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TR533, RADIOLOGICAL ASSESSMENT OF DREDGING APPLICATION FOR HINKLEY POINT C (2020). PART 1 –EVALUATION USING THE IAEA

ASSESSMENT PROCEDURE

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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


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


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




Revision 2.01 Alastair Dewar and Franck Dal Molin 04/02/2021

Internal QC 2.02 Katie Musgrave 04/02/2021



Revision 3.01 Dean Foden 09/02/2021


Executive QC and final draft 3.03 Katie Musgrave 09/02/2021


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Table of contents

Executive summary ....................................................................................................................................... 11

1 Introduction .............................................................................................................................................. 12

2 Description of sediment sampling ......................................................................................................... 14

3 Methodology and Assessment Details .................................................................................................. 21

4 Assessment of Doses ............................................................................................................................. 25

5 References ............................................................................................................................................... 27

Appendix A Activity concentration data ............................................................................................... 28

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Tables

Table 1 Number of sediment sampling stations required for different dredge volumes (from

OSPAR, 2014). ........................................................................................................... 16

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. ........................................................................................... 17

Table 3 The subsampling and analysis strategy for sediment cores and estimated subsample

volumes. ..................................................................................................................... 18

Table 4 Proposed sediment sample stations (intakes, outfalls and flotation pocket) as specified

by the sampling contractor. ........................................................................................ 19

Table 5 Summary of completed subsamples at all locations. Gray cells indicate sampling not

applicable. .................................................................................................................. 20

Table 6 Activity concentrations in sediment samples .................................................................. 28

Figures

Figure 1 Proposed sampling areas and indicative distribution of proposed sample station

locations (BEEMS Technical Report TR502). ............................................................ 13

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.

Subsample

depth (m)

Analysis completed Estimated subsample volume (ml)

Radiological Chemical PSA Radiological Chemical PSA1 Total per

replicate2

Sediment surface

(or grab samples)

✓ ✓ ✓ 500 - 1000 375 375 875 - 1750

0.25 ✓ X X 500 - 1000 - - 500 - 1000

0.5 ✓ ✓ ✓ 500-1000 375 375 875 - 1750

1.0 ✓ ✓ ✓ 500-1000 375 375 875 - 1750

2.0 ✓ ✓ ✓ 500-1000 375 375 875 - 1750

Etc. at 1.0 m

intervals to the

bottom of the core

or until

undisturbed

geological

material or almost

exclusively sand,

gravel or rock are

found.

✓ ✓ ✓

500-1000 375 375 875 - 1750

1 Dedicated PSA samples were only collected if material was coarse. 2 Double this volume was collected to give replicate material for each station.

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Table 4 Proposed sediment sample stations (intakes, outfalls and flotation pocket) as specified by the

sampling contractor.

Dredge area Station Sample type Easting (mE BNG) Northing (mN BNG)

Intake OS11

OS11 Grab 318591 148843

OS11-A Core 318632 148868

OS11-B Core 318642 148828

OS11-C Core 318549 148817

Intake OS13

OS13 Grab 318476 149007

OS13-A Core 318423 149025

OS13-B Core 318431 148984

OS13-C Core 318528 148992

Intake OS21

OS21 Grab 318137 148696

OS21-A Core 318090 148710

OS21-B Core 318097 148669

OS21-C Core 318188 148681

Intake OS23

OS23 Grab 318022 148854

OS23-A Core 318062 148837

OS23-B Core 318055 148879

OS23-C Core 317975 148826

Outfall OS01 OS01-A Grab 319129 147579

OS01-B Core 319191 147577

Outfall OS02 OS02-A Grab 319177 147521

OS02-B Core 319133 147514

Outfall Flotation

Pocket

OF-A Core 319112 147467

OF-B Core 319191 147459

OF-C Core 319159 147411

OF-D Core 319199 147375

OF-E Core 319161 147340

OF-F Core 319154 147630

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Table 5 Summary of completed subsamples at all locations. Gray cells indicate sampling not applicable.

Dredge

area Station

Sample depth [m] (representative range)

0

(surface

grab)

