project assessment report unique document id and …

Title of document

Template Ref: ONR-DOC-TEMP-005 Revision 12 of 44

PROJECT ASSESSMENT REPORT

Unique Document ID and Revision No:

ONR-OFD-PAR-17-015 Revision 0

TRIM Ref: 2018/5391

Project: Periodic Safety Review

Site: Dungeness B

Title: Assessment of the Dungeness B third periodic safety review (PSR3)

Licence Instrument No: (if applicable) N/A

Nuclear Site Licence No: 61

Licence Condition: LC 15 – Periodic Review

Document Acceptance and Approval for Issue / Publication

Role Name Position Signature Date TRIM Ref

Author Inspector 31 Jan 2018 NA

Reviewer Principal 31 Jan 2018 2018/43298 2018/43695

Accepted by1 Superintending Inspector

31 Jan 2018 Of completed form (see annex 1 NS-PER-GD-015)

Approval for publication2

Superintending Inspector

dd mm yyyy (as above)

Revision History

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

Change

A 30 Jan 2018 n/a 1st draft for DL review

B 31 Jan 2018 n/a 2nd draft incorporating DL comments

0 31 Jan 2018 n/a 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-OFD-PAR-17-015 TRIM Ref: 2018/5391

Office for Nuclear Regulation of 44

Organisation Name Date

Office for Nuclear Regulation

(Cover page and summary only)

Folder 4.4.2.18569.

Environment Agency

Licensee

Title of document

Template Ref: ONR-DOC-TEMP-005 Revision 12 of 44

Periodic Safety Review

Assessment of the Dungeness B third periodic safety review (PSR3)

Project Assessment Report ONR-OFD-PAR-17-015 Revision 0

31 January 2018



© Office for Nuclear Regulation, 2018 If you wish to reuse this information visit www.onr.org.uk/copyright for details. Published 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.



EXECUTIVE SUMMARY Title ONR Assessment of the Dungeness B third Periodic Safety Review Permission Requested This Office for Nuclear Regulation (ONR) Project Assessment Report (PAR) 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 periodic safety review (PSR) of the Dungeness B nuclear power station safety cases to justify continued safe operations1 at the facility for the period 2018-28.

Background A periodic safety review 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.

This was the second of the third round of periodic safety reviews (PSR3) which will be conducted on the fleet of nuclear reactors operated by NGL. The approach taken for PSR3 differed from previous PSRs in that the review structure was closely aligned to the latest International Atomic Energy Agency (IAEA) guidance on PSRs (SSG-25) and the focus was on the adequacy and effectiveness of the normal business arrangements in place to ensure plant safety.

The timings for the production of the DNB PSR3 meant that none of improvements sought by ONR through findings raised from the assessment of the Hinkley Point B and Hunterston B PSR3 submission were incorporated into the DNB PSR3 submission. Improvements to the PSR submissions will be monitored as the PSR3 programme progresses through the NGL fleet. Assessment and inspection work carried out by ONR in consideration of this request ONR’s main area of work was in considering the adequacy of NGL’s review of the Dungeness B power station safety cases and safety management arrangements. This was the second of the PSR3 submissions based around the NGL corporate safety management arrangements and it was decided that the assessments would focus on the evidence to demonstrate effective implementation of the arrangements to deliver safety and periodic review. A total of 15 regulatory assessments were commissioned. Matters arising from ONR's work The approach adopted for PSR3, focussing on demonstrating that nuclear safety is maintained through the routine NGL safety management arrangements, is considered appropriate. This approach demonstrates the effectiveness of the ongoing safety management arrangements rather than the snapshot in time often found in previous PSRs. Benefit was taken and lessons were learnt from the assessment of the HPB/HNB PSR3 submission which allowed a more in-depth review of the efficacy and implementation of the claimed safety management processes.

1 “Operations” include maintenance, examination, testing and operation of the plant and the treatment, processing, keeping, storing, accumulating or carriage of any radioactive material or radioactive waste and as such encompasses activities which continue after the cessation of electrical generation and through to decommissioning.



The safety case health review (SCHR) process was reviewed in greater depth to understand how it functioned and how it supported the periodic safety review process through a rolling programme of high level safety case reviews. Overall ONR found the process beneficial to ensure that the safety cases were adequate and shortfalls identified and addressed. ONR identified a number of weaknesses in the process and some improvements that would be needed to ensure that the SCHR process was sufficiently robust to support the expectations and requirements of a periodic safety review.

During the review of the seismic safety case for the graphite core, ONR identified a shortfall in the analysis which had a duration which was limited by an approaching reactor operating period. ONR wrote to NGL to ensure that they provided a shorter term seismic safety justification for the graphite core, pending provision of a longer-term case.

The predominant life-limiting factors at Dungeness B are the graphite core average weight loss and the deterioration of the boiler tubes. ONR fully acknowledges that NGL is delivering significant plant improvements at Dungeness B (boiler tube failure protection modifications and a more robust nitrogen plant) which should support the safe operation of the plant through to the end of electrical generation.

Safety shortfalls were identified by NGL then managed through the PSR3 recommendation process and have been categorised based on ALARP principles given their impact on safety. None of these were considered significant safety threats and NGL has a programme for all category B recommendations to be addressed by the end of 2020.

In total, ONR’s assessments have raised eleven findings and NGL will develop proposals for the resolution and close out these within agreed timescales. ONR considers the hazard and risk identified within each of the ONR findings are reasonable challenges which NGL has not adequately addressed. However, none are considered immediate threats to safe operation and can be dealt with on agreed timescales.

Conclusions ONR considers that NGL has carried out an adequate periodic safety review of the Dungeness B nuclear power station’s safety cases for the period 2018-28.

NGL’s arrangements for LC 15 have been followed in that an adequate review of the station’s nuclear safety case and safety management arrangements has been undertaken. The review did not identify any significant nuclear safety threats that would impact on station’s operations for the period through to end of generation, currently 2028.

ONR’s assessments of the Dungeness B PSR3 submission 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 Dungeness B power station. ONR identified eleven findings in its assessment work which NGL will close out within agreed timescales.

Recommendations It was recommended that ONR confirms the adequacy of NGL’s Dungeness B PSR submission by issuing a Decision Letter agreeing to the continued operation of the site for the period 2018-2028.

It was recommended that conditions are included in the Decision Letter with timescales to address the outstanding NGL category B recommendations and ONR findings.



LIST OF ABBREVIATIONS ABDS Automatic Boiler Depressurisation System

ACWL Active Core Weight Loss

AGR Advanced Gas-cooled Reactor

ALARP As low as reasonably practicable

BDB Beyond Design Basis

BED Boiler Emergency Depressurisation (valves)

BSL Basic Safety Level

C&I Control and Instrumentation

DB Design Basis

DNB Dungeness B

EAT Extreme Ambient Temperature

ER Equipment Reliability

ERR Equipment Reliability Review

fpy (reactor) full power years (of operation)

HNB Hunterston B

HPB Hinkley Point B

IAEA International Atomic Energy Agency

IJCO Interim Justification for Continued Operation

INA Independent Nuclear Assurance

IPRA Independent Periodic Review Assessment

JER Japanese Earthquake Response

LC Licence Condition

LLW Low Level Waste

LMfS Leadership and Management for Safety

LTFSC Long Term Fire Safety Case

NEC Non-Elective Closure

NGL EDF Energy Nuclear Generation Ltd

NNBR New Normal Business Recommendation

NSC Nuclear Safety Committee

NSP Nuclear Safety Principles

ONR Office for Nuclear Regulation

OPEX Operational Experience

PCPV Pre-stressed Concrete Pressure Vessel

PLEX Plant Life Extension

PSA Probabilistic Safety Analysis

PSR Periodic Safety Review



PSR3 Third round of PSRs undertaken on the NGL fleet of nuclear power stations

PVCW Pressure Vessel Cooling Water

RGP Relevant Good Practice

RWFI Radioactive Waste Focus Index

SAP Safety Assessment Principle(s)

