Assessment of Sizewell B Periodic Safety · PDF file · 2015-10-21ONR Assessment of the Sizewell B Power Station ... takes into consideration compliance with modern standards and

Title of document

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Template Ref: ONR-DOC-TEMP-005 Revision 9 Page 1 of 34

PROJECT ASSESSMENT REPORT

Unique Document ID and Revision No:

ONR-CNRP-PAR-14-020 Revision 0

TRIM Ref: 2015/21872

Project: Periodic Safety Review

Site: Sizewell B

Title: Assessment of Sizewell B Periodic Safety Review

Licence Instrument No: (if applicable) N/A

Nuclear Site Licence No: Sizewell B - 63

Licence Condition: LC 15

Document Acceptance and Approval for Issue / Publication

Role Name Position Signature Date

Author Inspector 28/1/15

Reviewer Principal Inspector 28/1/15

Accepted by1 Superintending Inspector

28/1/15

Approval for publication2

Superintending Inspector

Revision History

Revision Date Author(s) Reviewed By Accepted By Description of

Change

A 02 12 2014 n/a 1st draft forreview

B 24 12 2014 n/a 2nd draft incorporating

comments

0 21 01 2015 First accepted issue

Circulation (latest issue) 1 Acceptance of the PAR to allow release of LI 2 Approval is for publication on ONR web-site, after redaction where relevant

Report ONR-CNRP-PAR-14-020 TRIM Ref: 2014/405643

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OFFICIAL Office for Nuclear Regulation Page 2 of 34

Organisation Name Date

Office for Nuclear Regulation

Files: Programme Report File 4.4.2.11819

Environment Agency

Licensee


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Periodic Safety Review

Sizewell B Nuclear Power Station

Project Assessment Report ONR-CNRP-PAR-14-020 Revision 0

28th January 2015


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© Office for Nuclear Regulation, 2014 If you wish to reuse this information visit www.onr.org.uk/copyright for details. Published MM/YY For published documents, the electronic copy on the ONR website remains the most current publicly available version and copying or printing renders this document uncontrolled.


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EXECUTIVE SUMMARY

Title

ONR Assessment of the Sizewell B Power Station Periodic Safety Review (PSR).

Permission Requested

This Office for Nuclear Regulation (ONR) Project Assessment Report sets out the regulatory justification for the issue of a Decision Letter confirming that EDF Energy Nuclear Generation Ltd (NGL), “the licensee” has carried out an adequate PSR of Sizewell B Nuclear Power Station Safety Case to justify continued safe operation of the facility for the period 2015-25.

Background

A PSR is carried out every 10 years to comply with Nuclear Site Licence Condition 15: Periodic Review. The purpose of the review is to revalidate the extant safety case, to ensure the plant and operations remain adequately safe and fully reflect the site licence requirements. This is achieved by reviewing the previous 10 years of operation together with considering changes in activities that impact on nuclear safety over the following 10 years. The review takes into consideration compliance with modern standards and potential impact of ageing and obsolescence.

Assessment and inspection work carried out by ONR in consideration of this request

ONR carried out a detailed assessment of NGL’s Sizewell B’s PSR report and underpinning assessments. ONR’s approach was to establish those requirements set out in ONR’s Nuclear Safety Technical Assessment Guide for Periodic Safety Review had been met, together with confirming adherence to relevant good practice as set out in ONR’s Safety Assessment Principles (SAPs) for Nuclear Facilities. ONR Technical Guidance and SAPs take into account requirements set out in nuclear safety guidance produced by the International Atomic Energy Authority.

Matters arising from ONR's work

ONR’s assessment of NGL’s Sizewell B PSR2 report and underpinning technical assessments found that an adequate re-assessment of the station’s safety case had been undertaken; that the approach adopted by NGL was structured and systematic and safety claims and arguments presented were justified based on evidence provided.

No significant nuclear safety challenges were identified by either NGL or ONR in the assessment undertaken. NGL’s PSR2 review identifies safety shortfalls that are considered by ONR to have been appropriately categorised into high and low priority observations. NGL has given a commitment to address all high priority observations by January 2017, which is consistent with ONR’s expectations. In addition, ONR identified a number of issues that were not considered to have been adequately addressed in NGL’s Sizewell B’s PSR. NGL has given a commitment to address all of ONR’s findings by January 2017.

Conclusions

ONR considers that NGL has carried out an adequate PSR of the Sizewell B Station’s Safety Case that justifies safe operation for the period 2015-2025. This is based on assessment findings of both NGL and ONR. No significant nuclear safety issues have been identified and NGL has given a commitment to address safety shortfalls identified from its own assessment and ONR’s by January 2017.

Recommendations

It is recommended that ONR issues its Decision Letter to NGL confirming an adequate PSR of the Sizewell B power station safety case has been undertaken and requiring NGL to address all higher priority observations as well as ONR findings by January 2017.


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LIST OF ABBREVIATIONS

AFWS Auxiliary Feedwater System

AGR Advanced Gas-cooled Reactor

ALARP As Low As Reasonably Practicable

AR Action Request

CBDS Carbon Bed Delay System

C&I Control & Instrumentation

DR Discipline Review

EC Engineering Change

EDG Essential Diesel Generators

NGL EDF Energy Nuclear Generation Ltd

EPRI Electric Power Research Institute

ESWS Essential Service Water System

FBC Fuel Building Crane

HF Human Factors

HOW2 (Office for Nuclear Regulation) Business Management System

HSE The Health and Safety Executive

IAEA The International Atomic Energy Agency

INA Independent Nuclear Assessment

IPRA Independent Periodic Review Assessment

JER Japanese Earthquake Response

LC Licence Condition

LfMS Leadership for Management of Safety

MCR Main Control Room

MR Main Review

NSC Nuclear Safety Committee

NSORC Nuclear Safety Operational Review Committee

ONR Office for Nuclear Regulation

OPEX Operating Experience

PAR Project Assessment Report

PSA Probabilistic Safety Assessment

PSR Periodic Safety Report

PSIR PSR Significant Issues Report

PWR Pressurised Water Reactor

RGP Relevant Good Practice

RUHS Reserve Ultimate Heat Sink

SAP Safety Assessment Principle(s) (HSE)

SCUG Safety Case User Guide

SOI Station Operating Instruction

SPF Solution Proposal Form

SQEP Suitably Qualified and Experienced Personnel

SSC System, Structure and Component

SSR Station Safety Report

TAG (ONR) Technical Assessment Guide


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TCTS Technical Chemistry Technical Standards

UPS Uninterruptible Power Supplies


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TABLE OF CONTENTS

1. PERMISSION REQUESTED ............................................................................................... 9 2. BACKGROUND ................................................................................................................... 9 3. ONR’S ASSESSMENT AND INSPECTION WORK .......................................................... 10 4. MATTERS ARISING FROM ONR’S WORK ...................................................................... 11 5. CONCLUSIONS ................................................................................................................ 12 6. RECOMMENDATIONS ..................................................................................................... 13 7. REFERENCES .................................................................................................................. 14

APPENDIX 1 – ONR Assessment Topics ............................................................................ 17

APPENDIX 2 – ONR Assessment Topics ............................................................................ 18

Table 1 NGL High Priority Observations ......................................................................... 30

Table 2 ONR Findings .................................................................................................... 33


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1. PERMISSION REQUESTED

1 This ONR Project Assessment Report sets out the regulatory justification for issuing an ONR Decision Letter confirming that EDF Energy Nuclear Generation Ltd (NGL), “the licensee” has carried out an adequate Periodic Safety Review (PSR) of the Sizewell B Nuclear Power Station’s Safety Case.

2 The requirement to carry out a PSR is based on the need for compliance with Nuclear Site Licence Condition (LC) 15: Periodic Review. International standards (Ref 5) state that the period between PSRs should be 10 years. The Sizewell B PSR (Ref 4, 41) submitted to ONR covers the period January 2015 to 2025.

