Accidental Melting of Radioactive Sources
K. Baldry1, D. S. Harvey2, A. Bishop3
1
RWE NUKEM Limited, Windscale, Cumbria CA20 1PF, UK
Email: [email protected]
2
Corus RD&T, Rotherham, S60 3AR, UK
Email: [email protected]
3
RWE NUKEM Limited, Windscale, Cumbria CA20 1PF, UK
Abstract. The problem of accidental melting of radioactive sources during metal production is well known. It is,
however, impossible to prevent all incidents, since some radioactive sources cannot be detected, even by the best
detector systems. There continues to be a need to consider the consequences of accidental melting. Because these
incidents are rare, the plant workforce generally has limited experience and instrumentation to cope with them.
Melting events have been analysed and scenarios developed. Probable source sizes and nuclides are presented
with the fractions that partition to each phase of the melting process. Consequences of events are discussed and
the risks to each group of melting plant workers and to the off site public assessed. Guidance to assist plant
operators has been developed. This gives initial actions that can be taken by workers without expert knowledge,
and follow up actions once experienced staff are available. This study has been sponsored by the European
Commission Directorate General Environment.
1. Introduction
When a radioactive source is melted, there is a need for the melting plant operators to make a number
of important decisions in a short time. The staff of metal production plants have to make the necessary
decisions based on limited information, but they are not radiation specialists, and very rarely have they
had experience of such an incident. The decisions taken could affect the health and safety of the
workforce, and the general public. These decisions also affect the cost of making the situation safe,
and returning the plant to normal working. There is a potential conflict between ensuring health and
safety of the workforce, and minimizing the costs of lost production. Any melting incident causes
great anxiety among those involved. The costs of such incidents are typically measured in millions of
euros.
The purpose of this project, undertaken with the support of the European Commission, was to make
available existing experience with a view to minimizing the risk of exposure, direct or indirect, to
ionizing radiation of workers at metal plants, of workers at ancillary plants and of members of the
public following the accidental melting of a radioactive source.
2. Review of Previous Incidents
When a radioactive source is melted the three possible outcomes are that the radioactivity partitions
mainly to either the metal, the slag, or the off-gas dust. The first stage of the work was to examine
some examples of previous melting incidents of each kind. Well-documented examples of each type of
incident were selected. These were studied with the generous cooperation of the people at melting
plants where the incidents occurred and are documented by the authors [1].
3. Melting processes
Most of the recorded incidents have occurred in the production of steel in arc furnaces due to the
nature of the scrap source material. The practices of arc furnace steel production are similar at all sites.
It is normal to use large volumes of oxygen which cause turbulence in the melt, and create large
volumes of off-gas. The turbulence cause some of the slag, and metal to be entrained in the off gases.
1
In basic oxygen steel (BOS) production there is again strong turbulence, and entrainment of material
in the off gas.
The induction furnace process for steel production does not usually entail gas blowing, and is a very
much more quiescent process. The quantity of off-gas dust is minimal, and largely composed of
volatiles from the melt rather than slag, and metal entrained in the off gases. Hence any volatile
radioactivity will be in a concentrated form in the off gas dust.
Similar furnaces are used for the melting of copper and aluminium. In the production of copper there
may be some gas blowing and turbulence, causing entrainment of slag and metal in the off gases. In
the production of aluminium the use of oxygen is avoided, but it is common to use halide-containing
gases, in the refining process and these cause some turbulence. Salts that also may be halide, are used
in the refining process for aluminium.
4. Scenarios
4.1. Source Sizes
The IAEA report Methods to Identify and Locate Sealed Disused Sources [2] lists source activity for
various uses and is shown in Table I. It represents ‘worst case’ sources that might be melted
accidentally.
Table I: Disused Sources – Maximum Size of Each Radionuclide [2]
Radionuclide
Activity (GBq)
Comment
Americium 241
Caesium 137
Cobalt 60
800
600,000
1,000,000
Am-241/Be neutron well logging sources
Sterilization
Teletherapy
Yusko [3] lists known accidental melting events that have occurred across the world. This gives
another approach as shown in Table II. The numbers for Co-60 and Cs-137 reflect their widespread
use in industry. Am-241 is probably underrepresented for reasons described in section 4.2.2. The
source sizes quoted in this list are approximate because it can be difficult to estimate the size of the
source that was melted after the event.
