Radiation protection in nuclear power plants and the fuel cycle : proceedings of the conference held in Bristol, 27 November-1 December 1978

251 Pages·1978·6.269 MB·English

by  Harding, Bonny

Radiation protection in
nuclear power plants
and the fuel cycle
Volume 1
Proceedings of the conference held in Bristol
27 November - 1 December 1978
THE BRITISH NUCLEAR ENERGY SOCIETY, LONDON, 1978
/J
ORGANIZING COMMITTEE
Mr T. Beswick
DrJ. Butler
Mr J. W. Dawson
Dr L. M. Dutton
Mrl G. Pugh
Mr J. A. Williams
Mr P. B. Woods
Mr F. P. Youell
PRODUCTION EDITOR: Bonny J. Harding
ISBN: 0 7277 0072 3
© The British Nuclear Energy Society, 1978
All rights including translation, reserved. Except for fair copying, no part of this publication may be
reproduced, stored in a retrieval system, or transmitted in any form or by any means electronic, mechanical,
photocopying, recording or otherwise, without the prior written permission of the Managing Editor,
Publications Division, Institution of Civil Engineers, PO Box 101, 26-34 Old Street, London EC1P 1JH
The British Nuclear Energy Society as a body does not accept responsibility for the statements made or the
opinions expressed in the following pages
Published by the British Nuclear Energy Society, and produced and distributed by Thomas Telford Ltd,
PO Box 101, 26-34 Old Street, London EC1P 1JH
Printed by Inprint of Luton (Designers and Printers) Ltd
Contents
Regulatory requirements
2. Studies of the causes of mortality of radiation workers. U. A Reissland
3. Aspects of the historical, philosophical and mathematical background to the
statutory management of nuclear plant risks in the United Kingdom.
O. H. Critchley
5. US Nuclear Regulatory Commission practices for assuring worker protection.
K R Goller
6. Radiation protection of personnel engaged in maintenance work in nuclear
power plants - precautionary measures to be taken during the planning period of
power plants with a light water reactor. /. Mehl
Design and operating criteria
8. Development of radiological safety rules within the CEGB. E. R Goldfinch
9. Recommendations to designers aimed at minimizing radiation dose incurred
in operation, maintenance, inspection and repair of light water reactors.
WKaut
12. Safety requirements for remote and continuous inspection. /. C. Chicken
16. Problem areas and research needs on radiation protection in nuclear power plants.
D. W Moeller
Design features
18. Chemical factors controlling radiation fields around water reactor coolant
circuits. G. C. W. Comley and D. J. Ferrett
20. Concept and design of radiation shielding for nuclear power stations with
pressurized water reactors built by Kraftwerk Union. I. Geflitter
23. Central Inertial Collector - a novel device for controlling coolant activity.
R E. Davis and A. E. Souch
24. Practical design of internal shields for AGRs and the demonstration of their
effectiveness. S. J. Cripps and J. M. Tayler
25. Access provision for the AGR pressure vessel. J. B. Taylor
26. Design measures to provide radiation protection during operation and
maintenance of the irradiated fuel route of the Hartlepool/Heysham advanced gas
cooled reactors. L. M. C. Dutton
32. Radiological protection problems in the processing of PFR fuel.
/. A. B. Gibson
34. Radiation protection features of the new waste calcining facility.
G E. Bingham and B. R. Wheeler
35. Radiological aspects of the design of a facility to solidify radioactive sludge.
C. Smitton and W. M. Williams
Dose assessments, measurements and operating experience
37. Time integrated spent fuel storage biological doses. /. F. Strahl
40. Analysis of occupational radiation exposure in BWRs built by Kraftwerk
Union and its implications for the design of present and future power plants.
