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NNB GENERATION COMPANY LTD

The Choice of Interim Spent Fuel Management Storage Technology forforfor the Hinkley Point C UK EPRs

Version Issue 1 Date of Issue 26 October 2011 Document No. NNB-OSL-STR-000034

© 2010 Published in the United Kingdom by NNB Generation Company Limited (NNB GenCo), 90 Whitfield Street - London, W1T 4EZ. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, including photocopying and recording, without the written permission of the copyright holder NNB GenCo, application for which should be addressed to the publisher. Such written permission must also be obtained before any part of this publication is stored in a retrieval system of any nature. Requests for copies of this document should be referred to Head of Management Arrangements, NNB Generation Company Limited (NNB GenCo), 90 Whitfield Street - London, W1T 4EZ. The electronic copy is the current issue and printing renders this document uncontrolled. Controlled copy-holders will continue to receive updates as usual.

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DODODOCUMENTDO CUMENT CONTROL

Version Amendment Date Issue 1 Approved for issue 26 Oct. 2011

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GLOSSARY

EDF SA Électricité de France (EDF Energy’s parent company in France) EPR European Pressurised Water Reactor GDA Generic Design Assessment GDF Geological Disposal Facility GWd/t Gigawatt-days per tonne HPC Hinkley Point C IAEA International Atomic Energy Agency ISFS Interim Spent Fuel Store kW Kilowatt MADA Multi-Attribute Decision Analysis MOX Mixed Oxide MW(e) Mega-Watt (electrical) NDA Nuclear Decommissioning Authority NNB or NNB GenCo Nuclear New Build Generation Company (a subsidiary company of EDF Energy) PWR Pressurised Water Reactor RWMD Radioactive Waste Management Directorate (part of the NDA) SFA Spent Fuel Assembly

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CONTENTS

111 Introduction

222 Context for Spent Fuel Management at UK EPRs

333 TTThe The CCChoicChoichoicee of SSSpentSpent FFFuelFuel MMManagementManagement TechnoloTechnologygy for the HHHinkleyHinkley PPPointPoint CCC UK EPREPRssss

444 The Timing of Construction

555 The Location of the Site

666 Conclusions

777 References

Annex A --- Review of Hinkley Point C Interim Spent Fuel Store TechnologyTech nology Choice in the Light of Fukushima

A1A1A1 Introduction

A2A2A2 Approach to the Review

A3A3A3 Experience with the Spent Fuel Storage Facilities aatt FukushimaFukushima----11 during the accident

A4A4A4 Relevant Characteristics of the Proposed HPC Spent Fuel Store

A5A5A5 Discussion

A6A6A6 ConcConclusion lusion

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1 INTRODUCTION

NNB Generation Company Limited (Company number 06937084), part of EDF Energy, is the Company that will lead the new nuclear programme in the UK. For the purpose of this report, NNB Generation Company Limited is referred to as EDF Energy. EDF Energy plans to build and operate two UK EPRs at the Hinkley Point C site in Somerset, England. Spent fuel from the UK EPRs will need to be managed from the time it is discharged from the reactor until it is ultimately disposed of and this will involve storing the spent fuel for a period in the fuel building and thereafter in a dedicated interim facility until it can be emplaced within the UK Geological Disposal Facility. EDF Energy has proposed that this interim store should be located on the Hinkley Point site which is consistent with UK policy. The Generic Design Assessment (GDA) process is examining the technical alternative options proposed by EDF and AREVA for interim spent fuel storage for a UK EPR to gain confidence that the ALARP and BAT requirements can be fulfilled by either wet or dry storage options. The choice of option for a specific location has been left open to the future licensee who is expected to take into account site specific issues. EDF Energy has considered the alternative options and has decided that for Hinkley Point C wet storage in pools provides the best solution for interim storage. In determining the best solution a range of factors including health and safety and environmental protection and performance were considered. The purpose of this report is to explain this decision and to demonstrate that the choice of wet storage technology for HPC is justified. The report also sets out the reasons for a different choice of interim storage to that proposed for Sizewell B, where dry storage has been selected. In addition this report fulfils the commitment made in EDF Energy’s response to the ONR Chief Inspector’s interim report on the implications of the Fukushima accident to revisit the choice of the interim storage technology for Hinkley Point C. This is provided in Annex A to the report.

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2 CONTEXT FOR SPENT FUFUELEL MANAGEMENT AT UK EPRS

2.1 UK POLICY ISSUES In its 2008 White Paper 1 the government stated: “Having reviewed the arguments and evidence put forforward,ward, and in tthehe absence of any proposals from industry, the Government has concluded that any new nuclear power stations that might be built in the UK should proceed on the basis that spent fuel will not be reprocessed and that plans for, and financing of, waste managemanagemmentent should proceed on this basis. We are not currently expecting any proposals to reprocess spent fuel from new nuclear power stations. Should such proposals come forward in the future, they would need to be considered on their merits at the time and the Government wouldwould expect to consult on them.”

The UK Government is implementing a carefully developed strategy leading to the construction of a Geological Disposal Facility (GDF) for higher activity radioactive waste and spent fuel. In its Managing Radioactive Waste Safely White paper 2, the UK Government acknowledges that, although spent fuels are not currently classified as waste, they may need to be managed through geological disposal. The NDA is taking into account the possible inclusion of these materials within the design and development of the geological disposal facility. The disposability assessment carried out by the NDA’s Radioactive Waste Management Directorate (RWMD) for the UK EPR as part of the GDA process3,4 concluded that, compared with legacy wastes and existing spent fuel, no new issues arise that would challenge the fundamental disposability of the spent fuel expected to arise from operation of the UK EPR. This conclusion is supported by the similarity of these materials to those expected to arise from the existing PWR at Sizewell B. Given a disposal site with suitable characteristics, the spent fuel from the UK EPR is expected to be disposable. The time that would be required for the safe and secure interim storage of spent fuel prior to disposal depends on a two key factors: • the availability of a Geological Disposal Facility (GDF); and • the requirement that spent fuel characteristics are suitable to allow disposal to the GDF (i.e. the spent fuel has sufficiently cooled to allow its emplacement). With regard to the availability of a GDF, RWMD have published their plans and timescales for the expected implementation of the GDF 5. The current projection is that the UK GDF would become available around 2040 for the disposal of legacy ILW and 2075 for the start of emplacement of legacy spent fuel and HLW. It is assumed that ILW would be disposed of before

1 Her Majesty’s Government, “Meeting the Energy Challenge: A White Paper on Nuclear Power”, Cmnd 7296, January 2008 2 Managing Radioactive Waste Safely White Paper 3 Geological Disposal: Generic Design Assessment: Summary of Disposability Assessment for Wastes and Spent Fuel arising from Operation of the UK EPR. NDA Technical Note no. 11261814. 4 See also Annex B to the National Policy Statement for Nuclear Generation. 5 Geological Disposal – Steps towards implementation, March 2010, NDA/RWMD/013. Not Protectively Marked NNB-OSL-STR-000034 Issue 1 October 2011 Page 6 of 37

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HLW and spent fuel and that waste and spent fuel from existing facilities would be emplaced in the GDF before material from new stations. This schedules the end of legacy spent fuel disposal to the GDF in around 2130. Thereafter the GDF could be available to dispose of spent fuel from Hinkley Point C. Regarding disposability of spent fuel, recent work undertaken by RWMD 6 on behalf of the Nuclear Industry Association (NIA) has concluded that the spent fuel from the UK EPR could be suitable for disposal in the UK reference case GDF (based on the Swedish KBS-3V design) after approximately 50 years of storage post end of generation. It is therefore assumed that the date for start of transfer of spent fuel from the interim store to a GDF is around 2130. The process of transfer will take approximately 10 years and therefore all fuel would be expected to be removed from interim storage by around 2140. The precise timescales for which spent fuel will need to be stored remain subject to some uncertainty. EDF Energy is proceeding on the prudent basis that facilities could be needed to provide safe storage for spent fuel over timescales that extend well beyond the lifetime of the reactors themselves. There is currently no centralised storage facility for spent fuel in the UK, other than the pools tied to the reprocessing plants at Sellafield whose capacity is limited, and there are currently no plans in the UK to build a new centralised storage facility. EDF Energy plans, therefore, to store spent fuel from its UK EPRs at the site where it is produced and to seek the required Development Consent and regulatory permits and licences for these stores as part of the application for the power stations themselves; this approach is consistent with the Government’s “base case” (described in Section 4 of the Government’s 2008 Consultation on Funded Decommissioning Programme Guidance for New Nuclear Power Stations 7). It does not foreclose the option to manage the spent fuel differently over the lifetime of the station but it does provide a clearly defined solution that meets the UK policy requirements, is consistent with the national strategy developed by UK government, and which can be progressed without introducing potential delays to the introduction of the new low carbon nuclear generation that the country needs. It should be stressed that although this national strategy is for a potentially long period of interim storage at Hinkley Point C, this period will be time-limited since it will certainly end when the spent fuel is transferred away from the Hinkley Point C site for disposal in the national deep geological repository, or possibly to a future centralised spent fuel management or reprocessing facility should that option become preferable in the period prior to disposal. There is no intent or any proposal to dispose of radioactive waste at Hinkley Point, and the proposed storage facility would be unsuitable for such a purpose.