0.0 –

0.25

0.25 –

0.5 0.5 – 1.0 1.0 – 2.0 2.0 – 3.0 3.0 – 4.0 4.0 – 5.0 5.0 – 6.0 6.0 – 7.0

7.0 –

8.0

Intake

OS11

OS11 ✓

OS11-A ✓ ✓ ✓ ✓ ✓

OS11-AR* ✓

OS11-B ✓ ✓ ✓ ✓ ✓ ✓

OS11-C ✓ ✓ ✓ ✓ ✓ ✓

Intake

OS13

OS13 ✓

OS13-A ✓ ✓ ✓ ✓ ✓ ✓

OS13-B ✓ ✓ ✓ ✓ ✓ ✓

OS13-BR* ✓

OS13-C ✓ ✓ ✓ ✓ ✓ ✓

OS13-D** ✓ ✓ ✓ ✓ ✓ ✓

OS13-E** ✓ ✓ ✓ ✓ ✓ ✓

Intake

OS21

OS21 ✓

OS21-A ✓ ✓ ✓ ✓ ✓ ✓

OS21-B ✓ ✓ ✓ ✓ ✓ ✓ ✓†

OS21-C ✓ ✓ ✓ ✓ ✓ ✓

OS21-

CR*

✓ ✓ ✓

Intake

OS23

OS23 ✓

OS23-A ✓ ✓ ✓ ✓ ✓ ✓ ✓†

OS23-B ✓ ✓ ✓ ✓ ✓

OS23-BR* ✓ ✓†

OS23-C ✓ ✓ ✓ ✓ ✓ ✓

Outfall

OS01

OS01-A ✓

OS01-B ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓†

Outfall

OS02

OS02-A ✓

OS02-B ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

OS02_R* ✓ ✓ ✓

Outfall

Flotation

OF-A ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

OF-B ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

OF-C ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

OF-D ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

OF-E ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

OF-F ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

OF-FR* ✓ ✓ ✓ ✓ ✓

* 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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5 References

BEEMS Technical Report TR444. HPC intake and outfall location pre-dredge sediment sample analysis

results (Marine Licence 12/45/ML). HPC-DEV024-XX-000-REP-100007. Cefas, Lowestoft.

BEEMS Technical Report TR502. HPC 2019 sediment sampling plan for dredge disposal. HPC cooling

water intakes, outfalls, FRR and jetty. HPC-DEV024-XX-000-RET-100135. Cefas, Lowestoft.

BEEMS Technical Report TR534. Evaluation including radioanalysis of alpha/beta radionuclides – Part 2.

Radiological Assessment of Dredging Application for Hinkley Point C. Cefas, Lowestoft.

Fugro Geoservices Ltd (2020) Final Report Hinkley Point C Dredge Licence Site Investigation Bristol

Channel. Document reference C2095_FIN-REP 01.

IAEA (2003). Determining the suitability of materials for disposal at sea under the London Convention 1972

and London Protocol 1996: A radiological assessment procedure. TECDOC-1375, IAEA, Vienna.

IAEA (2015). Determining the suitability of materials for disposal at sea under the London Convention 1972

and London Protocol 1996: A radiological assessment procedure. TECDOC-1759, IAEA, Vienna.

Leonard, K.S., Smedley, P.A. and Cogan, S.M. (2017). Radiological Assessment of Dredging Application for

Hinkley Point C Power Station, Somerset (2017). Cefas Environment Report RL 05/17.

McCubbin, D. and Vivian, C. (2006). Dose assessments in relation to disposal at sea under the London

Convention 1972: judging de minimis radioactivity, Cefas Environment Report RL05/06.

OSPAR (2014). OSPAR Guidelines for the Management of Dredged Material at Sea. OSPAR Commission

Agreement 2014‐06.

United Kingdom - Parliament, 2009. Marine and Coastal Access Act, 2009. HMSO, London.

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Appendix A Activity concentration data

Table 6 Activity concentrations in sediment samples

Core sample Identifier

Core Sub-sample Identifier

and additional information* Representative depth range, m

Specific activity (Bq/kg, dry weight)

60Co 137Cs

226Ra 232Th 238U 241Am (via

214Pb) (via

228Ac) (via

234Th)

OF-A r1, 0.00m to 0.25m, 1rA 0.0 – 0.25 <0.22 5.8 23.3 35.7 18.6 <1.4

OF-A r1, 0.25m to 0.50m, 2rA 0.25 – 0.50 <0.23 <0.27 12.1 20.7 11.2 <0.54

OF-A r1, 0.50m to 1.00m, 3rA 0.50 – 1.0 <0.26 <0.18 22 37.1 27.8 <0.41

OF-A r1, 1.00m to 1.80m, 4rA 1.0 – 2.0 <0.35 <0.46 24.6 44.7 23.3 <1.1

OF-A r1, 2.00m to 2.75m, 5rA. 48.9g stones removed 2.0 – 3.0 <0.22 <0.17 22.5 36.9 20.1 <1.8

OF-A r1, 3.00m to 3.75m, 6rA. 153.0g stones removed 3.0 – 4.0 <0.30 <0.29 26.5 33.7 24.7 <0.68

OF-A r1, 4.00m to 4.75m, 7rA. 107.0g stones removed 4.0 – 5.0 <0.25 <0.38 31 31.2 32.4 <0.69