K Pfeiffer, H. Bindewald, N. Eickelpasch and H. Wachter
41. Occupational exposure to the personnel in nuclear power plants with pressurized
water reactors built by Kraftwerk Union. H. Untervossbeck and H Weber
42. Radiation level trends in Westinghouse pressurized water reactors.
F. /. Frank and J. Sejvar
43. Measurement of gamma ray dose rate distribution internal to a PWR steam
generator using LiF thermoluminescent dosimeters. 5. L. Anderson, L. demons,
A. K Few, S. Kang and J. Sejvar
44. Occupational exposure at Millstone 2. R. C. Rodgers, G F. Caruthers,
J. P. Donohue and H M. Swartz
45. Control of iron feed rate into reactor to reduce shutdown radiation level.
Y. Sugimitsu, M Izumiya, S. Uchida, K Ohsumi, M Miki and K Tanno
47. Influence of design and operation of Magnox reactors on personnel doses.
P. F. Heaton and H. C. Orchard
48. Experience of radiation and contamination control at Dungeness A Power
Station. F. G King and P. F. Heaton
49. Health physics contribution on a nuclear power station. B. W Skelcher
51. Measurements to aid design of corrosion product contamination control techniques
in AGR fuel plug maintenance facilities. P. B. Woollam and D. M. Johnson
54. Radiological protection when handling plutonium in a laboratory for
experimental fuels. D. C. Eraser
59. Radiation shield integrity testing at the new waste calcining facility. R N. Henry
and N. C. Olson
61. On-line computer application to radiological protection programme of Tokai-II
nuclear power station. A. Higashi
2. Studies of the causes of mortality a A. REISSLAND, BSC, PHD, MinstP, National
of radiation Workers
Radiological Protection Board, Harwell
There is very little direct evidence available to relate occupational levels of ionising radiation
to health effects in those exposed. Studies of morbidity are inhibited by factors such as the dif
ficulty in defining the biological end point, the need for regular clinical screening and the
psychosomatic feed-back from questioning. These combine to render the potential finding unquanti-
fiable, expensive and unreliable. Mortality is an unambiguous end point and causes are specified
on death certificates. The disadvantage here is the long study period that is anticipated to
accumulate sufficient information for useful analysis. However, because of centralisation of health
records in the UK, a survey of causes of death related to radiation doses received is efficient
and lifetime follow-up of workers is practicable. Such studies are underway and together with
similar studies in the US will be contributing during the next decade to the debate on the level of
effects of low doses of radiation experienced at low dose rates. A number of claims have been made
recently that radiation is an order of magnitude more carcinogenic than ICRP Publication 26 suggests.
A test of these claims will be the first objective of the studies.
1. INTRODUCTION details and will be primarily interested in the
During 1977* the intensity of the debate on probabilities of occurence of the stochastic
Britain's future nuclear power programme reached effects.
an all-time high. Scarcely an issue of any pop
ular scientific magazine was without an article At the present time, there is inadequate data
on nuclear power- Books appeared and television available on the effects of levels of radiation
documentaries together with news items on any experienced by workers to provide any direct
thing involving radiation conspired to keep the relationship between these levels and any associ
interest alive. The main events were the public ated effects. Because the system of dose limit
debate on energy policy and the 100 day planning ation is designed to restrict the probability of
inquiry into the proposal by British Nuclear effects to be very low, investigation of the
Fuels Ltd. (BNFL) to build a thermal oxide re relation between dose and biological response in
processing plant (THORP) at their Windscale site humans exposed within dose limits is very dif
in Cumbria. To some participants in the debate, ficult. Radiation does not induce any diseases
nuclear power was the answer to a dream and was which do not occur in an unexposed population so
imperative for the economic future of Britain, to the central problem is looking for a small
others it was an unnecessary nightmare. At the excess of some event against a large background
centre of the controversy lay the potential of the same event which is unrelated to radiation.
hazards to health from the effects of ionising Studies of morbidity among radiation workers would
radiation on biological matter. The magnitude of require regular clinical examination and even
these effects was the subject of considerable these are strongly influenced by the subjective-
dispute. Here we shall be concerned with the ness of both patient and doctor. Quantification
evidence that contributes to this part of the of the extent of any illness would be difficult
debate. and unreliable and the investigation necessary
to attempt this would impose large burdens on
The biological effects which result from ex medical resources and possibly infringe the
posure to ionising radiation fall into two types, privacy of the worker- A mortality study does
stochastic and non-stochastic. Non-stochastic not suffer from these disadvantages - death being
effects are those which do not appear if radia an unambiguous event at a known time and due to
tion doses remain below a threshold value and causes specified on a certificate which is
include damage such as erythema, cataracts of obtainable from central records.
