy subsector: physicians, nurses, technicians, other job categories. The
worldwide level of exposure could not be derived because of limited available data and, therefore, thehigh uncertainty of the predicted values. The data obtained from the survey are presented in table A.18.
Table 38. Estimated worldwide levels of occupational exposure in radiation therapy
Average annual effective dose(mSv)

PeriodMonitored
workers(103)

1975–1979a

84

190

2.2

1980–1984a

110

180

1.6

a

1985–1989

110

100

0.9

1990–1994a

120

65

0.6

a

1995–1999264

2000–2004

Measurably
exposed workers(103)

Average annual
collective effective
dose (man Sv)

48

Monitored
workers

Measurably
exposed workers

1.3

132

0.5

200

b

80

0.4

b

2005–2009

200

b

60

0.3

b

2010–2014

300

b

90

0.3

b

a

Values from earlier UNSCEAR reports [U3, U4, U6, U8, U10].

b

No worldwide estimation was possible because of limited data or no reliable data.

100 UNSCEAR 2020/2021 REPORT

Figure VI. Worldwide trends in occupational exposure at radiation therapy

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 101

4.

Veterinary medicine

312. Veterinary radiological practice refers to essential diagnostic radiography and the application of
nuclear medicine tools used by veterinary practitioners. Although the technology associated with thegeneration of X-rays is similar to conventional diagnostic radiology, doses to personnel depend largelyon the type of animal examined. Most veterinary radiological examinations are conducted withconventional diagnostic radiography systems but there are also special veterinary computer tomographyscanners and veterinary scintigraphy systems; the isotope 99mTc is widely used (90% of all examinations)in nuclear-medicine-type examinations. In general, the average annual effective doses to individuals
should be low, because they arise essentially from scattered radiation. Some practices may, however,result in the additional exposure of extremities if, for example, assistants hold animals in position while
the examination is being performed [C3].
313. National data on occupational exposure arising from veterinary medicine over the periods 2003–2004,
2005–2009 and 2010–2014 are provided in table A.14 in the electronic attachment. Twenty-six countries
have responded to the UNSCEAR Occupational Exposure Survey within the period 2003–2014. The data
provided in the UNSCEAR 2008 Report [U10] for 2000–2002 were added to the survey for the period
2003–2004 to form the broader period 2000–2004. There is a wide variation in the average annual
effective dose, and it is very likely that the doses are below 1 mSv. On average, female workers represent
about 55% of the workforce.
314. Staff carrying out veterinary medicine may receive high doses to the hands because of the nature of
nuclear-medicine-type procedures and having to hold animals during an exposure. Only four countries
provided average annual equivalent dose data for hands (skin dose) for the period 2010–2014; thereported average equivalent dose is 0.7 mSv (ranging from 0.2 to 1 mSv) as presented in table A.15 in
the electronic attachment.
315. The worldwide occupational exposure data in veterinary medicine are presented in table A.14 in theelectronic attachment. The worldwide level of occupational exposure was evaluated on the basis of themethodology described in section II.E.1. However, due to the lack of statistically significant correlation
between the occupational data and the predicted parameters applied to derive the mathematical models,
it was not possible to predict global estimates with suitable reliability. Therefore, the worldwide
occupational exposure levels were not estimated for the periods 2000–2004, 2005–2009 and 2010–2014.

5.

All other medical uses

316. The category “all other medical uses of radiation” was intended to cover new/expanding uses ofradiation within the medical sector that did not fit into the categories of diagnostic radiology, dental
radiology, nuclear medicine, radiation therapy and veterinary medicine.
317. The number of workers potentially exposed in these other uses may substantially exceed those in
the few occupations for which data have been separately presented in this section. The average exposurelevels of workers involved in other uses of radiation are in general very low. However, the way in which
the doses are aggregated may disguise somewhat higher average doses in particular occupations. The
only way to ascertain the existence of occupations, or subgroups within occupations, that receive doses
significantly above the average is for the data to be examined periodically.
318. National data on occupational exposure arising from “all other medical uses” over the periods 2003–
2004, 2005–2009 and 2010–2014 are provided in table A.14 in the electronic attachment. Twenty-three
countries responded to the UNSCEAR Occupational Exposure Survey and supplied data for the period

102 UNSCEAR 2020/2021 REPORT

2003–2014. The data provided in the UNSCEAR 2008 Report [U10] for 2000–2002 were added to thesurvey for the period 2003–2004 to form the broader period 2000–2004. On average, female workers
represent about 65% of the workforce.
319. The worldwide level of occupational exposure is evaluated on the basis of the methodology
described in section II.E.1. Due to the poor statistically significant correlation between the occupational
data and the predicted parameters applied to derive the mathematical models, the global estimate may be
calculated for the period 2010–2014 only. The worldwide occupational exposure data were not estimatedfor the three periods 2000–2004, 2005–2009 and 2010–2014. The reported number of monitored workers
is around 200,000. The average annual effective dose is below 1 mSv as in the previous evaluated periods.

6.

Summary320. There is a wide variation in the reported effective doses and the number of exposed workers. Thismay be explained by many factors, including the way data are recorded in the national databases, themixing of doses related to monitored and measurably exposed workers, the mixing of procedures
performed by the medical staff, workload, and protective measures implemented by each country. On
average, female workers represent about 60% of the workforce in the medical sector.
321. All worldwide estimates of occupational exposure are evaluated on the basis of the methodology
described in section II.E.1. The insufficient data supplied to the UNSCEAR Occupational Exposure
Survey resulted in a weak correlation between the original data and predicted global estimates and, thus,
some of them are statistically insignificant and were not presented in this annex.
322. Diagnostic radiology includes conventional diagnostic radiology and interventional radiology
pooled together. The worldwide number of monitored workers was estimated to be 8 million, withuncertainty interval from 3.9 to 14 million. The worldwide average annual effective dose was estimatedas 0.4 mSv, with uncertainty interval from 0.2 to 0.8 mSv. The average annual collective effective dose
was estimated as 3,000 man Sv. A trend observed was an increase in the numbers of workers and theaverage annual collective dose over the 40 years of analysis. The average annual effective dose has
gradually decreased by a factor of two, from 0.9 mSv (1975–1979) to 0.4 mSv (2010–2014). The
estimated worldwide number of workers represents about 90% of the total number of monitored workers
involved in the medical uses of radiation (excluding veterinary medicine).
323. On the basis of the data reported by the countries that responded to the UNSCEAR Occupational
Exposure Survey, the value for annual equivalent dose to the hands of an individual worker is unlikely
to exceed 500 mSv. The derived average equivalent dose to the lens of the eyes in all medical subsectors
is 7 mSv, but because of the limited data obtained through the survey, the derived value should not beassumed as representative. Some literature data indicate that the annual equivalent dose to the lens of theeye may exceed 20 mSv for some workers.
324. In dental practices, the estimated values for the workforce varied from about 270,000 to 500,000 in
the period 1975–1999; no clear trend was observed. In the current evaluation, the number of workers
increased from 350,000 in the period 2000–2004 to 450,000 in the period 2010–2014, which represents
about 5% of the total number of monitored workers involved in the medical uses of radiation. The
estimated average annual effective dose is 0.2 mSv while the average annual effective dose in the period
1995–1999 was 0.1 mSv. Both values are close to the MDL reported by countries. The uncertainty
interval for the worldwide number of workers for the period 2010–2014 ranges from 300,000 to 680,000
while the interval for the worldwide average annual effective dose ranges from 0.1 to 0.3 mSv.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 103

325. For nuclear medicine, no statistically significant changes in workforce were observed during thethree periods under consideration (2000–2004, 2005–2009 and 2010–2014). The estimated global
number of monitored workers for these periods is about 200,000 each, which represents about 2% of thetotal number of monitored workers involved in the medical sector. The average annual effective dose
decreased consecutively over these periods down to 0.4 mSv. The threefold increase in monitored
workers between the periods 1977–1999 and 2000–2014 is likely to be a consequence of the introductionof new radiopharmaceuticals and new equipment for nuclear medicine diagnostics and therapy. Positronemission tomography (and its hybrid solutions) and SPECT are effective sources of diagnostic
information and often replace traditional X-rays. The uncertainty interval for the worldwide number ofworkers ranges from 110,000 to 370,000 and the interval for the worldwide average annual effective dosefrom 0.2 to 0.8 mSv.
326. For radiation therapy, the number of workers exposed varies between 200,000 and 300,000 overthe periods 1995–1999, 2000–2004, 2005–2009 and 2010–2014. The estimated number of workers forthe period 2010–2014 is 300,000, which represents about 4% of the total number of monitored workers
involved in the medical uses of radiation. The estimated average annual effective dose for the same period
is 0.3 mSv; and the estimated average annual collective effective dose is 90 man Sv. The uncertainty
interval for the worldwide number of workers ranges from 170,000 to 540,000 and the interval for theworldwide average annual effective dose from 0.1 to 0.5 mSv. An increase in average annual equivalentdose to the hands from 1 mSv in 2000–2004 to 6 mSv in 2010–2014 was observed in data reported
through the UNSCEAR Occupational Exposure Survey. However, the trend cannot be taken as globally
representative since too few countries provided data.
327. Because of the lack of correlation between the reported survey data and the predictor parameters,
the worldwide level of occupational exposure in veterinary medicine and “all other medical uses” were
not derived. According to the reported data, the average annual effective dose seems to be below 0.5 mSv,
similar to previous evaluated periods.
328. The estimated number of workers involved in medical uses of ionizing radiation is about 9 million
workers worldwide; the average annual collective effective dose is estimated to be about 4,500 man Sv
and the average annual effective dose is 0.5 mSv. The uncertainty interval for the worldwide number ofworkers ranges from 5.0 to 17 million and the interval for the worldwide average annual effective dosefrom 0.26 to 1.0 mSv. Although the workforce for 2010–2014 is underestimated because it does notinclude veterinary medicine and all other medical uses of radiation, the uncertainty interval accounts forthat underestimation. The evaluation of the trends in occupational exposure for all medical uses together
showed an increasing number of monitored workers, dominated by those involved in diagnostic
radiology, while the annual average annual effective dose has been stable or more likely decreasing sincethe 1985–1989 period. The increasing number of workers correlates with the substantial increase inaverage annual collective effective dose presented in table 39. The relevant increase in the workforce
from 1990–1994 to 1995–1999 was due to an improvement of data collection through collaboration with
the World Health Organization (WHO).

104 UNSCEAR 2020/2021 REPORT

Table 39. Estimated worldwide levels of annual occupational exposure from all medical uses
Average annual effective dose(mSv)

Monitored
workers(103)

Measurably
exposedworkers(103)

Average annual
collective
effective dose(man Sv)

Monitored workers

Measurably exposed
workers

1975–1979a

1 280

650

1000

0.8

1.5

1980–1984a

1 890

520

1 140

0.6

1.7

a

1985–1989

2 220

590

1 030

0.5

1.7

1990–1994a

2 320

550

760

0.3

1.4

1995–1999a

7 440

b

3 540

0.5

b

2010–2014

9 000

b

4 500

0.5

b

Perioda

Values from earlier UNSCEAR reports [U3, U4, U6, U8, U10].

b

No worldwide estimation was possible because of limited data or no reliable data.

C. Industrial uses of radiation
329. Radiation sources, including sealed sources, X-ray machines, particle accelerators and unsealed
sources, are used in a number of industrial applications. Among these are industrial irradiation, industrial
radiography, luminizing, radioisotope production and distribution, well logging, accelerator operation,and industrial gauges. Because of the many different occupations involved and the ways in which
exposure is categorized, it is difficult to obtain comparable statistics for different countries. Most
radiation exposure in industrial uses of radiation is low, a fact that contributes to the lack of detail inrecorded data for occupational exposure.

1.

Industrial irradiation

330. The most widespread uses of industrial irradiation are the sterilization of medical andpharmaceutical products, the preservation of foodstuffs, polymer synthesis and modification, and theeradication of insect infestation. Usually, the irradiators use gamma emitting sources (such as 60Co) orelectron beams (e-beams). The required product doses are extremely high, and the involved source
activities or beam currents are correspondingly high. The highest used electron energy in commercial
irradiation is 10 MeV in order to avoid induced activity. Dose rates in a typical irradiation chamber would
be of the order of 1 Gy/s while e-beams are capable of delivering up to about 100 kGy/s; however, gamma
rays can penetrate deeper into studied material than electrons.
331. A survey conducted by the IAEA between 2004 and 2008 to assess the worldwide number ofsterilization facilities showed that over 200 gamma irradiators were in operation for a variety of purposesin 55 countries: 100–120 gamma irradiators were located in Europe and the United States [I6]. The
IAEA reported the number of workers for 30 operating gamma irradiators from 12 countries and thenumber of workers for 16 operating e-beam irradiators from six countries. These data are presented intable 40 and showed when using linear regression analysis and excluding e-beam irradiators that there isa statistically significant correlation between the number of gamma irradiators and number of workers
for each country (adjusted R2 = 0.65). Therefore, the number of gamma irradiators and the number ofworkers for each country were used to derive a mathematical model to estimate the total number ofANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 105

workers worldwide. Using the IAEA data, in 2008 the total number of irradiators was estimated tobe 6,249, and the total number of gamma irradiators 6,182 [I18].
332. On the basis of the total cumulative sale of 60Co by all suppliers, the IAEA survey estimated thatthe installed capacity of cobalt was increasing by about 6% per year. It was further noticed that theworldwide use of disposable medical devices was growing at approximately the same rate (5–6%), an
observation that could corroborate the estimated growth in installed capacity. The yearly increasing rateof 6% was applied to estimate the total number of gamma irradiators for the years 2009 to 2014.
Table 40. International Atomic Energy Agency survey results for industrial irradiation [I18]Gamma irradiators
Country