OF-A r1, 5.00m to 5.60m, 8rA. 31.45g stones removed 5.0 - 6.0 <0.27 <0.26 28.6 30.3 26.7 <1.4

OF-B v1, 0.00m to 0.25m, 1rA, 113.4g stones present. 0.0 -0.25 <0.27 10.6 26.3 38.7 26.3 <2.2

OF-B v1, 0.25m to 0.50m, 2rA, 9.7g of small stones 0.25 – 0.50 <0.28 <0.44 23.7 28.9 23.7 <0.33

OF-B v1, 0.50m to 1.00m, 3rA. 0.50 – 1.0 <0.29 <0.51 30.9 35.3 30.9 <0.44

OF-B r1, 1.00m to 1.4m, 4rA 1.0 - 2.0 <0.22 2.8 47.7 35.1 47.7 <4.0

OF-B v1, 2.00m to 2.75m, 5rA. 44.4g stones removed. 2.0 – 3.0 <0.16 <0.28 15 20.5 15 <1.2

OF-B r1, 3.00m to 3.70m, 6rA. 50.5g stones removed. 3.0 – 4.0 <0.27 <0.44 22.3 31.4 22.3 <0.88

OF-B r1, 4.00m to 4.80m, 7rA 4.0 – 5.0 <0.17 <0.28 29 27.5 29 <4.0

OF-B r1, 5.00m to 5.60m, 8rA 5.0 – 6.0 <0.26 <0.43 28.6 35.7 28.6 <0.68

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60Co 137Cs

226Ra 232Th 238U 241Am (via

214Pb) (via

228Ac) (via

234Th)

OF-C v1, 0.00m to 0.25m, 1rA 0.0 – 0.25 <0.21 7.6 21.2 34.3 42.9 <4.1

OF-C v1, 0.25m to 0.50m, 2rA 0.25 – 0.50 <0.22 <0.28 24 37.4 29.6 <2.0

OF-C v1, 0.50m to 1.00m, 3rA 0.50 – 1.0 <0.28 <0.26 24.5 39.5 25.8 <0.66

OF-C v1, 1.40m to 2.00m, 4rA 1.0 – 2.0 <0.31 <0.48 24.3 41.2 28.7 <0.83

OF-C v1, 2.00m to 2.60m, 5rA. 17.9g stones removed 2.0 – 3.0 <0.24 <0.24 26.5 42 27.1 <1.2

OF-C v1, 3.00m to 3.60m, 6rA. 83.3g stones removed. 3.0 – 4.0 <0.45 <0.45 23.9 33.5 26 <0.76

OF-C v1, 4.00m to 4.60m, 7rA 4.0 – 5.0 <0.17 <0.18 33.7 30.4 36 <4.9

OF-C r1, 5.00m to 5.70m, 8rA 5.0 – 6.0 <0.17 <0.12 32.2 28.2 58 <3.1

OF-C r1, 6.00m to 6.60m, 9rA 6.0 – 7.0 <0.17 <0.25 28.4 32.5 31.5 <5.1

OF-D v1, 0.00m to 0.25m, 1rA 0.0 – 0.25 <0.35 9.9 22.6 33.3 22 <1.3

OF-D v1, 0.25m to 0.50m, 2rA 0.25 – 0.50 <0.29 <0.28 23.6 37.3 30 <0.81

OF-D v1, 0.50m to 1.00m, 3rA 0.50 – 1.0 <0.33 <0.50 23.9 41.2 28 <0.96

OF-D v1, 1.00m to 1.60m, 4rA 1.0 – 2.0 <0.22 <0.20 23.5 41.6 16.3 <2.4

OF-D v1, 2.00m to 2.60m, 5rA. 41.1g stones removed 2.0 – 3.0 <0.29 <0.40 25.3 41.6 29 <0.68

OF-D v1, 3.00m to 3.60m, 6rA. 100.0g stones removed 3.0 – 4.0 <0.21 <0.27 19.9 25.3 17.6 <0.58

OF-D v1, 4.00m to 4.60m, 7rA 4.0 – 5.0 <0.18 <0.23 31.8 31.4 44.5 <2.7

OF-D r1, 5.00m to 5.70m, 8rA 5.0 – 6.0 <0.37 <0.12 27.6 31.8 24.1 <2.0

OF-D r1, 6.00m to 6.60m, 9rA. 54.7g stones removed 6.0 – 7.0 <0.27 <0.44 25.7 32.5 19.7 <0.88

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60Co 137Cs

226Ra 232Th 238U 241Am (via

214Pb) (via

228Ac) (via

234Th)

OF-E v1, 0.00 to 0.25m, 1rA. 30.3g stones present. 0.0 – 0.25 <0.29 10.3 20.1 31.6 22.3 0.83