the eye and acute radiation syndrome. Doses
large enough to produce such effects are well Causes of death which could be induced by
above occupational limits for external radiation. radiation are the various forms of malignant
For some nuclides which may become internally neoplasms coded by the eighth revision of the
incorporated in workers, the limits on intake International Classification of Diseases (ICD) as
based on preventing non-stochastic effects in 1*f0 to 239- The term nall-cancersM refer to the
body organs are more restrictive than those based number of deaths with a code in this range and,
on the probability of stochastic effects. How for example, leukaemias are coded 20*t to 207
ever, we shall not be concerned with such inclusive. Not all types of malignancy have the
Radiation protection in nuclear power plants and the fuel cycle. BNES, London, 1978, 1-9 1
REGULATORY REQUIREMENTS
same radiation induced rates, some being more 6 x I0~b Grays per hour). Thus the dose rates
radiogenic and others apparently being non- giving rise to the late effects in which we are
inducible by radiation- Thus, it is desirable to interested are several orders of magnitude lower
look carefully at some specific cancers as well than those required to produce acute radiation
as looking for any excess in the total number of syndrome in man.
cancers among exposed workers. The induction
rates for a few types of malignancies are given Table 1. Percentage of a population receiving a
in the following section. given radiation dose who would be expected to
die from acute effects
Although nuclear power has received the
greatest attention, other sources contribute to
Dose to bone marrow Expected mortalities
the radiation exposure of everybody. Fig. 1
(Grays) (.%)
shows the relative contributions to the radiation
dose received by the public in the UK. Since
6 95
here we are concerned with risks associated with
h.5 50
occupational exposures, we shall not analyse the
3 5
effects of these other sources except to note
2 0
that the exposures give rise to reasonably uni
form whole body doses which are not different in
character to the beta, gamma and X radiation The original restrictions to control effects
experienced by radiation workers. Hence induc were based on avoiding the occurrence of non-
tion rates derived from studies of occupational stochastic effects. Thus 500 mGy per year (or
exposures will also apply to the doses originat about 2 mGy per day) was permitted up to 1936
ing from these other sources. This imposes an being about 1$ of the dose required to produce
upper limit on induction rates that are erythema. (At that time radiation was measured
plausible, therefore, the collective dose to the and limits were expressed in terms of exposure
public should not be predicted to induce more units - Roentgens. All values quoted here have
cancers of any type than are observed. Since been converted into SI units of absorbed dose or
all malignancies of interest are induced by dose equivalent.) This was reduced to 1 mGy per
chemical and viral agents as well as radiation, day in 1936 following the analysis of the blood
acceptable values for the induction rates must of two exposed workers. In 19^9 it was further
be considerably lower than these upper limits. reduced to 3 mGy per week in the USA, the same
value being adopted by the International
This paper is presented in three parts. Commission on Radiological Protection (ICRP) in
Section 2 discusses the magnitude of the effects 1950. At this time there was no concrete evi
of radiation and how these effects may be asses dence to show the need for the lower figures
sed. Section 3 summarises the contributions of but more highly active sources were being brought
other studies to our current understanding of the into use as well as higher energy and hence more
probability of dying due to a radiation induced penetrating radiation. Until this time it was
disease at some time (possibly many years) after still generally believed that there was a thresh
the exposure. Section k describes a major old dose below which there would be no biological
survey currently in progress designed to collect injury. This belief governed the philosophy of
all available information about workers exposed all dose limitation despite doubts that were
to radiation and to maintain a permanent register growing about the validity of the threshold in
with up-to-date dose records. This will form the dose response relationship. In 1953, ICRP
the basic data which, together with causes of formally recognised that there might be some
death, will permit an extensive evaluation of risk from any exposure to radiation however
possible relationships between radiation dose small. Subsequent dose limitation philosophy
and mortality rates. SI units are used, in was based on the assumption of a linear dose
particular absorbed dose will be quoted in Grays response relationship for which risk became
(Gy) which is one Joule per kilogram and equiva zero only at zero dose. The current whole body
lent to 100 rads. The SI unit of dose equivalent dose limit for those occupationally exposed is
is the Sievert (Sv) and is related to the Gray 50 mSv per year and this, together with limits
by a factor to take into account the greater for specific organs for both internal and
effectiveness of some qualities of radiation in external radiation, is the foundation of radio
causing biological damage (such as alpha radia logical protection. However, these are intended
tion and neutrons). One Sievert is equivalent as maximum permissible doses and not values
to 100 rem. which workers should be allowed to approach
without comment, the overriding recommendation
2. THE MAGNITUDE OF EFFECTS of ICRP is to keep all exposures to the lowest
We shall be concerned mainly with relatively that is reasonably achievable.