Electron beam irradiators

Number ofirradiators

Number ofworkers

Argentina

335

Belarus2

25

Brazil3

12

Croatia

1

4

Czechia1

7Denmark

1

5

Germany

1

15

Hungary

2

13

India

6

98

Mexico5

57

Philippines

Number ofirradiators

Number ofworkers

3

16

1

5

1

2

2

27

Republic of Korea

4

8

6

24

United States

1

22

3

33

333. A total of 14 countries responded to the UNSCEAR Occupational Exposure Survey in the period
2003–2014. Nine other countries provided data within the period 2015–2018. The data available over thethree periods are provided in table A.20 in the electronic attachment. The data provided in the UNSCEAR
2008 Report [U10] for 2000–2002 were added to the survey for the period 2000–2004. The averageannual effective dose for monitored workers ranges from <MDL to 0.65 mSv in the latest period, 2010–2014. According to the survey data, female workforce represents about 10% of the monitored workers.
334. The worldwide level of occupational exposure is evaluated on the basis of the methodology
described in section II.E.1. As described before, the mathematical model was derived on the basis of thenumber of gamma irradiators as predictor parameters to estimate the number of workers for industrial
irradiation. The worldwide occupational exposure arising from industrial irradiation over the periods
2005–2009 and 2010–2014 are presented in table 41 and table A.20 in the electronic attachment. Assumingthat the average number of gamma irradiators was 6,182 for the period 2005–2009, the worldwide numberof monitored workers was estimated as 82,000 for that period. Assuming that the annual increasing rateof 60Co installed capacity was 6% since 2008, as predicted, the average number of gamma irradiators wasestimated as 7,830 for the period 2010–2014. Applying the same model derived for the period 2005–2009,
the estimated number of monitored workers worldwide was 110,000 for the period 2010–2014. There is106 UNSCEAR 2020/2021 REPORTno statistically significant correlation between the number of irradiators and the average annual effective
dose. The estimated average annual effective dose is the average values weighted by the workforce of thecountries that responded to the UNSCEAR Occupational Exposure Survey: 0.6 mSv for 2005–2009 and
0.4 mSv for 2010–2014. Assuming that the derived average annual effective dose represents theworldwide average annual effective dose, the average annual collective effective doses are 49 and 44 man Sv
for 2005–2009 and 2010–2014, respectively. The estimates for the period 2000–2004 were not madebecause of lack of data for the predictor parameter. The Committee recognized that the number ofmonitored workers and the average annual collective effective dose is underestimated, which is because
the estimated values were based on the number of gamma irradiators; the e-beam irradiators were notincluded in the calculation. The IAEA survey [I6] conducted between 2004 and 2008 estimated theworldwide number of sterilization facilities and showed that the number of e-beam irradiators represented
only 1% of the total number of irradiators.
Table 41. Estimated worldwide levels of annual occupational exposure from industrial irradiation
Number of monitored
workers(103)

Average annual collective
effective dose(man Sv)

Average annual effective
dose of monitored workers(mSv)

2005–2009

82

49

0.6

2010–2014

110

44

0.4

Period2.

Industrial radiography335. Industrial radiography uses non-destructive testing to inspect material and components with theobjective of locating and quantifying defects and degradation in material properties that would lead tothe failure of engineering structures. In general, industrial radiography uses X-rays or gamma emitters.
The most commonly used gamma emitter is 192Ir but other radionuclides, such as 75Se, are also used on asmaller scale. After crossing the specimen to be investigated, photons are captured by a detector such asa silver halide film, a phosphor plate or a flat panel detector. The examination can be performed in static
2D set-up (radiography), in real time 2D set-up (fluoroscopy), or in 3D set-up after image reconstruction(by computer tomography). It is also possible to perform tomography in nearly real time (4-dimensional
computer tomography). Detectors can also be used to analyse the X-ray spectrum. Techniques such as
X-ray fluorescence, X-ray diffractometry and several others complete the range of tools that can be used
in industrial radiography.
336. Industrial radiography is performed in two quite different situations. In the first, it is carried out ata single location, usually in a permanent facility that has been designed and shielded for the purpose, inwhich case, items to be radiographed are brought to the facility. In the second situation, the radiography
is conducted at multiple locations in the field, in which case the radiographic equipment is brought to thelocation where the radiograph is required, often referred to as “site radiography”. There are usuallysignificant differences in the degree of control that can be exercised in the two situations. Site radiography
with mobile sources is often performed under challenging environmental circumstances such as difficultaccess to the object to be radiographed, bad weather conditions, night-time when few people are in thevicinity of the controlled area. Thus, radiological incidents with high exposure could occur more often in
mobile radiography [U10].
337. The IAEA established ISEMIR, a web-based tool for companies performing non-destructive testingby industrial radiography. ISEMIR is used to regularly collect and analyse occupational radiation dose
data for industrial radiography workers and to use this information to improve and optimize their radiation

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 107

protection. A total of 423 radiographers provided data to the ISEMIR-IR database. Over 200 radiographers
provided a value for their effective dose in 2009: the average annual effective dose was 3.4 mSv, with areported maximum annual effective dose of 30 mSv. The majority of radiographers (76%) stated thatthey received an annual effective dose of less than 5 mSv in 2009, nearly one-quarter received a dose
between 5 and 20 mSv, and a small percentage (2%) received a dose greater than 20 mSv. The data on
average effective doses for different regions are shown in table 42. On the basis of data from 141 radiographers
who provided both annual doses and workloads, the estimate (at the 95% level) of the mean occupationaldose per exposure was 4.8 ± 2.3 µSv. Data for radiographers with workloads of less than 100 instancesof exposure per year were excluded from the analysis shown in table 42. Data from 129 radiographers
were used to estimate the average occupational dose per exposure, which was 2.9 ± 1.2 µSv. There wasno statistically significant difference in the mean dose per exposure for radiographers using only gamma
radiation sources and those using only X-ray sources [I8, I11, I20].
Table 42. Information on occupational exposure for radiographers in different regions [I11]
Number of
responses
with data

Number of
responses
without data

Mean

Min

Q1a

MedianQ3b

Max

Africa

9

8

1.9

0.0

0.0

0.6

2.4

8.5

Asia-Pacific

24

25

4.5

0.0

0.1

1.4

5.3

30

Europe

92

74

2.4

0.0

0.1

1.4

4.1

8.9

Central andSouthAmerica

41

31

3.0

0.0

0.3

1.6

2.9

20

North
America

68

60

5.0

0.0

0.7

3.1

8.0

30

Global

234

198

3.4

0.0

0.3

1.8

4.7

30

Regionsa

25th percentiles.

b

75th percentiles.

Effective dose (mSv)

338. The available data over the periods are given in table A.20 in the electronic attachment. Twenty-fivecountries responded to the UNSCEAR Occupational Exposure Survey within the period 2003–2014.
Three other countries provided data within the period 2015–2018. The data provided in the UNSCEAR
2008 Report [U10] for 2000–2002 were added to the survey for the period 2000–2004. Data obtained
from the literature have been used to supplement the available data for the periods 2005–2009 and 2010–2014 [B4, B27, E10, U10]. The average annual effective dose, reported by the countries for the studied
five-year periods between 2000 and 2014, ranges from 0.04 to 8.7 mSv.
339. The worldwide level of occupational exposure is evaluated on the basis of the methodology
described in section II.E.1. An attempt was made to use two predictor parameters, GDP per capita andpetroleum production, to estimate the worldwide level of exposure for industrial radiography. There wasno statistically significant correlation between the average number of workers and average annual
effective dose for each period of the analysis and parameters. No other worldwide data are available thatcan be used as a predictor parameter specific to industrial radiography. Due to the lack of an appropriate
predictor parameter to estimate reliable levels of occupational exposure, the estimated average numberof monitored workers for the 2005–2009 and 2010–2014 periods is assumed to be the same as for theperiod 2000–2002 previously estimated for the UNSCEAR 2008 Report [U10]. This assumption wasapplied because the analysis of the trends for the number of monitored workers in the countries that
responded to the UNSCEAR Occupational Exposure Survey showed that, in general, there was no change

108 UNSCEAR 2020/2021 REPORTin the number of workers over time. According to the reported data, the female workforce represents
about 5% of the number of monitored workers.
340. The average annual effective dose assumed in the current analysis is the average annual effective
dose of the countries that responded to the UNSCEAR Occupational Exposure Survey weighted by the
number of monitored workers in each country. The average annual effective dose values are 1.5, 1.7 and1.1 mSv for 2000–2004, 2005–2009 and 2010–2014, respectively. The average annual effective doses
are similar to the global median value estimated by the ISEMIR for 2009, which was 1.8 mSv [I20].
Additionally, there is a significant decreasing trend in the average annual effective dose for the years
1975–2014 for monitored workers’ average annual effective dose (from 2.6 to 1.1) as reported by theircountries. In order to estimate the average annual collective effective dose, the average annual effective
dose weighted by the number of workers will be assumed as the global estimate.
341. The worldwide estimated levels of occupational exposure are shown in table 43, table A.20 in theelectronic attachment and figure VII. There was an increase in the number of monitored workers from72,000 (1975–1979) to 116,000 in the first two periods (1975–1979 and 1980–1984) and then the numberof monitored workers remained about the same in the last six periods until 2014, at approximately
113,000. Assuming that the average annual effective dose estimated for the three last periods represents
the worldwide average values, it seems that the average annual effective dose dropped from 2.6 to
1.1 mSv from 1975–1979 to 2010–2014. The average annual collective effective dose follows the same
pattern as the number of workers, increasing from 190 to 230 man Sv in the first two periods, thendropping to 126 man Sv for the period 2010–2014 because of the decreasing average annual effective
dose. According to the UNSCEAR Occupational Exposure Survey conducted with IAEA assistance,
several countries in Africa use industrial radiography; however, no African countries responded to thesurvey. Uncertainties on the estimates were not evaluated because of the lack of data.
Table 43. Estimated worldwide levels of annual occupational exposure in industrial radiographyaNumber ofmeasurably
exposedworkers (103)

Average annual effective dose(mSv)

Average annual
collective
effective dose(man Sv)

Monitored
workers

PeriodNumber ofmonitored
workers(103)

1975–1979a

72

190

2.6

1980–1984a

116

230

2.0

a

1985–1989

108

160

1.4

1990–1994a

106

53

170

1.6

3.2

a

1995–1999

110

50

163

1.5

3.3

2000–2004

113

50

210

1.8

2005–2009

113

190

1.7

2010–2014

113

130

1.1

Values from earlier UNSCEAR reports [U3, U4, U6, U8, U10].

Measurably
exposed workers

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 109

Figure VII. Trends in number of monitored workers, average annual effective dose and averageannual collective effective dose for industrial radiography

110 UNSCEAR 2020/2021 REPORT

3.

Luminizing

342. Luminizing is one of the oldest industrial uses of ionizing radiation. For many years radioluminous
paint has been used in products where the ability to see an indication in the dark was considered useful.
Radionuclides have been used in the luminous paint industry for many years, the radiation emitted being
converted into light by a scintillator (usually zinc sulphide). For much of the 20th century, 226Ra was themost widely used radionuclide, but in recent years, for various reasons, this has been replaced by 3H(tritium) and 147Pm (promethium). In addition, improved technology has, in some cases, enabledmanufacturers to reduce the amount of radioactive material used in certain products.
343. More recently, gaseous tritium light sources have also been incorporated into products to provide asource of illumination. Some examples of widely available radioluminous products are timepieces, map
illuminators, navigational instruments (e.g., compasses), exit signs, torches, novelty items (e.g., key
rings) and fishing floats. Examples of radioluminous products available to only a small number of
specialists are weapon sights, signs, dials and switches (e.g., on boats and aircraft). When compared to
products containing radioluminous paint, significantly greater activities of tritium gas are required to
produce the same degree of brightness.
344. Some fluorescent lamps have small quantities of a variety of radionuclides in order to provide initial
ionization for the arc that energizes the phosphor coat on the inside surface of the lamp to produce visible
light. In addition, thoriated electrodes and thorium iodate are often used in halogen vapour lamps.
345. The available data for the periods of interest are shown in table A.20 in the electronic attachment.
Four countries responded to the UNSCEAR Occupational Exposure Survey within the period 2003–2014.
Due to the limited occupational data provided, the worldwide levels of occupational exposure in theluminizing subsector were not estimated. The average annual effective dose for monitored workers
provided from the survey ranged from 0.01 to 0.69 mSv. According to the reported data, the female
workforce represents about 30% of the number of monitored workers.
346. The data from the countries that responded to the UNSCEAR Occupational Exposure Survey for
2010–2014 showed that there are at least 1,700 monitored workers, 3% of whom are exposed tomeasurable doses. The average annual effective doses decreased over time, from 7.4 mSv in the period
1975–1979 to 0.05 mSv in the period 2010–2014.

4.