OF-E v1, 0.25m to 0.50m, 2rA. 113.4g stones present. 0.25 – 0.50 <0.38 <0.31 23.8 38.4 25.8 <1.2

OF-E v1, 0.50m to 1.00m, 3rA 0.50 – 1.0 <0.35 <0.44 20.7 37.8 22.2 <1.2

OF-E v1, 1.00m to 1.50m, 4rA 1.0 – 2.0 <0.29 <0.24 23.9 41.7 28.5 <0.78

OF-E v1, 2.00m to 2.65m, 5rA, 355.5g stones present. 2.0 – 3.0 <0.18 <0.11 17.5 26.2 22.6 <2.8

OF-E v1, 3.00m to 3.50m, 6rA 3.0 – 4.0 <0.27 <0.17 39.1 39.3 36.2 <0.88

OF-E v1, 4.00m to 4.65m, 7rA, 78.2g of stones 4.0 – 5.0 <0.17 <0.12 30 26.8 20.9 <4.1

OF-E r1, 5.00m to 5.85m, 8rA 5.0 – 6.0 <0.18 <0.34 33.9 36.1 <31.9 <4.0

OF-F v1, 0.00m to 0.25m, 1rA 0.0 – 0.25 <0.21 <0.18 21 32 23.9 <1.1

OF-F v1, 0.25m to 0.50m, 2rA 0.25 – 0.50 <0.23 <0.37 25.2 39.9 23.6 <1.9

OF-F v1, 0.5m to 1.00m, 3rA 0.50 – 1.0 <0.22 <0.26 22.3 39 25.3 <3.4

OF-F v1, 1.00m to 1.50m, 4rA 1.0 – 2.0 <0.28 <0.34 23.2 40.3 32.9 <0.38

OF-F v1, 2.00m to 2.60m, 5rA, 363.6g of stones 2.0 – 3.0 <0.28 <0.34 25 30.7 15.5 <0.78

OF-F r1, 3.00m to 3.70m, 6rA, 92.4g of stones 3.0 – 4.0 <0.18 <0.34 22.8 23.7 13.7 <1.3

OF-F r1, 4.30m to 5.00m, 7rA 4.0 – 5.0 <0.14 <0.26 17.9 16.3 29.2 <4.7

OF-F r1, 5.05m to 5.50m, 8rA 5.0 – 6.0 <0.17 <0.12 23.9 37 19.5 <1.6

OF-FR r1, 1.00m to 1.30m, 4rA, +33.8g of small stones 1.0 – 2.0 <0.27 5 22 33.5 27.7 <0.83

OF-FR r1, 2.00m to 2.60m, 5rA 2.0 – 3.0 <0.18 1.8 24.5 31.6 27.2 <3.2

OF-FR r1, 3.00m to 3.80m, 6rA, +307.4g of stones 3.0 – 4.0 <0.24 <0.41 19.5 19.9 18.6 <0.99

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60Co 137Cs

226Ra 232Th 238U 241Am (via

214Pb) (via

228Ac) (via

234Th)

OF-FR r1, 5.00m to 5.40m, 8rA, +145.0g of stones 5.0 – 6.0 <0.26 <0.40 25.8 45.1 25.6 <0.55

OF-FR r1, 6.00m to 6.50m, 9rA 6.0 – 7.0 <0.18 <0.13 33.2 42.7 24.7 <2.1

OS01-G1 g1, grab sample, 0.00m to 0.16m, 1rA, 8.7g small stones removed 0.0 – 0.16 <0.23 11.8 19.1 26.5 39 <1.9

OS01-B v1, 0.00m to 0.25m, 1rA, 6.6g small stones removed 0.0 – 0.25 <0.28 16.5 22.6 33.1 26.5 1.3

OS01-B v1, 0.25m to 0.50m, 2rA, 39.2g small stones removed 0.25 – 0.5 <0.34 5.5 21.3 34.8 27 <0.93

OS01-B v1, 0.50m to 1.00m, 3rA, 30.9g small stones removed 0.50 – 1.0 <0.23 <0.34 17.1 26.8 21.6 <0.65

OS01-B v1, 1.00m to 1.70m, 4rA, 107.9g small stones removed 1.0 – 2.0 <0.20 <0.41 19.9 37.9 47.7 <3.3

OS01-B v1, 2.00m to 2.70m, 5rA, 148.2g stones removed 2.0 – 3.0 <0.13 <0.33 20.4 26.7 23.5 <1.5

OS01-B v1, 3.00m to 3.70m, 6rA, 109.2g small stones removed 3.0 – 4.0 <0.29 <0.43 28 38.9 24.3 <0.79