low doses where only stochastic effects are
relevant. However, to put these into perspective Exposure of workers to radiation has to be
with the short term non-stochastic effects, that justified by benefits which result from the work.
is those occurring within hours or up to a year A full cost benefit analysis is complicated by
following exposure, Table 1 shows the percentage the benefits being available to the public
of acute radiation syndrome mortalities versus while the cost is borne largely by the workers.
dose. The doses in Table 1 may be delivered at The only cost we shall consider here is the
rates of several Grays per hour or higher, where health effect on the workers. At the present
as occupational dose rates for the highest time there is inadequate data to provide a
exposed worker are 50 mGy per year (or about good assessment of the actual risk to workers.
2
REISSLAND
All estimates are based on the studies summarised includes an effective weighting to count a higher
in the next section. Meanwhile we shall sum cost for the death of a younger person.
marise the ideas necessary for a quantitative
assessment of the effects of radiation. The reduced life expectancies for workers
of various ages are shown in Table 2, comparing
Radiation can cause cellular damage in bio radiation work with the risk of fatal accidents
logical material which may proliferate by suc in coal mining and in the manufacturing indus
cessive cell division and the malignant growth tries. These are tabulated for one year, ten
may eventually cause the death of the host. years and the remainder of working life in the
This sequence takes time but the actual period occupation. Two levels of exposed radiation
between the initial damage and death is influ worker are shown, 50 mSv per year (i.e. the
enced by many factors. Hence there is a maximum permitted level) and 5 mSv per year
distribution of elapse time between radiation which is the average exposure of a radiation
and death which may involve a wide spread even worker in the UK.
among a uniformly exposed population. A reason
able assumption is that no deaths due to Table 2. Reduced life expectancy in days
radiation induced cancers will occur within five
years of the exposure and that none will occur
more than fifty years after exposure. In the CyAegaer s) 20 30 ko 50 60
absence of direct evidence, we also assume that
any induced deaths occur uniformly in time
Coal mines
between five and fifty years following exposure.
1 5.7 k.6 3.6 2.5 1.7
Our estimates of radiation induced cancers are
10 52 31 23
based on these assumptions except for leukaemia
up to 65 155 103 61 30 8.9
which does not continue to occur for so long
after exposure and for which we assume a cut Manufact.
off at thirty years. These assumptions are 1 0.7 0.6 0.5 0.3 0.2
compatible with the majority of the observations 10 6.5 5.5 k.O 3.0
mentioned in the next section. The ICRP (ref.1) up to 65 20. 13.5 8.1 Jf.O 1.2
value for the induction rate of cancer (all
Radiation
types) corresponds to one death per 100 Grays
50 mSv
collective dose experienced by a population.