Radioisotope production and distribution

347. Radioisotopes are produced for a great variety of industrial and medical purposes. The main sourceof occupational exposure in radioisotope production and distribution is external irradiation; in somecases, internal exposure may make a slight contribution to the effective dose. In general, however, internal
exposure has not been included in reported statistics for occupational exposure except in more recent
years and, even then, their inclusion is far from universal. Reporting conventions for workers involved
in radioisotope production may also vary from country to country (e.g., with regard to whether thereported doses include only those arising during the initial production and distribution of radioisotopes
or whether they include also those arising in the subsequent processing, encapsulation, packaging anddistribution of radionuclides that may have been purchased in bulk elsewhere), and this may affect thevalidity of comparisons between reported doses.
348. The number of cyclotrons dedicated to the production of positron-emitting radionuclides isincreasing in medical institutions/hospitals owing to the well-established role of positron emission
tomography imaging in clinical practice. The radiation safety issues in a cyclotron facility are much

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 111

different from those in conventional nuclear medicine production facilities because of the presence ofpenetrating gamma radiation of 511 keV, higher specific gamma ray constant of positron emitters andthe secondary neutrons from the cyclotron during production. The radiation protection issues at such afacility are complex and the radiation and safety controls should be stringent.
349. A study on the risks of radiation exposure during cyclotron maintenance activities noted thatmaintenance of high workload cyclotrons may involve a potentially high risk of inhalation of strongly
activated particulate matter [C1]. The average annual effective dose for workers of the Cyclotron Centerin Taiwan, China, was estimated as 2.1 mSv for Hp(10) and the average equivalent dose (skin) to fingers
as 96.2 mSv for Hp(0.07) [K14].
350. The exposure of workers at a cyclotron accelerator radioisotope production facility in Brazil wasrecorded for the years 2007–2011. The average annual effective doses for three workgroups are presented
in table 44 [S11]. The target group receiving the highest exposure was described as being responsible forthe maintenance, preparation and switching of targets, and also for intervention in cyclotron beam lines,
which happens when the cyclotron must be turned off so that potential flaws can be repaired.
Table 44. Average annual effective dose for cyclotron facility workers in Brazil [S11]Workgroup

Average annual effective dose by year (mSv)
2007

2008

2009

2010

2011

Target

15.7

11.1

9.4

7.4

11.4

Operation

5.7

1.9

3.3

1.9

4.1

Radioprotection

7.0

5.2

6.1

3.9

5.0

351. National data on occupational exposure arising from radioisotope production and distribution overthe period 2000–2014 are given in table A.20 in the electronic attachment. Fourteen countries responded
to the detailed UNSCEAR Occupational Exposure Survey within the period 2003–2014. The data
provided in the UNSCEAR 2008 Report [U10] for 2000–2002 were added to the survey for the period
2000–2004. Data obtained from the literature have been used to supplement the available data for theperiod 2005–2009. The average annual effective dose from the survey data ranges for monitored workers
from 0.10 to 4.53 mSv. Data obtained from the literature [S3] provided a maximum average annual dose
for the “target” working group of 12 mSv. According to the reported data, the female workforce
represents about 8% of all monitored workers.
352. Two predictor parameters, GDP per capita and number of research reactors, were used in an attempt
to estimate the worldwide level of exposure for radioisotope production. The number of research reactors
were obtained on the IAEA Research Reactor Database [I21]. There was no statistically significant
correlation between the average number of workers and average annual effective dose for each period of
the analysis and parameters. No other worldwide data are available that can be used as a predictor
parameter specific for radioisotope production, which prevented worldwide extrapolation.
353. The data from the countries that responded to the UNSCEAR Occupational Exposure Survey for
2010–2014 showed that there are at least 4,400 monitored workers, 40% of whom are exposed tomeasurable doses. The average annual effective doses have decreased over time, from 2.2 mSv in the
period 1975–1979 to 0.8 mSv in the period 2010–2014.

112 UNSCEAR 2020/2021 REPORT

5.

Well logging

354. Mining, ground engineering and water industries, and oil and gas exploration and production(conventional and unconventional, e.g., fracking) make extensive use of radioactive sources, and in somecases radiation generators, for characterizing and evaluating geological formations and borehole and wellconstructions (IAEA SSG-57) [I17]. Well logging techniques are used to explore geological formations
by using sealed gamma 137Cs or neutron 241Am-Be sources to measure and record the density or porosityof geological strata along a borehole.
355. Exposure data from the UNSCEAR Occupational Exposure Survey (2000–2004, 2005–2009,2010–2014) for the well logging subsector are shown in table A.20 in the electronic attachment. Ninecountries responded to the detailed survey for the period 2003–2014. A total of 21 countries, including
those nine, responded to the simplified survey for the period 2011–2018; these data were added to theextrapolation. The data provided in the UNSCEAR 2008 Report [U10] for 2000–2002 were added to thesurvey for the period 2000–2004. The average annual effective dose of monitored workers from thesurvey data for the period 2000–2014 ranges <MDL to 2.7 mSv. According to the reported data, thefemale workforce represents 5% of the number of monitored workers.
356. The predictor parameters to estimate the worldwide level of occupational exposure in the welllogging subsector were petroleum production, mineral production and GDP per capita. There is no
statistically significant correlation between these parameters and the number of monitored workers andthe average annual collective effective dose. The adjusted R2 values stemming from the correlation
attempts were all below 0.5, and such correlations are not appropriate to use in deriving reliable predictedvalues. Because of lack of worldwide predictor parameter data, no further attempt was made to
extrapolate the level of occupational exposure in the well logging subsector. The data from the countries
that responded to the UNSCEAR Occupational Exposure Survey for 2010–2014 showed that of at least
11,290 monitored workers, 12% are classified as measurably exposed. The average annual effective dose
decreased over time, from 1.3 mSv in the period 1975–1979 to 0.3 mSv in the period 2010–2014.

6.

Accelerator operation

357. Consideration is limited here to occupational exposure arising from accelerators used for nuclear
physics research at universities and at national and international laboratories. Accelerators (generally ofsomewhat smaller size) are increasingly being used for medical, therapeutical and radiopharmaceutical
purposes. However, exposure arising from those uses is more appropriately considered under medical
uses of radiation in section IV.B. Similarly, accelerators are also found in radiography andcommercial radioisotope production but, again, these are dealt with under those work categories.
Most exposure resulting from accelerators arises from induced radioactivity and occurs mainly
during the repair, maintenance, and modification of equipment. The exposure results mainly fromgamma rays from the activation of solid surrounding material by leakage penetrating radiation such as
neutrons, high-energetic gamma rays and, in some cases, secondary induced heavy particles. The
potential committed effective dose from internal exposure in the normal operation mode ofaccelerators is usually negligible in comparison with the effective dose due to external irradiation.
358. Exposure data from the UNSCEAR Occupational Exposure Survey (2000–2004, 2005–2009,2010–2014) on occupational exposure in accelerator operation are given in table A.20 in the electronic
attachment. Seven countries responded to the detailed survey for the period 2003–2014. The data provided
in the UNSCEAR 2008 Report [U10] for 2000–2002 were added to the survey for the period 2000–2004.
The average annual effective dose of monitored workers from the survey data ranges from <MDL toANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 113

1.63 mSv. According to the reported data, the female workforce for the three periods is 1–20% of thenumber of monitored workers.
359. The predictor parameter to estimate the worldwide level of occupational exposure in the accelerator
operation subsector was GDP per capita. There is statistically significant correlation between thepredictor parameter and the number of monitored workers, the number of measurably exposed workers
and the average annual collective effective dose for the period 2010–2014. The adjusted R2 values were
all 0.9. However, the extrapolation model was derived from data of only six countries. In addition, thechallenge here is to define the countries that should be included in the extrapolation calculation. Becauseof limited information, the results of the extrapolation were not used here. The data from the countries
that responded to the UNSCEAR Occupational Exposure Survey for 2010–2014 showed that of at least
10,000 monitored workers, 10% are classified as measurably exposed. The average annual effective dose
decreased over time from 1.6 mSv (1975–1979) to about 0.1 mSv (2000–2014).

7.

Industrial gauges

360. Industrial gauges are mechanical tools used to measure, monitor, and control the thickness of sheet
metal, textiles, paper napkins, newspaper, plastics, photographic film, and other products as they are
manufactured. Non-portable gauging devices (i.e., gauges mounted in fixed locations) are designed formeasurement or control of material density, flow, level, thickness, or weight. The gauges contain sealed
sources that radiate through the substance being measured to a readout or controlling device. Portable
gauging devices, such as moisture density gauges, are used at field locations. These gauges contain agamma-emitting sealed source, usually 137Cs, or a sealed neutron source, usually 241Am-Be [U20].
361. Industrial gauges are required for industries where pressure and temperature are critical parameters.
Growing industrialization is one of the factors driving the demand for industrial gauges. The global
market for industrial gauges is divided into seven regions, namely North America, Latin America, Asia
Pacific excluding Japan, Western Europe, Eastern Europe, Japan and the Middle East and Africa. North
America and Western Europe account for a major share of the global industrial gauges market. This is
attributed to the presence of vast manufacturing bases such as those for chemicals, food, dairy products,
and paper & pulp, which require industrial gauges in the manufacturing plants. In the Pacific excluding
Japan region, the industrial gauge market is expected to be boosted by western companies shifting their
manufacturing facilities there because of its cheap labour and raw material resources. The Middle East
and Africa industrial gauge market is driven mainly by the oil and gas industry [P8].
362. Exposure data from the UNSCEAR Occupational Exposure Survey (2000–2004, 2005–2009,2010–2014) on the use of industrial gauges are given in table A.20 in the electronic attachment. Ninecountries responded to the survey for the period 2003–2014. Another 15 countries responded to thesimplified survey for the period ranging from 2011 to 2018. The average annual effective dose ofmonitored workers from the survey data ranges from <MDL to 0.84 mSv. According to the reported data,
the female workforce represents 10–15% of the number of monitored workers.
363. The predictor parameters applied to estimate the worldwide level of occupational exposure in theindustrial gauge subsector were petroleum production and GDP per capita. There is no statisticallysignificant correlation between these predictor parameters and the number of monitored workers and theaverage annual collective effective dose. The adjusted R2 values were all below 0.5, which are notappropriate for deriving any reliable predicted value. Because of lack of worldwide predictor parameter
data, no further attempt was made to extrapolate the level of occupational exposure in this subsector. The
data from the countries that responded to the UNSCEAR Occupational Exposure Survey for 2010–2014

114 UNSCEAR 2020/2021 REPORT

showed that there are at least 610 monitored workers. The average annual effective dose of monitored
workers from countries that reported data is 0.2 mSv. According to survey conducted with IAEA
assistance, several countries in Africa carry out practices involving industrial gauges [I18].

8.

All other industrial uses

364. The many other uses of radiation in industry include those in soil moisture gauges, thickness gauges
and X-ray diffraction but their occupational exposure data are, in general, not separately identified orreported. The number of workers potentially exposed in these other uses may substantially exceed thenumber in the few occupations for which data have been separately presented in this section. The average
exposure levels of workers involved in “other uses of radiation” is generally low.
365. Exposure data from the UNSCEAR Occupational Exposure Survey (2000–2004, 2005–2009,2010–2014) on all other industrial uses are given in table A.20 in the electronic attachment. Twenty
countries responded to the survey for the period 2003–2014. A total of 26 countries, including 13 whocompleted the detailed survey, responded to the simplified survey for the period 2011–2018. Dataobtained from the literature were used to supplement the available data for all periods [A2, B5, F1, H5,
U10]. The data provided in the UNSCEAR 2008 Report [U10] for 2000–2002 were added to the survey
for the period 2000–2004. The average annual effective dose of monitored workers from the survey data
ranges from 0.03 to 1.4 mSv. Japan, Germany, and France represent about 70% of the reported monitored
workers for the period 2000–2004. Feedback indicates that national systems for data collecting do notallow the data to be readily separated into the categories used in this review.
366. The predictor parameter applied to estimate the worldwide level of occupational exposure in the“all other industrial uses” subsector was GDP per capita. No statistically significant correlation between
this predictor parameter and the number of monitored workers or the average annual collective effective
dose could be established. The data from the countries that responded to the UNSCEAR Occupational
Exposure Survey for 2010–2014 showed that there are at least 120,000 monitored workers classified in
the category. The average annual effective dose of monitored workers from countries that reported data
is about 0.3 mSv, while the average annual effective dose of measurably exposed workers is 1.2 mSv forthe period 2010–2014. According to the reported data, the female workforce represents 15–20% of thenumber of monitored workers.

9.

Summary

367. The national data on all industrial uses of radiation grouped together are presented in table A.21 in
the electronic attachment. The data are more complete than for the separate categories. Because of the lackof a reliable predictor to estimate the worldwide level of occupational exposure in the industrial sector,
the estimate for all industrial uses was based on the trends for all countries. The same approach wasapplied in the UNSCEAR 2008 Report [U10]. The estimate of the worldwide workforce in the industrial
sector was 1.1 million for the period 2010–2014. The uncertainty interval of the worldwide number ofworkers ranges from 0.56 to 2.2 million. The workforce increased by a factor of two over the 40-year
period of evaluation, from 0.5 to 1.1 million. This value may be an underestimation due to the limited
representativeness of reported data. The estimated value for the average annual effective dose decreased
by a factor of four over the 40-year period of evaluation (1.6 to 0.4 mSv). The uncertainty interval of theworldwide average annual effective dose ranges from 0.2 to 0.8 mSv. The estimated average annual
collective effective dose was 440 man Sv for the period 2010–2014; it decreased by a factor of two overthe 40-year period of evaluation. The worldwide level of exposure for the total industrial sector isANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 115

presented in table 45, table A.21 and figure VIII. Because the estimate of the worldwide level of exposureis based on trends that countries reported to the UNSCEAR Occupational Exposure Survey, noassessment of uncertainties was conducted.
368. There is a wide variation in the average annual effective dose and the percentage of measurably
exposed workers. This variation may be explained by many factors, including the way data are recorded
in national databases, and the radiation protective measures implemented by each country.
369. For industrial irradiation, it is the first time that the Committee had enough information to derive
the worldwide number of monitored workers. This was carried out for the periods 2005–2009 and 2010–2014, using the number of gamma irradiators as a predictor parameter. The total number of workers in
the industrial irradiation subsector for the period 2010–2014 is estimated as 110,000, which represents
about 10% of the total number of monitored workers in the industrial sector. The average annual
collective dose is estimated to be 44 man Sv for the period 2010–2014, which represents about 9% of theaverage annual collective dose for the total industrial sector. The estimated average annual effective doseis below 1 mSv. The Committee recognizes that the number of monitored workers and average annual
collective effective dose are underestimated. That is because the estimated values were based on thenumber of gamma irradiators; the e-beam irradiators were not included in the calculation. An IAEA
Survey conducted in 2004–2008 to estimate the worldwide number of sterilization facilities showed thatthe number of e-beam irradiators represented about 1% of the total number of irradiators [I6].
370. For industrial radiography, the Committee has estimated the worldwide level of occupational
exposure since the period 1975–1979. Due to lack of statistically significant correlation between theoccupational parameters and the predictor parameter, the worldwide number of monitored workers forthe respective periods 2000–2004, 2005–2009 and 2010–2014 was derived on the basis of the observed
trend in the number of monitored workers for the countries that responded to the UNSCEAR
Occupational Exposure Survey. It was assumed that the size of the workforce was the same during theperiod 2000–2014. The industrial radiography subsector represents about 10% of the total number ofmonitored workers in the industrial sector. The estimated number of monitored workers increased from72,000 (1975–1979) to 113,000 (2010–2014). The average annual collective effective dose is estimatedas 126 man Sv for the period 2010–2014, which represents about 30% of the average collective dose forthe total industrial sector. It decreased from 190 man Sv (1975–1979) to 126 man Sv (2010–2014). The
estimated average annual effective dose was below 1.1 mSv, decreasing from 2.6 mSv (1975–1979) to
1.1 mSv (2010–2014). Since the trends of countries was the parameter applied to extrapolate the data, theestimate of the uncertainty was not feasible.
371. For luminizing, the worldwide number of monitored workers was not estimated due to the limited
number of countries responding to the UNSCEAR Occupational Exposure Survey. On the basis of thedata reported for 2010–2014, the number of monitored workers was approximately 1,700. The averageannual effective dose was 0.05 mSv. The average annual effective dose from the countries that responded
to the survey decreased significantly over time, from 7.4 mSv (1975–1979) to below 1 mSv during thelast three periods (2000–2014).
372. For radioisotope production, the worldwide number of monitored workers was not estimated dueto the limited number of countries responding to the UNSCEAR Occupational Exposure Survey and lackof statistically significant correlation between the data and the predictor parameters (GDP and number of
research reactors). The data reported for 2010–2014 show that there were at least 4,470 monitored
workers, 40% of whom were exposed to measurable doses. The average annual effective doses decreased
over time, from 2.2 mSv in the period 1975–1979 to 0.8 mSv in the period 2010–2014.