2.2 THE BENEFITS FROM ADOPTING A STANDARDISED DESIGN EPRs are currently being built in France (Flamanville), Finland (Olkiluoto) and China (Taishan), and the reactor is undergoing certification in the USA and the GDA process in the UK. The EPR

6 Geological Disposal: Feasibility studies exploring options for storage, transport and disposal of spent fuel from potential new nuclear power stations. NDA Report no. NDA/RWMD/060. November 2010. 7 BERR (2008), Consultation on Funded Decommissioning Programme Guidance for New Nuclear Power Stations Not Protectively Marked NNB-OSL-STR-000034 Issue 1 October 2011 Page 7 of 37

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represents an evolution from earlier designs of PWR in France and Germany, the most recent of which are the N4 reactors in France and the KONVOI reactors in Germany. Thus, the UK EPR design benefits from the experience gained from the past operation of more than eighty PWRs for several decades, plus all the associated research and development. There are a great many benefits to be gained from standardisation of reactor design, such as lower design and build costs, greater ease of licensing or certification and greater scope for sharing operational experience to help promote safe and efficient operation. These, and other, benefits are widely recognised by reactor vendors and operators, regulators and industry bodies. The EPR design will, so far as is possible, be standardised across different countries and different locations. The standardised and evolutionary nature of the EPR is relevant to the way in which spent fuel will be managed at UK EPRs. The high heat output of spent fuel from commercial power reactors immediately after it has been discharged from the reactor means that it must be stored under water for an initial cooling period. The standard design for the Fuel Building in the UK EPR includes a cooling pool large enough to accommodate spent fuel assemblies for a significant period of time. With the fuel burn-ups and refuelling strategies envisaged for EDF’s EPRs in France and England, this cooling pool will be sufficient to accommodate the spent fuel from ten to fifteen years of reactor operation. For the EPRs in France no extra on-site spent fuel storage capacity in addition to that provided by the Fuel Building cooling pool will be needed since the spent fuel will, after a period, be transferred off-site to La Hague for further pool storage and then reprocessing. The plan at Taishan is also for spent fuel to be transported away from the site after a period of cooling in the Fuel Building pool. At Olkiluoto in Finland, the spent fuel will be transferred from the EPR Fuel Building pool to an existing on site spent fuel storage facility for a period of interim storage prior to disposal in Finland’s national Geological Disposal Facility, which is under construction close to the site and is planned to open in 2020. For UK EPRs, however, where there are no plans for spent fuel to be transferred off-site for reprocessing, and where there is no existing or planned centralised storage facility, spent fuel storage capacity in addition to that provided by the Fuel Building cooling pools needs to be provided as part of the HPC project, and with sufficient capacity to accommodate all the spent fuel generated during the lifetime of the reactors. This new interim spent fuel storage facility will need to be designed specifically for the UK. The facility must, however, be one that is compatible with the design of the EPR and its fuel management. As this particular facility is not a standard feature of the design, the Generic Design Assessment process 8 did not examine the UK EPR interim spent fuel storage facility in the same way that it assessed the reactors themselves 9. Instead GDA is considering a range of several credible available options which could enable these facilities to be provided within the UK in a way that would be capable of meeting UK national policy and regulatory requirements. The choice of option for a particular site is a matter left to the future operator who would be expected

8 UK EPR Generic Design Assessment: PCSR – Sub-chapter 11.5 – Interim storage facilities and disposability for UK EPR. UKEPR-0002-115 Issue 02 9 The required level of design of waste plants for new build reactors in the Generic Design Assessment. http://www.hse.gov.uk/newreactors/wasteplants.pdf Not Protectively Marked NNB-OSL-STR-000034 Issue 1 October 2011 Page 8 of 37

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to substantiate its choice and submit the design through the normal site specific licensing and permitting processes.

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3 THE CHOICE OF SPENT FUEL MANAGEMENT TECHNOLOTECHNOLOGYGY FOR THE HINKLEY POINT C UK EPRS

3.1 OVERVIEW OF EDF ENERGY’S APPROACH The previous section has explained why in the UK context it is necessary to provide interim spent fuel storage additional to the UK EPR Fuel Building pool and why EDF Energy is proposing to provide this storage on the sites of its new UK EPR reactors. This Section explains how EDF Energy approached the choice of the right technical solution for this facility for the Hinkley Point C site. The starting point was knowledge of the range of spent fuel storage technologies in widespread use internationally, examples of which were considered within the GDA. In addition EDF Energy was aware of the work that had been initiated within British Energy Generation (prior to EDF acquiring the company in 2009) in order to provide additional spent fuel storage at Sizewell B 10 . EDF Energy was able as well to benefit from bringing in the experience available from EDF SA’s Engineering and Fuel Experts to assist in the assessment of the alternative options. EDF Energy drew on the experience from Sizewell B and used a similar Multi-Attribute Decision Analysis (MADA) process in order to bring all this experience together and inform the decision, with the support of an external consultant 11 . MADA is a structured tool for collecting and ordering information on the properties of various alternative options, set against the factors and attributes considered to be most important (whether beneficial or detrimental), and so provides a foundation for the exercise of engineering judgement. A robust option is one that, using the MADA tool, compares well against alternatives on a wide range of attributes. It is important to understand that the MADA process was not a substitute for the use of proper engineering judgement, nor did it deliver a mathematically precise answer. The MADA did not dictate the decision; instead the aim was to provide EDF Energy executives with a strategic level assessment to help inform the decision on the right technology for Hinkley Point C. In addition, the MADA did not determine how the design of interim storage could be further optimised with regards to safety and environmental impacts; this optimisation will be performed in line with the ALARP and BAT principles in the further development stages of the project. The starting point was to consider the technologies identified within GDA but the work was extended to include variations of these technologies to enable comparisons with Sizewell B.

10 The Sizewell B Spent Fuel Management Option Study (Appendix 2.1 to the Environmental Statement in support of the Section 36 Planning Application) 11 “Hinkley Point C: MADA Output Synthesis Report”, VT Group report, S. Hutt, July 2010 Not Protectively Marked NNB-OSL-STR-000034 Issue 1 October 2011 Page 10 of 37

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3.2 THE ASSESSMENT PROCESS (MADA) 3.2.1. Definition of Interim Spent Fuel Store (ISFS) Requirements 3.2.1.1 Spent Fuel Quantity and Characteristics The reactor core of a UK EPR would typically consist of 241 fuel assemblies providing a controlled fission reaction and a heat source for electrical power production. Each fuel assembly is formed by a 17x17 array of zirconium alloy (such as M5) tubes, made up of 265 fuel rods and 24 guide thimbles. The fuel rods consist of uranium dioxide pellets stacked in the zirconium alloy cladding tubes which are then plugged and seal welded. It is currently assumed that a maximum of 90 spent fuel assemblies (SFA) would be removed every 18 months of operation from each UK EPR. Taking into account the time allowed for planned maintenance outages over the anticipated 60 years operating life, a total of approximately 3,400 assemblies are expected to be generated by each UK EPR. The lifetime operation of HPC, comprising two UK EPRs, would therefore result in a total of around 6,800 spent fuel assemblies. Fuel cladding failures cannot be ruled out over this period and so the interim storage does need to be capable of receiving “failed fuel” within adequate packaging. Fuel composition and burn-up is a very important parameter for spent fuel management since it determines the heat load and the rate at which this reduces after the fuel is discharged from the reactor. The ISFS needs to be able to store enriched uranium fuel at the maximum design burn-up of 65 GWd/tU in accordance with the fuel envisaged in EDF Energy’s Development Consent application. However, the EPR is capable of accepting mixed oxide fuel (i.e. fuel where plutonium instead of uranium oxide is used to provide some or all of the initial fissile material) and, whilst EDF Energy has no current plans to use MOX fuel, it is considered prudent to ensure that the ISFS design could enable fuel with higher thermal power or different composition to be stored (noting, of course, that this eventuality would be subject to the receipt of all relevant Government and regulatory approvals).

