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DOCUMENT TITLE TR533, Radiological Assessment of Dredging Application for Hinkley
Point C (2020). Part 1 – Evaluation using the IAEA assessment
procedure
ISSUE REASON P6 - For Construction
CONTRACTOR DETAILS
CONTRACTOR NAME Cefas
CONTRACTOR DOCUMENT
NUMBER TR533 CONTRACTOR REVISION 04
ECS CODES
REVISION HISTORY
REVISION REVISION DATE PREPARED BY POSITION/TITLE CHECKED BY POSITION/TITLE APPROVED BY POSITION/TITLE
01 22/12/2020 Kins Leonard Head of Radiological
Protection
Alastair Dewar Senior Radiological
Protection Scientist Dean Foden
Hinkley Point
Programme Lead Franck Dal Molin
Principal Radiological
Protection Scientist
02 29/01/2021 Alastair Dewar Senior Radiological
Protection Scientist Franck Dal Molin
Principal Radiological
Protection Scientist Dean Foden
Hinkley Point
Programme Lead
03 05/02/2021 Alastair Dewar Senior Radiological
Protection Scientist Katie Musgrave
Hinkley Point Deputy
Programme Lead Dean Foden
Hinkley Point
Programme Lead
04 10/02/2021 Dean Foden Hinkley Point
Programme Lead Franck Dal Molin
Principal Radiological
Protection Scientist Katie Musgrave
Hinkley Point Deputy
Programme Lead
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REVISION STATUS/SUMMARY OF CHANGES
Revision Purpose Amendment By Date
01 P6 Initial submission to NNB GenCo Cefas 22/12/2020
02 P6 Minor amendments in response to NNB GenCo comments and removal of FRR and jetty from assessment.
Cefas 29/01/2021
03 P6 Amendments to address comments from P. Bryant (NNB GenCo)
Cefas 05/02/2021
04 P6 Further amendment to address NNB GenCo comments
Cefas 10/02/2021
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Radiological Assessment of Dredging Application for Hinkley Point C Power (2020). Part 1 – Evaluation using the IAEA assessment procedure
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Radiological Assessment of Dredging Application for Hinkley Point C Power
Station, Somerset (2020). Part 1 – Evaluation using the IAEA assessment procedure
Alastair Dewar, Paul Smedley, Mariusz Huk,
Stephanie Cogan and Kins Leonard
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Version and Quality Control
Version Author Date
Draft 0.01 Kins Leonard 17/12/2020
Internal QC and revision 0.02 Alastair Dewar 22/12/2020
Internal QC 0.03 Franck Dal Molin 22/12/2020
Executive QC and final draft 0.04 Dean Foden 22/12/2020
Submission to EDFE 1.00 22/12/2020
Revision 1.01 Alastair Dewar 28/01/2021
Internal QC 1.02 Franck Dal Molin 29/01/2021
Executive QC and final draft 1.03 Dean Foden 29/01/2021
Submission to EDFE 2.00 29/01/2021
Revision 2.01 Alastair Dewar and Franck Dal Molin 04/02/2021
Internal QC 2.02 Katie Musgrave 04/02/2021
Executive QC and final draft 2.03 Dean Foden 04/02/2021
Submission to EDFE 3.00 05/02/2021
Revision 3.01 Dean Foden 09/02/2021
Internal QC 3.02 Franck Dal Molin 09/02/2021
Executive QC and final draft 3.03 Katie Musgrave 09/02/2021
Submission to EDFE 4.00 10/02/2021
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Figure 2: Fugro Excalibur Jack Up Barge (JUB) ......................................................................... 16
Figure 3 Location site map of samples collected at the outfalls and flotation pocket. ................ 21
Figure 4 Location site map of samples collected eastern intakes. .............................................. 22
Figure 5 Location site map of samples collected at the western intakes. ................................... 23
Figure 6 Assessment of dose to individual members of crew and the public arising. (Doses were
derived using average activities listed in Appendix A). .............................................. 25
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Abbreviation Text
Cefas Centre for Environment, Fisheries and Aquaculture Science
DAERA Department of Agriculture, Environment and Rural Affairs
EDF Electricité de France
HPC Hinkley Point C
IAEA International Atomic Energy Agency
ICRP International Commission on Radiological Protection
keV Kilo electron Volts. This is a unit of energy
MCAA Marine and Coastal Access Act
MeV Mega electron Volts. This is a unit of energy
MMO Marine Management Organisation
NNB Gen Co Nuclear New Build Generation Company (HPC) Limited
NRW Natural Resources Wales
S. I. Statutory Instrument (UK legislation)
Becquerel (Bq) One radioactive transformation per second
µ Sv/year Micro Sieverts per year. The unit of effective dose used in this report
Man Sv/year man Sieverts per year. The unit of collective dose used in this report
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Executive summary
Nuclear New Build Generation Company (HPC) Limited (NNB Gen Co) (a subsidiary of EDF Energy) plans
to commission the second phase of dredging as part of the development of Hinkley Point C nuclear power
station in Somerset. NNB Gen Co will seek permission to dispose of dredged material at authorised disposal
sites within the Severn Estuary.