3 The regulatory process set out (Ref 2 and 32) requires ONR to issue a statement in writing (a "Decision Letter") confirming its position on the adequacy of the licensee’s PSR submission. The Decision Letter is issued one year after the Submission Date of the PSR. This Letter sets out any regulatory requirements from the assessment of the PSR.

2. BACKGROUND

4 The Sizewell B power station is a Pressurised Water Reactor (PWR) and is currently the only one of this type in the United Kingdom. It commenced generation in February 1995 and currently has a decommissioning date of 2035.

5 This is the second PSR to be carried out on Sizewell B and is commonly referred to as PSR2. NGL submitted its Sizewell B PSR2 report to ONR under unique Letter SZB 50782N dated 17 January 2014 (Ref 4). NGL concluded from its review that the station’s safety case was adequate and could be justified for the next 10 years of operation (2025) and potentially beyond.

6 ONR’s own guidance (Ref 2) states that the purpose of the PSR is to consider all factors that may alter the safety of the plant over its life-time which are summarised under the following bullet points:

The degree to which the safety case conforms to modern standards and good practices.

The degree to which the safety documentation addresses the remnant life of the facility given changes in plant status through construction, commissioning, operations, post operations and decommissioning.

The adequacy of the arrangements in place to maintain safety until the next PSR or end of life.

Safety improvements to be implemented to resolve any identified safety issues.

7 NGL commenced the Sizewell B PSR2 in 2010 consistent with the approach set out in NGL’s scoping document (Ref. 44). This document defining the scope of work to be undertaken, established a standardised methodology and a programme of defined deliverables. This strategy built upon NGL’s experience gained from carrying out PSRs on its Advanced Gas-cooled Reactors as well as incorporating international good practice and operational experience.

8 NGL initially carried out a significant issues review, which identified 16 issues (Ref 6). The work involved carrying out a number of high level reviews initially against defined Scope Requirement Specifications. This allowed early identification of potential significant issues to plant design and/or safety case. NGL judged that there was no collective impact from these issues to undermine the current safety case.

9 These significant issues reviews were then followed by more detailed technical assessments covering safety case requirements, plant operating history, system,


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structures and components. Plant walk-downs were also undertaken to support these work areas to confirm that the safety case claims were accurately underpinned by plant material condition. Appendix 1 provides a list of reviews undertaken by NGL through its PSR2 process in re-assessment of the Sizewell B safety case.

10 These technical assessments provide the evidence for PSR2 report claims and arguments. The PSR2 report comprises of the following chapters:

Chapter 1: Adequacy of Nuclear Safety Case Statement Chapter 2: Safety Management Systems Chapter 3: Operations and Safety Performance Chapter 4: Ageing, Obsolescence & Equipment Qualification Management Chapter 5: Safety Analysis Chapter 6: Systems, Structures and Components (SSCs)

11 In addition to the identification of significant issues from the scoping reviews, a number of strengths were also identified. These related to areas where nuclear safety good practice and standards had been exceeded, these were identified in probabilistic safety assessment development and issues, reactor coolant system and connected systems, fuel storage and handling.

12 The 16 identified issues were combined with the findings from the main technical assessments to form High Priority observations. A total of 44 High Priority PSR Observations as detailed in Table 1 have been identified by NGL from its PSR2 review. NGL has produced a plan to address all of its High Priority PSR Observations by January 2017 (Ref. 7). This approach is consistent with ONR’s expectations. A total of 276 Low Priority PSR Observations were also identified. These related to business improvement activities, which have negligible impact on nuclear safety and will be addressed through normal business and not followed up as part of ONR’s routine interventions.

13 NGL has followed its own internal assurance process in the production, review and assessment of its PSR2 and sentencing of observations. All of the chapters that incorporate the technical reviews produced for the Sizewell B PSR2 have been subject to an Independent Periodic Review Assessment (IPRA) by NGL’s Independent Nuclear Assessment Division (INA) (Ref. 29). INA also participates in a working group that endorses each high priority observation raised in the PSR2. The Sizewell B PSR2 has also received scrutiny from Sizewell B’s Nuclear Safety Operational Review Committee (NSORC) before being submitted to the NGL’s Nuclear Safety Committee (NSC) (Ref. 30).

3. ONR’S ASSESSMENT AND INSPECTION WORK

14 During the Sizewell B PSR2 process no formal compliance inspections against LC 15 were undertaken. This decision was based on evidence gathered from ONR’s inspection findings undertaken as part of NGL’s PSR reviews for their AGR stations, which confirmed that NGL’s PSR arrangements were adequate and consistently applied.

15 Throughout the Sizewell B PSR2 process, regular meetings were held to review progress and monitor the delivery of commitments given NGL’s declared PSR2 programme. This approach allowed ONR to have insight into NGL’s management of the Sizewell B PSR2 process and provided opportunity to challenge decisions and outcomes. An example of this was the categorisation of high and lower priority observations from NGL’s safety review. NGL had developed a prioritisation process and this was reviewed by ONR. I considered the approach adopted by NGL in prioritising observations adequate and consistent with its LC 15 arrangements. The process took into consideration factors such as potential impact on nuclear safety, ALARP requirements and impact on organisational reputation. Overall, I consider


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NGL’s identification of high priority observations work was adequate and measured given the potential impact on nuclear safety.

16 ONR’s main area of work was in considering the adequacy of NGL’s re-assessment of the Sizewell B power station’s safety case. A total of 12 regulatory assessments were commissioned (Refs. 9-21) covering the following topic areas:

Structural Integrity Mechanical Engineering Civil Engineering Probabilistic Safety Analysis Electrical Engineering Chemistry Internal Hazards External Hazards Fault Studies Human Factors Leadership for Management of Safety Radioactive Waste Management

17 A summary of ONR assessment views and findings are provided in Appendix 2. Although ONR considers that NGL’s re-assessment the Sizewell B power station’s safety case was carried out in a systematic way, a number of shortfalls were identified and have been appropriately prioritised. Regulatory issues were identified where NGL’s assessment findings could not reconcile queries raised by ONR and are detailed in Table 2.

18 A regulatory decision was taken not to review Sizewell B Emergency Arrangements as part of the PSR2 process. This was entirely appropriate given that this decision was based on the level of change occurring in this area as a result of NGL’s response to regulatory Fukushima stress test requirements and the fact these were being reviewed through a separate ONR work-stream (Ref. 31). This proportionate approach is consistent with other PSRs.

4. MATTERS ARISING FROM ONR’S WORK

19 Based on the findings of ONR’s assessments I consider NGL has carried out an adequate re-assessment of the Sizewell B Nuclear Power Stations safety case. This view is based on the findings of ONR Specialist Inspectors assessments reports for specified topic areas (Refs. 9-21). The ONR assessment confirmed NGL’s view that the safety case for a further 10 years electrical generation was adequate.

20 ONR Specialist Inspectors confirmed that a systematic approach had been undertaken in areas assessed and that the claims and arguments made in the Sizewell B PSR2 report were justified by evidence presented in NGL’s discipline based and main system reviews undertaken in support of the Sizewell B PSR2.

21 ONR assessment took into account NGL’s identification of Significant Issues from its initial scoping review and the merger of these findings with observations made from technical assessment of the main PSR2 reviews. I consider the process followed by NGL was structured and subject to independent scrutiny. I judge NGL’s categorisation of all observations into high and low priority work-streams reasonable with the appropriate consideration given their impact on nuclear safety and ALARP.

22 ONR Sizewell B PSR assessment also took into account other NGL activities being carried out on the Sizewell B site which ONR is monitoring through other regulatory work. These include the Dry Fuel Store Project and NGL’s response to Fukushima stress test requirements. After consideration of such areas ONR raised 12 findings.


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These are listed in Table 2. The findings include resolution of potential risk gaps relating to site flooding from both coastal and rainfall events. The assumption of Sizewell B being a “dry site” has been challenged by recent work (Refs. 24 and 25) that presents a reasonable challenge to the extant flooding safety case. Another finding relates to the development of arrangements to monitor corrosion across plant regardless of its safety function. This issue was raised in a number of assessment reports including external hazards (Ref. 10), civil engineering (Ref. 11), electrical engineering (Ref. 14), chemistry (Ref. 16) and structural integrity (Ref. 17).