SCAP Safety Case Anomalies Process

SCHR Safety Case Health Review

SDG Site Decommissioning Group

SF Safety Factor

SQEP Suitably Qualified and Experienced Person

SSC Systems, Structures and Components

SRRT Steam Release Reactor Trip

SRV Safety Relief Valves

SSR System Safety Review

TAG Technical Assessment Guide (ONR)

TMLS Through Life Management Strategy

WENRA Western European Nuclear Regulators Association

ZW Zonal Walkdown



TABLE OF CONTENTS 1 PERMISSION REQUESTED ............................................................................................. 10 2 BACKGROUND ................................................................................................................. 10

2.1 General ..................................................................................................................... 10 2.2 The Periodic safety review ........................................................................................ 11

3 ASSESSMENT AND INSPECTION WORK CARRIED OUT BY ONR IN CONSIDERATION OF THIS REQUEST ........................................................................... 12

4 MATTERS ARISING FROM ONR’S WORK ...................................................................... 13 5 CONCLUSIONS ................................................................................................................ 14 6 RECOMMENDATIONS ..................................................................................................... 15 7 REFERENCES .................................................................................................................. 16 APPENDIX 1 – PSR3 SUBMISSION STRUCTURE ............................................................... 17 APPENDIX 2 – ONR ASSESSMENT TOPICS ....................................................................... 18

Structural Integrity (Ref. 9) ................................................................................................... 18 Mechanical Engineering (Ref. 10) ........................................................................................ 19 Civil Engineering (Ref. 11) ................................................................................................... 20 Electrical Engineering (Ref. 12) ........................................................................................... 23 Control and Instrumentation (C&I) (Ref. 13) ........................................................................ 24 Chemistry (Ref. 14) .............................................................................................................. 25 Graphite (Ref. 15) ................................................................................................................ 27 Fuel Safety (Ref. 16) ............................................................................................................ 29 Internal Hazards (Ref. 17) .................................................................................................... 30 External Hazards (Ref. 18) .................................................................................................. 31 Fault Studies (Ref. 19) ......................................................................................................... 33 Probabilistic Safety Analysis (PSA) (Ref. 20) ...................................................................... 35 Leadership and Management for Safety (LMfS), Quality and Supply Chain (Ref. 21)......... 36 Radioactive Waste Management and Decommissioning (Ref. 22) ...................................... 37 Radiological Protection (Ref. 23) ......................................................................................... 39

Tables Table 1: DNB PSR3 Category B Recommendations Table 2: HNB/HPB PSR3 Category B Recommendations Applicable to DNB Table 3: ONR DNB PSR3 Assessment Findings



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 Dungeness B (DNB) nuclear power station’s safety cases.

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. 1) state that the period between PSRs should be 10 years. The Dungeness B PSR (Ref. 2) submitted to ONR covers the period January 2018 to 2028.

3. The regulatory process (Ref. 3) 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 formal submission date of the PSR. This letter sets out any regulatory requirements from the assessment of the PSR.

2 BACKGROUND

2.1 GENERAL

4. Dungeness B power station operates two Advanced Gas-cooled Reactors (AGR), which commenced generation in 1983 and are currently scheduled to cease electrical generation in 2028.

5. The PSRs are conducted by NGL in a ten year rolling programme across their fleet of nuclear power stations. The DNB PSR was the second of the third round of PSRs to be conducted, commonly referred to as PSR3 and formally submitted to ONR in January 2017 (Ref. 4). To maintain consistency across the PSR3 programme, the formal submission date was taken as 31 January 2017.

6. NGL concluded from its reviews that the current safety case for Dungeness B remains appropriate. The ongoing management of nuclear safety risk was considered and it was concluded that adequate risk management arrangements were in place to ensure that the risk from operation of the station will be maintained as low as reasonably practicable (ALARP) over the next PSR period. It was considered that continued operation of Dungeness B was acceptable for the next 10 year period.

7. ONR’s guidance (Ref. 3) states that the purpose of the PSR is to consider all factors that may affect 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.



2.2 THE PERIODIC SAFETY REVIEW

8. NGL commenced the DNB PSR3 in 2014 consistent with the approach set out in NGL’s scoping document (Ref. 5). This document defined the scope of work to be undertaken and established the methodology, which was consistent with the HPB & HNB PSR3 submission. The structure of the review was aligned to the International Atomic Energy Agency (IAEA) PSR guidance (Ref.1), based around safety factors (SF), and better use of company processes to deliver PSR evidence where practicable to enable delivery of a more continuous review. The structure of the PSR3 submission is detailed in Appendix 1.

9. To enhance the continuous review activities, NGL introduced a safety case health review (SCHR) process which complimented the extant system safety reviews (SSR), now equipment reliability reviews (ERR), which focused on plant condition and reliability.

10. Zonal walkdowns were conducted to provide a high-level stand back review of the design and current actual configuration of the plant against the hazard safety case requirements. The walkdowns are termed ‘zonal’ as they were performed on the basis of physical zones containing nuclear safety related plant with the zones assigned according to the physical segregation provided by fire barriers and/or by separation.

11. To ensure consistency across the safety factor reviews and the PSR3 programme, NGL produced a synopsis document for each safety factor early in the PSR3 process. The synopsis documents set down the claims and arguments for each Safety Factor, to meet the IAEA objectives, and specified the review methods to be used to underwrite each claim.

12. The safety factor reviews focussed on providing evidence to support the claims and arguments laid out in the synopsis documents, demonstrating that the NGL processes had adequately managed safety, and would continue to adequately manage safety, and the station would therefore be safe to operate for the forthcoming PSR period.

13. The reviews identified PSR recommendations which were categorised by their nuclear safety significance:

Category A: PSR identified nuclear safety significant issue which must be resolved by the ONR decision date.

Category B: PSR identified nuclear safety significant issue, which will be resolved by a timescale commensurate with its safety significance. The timescale will be shared with ONR.

New Normal Business Recommendations (NNBR): PSR identified issues of a low nuclear safety significance, e.g. potential improvement comprising good practices but with limited nuclear safety benefit. Timescales will be determined by existing normal business processes for prioritisation of work.

14. NGL identified no category A recommendations and six Category B recommendations specific to DNB, see Table 1, in addition to four Category B recommendations arising from the earlier Hinkley Point B / Hunterston B PSR3 that were also considered relevant to DNB, see Table 2.

15. NGL produced a plan to address all of its Cat B recommendations by the end of 2020 (Ref. 6). These timescales were slightly longer than the expected 2 years from the ONR decision letter but for nature of some of the remedial work; including building repairs and equipment replacement, ONR considered this to be acceptable. A further



37 issues were identified of low nuclear safety significance and were categorised as new normal business recommendations which would be addressed through the routine processes and prioritisation.

16. NGL has followed its own internal assurance process in the production, review and assessment of its PSR3 and sentencing of observations. The final submission document and all of the supporting safety factor reports produced for the Dungeness B PSR3 have been subject to an Independent Periodic Review Assessment (IPRA) by NGL’s Independent Nuclear Assurance (INA) (Ref.7). INA also participated in the working group that endorsed each category B recommendation raised in the PSR3.

17. The PSR3 Final Submission had been considered by the NGL Nuclear Safety Committee (NSC) (Ref. 8) which noted that a number of important issues were discussed in the PSR submission and argued to be being managed appropriately in normal business. The Committee was disappointed to note that there were still six outstanding actions from PSR2, but ONR confirmed that these were completed prior to the submission of the DNB PSR3 to ONR.