In 2020, Fugro Geoservices Limited collected several sediment cores (surface and sub-surface samples)
from various locations (from the future locations of the Hinkley Point C (HPC) cooling water intakes, outfalls
and flotation pocket), at the HPC power station, currently under development. The radioanalysis of these
samples by gamma-ray spectrometry, and for the determination of americium-241 and plutonium
radionuclides (by alpha spectrometry), and tritium (total tritium and Organically Bound Tritium), was
undertaken by Cefas.
This report (part one of two reports) provides a radiological assessment using surface and sub-surface
sediment samples (taken from cores or grab samples at each of the sampling locations) collected from the
future locations of the HPC cooling water intakes, outfalls and flotation pocket. The conservative generic
radiological assessment procedure developed by the International Atomic Energy Agency (IAEA) has been
used in this assessment to determine doses. The assessment procedure requires the results from the
radioanalysis by gamma-ray spectrometry and includes derived estimates of plutonium radionuclide
concentrations (alpha- and beta- emitting radionuclides) from the measured americium-241 concentrations in
sediment samples.
Using the conservative generic radiological assessment procedure developed by the IAEA to convert
radionuclide concentrations in disposed material into radiation doses due to disposal, the derived total doses
to individual members of the crew and public were 3.9 µSv/year and 1.2 µSv/year, respectively. The total
collective dose was 0.038 manSv/year. The values for individual members of the crew and public, and the
collective dose, were within the de minimis criteria of 10 µSv/year (individual doses) and 1 manSv/year
(collective dose), respectively. The estimated doses, using surface sediment samples only, for a previous
dredging application for Hinkley Point C nuclear power station in 2017 were reported as 5.8 µSv/year,
1.9 µSv/year (individual doses) and 0.035 manSv/year (collective dose). Corresponding doses estimated in
2020 and 2017 were similar in magnitude and were less than the de minimis criteria of 10 µSv/year and
1 manSv/year for individual and collective doses.
In this report the appropriateness of the conservative generic IAEA radiological assessment procedure was
demonstrated.
Since the conservative generic radiological assessment procedure indicated that doses received were below
recommended limits, a subsequent more detailed case specific assessment was not necessary. Therefore,
from radiological considerations, there is no objection to this material being dredged and disposed of to sea.
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1 Introduction
During 2018, capital dredge works of the cooling water intake and outfall areas were completed and
disposed of at Cardiff Grounds disposal site (LU110) under Natural Resources Wales (NRW) Marine Licence
12/45/MLv1. Further details of the radiological assessment carried out as part of the licensing application
lodged by NNB Gen Co (a subsidiary of EDF Energy) have been previously reported (Leonard et al., 2017
and BEEMS Technical Report TR444). These reports concluded, based on undertaking a conservative
generic radiological assessment procedure developed by the IAEA, that from radiological considerations,
there was no objection to material being dredged and disposed of to sea.
EDF now plans further work at the site to dredge and dispose a further volume of up to 469,000 m3. The
dredge sampling plan (BEEMS Technical Report TR502) assumed a total potential dredge volume of
600,000 m3 for the HPC intakes, outfalls and flotation pocket, fish return and recovery (FRR) outfall and jetty
berthing pocket. This included up to 526,342 m3 from the intakes, outfalls and flotation pocket. By refining
the dredge plan, the requirement for the intakes, outfall and flotation pocket has been reduced to the current
volume of 469,000 m3. No dredging at the FRR outfall or jetty berthing pocket is considered in this report.