116 UNSCEAR 2020/2021 REPORT373. For the well logging subsector, the worldwide number of monitored workers was not estimated dueto the lack of an appropriate predictor parameter for the extrapolation model. On the basis of the datareported by the countries that responded to the UNSCEAR Occupational Exposure Survey, the numberof monitored workers increased over time. The reported total number of monitored workers for the period
2010–2014 was approximately 11,000. The average annual effective dose decreased over time from
1.3 mSv (1975–1979) to 0.3 mSv (2010–2014).
374. For accelerator operation, the worldwide number of monitored workers was not estimated because
no suitable correlations for extrapolations could be established. On the basis of the data reported by the
responding countries, the number of monitored workers increased over time. The reported total numberof monitored workers for the period 2010–2014 was approximatively 10,000. The average annual
effective dose was below 1 mSv for 2010–2014; it decreased over time from 1.6 mSv (1975–1979) to
0.06 mSv (2010–2014).
375. For the industrial gauge subsector, the worldwide number of monitored workers was not estimateddue to the lack of an appropriate predictor parameter for the extrapolation model. On the basis of the datareported by the countries that responded to the UNSCEAR Occupational Exposure Survey, the total
number of monitored workers for the period 2010–2014 was approximately 600 and the average annual
effective dose was about 0.2 mSv.
376. For the “other industrial uses of radiation” subsector, the worldwide number of monitored workers
was not estimated due to the inability to establish an appropriate predictor parameter. Based on the datareported, the number of monitored workers decreased over time. The reported total number of monitored
workers was 127,000 for the period 2010–2014; approximately 50% of the reported workforce. The
estimated average annual effective dose during that period was about 0.3 mSv.
377. The summary of the estimated worldwide levels of occupational exposure in the industrial sector ispresented in table 45, table A.21 and figure VIII. The number of monitored workers has doubled over the
past four decades. The average annual effective doses to monitored workers involved in industrial usesof radiation consistently decreased to a level of around 0.5 mSv since the 1990s. The largest contribution
to the occupational exposure comes from industrial radiography, industrial irradiation and the “otherindustrial uses of radiation” subsectors. The occupational exposure data presented in table 45 are roughestimates of the number of workers, average annual effective dose and average annual collective effective
dose. The estimated values were derived on the basis of trends in the countries that provided data.
Table 45. Estimated worldwide levels of occupational exposure in industrial sector
Number of monitored
workers(103)

Average annual collective
effective dose(man Sv)

Average annual effective
dose to monitored workers(mSv)

1975–1979a

530

870

1.6

1980–1984a

690

940

1.4

1985–1989a

560

510

0.9

a

1990–1994

700

360

0.5

1995–1999a

790

315

0.4

2000–2004

869

348

0.4

2005–2009

1 043

419

0.4

2010–2014

1 100

440

0.4

Perioda

Values from earlier UNSCEAR reports [U3, U4, U6, U8, U10].

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 117

Figure VIII. Trends in number of monitored workers, average annual effective dose and averageannual collective effective dose for all industrial uses

118 UNSCEAR 2020/2021 REPORT

D. Military uses
378. Radiation exposure of workers in military activities can be grouped into three broad categories:(a) those arising from the production and testing of nuclear weapons and associated activities; (b) thosearising from the use of nuclear energy as a source of propulsion for naval vessels; and (c) those arisingfrom the use of ionizing radiation for the same wide range of purposes for which it is used in civilian
spheres (e.g., research, transport and non-destructive testing).
379. According to the information published in 2014, the United States military has effectively employedionizing radiation since it was first introduced during the Spanish-American War in 1898. Currently, themilitary annually monitors 70,000 persons for occupational exposure, about 2% of its workforce. In
recent years, the Departments of the Navy (including the Marine Corps), the Army, and the Air Force all
have a low collective dose that remains close to 1 man Sv annually. Only a few coast guards are now
routinely monitored. As with the nuclear industry as a whole, the Naval Nuclear Propulsion Program
records a higher collective dose than the remainder of the United States military. The average annual
collective effective doses for 2006 are presented in table 46. Responsible for measuring the individual
radiation exposure are the Army, Naval, and Air Force Dosimetry Centers, and various naval reactor sites
comprising more than 50% of the National Voluntary Laboratory Accreditation Program’s accredited
radiation dosimeter processors [N8]. External exposure is monitored for whole body exposure andextremity exposure. The measurement techniques include thermoluminescent and optically stimulated
luminescent dosimeters, and electronic pocket dosimeters. Individual monitoring to evaluate the intakeof radionuclides is performed for the personnel in Army, Navy, Air Force, and the naval reactor sites.
The internal monitoring techniques include in vivo and in vitro bioassays. The United States military
maintains occupational exposure records on over two million individuals from 1945 through the present.
These records are controlled in accordance with the Privacy Act of 1974 but are available to affectedindividuals or their designees and other groups performing sanctioned epidemiology studies [B19].
Table 46. Radiation occupational exposure data for United States military personnel in 2006 [B19]
Number of monitored
workers (103)

Average annual collective
effective dose (man Sv)

Average annual effective
dose (mSv)

Naval reactors

46

20

0.44

Army

12

1.0

0.08

Air Force

6.6

0.6

0.09

Navy and Marine Corps

6.0

1.3

0.22

Total

70.6

22.9

0.32

Armed services

380. The occupational exposure data of the military personnel assigned to tenders, bases, andnuclear-powered ships from operation and maintenance of naval nuclear propulsion plants and to ship
ward personnel are evaluated annually by the United States Department of Navy. The annual data for
number of monitored workers, dose distribution and total effective dose are presented for 64 years (from1954 to 2018). The data presented in the reports provide a good picture of the trend of occupational
exposure showing that, despite the significant increase of the number of ships being overhauled, there isa substantial decrease in effective doses [M8].
381. Radiation exposure at the prototype naval nuclear propulsion plants originates primarily from
PWRs. In this type of reactor, water circulates through a closed piping system to transfer heat from thereactor core to a secondary steam system isolated from the reactor cooling water. Trace amounts ofcorrosion and wear products are carried by reactor coolant from reactor plant metal surfaces. Some of

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 119

these corrosion and wear products are deposited on the reactor core and become radioactive fromexposure to neutrons. Reactor coolant carries some of these radioactive products through the piping
systems where a portion of the radioactivity is removed by a purification system. Most of the remaining
radionuclides transported from the reactor core are deposited in the piping systems. The reactor core is
installed in a heavy-walled pressure vessel within a primary shield [M9].
382. The primary shield limits radiation exposure from the gamma rays and neutrons produced when thereactor is operating. Reactor plant piping systems are installed primarily inside a reactor compartmentthat is itself surrounded by a secondary shield. Access to the reactor compartment is permitted only afterreactor shutdown. Most radiation exposure to personnel comes from inspection, maintenance, and repair
inside the reactor compartment. The major source of the radiation exposure is 60Co deposited inside thepiping systems. Radiation exposure to personnel from neutrons during reactor operation is much less thanfrom gamma radiation. After reactor shutdown, when maintenance and other support work is executed,
no neutron exposure is detectable. Therefore, the radiation exposure at prototypes is primarily fromgamma radiation [M9].
383. Radiation exposure at the expended core facility at the naval reactor facility is due primarily to
gamma rays emitted by irradiated reactor fuel and structural components that were inside the reactor
vessel during operation and became radioactive by exposure to neutrons. Work on these components is
performed remotely in specially designed shielded cells, in deep water pits that shield personnel, or withshielded equipment used to place spent fuel into interim dry storage [M9].
384. Radiation exposure at the naval reactor’s laboratories is basically external, attributable toexamination and analysis of irradiated fuel and other material, and to decontamination anddecommissioning of obsolete facilities. Gamma rays is the significant contributor to dose. Although alphaand beta radiation are present, they are generally well shielded. Neutron radiation contributes very little
to doses at the laboratories [M9].
385. The UNSCEAR 1993 Report [U6] addressed the potential for extrapolation based on normalized
collective dose, with the normalization performed in terms of unit explosive yield for weapons, and per
ship or installed nuclear capacity for the Naval Nuclear Propulsion Program. It concluded that such
extrapolation was not viable. Pending the acquisition of further data, the UNSCEAR 1993 Report [U6]proposed adopting a very simple approach for estimating worldwide exposure from this source, namelythat the worldwide collective dose from military activities is greater by a factor of three than the sum of
the collective dose in the United Kingdom and the United States. Four assumptions underlay the choiceof this factor. First, the levels of military activities in the former Soviet Union and the United States werebroadly comparable. Second, the levels of exposure in the former Soviet Union were greater than in the
United States by an indeterminate amount thought to exceed a factor of 2 in 1975–1989. Third, the levelsof exposure in France have been comparable to those in the United Kingdom. Fourth, the exposure in
China was not as high as that in the former Soviet Union or in the United States.
386. Until its UNSCEAR 2000 Report [U8], the Committee reviewed the occupational exposure
separately for weapon fabrication and associated activities and for nuclear ships and their support
facilities. This approach was not applied in the UNSCEAR 2008 Report [U10] because the data provided
by countries were pooled together. Based on the described assumptions, the estimated worldwide numberof monitored workers has been roughly constant, at between 300,000 and 400,000. The average annual
collective effective dose from military activities would have been about 400 man Sv in 1975–1979, fallingto about 250 man Sv in 1985–1989, 100 man Sv in 1990–1994, 58 man Sv in 1995–1999 and 52 man Sv
in 2000–2002. Given the crudeness of the underlying assumptions, it was not possible to give a precise
estimate of the collective dose: the worldwide average annual collective dose during the evaluated period
was about 50–150 man Sv.

120 UNSCEAR 2020/2021 REPORT

387. Exposure data from the UNSCEAR Occupational Exposure Survey (2000–2004, 2005–2009,2010–2014) for military activities are given in table A.23 in the electronic attachment. For weapon
fabrication and associated activities, only three countries (France, United Kingdom and United States)
responded to the detailed survey within the period 2003–2014. The same countries also provided data forthe subsector covering nuclear ships and their support facilities for the period 2003–2014. Twelve
countries responded to the simplified survey providing data for total military activities. Most of them
reported only data on the number of monitored workers. Some countries provided data for 2015 and 2017.
There has been an improvement in data collection since the Russian Federation provided the number ofworkers for the year of 2016 for its total military activities.
388. The total number of monitored workers reported by the countries that responded to the UNSCEAR
Occupational Exposure Survey in the period 2010–2014 is about 80,000. The Russian Federation, theUnited Kingdom and the United States account for 98% of the total reported workforce. The United Statesaccounts for 66%, the Russian Federation for 19% and the United Kingdom for 13%.
389. On the basis of the trend of occupational exposure in the United Kingdom and in the United States,
the number of monitored workers involved in weapon fabrication and associated activities decreased
from about 21,000 during the period 1975–1979 to 14,200 during 2010–2014. The average annual
effective dose decreased from 0.7 mSv during 1975–1979 to 0.1 mSv during 2010–2014. The averageannual collective effective dose decreased from 14 man Sv (1975–1979) to 1.4 man Sv (2010–2014).
390. On the basis of the trend of occupational exposure in the United Kingdom and in the United States,
the average number of monitored workers involved in nuclear ships and their support facilities increased
from about 42,000 to 47,000 in the period 1975–1979 and 2010–2014. The average annual effective dose
decreased from 2.1 mSv during the period 1975–1979 to 0.2 mSv during 2010–2014 and the averageannual collective effective dose decreased from 92 to 8 man Sv in the same periods.
391. On the basis of the trend of occupational exposure in the United Kingdom and in the United States,
it is shown that the number of monitored workers involved in all military activities decreased from about
104,000 during the period 1975–1979 to 64,000 during the period 2010–2014. The average annual
effective dose decreased from 1.3 mSv (1975–1979) to 0.15 mSv (2010–2014) and the average annual
collective effective dose decreased from 137 to 9.7 man Sv between the same periods.
392. Because very little occupational exposure data were available, the Committee was unable to deriveworldwide levels of occupational exposure from sources for military use. The occupational data collected
through the UNSCEAR Occupational Exposure Survey are few and insufficient for extrapolation. The
data would also need to be qualified in terms of completeness, in particular as to whether they cover all
significant occupational exposure related to military activities. For example, they do not include
occupational exposure arising in the mining of uranium used in either nuclear weapon or nuclear naval
programmes; nor is it clear to what extent the reported data include exposure arising during theenrichment of uranium for the weapon and naval programmes or exposure arising in the chemical
separation and subsequent treatment of plutonium.
393. In summary, data provided by the countries that responded to the UNSCEAR Occupational
Exposure Survey do not allow the derivation of a reliable estimate of the worldwide level of occupational
exposure to sources used in military activities. However, data from the United States and the United
Kingdom showed a substantial decrease in the average annual collective effective dose over time, due tothe reduction in both the workforce and the average annual effective dose.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 121

E. Miscellaneous uses of radiation
394. There are a number of occupations where radiation exposure may be involved that are not coveredby other categories. These include research in educational establishments, the management of spentradioactive sources, and transport of radioactive material outside the nuclear fuel cycle. The data reported
by countries are given in table A.22 in the electronic attachment.