23 Although NGL had raised a High Priority observation regarding general plant material condition (4.1H in Table 1) ONR judged that this observation needed to be expanded. The focus was of the observation was targeted on nuclear safety related plant; however no consideration was given to plant that may pose a conventional safety risk or non-nuclear safety related plant the failure of which may prevent access to or damage of nuclear safety related plant. The ONR finding requires NGL to develop its arrangements for the maintenance and inspection of all systems, structures and components, irrespective of their safety function, in order to maintain their material condition. Additional detail regarding the findings can be found in Appendix 2.

24 NGL has given its commitment to address ONR’s findings within agreed timescales (Ref. 40). I consider the hazard and risk identified within each of the ONR findings are reasonable challenges which NGL has not adequately addressed. I consider the resolution of these issues given ONR Specialist Inspectors advice will enhance Sizewell B safety case and support its continuing adequacy for the period 2015-25.

25 ONR will monitor the close out of all NGL’s high priority observations and ONR findings by January 2017 through normal business activities delivered by the ONR Sizewell B PSR2 Project Inspector. Attention will be given to ensure the adequacy of response and effectiveness of implementation.

5. CONCLUSIONS

26 I consider that NGL has carried out an adequate re-assessment of the Sizewell B nuclear power station safety case for the period 2015-25. This view is based on the following:

Sizewell B Site’s arrangements for LC 15 have been followed in that a systematic re-assessment of the Station’s nuclear safety case has been undertaken. This review was subject to independent review via NGL’s internal assurance process and Nuclear Safety Committee.

NGL’s re-assessment did not identify any significant nuclear safety threats that would impact on station’s operability for the period 2015-25 and beyond. Safety shortfalls were identified through the PSR2 observation process and have been categorised based on ALARP principles given their impact on safety. NGL has given a commitment for all High Priority Observations to be addressed by January 2017.

ONR’s own assessment of the NGL’s re-assessment of the Sizewell B PSR2 safety justification for continued safe operations until 2025 were considered to be thorough and systematic.

ONR’s assessment findings supported NGL’s conclusion that no serious nuclear safety threats existed in continued operation of the Sizewell B nuclear power station. ONR identified a number of Findings in its assessment work, which NGL


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has not adequately addressed. Commitment has been given to close all regulatory Findings by January 2017, which is considered reasonable

6. RECOMMENDATIONS

27 I recommend that ONR confirms the adequacy of NGL’s Sizewell B PSR submission by issuing a Decision Letter agreeing to the continued operation of the site for the period 2015-2025.

28 I recommend that conditions are included in the Decision Letter with timescales to address the outstanding NGL high priority observations and ONR findings.


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7. REFERENCES

1 Safety Assessment Principles for Nuclear Facilities. 2006 Edition Revision 1. HSE. January 2008. http://www.onr.org.uk/saps/saps2006.pdf.

2 Periodic Safety Review, NS-TAST-GD-050 Revision 4. ONR. April 2013 http://www.onr.org.uk/operational/tech_asst_guides/index.htm

3 Not used

4 NGL – Sizewell B – SZB 50782 N – Sizewell B Power Station Periodic Safety Review PSR2 Submission – 17 January 2014, TRIM 2014/36257

5 Periodic Safety Review For Nuclear Power Plants. International Atomic Energy Agency (IAEA). Specific Safety Guide SSG-25. IAEA. Vienna. 2013. www.iaea.org.

6 NPSC 7601 Addendum 1 Issue 1 Summary of Significant Issues, May 2012, TRIM 2014/40228

7 Sizewell B PSR2 – Consolidated Presentation and Integrated Delivery Plan for High Priority Observations – 30 January 2014, TRIM 2014/46332

8 Not used

9 Assessment of Internal Hazards within Sizewell B PSR2, ONR-SZB-AR-14-092, TRIM 2014/439937

10 Assessment of External Hazards, ONR-CNRP-AR-085, TRIM 2015/1713

11 Sizewell B Power Station - PSR2: Civil Works and Structures, ONR-CNRP-AR-086, TRIM 2014/447408

12 Sizewell B Periodic Safety Review – Mechanical Engineering Specialist Assessment, ONR-CNRP-AR-14-093, TRIM 2014/21161

13 ONR (CNRP) Control and Instrumentation assessment of EDF Energy Nuclear Generation Ltd, Sizewell B Periodic Safety Review 2, ONR-CNRP-AR-14-098, TRIM 2014/475004

14 Assessment of Electrical Systems Review, ONR-CNRP-AR-14-091, TRIM 2014/465290

15 Assessment of Radioactive Waste Management System, ONR-CNRP-AR-088, TRIM 2014/442121

16 Assessment of the Chemistry aspects of the Sizewell B Periodic Safety Review for the Period 2015 – 2025, ONR-SZB-AR-14-90, TRIM 2014/359695

17 Assessment of the Structural Integrity aspects of the Sizewell B Periodic Safety Review for the Period 2015 – 2025, ONR-SZB-AR-14-081, TRIM 2014/414819

18 Sizewell B Periodic Safety Review – Probabilistic Safety Analysis Specialist Assessment, ONR-CNRP-AR-14-084, TRIM 2014/453481

19 Sizewell B Periodic Safety Review – Fault Studies Specialist Assessment, ONR-CNRP-AR-076, TRIM 2014/115776

20 Assessment of Human Factors, ONR-CNRP-AR-071, TRIM 2014/350702


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21 Assessment of the Leadership and Management for Safety aspects of the second Sizewell B Periodic Safety Review, ONR-CNRP-AR-14-058, TRIM 2014/354051

22 Queries/observations from Sizewell B Radwaste PSR2 Meeting held on 5th February 2014 TRIM Ref 2014/54740

23 Responses to ONR Queries/observations from Sizewell B Radwaste PSR2 Meeting held on 5th February 2014, TRIM Ref 2014/114703

24 HR Wallingford, TN_EBR4584-issue 2, Sizewell Power Station extreme sea level studies, Joint probability of waves and sea levels and structure response (2010) – TRIM Ref. 2014/308960

25 Royal Haskoning, 31018-C127, Japanese Earthquake Response Flood Modelling, Flood Summary Report Sizewell B (2012) – TRIM Ref. 2014/137824

26 NGL Report - Fukushima Close Out Report – TRIM Ref. 2014/285997

27 Sizewell B PSR2 Chemistry Main Review, SXB-IP-821238, TRIM 2014/40488

28 Sizewell B Power Station Periodic Safety Review : PSR Report Submission, -NUC/552/80/15/0/0/0//02~23, November 2004

29 INA Consolidated Sizewell B PSR2 IPRA Report, TRIM 2014/46376

30 NGL Nuclear Safety Committee Minutes 12/13, December 2013, TRIM 2014/446312

31 Assessment of EDF Energy’s Japanese Earthquake Response Programme Interim ONR Recommendation Closeout Report – Emergency Arrangements Aspects, ONR-CNRP-AR-14-049, TRIM 2014/398638

32 ONR HOW2 Guide NS-PER-GD-014 Revision 4 - Purpose and Scope of Permissioning. July 2014. http://www.onr.org.uk/operational/assessment/index.htm

33 EDF NGL. Sizewell B Power Station: PSR2 Main Review: Civil Works and Structures – SXB-IP-821236, Rev. 001, TRIM 2014/40438

34 Notes of meeting from SZB PSR2 ONR Findings Meeting for Civil Engineering 26th August 2014,TRIM 2014/386899

35 Sizewell B PSR2 Main Review – PSA developments and issues, SXB-IP-821219, K.Brook, June 2011, TRIM 2014/50597

36 Review of Sizewell B Seismic PSA and Level 2 PSA (draft report). Jacobsen Analytics Ltd, JA1-ONR-1402, October 2014, TRIM 2014/453365

37 Sizewell B, Periodic Safety Review 2 Main Review: Hazards, SXB-IP-82122, Revision 000, October 2013, TRIM 2014/50639

38 ONR Nuclear Safety Technical Assessment Guides within ONR How2 Business Management System: Internal Hazards, NS-TAST-GD-014 Revision 3, April 2013 http://www.onr.org.uk/resources

39 Atkins Technical Note R5109310-001 dated 8 October 2012, FBC Main Hoist Gear Review – Summary of Review Findings, Rev A, TRIM 2014/81367

40 Meeting minutes, Notes / Action Points from SZB PSR2 ONR L4 Meeting 2nd Dec 2014, TRIM 2015/18651


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41 Adequacy of Nuclear Safety Statement, NP7601 Addendum 2, TRIM 2014/46455

42 Email from EDFNGL to ONR 28/11/2014 (Trim 2014/470463)

43 Email from EDFNGL to ONR 13/01/2015. (Trim 2015/19886)

44 Scope Arrangements and Programme Document, SXB-IP-821203, TRIM 2014/40242


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APPENDIX 1 – ONR Assessment Topics

The following list identifies the technical reviews carried by NGL in producing the Sizewell B PSR 2 report.