Table II: Known Accidental Melting Events – Maximum Size of Each Radionuclide [3]
Radionuclide
Activity (GBq)
Americium 241
Caesium 137
Cobalt 60
Radium 226
1.7
1000
15,000
0.7
The very largest sources are generally under producer control as well as user control. In addition they
are more readily detected when scrap is monitored for radioactivity. For these reasons they are less
likely to be accidentally melted. The very low likelihood of encountering such a source is confirmed
by looking at known melting events (i.e. it has not occurred). The risk of melting these worst-case
sources is not quantified but considered very low. The consequences of the worst-case sources are
included in this report to provide bounding conditions.
Angus [4] and Crumpton [5] discuss the frequency of loss of control of sources. Angus concludes that
the most significant risk from the sources under consideration in this report comes from large Cs-137
sources (in excess of 400 GBq). These have a ‘medium’ frequency of control being lost, and a ‘low’
frequency of being melted. In terms of potential radiation doses, these are considered the highest risk
melting events.
2
The more typical sources under consideration are generally not under producer control and hence can
more readily be lost (for example a company goes bankrupt and its radioactive sources are forgotten).
The sizes of the ‘typical’ sources considered in this report are taken from known melting events. The
likelihood of a particular plant encountering such a source is low, but it is likely that similar sources
will be found at some plant in the future. It is therefore reasonable to prepare responses to the typical
rather than worst-case source sizes.
4.2. Behaviour of radionuclides
4.2.1. Radioactivity partitioning to the off gas dust
There have been many incidents in which caesium 137 has been melted in steel production. This
volatile radioisotope always partitions to the off-gas dust and so the radioactivity is almost completely
confined to the gas cleaning system and very little is retained in either the steel or the slag. The
amounts of Cs-137 radioactivity retained in the steel and the slag are not readily detectable.
Hence the experience has been that the radioactivity is almost wholly extracted by the gas cleaning
system. The result is that there can be high levels of radioactivity throughout the system, and there can
be significant levels of radioactive contamination emitted by the gas cleaning plant.
Some radioactivity will pass through the gas cleaning plant and be emitted to atmosphere. A typical
plant removes 99% of the dust from the gas stream [6], and since the volatiles will have condensed by
the filtration stage it is suggested that the amount of radioactivity captured will be the same. Hence the
amount emitted to atmosphere will be of the order of 1% of that melted in the furnace.
4.2.2. Radioactivity partitioning to the slag
The radioisotopes that partition to the slag include radium, and Am-241 and the other actinide
elements. These emit alpha radiation, and so the main hazard is from radioactive dust absorbed in to
the body. There have been few melting incidents reported in which radioactivity partitions to the slag.
It is believed that many incidents of this kind may go undetected because slag is not usually checked
for radioactivity. If the slag remains in bulk form the exposure of the workforce to radiation is likely to
be very low. Exposure can be higher if the slag is broken down in to a dusty form, as can occur during
slag processing. The dust containing the radioactivity can then be inhaled and result in internal
radiation exposure.
For any radioactivity that is absorbed by the slag some will be retained in the melting furnace, and will
cause some contamination of the slag on the subsequent melt unless the furnace is decontaminated.
Some slag will also pass in to the gas cleaning system, since there is always some physical
entrainment of slag in the off-gases. Hence there might be contamination of the gas cleaning system.
The basis for such a scenario is the melting of an actinide element such as Am-241 in steel production.
This radioisotope is representative of the actinides (e.g., thorium, uranium, plutonium, and
americium), all of which behave similarly in metals production.
4.2.3. Radioactivity partitioning to the metal
Most of the incidents in which radioactivity is absorbed by the metal have involved the radioisotope
cobalt 60. This radioisotope always partitions to metal and is distributed throughout it. There is then
some radiation hazard if people spend time near large amounts of the metal, such as a store of slabs.
For any radioactivity that is absorbed by the metal some will be retained in the melting furnace, and
will cause some contamination of the metal on the subsequent melt unless the furnace is
decontaminated.
Cobalt 60 does not become chemically combined with the slag. In practice, however, the slag will
contain metal that has become physically entrained. Hence when Co-60 is melted there will be some
contained in particles of metal in the slag. The amount in the slag will depend on the steelmaking
process, the properties of the slag, and the care with which slag and metal are separated in the process.
3
For any radioactivity that is absorbed by the metal some will also pass in to the gas cleaning system,
since there is always some physical entrainment of metal, and metal oxides in the off-gases. Hence
there might be contamination of the gas cleaning system.
4.2.4. Partition percentages
Kopsick [7] reports the percentages of each type of radionuclide to each partition (arc furnace).