OS01-B r1, 4.00m to 4.80m, 7rA, 286.4g small stones removed 4.0 – 5.0 <0.23 <0.42 20.4 23.7 20 <0.77

OS01-Ba r1, 4.80m to 5.60m, 8rA, 151.7g small stones & gravel removed 5.0 – 6.0a <0.18 <0.24 30.1 39.6 43.3 <4.8

OS02-G1 g1, grab sample, 0.00m to 0.16m, 1rA 0.0 – 0.16 <0.36 13.6 23.8 29.6 34.2 1.6

OS02-B r1, 0.00m to 0.25m, 1rA, 4.4g small stones removed 0.0 – 0.25 <0.24 5.8 18.2 27.5 17.7 <0.61

OS02-B r1, 0.25m to 0.50m, 2rA, 27.8g small stones removed 0.25 – 0.50 <0.31 <0.31 21.4 31.8 16 <0.97

OS02-B r1, 0.50m to 1.00m, 3rA, 121g of small stones 0.50 – 1.0 <0.28 <0.31 22.8 37.5 26.9 <0.64

OS02-B r1, 1.00m to 1.40m, 4rA 1.0 – 2.0 <0.37 <0.64 24.9 44.6 21.1 <1.0

OS02-B r1, 2.00m to 2.40m, 5rA. 57.2g stones removed. 2.0 – 3.0 <0.35 <0.56 22.4 38.9 26.5 <1.3

OS02-B r1, 3.00m to 3.75m, 6rA, 163.4g of stones 3.0 – 4.0 <0.17 <0.23 25.8 31.6 19.3 <1.4

OS02-B r1, 4.00m to 4.70m 7rA, 256.4g of stones 4.0 – 5.0 <0.18 <0.19 31.4 32.6 36.2 <4.3

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60Co 137Cs

226Ra 232Th 238U 241Am (via

214Pb) (via

228Ac) (via

234Th)

OS02-B r1, 5.00m to 5.50m, 8rA 5.0 – 6.0 <0.29 <0.36 31.2 41.5 28.6 <0.85

OS02-BR r1, 5.00m to 5.80m, 8rA 5.0 – 6.0 <0.30 <0.42 35.1 52.4 31.4 <1.1

OS02-BR r1, 6.00m to 6.50m, 9rA 6.0 – 7.0 <0.19 <0.32 35.4 49.8 44.9 <5.0

OS02-BR r1, 7.15m to 7.60m, 10rA 7.0 – 8.0 <0.30 <0.39 35.7 44.5 27.2 <1.3

OS11_G g1, grab sample, 0.00m to 0.16m, 1rA 0.0 – 0.16 <0.23 10 20.8 27.6 21.7 <1.8

OS11-A v1, 0.00m to 0.25m, 1rA 0.0 – 0.25 <0.60 34.8 25.1 40.6 32.2 <3.5

OS11-A v1, 0.25m to 0.50m, 2rA 0.25 – 0.50 <0.52 <0.43 13.3 19.1 16.3 <0.81

OS11-A v1, 0.50m to 1.00m, 3rA 0.50 – 1.0 <0.20 <0.28 9.1 9.8 7.2 <0.78

OS11-A r1, 1.05m to 1.55m, 4rA. 45.4g small stones removed. 1.0 – 2.0 <0.14 0.8 13 12.6 <10.2 <1.5

OS11-A r1, 2.05m to 2.70m, 5rA, 90.4g of small stones 2.0 – 3.0 <0.26 0.66 44.5 22.1 37.8 <0.62

OS11-AR r1, 3.00m to 3.51m, 6rA 3.0 – 4.0 <0.29 <0.37 56.8 23.7 58 <1.4

OS11-B r1, 0.00m to 0.25m, 1rA 0.0 – 0.25 <0.62 25.5 24.1 37.1 30.8 <3.6

OS11-B r1, 0.25m to 0.50m, 2rA 0.25 - 0.50 <0.24 29.2 22 35.2 22.5 2.4

OS11-B v1, 0.50m to 1.00m, 3rA, +72.3g of stones/etc 0.50 – 1.0 <0.14 0.33 8.9 11.5 10.1 <1.4

OS11-B r1, 1.05m to 1.75m, 4rA 1.0 – 2.0 <0.30 6.9 15.4 22.5 19 <1.1

OS11-B r1, 2.02m to 2.40m, 5rA, 19.8g small stones removed 2.0 – 3.0 <0.21 <0.13 34 19.7 30.7 <0.50

OS11-B r1, 3.00m to 3.80m, 6rA 3.0 – 4.0 <0.30 <0.51 44.1 25.3 28.3 <0.81

OS11-C r1, 0.00m to 0.25m, 1rA. 1.6g stones removed during sieving 0.0 – 0.25 <0.61 30.4 23.6 39.7 29.4 <3.4