1 k.6 2.7 1.3 0.5 0.1
Because of the assumed linear dose response the
10 36 20 9 3.0
size of the population is irrelevant provided it
is large enough for the dose to individuals to up to 65 68 32 12 0.6
be below the threshold for non-stochastic
5 mSv
effects. Examples of other corresponding induc O.k 0.3 0.1 0.1 0.0
1
tion rates are two leukaemia deaths per 1000 Gy, 3.6 2.0 0.9 0.3
10
five bone cancer deaths per 10,000 Grays and two 6.8 3.2 1.2 0.3 0.1
up to 65
lung cancer deaths per 1,000 Grays. These
figures are necessary to calculate the impact of
The greatest risk measured in terms of
radiation on a working group but it is important
reduced life expectancy is incurred by the
to choose an appropriate method of expressing
younger workers but the differential is most
this impact so that comparisons may be made
pronounced for radiation workers. This is
between different methods of achieving the same
because a radiation induced death is a late
benefit.
effect. From the Table we see that the risk of
a fatal accident in the next ten years reduces
Since everybody dies ultimately, hazards do
the life expectancy of a 20 year old miner by
not cause any extra deaths but they do cause
52 days. In addition the miner is subjected to
some deaths to occur earlier and hence shorten
late effect risks such as respiratory diseases.
the life expectancy of those exposed to the
Pneumoconiosis alone will reduce life expectancy
hazards. Thus it is logical to express the
by about two days per year worked even- under
impact of hazards in terms of reduced life
modern conditions. Other diseases may contribute
expectancy. Life expectancy L(i) is age (i)
as much again which will result in a total
dependent so that if the risk of dying during a
reduced life expectancy of around 100 days.
working year at age i due to some occupation
Over ten years a radiation worker's risk of a
hazard is R, the worker has a reduced life
fatal accident is 2.2 days loss of life expec
expectancy of L(i) x R years. There will be a
tancy, so we see that a radiation worker
contribution to the reduction for every year
exposed for ten years at the maximum permitted
the worker is exposed to the risk so for
level has a reduced life expectancy of about 39
workers aged i who plan to stay in the job
days while for a worker exposed at the average
until retirement (say aged 65) the reduced life
level for ten years it is six days, similar to
expectancy is:
that for a worker in the manufacturing industry.
65
For older workers the comparative risks become
R x X L(j) years (l) much less for radiation workers. Further com
1 = i parisons may be found in ref. 2.
(if we assume that the annual risk is not age
Some epidemiologists prefer to express
dependent). This measure of the risk permits
occupational health effects in terms of relative
a comparison of deaths due to fatal accidents
risk rather than evaluating absolute risk co
with the delayed effects of radiation and
efficients. For radiation induced effects the
3
REGULATORY REQUIREMENTS
1 • • • • • * 1
16 24 32 40 48 56 64
Age
Fig.2. Population
Fraction
of risk
per year
0 10 20 30 40 50
Years (following exposure)
Fig.3. Risk with time
* TAYLOR, F. E. and WEBB, G. A. M. Radiation exposure of the UK population. National Radiological
Protection Board, NRPB-R77. HMSO, London, to be published.
4
REISSLAND
relative risk approach is often couched in terras leukaemias (Court-Brown and Doll (ref. 6)), with
of a doubling dose - that is the radiation dose an induction rate in the range (7-3 - 16.*+)
required to double the natural rate of a disease 10"^" Gy"1. Leukaemia has also been an observed
or cause of mortality. This has the severe draw effect of the use of Thorotrast as a contrast
back of being different for every population medium for diagnostic examination at a rate of
since natural incidence of a disease can vary (2*f - 39) 10-^" Gy-1. Other groups treated
widely from one country to another and even within radiologically have shown excesses of certain
a country as small as England. Thus relative cancers such as breast cancer among women treat
risk coefficients must be treated with some care ed for mastitis and various benign diseases of
since they apply only to the population from the breast, thyroid cancers among Israeli
which they were derived or one which has been children treated for scalp ringworm and skin
adjusted to take account of differences. cancer among patients subjected to multiple
fluoroscopies.