Table III: Partition of Radionuclides in an Arc Furnace [7]
Type of radionuclide
Metal seeking
Slag seeking
Off gas seeking
Steel
Slag
Off gas
99.2%
1.0%
0.001%
0.5%
94.5%
0.001%
0.3%
4.5%
99.98%
4.3. Dose model methodologies
External radiation from steel product, slag and off gas dusts is calculated by taking the source sizes in
Table II, partitioning them according to the percentages in Table III and then using proprietary
software Microshield™ to calculate the external dose rates.
The dispersal and inhalation methodology for internal doses discussed by Ford [8] is used:
The calculated dose d = Q × C × V × R × e
where:
Q
C
V
R
e
(1)
Source size (Bq)
Dispersion coefficient (s/m3)
Reference man breathing rate (m3/s)
Release fraction
Dose coefficient (Sv/Bq) [9]
The dispersion coefficient C (s/m3) is the integrated air activity concentration per unit release of
activity. It is a measure of the total air activity concentration a person would be exposed to if a unit of
activity (1 Bq) was released and the resulting cloud of activity passed by that person. Atmospheric
conditions (e.g. wind, turbulence) provide the mechanisms for dispersion. They have been calculated
using the Gaussian Plume dispersion model.
Source sizes Q from Table II are used, partitioned to off gas, slag and product in accordance with the
percentages in Table III. In the summary Table V, doses from the worst case source sizes (Table I) are
included for comparison, though it is noted that events of this scale have not been recorded.
Calculated exposures for the following exposure scenarios are considered:
• External radiation from metal product.
• Radioactivity released early in the melt in an arc furnace as fugitive emissions
• Radioactivity released from the melt into the melting shop environment with dusts
• Off gas dusts in the ventilation system and bag house inhaled during handling maintenance
• Dust raised from the slag as it is handled
• Dust raised by flame cutting and other treatments of contaminated product
• Radioactive contamination emitted from the plant to the areas surrounding the plant.
The hazard from unmelted scrap awaiting entry to the process was outside the scope of this study.
4
4.4. External radiations
Geometry affects the dose rates. The following is assumed. The geometries are typical of slab product,
slag piles and dust collection bags. This approach is justified as including the likely worst cases. It is
noted that individual situations will vary, but it is believed that alternative credible geometries will
tend to produce lower dose rates:
•
•
•
For the metal product, 120 tonne (t), density of iron (7.86 g/cm3), slab size 1.5 m × 0.3 m × 35 m
For the slag, 10 t, density ~50% iron (3 g/cm3), slag pile dimensions 1 m × 1.6 m × 1.6 m
1 t off gas dust, density (1 g/cm3) diluted in 10 t other (non-contaminated) dusts, dimensions 1.1 m
× 1.6 m × 1.6 m
Table IV: Calculated dose rates (mSv/h at 1 m) for realistic source sizes
Radionuclide
Co-60
Am-241
Cs-137
Size (Bq)
1.5 E13
1 E10
1 E12
Steel
7.5
negligible
negligible
Slag
1.1
negligible
negligible
Off gas dust
0.72
negligible
3.0
A Co-60 source of 1 E15 Bq could theoretically produce dose rates from the product of 500 mSv/h at
1 m, and a Cs-137 source greater than this from the off gas dusts. It is noted that this extreme level of
radiation has not been measured following a melting event, and the risk is considered low, however it
indicates the importance of monitoring and access control in the early stages following detection.
4.5. Internal radiations
4.5.1. Internal doses - fugitive emissions
Fugitive emissions could be significant if a source is volatilised early in the melting process. This will
occur only with volatile radionuclides such as Cs-137. Assume that Cs-137 melts in an arc furnace and
that 1% is released with fugitive emissions. The majority will be in a buoyant plume of gas and goes
directly upwards and is taken out with the melting shop ventilation system. Empirical data are not
available for such a scenario – indeed the outcome would vary considerably depending on source
placement and time of melting – but it is considered reasonable to assume pessimistically that 1% of
this emission remains in the operating area and that a crane driver or other worker is exposed. A
dispersion coefficient of 6.7 E-3 s/m3, release fraction of 1 E-04 and a dose coefficient of
6.7 E-9 Sv/Bq gives a scenario exposure to a melting shop worker of 1.5 µSv.
4.5.2. Internal doses - dust in operating areas
For internal doses resulting from dust in the operating areas, Cs-137 is addressed, as it generates the
highest workplace concentrations. In a 100 te melt, 1 te of off gas dust is released. The measured
quantities of inhalable dust in an arc furnace melting shop are 1.5 mg/m3 [6]. Assume that the Cs-137
is uniformly distributed amongst the dust. The activity concentration would be 3 kBq/m3 from one
melt, which forms, say, 20% of the dust in the shop. A 30 minute exposure to this Cs-137 would lead
to a dose of 1 µSv. The same scenario with Am-241 would lead to a dose of 2 µSv.