Main Reviews

Nuclear Safety Principles Probabilistic Safety Assessment Development and Issues Transient Analysis Radiological Analysis Hazards Human Factors Reactor Core Reactor Coolant System and Connected Systems Engineering Safety Features Control and Instrumentation Computing Systems Main and Essential Electrical Systems Auxiliary Systems Steam Generators Rotating Plant and Main Steam Systems Radioactive Waste Management Radiological Protection Fuel Storage and Handling Civil Works and Structures Structural Integrity Chemistry Equipment Qualification In-Service Inspection Emergency Planning External Experience Procedures Technical Specifications In-Service Testing

Discipline Based Reviews

Structural Integrity Development and Issues Radioactive Waste Management Issues Mechanical Plant Developments and Issues Electrical Plant Development and Issues Control and Instrumentation and Safety Systems Development and Issues Civil Development and Issues Human Factors Development and Issues Hazards Development and Issues


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APPENDIX 2 – ONR Assessment Topics

29. This appendix gives an overview of the various topics assessed within the Sizewell B PSR2 submission and presents the conclusions and ONR findings (where applicable) for each of the topics. Where similar findings are raised across several topic areas a consolidated ONR finding is listed in Table 1 following discussion and agreement with the assessment team.

Radwaste

30. The scope of this section covers an assessment of the adequacy of the Radioactive Waste Management Systems and associated arrangements to meet their nuclear safety role at present, and their continuing ability to do so until completion of the next PSR. ONR is broadly satisfied with the claims, arguments and evidence laid down within the NGL’s safety case with respect to radioactive waste management to support and recommend the continued operation of Sizewell B power station for the period until the next PSR (Ref. 15).

31. The Radwaste assessment (Ref. 15) identified 4 recommendations; however these were minor and are not subject to formal ONR Findings. These recommendations will be tracked to completion within normal regulatory business.

32. The scope of the assessment covered NGL’s main review of the radioactive waste management systems and supporting documents during an inspection at Sizewell B. Based on knowledge of the plant from a number of inspections and the main review report several queries/observations were raised with NGL (Ref. 22) from this assessment. These queries were followed up (Ref. 23) and reported to confirm that there were no other significant queries. No further inspections of the plant were undertaken at the site.

Leadership for Management of Safety (LfMS)

33. From the evidence presented in the PSR2 report, it is ONR’s judgement that a challenging LfMS review has been undertaken as envisaged in ONR’s guidance on PSRs (Ref. 2). ONR is satisfied that the PSR2 review has been adequately scoped, executed and subjected to an appropriate due process for checking verification and approval.

34. There is a good level of understanding of issues raised where shortfalls were identified and that satisfactory arrangements are in place to address the findings. There are no LfMS based ONR Findings. ONR is also satisfied that there has been robust, independent oversight throughout the whole process. Therefore, ONR concludes that the LMfS aspects of PSR2 are adequate for continued operation until the next PSR review.

35. Assessment (Ref. 21) focused on PSR2 documentation provided by NGL, findings from a site visit, structured telephone conversations and a review of the findings of recent ONR interventions at the site.

36. The review undertaken by NGL for LfMS has been thorough, has addressed relevant areas and the outcome appears well balanced and evidentially based. The review has been subjected to a relevant due process and has taken into account relevant standards, guidance and learning from PSR1.

37. Whilst NGL does not always present clear and robust evidence to demonstrate the effectiveness of some aspects of its organisational arrangements, its PSR2 submission generally meets ONR’s expectations. Supporting reviews have been thorough and


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recommendations for improvement are well founded. They provide the station with good information on which to base its improvement plans. The findings of a range of recent ONR interventions have also been reviewed. They provide assurance that the licensee’s arrangements for ensuring leadership and management for safety are adequate.

Fault Studies

38. ONR has concluded that NGL have undertaken a systematic review of the modifications to plant and the safety case which have taken place over the relevant period to identify whether the design documentation remains consistent with the operation of the plant. While it is evident that improvements to the documentation of evidence which supports the safety case are required, no serious shortcomings have been identified and ONR is satisfied that improvements identified are planned and will proceed. As such ONR is content that the PSR with respect to Fault Studies is adequate for the next PSR period.

39. A total of 9 observations were made in the course of the fault studies assessment (Ref. 19). ONR considers that 7 of the observations can be dealt with through normal business interventions but the remaining 2 have higher priority to warrant being raised to ONR Findings.

Fuel Assembly

40. ONR supports NGL’s approach to develop a written procedure to verify the acceptance criteria for fuel inspections. This is important to ensure that early action is taken to prevent developing problems. ONR judges that in respect to fuel, Sizewell B does not currently have a strong case to demonstrate that they meet the requirement of Ref. 1 that Structures, systems and components important to safety should receive regular and systematic examination, inspection, maintenance and testing. Also Sizewell B practice currently falls short of good practice internationally as recommended by (Electric Power Research Institute) EPRI in its guidelines on surveillance and inspection. ONR will monitor the implementation of the proposed changes to ensure that they will be suitable, sufficient and align with both the requirements of Ref. 1 and international good practice.

41. ONR also supports the initiative to start measurements of fuel assembly growth and distortion and to further consider this issue. Fuel assembly bowing is a potentially significant safety concern and ONR has asked NGL to consider the case of distortion causing closure of the gap between two adjacent spacer grids. This forms the basis of the following ONR finding:

ONR Finding SZB-PSR2-01

NGL should complete analysis of the flow distribution down-stream of the fuel spacer grids in the case where the gap between two assemblies has been closed. This should include an assessment of the margin to the critical heat flux, taking into account the difficulty in translating the results of rig tests to the reactor geometry.

42. ONR notes that a policy relating to failed fuel is under development. ONR expects that NGL will submit a safety-case proposal to ONR for agreement. There is ongoing engagement with NGL on the topic of failed fuel generally and any safety case assessment will take place under this current intervention.

Reactor Systems and Hydraulic Models


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43. ONR’s review of recent analysis found that two versions of RELAP 5 were used to conduct analysis of a particular fault. The first had previously been subject to a detailed validation study, but was clearly not fit for purpose in this case because of excessive numerical error, while the second was reasonably numerically accurate, but had not been validated. This situation is unsatisfactory.

44. This issue is recognised by NGL which conclude that code validation age (and a number of related issues) should be kept under consideration in future, as part of ‘normal business’ work planning, to improve the situation and ensure it does not deteriorate. Whilst ONR accepts that it is impractical to make significant progress before a PSR decision is required, this work is important not only to ensure that the tools are in appropriate condition, but also to ensure that the staff are suitably experienced and fully understand the limitations of the analysis. This leads to the following ONR finding:


NGL to provide assurance that proposed investment in developing analysis methods (to replace those about to become obsolete) will proceed

45. Although there are unlikely to be serious shortcomings at present, this issue is becoming more serious over time as support for the codes diminishes.

External Hazards

46. ONR is broadly satisfied with the claims, arguments and evidence laid down within NGL’s safety case, and does not have any objections following the review of the PSR submission on External Hazards to ONR issuing a decision Letter for continued operations until the next review period covered by PSR3.