18. Following this periodic safety review, the licensee concluded that the current safety case for Dungeness B remained appropriate and adequate risk management arrangements were in place to ensure that the risk from operation of the station would be maintained ALARP over the next periodic safety review period. The licensee considered that continued operation of Dungeness B power station was acceptable for the next 10 year period.

3 ASSESSMENT AND INSPECTION WORK CARRIED OUT BY ONR IN

CONSIDERATION OF THIS REQUEST

19. The assessment of the Dungeness B PSR3 submission took benefit from the work conducted during the HNB and HPB PSR3 assessment which had reviewed many of the NGL corporate processes.

20. ONR’s main area of work was in considering the adequacy and implementation of NGL’s review processes for the Dungeness B safety cases and safety management arrangements. Sampling of the outputs and outcomes of their arrangements was used to provide evidence of the effective implementation of the arrangements described and claims made in the PSR3 submission.

21. A total of 15 regulatory assessments were commissioned covering the following topic areas:

Structural Integrity (Ref. 9) Mechanical Engineering (Ref. 10) Civil Engineering (Ref. 11) Electrical Engineering (Ref. 12) Control and Instrumentation (Ref. 13) Chemistry (Ref. 14) Graphite (Ref. 15) Fuel Safety (Ref. 16) Internal Hazards (Ref. 17) External Hazards (Ref. 18) Fault Studies (Ref. 19) Probabilistic Safety Analysis (PSA) (Ref. 20)



Leadership and Management for Safety, Quality and Supply Chain (Ref. 21) Radioactive Waste Management and Decommissioning (Ref. 22) Radiological Protection (Ref. 23)

22. A summary of ONR assessment views and findings are provided in Appendix 2. Although ONR considers that NGL’s review of the Dungeness B safety cases was carried out in a systematic way, a number of shortfalls were identified and have been appropriately prioritised. Regulatory issues were raised where ONR’s significant assessment findings could not be resolved within the assessment period and these are detailed in Table 3. The remainder of the recommendations raised during the assessments will be addressed through routine regulatory interventions.

4 MATTERS ARISING FROM ONR’S WORK

23. Based on the findings of ONR’s assessments, I consider that, overall, NGL has carried out an adequate review of the Dungeness B Nuclear Power Station safety cases. This view is based on the findings of ONR specialist inspectors’ assessment reports for specified topic areas (Refs. 9-23). The ONR assessments confirmed NGL’s view that the safety case and safety management arrangements justify ongoing operations for a further 10 years.

24. The approach adopted for PSR3, focussing on demonstrating that nuclear safety is maintained through the routine NGL safety management arrangements, is considered appropriate and achieves the purpose stated in ONR’s guidance (Ref. 3). This approach demonstrates the effectiveness of the ongoing safety management arrangements rather than the snapshot in time often found in previous PSRs. ONR took benefit from and learnt lessons from the assessment of the HPB / HNB PSR3 submission which allowed a more in-depth review of the efficacy and implementation of the claimed safety management processes for the DNB PSR3 submission.

25. Whilst the NGL process for conducting the PSR had improved, the timing of the DNB PSR3 meant it did not adequately address the PSR shortfalls identified by ONR in the earlier HPB/ HNB assessment. The primary finding from the previous assessment was concerned with the provision of adequate evidence in the PSR and ONR noted a marginal improvement in this PSR submission, through NGL’s improvements to their PSR process, but ONR will still expect to see improvements in the later PSR3 submissions.

26. The lack of included evidence was mitigated by NGL’s prompt response to queries and facilitation of evidence gathering visits to Dungeness B and the Barnwood corporate headquarters.

27. The safety case health review (SCHR) process was reviewed in greater depth than previously to understand how it functioned and how it supported the periodic safety review process through a rolling programme of high level safety case reviews. Overall, ONR found the process beneficial to ensure that the safety cases were adequate and shortfalls were identified and addressed. ONR identified a number of weaknesses in the process and some improvements that would be needed to ensure that the SCHR process was sufficiently robust to support the expectations and requirements of a periodic safety review. The following finding was raised:

ONR-DNB-PSR3-01

NGL should review their SCHR process to ensure it is adequate to support the requirements of a PSR



28. During the review of the seismic safety case for the graphite core, ONR identified a shortfall in the analysis which was constrained by an approaching reactor operating period limit. ONR wrote to NGL (Ref. 24) for them to provide a short term seismic safety justification for the graphite core before the end of 2017. This has now been received and is being reviewed by ONR.

29. At Dungeness B the life limiting factors are currently the graphite core average weight loss and the vulnerability of the boilers to tube failures resulting in water ingress in the core. To support the safe operation of the plant until its current end of generation date of 2028, the NGL plant life extension (PLEX) project identified a number of boiler tube failure protection modifications, now known as boiler lifetime modifications, during the plant life extension work. The project to deliver the modifications is currently ongoing but throughout the PSR3 submission significant claims were made on the completion of these modifications for long term safe operation of the plant. ONR recognises the importance of these modifications and raised a finding to ensure their timely delivery:

ONR-DNB-PSR3-06

NGL should ensure timely implementation the PLEX-identified boiler tube failure protection modifications.

30. ONR fully acknowledges that NGL is implementing significant improvements at Dungeness B, such as the updated nitrogen storage and injection system, the boiler modifications and other general plant condition improvements. These will be needed to support the safe operation of the plant through to the end of electrical generation.

31. ONR’s assessment took into account NGL’s identification of shortfalls and I consider the process followed by NGL was structured and subject to independent scrutiny. I judge NGL’s categorisation of all shortfalls into category B or new normal business work-streams reasonable with the appropriate ALARP considerations and the impact on nuclear safety.

32. In total, ONR’s assessments have raised eleven findings (Table 3). The two which were common to many topics are summarised above; the more topic-specific findings are summarised in Appendix 2. NGL will develop proposals for the resolution of the eleven ONR findings by 31 March 2018 and close out the findings within agreed timescales. I consider the hazard and risk identified within each of the ONR findings are reasonable challenges which NGL has not adequately addressed. However, none are considered immediate threats to safe operation.

33. ONR will monitor the close out of all NGL’s category B recommendations and ONR findings by the end of 2020 through normal business activities delivered by the ONR Dungeness B PSR3 project and specialist inspectors. Attention will be given to ensure the adequacy of response and effectiveness of implementation.

5 CONCLUSIONS

34. I consider that NGL has carried out an adequate periodic safety review of the Dungeness B nuclear power station safety cases for the period 2018-28. This view is based on the following:

NGL’s arrangements for LC 15 have been followed in that an adequate review of the station’s nuclear safety case and safety management arrangements has been undertaken. This review was subject to independent review via NGL’s internal assurance process and Nuclear Safety Committee.



NGL’s review did not identify any significant nuclear safety threats that would impact on the station’s operations for the period through to end of generation, currently 2028. Safety shortfalls were identified through the PSR3 recommendation process and have been categorised based on ALARP principles given their impact on safety. NGL has a programme for all category B recommendations to be addressed by the end of 2020.

ONR’s own assessment of the Dungeness B PSR3 submission in support of continued safe operations until 2028 were considered to be thorough and systematic.

ONR’s assessment findings supported NGL’s conclusion that no serious nuclear safety hazards exist in continued operation of Dungeness B power station that are not already controlled through normal operational processes to reduce the risks ALARP. ONR identified eleven findings in its assessment work for which NGL will develop proposals for resolution by 31 March 2018 and close out the findings within agreed timescales.

35. However, the continued safe operation of the reactors will be dependent on the outcomes of the ongoing programme of graphite core inspections and inspections of other key structural components as part of the continued examination, inspection, maintenance and testing which will also be required to justify continued generation. Adequacy of the ongoing safety case and the safety of operations will also be confirmed by ONR as part of its permissioning process following each statutory shutdown of the reactors and through regular inspection activities.