Mobbs [6] addresses continual processing of low activity scrap over a 12 month, 1800 hour working
year, with such scrap forming 1% of the total. A simple comparison between the methodologies
applied by Mobbs and by this report can be made by attempting to extend this report’s assumptions
out to 12 months. This is done by standardizing the activity concentration, decreasing the percentage
of contaminated scrap as part of the total from 20% to 1%, and increasing the exposure time from one
to 1800 hours. The dose is then reduced by a factor of 9 E-03. The dose over 12 months is 1.8 E-08
Sv/y, in comparison to Mobbs’ 1.5 E-08 Sv/y.
4.5.3. Internal doses - dust in gas cleaning plant
If 1 E+12 Bq Cs-137 is distributed in 10 te dust in the bags of the gas cleaning plant, the activity
concentration is 1 E05 Bq/g. The highest levels of dust during handling operations can be defined by
5
the maximum levels that would be physically credible to breathe. A figure of 10 mg/m3 is used and the
consequent activity concentration would be 1000 Bq/m3. A half hour exposure would result in a dose
of 4 µSv, with no respiratory protection being worn. Taking Am-241, with 4.5% going to the off gas,
the dose would be 155 µSv in half an hour. It is noted that dust handling operations are generally
undertaken using respiratory protection, and the protection factors are not accounted for in this
calculation.
4.5.4. Internal doses - dust raised by flame cutting
Flame cutting is the technique that will raise the most particulate and is considered the worst case for
contamination raised by product treatment. Take the slab discussed in section 4.4. A 1000 GBq Co-60
source results in activity levels of 8 kBq/g in the product. The surface area of the end of a slab being
cut is 1.5 m x 0.3 m, or approximately 5000 cm2. Say the cut is 0.5 cm thick and 10% of the metal
resuspended in inhalable form by the cutting. The resulting dose to the operator would be 350 µSv,
assuming that no respiratory protection is worn.
4.5.5. Internal dose from handling slag
Taking an Am-241 source of 10 GBq, a melt size of 100 te and consequent slag mass of 10 te, the
activity concentration is 950 Bq/g. If a dust concentration of 3 mg/m3 is raised during slag handling,
then the local activity concentration is 2.85 Bq/m3. An exposure of 46 µSv would result in half an
hour.
4.5.6. Internal doses – Off site doses to members of the public
Assume that a Cs-137 source melts and that 1% is released [6] to the environment. Assuming a ground
level discharge, H=0, worst case weather conditions (very stable), and the distance from source, x is
200 m, the dispersion coefficient C is 1.7 E-03 s/m3. The resultant exposure is 38 µSv. Taking the
same scenario, with 4.5% of a 10 GBq Am-241 source going to the ventilation system and 1% being
discharged to the environment. The resultant dose would be 68 µSv.
The dispersion coefficient for mean weather conditions (an example location in south central UK is
used) and a 10 m stack release height is 1.1 E-04 s/m3. The resultant dose for the most exposed
member of the public would be 2.4µSv.
The risk presented by such events must consider the frequency that such events are likely to occur.
Angus [4] indicates that the maximum typical size of Cs-137 sources available to be lost from
regulatory control and then accidentally melted is only 100 GBq. However, there is a possible
exposure route for members of the public, and environmental monitoring must form part of the follow
up actions in the event of an off-gas or slag seeking radionuclide melting event.
4.5.7. On site – doses to members of the workforce
A member of the workforce is likely to be necessarily nearer the point of discharge. For a ground level
discharge, the dispersion coefficient for a distance, x of 30 m is 4.3E-02 s/m3 [8]. With a 1 E12 Bq
source the dose would be 950 µSv. A 10 m stack height reduces this by a factor of 4.