47. Due to the recent extreme weather and flooding experienced within the PSR review period and the sensitivity within the UK following Fukushima to external flooding, ONR focussed the review (Ref. 10) on flooding related external hazards.

48. The list of hazards reviewed by NGL is reasonable. A total of 6 recommendations were made in Ref. 10 along with two ONR Findings, one of which is a generic Finding covering many topics. The recommendations were not judged by the specialist assessor to be of sufficient concern to warrant an ONR Finding, however these will be followed up under normal regulatory business.

Coastal Flooding (Tidal Effects, Standing Wave, Storm Surge, Seiche, Tsunami)

49. The NGL analysis assumes a dry site with respect to coastal flooding. This is based on historical data from the 1980’s and 90’s. However more recent independent reports (Refs. 24 and 25) indicate the potential for a substantial hazard gap when compared to the current design basis level.

50. The risk to the site from the design basis coastal flooding event is heavily dependent on the sea defences due to the relatively low site platform height. NGL claims that the combination of the sea defences and the low lying land to the north of the site will effectively ensure a dry site. However, this is not consistent with the modern relevant good practice, which anticipates a dry site to be incapable of being flooded to a level where System, Structure and Components (SSCs) are placed.

51. Clearly, as an existing site, SZB cannot now meet this piece of relevant good practice, but it highlights the importance of claims on engineered defences when these are the


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primary means of protecting the site and the significant safety burden now placed on their effectiveness and reliability.

52. The PSR does not provide adequate evidence, in light of the challenge presented by the recent independent reports (Refs 24 and 25), that the existing safety case claim of a dry-site following a design basis event, remains credible. According to the reports, a flood risk is present whether or not the sea defences are breached. Neither the PSR submission, nor the Fukushima Close-Out report (Ref. 26) provides any indication of the likely impact on SSC safety functions. ONR has sought confirmation on this matter.

53. On the basis of the information available ONR concludes there is a substantive and credible challenge to the extant coastal flooding safety case, and that the NGL has likely been aware of this fact for a significant period, but has not responded to the implied safety case gap. This gives rise to the following finding:


NGL should review and resolve the potential hazard and risk gaps via an appropriate site specific hazard & flood risk assessment.

Ageing Issues

54. During the assessment, ONR noted the corrosion present on some of the external structures such as the Reserve Ultimate Heat Sink (RUHS) building. Also of concern is the condition of some ancillary items such as the seismic restraints. These issues relating to ageing and corrosion management are discussed within the PSR.

55. Given the requirements of License Condition 28 to carry out examination, inspection, and maintenance, NGL is expected to have adequate arrangements for any plant which may affect safety. Given the condition of some of the observed plant ONR questioned the adequacy of some of these arrangements. NGL has raised two high priority observations (4.1H and 4.3H), which are relevant to this area but given that corrosion issues have been raised across many ONR assessment topics this has led to the following generic ONR Finding:

ONR Finding SZB PSR2-04

NGL to develop its arrangements for maintenance and inspection of those lower class systems, structures and components, which irrespective of their safety function may be prone to degradation of material condition. This should include those systems identified in observation 4.1H plus others as necessary.

Human Factors

56. The HF assessment of the PSR2 submission (Ref. 20) recommends accepting the SZB PSR2 for period to the next PSR (2025).

57. In support of the SZB PSR2 the Licensee has undertaken an extensive review to establish current Relevant Good Practice (RGP) across a broad range of HF topics. There is clear evidence that this RGP has been used during the SZB PSR2 to identify where gaps exist between the station’s current practice and RGP. With the exception of qualitative Human Factors assessment of maintenance tasks ONR has found no evidence of additional significant gaps between current practice and RGP not already highlighted by NGL in the SZB PSR2 documentation. In general, ONR is satisfied that NGL has identified appropriate recommendations to bring station’s practice in-line with RGP in the future.


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58. However, ONR is not satisfied that the NGL proposals to close out 5.3.H (see Table 2) with an agreed programme of work to be delivered under “normal business” are ALARP. ONR is continuing discussions with NGL to obtain assurance that a credible forward programme of work to close out the shortfall identified in 5.3.H. There is evidence that this has been a long running issue at Sizewell B, from at least the time of PSR1, and hence an ONR Finding (SZB-PSR2-05) has been raised against this issue.


NGL to provide sufficient evidence to demonstrate that claims made on operators in the facility safety case are supported by modern standards Human Factors substantiation which remains valid today / throughout the PSR period.

Chemistry

59. Overall, whilst some weaknesses were identified in the submitted PSR, ONR is broadly content to recommend that ONR accept the submitted PSR for the period until January 2025 (Ref. 16).

The Extent to which the Safety Documentation, including the Licensing Basis, Remains Valid

60. The PSR, in itself, is not meant to be a safety case. Instead it should be a structured, methodical and challenging review of the adequacy of the safety case to support future operations. In line with Licence Condition 14, the extant safety case for Sizewell B is regarded as a 'living' suite of documents which are amended in line with plant modifications in accordance with Licence Condition 22. The top-tier document is the Station Safety Report (SSR). This is a controlled document comprising 18 Chapters of main text and identified references. The SSR provides a description of the plant design and a summary safety case and is updated in response to modifications to the plant and safety case.

61. There is no specific part of the SSR that deals with operational chemistry control for any system at Sizewell B. However, the SSR is supplemented by Safety Case User Guides (SCUGs), which includes a chemistry specific SCUG. The SCUGs provide a route map through the safety case documentation. These provide the cross reference to all related aspects of the safety case. This includes relevant sections of the SSR, supporting reports, calculations, design reports and any "stand-alone" safety cases provided in support of plant, safety case or technical specification modifications.

62. The chemistry specific SCUG appears to mainly consider primary circuit chemistry, with some limited secondary circuit chemistry. Chemistry control is important to nuclear safety in many other systems, as evidenced by the much larger number of systems considered as part of PSR2. There also appears to be underlying assumptions in the SCUG that strict chemistry control is maintained at all times and that some quick effects are neglected, for example boric acid corrosion or flammable gases.

63. In addition, the SSR is in essence a snap shot in time of the chemistry control arrangements at Sizewell B, and therefore much of the chemistry related information is over 30 years old, and is often no longer relevant. While it is important to retain these links to the original design basis, there is very little in the SCUG to highlight the current state of chemistry control, and most importantly what safety claims are actually made on chemistry control.

64. Overall, ONR does not consider the SCUG to be a particularly useful document in understanding the chemistry aspects of the Sizewell B safety case. It does provide a useful link to historic information but is poor at presenting both the impact of chemistry


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on nuclear safety and describing how this is delivered by the licensee’s arrangements. While ONR accepts that it may be unreasonable to expect the SSR to be fully updated to reflect this, there are merits in updating the SCUG or some other aspects of the safety case. Therefore ONR raises the following finding:


NGL should review the chemistry aspects of the Sizewell B safety case to ensure that it adequately summarises the operational chemistry aspects of the safety case, in particular the impact of the operating chemistry on nuclear safety and the licensee’s arrangements for ensuring adequate chemistry control.

The Adequacy of the Arrangements in place to Maintain Safety until the next PSR or the End of Life

65. There are a number of tiers to the operational chemistry control arrangements at Sizewell B. In terms of safety significance they are (highest first), Technical Specifications and Environmental Specifications, Station Operating Instructions (SOIs), Technical Chemistry Technical Standards (TCTS) and Procedures.

66. It is not clear why some parameters are included in specifications (technical or environmental) and others are not. ONR considers this particularly relevant to those chemistry parameters that already have an Action Level 3 in the corresponding TCTS (i.e. “Action Level 3 represents the limits beyond which data or engineering judgement indicates that it is inadvisable to continue to operate the plant. The station to commence a controlled shutdown to Mode 3, and ultimately be taken to Mode 5 as rapidly as other plant constraints permit”). There may also be other parameters which would warrant inclusion at this highest level, based on their safety significance, but do not have an Action Level 3 specified in the corresponding TCTS. ONR therefore raises the following finding:


The licensee should review the adequacy of its chemistry related limits and conditions and where the chemistry control parameters needed for safety are included within the hierarchy of limits and conditions (operating rules).