3.2.1.2 Timing of Transfer of Spent Fuel to the ISFS Due to its very high initial heat content, the spent fuel removed from a reactor must have an initial period of cooling before it can be transferred and placed into interim storage. For the UK EPR, fuel assemblies removed from the reactor would be cooled underwater in a reactor fuel pool for about 10 years. The ISFS therefore needs to be capable of taking fuel with a residual heat load equivalent to its having been stored for this time period; the ability to receive fuel with a higher heat loading (for example representing transfer at less than 10 years cooling) would also be advantageous as this would provide flexibility. Additionally, the final core fuel would have a shorter cooling period (around 3 years) prior to its transfer to the ISFS in order to avoid delaying the decommissioning programme.

3.2.1.3 Timing of Transfer of Spent Fuel out of the ISFS As explained in Section 2, there are two factors that influence the time at which spent fuel could be removed from the ISFS:

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• The time at which the GDF becomes available for new build spent fuel disposal • The length of cooling time necessary before spent fuel could be accepted as suitable for emplacement within the GDF On this basis the HPC ISFS could be required to remain available for a period of 50 or more years after the reactors reach the end of their assumed 60 year lifetime. This extends beyond the timescale for the decommissioning of the station which will be fully decommissioned around 20 years after the end of generation. EDF Energy has therefore determined that the ISFS should be designed against a potential lifetime of at least 100 years and should incorporate features that enable its refurbishment and, if necessary, its re-equipment over its lifetime. The ISFS must also be designed to enable it to be capable of remaining as an autonomous facility (i.e. of becoming independent of those systems provided to support the UK EPR reactors that will be decommissioned at the end of station operation). The potentially long period over which the Hinkley Point C ISFS could be required to operate leads to another important consideration for the fuel management strategy. While there is a very large amount of experience worldwide with managing spent fuel safely, none extends to the 100 years timescale that could be necessary for this facility. There needs therefore to be confidence that the strategy would, if necessary, be capable of adaptation to ensure that the fuel remained safely stored and that high standards of protection of the environment would be maintained; and that, at the end of its storage period, the fuel would be in a state that would allow its disposal. This confidence is provided in three main ways: • The technology used for spent fuel storage will be based on approaches already utilised internationally and for which there is a substantial body of international experience that continues to grow every year. • At any time this international experience will comprise spent fuel that will be significantly older than will the fuel then being stored at Hinkley Point C. The study of ageing fuel behaviour is likely to be one of the most important sources of knowledge for spent fuel management, and the approach taken for Hinkley Point C will be able to take this knowledge into account. • The strategy for storage will ensure that there is always the ability, if necessary, for spent fuel to be removed from storage, inspected and, if necessary, put into some alternative management regime.

3.2.2. Options Considered The Solid Waste Strategy Report 12 , which formed part of the material submitted to the GDA, identified four fuel storage technologies that have been utilised worldwide: • Pool storage (wet storage) • Metal cask storage (dry storage) • Vault storage (dry storage)

12 UK EPR GDA: Solid Radioactive Waste Strategy Report (SRWSR). NESH-G/2008/en/0123. Not Protectively Marked NNB-OSL-STR-000034 Issue 1 October 2011 Page 12 of 37

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• Canister storage (dry storage) In addition a sensitivity study was carried out within the MADA to evaluate the canister storage option selected for Sizewell B as this was different to the canister storage exemplar included within GDA.

3.2.2.1 Pool Storage Spent nuclear fuel has been stored in pools since the late 1950s. There are hundreds of examples of pool storage – principally at power reactor sites who almost universally employ this technology for the receipt of fuel discharged from the reactor. For the MADA the exemplar of pool storage were the La Hague * facility pools in France. Spent fuel would be removed from the HPC Fuel Building pool and loaded into a transfer cask. The cask would then travel to the ISFS building where the fuel would be unloaded and placed in vertical storage racks using special handling equipment. The fuel would be moved within these racks away from the unloading area and placed in the appropriate part of the storage pool. The pool water provides shielding and protects operators and the wider environment from radiation. Whilst in storage, water cooling and clean-up systems remove heat generated within the spent fuel and maintain water quality – in part to ensure that the spent fuel does not degrade during storage. The pool and the associated unloading/loading facility would be located within a strong building that protects it from external hazards (for example aircraft crash). At the end of interim storage the handling equipment would be used to retrieve the spent fuel assemblies which would be placed in transport casks for transportation to the encapsulation facility and subsequent disposal. Once all the fuel has been removed from the ISFS the facility would be decommissioned.

3.2.2.2 Dry Storage in a Cask Storage System Dry storage in casks has been utilised worldwide since approximately 1990 and there are numerous designs of cask systems from a range of different suppliers. The MADA study was based on the Areva TN family of storage casks with a maximum capacity of 32 spent fuel assemblies per cask. Spent fuel would be removed from the Fuel Building in a transfer cask (as described in the pool option) and would be transferred to a hot cell where the spent fuel assemblies would be loaded into the storage cask. The TN cask is a leak-tight steel cylinder with a bolted lid and each cylinder is surrounded by additional steel or concrete to provide radiation shielding to operators and the environment. Once the cask has been sealed and decontaminated it is placed in its storage location where it is subject to periodic testing/maintenance.

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Air flow around the storage cask provides natural convection cooling. It was assumed an external building would be required at HPC to meet security requirements although this building would not be needed to provide either radiation shielding or external protection. At the end of interim storage, the storage casks would taken back into the hot cell where, if necessary (for example, in the case where the storage cask was not suitable for offsite transport), the casks would be opened, the spent fuel inspected, and then re-packaged into a new transport cask for despatch to the encapsulation facility and subsequent disposal. Once all the spent fuel has been removed, the ISFS facility would be decommissioned.

3.2.2.3 Dry Storage within a Vault Dry storage of spent oxide fuel in vaults has been used since around 1990 albeit in fewer instances than either pool or dry cask storage. The MADA study used the Habog facility in the Netherlands as the exemplar. As in the previous option, the spent fuel would be transferred from the Fuel Building to a hot cell which would form part of the ISFS. Here it would be loaded into a cylindrical storage canister which would have a maximum capacity of six spent fuel assemblies. Each storage canister would then be filled with an inert gas, sealed with a welded lid, decontaminated and then transferred to the vault canister handling machine. This machine would place each canister within a vertical storage compartment (pit) set into a reinforced concrete slab. The machine would also render the atmosphere within the compartment (pit) inert and fit a plug to the top of the compartment. Each storage compartment could receive two storage canisters. The canister handling machine would be used to retrieve canisters at the end of storage and could be used to remove canisters for visual inspection during storage if required. Natural air convection is used to remove the heat from the storage canisters. The concrete structure of the vault protects people from radiation and protects the fuel from damage due to external events. At the end of interim storage and prior to despatch to the encapsulation facility, the canisters would be recovered from the vault, placed in the hot cell where, if necessary, they would be opened, the spent fuel inspected, and then re-packaged into a transport cask for despatch to the encapsulation facility and subsequent disposal. Once all the spent fuel has been removed, the ISFS facility would be decommissioned.

3.2.2.4 Dry Storage in a Canister Storage System Canister storage systems have been used worldwide for around 20 years. The sealed canisters are placed within individual shielded storage modules that are usually stored in the open and may be configured so the cylindrical canister is stored in either the horizontal or vertical position. The MADA used as its exemplar the Areva NUHOMS system. The Holtec Hi- Storm canister storage system was subsequently also evaluated as a sensitivity study within the MADA (because this was the technology selected for Sizewell B).

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As for the previous dry storage systems, the spent fuel would be transported from the Fuel Building to a hot cell and loaded within a steel canister with a capacity for up to 17 fuel assemblies. The canister would be vented, vacuum dried and back-filled with helium prior to sealing and decontamination. The canister would then be placed into a site transfer cask and taken to the storage area and placed within a horizontal storage module (or a vertical module in the Holtec system). This module would then be closed and provide the shielding and external protection of the canister containing the spent fuel. Internal air flow passages within the storage module provide natural convection cooling. It was assumed an external building would be required at HPC to meet security requirements although this building would not be needed to provide either radiation shielding or external protection. At the end of interim storage and prior to despatch to the encapsulation facility, the canisters would be recovered from the storage modules, placed in the hot cell where, if necessary, they would be opened, the spent fuel inspected, and then re-packaged into a transport cask for despatch to the encapsulation facility and subsequent disposal. Once all the spent fuel has been removed, the ISFS facility would be decommissioned.