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60Co 137Cs

226Ra 232Th 238U 241Am (via

214Pb) (via

228Ac) (via

234Th)

OS11-C r1, 0.25m to 0.50m, 2rA. 73.0g removed during sieving 0.25 - 0.50 <0.93 29.5 23.1 37.8 27.7 1.6

OS11-C v1, 0.50m to 1.00m, 3rA 101.1g of stones/etc 0.50 – 1.0 <0.21 <0.21 11.5 13.5 11.7 <0.94

OS11-C r1, 1.00m to 1.55m, 4rA 1.0 – 2.0 <0.17 0.58 13.9 14.7 <21.8 <3.2

OS11-C r1, 2.00m to 2.40m, 5rA, 186.8g of stones 2.0 – 3.0 <0.21 <0.34 25.5 28.2 28.3 <0.40

OS11-C r1, 3.00m to 3.50m, 6rA 3.0 – 4.0 <0.25 <0.38 36.3 25.8 28.2 <0.62

OS13-A r1, 0.00m to 0.20m, 1rA. 18.6g removed. 0.0 – 0.25 <0.13 <0.13 7.8 9.3 9.4 <2.6

OS13-A v1, 0.25m to 0.50m, 2rA. Sand with Small Shells 0.25 - 0.50 <0.14 <0.15 7.9 9.2 9.4 <0.84

OS13-A v1, 0.60m to 0.70m, 3rA, 8.68g disposed from sieving 0.50 – 1.0 <0.21 <0.18 8.5 9.9 6.6 <0.63

OS13-A v1, 1.10m to 1.25m, 4rA 1.0 – 2.0 <0.22 <0.23 9.9 10.4 8 <0.90

OS13-A r1, 2.72m to 2.86m, 5rA, 95.6g removed. 2.0 – 3.0 <0.27 <0.33 39.9 25.4 28 <0.75

OS13-A r1, 3.05m to 3.40m, 6rA, clay 3.0 – 4.0 <0.18 <0.13 36.6 28.9 37.3 <4.4

OS13-B v1, 0.10m to 0.25m, 1rA. 321.0g removed. 0.0 – 0.25 <0.14 0.54 10.2 13.5 13 <2.8

OS13-B v1, 0.25m to 0.35m, 2rA, 38.1g disposed from sieve 0.25 – 0.50 <0.15 <0.28 9.2 11.6 11 <1.5

OS13-B v1, 0.60m to 0.75m, 3rA 0.50 – 1.0 <0.13 <0.10 9.3 10.3 7.8 <1.4

OS13-B v1, 1.00m to 1.10m, 4rA 1.0 – 2.0 <0.14 <0.27 8.6 9.7 7.2 <1.1

OS13-B r1, 2.25m to 2.55m, 5rA 2.0 – 3.0 <0.17 <0.26 39 26.4 46.1 <2.0

OS13-B r1, 3.05m to 3.35m, 6rA, 181.8g small stones removed 3.0 – 4.0 <0.18 <0.12 39.8 22.2 26.3 <1.5

OS13-BR r1, 3.00m to 3.65m, 6rA 3.0 – 4.0 <0.31 <0.47 72.8 26 49.5 <0.86

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60Co 137Cs

226Ra 232Th 238U 241Am (via

214Pb) (via

228Ac) (via

234Th)

OS13-C-G1 g1, grab sample, 0.00m to 0.15m, 1rA 0.0 – 0.15 <0.68 12.1 24.3 31.8 29.9 <1.0

OS13-C v1, 0.00m to 0.25m, 1rA 0.0 – 0.25 <0.26 17.7 16.9 24.3 17.2 1.1

OS13-C v1, 0.25m to 0.50m, 2rA 0.25 – 0.50 <0.20 <0.20 8.9 11.1 9.3 <0.96

OS13-C v1, 0.50m to 1.00m, 3rA 0.50 – 1.0 <0.12 <0.14 8.6 10 9.2 <1.1

OS13-C v1, 1.00m to 1.50m, 4rA, 5.1g disposed from sieve 1.0 – 2.0 <0.22 <0.33 8.2 9.8 11.7 <0.87

OS13-C v1, 2.00m to 2.66m, 5rA. 17.8g removed during sieving 2.0 – 3.0 <0.24 <0.24 59 28.2 54.2 <0.73