1.

Educational establishments

395. Research workers in educational establishments use radioactive sources, X-ray equipment,
irradiators using 60Co or 137Cs sealed sources, training research reactors and unsealed radioactive sources
for a wide range of activities. Examples of uses include X-ray crystallography and radioactive labels (e.g.,3
H, 14C, 32P, 35S, and 125I). Also, preclinical, multimodal imaging equipment (such as micro-computer
tomography, and micro-positron emission tomography equipment) for small animals, using radionuclides
such as 18F and 99mTc.
396. Exposure data from the UNSCEAR Occupational Exposure Survey (2000–2004, 2005–2009,2010–2014) in educational establishments are given in table A.22 in the electronic attachment. Nineteen
countries responded to the detailed survey for the period 2003–2014. Several other countries responded
to the simplified survey, providing data on the number of monitored workers for the period 2013–2018.
Data obtained from the literature have been used to supplement the available data for all periods [U10].
The data provided in the UNSCEAR 2008 Report [U10] for 2000–2002 were added to the survey for theperiod 2000–2004. The average annual effective dose of monitored workers from the survey data ranges
from ≤MDL to 2 mSv.
397. The predictor parameters applied to estimate the worldwide level of occupational exposure ineducational establishments subsector were GDP per capita and the number of training research reactors.
No statistically significant correlation was found between these predictor parameters and the number ofmonitored workers and the average annual collective effective dose. The estimated worldwide number ofworkers for all educational establishments was based on the trends in increase in the sector for all
countries, which is the same approach applied in the analysis of the reported data for the UNSCEAR
2008 Report [U10]. According to the collected data, the average increase in the number of monitored
workers from 2000–2004 to 2005–2009 was 8% and from 2005–2009 to 2010–2014 it was 12%. For
measurably exposed workers, the corresponding increase from 2000–2004 to 2005–2009 was 6%, while
no change was observed from 2005–2009 to 2010–2014.
398. The estimated worldwide workforce in educational establishments increased by a factor of four
over 40 years of evaluation, from 140,000 during the period 1975–1979 to 540,000 during 2010–2014.
This number may be an underestimation due to the possible limited representativeness of the reporting
countries. The average annual effective dose was below 1.0 mSv and it decreased from 0.6 mSv (1975–1979) to 0.07 mSv (2010–2014). The estimated average annual collective effective dose decreased by afactor of two, from 74 man Sv in the period 1975–1979 to 38 man Sv in 2010–2014. The worldwide levelof exposure for the educational establishment subsector is presented in table 47 and table A.22.

122 UNSCEAR 2020/2021 REPORT

Table 47. Estimated worldwide levels of annual occupational exposure in the educational sector

Perioda

Number ofmonitored
workers(103)

Number ofmeasurably
exposed workers(103)

Averageannualcollective
effective dose(man Sv)

Average annual effective dose(mSv)
Monitored
workers

Measurably
exposedworkers

1975–1979a

140

74

0.55

1980–1984a

180

43

0.24

1985–1989a

160

22

0.14

1990–1994a

310

30

33

0.11

1.1

1995–1999a

372

29

36

0.10

1.2

2000–2004

446

30

27

0.06

0.9

2005–2009

482

32

34

0.07

2010–2014

540

32

38

0.07

1.2

Values from earlier UNSCEAR reports [U3, U4, U6, U8, U10].

2.

Disused radioactive sources399. Radioactive sources are used worldwide in various applications in medicine, agriculture, industry,transportation, construction, geology, mining, and research. Disused sources are those that are no longer
used and with no intention of being used again in the practices for which they were authorized. Spentsources, which can no longer be used for their intended purposes as a result of radioactive decay, are asubset of disused sources.
400. Short-term storage of a disused source is not itself a management option but rather a necessary interim
step in implementing one or more of the management options, such as reuse, recycling, return to a supplierand long-term storage and disposal. When a radioactive source is declared disused, it is often stored at theuser’s site pending further management. Another example is the interim storage of orphan sources (i.e.,
those outside regulatory control), found at a border control point of a State or in a facility within the metal
recycling industries. The appropriate duration for short-term storage is likely to depend on the national
strategy applicable to the disused source and the capability of the user to provide safe and secure storage. A
disused source with a relatively short half-life (e.g., less than 100 days) could be stored in a safe and secure
facility for a period necessary to allow for radioactive decay to decrease the activity concentration to a levelat which it can be released from regulatory control and managed as non-radioactive material [I14].
401. According to the IAEA definition, a disused radioactive source is no longer used, and is not intended
to be used, for the practice for which an authorization has been granted; however, the source may besuitable for other uses (e.g., research and training activities, calibration of radiation detection equipment).
Management options for disused sources, therefore, include reuse or recycling, long-term storage anddisposal, and return to supplier [I14]:(a) Reuse, in some cases, may be as simple as transferring the device to another user, whereas
recycling is always a technically demanding task that requires particular expertise and authorization;(b) Reuse of a disused source is normally subject to source integrity and quality verificationaccording to regulatory standards;

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 123(c) Reuse and recycling may require the removal of the radioactive source from the device in which
it is housed and its emplacement in a new device, which are potentially hazardous operations. If these
operations are required, they should be carried out only with appropriate authorization, knowledge,
equipment, facilities, and skills;(d) Long-term storage of disused sources, even if planned for an extended period, is not meant tobe a permanent solution but rather a stage prior to disposal. Where disposal facilities are available,consideration should be given for disused sources to be disposed of, rather than stored in a long-term
storage facility. Disposal of disused sources declared as radioactive waste (i.e., their emplacement in
an appropriate facility with no intention of retrieval) is the final step in secure management.
402. Six countries responded to the detailed UNSCEAR Occupational Exposure Survey for the period
2003–2014. Additionally, five countries responded to the simplified survey for the period between
2016–2017. Due to the limited data, the Committee was unable to estimate the worldwide level ofoccupational exposure to disused radioactive sources. About 1,000 workers were reported for the period
2010–2014. The average annual effective dose for monitored workers is of the order of 0.1 mSv during
the period 2010–2014.

3.

Transport of radioactive sources outside nuclear fuel cycle

403. Radioactive substances are used extensively in medicine, agriculture, research, manufacturing, nondestructive testing, and mineral exploration. Globally, about 20 million consignments of radioactive
material are transported each year on public roads, railways, and ships. The significant majority – about
95% – of radioactive consignments are not related to the nuclear fuel cycle. Most radioactive material
packages transported emit some penetrating ionizing radiation, and radiation exposure of transport
workers and the public may occur during their transport. The radiation exposure incurred by transport
workers can vary significantly depending on a number of factors: most important is the type of radiation
emitted (primarily gamma rays and neutrons), the radiation field intensity in the surrounding of a package
and conveyance, and the duration of exposure. However, if the international transport regulations arefollowed, the levels of exposure to the public are low during normal transport and the average annual
effective doses to transport workers are typically of the order of less than 1 mSv. Nevertheless, a few
workers, usually involved in the distribution of medical, research and industrial isotopes, could
occasionally receive somewhat higher doses [S7].
404. Ten countries responded to the UNSCEAR Occupational Exposure Survey for the period
2003–2014. Twelve countries responded to the simplified survey for the period 2010–2017.
Consequently, the Committee was unable to estimate worldwide levels of occupational exposure intransport of radiation sources due to lack of data. For the period 2010–2014, about 6,200 monitored
workers were reported by the countries responding to the survey. About 8% of the workers were classified
as measurably exposed. The average annual effective dose during this period was 0.3 mSv and formeasurably exposed workers it was 1.6 mSv.

4.

Other occupational groups

405. The “other occupational groups” category was included in the UNSCEAR Occupational Exposure
Survey to ensure that no sizeable group of exposed persons was overlooked. The data cover disparate
groups that often cut across the other categories.

124 UNSCEAR 2020/2021 REPORT

406. Nineteen countries responded to the detailed UNSCEAR Occupational Exposure Survey for theperiod 2003–2014. Additionally, 14 countries responded to the simplified survey for the period 2003–2017.
Data from the literature were used to supplement the supplied data [I5, N1, U10]. The tentative predictor
parameters applied to estimate the worldwide level of occupational exposure for the “other occupationalgroups” subsector was GDP per capita. No statistically significant correlation between the predictor
parameter and the number of monitored workers or the average annual collective effective dose oreffective dose was found. The adjusted R2 values were not appropriate for deriving reliable estimates.
For the period 2010–2014, about 35,000 workers were reported in this category by the data reported tothe survey. The average annual effective dose during the period is reported to be in the order of 0.1 mSv.

5.

Summary

407. The national data from all miscellaneous uses of radiation are presented in table A.22 in theelectronic attachment. An estimate of the worldwide level of exposure could be performed only for the
category of educational establishments. Extrapolation for other categories was not performed due to thelimited data provided by countries participating in the UNSCEAR Occupational Exposure Survey andthe lack of statistically significant correlations between the studied occupational exposure variables andthe tentative predicted parameter, GDP per capita.
408. For educational establishments, the number of monitored workers was about 90% of the total
workforce for all miscellaneous uses of radiation. The average annual collective effective dose represents
about 87% of the collective dose for all miscellaneous uses. The average annual effective dose estimatedfor monitored workers is less than 1 mSv for all studied five-year periods. The estimate of the size of theworldwide number of monitored workers is 540,000, and the corresponding average annual collective
effective dose is calculated as 38 man Sv.
409. The reported number of monitored workers, obtained through the UNSCEAR Occupational
Exposure Survey, in the category of “spent sources” or disused radioactive sources was 540, 500 and 900
for the periods 2000–2004, 2005–2009 and 2010–2014, respectively. The average annual effective dose
reported for these monitored workers was for all periods below 0.5 mSv. The average annual collective
effective dose for the period 2010–2014 was 0.1 man Sv.
410. The number of monitored workers reported in the category of transport of radiation sources(excluding transport in the nuclear fuel cycle) was 2,330, 2,400 and 6,210 for the periods 2000–2004,
2005–2009 and 2010–2014, respectively. The average annual effective doses reported for monitored
workers during all studied five-year periods were below 1 mSv. The reported average annual collective
effective dose during the period 2010–2014 was 2.1 man Sv.
411. Finally, the number of monitored workers reported through the UNSCEAR Occupational Exposure
Survey in the “other occupational groups” category was 82,800, 42,000 and 35,600 for the periods
2000–2004, 2005–2009 and 2010–2014, respectively. The average annual effective doses reported formonitored workers during all periods were about 0.1 mSv. The reported average annual collective
effective dose during the period 2010–2014 was 3.8 man Sv.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 125

F. Conclusions on occupational exposure to human-madesources412. The category of human-made sources of radiation includes the subsectors of the nuclear fuel cycle,
medical uses of radiation, industrial uses of radiation, military activities, and miscellaneous uses ofradiation. The Committee has been evaluating the level of occupational exposure for the sectors includedin the category of human-made sources of radiation since 1975. The trends in worldwide occupational
exposure arising from each sector are summarized in table 48, except for military uses, for which areliable estimate of the worldwide level of exposure was not possible. The table presents the estimates of
the worldwide number of monitored workers, average annual collective effective dose, and averageannual effective dose; the data represent the annual averages during five-year periods over 40 years, from
1975–1979 to 2010–2014. In comparison with many other sources of exposure, the activities in the
nuclear fuel cycle are well documented, and considerable amounts of data on occupational dose
distributions are available, in particular for reactor operation. The same is not true for the subsectors of
medical, industrial, and miscellaneous uses of radiation, where uncertainties of the estimated values arehigher than the ones for reactor operation and even for uranium mining.
413. The number of monitored workers was not estimated for several subsectors, such as veterinary
medicine from medical sector; for most of the subsectors of the industrial sector (luminizing, radioisotope
production and distribution, well logging, accelerator operation, industrial gauges and all other industrialuses); several subsectors of miscellaneous use of radiation (disused radioactive sources, transport ofradiation sources outside the nuclear fuel cycle and other occupational groups). The reason is either thelimited available data obtained from the UNSCEAR Occupational Exposure Survey, or the lack ofappropriate predictor parameters needed to derive the extrapolation mathematical model. This leads tothe conclusion that the number of monitored workers is underestimated for the medical, industrial, andmiscellaneous sectors. The total number of workers for the industrial sector was derived from a different
set of data, and not a sum of the number of monitored workers of the subsectors. A large number ofcountries have provided the occupational data for industrial sector, pooling together all the subsectors.
For some subsectors, no estimates for the periods 2000–2004 and 2005–2009 were made. Again, this wasdue to the limited available data or lack of appropriate predictor parameters to derive the model althoughseveral attempts to derive the mathematical models were made using the parameters available worldwide.
Thus, the period 2010–2014 has a more complete set of analysis.
414. On the basis of the analysis for the period 2010–2014, the total number of monitored workers forthe category of human-made sources of radiation is estimated as at least 11.4 million. The uncertainty
interval of the worldwide number of workers ranges from 6.2 to 21 million. The number of monitored
workers in the medical sector represents about 79% of the total workforce of the sectors comprising thehuman-made sources of radiation. The industrial sector represents about 10%, the nuclear fuel cycle
sector about 7% and the miscellaneous sector about 4% of the total workforce in the category of humanmade sources of radiation. The number of monitored workers increased over the course of the reported
40-year period (1975–1979 to 2010–2014) for all sectors. The nuclear fuel cycle had a different pattern:
it increased by a factor of 1.6 from 1975–1979 to 1987–1989, then decreased by a factor of about 1.5 up
to 2000–2004, when it started to increase slightly. It seems that the workforce for the medical sector wasunderestimated in the UNSCEAR evaluations previous to the UNSCEAR 2008 Report. The total numberof monitored workers consistently increased over the 40-year period, from 2.8 to 11.4 million. The
Committee recognizes that the total number of monitored workers for all sectors, except for the nuclear
fuel cycle, has been underestimated.