3.2.3. Key Attributes assessed The identification and selection of the attributes against which these options needed to be evaluated built on the experience of EDF Energy’s MADA contractor (who carried out the similar study for Sizewell B) and more generally on guidance published by the Environment Agency and the Scottish Environment Protection Agency 13 . Workshops were run to confirm and then refine the choice of attributes to ensure the key areas were covered and included the attributes that would help differentiate between the available options. The final list of attributes and categories is set out below.

13 Guidance for the Environment Agencies’ Assessment of Best Practicable Environmental Option Studies at Nuclear Sites. 2004 Environment Agency & Scottish Environment Protection Agency Not Protectively Marked NNB-OSL-STR-000034 Issue 1 October 2011 Page 15 of 37

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High Level Attribute Category

Health and Safety S2.1 Operator Dose from Routine Activities

S2.2 Operator Dose from Fuel Failure

S3 Nuclear Safety – Active and Passive Systems

Technical T1.1 Technical Robustness - Flexibility to Changes in Fuel Performance, Type Safety and Practicability T1.2 Technical Robustness - Flexibility to Changes in Fuel Quantity

T2 Development Status - Worldwide Experience

T3 Compatibility with Existing Plant and Equipment

T4.1 Waste Form Acceptability - Inspectability

T4.2 Waste Form Acceptability - Fuel Integrity during Storage

T5 Ease of Deployment - Fuel Retrievability

Environmental EN1.1 Active Waste Generation - Operational and Decommissioning Wastes (ILW)

EN1.2 Active Waste Generation - Operational and Decommissioning Wastes (LLW)

EN2 Radiological Discharges

EN3 Chemical Discharges

EN7.1 Land Usage

EN7.2 Visual Impact

Economic EC1 Lifetime Costs

EC2 Discounted Costs

EC4 Financial Risk

The MADA process involves both scoring the different options against each of the attributes and also weighting the importance of each attribute. These scores and, in particular, the weightings involve judgements and one feature of MADA is that it enables the impact of different judgements to be tested. The process can be also used to identify which features are those that really differentiate between the options available.

3.2.4. The Insights from the MADA Process As the position stands currently, the GDA suggests that all the spent fuel options included within the MADA would be potentially acceptable options – i.e. should be capable of meeting UK

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regulatory requirements. Nevertheless, safety and environmental protection criteria remained extremely important attributes considered within the MADA for the Hinkley Point C ISFS. Indeed issues relevant to these areas were considered and scored within three of the four attribute categories: “Health and Safety”, “Environmental”, and “Technical Performance, Safety and Practicability”, the last of which includes some key features relating to safety and environmental protection, see section 3.2.4.4. However, despite placing considerable emphasis on these areas, the MADA demonstrated that there was little to discriminate between the options on the grounds of either safety or environmental protection. This finding is consistent with the fact that each option has been and is still being utilised internationally and is therefore clearly capable of meeting regulatory requirements governing safety and environmental protection in a wide range of countries. Additional insights gained from the MADA study are summarised below.

3.2.4.1 Health and Safety The pool system was recognised to be somewhat more complex than the dry cask storage systems and to have more active systems (e.g. pool water chemistry control) than cask or canister storage systems. It was felt however that the degree of reliance on these systems for ultimate safety and environmental protection could be minimised. On the other hand the pool benefited from enabling easier inspection of the spent fuel assemblies during storage and maintained the fuel cladding at a lower temperature than did the dry systems. Radiological exposure of both workers and the public was extremely low for all systems.

3.2.4.2 Environmental The pool system did score somewhat lower due to the need for some discharge of radioactive material associated with ventilation and pool water clean-up and as a result of its higher arisings of operational intermediate level waste than from the dry systems. However, in absolute terms these discharges were recognised as being small. The dry systems all required that fuel be loaded, unloaded and, where necessary, inspected within a hot cell and it was noted that some discharges would arise from these processes although, again, these would be very small. The horizontal canister storage option did require a larger site footprint than the other systems. Dry cask and pool systems were the most compact. The vault option scored slightly less than others on visual appearance due to its higher ventilation stack heights. Overall, there was no compelling basis for differentiating between options under this heading.

3.2.4.3 Economics The key finding in this area was the different nature of the economic risk between the options. The pool and vault systems required a larger initial investment but provided longer term certainty in cost thereafter. The cask and canister systems required a smaller initial investment but there was greater uncertainty in future costs since these would depend on the price of casks or

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canisters many decades from now. Since the economics of these systems depended critically on the maximum number of assemblies each cask or canister could hold, there was also the risk that possible future changes in fuel composition or burn-up could adversely affect costs.

3.2.4.4 Technical Performance, Safety, and Practicability This category included attributes relating to the ability of the storage system to demonstrate or ensure integrity of fuel during storage, and included ease of inspectability, retrievability, and ultimately disposal. These attributes are important for the storage system’s safety and environmental protection performance as well as its technical performance and practicability. Consideration was given to the potential impact of long term storage on fuel integrity. Even with the proposed higher burn-up of EPR fuel it was considered that for wet storage with suitable controls on pool chemistry, there were no credible phenomena that could occur during long-term wet storage that would challenge the integrity of the fuel rod cladding over storage periods of up to 100 years. In addition, the MADA valued the pool option’s ability to provide inspectability of the spent fuel without extensive work and without the need to interfere with its packaging. This relative ease of inspection is an advantage in terms of providing evidence of future disposability compared with options that could require packages to be opened during the period of storage. The pool storage option was also found to provide the greatest long term flexibility in terms of its adaptability to accommodate future developments in fuel characteristics over the lifetime of the UK EPR. Dry systems could in principle also be adapted to these changes but if it became necessary to store fuels with a higher thermal content (due to higher burn-up or different fuel composition) within these types of facility, this would mean either reduced loadings in the casks or canisters, or longer cooling times in the UK EPR Fuel Buildings at Hinkley, or possibly both.

3.3 STEERING GROUP REVIEW AND RECOMMENDATION The insights reported above from the MADA led to the conclusion that the wet storage option should be the preferred option for HPC UK EPR. These results were presented to EDF Energy’s Fuel & Waste Strategy Steering Group, which comprises senior staff with expertise in these areas from within EDF Energy’s existing licensed operator, from within its new nuclear operator and from EDF SA (the French parent company). The Steering Group agreed that for HPC pool storage should be the recommended option. Prior to reaching this conclusion there was a discussion over the rationale for choosing a different technology at Hinkley Point C to that selected for Sizewell B. The following factors were noted as influencing this outcome: The heat load The fuel that will be removed from Sizewell B’s Fuel Building pool and placed in the proposed Dry Fuel Store will have been stored for around twice as long as the equivalent fuel Not Protectively Marked NNB-OSL-STR-000034 Issue 1 October 2011 Page 18 of 37

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from HPC. As a result the heat load within each Sizewell B fuel assembly will be lower and this makes it possible to load more fuel per canister while still meeting the fuel cladding temperature criterion (which is a limiting factor for ensuring the long term integrity of the cladding). This difference would significantly increase the number of packages required at HPC. The importance of future flexibility At Sizewell B the fuel burn up is currently lower than is planned for the EPR generic design. Because HPC would be operating many years after Sizewell B has closed, future flexibility to accommodate further fuel development is more important to HPC than it is to Sizewell B, in particular with regards to possible future changes in heat load or fuel composition. The fuel handling differences The benefits of adopting a standardised EPR design were noted in Section 2. Without making significant changes to the UK EPR Fuel Building (which uses a ‘bottom loading’ method, rather than loading by immersion) it would not be possible to load HPC fuel into the large storage canisters proposed for Sizewell B. While this is not an over-riding issue, it does mean that one of the benefits identified in the evaluation of the Dry Store solution proposed for Sizewell B (i.e. the avoidance of double handling of irradiated fuel assemblies) would not be available to HPC. The fuel quantities Pool storage becomes more economically attractive as the quantity of fuel needing to be accommodated increases. This is partly a result of the more compact storage conditions (as a result of the better cooling properties of water) and partly because the incremental costs of additional cask or canister storage are higher. The requirement to store the fuel from two EPRs at HPC tends to make the pool option more attractive there than at Sizewell B. Disposal optimisation Due to the higher burn-up of EPR fuel there is greater benefit from enabling flexibility in fuel retrieval prior to disposal and making it possible to mix fuel assemblies of different cooling times so as to optimise the heat load within each GDF disposal package. The work carried out by RWMD for the NIA 6 showed that by applying this approach it should be possible to meet the temperature constraints of the GDF with UK EPR spent fuel after around 50 years cooling post end of generation instead of the around 100 year cooling period estimated without this “mixing”. This package optimisation would be much more straightforward to achieve with pool storage and the benefits from it were noted to be more significant for HPC than would be the case for lower burn up and longer cooled Sizewell B fuel. The project risks of delivering the facility on time The Sizewell B facility is needed by 2015 and has to be engineered on the site of an operating nuclear power station. The HPC facility is not needed until around 10 to 15 years after the first reactor has started operation and its design and construction can be planned from the outset. The Steering Group recognised that the relatively simpler dry canister option selected for Sizewell B had some advantages over a pool system under these different circumstances.