4.6. Induction furnace
Induction furnaces melting steel produce higher internal doses to workers than arc furnaces, though as
has been noted the arc furnace is more likely to accidentally melt a source due to the nature of its
source material
4.7. Copper and aluminium smelting
The report has addressed the more commonly encountered situation of sources involved in steel
melting accidents. Copper and aluminium events will be similar in outcome, with slightly modified
dose outcomes. Data from Mobbs compares directly the consequences for steel, copper and
aluminium. External doses are similar for steel and aluminium, but less for copper.
6
4.8 Summary of dose consequences
The study has estimated the likely exposure of the workforce during the accidental melting of a range
of radioactive sources. The main results are shown in Tables V and VI. Working times are likely to be
less if the event has been detected.
Table V: Potential external exposure
Task (30 minute working time)
Product handling
Slag handling
Off gas dust handling
Dose (mSv)
3.3
0.6
1.5
Radionuclide
Co-60
Cs-137
Cs-137
Table VI: Potential internal exposure
Source of exposure (30 minute working time where applicable)
Fugitive emissions
Melting shop general environment
Dust in gas cleaning plant (assuming no respiratory protection)
Dust raised from the slag
Dust raised from flame cutting (assuming no respiratory protection)
External to the plant - public exposure (worst case weather conditions)
External to the plant - public exposure (typical weather conditions)
External to the plant - worker exposure (ground level discharge)
Dose (mSv)
0.002
0.001
0.004
0.046
0.35
0.04
0.002
0.95
Radionuclide
Cs-137
Cs-137
Cs-137
Am-241
Co-60
Cs-137
Cs-137
Cs-137
The theoretical worst case sources (Table I) are larger than the source sizes used in the above
calculations (Table II); by a factor of 60 for Co-60 a factor of 600 for Cs-137. The risk of the worst
case events is extremely small and no such event has been recorded. The largest Am-241 can generate
higher theoretical internal doses than the Cs-137 values quoted, however they are very much less
likely to be encountered.
5. Guidance for Responding to a Melting Incident
5.1. Emergency arrangements
The melting plant emergency arrangements (disaster plan) needs to address the likely sources to be
encountered and the probable outcomes. The authors give guidance for such plans [1], which is
summarized below.
5.2. Workers affected by each scenario
Taking the external and internal dose consequences, the groups of workers that are potentially affected
by a melting event are those who undertake hands-on work with the product and by-products. Such
activities include:
•
•
•
•
•
•
Working close to the product
Flame cutting or other aggressive treatment of the product
Slag handling
Off gas dust handling
Working in or close to ventilation and bag house systems
Working outside in the path of the plume
Controls should focus on these activities. Other personnel such as crane drivers, general shop workers,
and other personnel on site are most unlikely to be affected
7
5.3. Emergency Actions (initial response)
Alarms should be verified by repeat measurements and gamma spectrometry of product samples. On
confirmation, a ‘first response’ is required that can be undertaken by personnel on plant without any
expert knowledge and prior to assessment of analytical results:
•
•
•
•
•
Keeping ventilation systems running to maximise extraction from operating areas.
Minimise personnel access to the product
Segregate and minimise handling of product and slag
Do not handle the off gas dusts prior to the arrival of expert advice.
Continue pour and processing of product
5.4. Management of the incident after initial emergency actions
Once technical or management staff familiar with radiation protection are available, further controls,
assessment and monitoring can be implemented as detailed below and developed in the contingency
plan.
Action levels are proposed to enable radiological safety, legislation and plant operational requirement
to be best met:
• If radioactive content does not exceed 0.3 Bq/g then product can be processed normally [10].
• If dose rates do not exceed 10 µSv/h then no action is required to restrict external dose.
• If dose rates are between 10 µSv/h and 1 mSv/h then access should be restricted so far as possible
in order to minimise exposure.
• If dose rates exceed 1 mSv/h then access should be carefully managed. Dose control levels of
1 mSv for any employee would be appropriate.
5.5. Other considerations
A melting plant would want to establish relations with an expert body that can provide detailed
monitoring assistance and advice.
Expert advice should be sought before process materials known to have radioactive content are
disposed of. This is because of the expertise required to accurately assess radioactive content, and
because of possible specific national legal requirements.
Guidance is given for the use of contaminated metals by European Commission report
recommendations [10]. The levels for the major nuclides discussed in this report are 1 Bq/g.
Contaminated liquors are more difficult to assess and should be quarantined so far as possible pending
expert advice.