6 RECOMMENDATIONS

36. I recommend that ONR confirms the adequacy of NGL’s Dungeness B PSR submission by issuing a Decision Letter agreeing to the continued operation of the site for the period 2018-2028, subject to the caveats highlighted above.

37. I recommend that conditions are included in the Decision Letter with timescales to address the outstanding NGL category B recommendations and ONR findings.



7 REFERENCES

1 Periodic Safety Review For Nuclear Power Plants. International Atomic Energy Agency

(IAEA). Specific Safety Guide SSG-25. IAEA. Vienna. 2013. www.iaea.org. 2 NP-SC 7746 - Dungeness B Third Periodic Safety Review Final Submission - Version

04 - EC357431, 22 Nov 2016, 3 Periodic Safety Review, NS-TAST-GD-050 Revision 6. ONR. July 2017

http://www.onr.org.uk/operational/tech_asst_guides/index.htm 4 DNB50931Y - Dungeness B PSR3 NP-SC 7746 - Submission letter, 20 January 2017,

5 NGL - PSR3 - DNB Scope and arrangements - EC349627 - NP/SC 7689 - Rev 000 Ver 04, Oct 2013,

6 DNB PSR3: Status of DNB PSR3 RMFs, 26 Jan 2018, 7 INSA and IPRA certificates for the DNB PSR3 Final Submission and SF reports, 30

Nov 2016, 8 EDF NGL - NSC Minutes - Meeting Held at Barnwood on 12th October 2016,

9 NGL - Dungeness B - ONR-OFD-AR-17-014 - Assessment of the Structural Integrity aspects of the DNB PSR3, Aug 2017

10 NGL - Dungeness B - ONR-OFD-AR-17-029 - Mechanical Engineering Assessment of the DNB PSR3, Nov 2017,

11 NGL - Dungeness B - ONR-OFD-AR-17-011 - Civil Engineering Assessment of the DNB PSR3, Sept 2017,

12 NGL - Dungeness B - ONR-OFD-AR-17-012 - Assessment of the Electrical Systems aspects of the DNB PSR3, July 2017,

13 NGL - Dungeness B - ONR-OFD-AR-17-028 - Control and instrumentation assessment of the DNB PSR3, Nov 2017,

14 NGL - Dungeness B - ONR-OFD-AR-17-032 - Assessment of the Chemistry Aspects of the DNB PSR3, Oct 2017,

15 NGL - Dungeness B - ONR-OFD-AR-17-025 - Assessment of the Graphite Aspects of the DNB PSR3 for the Period 2018–2028, Sept 2017,

16 NGL - Dungeness B - ONR-OFD-AR-17-024 - Assessment of the Fuel Safety aspects of the DNB PSR3 for the Period 2018 – 2028, Sept 2017,

17 NGL - Dungeness B - ONR-OFD-AR-17-034 - Internal Hazards Assessment of DNB PSR3, Jan 2018,

18 NGL - Dungeness B - ONR-OFD-AR-17-021 - External Hazards Assessment of the DNB PSR3, Nov 2017,

19 NGL - Dungeness B - ONR-OFD-AR-17-019 - Fault Studies Assessment of DNB PSR3, Sept 2017,

20 NGL - Dungeness B - ONR-OFD-AR-17-030 - PSA Assessment of the DNB PSR3, Nov 2017,

21 NGL - Dungeness B - ONR-OFD-AR-17-015 - Review of Supply Chain and Leadership and Management of Safety of the DNB PSR3, Nov 2017,

22 NGL - Dungeness B - ONR-OFD-AR-17-023 - Assessment of the Radioactive Waste Management and Decommissioning Aspects of the DNB PSR3, Jan 2018,

23 NGL - Dungeness B - ONR-OFD-AR-17-057 - Radiological Protection Assessment of DNB PSR3, Dec 2017,

24 EDF – Dungeness B – DNB 71296 R – Letter to - Graphite Seismic Safety Case and Graphite Weight Loss, 2 Oct 2017,



APPENDIX 1 – PSR3 Submission Structure 38. The documentation provided by NGL follows the guidance laid out in International

Atomic Energy Agency (IAEA) document number SSG-25 (Periodic Review for Nuclear Power Plants) (Ref.1). The documentation included a final submission document, zonal walkdown reports for DNB and an early stand back review. The document structure and relationships are shown in the figure below.

39. The submission included a number of specified Safety Factor (SF) documents, as

identified below:

SF 1: Plant design SF 2: Actual condition of plant important to safety SF 3: Equipment qualification SF 4: Ageing, obsolescence and lifetime management SF 5: Deterministic safety analysis SF 6: Probabilistic safety analysis SF 7: Hazards analysis SF 8: Safety performance SF 9: Use of experience from other plants and research findings SF 10: Organisation, the management system and safety culture SF 11: Procedures SF 12: Human factors SF 13: Emergency planning SF 14: Radiological impact on the environment SF 15: Radiological protection SF 16: Decommissioning

PSR3 Supporting Documents

PSR3 Submission DocumentsNSC Paper- Head Document- Global Assessment

Codes & Standards

Management of Risk

Discipline Review

Early Stand Back Review (ESBR)

SF16

SF15

SF14

SF13

SF12

SF11

SF10

SF9

SF8

SF7

SF6

SF5

SF4

SF3

SF2

SF1

SF16

SF15

SF14

SF13

SF12

SF11

SF10

SF9

SF8

SF7

SF6

SF5

SF4

SF3

SF2

SF1

Hazards Analysis

HF Analysis Docs

PSR3 Guidance Documents

Scope, Process & Guidance

Docs

Key Normal Business Documents

Equipment Reliability Reviews (ERR) or System Safety Reviews (SSR

)

Safety Case Health Reviews (SCHR)

Zonal Walkdowns (ZW)

Process Docs Process Docs Process Docs



APPENDIX 2 – ONR Assessment Topics 40. This appendix gives an overview of the various topics assessed within the

Dungeness B PSR3 submission and presents the conclusions and ONR findings (where applicable) for each of the topics.

Structural Integrity (Ref. 9) 41. Overall ONR was satisfied, from a structural integrity perspective, that NGL produced

the PSR3 for DNB based on a reassessment of its processes and safety cases in line with ONR’s expectations and that it has completed an assessment of current plant condition to compare it against the design intent and the predicted operating life of the stations.

42. The PSR3 identified a number of category B and normal new business recommendations but few relevant to structural integrity. ONR considered that issues related to structural integrity identified within the PSR3 review were being suitably dealt with through other standard NGL processes and where ONR deemed these were important have made ONR recommendations to track their progress/outcome.

43. ONR was satisfied that NGL had conducted suitable plant walkdowns as part of the PSR3 process, focussed on areas of nuclear safety significance and following a zoned approach. The walkdowns identified a number of common themes relevant to structural integrity, such as insufficient support, segregation or protection for equipment, equipment damaged or in poor condition and previously unidentified potential hazard/plant interactions. In general ONR was satisfied with the remedial actions performed by NGL but made recommendations in relation to some findings of the plant walkdowns.

44. Regarding NGL’s submission for Safety Factor 1 “Plant Design”, ONR judged that NGL had provided a suitable demonstration that it had implemented processes to address the issues posed by revisions to codes and standards. It had identified relevant structures, systems and components and had maintenance activities applied where required. Future ONR interventions during system based and licence condition inspections will monitor and assess the adequacy of NGL’s arrangements.

45. ONR was satisfied that NGL had made effective use of their management systems to monitor and understand plant condition and was encouraged to review evidence that defect backlogs were showing a downward trend at DNB. ONR had recently been concerned that the necessary additional inspection activity relating to corrosion under insulation, buried and trenched pipework had challenged the process of defect remediation at DNB. ONR had taken appropriate enforcement steps to align NGL with relevant good practice and ONR was satisfied with the corrective actions taken by DNB. However, this remains an on-going focus for ONR and interactions on this matter will continue until ONR is satisfied that DNB is managing plant material condition effectively.