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Summary For the reasons set out above, the conclusion was reached that for the proposed UK EPR development at HPC the optimum technology for interim spent fuel storage was pool technology. The option was consistent with a high level of safety and environmental performance, was well- proven and, of the options that had been identified and were being considered within the GDA, it offered potentially valuable benefits through its greater long term flexibility. While detailed aspects and further optimisation of the design would be subject to regulation through licensing and permitting, this technology was judged as being consistent with the principles both of BAT and ALARP: • The approach builds on experience from widely used facilities that are demonstrably capable of meeting regulatory requirements and delivering very low doses to workers and public together with high levels of environmental protection; • The intent to store only well-cooled fuel in a location physically separate from the reactors themselves will enable the store to provide a very high level of assurance of fuel integrity for protracted periods utilising predominantly passive systems, even in the event of extreme accident scenarios; • Staged implementation allows advances in operational experience, technology and scientific understanding to be taken into account as part of ongoing optimisation to keep doses, already low, as low as reasonably achievable; • Experience in the UK and within the wider EDF group provides confidence in the ability to develop a safe, environmentally optimised and economical design and to operate it successfully – including developing and maintaining safety and environmental cases; • Alternatives could deliver comparably safe and environmentally benign performance, but no significant benefit has been identified in these respects to offset the balance of disadvantage for HPC with regards to the previously presented attributes of a pool solution.

3.4 THE DECISION The Steering Group’s recommendation that HPC’s ISFS be based on pool storage was endorsed at a special meeting convened between EDF Energy’s existing licensed and new nuclear operators and EDF SA. In reaching this decision it was specifically noted that the Steering Group had stated: “It must be emphasised that safety and environmental issues were key parts of the assessment. However, as all options considered would meet high standards, other factors in the end determined the preferred option.”

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4 TIMING OF CONSTRUCTICONSTRUCTIONONONON

As explained above, each UK EPR Fuel Building pool will have the capacity to store all the spent fuel that is produced within a period of up to around 15 years of reactor operations. There will therefore be no need to transfer any spent fuel from the Fuel Building to the Interim Spent Fuel Store for at least the first 10 years of operation. EDF Energy has therefore had to consider whether to build the ISFS as part of the main construction of the rest of the power station or to delay its construction until a time nearer to when the facility is needed. In considering this EDF Energy has weighed the benefits and disadvantages of earlier construction against those of later construction.

Early Build Later Build

Disturbance to Better (confines impact neighbours period)

Environmental impact Better - jetty available for delivery of materials

Site disruption Better (major works completed before both reactors operational)

Technology Better – potential to benefit refinement from technical and other developments

Ageing/Obsolescence Better – eliminates the care and maintenance period prior to operation

Economics Better – later financing (but funds may need to be set aside within the Funded Decommissioning Plan)

The safety and security implications were assessed as broadly the same for each scenario. Both scenarios will require construction to be managed in parallel with some nuclear plant operation: if the facility is built early this would take place alongside unit 1 operation; whereas a later build would take place in parallel with unit 1 and 2 operations (although unit 1 is closer to the allocated ISFS location on the plot plan). On balance EDF energy has decided that its proposal to the Infrastructure Planning Commission will be based on completing the excavations and the building of the major structures that will comprise the ISFS within the period of the main project. This will enable the jetty to be utilised to the full for the relatively large quantity of materials required to construct the Not Protectively Marked NNB-OSL-STR-000034 Issue 1 October 2011 Page 21 of 37

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pool and the substantial building protecting the facility, and will mean that the local disturbance from these activities is confined within the main construction “window”. The exact completion schedule of the fitting-out of the ISFS with internal equipment, etc. will be defined during the basic design phase when more detailed information is available. However, whatever schedule is finally adopted for completing/commissioning the store, these activities would be minor in terms of their scale of disturbance compared to the previous phase comprising the major excavations and the construction of the civil structures.

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5 LOCATION ON THE SITE

The ISFS is proposed to be constructed in an area at the north east corner of the HPC site. This section explains how this choice was made. The overall layout of the power station has to take into account the need to accommodate all the necessary facilities within the land area designated as suitable and do so in a way that maximises the benefits from replicating the EPR design while also taking into account local geological conditions. This placed a number of restrictions on the areas potentially available. At the time the layout was being developed EDF Energy had not chosen its preferred storage technology or defined its design and construction schedule and so it was important to retain flexibility. In addition to requiring a sufficiently large area to accommodate the store, the following factors were also important: • It was considered desirable to be reasonably close to the cooling water pump house in case a sea water cooling system was chosen; (the plot location decision had to be taken before the conceptual design had developed to its present position which does not utilise sea water cooling) • The potentially long lifetime of the facility (longer than that of the rest of the station) led to a preference for a location towards the edge of the site as this would reduce the impact the ISFS could have in restricting opportunities for future development on other parts of the site and make it easier to manage its ultimate decommissioning • Security issues were also important. In its chosen location the ISFS will be completely enveloped within a very robust external building with the only access point on the southern side (i.e. facing into the site) • The proximity to Unit 1’s Effluent Treatment Building results in shorter galleries and shorter solid waste transfer routes during the power plant operational phase • The radiological implications of locating the store relatively close to the coastal footpath were considered. However, the very low external dose rates outside the ISFS (far below any dose constraints or limits) meant this was not ultimately a significant factor

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6 CONCLUSIONS

As explained in this report, the UK strategy and policy for new nuclear power stations leads to the requirement for an interim period of storage for spent fuel until the national deep geological repository is available and the heat level in the fuel is compatible with disposal. As part of EDF Energy’s proposal to build two UK EPRs at Hinkley Point C it is necessary to meet this requirement. EDF Energy has therefore set out its plans to construct an Interim Spent Fuel Storage facility on the site as part of the Hinkley Point C development 14 . The GDA Pre-Construction Safety Report examined several technologies that provide options for safe and environmentally sound interim spent fuel storage. All the options being considered within GDA have been licensed and operated internationally and, for some, several decades of operational experience are available. The expectation is that a prospective licensee for a new nuclear power station in the UK will take the GDA assessment into account, then demonstrate how its chosen strategy and storage technology meets the requirements for a particular site, and ultimately will provide a site specific detailed design which meets the safety, security and environmental requirements, embodying the principles of BAT and ALARP. This report describes how EDF Energy selected pool storage of spent fuel within a robust external protection building as its preferred interim storage technology for HPC and why this choice is consistent with regulatory requirements and national policy. While safety and environmental protection were the most important qualities sought, these on their own did not provide a basis for preferring one technology over other equally sound alternatives identified within GDA. In the end it was therefore other attributes, including the value EDF Energy attaches to long term flexibility and adaptability for a facility that will need to support the HPC EPRs over their full lifetime that led to EDF Energy’s preference for pool storage over the available alternatives. In the Annex to this report EDF Energy has revisited the basis for its choice of pool storage for the HPC ISFS and examined whether the conclusion remains sound in the light of the experience with spent fuel storage facilities at Fukushima in the aftermath of the catastrophic earthquake and tsunami in March 2011. This review was a commitment within EDF Energy’s response to the interim report on Fukishima by Dr Weightman, the UK’s Chief Inspector of Nuclear Installations. The conclusion reached is that EDF Energy’s original selection of this technology remains correct and is well-founded.