OS13-C r1, 3.05m to 3.65m, 6rA 3.0 – 4.0 <0.27 <0.36 34.6 24.1 28.3 <0.93

OS13-D v1, 0.00m to 0.25m, 1rA 0.0 – 0.25 <0.21 10.9 13.8 19.6 11.6 <0.52

OS13-D v1, 0.25m to 0.50m, 2rA 0.25 – 0.50 <0.13 0.28 8.9 10.4 <7.4 <0.85

OS13-D v1, 0.50m to 1.00, 3rA 0.50 – 1.0 <0.20 <0.22 9.3 10.9 <11.1 <0.95

OS13-D v1, 1.00m to 1.50m, 4rA 1.0 – 2.0 <0.25 <0.36 11.2 11.7 6.8 <1.0

OS13-D r1, 2.00m to 2.70m, 5rA 2.0 – 3.0 <0.18 <0.32 41.5 27.3 32.2 <4.0

OS13-D r1, 3.00m to 3.70m, 6rA 3.0 – 4.0 <0.30 <0.28 62.1 28.5 44.1 <0.98

OS13-E v1, 0.00m to 0.25m, 1rA 0.0 – 0.25 <0.23 21 18.6 31.1 23.2 <1.8

OS13-E v1, 0.25m to 0.50m, 2rA 0.25 – 0.50 <0.13 <0.19 8.1 9.3 11.7 <3.6

OS13-E v1, 0.50m to 1.00m, 3rA 0.50 – 1.0 <0.19 <0.31 7.7 9.4 9.8 <0.51

OS13-E v1, 1.00m to 1.50m, 4rA 1.0 – 2.0 <0.13 <0.14 9.2 9.9 12.7 <1.9

OS13-E v1, 2.00m to 2.50m, 5rA 2.0 – 3.0 <0.28 <0.36 33.4 24.1 30.8 <1.2

OS13-E r1, 3.10m to 3.75m, 6rA 3.0 – 4.0 <0.17 <0.29 28.5 24 18.9 <1.8

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226Ra 232Th 238U 241Am (via

214Pb) (via

228Ac) (via

234Th)

OS21_G1 g1, grab sample, 0.00m to 0.16m, 1rA. 16.5g removed during sieving 0.0 – 0.16 <0.61 13.4 20.8 32.4 18 <2.6

OS21-A v1, 0.00m to 0.25m, 1rA, 103.2g of small stones 0.0 – 0.25 <0.25 23.7 22.3 37.4 26 <1.7

OS21-A v1, 0.25m to 0.50m, 2rA, 444.7g of stones 0.25 – 0.50 <0.28 1.4 23.4 26.3 21.2 <1.1

OS21-A v1, 0.50m to 1.00m, 3rA, 346.5g of stones 0.50 – 1.0 <0.19 <0.29 36.8 30.9 31.1 <3.0

OS21-A r1, 1.00m to 1.70m, 4rA 1.0 – 2.0 <0.23 <0.38 19 22 21.2 <0.6

OS21-A r1, 2.00m to 2.80m, 5rA, 147.5g small stones removed 2.0 – 3.0 <0.23 <0.41 16.8 19.2 12.6 <0.91

OS21-A r1, 3.00m to 3.80m, 6rA, 67.6g small stones removed 3.0 – 4.0 <0.31 <0.27 51.5 37.8 45.1 <1.3

OS21-B r1, 0.00m to 0.25m, 1rA, 19.4g of small stones 0.0 – 0.25 <0.24 32.2 23.8 39.4 22.5 <5.4

OS21-B r1, 0.25m to 0.50m, 2rA, 265.5g stones removed 0.25 – 0.50 <0.20 16.5 21.2 32.9 20.2 <3.1

OS21-B v1, 0.50m to 1.00m, 3rA 0.50 – 1.0 <0.23 1.2 24.4 29.1 28 <0.61

OS21-B r1, 1.00m to 1.75m, 4rA 1.0 – 2.0 <0.17 <0.16 22.7 26.7 22.1 <1.8

OS21-B r1, 2.00m to 2.25m, 5rA 2.0 – 3.0 <0.26 <0.42 34.6 29.6 22.9 <1.1

OS21-B r1, 3.00m to 3.40m, 6rA 3.0 – 4.0 <0.32 <0.50 50.5 50.5 54.9 <1.5

OS21-B a r1, 3.80m to 4.12m, 7rA 4.0 – 5.0a <0.20 <0.30 50.7 41.2 53.3 <4.3

OS21-C r1, 0.00m to 0.25m, 1rA 0.0 – 0.25 <0.45 0.98 15.7 22.1 19.4 <0.82

OS21-C r1, 0.25m to 0.50m, 2rA. 309.6g removed. 0.25 – 0.50 <0.19 <0.30 14.1 16.7 18.4 <0.61

OS21-C v1, 0.50m to 1.00m, 3rA. Mud with Shell. 159.4g of Shell and Stones 0.50 – 1.0 <0.25 8 14.9 22.3 13.8 <0.88