126 UNSCEAR 2020/2021 REPORT

Table 48. Estimated worldwide occupational exposure due to human-made sources of radiation
Sectors

1975–1979 1980–1984 1985–1989 1990–1994

1995–1999 2000–2004 2005–2009 2010–2014

NUMBER OF MONITORED WORKERS (103)
Nuclear fuel cycle

560

800

888

800

670

652

660

762

Medical

1 280

1 890

2 220

2 320

7 440

Industrial

530

690

560

700

790

870

1040

1 100

Miscellaneous

140

180

160

360

476

446

482

540

Total

2 820

3 910

4 228

4 600

9 754

9 000

11 400AVERAGE ANNUAL COLLECTIVE EFFECTIVE DOSE (man Sv)
Nuclear fuel cycle

2 300

3 000

2 500

1 400

1 000

Medical

1 000

1 140

1 030

760

3 540

Industrial

870

940

510

360

315

348

419

440

Miscellaneous

70

40

20

40

53

38

34

38

4 660

5 370

4 310

2 660

4 960

Total

602

523

483
4 500

5 460

AVERAGE ANNUAL EFFECTIVE DOSE (mSv)
Nuclear fuel cycle

4.4

3.7

2.6

1.8

1.4

0.9

0.8

0.6

Medical

0.8

0.6

0.5

0.3

0.5

Industrial

1.6

1.4

0.9

0.5

0.4

0.4

0.4

0.4

Miscellaneous

0.5

0.3

0.2

0.1

0.1

0.1

0.1

0.1

Total

1.7

1.3

1

0.6

0.5

0.5

0.5

415. The average annual effective dose for the category of human-made sources of radiation is estimatedas 0.5 mSv for the period 2010–2014. The uncertainty interval on the average annual effective dose ranges
from 0.3 to 0.9 mSv. In the nuclear fuel cycle sector, the workers’ higher exposure is due mainly to the
exposure in the uranium mining industry and estimated as 0.6 mSv for the period 2010–2014. The averageannual effective dose for the medical sector is estimated as 0.5 mSv and for the industrial sector as
0.4 mSv. The average annual effective dose for the miscellaneous sector is estimated as 0.1 mSv. The
average annual effective dose for the whole category of human-made sources consistently decreased overthe 40-year period from 1.7 to 0.5 mSv. The main contribution of the reduction of dose comes from thenuclear fuel cycle sector, which decreased from 4.4 to 0.6 mSv over that period. It is followed by theindustrial sector, which decreased from 1.6 to 0.4 mSv over the same period. The average annual effective
doses for medical and miscellaneous sectors were, in general, below 1 mSv.
416. The average annual collective effective dose for human-made sources of radiation is estimated as
5,460 man Sv for the period 2010–2014. The average annual collective effective dose for the medical
sector represents about 83% of the total average annual collective effective dose for human-made sourcesof radiation. The nuclear fuel cycle and the industrial sectors represent about 16% (8% for each sector).
The miscellaneous sector represents about 1% of the average annual collective effective dose for humanmade sources of radiation. There is no trend in the average annual collective dose over the 40-year period.
It fluctuated between 5,500 and 4,500 man Sv; this excludes the period 1990–1994, which was estimatedas 2,660 man Sv. Since the estimated total number of monitored workers for all sectors of the categoryof human-made sources of radiation is underestimated, the same statement is true for the average annual
collective effective dose.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 127

V. ASSESSMENT OF GLOBAL PRACTICES
417. This annex supplements and updates the previous UNSCEAR publications on the subject ofoccupational exposure [U3, U4, U6, U8, U10]. Occupational exposure has been evaluated for two broad
categories of work: natural sources of radiation and human-made sources of radiation. There are four
sectors associated with exposure to natural sources of radiation: (a) cosmic ray exposure of aircrew andspace crew; (b) exposure in extractive and processing industries; (c) gas and oil extraction; and (d) radon
exposure in workplaces other than mines. There are five sectors associated with human-made sources ofradiation: (a) nuclear fuel cycle; (b) medical sector; (c) industrial sector; (d) military purposes; and(e) miscellaneous applications. The last sector includes educational establishments, disused radioactive
sources resulting from industrial research applications, transport of radiation sources outside the nuclear
fuel cycle, and other specific occupational groups.
418. The estimate of the worldwide levels of occupational exposure improved in comparison to theprevious evaluations. In the previous UNSCEAR reports, due to the limited data for the sectors of natural
sources of radiation category, the Committee was unable to extrapolate the data for those sectors (civilian
aviation, mineral extraction, and processing (of minerals other than coal and uranium), oil and gas
extraction and radon exposure in workplaces other than mines). In the current evaluation, theextrapolation of the levels of occupational exposure was significantly improved for civilian aviation,
extraction and processing of coal and extraction and processing of minerals other than coal and uranium.
However, for the extraction and processing industry, the improvement is related to the estimate of thenumber of workers. The average annual effective dose might be underestimated because it is not clear if
the available data include the contribution of exposure to radon and its progeny. No improvement wasseen for oil and gas extraction, which was due to limited data obtained from the UNSCEAR Occupational
Exposure Survey and the lack of a statistically significant correlation between the data and the predictor
parameter (petroleum production). Due to the complexity of the exposure and the lack of appropriate
data, the Committee was unable to estimate the level of occupational exposure for the sector of radon
exposure in workplaces other than mines.
419. The estimate of the worldwide level of exposure for the subsector of civilian aviation has improvedin comparison to previous analyses. This is due to the detailed information on worldwide air traffic andcivilian aviation personnel provided by ICAO. However, because there were only few responses to the
UNSCEAR Occupational Exposure Survey, the worldwide estimation of the average annual effective
dose could not be improved in the same way. The uncertainties in the estimation arise from internationallydifferent limits on working hours, heterogeneous definitions of short/medium/long haul, and location ofoperation, i.e., latitude and altitude. Estimations are also hampered by a lack of information about theroute nets that are predominantly covered by each country’s airlines and the number of executed flights.
420. The estimate of the worldwide level of exposure for the subsectors of the nuclear fuel cycle has
improved in comparison to the previous analyses. The methodology applied for the extrapolation was thesame as the one applied in the previous UNSCEAR reports. For uranium mining, the amount of extracted
ore is used as predictor variable. The variable used for fuel fabrication and reactor operation is the averageenergy generated. A wide coverage of data meant that just small adjustments were required to derive theworldwide level of exposure for these subsectors of the nuclear fuel cycle. Moreover, the available datato conduct the analysis from the UNSCEAR Occupational Exposure Survey were supplemented withdetailed information from IAEA, OECD/NEA and WNA. These data resulted in an improved
understanding of the radiation exposure to workers employed in the sectors of uranium mining, nuclear
fuel fabrication, spent fuel reprocessing, and nuclear power plant decommissioning. While the global
estimate of occupational exposure within the nuclear fuel cycle is more robust, it is likely underestimated.
The lack of national registries for occupational exposure, differences in national requirements for128 UNSCEAR 2020/2021 REPORT

monitoring of occupational exposure, incomplete dosimetry records for active and decommissioned
nuclear fuel cycle facilities, lack of records for occupational exposure to radon and radon progeny
radionuclides and incomplete responses to the UNSCEAR Occupational Exposure Survey by United
Nations Member States have contributed to the underestimation of global exposure to occupationalradiation in the nuclear fuel cycle.
421. The estimate of the worldwide level of exposure for the subsectors of the medical sector was also
improved for the estimate of the number of monitored workers. The method applied for the current
analysis is based on multivariate regression modelling. The predictor parameters applied to derive theextrapolation mathematical models are described in table 1. The model was not applied for the calculationof the average annual effective dose and the collective effective dose because the quality of fit to the dataof the model with predictor parameters was not high enough (i.e., the coefficient of determination,
adjusted R2, was below 0.7) between the data and the predictor parameters. The application of derived
mathematical models resulted in the estimation of reliable values for the number of monitored workers.
However, the methodology has a limitation: the mathematical models are appropriate for estimating theparameters only for countries classified as having high and upper-medium GNI, according to the WorldBank classification [W15]. The reason is that the model was derived on the basis of data from countries
that belong to those two GNI categories. The developed model was not applied to derive the worldwide
average annual effective dose because of lack of statistically significant correlation between the data andthe predictor parameters. The worldwide average annual effective dose was derived as the average
effective dose weighted by the number of workers in each country. In order to estimate the average annual
collective effective dose, it was assumed that the weighted average annual effective dose reflected theworldwide value.
422. The estimate of the worldwide level of exposure for the subsectors of the industrial andmiscellaneous sectors used the same methodology described for the medical sector. However, due tolimited data obtained from the UNSCEAR Occupational Exposure Survey and the lack of statisticallysignificant correlation between the data and the predictor parameters, the estimate of the worldwide levelof exposure was made for only few subsectors, resulting in an underestimation of the number ofmonitored workers.
423. It is difficult to compare doses between countries because of different national approaches todefining the doses recorded in their databases. For example, the way doses below the recording level arerecorded and criteria for including workers in the individual monitoring programme differ between
countries. Some countries include workers who do not work in controlled areas, resulting in an increaseof the monitored workforce and a decrease in the average annual effective dose.
424. The worldwide levels of occupational exposure are presented in table 12 for workers exposed tonatural sources (excluding oil and gas extraction and radon exposure in workplaces other than mines),
and in table 48 for workers exposed to the human-made sources of radiation. A comparison of theworldwide levels of occupational exposure due to exposure to natural and human-made sources ofradiation for the periods 1995–1999 and 2010–2014 is illustrated in figure IX.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 129

Figure IX. Comparison of worldwide levels of occupational exposure due to exposure to natural andhuman-made sources of radiation between 1995–1999 and 2010–2014

425. The total number of monitored workers exposed to ionizing radiation is estimated to beapproximately 24 million in the period 2010–2014. About 52% are employed in the sectors that include
exposure to natural sources of radiation (12.6 million workers) and about 48% in the sectors that include
exposure to human-made sources of radiation (11.4 million workers). The Committee recognizes that the
number of monitored workers is underestimated for both categories: natural sources and human-madesources of radiation, and could be as high as 41 million workers. No estimation of the total number ofworkers was made for the periods 2000–2004 and 2005–2009 due to limited available data or lack ofappropriate predictor parameters to derive the extrapolation mathematical models for several subsectors
in human-made sources and natural sources. In the period 1995–1999, the estimated number was about
21.5 million workers, excluding the contribution from radon at workplaces other than mines for reasonof comparison. This increase is due to the large number of workers exposed to both natural sources andhuman-made sources of radiation.

130 UNSCEAR 2020/2021 REPORT426. For exposure to natural sources of radiation during the period 2010–2014, the extraction andprocessing of coal and minerals other than coal and uranium accounts for 94% of the number of workers.
About 11.8 million were employed in mining operations: 70% in coal mining and 30% in other mining
operations, excluding uranium mining. The estimated number employed in civilian aviation (mainly
exposed to cosmic radiation) was about 0.7 million. The estimated number of workers for the sector“radon exposure in workplaces other than mines”—which includes industries (e.g., food industries,
breweries, laundries), waterworks, shops, public buildings and offices, schools, subways, spas, caves andclosed mines open to visitors, underground restaurants and shopping centres, tunnels (construction andmaintenance) and sewerage facilities—was not estimated due to its complexity and also because oflimited available data.
427. For exposure to human-made sources of radiation, the greatest contribution comes from medical
uses of radiation (80% of the number of workers). About 9 million workers are involved in the medical
sector, 0.76 million in the nuclear fuel cycle sector, 1.1 million in the industrial sector and 0.5 million(underestimated number) in the miscellaneous sector. Due to the limited data obtained from the
UNSCEAR Occupational Exposure Survey and lack of predictor parameters, the worldwide number ofmonitored workers was not estimated for military activities.
428. The worldwide average annual collective effective dose to workers exposed to radiation during theperiod 2010–2014 is estimated to be around 30,000 man Sv. The worldwide average annual collective
effective dose to workers exposed to natural sources of radiation (in excess of the average levels of natural
background radiation) is estimated to be around 24,300 man Sv, which represents about 80% of theaverage annual collective effective dose. The largest component of this, 22,300 man Sv, comes fromextraction and processing: about 57% in coal mining and about 43% in other mining operations(excluding uranium mining, which is dealt with as part of the nuclear fuel cycle). The estimated averageannual collective effective dose for the civilian aviation sector, due to exposure to cosmic radiation, isabout 2,000 man Sv. The estimation of the average annual collective effective dose for the sector“workplaces other than mines” was not calculated for the reasons described in the estimation of theworkforce. However, the estimated collective dose due to exposure to natural sources of radiation isassociated with much greater uncertainty than that due to human-made sources of radiation. This isbecause of the limited data obtained from the UNSCEAR Occupational Exposure Survey, which
restricted the estimate of the worldwide number of workers, especially for oil and gas extraction andradon exposure in workplaces other than mines. The other limitation is the scarce available data foraverage annual effective dose because the majority of the workers exposed to natural sources of radiation
are not individually monitored.
429. The worldwide average annual collective effective dose to workers exposed to human-made sourcesof radiation during the period 2010–2014 is 5,460 man Sv. The average annual collective effective dose
to workers in the nuclear fuel cycle sector for the period is estimated to be about 480 man Sv. The
contribution of medical sector is estimated to be 4,500 man Sv, and 440 man Sv for the industrial sector.
The average annual collective effective dose to workers in the miscellaneous sector is about 38 man Sv.
The Committee recognizes that the value is underestimated. This is because of the limited data obtained
from the UNSCEAR Occupational Exposure Survey, which restricted the estimate of the worldwide
number of workers, especially for most medical subsectors. A challenge is to obtain worldwide data forthe appropriate application of predictor parameters for each subsector to derive mathematical estimation
models. Another limitation is the scarce available data for the average annual effective dose. On the basisof the current estimate, the medical uses of radiation contribute about 82% of the average annual
collective effective dose due to exposure to human-made sources of radiation.
430. The worldwide average annual effective dose to workers exposed to radiation during the period
2010–2014 is estimated to be around 1.2 mSv. The uncertainty interval for the worldwide average annual

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 131

effective dose is from 0.7 to 2.1 mSv. In the period 1995–1999, the estimation was 1.8 mSv. The
worldwide average annual effective dose to workers exposed to natural sources of radiation (in excess of
the average levels of natural background radiation) is roughly estimated to be around 2 mSv. The averageannual effective dose to monitored workers varies widely from occupation to occupation and also fromcountry to country for the same occupation. On the basis of the reported data, the average annual effective
dose to monitored workers from human-made sources of radiation are around 0.5 mSv. The averageannual effective doses to workers in the nuclear fuel cycle sector are, in most cases, higher than the doses
to those in other occupations. For the period 2010–2014, the estimated worldwide average annual
effective dose for the nuclear fuel cycle is about 0.6 mSv (table 48). Uranium mining contributes to thehigher exposure, the average annual effective dose is 2.8 mSv. Fuel fabrication is ranked as the second
sector that delivers high radiation exposure; the average annual effective dose is 0.9 mSv. Reactor
operation is the third sector with high radiation exposure: the average annual effective dose is 0.5 mSv.
All estimations for the nuclear fuel sector are summarized in table 27. The average annual effective dosein the medical sector is estimated as 0.5 mSv, in the industrial sector is estimated as 0.4 mSv.