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7 REFERENCES

1 Her Majesty’s Government, “Meeting the Energy Challenge: A White Paper on Nuclear Power” , Cmnd 7296, January 2008.

2 Managing Radioactive Waste Safely White Paper, http://mrws.decc.gov.uk/

3 Geological Disposal: Generic Design Assessment: Summary of Disposability Assessment for Wastes and Spent Fuel arising from Operation of the UK EPR. NDA Technical Note no. 11261814.

4 Annex B to the National Policy Statement Nuclear

5 Geological Disposal: Steps towards implementation, March 2010, NDA/RWMD/013.

6 Geological Disposal: Feasibility studies exploring options for storage, transport and disposal of spent fuel from potential new nuclear power stations. NDA Report no. NDA/RWMD/060. November 2010.

7 BERR (2008), Consultation on Funded Decommissioning Programme Guidance for New Nuclear Power Stations.

8 UK EPR Generic Design Assessment: PCSR – Sub-chapter 11.5 – Interim storage facilities and disposability for UK EPR. UKEPR-0002-115 Issue 02.

9 The required level of design of waste plants for new build reactors in the Generic Design Assessment. Generic Design Assessment guidance document published by the HSE and the Environment Agency.

10 The Sizewell B Spent Fuel Management Option Study (Appendix 2.1 to the Environmental Statement in support of the Section 36 Planning Application)

11 “Hinkley Point C: MADA Output Synthesis Report”, VT Group report, S. Hutt, July 2010

12 UK EPR GDA: Solid Radioactive Waste Strategy Report (SRWSR). NESH- G/2008/en/0123.

13 Guidance for the Environment Agencies’ Assessment of Best Practicable Environmental Option Studies at Nuclear Sites. 2004 Environment Agency and Scottish Environment Protection Agency

14 Hinkley Point C Project Environmental Statement: Volume 2, Chapter 7 - Spent Fuel and Radioactive Waste Management, October 2011

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15 Japanese earthquake and tsunami: Implications for the UK Nuclear Industry Interim Report, HM Chief Inspector of Nuclear Installations. ONR, May 2011

16 Japanese earthquake and tsunami: Implications for the UK nuclear industry: Final Report, HM Chief Inspector of Nuclear Installations. ONR, Sept. 2011

17 Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety - The Accident at TEPCO's Fukushima Nuclear Power Stations. Nuclear Emergency Response HQ, Government of Japan. June 2011

18 Mission Report: IAEA International Fact Finding Expert Mission of the Fukushima Dai-Ichi NPP Accident following the Great East Japan Earthquake and Tsunami. IAEA, June 2011

19 Communication from Japan Nuclear Technology Institute (JANTI) to EDF SEPTEN (Service Etudes et Projets Thermiques et Nucléaires) dated June 5 2011

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ANNEX A – REVIEW OF HINKLEY POINT C INTERIM SPENT FUEL STORE TECHNOLOGY CHOICE IN THE LIGHT OF FUKUSHIMA

A1. INTRODUCTION The proposals described in the main body of this report for providing an Interim Spent Fuel Store as part of the Hinkley Point C power station were developed prior to the devastating earthquake and subsequent tsunami that struck the north-east coast of Japan on March 11 th 2011. The impact of these events on the Fukushima-1 (sometimes referred to as Fukushima Dai- ichi) nuclear power station was very serious and led to the release of significant quantities of radioactivity from a number of the facilities on that site. The releases were such that the accident was graded at Level 7 on the INES scale (the highest level). The UK’s Chief Inspector of Nuclear Installations, Dr Mike Weightman, was asked by the Secretary of State for Energy and Climate Change to advise on the implications of the events in Japan, and at Fukushima in particular, for the UK. As part of this, EDF Energy was invited to submit material to Dr Weightman. EDF Energy’s response committed the company to learning all the lessons from the event. Dr Weightman’s interim report 15 was published on May 18 th 2011 and contained eleven Conclusions and 26 Recommendations. 18 of the Recommendations were specifically directed to the UK nuclear industry and, of these, two Recommendations (12 and 14) referred explicitly to new proposals for spent fuel management and the design of any new spent fuel pools. Three other Recommendations (20, 21 and 22) related to existing storage facilities or are relevant to reactor fuel pools (see below):

Recommendation No. Recommendation Text

12 The UK nuclear industry should ensure the adequacy of any new spent fuel strategies compared with the expectations in the Safety Assessment Principles of passive safety and good engineering practice. 14 The UK nuclear industry should ensure that the design of new spent fuel ponds close to reactors minimises the need for bottom penetrations and lines that are prone to siphoning faults. Any that are necessary should be as robust to faults as are the ponds themselves. 20 The nuclear industry should review site contingency plans for pond water make up under severe accident conditions to see whether they can and should be enhanced given the experience at Fukushima.

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Recommendation No. Recommendation Text

21 The UK nuclear industry should review the ventilation and venting routes for nuclear facilities where significant concentrations of combustible gases may be flowing or accumulating to determine whether more should be done to protect them.

22 The UK nuclear industry should review the provision of on-site emergency control, instrumentation and communications in light of the circumstances of the Fukushima accident including long timescales, wide spread on and off-site disruption, and the environment on-site associated with a severe accident.

EDF Energy submitted its initial response to the interim report on June 18 th 2011 (as required by Recommendation 26); this response provided ONR with EDF Energy’s view on applicability and the timescale on which an action plan would be available addressing each recommendation. The response to Recommendation 12 committed EDF Energy (amongst other things) to “A review to confirm whether the use of wet storage for the Interim Fuel Storage Facility remains appropriate”. Clearly the choice of storage technology is fundamental to the design of this part of the power station and so needs to be clearly explained within the application to the IPC for development consent. This Annex is therefore being provided to fulfil this specific element of the EDF Energy response to Recommendation 12. Other parts of the response to Recommendation 12 (as well as the response to the other recommendations) will be provided in separate documentation and in accordance with the plans being developed.

A2. APPROACH TO THE REVIEW The main body of this report has explained the reasons why EDF Energy selected pool storage as the basis of the design for the Hinkley Point C ISFS. The ability to meet very high standards of safety and environmental performance was essential but it was not the attributes of pool storage in these areas that ultimately led to this technology being selected for Hinkley Point C. This was because the conclusion was reached during the assessment that wet (pool) storage and dry cask storage technologies were both capable of delivering a very high standard of safety and environmental performance. The critical question in reviewing the choice made for interim spent storage at Hinkley Point C is therefore whether the Fukushima events raise any new questions over the level of safety or environmental performance provided by this technology. If it were to be established that in the light of Fukushima there were potentially significant safety or environmental performance weaknesses associated with pool storage when compared with another alternative available technology, then the decision taken during the process described in this report would be in doubt.

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EDF Energy has therefore examined the evidence from Fukushima that could be relevant to the storage of spent fuel on a reactor site after it has been removed from the reactor building spent fuel pool following several years cooling – i.e. the situation relevant to interim spent fuel storage at Hinkley Point C. It should be stressed this review is only concerned with the choice of technology for the Interim Spent Fuel Store. The Review is structured as follows: • A summary of relevant facts from Fukushima in regard to spent fuel storage (for completeness this looks at both the reactor pools and the “common pool” on that site although it is the latter pool that more closely resembles the interim spent fuel storage facility) • A description of key features of the conceptual design of the proposed ISFS for Hinkley Point C that are relevant to its performance under accident conditions • Observations and conclusions on the impact of Fukushima on the HPC choice of storage technology It should be noted that after this review was completed Dr Weightman’s final report on Fukushima was published 16 . The conclusions and recommendations relevant to this Annex did not change in the Final Report and the additional information provided in the Final report on the experience from Fukushima is consistent with that given in this Annex. Fukushima-1 has 3 types of facility in which spent fuel is stored: • Each of the 6 reactors on the Fukushima-1 site has an associated reactor spent fuel pool located close to the reactor • There is also a central pool (sometimes referred to as the “common pool”) serving all 6 reactors housed in an independent building on the site into which spent fuel is transferred after a period of cooling. (This is the facility that is most comparable to the ISFS proposed for HPC.) • There is also a dry storage facility in which spent fuel from any of the 6 reactors is stored in casks within a separate building on the site, again after a suitable cooling period in the reactor pools The following sections describe how these 3 types of facilities are understood to have performed after the earthquake and tsunami.