OS21-C v1, 1.00m to 1.65m, 4rA. Sand with Small Shells 1.0 – 2.0 <0.23 <0.23 18.3 18.9 15.3 <0.92

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60Co 137Cs

226Ra 232Th 238U 241Am (via

214Pb) (via

228Ac) (via

234Th)

OS21-C r1, 2.00m to 2.5m, 5rA. 37.0g Removed during Sieving 2.0 – 3.0 <0.33 <0.63 42.8 43.2 34.7 <0.89

OS21-C r1, 3.00m to 3.30m, 6rA 3.0 – 4.0 <0.21 <0.34 45.3 52.8 42.5 <2.0

OS21-CR r1, 3.30m to 3.85m, 6rA 3.0 – 4.0 <0.33 <0.4 52.1 56.2 52.5 <1.5

OS21-CR r1, 4.10m to 4.55m, 7rA 4.0 – 5.0 <0.18 <0.16 36.5 49.6 81.6 <2.8

OS21-CR r1, 5.41m to 5.87m, 8rA 5.0 – 6.0 <0.3 <0.55 44.6 44.6 41.9 <1.3

OS23_G1 g1, grab sample, 0.00m to 0.16m, 1rA, 14.6g small stones removed 0.0 – 0.16 <0.24 11.8 19.9 27.3 26.2 <1.5

OS23-A v1, 0.00m to 0.25m, 1rA, 124.3g of small stones 0.0 – 0.25 <0.27 30.1 24.4 36.9 26.2 1.2

OS23-A v1, 0.25m to 0.50m, 2rA 0.25 – 0.50 <0.21 8.8 15.4 20.1 17.9 <0.66

OS23-A v1, 0.50m to 1.00m, 3rA. 58.3g removed. 0.50 – 1.0 <0.24 <0.26 11 12.1 11.3 <1.1

OS23-A r1, 1.00m to 1.75m, 4rA 1.0 – 2.0 <0.24 <0.36 32 30.6 37.8 <0.51

OS23-A r1, 2.00m to 2.60m, 5rA 2.0 – 3.0 <0.27 <0.36 37.1 30.5 40.1 <1.1

OS23-A r1, 3.00m to 3.60m, 6rA 3.0 – 4.0 <0.30 <0.42 32 31.7 27.8 <0.88

OS23-A a r1, 3.80m to 4.20m, 7rA 4.0 – 5.0a <0.18 <0.30 33.5 32.5 35.3 <4.3

OS23-B v1, 0.00m to 0.25m, 1rA, 40.6g of small stones 0.0 – 0.25 <0.16 8.1 13.3 18 20.7 <2.1

OS23-B v1, 0.25m to 0.50m, 2rA. 292.3g removed. 0.25 – 0.50 <0.13 0.38 9.3 11.8 <12.3 <3.8

OS23-B v1, 0.50 to 1.00m, 3rA. 24.3g removed. 0.50 – 1.0 <0.19 <0.18 9.5 10 9.1 <0.58

OS23-B v1, 1.00m to 1.50m, 4rA 1.0 – 2.0 <0.27 <0.41 22.6 24.4 35.6 <0.99

OS23-B r1, 2.00m to 2.70m, 5rA 2.0 – 3.0 <0.17 <0.13 28.2 28.5 23.7 <2.2

OS23-BR r1, 3.00m to 3.70m, 6rA 3.0 – 4.0 <0.17 <0.3 28.6 25.8 22.6 <1.5

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60Co 137Cs

226Ra 232Th 238U 241Am (via

214Pb) (via

228Ac) (via

234Th)

OS23-BR a r1, 3.70m to 4.20m, 7rA 4.0 – 5.0a <0.20 <0.36 26.8 26 30.7 <0.84

OS23-C v1, 0.00m to 0.25m, 1rA 0.0 – 0.25 <0.24 27.6 21.1 36.4 29.9 <2.2

OS23-C v1, 0.25m to 0.50m, 2rA, 57.0g of stones 0.25 – 0.50 <0.25 4.1 13.1 17.6 <12.5 <3.5

OS23-C v1, 0.50m to 1.00m, 3rA 0.50 – 1.0 <0.17 <0.19 19.4 22.6 13.1 <4.0

OS23-C v1, 1.00m to 1.50m, 4rA 1.0 – 2.0 <0.27 <0.26 37.4 38.9 37.9 <0.58

OS23-C r1, 2.00m to 2.70m, 5rA 2.0 – 3.0 <0.25 <0.29 27 24.6 29.8 <0.75

OS23-C r1, 3.00m to 3.50m, 6rA, 194.7g stones removed 3.0 – 4.0 <0.23 <0.42 41 35.4 41.5 <0.70

**Average 0.25 3.3 25.16 29.11 25.96 1.66

Notes

* 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

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