46. ONR considered that NGL had satisfied the claim that the actual condition of safety related plant and structures was understood and will meet the design basis and functional requirements for the next PSR period. The condition of the plant was documented; maintenance, surveillance and in-service inspection programmes were subject to appropriate review.

47. ONR considered that NGL had been able to demonstrate that processes were in place for ageing, obsolescence and lifetime management at DNB, so that the required safety functions were maintained for the plant lifetime, including the decommissioning phase.



However ONR did not consider that NGL had fully embedded or implemented these arrangements. A recommendation for future progress monitoring was made in the HNB / HPB PSR3 structural integrity assessment, which recommended that ONR interventions on concealed systems and tanks and vessels were utilised to address this issue. These were on-going and ONR was satisfied that these were suitably addressing this issue.

48. ONR was satisfied that NGL had carried out an adequate review of their ageing management process against IAEA guidance, concluding that it was implemented via several processes, rather than one. Whilst ONR was content that the various processes used collectively by NGL would enable ageing management of plant, ONR also recognised the merits and benefits of a more centralised approach to ageing management.

49. Whilst NGL had developed suitable processes to manage ageing (i.e. corrosion, particularly corrosion under insulation) they have historically failed to address the degraded material condition of some plant on the Dungeness B site. Remediation of this degradation was on-going but in ONR's opinion, the Dungeness B site now needed to review the oversight arrangements for managing such plant ageing to ensure they were fully embedded within the site management system and were effective. The following finding was raised:

ONR-DNB-PSR3-10

NGL to review the oversight arrangements for managing plant ageing (i.e. corrosion, particularly corrosion under insulation) on the Dungeness B site.

50. Recognising the importance of the relationship of decommissioning with ageing and degradation, ONR conducted a high level review of relevant SF16 (Decommissioning) documentation. ONR considered the aspect of plant material condition during the assessment but in its opinion there were no issues of relevance to structural integrity in addition to those already covered by Safety Factors 2 & 4.

51. In addition to assessing the documentation provided, ONR used regulatory intelligence already known to ONR regarding DNB, through interactions with the site and with the NGL Central Technical Organisation to consider other important issues which related to the on-going safety of the plant over the next 10 year period. For example it was recognised that DNB has many more welds with a high integrity claim due to the nature of the design. ONR reviewed the position on this and was satisfied that the highest reliability welds had been adequately discussed within the PSR3 documentation.

Mechanical Engineering (Ref. 10) 52. Overall, no significant specific mechanical shortfalls relating to the systems ONR

sampled were identified and ONR was therefore content that the processes described within DNB PSR3 were proactively managing safety to an adequate level. ONR was therefore satisfied with the adequacy of the third Dungeness B Periodic Safety Review.

53. NGL had identified the DNB boilers as life limiting plant items which could not be replaced. ONR therefore chose to sample how the PSR3 processes were applied to the main boiler safety relief valves (SRV) which were also used as manual boiler emergency depressurisation (BED) valves.

54. Gap analysis conducted by NGL had identified good practice from a benchmarking visit to a foreign plant related to system and component engineers. This had resulted in



the implementation of Fleet System Engineers, to become the focal point of contact for problems and queries with particular systems. NGL was also establishing Fleet Component Engineers to provide support for the worst performing components across the fleet and the industry, identified from internal and external operational experience (OPEX).

55. ONR considered this use of gap analysis to identify engineering improvements to be a good example of how NGL’s processes continuously improve their internal normal business procedures to support reliability and safety.

56. NGL had reviewed the ageing management arrangements against international standards and did not identify any significant gaps in the NGL processes, but did identify that there was no overall ageing management policy in place. This was now enacted by a combination of the equipment reliability and technical governance process, which although not fully implemented, the majority of the processes were in place.

57. ONR was satisfied that NGL identified a compliance gap to IAEA relevant good practice (RGP) and they were implementing suitable processes to close it. ONR also considered this gap did not represent a significant reduction in NGL’s capability to identify and manage ageing and obsolescence.

58. The PSR 3 Lifetime and Inaccessible Systems Review identified boiler ALARP modifications to address the long term boiler tube leak failure shortfalls, including modifications to the main boiler SRVs to provide an automatic boiler depressurisation system (ABDS) to minimise water ingress into the reactor core following a boiler tube failure.

59. ONR was aware that during the new ABDS actuator verification testing, an unrevealed fault associated with the SRV bearings was identified. The identification and sentencing of this issue by NGL was performed using its normal business process, namely interim justification for continued operation (IJCO) and safety case anomalies process (SCAP). ONR undertook a review of this IJCO and judged that NGL had adequately justified that the BED SRV would continue to perform adequately.

60. ONR was satisfied that this was an appropriate example of how NGL’s normal business processes (e.g. IJCO and SCAP) adequately maintain ongoing safe operations as claimed in PSR3.

61. ONR did not identify any significant specific mechanical shortfalls relating to the systems and documentation sampled and was therefore content that the processes identified within PSR3 were effectively managing safety to an adequate level.

Civil Engineering (Ref. 11) 62. ONR concurred, from a civil engineering perspective, with the overall conclusions of

the PSR and concluded that the PSR was adequate and that the licensee’s arrangements and strategic programmes were appropriate for the safe operation of the reactors at Dungeness B for the next PSR period.

63. ONR was satisfied that NGL produced the PSR3 for Dungeness B based on a reassessment of its processes and safety cases in line with ONR’s expectations and that it has completed an assessment of current plant condition to compare it against the design intent and the predicted operating life of the station.



64. The PSR3 identified a number of NGL recommendations relevant to civil engineering that need to be addressed in order to support safe operation during the next PSR period. ONR concurred with the recommendations and was content that NGL had adequate plans in place to resolve these recommendations to an appropriate timescale and that none posed an immediate risk to continued operation.

65. ONR was satisfied that NGL conducted suitable plant walk-downs as part of the PSR3 process, focused on areas of nuclear safety significance.

66. ONR considered that the civil engineering related recommendations raised by ONR as part of its assessment of the Hinkley Point B and Hunterston B PSR3 were equally applicable to Dungeness B, and closure should be based on fleet-wide considerations.

67. A number of improvements were introduced towards the end of the review period, including the issue of new company technical standards, the appointment of a dedicated civil engineering suitably qualified and experienced person, and the establishment of a number of working groups to share experience between all NGL sites. These enhanced arrangements should improve the inspection and maintenance of civil engineering assets and reduce the number of defects requiring remediation. ONR judged that although the position regarding outstanding defects reported in PSR3 was less than satisfactory, adequate progress is being made in addressing these defects.

68. In relation to the rubber bearings that support the PCPV, ONR considered that an adequate case had not been made for the lack of bearing inspections and that it would be reasonably practicable to carry out periodic visual inspections. ONR has had discussions with the NGL Civil Design Group (CDG) on the fleet wide aspects of such inspections and the CDG prepared an Engineering Advice Note (EAN) on this subject. The EAN established that the bearings at Dungeness B, unlike those for Hinkley Point B and Hunterston, were a composite of rubber and steel strips. This type of bearing was normally required to accommodate horizontal movement and can be vulnerable to deterioration if the rubber splits and exposes the steel strips. As the EAN did not recommend bearing inspections ONR raised the following finding:

ONR-DNB-PSR3-02

NGL should carry out sample visual inspections of the rubber bearings that support the Pre-stressed Concrete Pressure Vessels, or provide an adequate ALARP justification for the current lack of such inspections.