NNB Gen Co plans to commission the second phase of dredging as part of the development of HPC nuclear
power station. Installation of the cooling water intake, outfall structures and flotation pocket requires these
locations to be dredged down to bedrock, with the dredged material being taken to a designated disposal
site. The proposed locations of these sites are shown in Figure 1. NNB GenCo will seek permission to
dispose of this dredged material at authorised disposal sites within the Severn Estuary designated area as
per the HPC Development Consent Order (S.I. 2013 No. 648). During 2018, capital dredge works of the
cooling water intake and outfall areas were completed under Marine Management Organisation (MMO)
Marine Licence L/2013/00178/4 including disposal to LU110 under NRW Marine Licence 12/45/ML v1.
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Figure 1 Proposed sampling areas and indicative distribution of proposed sample station locations (BEEMS
Technical Report TR502).
The Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter (London
Convention 1972) prohibits the disposal at sea of radioactive wastes and other radioactive matter. Under the
Convention, only materials with de minimis levels of radioactivity may be considered for disposal to sea.
Guidance on performing specific radiological assessments of candidate materials, to determine whether the
materials are de minimis in the meaning of the Convention 1972, have been reported by the International
Atomic Energy Agency (IAEA) that incorporate a Stepwise Evaluation Procedure for screening candidate
material to determine if it can be treated as ‘non-radioactive’ (i.e. de minimis) under the Convention (IAEA,
2003; 2015).
Disposal of dredged material from harbours and other areas is licensed under the Marine and Coastal
Access Act (MCAA), 2009 (United Kingdom - Parliament, 2009), and the equivalent for the Devolved
Administrations. The Marine Management Organisation (MMO), Natural Resources Wales (NRW), Marine
Scotland, Department of Agriculture, Environment and Rural Affairs (DAERA) are the licensing authorities
(regulators) for England, Wales, Scotland and Northern Ireland respectively, with regards to the disposal of
dredged materials to sea.
The purpose of this report is to provide an initial evaluation of the radiological assessment to determine
whether the sediments are suitable for dredging and subsequent disposal to sea.
Although this initial generic radiological assessment is based on an inherently conservative procedure consistent with the precautionary approach, a supplementary assessment report (Part 2; BEEMS Technical Reports TR534) has been provided to ensure the use of these conservative models and cautious assumptions are appropriate for the disposal at sea in near coastal waters under de minimis provisions.
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2 Description of sediment sampling
The sediment sampling campaign and rationale for sampling locations and subsample depths is specified in
the sampling plan (BEEMS Technical Report TR502) which was consulted on an agreed with NRW and the
MMO. Sampling station locations were chosen so that representative sediment samples were collected
within proposed dredging licence areas. The number of sample stations proposed was based on OSPAR
dredge disposal guidelines (OSPAR, 2014) which specify the number of stations according to the proposed
dredge volume (Table 1). Surface samples were collected (using a Day grab) from previously dredged (i.e.
maintenance dredge) areas. In areas which had not been previously dredged (i.e. capital dredge areas)
push, rotary or vibrocoring was used to collect sediment cores to either the maximum planned dredge depth,
or until undisturbed geological material was reached. The proposed locations of the sampling stations are
presented in Table 4 and the actual locations (for both cores and grabs) are provided in Appendix A and
displayed in Figure 3 (outfalls and flotation pocket), Figure 4 (intakes east) and Figure 5 (intakes west).
Cores were subsampled at pre-determined nominal depths in accordance with the sampling plan in Table 3.
Table 5 provides a summary of the completed sampling at each station and details the depth to which sub-
sampling was achieved for each core station. Subsampling was undertaken to the bottom of the core or until
undisturbed geological material or almost exclusively sand, gravel or rock were found in accordance with the
sampling plan (BEEMS Technical Report TR502) and OSPAR guidelines (OSPAR, 2014). Additional cores
were collected at six stations with subsamples collected to the maximum core depth (i.e. into the sediment
determined to be ‘undisturbed geological material’ where no anthropogenically derived contamination would
be present). These subsamples were collected and analysed as a precautionary measure, beyond the
sampling scope agreed with the regulators, to ensure there is no doubt that all applicable sediment had been
tested.