A. Trends in occupational exposure
431. For exposure to natural sources of radiation, the evaluation of the level of exposure was first
introduced in the period 1990–1994. Due to limited data available at that time, the Committee was unable
to derive the worldwide levels of exposure in its previous evaluations. However, the data available forthe current evaluation, especially for the period 2010–2014, enabled a reliable assessment of the numberof workers in civilian aviation, mining operations and mineral processing. As a result, the estimatedworldwide number of workers is greater than the estimate in previous UNSCEAR evaluations, but might
still underestimate the actual number of workers because it was not possible to derive the worldwide
estimates for oil and gas extraction and for radon exposure in workplaces other than mines.
432. The worldwide average annual number of monitored workers exposed to human-made sources ofradiation consistently increased from 1975–1979 to 1990–1994, then it increased by a factor of two in
the following period (1995–1999) due to a more realistic estimate of the workforce for the medical sector
derived for that period. An increase in the workforce of about 20% was observed from 1995–1999 to
2010–2014. The estimated workforce increased from about 2.8 million to about 11.4 million over the
40-year period of evaluation (table 48). The greatest increase (from about 1.3 million to about 9.0 million)
was in the number of workers in the medical sector, which represents about 79% of the workforce.
433. The number of monitored workers for the nuclear fuel cycle also increased significantly in the first
three periods (1975–1989), from about 0.6 million in the first period to about 0.9 million in the third
period, but it dropped to 0.8 million in 1990–1994 and to about 0.76 million in 2010–2014. The averageannual collective effective dose averaged over the five years for each of the first three periods (1975–1989) for all operations in the nuclear fuel cycle varied little around the average value of 2,500 man Sv,
despite a factor of 3–4 increase in electrical energy generated by nuclear means. The amount of electricalenergy generated continued to increase, but the average annual collective effective dose decreased by afactor of about 2, to 1,400 man Sv, in 1990–1994. Since then, it consistently decreased to around
480 man Sv (2010–2014). A relevant part of this decrease came from the reduction in the reactor operation
component, from 1,100 man Sv in 1985–1989 to 328 man Sv in 2010–2014. The average annual effective
dose to monitored workers in the nuclear fuel cycle was consistently reduced over the whole period, from
4.4 to 0.6 mSv. There are some variations between parts of the nuclear fuel cycle and between countries.

132 UNSCEAR 2020/2021 REPORT434. The worldwide number of monitored workers in the medical sector increased by a factor of almost
seven over the 40-year period, from 1.3 million to 9.0 million. This number is probably underestimatedand could be as high as 17 million. The largest increase, from 2.3 million to 7.4 million, was observed in
the two periods within 1990–1999 because then the estimate was based on more complete informationfrom the UNSCEAR Global Survey of Medical Exposure. The worldwide average annual collective
effective dose due to all medical uses of radiation, about 1,000 man Sv, changed little over the first three
five-year periods. It then dropped significantly, to 760 man Sv, in 1990–1994, but increased to 3,500 man Sv
following the increase of the workforce in 1995–1999, which increased by about 25% over the lastperiods. Some downward trend is seen in the worldwide average annual effective dose to monitored
workers, as the uncertainties of the estimates are rather high. The worldwide average annual effective
dose decreased from about 0.8 mSv in 1975–1979 to about 0.5 mSv in 1985–1989, and this value has
been steady since then. On the basis of the data obtained from the UNSCEAR Occupational Exposure
Survey for diagnostic radiology, conventional diagnostic radiology represents about 90% of theworkforce of diagnostic radiology; the other 10% is related to interventional radiology. The “veterinary
medicine” subsector was part of the miscellaneous sector in previous UNSCEAR reports.
435. The worldwide number of monitored workers in the industrial sector increased by a factor of two
over the 40-year period, from 0.5 million to 1.1 million. The worldwide average annual collective
effective dose due to all industrial uses of radiation was fairly uniform over the period 1975–1984 atabout 900 man Sv. It decreased, however, by a factor of almost two in the second half of the 1980s to
510 man Sv and then decreased further, to about 360 man Sv in 1990–1994, and to about 315 man Sv in
1995–1999. The last two periods of analysis showed an increase: 419 man Sv (2005–2009) and 440 man Sv(2010–2014). Because of the lack of statistically significant correlation between the data and the predictor
parameters applied to extrapolate the data for several subsectors of the industrial sector, it is difficult to
identify which subsector is responsible for the increase in the average annual collective effective dose.
The average annual effective dose decreased by a factor of almost four from 1975–1979 to 1995–1999,
from 1.6 and 0.4 mSv, and the average annual effective dose values did not change over the last three
periods. It should be noted that in UNSCEAR reports prior to 1990–1994, “industrial uses” included acomponent reflecting “educational uses”, which tended to distort the data. Since then, educational uses
have been dealt with in a separate subsection, and the industrial data for earlier years have been adjusted
to remove the educational component.
436. The worldwide levels of occupational exposure for the miscellaneous sectors were underestimateddue to the limited data available and also to the lack of statistically significant correlation between thedata and the predictor parameters available to derive the mathematical models. Further, the worldwide
levels of occupational exposure for human-made sources of radiation for military uses were not estimateddue to the limited data available.

B. Dose to lens of eye
437. The analysis of occupational doses to the lens of the eye is a new, challenging task. It is aconsequence of the ICRP recommendations published in 2012 [I32], which proposed lowering the annual
limit of the equivalent dose to the lens of the eye in occupational exposure from 150 to 20 mSv averaged
over five consecutive years but not more than 50 mSv in a single year. In 2013, the reduced dose limit
was introduced in the European Union Member States [E8], and in 2014 it was recommended by theInternational BSS [I12]. The available topical literature indicates many challenges in the implementationof the new limit due to the lack of dosimetry data and to the problems relating to the dose estimation athigh angles and at low energies.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 133

438. A literature review showed that lowering the annual limit of the equivalent dose to the lens of theeye makes it possible that some workers (in medical and industrial sectors) may receive annual equivalentdoses above this limit. This applies, in particular, to personnel in interventional radiology (more than
5 mSv per quarter) and in industrial radiography (up to 60 mGy per year in terms of absorbed dose).
Failing to use goggles and personal shields can obviously lead to an increase in the equivalent dose to thelens of the eye. On the other hand, a decrease in the dose can be expected with the introduction of newtechnologies and protocols, and also with wider recognition of workplaces where the possibility of such
exposure may occur.
439. Data on the equivalent doses to the lens of the eye derived from the UNSCEAR Occupational
Exposure Survey are limited. Thus, they could not be used in a mathematical model described in
section II.E.1 to determine global estimates. Data on occupationally exposed workers to whomquestionnaires on the annual equivalent doses to the lens of the eye were assigned were provided by only
a few countries: in diagnostic radiology (3 of 24 countries that provided data), conventional diagnostic
radiology (2 of 14 countries), nuclear medicine (3 of 25 countries), radiation therapy (1 of 25 countries)
and veterinary medicine (1 of 25 countries). The reported average annual equivalent doses to the lens of
the eye for diagnostic radiology, radiation therapy, and veterinary medicine are the average annual
equivalent doses for these sectors. These average annual values are lower than 20 mSv. In diagnostic
radiology (interventional and conventional) doses are lower than 7 mSv, in radiation therapy(brachytherapy) about 0.1 mSv, and in veterinary medicine 1 mSv. In nuclear medicine the provided
maximum equivalent dose was 7 mSv.

VI. IMPLICATIONS FOR FUTURE EVALUATIONS
440. The global assessment of occupational exposure is a complex task. The most important issue forthe assessment is to have relevant and sufficient data provided by United Nations Member States. As
indicated in various chapters above, this assessment was based mainly on data collected through the
UNSCEAR Occupational Exposure Survey, which was not sufficient to ensure representative data forrobust and reliable evaluations and predictions in many sectors. Based on experiences from thisassessment, the following observations and recommendations are intended to facilitate the data collection
process to enable improved robustness and coverage of future global evaluations by the Committee.
441. Since most United Nations Member States do not have a national dose registry or a central point
for the collection and maintenance of dose records, the Committee recommends the use of its survey
questionnaire (especially for the essential data sets) to collect occupational exposure data on a regularbasis. With involvement of national contact persons and more frequent data collection, the Committee
intends to update its evaluations more frequently with a focus on essential data. These include annual
total numbers of occupationally-exposed workers (with breakdown into monitored workers and female
workers, when possible) nuclear fuel cycle, medical uses of radiation, industrial uses of radiation, civilian
aviation, and industrial processes involving NORM (e.g., mining, processing, oil and gas extraction).
442. In the radon at workplaces other than mines subsector, there are large variations in the averageannual effective dose that depend on the workplace and ventilation. As monitoring of worker exposure is
not a requirement in many countries, it will continue to be a challenge in future evaluations. It is,nevertheless, important to continue collecting information, and a way forward may be that in future
surveys, in addition to exposure data, information on the type of workplaces where radon may be apotential source of exposure will be requested.

134 UNSCEAR 2020/2021 REPORT443. A review and revision of the present version of the questionnaire is necessary, to include
developments in work activities with different sectors and subsectors. In the reactor operation subsector,
the type of reactor needs to be included. For the uranium mining subsector, the current work activities in
the questionnaire (mining and milling) may need to be changed. Moreover, due to a general improvementin occupational radiation protection, the number of workers receiving high doses is decreasing and areview of the current dose intervals in the questionnaire may be needed. To facilitate future evaluation ofoccupational exposure in the gas and oil industry, it is recommended that the relevant work tasks be
specified in the survey.
444. Initiatives for future assessments should focus on motivating submission, of even partial data setsof the identified essential data, from countries not represented in this assessment. For the broad range ofoccupations where workers are exposed to natural and human-made sources of radiation, the collection
and collation of national data is not a simple process. The Committee recommends targeting countries
with large populations (and so potentially significant contributions to global workforce). The Committee
suggests approaching regional organizations, such as the African Regional Cooperative Agreement for
Research, Development and Training related to Nuclear Science and Technology, regional networks (e.g.,
AFAN) 2 with the objective of improving data collection from regions underrepresented in this evaluation.
The current collaboration with international organizations, e.g., IAEA, ICAO, ILO, OECD/NEA, WHO
and WNA has been important for the evaluation. The Committee recommends expanding thesecollaborations to support Member States in the collection of occupational exposure data for future
UNSCEAR surveys.
445. Due to lack of data, worldwide levels of exposure can only be roughly estimated. For the most part,
quantitative estimation requires the use of available predictor variables (independent variables of themathematical models) to derive the mathematical models to extrapolate the worldwide estimates. Since
extrapolation is an inevitable task, the Committee recommends including essential predictor parametersin the survey questionnaires. Also, it suggests conducting a thorough review of the outreach process andfocusing the request for data on the most needed information and parameters presented in table 1.
446. The global assessment of occupational exposure has focused on the estimation of average annual
effective doses to workers and temporal dose trends in various sectors. This approach assesses the overallcollective exposure but does not provide information on the distribution of doses to individual workers.
Collection of data on cumulative doses to workers is important for improved analysis of trends and forthe implications for management of radiation exposure in workplaces.

2

https://african-alara.net.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 135

VII. SUMMARY AND CONCLUSIONS
447. The Committee has been collecting and evaluating sources and levels of occupational exposure
since 1975. Occupational exposure to ionizing radiation can occur as a result of activities utilizing
radiation or radioactive substances in industry, medicine, education and research and can also occur when
workers are exposed to natural sources of radiation. The Committee’s evaluations of worldwide
occupational exposure to ionizing radiation provide information relevant for policy- and decision-making
regarding the safe use of radiation. The resulting dose distributions and trends provide insight into themain sources and situations of exposure and information about the main factors influencing exposure.
The evaluations assist in identifying emerging issues and may identify situations that should be subjected
to more attention and scrutiny by relevant stakeholders.
448. The Committee’s assessment of worldwide occupational exposure levels and trends is based on two
sources: (a) data from the UNSCEAR Global Survey of Occupational Radiation Exposure; and(b) reviews and analyses published in peer-reviewed literature. Its evaluation of occupational exposure
to ionizing radiation is based on the individual monitoring of workers or their workplaces and therecording of their exposure. Data on occupational radiation exposure in Member States are generallycollected in terms of effective dose as it is used for radiation protection purposes. Therefore, occupational
exposure is expressed in operational terms like “effective dose” and “collective effective dose”. These
are the radiation protection quantities used by the international safety standards established under theaegis of the IAEA with the co-sponsorship of relevant international intergovernmental organizations.
449. In this assessment, the Committee has analysed new available data collected for the period 2003–2014
and considered the results of the evaluation on occupational exposure in comparison with the results inprevious UNSCEAR reports and it has reached the following conclusions.
450. The worldwide annual number of workers exposed to natural and human-made sources of ionizing
radiation is estimated by the Committee to be approximately 24 million in the period 2010–2014. About
52% of those were employed in the sectors that involve exposure to natural sources of radiation(12.6 million) and about 48% were employed in sectors that involve exposure to human-made sources ofradiation (11.4 million). The total number of workers showed a slight increase compared with the period
1995–1999, when the annual number estimated by the Committee was about 21.5 million workers forboth sources combined.
451. For exposure to natural sources of radiation during the period 2010–2014, the extraction andprocessing of coal and minerals other than coal and uranium accounted for 94% of the annual number ofworkers. About 11.8 million were employed in mining operations: 70% in coal mining and 30% in othermining operations, excluding uranium mining. The estimated number of people employed in civilian
aviation (who are exposed mainly to cosmic radiation) was about 0.7 million. The annual collective
effective dose for natural sources was about 24,300 man Sv (excluding oil and gas extraction and radon
exposure in workplaces other than mines, due to lack of data).
452. The average annual collective effective dose for the period 1995–1999 in UNSCEAR 2008 Report[U10] was estimated as 31,260 man Sv, of which 30,360 man Sv was due to extraction and processing ofcoal and minerals other than coal and uranium, and 900 man Sv due to the exposure of civilian aviation
exposed to cosmic radiation. In the current evaluation, the estimate for the collective dose has decreased
to 24,300 man Sv, the largest contribution coming from mining operations—12,800 man Sv from coalmining and processing and 9,500 man Sv from other minerals extraction and processing of coal andmineral other than coal and uranium mining. About 2,000 man Sv is due to the exposure of aircrew tocosmic radiation. Due to lacking data, the Committee was unable to derive the average annual collective