69. One of the key features of the Equipment Reliability (ER) process was to identify critical components; one whose failure effects are intolerable to the facility. In response to an ONR query, NGL confirmed that nuclear significant buildings and structures (not including the prestressed concrete pressure vessel (PCPV) were classed as non-critical1 because it was difficult to see how normal building degradation could lead to the building failing to meet its safety duty.

70. ONR was only partially satisfied with the response given and while ONR agreed that in general terms, a building as a whole would be unlikely to be considered as a critical component, there may be parts of the structure whose failure would be intolerable and would warrant being treated as critical components. For example, the failure of a crane support may lead to significant dropped loads onto critical plant and equipment or a

1 Non-critical is an intermediate classification between Critical and Low Significance (run to failure) components. It describes a component with failure consequences that are tolerable to the Station but are judged beneficial to prevent or reduce, by preventive maintenance or other means.



leaking roof might allow rainwater to impair the function of critical electrical equipment. ONR therefore raised the following finding:

ONR-DNB-PSR3-03

NGL should clarify how the Equipment Reliability process is applied to the management of Civil Structures and should identify and rectify any compliance gaps.

71. ONR considered the extent of alignment between NGL processes and relevant good practice and concluded that, with the exception of the PCPV, the ageing management programme for safety significant structures was not fully in compliance. In particular, when compared with IAEA Safety Guide ND-G-2.12, ONR did not find evidence of a screening process for selecting structures for inclusion in an ageing management programme, or the development of specific programmes for selected systems, structures and components (SSC). ONR therefore raised the following finding:

ONR-DNB-PSR3-04

NGL should develop a site-specific ageing management programme for safety significant civil structures that takes account of relevant good practice in IAEA Safety Guide ND-G-2.12.

72. EDF’s recommendations raised in the fleet-wide civil Through Life Management Strategy (TLMS) are mainly generic in nature and there is no specific focus on particular buildings or issues applicable only to certain sites. As an example, there have been particular issues at DNB with the condition of the reactor building and the fuel pond but these were not discussed in the report.

73. The Fuel Pond has a long-standing issue with concrete cracking and water seepage. Non-destructive testing (half-cell potential and hammer tests) have twice been carried out in order to assess the risk of reinforcement corrosion and concrete degradation. These tests were not included in the Maintenance Schedule.

74. The Fuel Pond Steering Group held a recent workshop to review the integrity of the pond and the acceptability of water seepage. The review did not identify any concerns for the safety case for continued operation but did raise four recommendations, with which ONR broadly concurred. These included a recommendation to carry out further half-cell potential tests to align with the 2018 LC 28 inspection, and following these inspections to determine a forward strategy for the frequency of monitoring.

75. ONR considered that there may be other suitable non-destructive tests, which may allow for continuous monitoring. Such tests should provide additional confidence that the concrete cracks are not resulting in significant deterioration of the concrete or reinforcement. The half-cell potential method has known limitations, as there is uncertainty whether corrosion is occurring, and it provides no information on the corrosion rate. ONR considered that as part of its proposed forward strategy for the Fuel Pond, NGL should carry out a review of available monitoring techniques to establish whether it would be reasonably practicable to use alternative methods to detect corrosion of reinforcement. ONR raised the following finding:



ONR-DNB-PSR3-05

NGL should develop and implement a lifetime strategy and ageing management programme for the Fuel Pond. The work should identify all relevant ageing and degradation mechanisms, review available options to address ageing and degradation, and define any reasonably practicable improvements to the inspection, monitoring, maintenance and repair regimes. Where appropriate, the programme activities should be included in the Maintenance Schedule.

76. The ONR assessment raised other recommendations to be addressed by the licensee. The recommendations relate to opportunities for improvement in a number of areas relating to the management of the civil engineering assets, to better align the current procedures and practices with modern standards and relevant good practice. ONR has raised recommendations so that the licensee can develop an acceptable improvement programme and to enable ONR to monitor progress with addressing these areas.

77. ONR noted that the licensee submitted the PSR on time and it was of adequate technical quality. ONR found that there was general compliance with relevant good practice, with a small number of shortfalls and areas for improvement identified. The report was self-critical and raised recommendations, some of which had already been progressed at the time of writing the assessment report. The response of the licensee to requests for clarification or further information was good showing a proactive and positive approach to its responsibilities.

Electrical Engineering (Ref. 12) 78. ONR found minor deficiencies in the content of the PSR3 submission in that NGL had

not, on this occasion, submitted an assessment of all of its electrical structures systems and components. In ONR’s opinion, for electrical equipment and systems important to safety, NGL had failed to submit a comprehensive assessment of the performance of all of its electrical structures systems and components in its PSR3 submission, demonstrating that the established and continuous arrangements were both adequate and effective. However, from a review of the implementation of the arrangements at DNB and the additional supporting activities undertaken there, ONR was content that DNB was managing plant and equipment in an appropriate manner and duly considered transitioning to a post-operational phase in their lifetime plans for plant and equipment.

79. The licensee’s reports concluded that generally the processes in place were adequate to ensure the systems and equipment were well maintained and remained fit for their intended purpose.

80. ONR assessed the adequacy of the review in respect of electrical systems and equipment presented in PSR3: Against its original equipment qualification criteria, Consideration of the effects of plant ageing and degradation together with

obsolescence, Use of operational experience, and Changes made to relevant electrical engineering codes and standards.

81. As part of the assessment, ONR undertook an inspection at Dungeness B Power Station of the activities being undertaken in each operational area and to observe the condition of the plant and equipment.



82. ONR supported the category B recommendations related to electrical equipment made in the PSR reviews, noting that work had already commenced or plans had been developed for their implementation and management over the forthcoming years.

83. ONR considered that there were minor deficiencies in the content of the PSR3 submission relating to the assessment of all of its electrical structures systems and components and therefore the submission did not align with ONR’s assessment criteria. However, ONR did not consider this to be a significant finding from its assessment as ONR had observed, during a site inspection, the processes established to systematically review the safety case which included electrical engineering structures, systems and components that were not explicitly reported within the PSR submission.

84. ONR did not consider from a regulatory perspective any significant benefit would be accrued by requesting NGL to undertake a further review to ensure all of its electrical systems, structures and components are included in its PSR3. However, ONR would expect that future PSR submissions should ensure that adequate and effective reviews of all of its electrical engineering related structures systems and components important to nuclear safety, be explicitly reported as part of their periodic review.

85. From its assessment, ONR considered that Dungeness B was managing plant condition, ageing and obsolescence issues in an acceptable manner and considered that relevant good practice was generally satisfied when assessed against ONR or other published guidance.

Control and Instrumentation (C&I) (Ref. 13) 86. Overall, ONR considered that the Dungeness B third period safety review submission,

supporting documentation and requested information sufficiently supported the adequacy of the existing arrangements to maintain control and instrumentation systems and equipment to support safe operation of Dungeness B power station for the period until the next periodic safety review.

87. This ONR assessment focused on the arrangements for the management of control and instrumentation equipment reliability, an assessment of a sample of safety systems at Dungeness B to assess the application of these arrangements in practice and the licensee’s arrangements for the examination, inspection, maintenance and testing of safety systems.

88. ONR reviewed the INA IPRA Consolidated Review and relevant IPRA certificates and considered their findings and conclusions appropriate. In particular, the ONR assessment of the DNB PSR3 , and earlier HPB / HNB PSR3, supported the finding that NGL would benefit from undertaking analysis of events, developing learning and using this knowledge proactively to manage ageing and obsolescence across the licensee’s fleet.

89. The ONR assessment of the AGR PSR3 codes and standards review was conducted during the HPB / HNB PSR3 assessment. Recommendations from that assessment, which were also considered applicable at DNB, were captured in a regulatory issue and were being managed through normal regulatory business.