Sediment sampling operations were undertaken by Fugro Geoservices Ltd. from the Fugro Excalibur jack-up
barge (Figure 2) between 28 August and 15 November 2020. Within the proposed dredge areas for the
cooling water intakes and outfalls (including flotation pocket), core samples were collected at 20 (plus eight
repeated) sample stations in capital dredge areas, and surface samples were collected at six grab sample
stations in maintenance dredge areas. The sample stations were evenly spaced across five discrete dredge
zones (see Table 2). Sub-samples were collected from grab and core samples for chemical, particle size,
and radiological analysis. The relevant survey details and sampling logs from Fugro (2020) are included and
summarised herein.
Grab samples were collected with a pentane-cleaned 0.1 m2 stainless steel Day grab. To avoid
contamination, care was taken not to subsample sediment that had been in contact with the side wall, base,
or lid of the grab.
Cores were collected using either a rotary, vibrocore or push core (Shelby core). Where push cores were
used, they were deployed inside a 10-inch rotary core sleeve and subsamples were therefore labelled as
rotary cores in sample logs. For the purpose of sampling and analysis, all the three coring methods provided
suitable sediment samples and the coring methodology used does not affect validity of results.
In each sediment core, top-down subsampling was employed at required depths specified in Table 3. For a
subsample acquired at a nominal depth of 1 m (for example), subsampling began at the nominal depth of
1 m and extended downward through the core until sufficient sediment was subsampled for chemical, PSA
and radiochemical analyses. Therefore, sediment at a 1 m nominal depth may have been subsampled at
1 - 1.40 m, 1 - 1.60 m, or 1 - 1.25 m, however, top-down subsamples did not cross into the next sampling
depth interval. For example, a sample at 0.5 m never extended into the next ‘sampled’ depth (starting at
1 m), and where there was insufficient sediment volume for all required samples, additional sediment cores
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were collected at that station. The survey scope stipulated that cores at the same sample stations had a
maximum spacing of 15 m.
Top-down subsampling was not applied for the first two core sample stations (OS13-A and OS13-B)
between the 2 - 3 m depth range. Instead, based on the observed geological stratification of the sediment
core, the dominant horizon in the depth interval (between 2 and 3 m) was subsampled, instead of
subsampling from 2 m down. This was identified by the on-board Client Representative and consequently
repeat sampling was undertaken at two additional stations within the OS13 dredge area (OS13-D and OS13-
E). Samples from the original stations (OS13-A and OS13-B) were analysed by the laboratories in addition to
the repeat stations.
At four core stations bottom-up subsampling was undertaken for the deepest subsample in the core. This
was undertaken where the volume of sediment below the final nominal sampling depth was not sufficient to
provide enough sediment for all required subsamples. In these instances, subsamples were taken from the
bottom of the core upward, until the depth in the interval above required to attain sufficient sediment volume
for all subsamples. The subsamples where this was employed were identified in Table 5. Bottom-up
subsamples can be interpreted to be representative of their nominal depth range (for example, although a
bottom-up subsample may consist of sediment from 4.20 m up to 3.70 m, its representative depth range
would be 4 – 5 m). Depth ranges sampled on the four occasions where this occurred were:
OS21-B: 4.12 up to 3.80 m sampled for 4 – 5 m representative range.
OS01-B: 5.60 up to 4.80 m sampled for 5 – 6 m representative range.
OS23-A: 4.20 up to 3.80 m sampled for 4 – 5 m representative range.
OS23-BR: 4.20 up to 3.70 m sampled for 4 – 5 m representative range.
Sediment was subsampled for radiological analysis using plastic scoops. In some instances, where plastic
scoops were not strong enough to subsample firm or stiff sediment, pentane-cleaned stainless-steel scoops
were used. For each subsample, 500 – 1000 ml of sediment was placed into either one or two 500 ml plastic
containers and sealed with an airtight lid. Subsamples were labelled and refrigerated as soon after collection
as possible. Subsamples were stored in dark conditions.
.
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Figure 2: Fugro Excalibur Jack Up Barge (JUB)
Table 1 Number of sediment sampling stations required for different dredge volumes (from OSPAR, 2014).