A3.1 Performance of Spent Fuel Storage Pools at Fukushima Each of the 6 reactors at the Fukushima-1 power station has an associated spent fuel cooling pool. These pools are situated close to the reactors within each of the Reactor Buildings so that spent fuel can be transferred under water from the refuelling cavity above each reactor through a linking channel into the storage pool. These pools are built at a significant elevation above ground so as to be at the same level as the refuelling cavity they connect with.

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In addition to these 6 reactor pools there is also a “common spent fuel storage pool” located at ground level in a separate building behind Unit 4 used to store fuel that had already undergone a period of cooling within the reactor pools. The Weightman Interim Report, the report to the IAEA from the Japanese Government 17 and the IAEA’s own report 18 provide the following key facts concerning these reactor spent fuel pools: • Around 1/3 of the spent fuel stored on site was within these reactor pools (the remaining 2/3 was in the common pool and the dry store). However the reactor pools accounted for over 80% of the heat load from spent fuel within Fukushima-1 pools. • The total number of fuel assemblies stored and the heat load within the pools was provided in the report from the Japanese Government (extract reproduced below). [Note: the unit of decay heat in the Table below is understood to be megawatts; the “new fuel assemblies” stored in the pools (i.e. the number of assemblies shown below in brackets) would not contribute to decay heat levels in the pool]:

• It can be seen that the Unit 4 reactor pool had the highest heat load at the time of the accident and, with the exception of the “common pool”, contained the greatest quantity of spent fuel (1,331 assemblies). This was because all the fuel from Reactor 4 had been discharged into the pool to facilitate work during the reactor’s outage. • Spent fuel pools for Reactors 1-4 lost the electrical supplies powering their cooling water systems after the earthquake/tsunami on March 11 th . Instrumentation showing pool water level was also disabled. • It was important for safety to ensure that the spent fuel in the pools remained covered with water since this provided a barrier to radiation and most importantly kept the fuel

17 Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety - The Accident at TEPCO's Fukushima Nuclear Power Stations. Nuclear Emergency Response HQ, Government of Japan. June 2011 18 Mission Report: IAEA International Fact Finding Expert Mission of the Fukushima Dai-Ichi NPP Accident following the Great East Japan Earthquake and Tsunami. IAEA, June 2011 Not Protectively Marked NNB-OSL-STR-000034 Issue 1 October 2011 Page 30 of 37

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cooled so that the cladding responsible for retaining the radioactivity within the fuel rods would remain intact. After the accident there was no reliable measurement of the water levels in these reactor pools. • To maintain this water coverage it was important that water was not lost from the pools through leakage, evaporation or boiling at a rate faster than it could be replenished. The operators had no evidence of gross leakage and would have been aware that the rate at which the pool water temperature would increase in the absence of active cooling would be relatively slow. It should be several days before the pool water would boil and so result in the water level falling so that eventually the fuel would be uncovered. Spent fuel facilities were thus not initially as much a priority area for operator concern as were the 3 reactors that had been operating at the time of the earthquake and which contained fuel requiring urgent cooling (Units 1-3). • Both the Unit 5 and Unit 6 reactors at Fukushima-1 were shutdown as part of their outages at the time of the earthquake. Fuel was loaded in both these reactors but the decay heat load was much lower than in Units 1-3. The Unit 5 and 6 reactors and reactor pools lost their cooling after the tsunami, but operators did manage to re- establish cooling to both units on March 13 th and to their pools from March 19 th using electrical power from a single Unit 6 diesel which was located at a higher elevation and had not been damaged. This cooling was made more secure as power supplies were restored to the site. There has been no evidence that any spent fuel in the Unit 5 and 6 reactor pools was damaged or that any radioactivity release from these pools occurred. • No action is recorded as having been taken to provide emergency cooling or water replenishment for the shared “common pool” over the first 10 days after the earthquake. It is understood 19 that on March 18 th the pool temperature was measured as 55°C and the pool water level confirmed; then on March 21 st around 130 cubic metres of water were added using fire engines; and forced cooling of the pool was re- established on March 24 th . This response almost certainly reflects the lower heat load in this pool and less concern about its condition following the earthquake. There is no evidence that any spent fuel within this pool was affected. • The Reactor 4 pool had the highest heat load. Water in this pool was recorded as reaching 84°C at 04.08h on March 14 th (i.e. around 2½ days after the earthquake). The significance of this was that, if the reading was accurate and on the assumption that the pool was not losing water through leakage, there should still have been considerable time before the significant volume of water (some 7-8 metres depth above the top of the fuel assemblies) could be lost through boiling allowing the fuel to become uncovered and overheat. Thus on March 14th there still appeared to be time available to the operators to re-establish cooling and/or pool water make-up supplies to add water to the pool with the highest heat loading.

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• The explosion of hydrogen gas at 06.00h on March 15th that severely damaged upper parts of the Unit 4 Reactor Building led to real concern that, despite the above analysis, the fuel in the Unit 4 reactor pool might have become uncovered, had overheated and that this had led to the production of hydrogen. This concern arose from the fact that, since Reactor 4 was defuelled, it could not have been the source of the hydrogen in Unit 4 – unlike the case with the previous hydrogen explosions on Unit 1 on March 12 th and on Unit 3 on March 14 th . These explosions had destroyed the upper parts of the Unit 1 and 3 Reactor Buildings in a similar way to the explosion on Unit 4. (A suspected hydrogen explosion is also believed to have occurred within Unit 2 on March 15 th although not in the same area.) Two reports of fires within the Unit 4 Reactor Building – the first at 09:38 on March 15 th and the second at 05:45 on March 16 th may also have added to concern that a zirconium-water reaction had initiated within the Unit 4 reactor pool. • This concern led to the exceptional actions that were taken (beginning March 17 th and 20th for Units 3 and 4 respectively) to add water to the reactor pools. These efforts included using helicopters, fire hoses, cement pumping trucks, etc. and took advantage of the access possible through the now open roofs of the badly damaged Reactor Buildings of Units 1, 3 and 4; these actions continued for many days. The roof of Unit 2 was intact and so an alternative approach was devised for this pool using temporary pumps connected to existing pool filling lines from March 20 th . • It now appears unlikely that fuel within any of the reactor pools was in fact uncovered during the accident although there remains some uncertainty over this. Photographic evidence for Unit 3 and 4 pools has shown the fuel to be water covered and appearing to be intact. Both these pools were seen to contain debris – presumed to be the result of the explosions within the building but to date there is no evidence of structural failure within the pools leading to significant water loss. It is possible that the debris may have damaged some fuel in particular locations or have impeded cooling but there is no evidence of major damage. This description is also supported by measurements taken of the radioactivity within the Unit 4 pool water which suggests that no major fuel damage has occurred. • The evidence now available has led the Japanese authorities to look for an alternative explanation for the source of the hydrogen that caused the Unit 4 explosion on March 15 th . A possible explanation outlined within their report is that the hydrogen source was overheating fuel within Unit 3 reactor (in the adjoining building). Unit 3 and 4 share the same vent stack and it is postulated that hydrogen vented from Unit 3 could have flowed backwards into the Unit 4 building and caused the explosion there.

Summary for Spent Fuel Pools It is clear the Unit 1-4 pools were a very serious safety concern during the Fukushima-1 accident because it was feared that fuel might have been uncovered raising the possibility of overheating leading to a possibly very large release of radioactivity. The key issues that gave rise to this concern were: Not Protectively Marked NNB-OSL-STR-000034 Issue 1 October 2011 Page 32 of 37

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• The fact that cooling systems had been disabled as a result of the loss of electrical supplies and could not be restored for several days

• Their inability to measure water levels or be confident as to the conditions within the pools resulted in operators having to take action on the basis of inadequate information and to take into account “worst case” assumptions.

• The operators were faced with major difficulties in devising emergency methods to add water to the pools due to the disruption caused by the earthquake and tsunami, the high radiation levels on parts of the site, and the lack of a pre-planned, alternative make-up system for such an event

• The location of the reactor pools within the Reactor Buildings in which hydrogen explosions had occurred exacerbated concern over their condition. Additionally the possible interactions between the reactor pools and neighbouring facilities (e.g. the existence of flow paths that may have allowed hydrogen to pass from Unit 3 into Unit 4 buildings) made it more difficult for operators to be sure of what was happening and to determine the right response

• In contrast, the Common Pool appears not to have been a significant concern. It was further away from the reactors and located in a separate building at a lower level. It was therefore less likely to be impacted by the hydrogen explosions associated with the venting of gases arising from damaged reactor fuel. It also contained longer cooled fuel, had a lower heat load and a higher water volume than the Unit 4 pool into which irradiated fuel had recently been unloaded from the reactor. It seems that operators were more confident of its status and that this confidence was justified. There has been no indication of any fuel damage in this “common pool”.