The relative probability of a death occuring
as a result of radiation exposure or for some Uranium miners have shown excess lung
other reason determines the chance that a survey cancers attributed to irradiation of the bron
has of detecting the proportion in a population chial epithelium by the short-lived daughters
which may be attributed to radiation. A survey of the radon gas in the mine. Induction rates
of occupationally related causes of death must of these lung cancers are expressed in the ex
resolve any excess in the study group from the posure unit "working level months" which is not
background that occurs anyway. This is usually readily converted into absorbed dose units and
attempted by identifying a control group of hence does not contribute usefully for our
workers similar in all respects to the exposed purpose. Similarly, the American radiologists
group except in the extent to which they are studied by Matanoski et al. (ref. 7) although
exposed. Section k develops this idea for radi exposed to levels more comparable with those
ation workers and includes estimates of the experienced by workers, do not have reported
magnitudes of the effects that could be detected. doses and so risk factors are not derivable.
3. EVIDENCE ON RADIATION-INDUCED CANCERS IN Summarising the indications from all the
MAN available evidence leads to the following
The fullest and most conveniently organised values given by UNSCEAR (ref. 3) for induction
review on data relating to ths induction of rates of fatal malignancies by low LET
cancer in humans exposed to radiation may be radiation.
found in UNSCEAR (ref. 3). This reference also
gives a clear account of the requirements which Table 3
should be met by a survey which is designed to
study an irradiated population.
Induction Mean Interval
The Atomic Bomb Casualty Commission (ABCC) Malignancies rate (Exposure to
in conjunction with the Japanese National 10-*+ Gy"1 Death)
Institute of Health (JNIH) undertook an extensive
Leukaemia 30 (high 10y
follow-up study on the survivors of the atomic
bombs exploded at Hiroshima and Nagasaki in 19^5* doses) - 20
Doses were estimated by reconstruction for every (low doses)
individual, taking into account location relative Thyroid cancer 10 2*fy
to hypocentre, shielding by buildings and
activity immediately after the bomb. 23,979 Lung cancer 23 - 50 I3y
survivors with absorbed dose above 0.1 Gy were Breast cancer 50 25y
included in a life-span study (Jablon and Kato,
ref. *f). This gave indication of induction All cancer 200 (high 25y
rates for leukaemia of an upper level of doses) - 100
3 x 10-3 Gy"1, lung cancer of 2 x 10"' Gy"1 and (low doses)
all cancers of about 10"^ Gy~1. The dose ranges
for this exposed group was 0.1 Gy to about *f Gy.
The actual number of excess cases of
cancer on which these estimates are based is
Two hundred and forty-three inhabitants of small, as illustrated in Table *f. (See next
the Marshall Islands were exposed to bomb test page). These tables show a clear need for an
fallout in 195^- Nearly 120 Gy of collective extensive study of those workers exposed to
whole body dose was received, the only excess radiation at levels up to 50 mGy.
malignancies reported were seven cases of thyroid
cancer, all in females. No cases were observed
in the 50*f unexposed inhabitants.
The therapeutic use of X radiation has
produced excess cancers of certain types. Women
treated for metropathia haemorrhagia showed
excess leukaemia at an induction rate of between
(3 - 36) 10"^ Gy~1 (9Q# confidence intervals)
and some excess pelvic malignancies (Smith and
Doll)(ref. 3). Follow-up of patients treated
for ankylosing spondylitis demonstrated excess
5
REGULATORY REQUIREMENTS
Table 4. Data on which risk estimates may be example, industrial radiographers, hospital work
based (low LET) ers and metalliferous mine workers (exposed to
radon daughter irradiation of the lung), but
there is a much greater turn-over of staff in
these groups and the transfer of dose records
Dose
Excess will be mostly a manual operation.