90. The DNB PSR3 submissions present a historical view of the performance of systems over the previous PSR period. ONR considered there was little evidence presented that this operational experience had been reviewed in totality to either provide confidence in the current arrangements or identify areas where C&I ageing



mechanisms were not fully understood. In line with the recommendation raised previously in relation to the assessment of HPB / HNB PSR3, ONR recommend that NGL consider providing further information in subsequent PSR3 submissions relating to C&I ageing mechanisms. It was noted that due to the timing of the production of the PSR3 submissions there was little opportunity to incorporate improvements recommended from the HPB / HNB PSR3 assessment into the DNB PSR3 submission.

91. There was little information in the PSR3 submissions relating to control and instrumentation systems and equipment important to safety. However, additional evidence provided by the licensee on a number of sampled systems demonstrated that arrangements for the management of ageing and obsolescence resulted in the necessary action being taken to maintain equipment reliability and ensure the safety case was maintained.

92. ONR concluded that NGL’s through life management arrangements for the nuclear significant systems; such as the fuelling machine, single channel trip system and data processing and control systems, has resulted in replacement equipment being identified and arrangements were in place to ensure units were in stock to take the station to the end of life. ONR considered this to be an adequate situation and a demonstration that the procedures in place to manage ageing and obsolescence have resulted in an improved position regarding the availability of C&I equipment.

Chemistry (Ref. 14) 93. While ONR identified a number of recommendations based on the submitted PSR

information, ONR judged there to be sufficient evidence within the suite of PSR submissions, supporting documentation, responses to queries and visits to station and NGL Barnwood to be able to support acceptance of PSR3 for DNB for the period until January 2028.

94. Overall, ONR judged that the approach, process and scope applied for PSR3 of DNB was adequate and in some aspects an improvement over the PSR3 process applied for HPB and HNB. However, ONR judged that the adoption of PLEX based recommendations was poorly executed, and it remained unclear as to which PLEX based findings had been captured by PSR3. Importantly, ONR also judged that some PLEX based findings important to safety were not captured by PSR3 processes.

95. Of the six DNB specific category B recommendations identified, ONR judged that one was relevant to chemistry. It was recognised that the autoclaves at DNB were important for predicting degradation of high temperature steel specimens and therefore important for substantiating future operation of the boilers and they were currently operating at an ageing factor behind that of the reactor. The recommendation sought to improve the reliability of the autoclaves. ONR agreed with this recommendation and its relative importance for substantiating the safe future operation of DNB and noted that NGL had already started to improve the reliability of the autoclaves.

96. On balance, while ONR noted some minor shortfalls for the review of codes and standards relevant to chemistry for DNB, based upon the previous ONR assessment and information gleaned from PSR3 queries and other strands of assessment ONR was content that NGL had appropriately reviewed codes and standards relevant to chemistry.

97. Based upon the assessment, ONR was satisfied that while historical primary chemistry control related to graphite had been poor, there was an improving trend with notable



improvements on R22 with R21 predicted to follow. Additionally, ONR was content from interactions with station that the root causes behind chemistry non-compliance had been identified and have either been rectified or there are sufficient plans in place to address these, with investment appropriately captured by TLMS documents and accounted for by the medium term investment plan.

98. ONR noted that the graphite weight loss safety case was heavily reliant upon FEAT-DIFFUSE6 modelling and PLEX identified boiler modifications. As such, ONR judged that NGL should demonstrate the chemistry assumptions, sensitivity, data input and link to the chemistry safety case.

99. ONR acknowledged that the PLEX identified boiler failure protection modifications cited in the PSR3 submissions to support continued safe operation over the period were captured in relevant TLMS documents and investment plans. However, given these modifications were important to safety, were relied upon in PSR3 submissions and have been subject to delays, ONR judged that these should be implemented within the original timescales, by the end of the 2021 statutory outage, to support future safe operations.

100. Based upon the assessment ONR was satisfied that primary chemistry control related to boilers was being appropriately managed. While secondary chemistry control had been less well controlled (specifically in relation to dissolved O2), ONR acknowledged this was an improving trend, with station focus and investment to improve chemistry control in the future.

101. Chemistry control for the pressure vessel cooling water (PVCW) system at DNB was demonstrated to be very good from ONR’s sample. ONR noted that minor perturbations in chemistry control (well below action levels) had been proactively identified. Additionally, plant appeared to be largely in good condition. Where plant monitoring had caused issues for the PVCW, ONR noted that sensors had been replaced or were ready to be replaced as required. ONR was therefore satisfied that the station was demonstrating appropriate control of chemistry and plant condition within the PVCW system and going forward, while safety case improvements had also been made in respect of this system.

102. ONR considered that while the provision of a supporting evidence report for the discipline review was an improvement on PSR3 of HPB and HNB in terms of presentation of actual chemistry data, it did not always fulfil its main intent of identifying evidence of chemistry parameters important to safety, providing a discussion of issue root causes and identifying remedial actions taken (over and above that already discussed in the main Discipline Review). While ONR had been able to gather this information from visits to station and during outage inspections for areas focused upon within the assessment, this was less apparent for the remainder of systems important to chemistry presented within this report.

103. During the assessment of PSR3 of HPB and HNB, ONR considered whether the PSR process had sufficiently considered the effect of chemistry in faults. NGL highlighted that chemistry in fault progression hadn’t been considered explicitly as part of PSR3, stating that the relevant SCHR had included the review of all significant safety cases explicitly or been judged to be of low risk. However, ONR noted that the SCHRs provided for PSR3 of DNB had not yet covered all systems, remained at a high level and did not consider chemistry effects during accidents. Weaknesses in the SCHR process were being addressed through a generic assessment finding and issue. The specific chemistry concern was being addressed through a regulatory issue raised initially for HNB / HPB.



104. While ONR recognised a number of challenges relating to plant condition across targeted systems from its assessment, ONR was satisfied that NGL had identified the main chemistry risks and degradation mechanisms related to these. Additionally, where plant condition was challenged, ONR was satisfied that improvements had either been implemented or there were appropriate plans in place to address these.

105. ONR recognised improvements to DNB safety case documentation with regard to the visibility and consistency of chemistry parameters, and based on discussions with NGL ONR was satisfied that remaining shortfalls will be addressed to improve expectations in line with modern standards and good practices. Similarly, ONR was content NGL has appropriate processes to review technical governance important to chemistry.

106. Based on its assessment ONR was content that sufficient evidence had been provided to demonstrate the adequacy and effectiveness of arrangements for managing both chemistry control and chemistry impacts on the safety case until the next PSR or end of station life.

Graphite (Ref. 15) 107. Whilst ONR identified a number of findings and recommendations through its

assessment of the DNB PSR3 submission and the general management of the graphite core, ONR considered the PSR adequate to support the operation of the station for the next PSR period.

108. The situation with graphite is constantly changing as the models are updated and the graphite weight loss database is extended after each periodic shutdown inspections. As a result, most parts of the PSR3 relevant to graphite were already out-of-date when ONR reviewed it. ONR therefore considered the information provided in the PSR3 documents and more up-to-date information from recent meetings and periodic shutdowns to obtain a clearer view on the state of the graphite core and the relevant safety cases.

109. At DNB, graphite weight loss is likely to be the most significant damage mechanism for the graphite core. The leading reactor, R22, has an estimated active core weight loss (ACWL) of around 7% in 2017. This compares to the current limit of 8%, giving a margin of only 1%. NGL has recently submitted a proposal to justify raising this limit to 10%. This proposal was being considered separately by ONR at the time of the PSR3 review. Consequently, ONR considered the 8% limit as a baseline for the assessment. It was likely that plant modifications would be required to support operation beyond 10% ACWL.