Volume dredged (m3) Number of stations
Less than 25,000 3
25,000 - 100,000 4 - 6
100,000 - 500,000 7 - 15
500,000 - 2,000,000 16 - 30
Greater than 2,000,000 An extra 10 per million m3
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Table 2 Proposed volumes of sediment to be dredged from each location and number of sample stations at
the intakes and outfalls (and flotation pocket) updated table from BEEMS Technical Report TR502.
Dredge
purpose Location
Dredge volume (m3) Number of sample stations
Capital Maintenance Total Stations in
capital zones
Stations in
maintenance
zones
Intakes
OS11 24,757 36,743 61,500 3 + 1 additional
repeated station 1
OS13 24,757 36,244 61,001
3 as proposed +
3 additional
repeat stations
1
OS21 24,757 36,897 61,654 3 + 1 additional
repeated station 1
OS23 24,757 37,202 61,959 3 + 1 additional
repeated station 1
Outfalls
and
flotation
pocket
OS01 and
OS02 118,657
72,914 280,228 8 + 2 additional
repeated station 2
Flotation
pocket 88,657
Total: 306,342 220,000 526,342 20 + 8 repeat
stations 6
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Table 3 The subsampling and analysis strategy for sediment cores and estimated subsample volumes.
* Replicate core samples obtained at six stations to collect further samples below ‘undisturbed geological
material’ for reassurance purposes. Each replicate core corresponds to the station in the above line in the
table (e.g. OS23-BR was collected at station OS23-B). In some instances, duplicate subsamples were
collected at certain depths and results were included herein.
**OS13-D and OS13-E are repeat stations for OS13-A and OS13-B.
† Bottom-up subsampling was undertaken for these subsamples due to limited sediment volume at the end of
the core.
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3 Methodology and Assessment Details
In 2020, Fugro Geoservices Limited collected sediment cores and grab samples (surface and sub-surface
samples) from the future locations of the HPC cooling water intakes, outfalls and flotation pocket. Surface
and sub-surface sediment samples were collected using a selection of sediment coring techniques and
sediment grabs (locations, details and depth of sub-samples are provided in Figure 3 - Figure 5 and
Appendix A, respectively).
The sediment samples reported herein were received at the Cefas laboratory for preparation and
radioanalysis between September and November 2020. Following freeze-drying and homogenisation,
radionuclide assay on sediment sub-samples was achieved by gamma-ray spectrometry on a high purity
germanium (Ge) detector.
Sample aliquots were also taken for additional supplementary analyses using radiochemistry techniques for
alpha-emitting radionuclides (e.g. plutonium-238, plutonium-239+240 and americium-241 (238Pu, 239+240Pu
and 241Am, respectively)) by alpha spectrometry, and tritium (total tritium and Organically Bound Tritium
(OBT)) and plutonium-241 (241Pu) by liquid scintillation counting. Results from alpha spectrometry and liquid
scintillation counting, and subsequent radiological assessment will be reported in part 2 of this report series
(BEEMS Technical Report TR534).
Figure 3 Location site map of samples collected at the outfalls and flotation pocket.
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Figure 4 Location site map of samples collected eastern intakes.
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Figure 5 Location site map of samples collected at the western intakes.
Gamma-emitting radionuclides emit characteristic gamma rays in the energy range 60 keV to 2 MeV,
corresponding to the typical energy levels in nuclei with reasonably long half-lives. These gamma rays
generally accompany alpha and beta radiation. Gamma-ray spectrometry is an analytical technique that
allows the direct identification and quantification of gamma-emitting radionuclides (and therefore alpha- and
beta-emitting radionuclides indirectly). The measurement gives a spectrum of lines (i.e. many photons
emitted at discrete energies) the amplitude of which is proportional to the activity concentration of the
radionuclide.
This means that all potential gamma-emitting radionuclides (both naturally occurring and artificial) in a
sample, in the energy range 60 keV to 2 MeV, are simultaneously scanned to identify and determine their
activity concentrations. For the purposes of radiological assessment, under de minimis criteria, only selected
gamma-emitting radionuclides (both naturally occurring and artificial) are reported. The assessment includes
those radionuclides that are positively detected, and also those that are not detected (because they are
absent, or present below their respective detection limit) but could potentially contribute to the dose at the
limit of detection (i.e. the dose is assumed to have occurred at the limit of detection, and the limit of detection
values are included in the assessment as a conservative approach). This is consistent with the developed
methodology to assess dose in relation to disposal at sea under the London Convention 1972 (McCubbin
and Vivian, 2006).