Cancer Exposure range
cases
(Gy)
It is useful at the planning stage of such
a project to have a guide to the level of
Breast FFlluuoorroossccooppiieess 22.7 10
effects to be expected. We can make such predic
18 1.5
Mastitis 20 0.7 - k tions by modelling the registry taking into
Benign disease 93-3 8.5 account the age distribution of the working pop
Nagasaki 3.6 0.1 - Jf ulation, the turn-over rate of workers, the dose
distribution over the population, the induction
Leukaemia Nagasaki 12.8 0.1 - if
rate of malignancies of interest and the distri
Metropathia ^7 1.Jf
bution of elapse times between exposure and
Spondylitis 3
death. Such modelling has been carried out (ref.
Thyroid Marshall 8) and from this we can make estimates of the
Islanders 7 OA - 16 effects we may expect. Let us consider a
Thymic register of 30,000 workers with an average dose
enlargement 19 0.3 - 6 of 5 mSv/year. If 5% of them leave radiation
Neck work annually and are replaced by workers with
irradiation 8 88 -- 1133 no previous exposure to radiation, when equilib
Israeli rium is reached there will be 87,000 ex-workers
children 10 0.1 as well as 50,000 current workers on the
register. Workers are assumed to be subject to
the same mortality rates as the general popula
k. THE NATIONAL REGISTRY FOR RADIATION WORKERS
tion in addition to any radiation induced
(NRRW)
effects, to retire at 65 years of age and to all
A registry has been established by NRPB to
die by 95 years of age. The age distribution of
collect as much data as possible on those exposed
a typical British male work force (Fig. 2) is
to low levels of radiation. One factor is clear
used together with the distribution of elapse
from the outset, if a survey is to show any
time between exposure and death described in
effects of radiation above the random variations
section 2 (Fig. 3)- Also shown in Fig. 3 are
from year to year, it has to be big. There are
two other distributions of elapse times employed
about 7°i°00 workers in Britain who are monitored
to estimate the sensitivity to this assumption.
for exposure to radiation in the course of their
BJQ is Gaussian and C^ concentrates all the
work. The majority of personal dosemeters issued
risk in a single year - the eleventh. B^Q pre
receive little or no radiation dose, however, in
dicted about 3% more induced deaths while C^
some areas of work finite doses are recorded in
predicted 15% more both being due to bringing
most issue periods. Records are kept of dose-
forward the risk. This seemed to be reasonable
meter readings and it is these records that
evidence that the shape of the curve was not too
provide a representation of the dose to each
critical. Table 5 shows the annual number of
worker. The first objective of the Registry is
excess leukaemia deaths and all cancer deaths
to compare age specific mortality rates for high
that the model predicts compared to the numbers
er exposed workers with those for low exposure
expected normally. There are two important
workers, that is to use low dose workers as
points to be seen from this table:-
controls for those more significantly exposed.
(i) The restriction of the analysis to an upper
Death certificates giving causes of death
age of 65 reduces the background very much more
are obtained by flagging workers with the Office
than the radiation induced deaths.
of Population Censuses and Surveys (OPCS) or with
the General Registrars Office (GRO) for Scotland.
(ii) The ratio of induced to background is much
These come to the Registry with the causes coded
greater for leukaemias than for all cancers
with the ICD numbers and are collated with the
indicating better prospects of detection of
dose records of the deceased worker. The study
leukaemias.
is intended to be long terra with the periodic
issue of reports as the data justifies.
Table 5. Predicted annual number of excess malig
nancies based on 30 leukaemias per 10h Gy and
Initially the NRPB negotiated with the nuc 100 all-cancers per 10h Gy
lear energy industry to register those workers
employed by BNFL, the Atomic Energy Authority
Leukaemia All cancers
(AEA), the generating boards (CEGB and SSEB) and
the Ministry of Defence (MOD). These employ about
30,000 monitored radiation workers and hence have Age Radiat. ICD* Radiat. ICD*
induced 20^-207 : induced ito-239
the greatest concentration of readily available
data in a form convenient for rapid transfer to
16-65 0.-5 6 1.0 233
the register. Ninety percent of the data from
16-95 0.6 16 1.4. 703
these organisations is transferred directly
between computers. Other groups of workers will
•These are calculated from UK rates for males
be included on the register in due course, for
as given by the Registrar General.
6