67. It is notable that the ONR assessment of PSR1 for Sizewell B (Ref. 28) identified a finding on a related matter to “Review the status, within the hierarchy of the Sizewell B safety documentation of the chemistry technical standards”. The resolution of which led to the inclusion of the TCTS documents into LC23(1) arrangements. However, it is clear that the licensee did not consider the implications of the intent behind this finding fully, further reinforcing the need for the finding above.

Material condition

68. Observation 4.1.H was raised by NGL as a result of the numerous system specific material condition related observations raised in PSR chapter 6. This more general observation attempts to address the fact that collectively, the large number of material condition related observations tends to point towards a more general failing in NGL arrangements. ONR considers it a benefit that NGL has identified this wider pattern as part of its PSR. The resolution strategy involves a self-assessment and follow up actions. However, while this should address the lack of a longer term strategy, it does not appear to address the fact that the plant was allowed to degrade to the present state, which suggests that further improvements to the inspection and maintenance strategy may be warranted. ONR has therefore identified the following generic Finding:


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NGL should review the adequacy of its arrangements for maintenance and inspection of structures, systems and components, which provide a safety function but may be prone to degradation in their material condition. This should include those systems identified in observation 4.1.H. plus others as necessary.

69. Uniquely, the chemistry MR (Ref. 27) also includes a number of lower level conclusions from the PSR, which were termed as “areas for note” and represent additional areas for potential improvement. In the context of continuous improvement this is a good step, but is somewhat out with the PSR process.

70. Firstly, not all of the systems considered identify any areas for note. For those that do a number appear more as conclusions, rather than matters that could potentially be actioned (e.g. “chemistry control in this system has been good for the PSR period”). However, a number do appear to be specific and discrete areas where actions could be taken. In some instances they appear to be similar to some of the other low priority observations raised. This appears to be commensurate in nature and significance with some of the low priority observations raised. ONR therefore considers that further attention needs to be given to the identified areas for note and raises the following Finding:


NGL should review the “areas for note” identified in the chemistry main review to ensure those related to safety are adequately captured as part of normal business activities.

Civil Engineering and Structures

71. ONR is broadly satisfied with the extent and depth of the PSR carried out in the civil engineering topic area and considers that NGL has fulfilled its obligations under Licence Condition 15. No significant residual issues remain after completion of this assessment (Ref. 11), other than those captured by the NGL’s PSR process and incorporated into its Integrated Delivery Plan. Following assessment of the PSR submission on civil works and structures, ONR does not have any objections to ONR granting consent for NGL to continue its operations at Sizewell B for the next PSR review period.

72. Recommendations from the previous PSR are presented and discussed in the Civil Works and Structures MR (Ref. 33). Of 14 recommendations originated in this topic area, 5 ‘Category C’ items remain (defined as ‘potential improvements comprising good practices but with no appreciable nuclear safety benefit’) and have been incorporated into 3 new ‘Observations’. ONR questioned the need or benefit from ‘rolling over’ a recommendation from the previous PSR with NGL and was satisfied with the received response (Ref. 34).

73. Some valuable, self-critical observations were made on various aspects such as inspection and maintenance procedures and their implementation relating to general plant corrosion. NGL has raised low priority observations to address these issues, which are accepted by ONR. However, the observation relating to general plant corrosion has been raised in several areas across ONR’s assessment, hence an ONR Finding was raised:



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Electrical Engineering

74. Overall, ONR judges that NGL has presented an acceptable electrical engineering safety case for the 2015-2025 PSR period and is content to support acceptance of the PSR. No issues have been identified of an electrical engineering aspect that could prevent the power plant from generating electricity for a further ten years.

75. Two recommendations were raised in the electrical engineering review (Ref. 14) and these will be dealt with as part of normal regulatory business. One generic ONR Finding was also raised.

Plant Ageing and Degradation

76. Sizewell B has been generating for twenty years. With a site of this age, performance issues associated with equipment ageing can be expected, especially when the salt laden air associated with a site located adjacent to the sea is taken into account

77. NGL identified that outdoor transformers, such as station and essential transformers together with the associated control equipment and Uninterruptible Power Supplies (UPS) as areas that are at risk from ageing and degradation, low priority observations have been raised accordingly. This is especially relevant following the failure of a UPS due to a degraded component, which led to unplanned reactor trip. ONR considers that NGL has appropriately recognised UPS reliability as an area of concern prior to the PSR2 activity, putting in place Technical Guidance Notes for obsolescence management associated with C&I UPS systems and managing power conversion systems through the Fleet Critical Programmes part of the business. This forms an appropriate mechanism to ensure their timely replacement. ONR therefore considers that NGL has appropriately considered UPS systems within the review and that it was appropriate to raise the low priority observations.

78. NGL has recognised ageing and degradation as an issue affecting Sizewell B through the raising of the high and low priority observations in the electrical plant reviews. However, ONR is concerned that NGL may not have sufficient resource to deliver all the low priority observations. NGL has highlighted that it has raised high priority observation 4.1.H to consider the underlying factors that may have contributed to the position and implement and process improvements. However, despite the raising of this observation, ONR is concerned that NGL is only focusing on classified SSCs and not including those SSCs (classified and non-classified) which could challenge safety functions. This has contributed to the generic ONR Finding SZB PSR2-04 that has been discussed in previous sections:




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Probabilistic Safety Analysis (PSA)

79. ONR is broadly satisfied with the claims, arguments and evidence laid down within NGL’s PSR2 main review for PSA (Ref. 35). Through the work completed in support of the PSR2, NGL has assured itself that there are no immediate safety significant shortcomings associated with the PSA issues identified in its review. Although one Finding has been raised relating to PSA, ONR is satisfied with the process that NGL has applied to reach this conclusion and has found no evidence during assessment (Ref. 18) to challenge the majority of its outcomes. In conclusion ONR has not identified any further issues during assessment that would affect the decision to recommend Sizewell B is safe to operate for the next PSR period of operation of 2015 to 2025.

Results from the Seismic PSA review

80. Following Jacobsen Analytics’ detailed technical review of Sizewell B’s seismic PSA (Ref. 36); ONR considers that there are numerous areas where NGL has not satisfied ONR’s expectations related to SAPs FA. 11 (validity), FA.13 (adequate representation) (Ref. 1). Some of these areas are significant as they could have an impact on the insights and results delivered from the seismic PSA. For example, uncertainties within the seismic PSA and some areas of the analysis could be considered to be non-conservative. Therefore a PSR2 Finding has been raised in an effort to address this issue:


EDF NGL should develop its Sizewell B seismic PSA to be consistent with modern standards. This should take account of the findings from the ONR commissioned review and the NGL commissioned review of the Sizewell B seismic PSA.

81. The wording of the Finding is high level in order for NGL to address all of the areas of concern without the need to list them explicitly. The Finding has been raised with consultation from External Hazards specialists who also consider this area in the PSR2 External Hazards assessment (Ref. 10).

Structural Integrity

82. Overall ONR is content with the PSR submitted for the second Sizewell B Periodic Safety Review from a structural integrity perspective and recommends, from a structural integrity perspective, that ONR accept the submitted PSR for the 10 year period to January 2025.

83. One ONR Finding was raised in the structural integrity review (Ref. 17). This was the generic Finding, already described under several assessment topics and relates to development of a generic cross-discipline management of the material condition of system, structures and components in a suitable manner.

84. Although ONR supports high priority observation 4.1H on Plant Material Condition, it is of concern that this aspect has not been managed effectively over the past period of operation, hence the introduction of an ONR Finding to explicitly monitor progress on this aspect:


NGL should review the adequacy of its arrangements for maintenance and inspection of structures, systems and components, which provide a safety function but may be


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prone to degradation in their material condition. This should include those systems identified in observation 4.1.H. plus others as necessary.