Activity concentrations of gamma-emitting radionuclides radium-226 (226Ra), thorium-232 (232Th) and uranium-238 (238U) were determined via one of their respective decay products lead-214 (214Pb), actinium-228 (228Ac) and thorium-234 (234Th) and assuming secular equilibrium, where the activity concentrations of the decay products (e.g. 214Pb) are equal to their respective parent radionuclides (e.g. 226Ra).
In addition to the radionuclides detected by gamma-ray spectrometry, sediments are also known to contain activities of plutonium (Pu) radionuclides. The 241Am data were used to derive estimates for 239+240Pu and
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241Pu (for the radiological assessment), assuming their activity was proportional to the ratio in the time integrated Sellafield discharges. This approach is reasonable given that both radionuclides are highly particle-reactive, hence the fate following discharge is similar. The activity concentrations for lead-210 (210Pb) were derived using data for its parent nuclide (226Ra) and assuming secular equilibrium.
The gamma-ray spectrometry results from sediment collected from from the future locations of the HPC
cooling water intakes and outfalls locations are a summarised in Appendix A, together with other supporting
information.
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4 Assessment of Doses
Under the London Convention, only materials with de minimis levels of radioactivity may be considered for
disposal to sea. Using the conservative generic radiological assessment procedure developed by the IAEA
(IAEA, 2003) and Cefas (McCubbin, and Vivian 2006), and the averaged (over all sediment cores and depth
ranges) activity concentration data in Appendix A (Table 6) to convert radionuclide concentrations in
disposed material into radiation doses due to disposal at sea, the derived total doses to individual members
of the crew and public were 3.9 µSv/year and 1.2 µSv/year, respectively. The total collective dose was
0.038 manSv/year.
The dose estimates for individual crew/public (by nuclide), derived using the generic IAEA model, are shown
in Figure 6.
Figure 6 Assessment of dose to individual members of crew and the public arising. (Doses were derived
using average activities listed in Appendix A).
In 2020, the values for individual members of the crew and public, and the collective dose, were found to be
below the de minimis criteria of 10 µSv/year (individual doses) and 1 manSv/year (collective dose),
respectively.
The estimated doses, using surface sediment samples only, for a previous dredging application for Hinkley
Point C nuclear power station in 2017 were reported as 5.8 µSv/year, 1.9 µSv/year (individual doses) and
0.035 manSv/year (collective dose). Corresponding doses estimated in 2020 and 2017 were similar in
magnitude.
The estimation of plutonium radionuclide concentrations (using ratios) within the IAEA methodology has also
been demonstrated to be robust (BEEMS Technical Reports TR534). Therefore, the appropriateness of the
conservative generic IAEA radiological assessment procedure (IAEA, 2003; 2015) has been demonstrated in
this report.
Using the conservative generic radiological assessment procedure developed by the IAEA, to convert
radionuclide concentrations (from surface and sub-surface samples) in disposed material into radiation
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doses due to disposal to sea, the derived total doses to individual members of the crew and public were
3.9 µSv/year and 1.2 µSv/year, respectively. The total collective dose was 0.038 manSv/year. The values for
individual members of the crew and public, and the collective dose, were within the de minimis criteria of
10 µSv/year (individual doses) and 1 manSv/year (collective dose), respectively.
Since the conservative generic radiological assessment procedure indicated that doses received were well
below recommended limits, a subsequent more detailed case specific assessment was not necessary. All
the derived total dose values were less than the de minimis criteria of 10 µSv/year and 1 manSv/year for
individual and collective dose, respectively.
Therefore, from radiological considerations, there is no objection to this material being dredged and disposed
of at sea.
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* g1, r1 and v1 denote the sample collection method used (grab, rotary and vibrocoring, respectively), the second term is the depth range of the core sub-
sample. The remaining two terms are additional information, provided by the sample collectors and Cefas preparation staff (quantity and removal of stones,
as appropriate)
** Average determinations use < results as positively measured values to produce a conservative estimate
a Indicates where maximum sampling depth was reached and 'bottom up' sampling method used