136 UNSCEAR 2020/2021 REPORT

effective dose for workers exposed to elevated levels of radon and its progeny in workplaces other thanmines; however, the average annual effective dose was estimated based on data from the literature.
453. The estimated worldwide annual number of monitored workers exposed to human-made sources
increased to over 11.4 million in 2010–2014 compared with about 10 million in the period 1995–1999.
The medical sector dominated the workforce exposed to human-made sources, accounting for about 80%of the total workforce and about 75% of the collective dose. The average annual effective dose for theperiod 2010–2014 for all human-made sources was about 0.5 mSv, a substantial decrease from 1.7 mSv
some 40 years ago, and the average annual collective effective dose was about 5,500 man Sv (about
480 man Sv to workers in the nuclear fuel cycle, about 4,500 man Sv to workers in medical uses andabout 440 man Sv to workers in industrial uses).
454. Occupational exposure from human-made sources has changed greatly since 1970, when it was
dominated by the practices in the nuclear fuel cycle. Except for medical uses, all other practices haveshown a reduction in the level of exposure. A significant part of the reduction of the average annual
effective doses is observed in the nuclear fuel cycle and industrial sectors. In the nuclear fuel cycle,
reactor operation continues to be the major contributor to occupational exposure. In the future,decommissioning of reactors will increase and, therefore, the collection of data started during thisevaluation period. However, it was not possible to make a worldwide estimation for this annex.
455. The worldwide average annual effective dose for all workers during the period 2010–2014 wasestimated to be around 1.2 mSv—about two thirds of the value estimated for the period 1995–1999. The
annual effective dose was estimated to be around 2 mSv for workers exposed to natural sources and
0.5 mSv for workers exposed to human-made sources. In the period 1995–1999, the estimated annual
effective dose to workers exposed to natural sources was 2.7 mSv (excluding radon exposure in
workplaces other than mines), while the dose from exposure from human-made sources remained at
0.5 mSv. The Committee’s current estimate of the worldwide average annual collective effective dose isaround 30,000 man Sv.
456. The Committee’s estimates presented in this annex for natural and human-made sources are basedon a process of mathematical and statistical extrapolation using the limited available data provided by thecountries in response to the UNSCEAR Global Survey of Occupational Radiation Exposure. Uncertainty
estimates for occupational exposure are provided to characterize the precision and accuracy of thereported estimates of number of workers, expressed as a range of the average annual effective dose, andthe annual collective effective dose. Occupational sectors with more data generally have a narrower
range, clearly demonstrating the value of having more data, from more countries, available for analysis.
457. Improvements for the period 2010–2014 were possible for several reasons, including thecooperation of international organizations and use of improved mathematical and statistical techniques.
For example, (a) improvement in the estimation of crew exposure in civilian aviation was due to thedetailed information on worldwide air traffic and civilian aviation personnel provided by ICAO;(b) improvement in the estimates for the subsectors of the nuclear fuel cycle was due to availability of
information from the ISOE database (jointly maintained by the IAEA and NEA/OECD); and(c) improvements in the medical sector estimates due to use of mathematical multivariable models withmathematical derivation of uncertainties.
458. While some improvements were possible, the limited data received through the UNSCEAR Global
Survey of Occupational Radiation Exposure and the lack of correlation between the data and available
predictor variables resulted in the estimation of the worldwide level of exposure for many subsectors but
not all. Relatively complete data submission for the nuclear fuel cycle worker sectors and the reliabilityof this information is well documented. There is a likely underestimation of the number of workers andANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 137

estimated collective effective doses, owing to the lack of data for some occupational sectors in thereported periods. For most of the subsectors of the industrial sector, military, occupations involving
exposure to radon and several subsectors of the nuclear fuel cycle, the reported data did not allow theCommittee to make sufficiently robust worldwide estimates, and this remains an area for its future work.
459. Data on the equivalent doses to the lens of the eye are limited. It is expected that for the Committee’s
next evaluation of occupational exposure, more countries will be able to provide reliable data on theequivalent doses to the lens of the eye due to the implementation of new radiation protection regulations.
Radiation exposure of the hands and of the lens of the eye due to scattered radiation can potentially behigh, which could be the case for operators conducting interventional radiology procedures.
460. The current evaluation of occupational exposure has not identified any group of workers receiving
high average annual effective doses due to implementation of new techniques in applying radiation
sources. However, it has been noticed that the average annual equivalent dose values for the skin of thehands of the nuclear medicine workforce have increased over the last three periods. The high equivalentdoses to the skin of the hands, especially to the fingers in contact with the syringe, may be explained by
the increasing use of high-energy beta-emitting radioisotopes, also due to high workload combined withthe poor implementation of adequate radiological protection measures.
461. Although the data received from the UNSCEAR Occupational Exposure Survey are in some cases
very limited, extensive new data have been reviewed. Essential data collection from a larger number andbroader representation of Member States (e.g., regions, income levels, and activities in subsectors) is anarea that the Committee has identified as a future area of work in order to reduce uncertainties, allow
extrapolation of estimated occupational exposure doses (e.g., for gas and oil extraction, for subsectors of
the industrial sector and for miscellaneous uses of radiation) and enhance estimates of trends in different
work sectors and for different organs (e.g., hands and lens of the eye). This will require further
clarification and harmonization of the required data.

138 UNSCEAR 2020/2021 REPORTACKNOWLEDGEMENTS
The Committee acknowledges with gratitude the work of the members of the Expert Group involved in
preparing this annex and especially P. Hofvander (Sweden) for chairing the Expert Group and V. Holahan(United States) for serving as senior technical adviser. The Committee also thanks, in particular, D. Melo
(United States) for acting as coordinating lead writer and C. Lawrence (Australia), J. Chen (Canada),
U. Oeh and T. Rosentreter (Germany), D. Kluszczyński (Poland), I. Lund (Sweden) and S. Simon(United States) for acting as contributing writers. Further, A. Jahnen (Luxembourg) kindly contributed
to data extraction and evaluation as well as to the check on the modelling applied. The Committee would
like to thank D. de Souza Santos (Brazil), D. Chambers (Canada), G. Frasch (Germany), E. Salminen(Finland) and H. Okyar (IAEA) for critically reviewing the manuscript.
Further, the Committee expresses its appreciation to the IAEA, ICAO, ILO, NASA, OECD/NEA and
WNA for the provision of relevant data and information for this evaluation. Finally, the Committee
acknowledges the contributions of the national contact persons and the national experts who wereinvolved in collecting, submitting, and checking the national data (list below). The views expressed in
the annex remain those of the Committee and do not necessarily represent the views of the United Nations
or its Member States.

Members of Expert Group
Chair: P. Hofvander (Sweden); Members: C. Lawrence (Australia), J. Chen (Canada), M. Berčíková
(Czechia), U. Oeh and T. Rosentreter (Germany), S. Saigusa and N. Juto (Japan), F. Ortega (Mexico),
G. de With (Netherlands), D. Kluszczyński (Poland), J. Kim and S. Seo (Republic of Korea), I. Lund
(Sweden) and V. Holahan, D. Melo and S. Simon (United States); Observers: J. Ma and H. Okyar(IAEA), and T. Zodiates (ILO).

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 139

List of national contact persons and national experts contributors to
UNSCEAR Global Survey on Occupational Exposure
Country
codea

Country nameNational contact person(s)DZAAlgeriaZ. Mokrani

M. Bouchefer, B. Boudena, A. Mellah

ARG

Argentina

M. Ermacora

D. Álvarez

ARM

Armenia

AUS

Australia

G. Hirth

BGD

Bangladesh

J. Ferdous

BLR

BelarusN. Vlasova

BEL

Belgium

A. Fremout, P. Willems,
Th. Vanaudenhove

BIH

Bosnia andHerzegovina

I. Coralic

BRA

BrazilL. Vasconcellos de Sa

C. de Pinho Maurício, D. de Souza Santos, C. Ribeiro
da Silva

CAN

CanadaJ. ChenT. Prendergast, P. Prince, V. Young

CHL

Chile

L. Vironneau Janisek

O. Delgado, A. Espinosa, V. Verdejo

CHN

China

Sh. ZhaoJ. Deng, L. Liu, Y. Wang, X. Wei, D. Yang, E. Yu

HRVCroatia

CYP

CyprusD. Sakkas

CZE

Czechia

K. Petrova

B. Kotrčová, J. Vinklář, I. Zachariášová

DNK

Denmark

K. Breddam

H. RoedEST

Estonia

I. Puskar

K. Kornõševa, M. Lacis, J. Šubina

FIN

Finland

R. BlyJ. Liukkonen

FRA

FranceP. Scanff

J. Feuardent

DEU

Germany

T. Jung

L. Kammerer, U. Oeh, T. Rosentreter

GRC

GreeceE. Papadomarkaki

P. Askounis, E. Carinou, G. Kiranos, Ch. Kyrgiakou

HUN

Hungary

G. Sáfrány

R. Elek, N. Fülöp, N. Glavatszkih

ISL

Iceland

J. Gudjonsdottir

IND

India

S. Harikumar

IRN

Iran (Islamic
Republic of)

M.R. Kardan

IRQ

Iraq

B. Ahmed

S. Abbas, T. Hasan, Z. Khlil, S. Mansur, G. Mehdi

IRL

Ireland

V. Smith

D. Fenton, H. Synnott

ITA

Italy

F. Bochicchio

C. Nuccetelli

JPN

Japan

K. Akahane, Sh. Saigusa

N. JutoNational expert(s)A. Mnatsakanyan
C. Lawrence

A. Mataras, E. Drozd, L. Eventova, G. Evtushkova,
V. Korol, L. Fedarushchanka, N. Vlasova

D. FajSh. Arshad Khan, B.K. Sapra

140 UNSCEAR 2020/2021 REPORTaCountry
codea

Country nameNational contact person(s)

KEN

Kenya

A. O. Koteng

KWT

KuwaitE. Alfares

LBN

Lebanon

M. Roumie

C. Rizk

LTU

Lithuania

J. Ziliukas

A. Jakutytė, A. UrbonienėLUX

Luxembourg

N. Harpes

MDG

Madagascar

T. Harivony

M. Ralaivelo, R. Randriantsizafy

MUS

Mauritius

F.A. Ollite

J. Chrishna

MEX

MexicoJ. Aguirre Gómez

F. Ortega

NER

Niger

I. KaneD. Abdou, F. Lawali, S.O. Mahamadou

NGA

Nigeria

T.C. Akpa, G.B. Ekong

E.C. Ebele, M.C. Ebong, V. Okoye, I. Sambo

NOR

NorwayA. Liv Rudjord

G.U. Paulsen, M. Komperød

PAK

Pakistan

R. Ali Khan

PHL

Philippines

K. Romallosa

M. Cabrera, T. Madrid

POL

PolandD. Kluszczyński

Z. Baranowska, I. Milcewicz-Mika, T. Pliszczyński,M. Wysocka, K. Ziemkiewicz, M. Zmyślony

KOR

Republic of
Korea

J.K. Lee

J.I. Kim, K.J. Lim

RUS

RussianFederation

S. Kiselev

A. Tsovianov, V. Usoltsev

SMR

San Marino

C. Muccioli

SVN

Slovenia

N. Jug

ZAF

South Africa

A. Muller

ESP

Spain

A.M. Hernandez Alvarez,
M.J. Muñoz

SWE

SwedenP. Eriksson

P. Hofvander

CHE

Switzerland

Ph. Trueb

B. Ott

THA

ThailandP. KanchanaS. Srimanoroth

TUR

TurkeyS. Turkes Yilmaz

B. Yucel

ARE

United ArabEmiratesA. Al Shehhi, J. Al Suwaidi

A. Al Ameri, B. Al Ameri, M. Al Hajri, N. Al Shehhi

GBR

United Kingdom

A. Bexon

USA

United States

V. Holahan

URY

Uruguay

F. SocaNational expert(s)D. Hagemeyer

ISO 3-digit country code was used in this annex and its electronic attachment for presenting country data in tables.

ANNEX D: EVALUATION OF OCCUPATIONAL EXPOSURE TO IONIZING RADIATION 141

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unscear.org

This publication contains:
VOLUME IV
Scientific annex with appendices
Annex D: Evaluation of occupational exposure to ionizing radiation

E VA L U AT I N G R A D I AT I O N S C I E N C E F O R I N F O R M E D D E C I S I O N - M A K I N G
In 1955 the United Nations General Assembly established the Scientific Committee on the Effectsof Atomic Radiation (UNSCEAR) in response to concerns about the effects of ionizing radiation
on human health and the environment. At that time fallout from atmospheric nuclear weapons
tests was reaching people through air, water and food. UNSCEAR was to collect and evaluate
information on the levels and effects of ionizing radiation. Its first reports laid the scientific grounds
on which the Partial Test Ban Treaty prohibiting atmospheric nuclear weapons testing was
negotiated in 1963.
Over the decades, UNSCEAR has evolved to become the world authority on the global levels
and effects of exposure to ionizing radiation. UNSCEAR’s independent and objective evaluationsof the science are to provide for—but not address—informed policymaking and decision-making
related to radiation risks and protection.

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