85. There are a number of other matters related to structural integrity that need to be addressed in order to secure the long term justification of the plant that have not been identified as PSR observations. For example the test results from surveillance programme 9 suggest that the fracture toughness properties are degrading more quickly than anticipated, which could limit the life of the reactor pressure vessel. These matters have not been identified as PSR observations as they were already the subject of on-going work. ONR is satisfied that none of these pose an immediate risk to plant operations and is content that these are progressed through the on-going work rather than a PSR observation. However, it should be recognised that the PSR observations do not in themselves provide a complete picture of the on-going work necessary to support the through life justification in terms of structural integrity.

Internal Hazards

86. Overall, the Sizewell B review of hazards is an adequate review as part of the overall periodic safety review. In many ways, it has been performed to a standard higher than that achieved in the hazards reviews of recent PSRs on NGL’s AGR fleet.

87. The internal hazards assessment (Ref. 9) focussed on areas including fire, site generated flooding, missile impact, lifting/dropped loads, steam release, explosions and combinations of hazards. One ONR Finding was raised regarding internal flooding.

88. Overall NGL has carried out work of adequate quality to close out ONR’s issues on internal flooding from moderate energy pipework. ONR has had continuing regulatory interest in this area for two years. This work was integrated into the PSR, and has been performed to what appears to be an appropriate standard. Unfortunately, at the time of submission and throughout the assessment report the work undertaken has resulted in the SPF being vague on what precise changes will be made in order to increase the robustness of the safety case to larger leaks in moderate and low pressure pipework. ONR had been persuaded that this issue should be integrated into the PSR2 project, but at the end of the project the company still has decisions to make and then enter into commitments for a plan to implement the identified improvements. As an ONR PSR Finding this may lead to an item on the Action Plan for PSR2 closeout that will be agreed between ONR and NGL. Hence, ONR has raised the following Finding:


NGL should make decisions consistent with the ALARP principle on what improvements will be made to increase the robustness of the safety case to larger leaks in moderate and low pressure pipework, and then commit to a plan to implement these improvements.

89. In the other assessed areas Ref. 9 describes some caveats regarding the NGL Internal Hazards review (Ref. 37). In all cases reasons are given within the text of Ref. 9 as to why these do not require to be classed as an ONR PSR Finding. Some of these caveats have already been discussed with NGL at project meetings. ONR will share other insights from the internal hazards assessment with NGL as they plan future reviews and safety case updates, including the reviews that will contribute to PSR3.

90. A benefit for ONR in assessing power station periodic reviews is that they provide a useful opportunity for ONR assessment specialists to re-acquaint themselves with the


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safety case in their area, and bring to it fresh insights from their more recent work. This has been the case for internal hazards with the Sizewell B PSR2. Apart from identifying some themes that ONR may develop in future interactions with the station, some insights have been gained that will help input on revised ONR guidance. The TAG relating to internal hazards (Ref. 38) will be subject to a major update over the next year or so, but there is also a need for some additional holding statements as appendices whilst the TAG is being rewritten. This will include appendices on turbine disintegration and on the use of conservative methods in the modelling of hazards consequences, and both will be responsive to lessons learned from the assessment of Sizewell B PSR2.

Mechanical Engineering

91. Based on the sampled assessment undertaken (Ref. 12) ONR supports, from a mechanical engineering perspective, the continued operation of Sizewell B for a further 10 years of operation subject to routine regulation. On the basis of the assessment ONR considers that the mechanical plant and systems important to nuclear safety should continue to meet their safety duties during the next review period subject to planned periodic surveillance and maintenance and the timely resolution of the PSR observations.

92. The Mechanical Engineering assessment covered a large area of plant including Reactor Coolant System and Connected Systems, Essential Safety Features, Auxiliary Systems, Equipment Qualification and In-Service Testing. Across these area just one ONR Finding was raised that related to design codes across the plant but specifically focussed on the Polar Crane.

93. ONR accepts that both the Polar Crane and Fuel Building Crane (FBC) are conservatively designed with calculated operational stresses which are relatively low compared to the allowable stresses. ONR also understands that fatigue life calculations are also considered very conservative with the number of cycles used in the calculations being far greater than the estimated service life cycles.

94. The design and manufacturing codes and standards for cranes and lifting equipment have not been subject to major revision or significant changes since they were reviewed for the first periodic safety review for Sizewell B.

95. BS EN 12077 has been introduced since the design of the Polar Crane and FBC; two areas have been identified where a gap exists between the current crane design and the requirements specified in the new standard. The DR recommends that further work is carried out to assess the requirements for slack rope protection devices and rated capacity limiters and indicators on all the hoist systems; this is reflected in the Auxiliary Systems MR with a ‘Low’ priority PSR Observation. ONR agrees with this Observation.

96. BS 436 used for designing the polar crane gearbox was withdrawn prior to Sizewell B’s PSR1 with no direct replacement. During the Mechanical Engineering review (Ref. 12) ONR noted that the refurbishment of the fuel building crane in support of the Dry Fuel Store project (Ref. 39) assessed the gearbox against BS ISO 6336: 2006 ‘Calculation of Load Capacity of Spur and Helical Gears’.

97. ONR is satisfied that the comparison with current codes and standards has not shown any significant shortfalls that would compromise the safety claims made on the lifting equipment important to nuclear safety. However, the following finding is raised for station to review the relevance and applicability of BS ISO 6336:2006 and to take appropriate remedial measures.


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In light of the recent assessment undertaken against BS ISO 6336:2006 for the fuel building crane gearbox the Station should undertake a review of other equipment important to nuclear safety (with a particular focus on the polar crane) and address any shortcomings identified.

Control & Instrumentation

98. Overall, ONR judges that NGL has presented an acceptable C&I safety case for the 2015 to 2025 period and is content to support acceptance of the PSR subject to satisfactory resolution of the Finding detailed in the C&I assessment report (Ref. 13).

99. ONR considers the review of C&I, Safety Systems and Computer Systems to be well structured and methodical and provides an adequate level of detail. However, the review of aspects of the Polar Crane is lacking and proposed closeout of the associated high priority observations needs to be developed.

100. NGL identified two Polar Crane related high priority observations, 6.13H and 6.15H (see Table 2). These two observations relate to the existing load monitoring and protection system and the Polar Crane collective issues in respect of equipment condition, operations and safety case respectively.

101. Regarding observation 6.13H, ONR considers that in addition to an ALARP study regarding implementation of a load protection system (as implemented in the original design), NGL should take due cognisance of relevant good practice in this respect. This should also be undertaken in a timelier manner than indicated to inform NGL of any safety benefits. Although NGL has provided responses (Refs 42 and 43) on this issue ONR does not consider these responses to have resolved the matter adequately.

102. In respect of observation 6.15H, ONR judges that the SPF does not provide adequate detail to determine the scope of the resolution to these cumulative issues. ONR has again corresponded with NGL regarding 6.15H, however the level of information provided in the response is judged to be inadequate and proposed timescales for the Polar Crane refurbishment too long.

103. Reviewing both of the Polar Cane high priority observations, ONR considers it appropriate to raise a Finding against the polar crane.


NGL should, when undertaking the review of the Polar Crane load monitor and protection system, consider the existing design and safety requirements and relevant good practice in addition to their suggested ALARP study. This review should be undertaken in a timely manner to inform NGL of any appropriate safety benefits. In addition, NGL should also provide a detailed technical scoping document and programme of work covering the refurbishment of the Polar Crane.