6. Conclusions
Information has been gathered on a number of incidents in which radioactive sources have been
melted. The radioisotope involved affects the outcome of an incident. Some radioisotopes partition
mainly to the off-gas dust, some to the slag, and some to the metal. In all cases the radiation exposure
of the people involved in the melting and casting of the metal is likely to be below 1 milliSievert if the
event has been detected. (1 milliSievert is the annual maximum exposure allowed from work with
radioactivity for a member of the public in the European Union).
The radiation exposure of members of the public has been negligible in all melting incidents, though
the theoretical highest doses can be significant. Contingency arrangements would not need to address
evacuation of homes and other facilities in the vicinity of the works as doses are likely to be much less
8
than evacuation reference levels. Note that undertaking radiation and contamination surveys of the
areas surrounding the melting shop and bag house following a melting event will still be required.
The work required for decontamination can be minimised if action is taken as soon as possible after
the melting has occurred, but other factors must also be considered. For example, if the radioactivity is
mainly in the metal then further processing of the metal will tend to spread the contamination. It may,
however, be more practical to cast the steel in the normal manner than to leave it as in a ladle. If
contaminated material is moved off the melting plant site before the radioactivity is detected then the
work required for decontamination is likely to be greatly increased.
The decontamination of a melting plant can be time-consuming, and the radiation exposure of some of
the people involved might exceed 1 milliSievert.
7. Recommendations
Contingency plans need to be prepared by plant management in advance of a melting incident. These
need to be based on knowledge of both the melting process and the practice of radiation safety.
Individuals need to be trained in the principles of radiation safety, and instruments for monitoring of
radiation levels should be available. External contacts should be identified who can offer specialist
expertise in event of a melting incident. The role of government authorities, and the level of assistance
they provide varies from state to state, and should be explored.
8. Acknowledgements
The authors wish to thank the people and companies who have been willing to assist in providing help
and information. The information, derived from actual incidents and experiences, has been
fundamental to the completion of this report.
The work has been undertaken with the support of the European Commission (Directorate General
Environment; Radiation Protection) and this paper reflects the findings in the report submitted to the
Commission.
9. References
1. Baldry, K., Harvey D.S., Bishop, A., Handbook for Radiation Safety Interventions Following
Accidental Melting of Radioactive Sources at Metal Plants, European Commission Directorate
General Environment (2003)
2. IAEA, Methods to Identify and Locate Sealed Disused Sources, IAEA - TECDOC - 804, July
1985 (quoted in European Commission proposed Council Directive on the Control of High
Activity Sealed Radioactive Sources, COM(2002) 130, 18/03/02)
3. Yusko, J., Pennsylvania Department of Environmental Protection, USA
4. Angus, M.J., Crumpton, C., McHugh, G., Moreton, A.D., Roberts, P.T., Management and
Disposal of Disused Sealed Radioactive Sources in the European Union, EUR 18186
5. Crumpton, C., Management of Spent Radiation Sources in the European Union: Quantities,
Storage, Recycling and Disposal (1996), EUR 16960
6. Mobbs, S.F., Harvey, M.P., Methodology and models used to calculate individual and collective
doses from the recycling of metals from the dismantling of nuclear installations, European
Commission, Radiation Protection 117
7. Kopsick, D., Potential recycling of scrap metal from nuclear facilities; EPA contract No. 1W2603-LTNX; Technical support document prepared for the US Environmental Protection Agency
(Sept 2001)
8. Ford, Harrison, Potts, UKAEA Safety Assessment Handbook, UKAEA/SAH (2001), utilizing:
a. Morris, B.W., Darby, W.P., Jones, G.P., Radiological Consequence Models for Workers
on a Nuclear Plant, AEA/CS/RNUP/47820021/Z/1 (1995)
b. Holloway, N., Models for Operator Dose Assessment in Radioactive Material Handling
Accidents, SRD/CLM(93) P47 (1993)
9
c. Morris, B.W, Review of In-building Worker Dose Models for use in AEA Safety Cases Part 1: Inhalation Dose. SDG/TA/Tech Note 93/1 (1993).
d. Clarke, R.H., A Model for Short and Medium Range Dispersion of Radionuclides
Released to the Atmosphere, NRPB-R91 (1979).
e. Cooper, P.J., Underwood, B.Y. Guidance on Calculation of Doses Close to the Release
Point Arising from Accidental Atmospheric Releases, SRD/94852110/92/R1 (1992).
9. ICRP, Dose Coefficients for Intakes of Radionuclides by Workers, ICRP Publication 68, 1994
10. European Commission, Recommended radiological protection criteria for the recycling of metals
from the dismantling of nuclear installations, Radiation Protection 89 (1998)
10