A3.2 Performance of the Dry Cask Spent Fuel Store The dry cask storage building is located adjacent to the Unit 5 turbine building on the Fukushima-1 site. The building was damaged by the tsunami but there is no evidence of any release of radioactivity from the casks which are all believed to have remained intact. As in the case of the Common Pool, it would appear that the dry cask store was not a major concern to operators as they correctly determined that it was unnecessary to take urgent emergency measures to ensure continued safety of this facility despite the severity of the event. Cask storage of spent fuel generally only requires natural convective cooling to maintain safety. Depending on the nature of the damage to the cask store building at Fukushima-1, it is possible that there may have been some impact on airflows; however, operators would have been aware that the timescale for addressing this issue would be long, just as it was in the case of restoring cooling to the “common pool”.

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A3. RELEVANT ATTRIBUTES OF THE PROPOSED HPC INTERIM SPENT FUEL STORE Although the basic design of the HPC ISFS is still being developed, it is possible to set out key aspects of the conceptual design that are relevant to its future safety and the level of protection it will provide against any releases of radioactivity under accident conditions. These are important when considering whether the experience reported above in respect of Fukushima’s spent fuel facilities raises any questions over the safety of the proposed pool technology-based ISFS at HPC. Heat Load and Cooling Systems The HPC ISFS will only contain fuel that has already undergone a significant period of cooling within the reactor pools. Although the interim storage spent fuel pool would be equipped with active cooling systems, the design aim will be that the active elements would not ordinarily be required and the system would have a significant passive cooling capability sufficient to maintain safety for very long time periods even if the power supply were to fail. In a very severe event, such as the one at Fukushima, the most important objective is to prevent the spent fuel in the pool from becoming uncovered. If this can be assured, fuel cladding integrity can be maintained and significant releases of radioactivity prevented. The relatively low heat load within the ISFS proposed for Hinkley Point C in relation to the large volume of water in the pool means that, even if all cooling were to be lost, there would be a very long time before the water level in the pool would fall to the extent that spent fuel cooling and hence cladding integrity could be at risk. Very conservative analysis based on the assumption of a complete loss of pool water cooling together with a failure to add any water to the pool indicates a “grace period” of at least 500 hours (nearly 3 weeks) before the fuel could become exposed. Control of criticality A design principle for the HPC ISFS is that prevention of criticality within the pool should not require the presence of a dissolved neutron absorber (e.g. boron) in the pool water. Instead criticality will be ensured through the design of the racks within which fuel assemblies will be restrained. This is another measure taken to minimise reliance on active systems to ensure safety and also makes the provision of make-up water under extreme accident conditions simpler for operators. Control of water chemistry In order to maintain the integrity of the fuel cladding barrier during storage, the pool water chemistry needs to be controlled. The chemistry control system is not required to operate continuously and the safety impact of any interruption would be longer term rather than immediate. At Fukushima seawater was used in some instances to provide cooling in place of the normal demineralised water supplies because this was the only option available. It should be noted however that there is no report of this having been necessary for the “common pool” that was used to store longer cooled spent fuel at the site. The pool water chemistry control system at HPC will be designed to deliver high reliability and great attention will also be given to providing systems for refilling spent fuel pools in emergencies as is required by

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Recommendation 20 of the Weightman Report. [NB EDF Energy will respond separately to this Recommendation.] Civil and Mechanical Construction Aspects The HPC ISFS will be designed and constructed to withstand severe external hazards. The pool will be partially embedded below ground level. The civil structures will be designed to meet the required seismic criteria. The pool will have a stainless steel liner and any leakage will be contained in a void space below the pool and monitored. The design will take full account of Recommendation 14 in the Interim Report from Dr Weightman which calls for the industry to “minimise the need for bottom penetrations and lines that are prone to siphoning faults.” [NB EDF Energy will respond separately to this Recommendation.] Location and Interconnectivity The HPC ISFS will be well separated from the nearest reactor building and will not share any ventilation connections that could allow hydrogen from damaged reactor fuel to flow into the ISFS (in the remote possibility that such severe damage were ever to occur). Recommendation 21 in the Interim Report from Dr Weightman calls for a review of the ventilation and venting routes for nuclear facilities where significant concentrations of combustible gases may be flowing or accumulating. The results of this review will be taken into account as necessary in the detailed design. [NB EDF Energy will respond separately to this Recommendation.] The external building will provide the spent fuel within the ISFS from protection against external hazards including any debris from low frequency or hypothetical events elsewhere on the site. Protection against flooding will be provided as part of the external hazard safety case. Security of instrumentation and power supplies The diversity, redundancy and degree of segregation of electricity supplies and control and instrumentation provided for the HPC ISFS will be commensurate with their importance to safety and environmental protection. As noted above, however, even with a loss of all cooling (active and passive) there will be a very substantial grace period for emergency action. Provisions for Emergencies Recommendation 20 in the Interim Report from Dr Weightman calls on the industry to review site contingency plans for pool water make up under severe accident conditions. The design of the HPC ISFS will address this and ensure that appropriate facilities are provided to allow water make up to the pool under these conditions. As explained above, even with total loss of cooling to the ISFS, there would be a period of around 3 weeks before this make up would be essential to prevent fuel uncovering in the ISFS. [NB EDF Energy will respond separately to this Recommendation.]

A4. DISCUSSION As described in Section A3 above, at the present time there is no evidence that any of the spent fuel storage pools at Fukushima actually contributed to the release of radioactivity during the accident and it appears that these facilities may in fact have successfully prevented fuel

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damage. However, the fact that their safety was in severe doubt during the accident and the possibility that some fuel may yet turn out to have been affected, means it is important to consider carefully whether this experience puts in any doubt the future safety of the type of pool that was identified as the preferred interim spent fuel storage technology for HPC. By examining the factors that led to concern over the safety of the reactor spent fuel pools at Fukushima-1 and then considering whether and how these might apply to the performance of the ISFS pool proposed for HPC, the following fundamental differences emerge: • At HPC the ISFS heat load and pool volume will mean that even with a complete loss of all cooling there would be no need for operator action for several weeks to prevent a severe accident occurring. While its design will certainly differ in some respects from the HPC ISFS, the fact that the “common pool” at Fukushima-1 appears to have required no emergency actions from operators to ensure continued safety for several weeks after the occurrence of an extremely severe event does, if anything, appear to underline this. • Additionally, the HPC ISFS will benefit from safety features that appear not to have applied at Fukushima-1 o The ISFS cooling systems will operate predominately in a passive mode o The ISFS will be protected by a very robust external building that will minimise the potential for any event outside the ISFS adversely to affect the integrity of the pool o The electrical power, water make up and instrumentation systems supporting the ISFS will be designed to a high level of reliability and will incorporate any additional features required to address the wider lessons from the Fukushima-1 accident There are therefore good reasons to conclude that the Fukushima experience does not undermine the basis of understanding which led to the conclusion that pool storage technology would lead to a very high standard of safety and environmental protection if selected for the interim storage of spent UK EPR fuel at HPC.

A5. CONCLUSION This Annex has examined the selection of pool storage for the HPC ISFS in the light of the experience with spent fuel storage at Fukushima-1 following the massive earthquake and tsunami on March 11 th 2011. The GDA process has indicated that pool storage is an available option for interim spent fuel storage and EDF Energy’s own selection process for the HPC ISFS (described in the main body of this report) had assessed pool storage as being capable of providing a very high standard of safety and environmental protection. This review has found nothing to change these conclusions. The at-reactor spent fuel pools at Fukushima were certainly a major source of concern during the aftermath of the earthquake and tsunami but it is also clear that the factors and circumstances that caused this did not apply to

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the "common pool" at Fukushima and would not apply to the proposed HPC ISFS, even were such extreme conditions ever to be postulated. EDF Energy is therefore confident that its original selection of this technology remains correct and is well-founded. This does not mean that there are not lessons to be learned from Fukushima. It is simply that Fukushima provides no basis for rejecting well-tried and well-implemented pool technology as the basis for interim spent fuel storage at HPC. EDF Energy is totally committed to its plan to address all the issues from the Fukushima event and will take the opportunity to make improvements wherever practicable in all parts of the development.

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