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Table 1 NGL High Priority Observations

NGL High priority Observations Discipline Timescales for Close Out(T3 Date 80% confidence)

Chapter 2 – Safety Management Systems

2.1.H Justification of the staffing levels for the roles which are identified within the Sizewell B safety case

Human Factors Q1 2016

2.2.H Assessment and implementation of management of organisational change processes

LfMS Q1 2016

2.3.H SQEP resources & succession management

LfMS Q1 2018

2.4.H Fatigue level management Human Factors Q4 2016

2.5.H Management of resource implications associated with a large volume of processes

LfMS Q3 2018

2.6.H Weaknesses in the implementation of the Work Management processes

LfMS Q4 2018

2.7.H Provision of effective means of communication, including management of obsolescence issues

LfMS with input from C&I and Electrical Engineering

Q3 2016

2.8.H Management of interactions with the Japanese Earthquake Response (JER) work programmes

All assessed disciplines

Q1 2018

2.9.H Provision of services following Sizewell A decommissioning

Emergency Planning Q3 2015

2.10.H Infrequently used nuclear safety related procedures are not periodically reviewed, except during their occasional use

LfMS Q2 2017

Chapter 4 – Ageing, Obsolescence & Equipment Qualification Management

4.1.H Potential to improve the management of plant material condition

Structural Integrity, Chemistry, Civil Engineering, Electrical Engineering

Q3 2017

4.2.H Proactive management of Control & Instrumentation (C&I) and computing systems obsolescence


Q2 2017

4.3.H Review of maintenance requirements of external equipment

External Hazards Q1 2017

4.4.H Provision of future support for the Westinghouse Distributed Process Family (WDPF) components and systems


Q4 2015

4.5.H Performance, ageing and obsolescence of Eagle Highway Transceiver (EHX) Communication Circuit Boards


Q4 2015


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4.6.H Gaseous Radwaste System Defects –obsolescence of radiation monitor

Radwaste Q3 2016

4.7.H Gaseous Radwaste System Defects –poor reliability of carbon bed delay analyser cubical instrumentation panel

Radwaste Q3 2016

4.8.H Obsolescence problems with the Pond Fuel Handling Machine

Fuel/Mechanical Engineering

Q1 2016

4.9.H Potential swelling of the Boral Panels in the Fuel Storage Racks

Fault Studies / Fuel Q3 2017

4.10.H Potentially more onerous fatigue curve code changes (austenitic and ferritic)

Structural Integrity Q4 2015

4.11.H Changes to ASME code cases: environmental factors and fatigue curves


Chapter 5 – Safety Analysis

5.1.H Clad oxidation and embrittlement operational experience (OPEX) in Loss Of Coolant Accident (LOCA) analysis codes

Fault Studies Q3 2016

5.2.H Potential pre reflood clad ballooning in LOCA transient analysis

Fault Studies Q2 2015

5.3.H Reassessment of operator actions in the Living Probabilistic Safety Assessment (LPSA) and identification and implementation of potential enhancements

PSA / Human Factors Q4 2015

5.4.H Further analysis to support flooding from moderate energy pipework assumptions

Internal / External Hazards

Q4 2016

Chapter 6 – Systems, Structures and Components

6.1.H Potential water hammer damage to Residual Heat Removal (RHR) Safety Relief Valves (SRVs)

Mechanical Engineering / Structural Intergrity

Q1 2018

6.2.H Refuelling Water Storage Tank (RWST) modifications to address water freezing in the transmitter impulse lines


Q2 2017

6.3.H Comparison of external experience on Reactor building re-circulation sumps potential debris blockage


Q1 2017

6.4.H Ottermill Reactor Trip Circuit Breakers performance issues and obsolescence management


Q2 2017

6.5.H Review and assessment of Reactor Vessel Level Indication System technical specifications


Q4 2016

6.6.H Work to address material condition of Essential Diesel Generator (EDG) stacks

Electrical Engineering Q4 2015

6.7.H Work to minimise risk of flooding of control building from frequent Essential Service Water (ESW) heat exchanger break-ins

Internal Hazards Q1 2016


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6.8.H Work to address material condition of Essential Service Water System (ESWS) pipework


6.9.H Work to address material condition of Reserve Ultimate Heat Sink (RUHS)

Civil Engineering Q3 2017

6.10.H Auxiliary Feedwater System (AFWS) initial signs of degradation need to be addressed


6.11.H Main Control Room (MCR) post fault habitability testing review and comparison against international standards

Internal Hazards Q1 2018

6.12.H Work to address material condition of Heating, Ventilation and Air Conditioning (HVAC) Systems


Q3 2017

6.13.H Availability of polar crane load monitoring (MIPEG)


Q4 2016

6.14.H Human Factors assessment of polar crane design and operation

Human Factors Q2 2017

6.15.H Review of polar crane collective issues: equipment condition, operations and safety case

Mechanical Engineering / Human Factors

Q4 2016

6.16.H Presence of low level activity in liquid Radwaste discharge pipeline

Radwaste Q1 2016

6.17.H Further assessment of structural analysis of containment against modern standards


6.18.H Changes to ACI-349 design code relating to concrete anchorages

Civil Engineering Q3 2016

6.19.H Further assessment of design and analysis of containment liner against modern standards

Civil Engineering / Structural Integrity

Q3 2016


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Table 2 ONR Findings

ONR Finding Detail

SZB-PSR2-01 Fault Studies Issues Database Number: 2885

NGL should complete analysis of the flow distribution down-stream of the fuel spacer grids in the case where the gap between two assemblies has been closed. This should include an assessment of the margin to the critical heat flux, taking into account the difficulty in translating the results of rig tests to the reactor geometry.

SZB-PSR2-02 Fault Studies Issues Database Number: 2886

NGL to provide assurance that proposed investment in developing analysis methods (to replace those about to become obsolete) will proceed.

SZB-PSR2-03 External Hazards Issues Database Number: 3118

NGL to resolve both the hazard gap and the potential risk gap via an appropriate site specific hazard & flood risk assessment.

SZB-PSR2-04 External Hazards Power Electrical Chemistry Structural Integrity Civil Engineering Issues Database Number: 3159

NGL to develop its arrangements for the maintenance and inspection of all systems, structures and components, irrespective of their safety function, in order to maintain their material condition. This should include those systems identified in observation 4.1H plus others as necessary.

SZB-PSR2-05 Human Factors Issues Database Number: 3166

NGL to provide sufficient evidence to demonstrate that claims made on operators in the facility safety case are supported by modern standards Human Factors substantiation which remains valid today / throughout the PSR period.

SZB-PSR2-06 Chemistry Issues Database Number: 3139

NGL should review the chemistry aspects of the Sizewell B safety case to ensure that it adequately summarises the operational chemistry aspects of the safety case, in particular the impact of the operating chemistry on nuclear safety and the licensee’s arrangements for ensuring adequate chemistry control.

SZB-PSR2-07 Chemistry Issues Database Number: 3140

NGL should review the adequacy of its chemistry related limits and conditions and where the chemistry control parameters needed for safety are included within the hierarchy of limits and conditions (operating rules).

SZB-PSR2-08 Chemistry

NGL should review the “areas for note” identified in the chemistry main review to ensure those related to safety are adequately captured as part of normal business activities.


OFFICIAL


Issues Database Number: 3141

SZB-PSR2-09 PSA Issues Database Number: 3176

NGL should develop its Sizewell B seismic PSA to be consistent with modern standards. This should take account of the findings from the ONR commissioned review and the NGL commissioned review of the Sizewell B seismic PSA.

SZB-PSR2-10 Internal Hazards Issues Database Number: 3167

EDF NGL should make decisions consistent with the ALARP principle on what improvements will be made to increase the robustness of the safety case to larger leaks in moderate and low pressure pipework, and then commit to a plan to implement these improvements.

SZB-PSR2-11 Mechanical Engineering Issues Database Number: 3132

In light of the recent assessment undertaken against BS ISO 6336: 2006 for the fuel building crane gearbox the Station should undertake a review of other equipment important to nuclear safety (with a particular focus on the polar crane) and address any shortcomings identified.

SZB-PSR2-12 Control & Instrumentation Issues Database Number: 3164, 3165

NGL should, when undertaking the review of the Polar Crane load monitor and protection system, consider the existing design and safety requirements and relevant good practice in addition to their suggested ALARP study. This review should be undertaken in a timely manner to inform NGL of any appropriate safety benefits. In addition, NGL should also provide a detailed technical scoping document and programme of work covering the refurbishment of the Polar Crane.

Assessment of Sizewell B Periodic Safety · PDF file · 2015-10-21ONR Assessment of the Sizewell B Power Station ... takes into consideration compliance with modern standards and

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