110. NGL updates the ACWL calculation at every three-yearly periodic shutdown and provides an estimate for the three subsequent operating years. Knowledge of the ACWL relies on a computer model called FEAT-DIFFUSE 6 and on materials data measured from ‘trepanned’ graphite samples. These samples are small cylinders of graphite which are retrieved from the graphite core by using a drilling tool during periodic shutdowns. Due to their relatively high dose, the subsequent analysis of these samples is potentially hazardous and requires designated equipment at NNL. However, the materials data provides an important source of information for the ACWL models. These samples must therefore be analysed and implemented into the graphite weight loss database in a timely manner after the outage. This should ensure that the ACWL limit is not inadvertently breached once the reactor is returned to service and is examined by ONR during outage permissioning.



111. With regards to graphite weight loss, ONR noted the need for continuing careful assessment of the graphite weight loss, supported by regular sampling of core properties using trepanning. ONR considered the calculation of graphite weight loss to be a process containing a number of uncertainties and currently considered that the long term operation of DNB could only be justified by the implementation of system improvements that would allow new limits on the graphite weight loss to be justified.

112. In recent ONR reviews, gas chemistry control had been deemed to be requiring improvement. NGL has addressed ONR’s concerns to some extent by modification of the gas bypass plant and of the chemistry processes. However, ONR noted that adequate chemistry control of the gas primary coolant is required to ensure that the graphite weight loss models predicting ACWL remain conservative.

113. The core temperatures were calculated by a computer program called PANTHER, which was developed and maintained by NGL. Although the PANTHER code was reviewed and validated in 2005, there had not been any new review of the graphite temperatures since. ONR considered that it was important to ensure that the assumptions made in the models remain valid and the graphite temperature should be reviewed sufficiently regularly to ensure that any unexpected trend is identified early. The following finding was raised:

ONR-DNB-PSR3-07

NGL should re-review the long-term steady-state temperatures in the graphite core and ensure that they continue to be reviewed with sufficient regularity to ensure that any unexpected trend is identified early.

114. To support the seismic safety case for the graphite core, NGL produced an assessment considering an equivalent 15 full power years of operation (fpy) in 1997, which predicted that failure of the reflector bricks could occur during a seismic event after an equivalent 11.5fpy. A subsequent analysis in 1999 provided revised safety margins in excess of the minimum requirement up to 15fpy. The core burn-up equivalent to 15fpy was reached in June 2017 for R22 and was predicted to be reached by the end of 2017 for R21. ONR was concerned that the current analyses supporting the seismic safety case did not consider operation beyond 15fpy.

115. On that basis, ONR wrote to NGL (Ref. 24) to request that it provided a demonstration before the end of 2017 that the 1997 and 1999 seismic analyses did not give an optimistic or inadequate prediction of the likely seismic response of the core, in the light of newer materials property data and greater knowledge developed from seismic analyses of the other AGR power stations. This would be necessary by the end of 2017, when other safety cases concerning the core restraint and core support had been revised. A short term seismic safety justification for the graphite core has now been received and is being reviewed by ONR.

116. ONR also requested a commitment from NGL to develop a full revised category 1 safety case with modern standards of stress analyses and whole core modelling for DNB. Such safety cases exist for the other AGRs. DNB is alone in not having such analysis. The reasons for this are that, the core irradiation lags behind that of the other stations and NGL has linked the production of revised safety case to the occurrence of stress reversal in the graphite, which may not occur at DNB for some years. This was viewed as essentially an arbitrary decision and ONR considered that NGL should have an up-to date category 1 safety case for the graphite core, as at best the existing case was spread over several documents and did not reflect new standards of stress analysis and modelling that were now possible.



117. These requests were also repeated in the following finding:

ONR-DNB-PSR3-08

NGL should: - Provide a shorter term seismic safety justification for the graphite core. This should consider stress margins, particularly in the key/keyway area, and ensure no control rod control rod obstructions could occur within a current period of operation of the reactors. - Inform ONR of the time necessary to produce a safety case that includes full whole core modelling and associated stress analysis for DNB.

Fuel Safety (Ref. 16) 118. Overall, ONR considered that, from a nuclear fuel safety perspective, NGL provided a

suitable periodic review for DNB against the requirements of LC 15. However, in coming to this conclusion ONR found it necessary to carry out a significant amount of work outside of the PSR3 submission and ONR therefore considered that the submission could be substantially improved and hence fell short of expectations.

119. The AGR fuel topic was relatively mature given there were 14 reactors in operation with up to 40 years life behind them. DNB was the oldest design having been the first AGR commissioned for construction. As a result the fuel and core design varied from the rest of the AGR fleet to some degree, though the main issues were the same. Throughout the AGR operational period the fuel design has evolved based on operational feedback and data from post-irradiation evaluation.

120. ONR found the performance of DNB with respect to fuel failures in normal operation to be adequate. This was evidenced by the decreased and now low fuel failure rate compared to that seen in the period between 2000 and 2010. This improvement had been brought about by changes in fuel design established specifically in response to fuel failures in normal operation caused by pin-brace interaction.

121. Slow progress had been made regarding the implementation of a replacement coolant gas activity monitoring system, and the stated delivery dates were extending and there had been inconsistencies in the plans provided. This system was used for monitoring of primary circuit radioactivity and was therefore a means of confirming the fuel cladding integrity in the reactor. NGL identified that the project delivery of this system was poor but elected not to raise a finding as the work was already planned. ONR raised a recommendation to track the delivery of this upgrade.

122. Although the ongoing fuel failure rate at DNB was now adequately low there was failed fuel remaining in storage on site in the decay stores and fuel storage pond. The management of failed fuel was being actively pursued through a fleet critical programme within NGL and was a matter of high priority. Through ongoing interactions with NGL, ONR has sight of this recovery programme and judged that adequate progress was being made with respect to DNB within the fleet wide constraints. ONR therefore considered that the arrangements for management of failed fuel disposals at DNB were adequate.

123. As well as looking back at the recent operational history, PSRs should look forward to the next ten years of operation, and systematically review the whole remaining life of the facility. Within the submission, lifetime issues were confronted through a discipline focused review which included a TLMS for the fuel system. The TLMS was generally aligned with the ONR expectations with respect to lifetime management but was



heavily focused at the organisational approach needed towards end of operating life. ONR considered that the TLMS was an important and useful document and formed a substantial part of the PSR submission in terms of looking forward and learning from the past success and failures. The TLMS made recommendations and provided an outline forward plan at an AGR generic level, which therefore applied to DNB. Given the value in the TLMS, ONR will track the delivery of the work proposed.

124. A separate assessment note covering Criticality Safety was produced in support of this assessment. This supporting assessment identified no apparent shortfalls with respect to nuclear criticality safety. However, in order to draw this conclusion ONR found it necessary to sample the criticality safety case outside of the PSR3 submission. ONR also identified through interactions with NGL that the criticality specialists within the central support functions had not been consulted on the PSR submission. ONR recommended that the criticality safety case is summarised in the next PSR submission and relevant criticality specialists are consulted in the production of next PSR. In order to assess the condition of the plant and the implementation of the safety case ONR reviewed its records of system based inspections covering the fuel route facilities, including an inspection associated with fuel assemblies in 2016. Based on this review and combined with NGL’s own zonal walkdowns ONR considered that the plant condition and implementation of the safety case on site was adequate.

125. ONR was provided with a draft version of the fuel and fuel performance SCHR which was considered to be generally adequate. However, the document did not consider the findings of NGL’s TLMS, which was a critical review that in ONR’s view should be considered in the SCHR process. Since this SCHR was in draft at the time of the review, ONR recommended that the SCHR was issued and the actions addressed.

Internal Hazards (Ref. 17) 126. ONR judged that the PSR3 along with the new normal business processes (ZWs and

SCHRs) were in line with the requirements of LC15 and the guidance presented in ONR and IAEA guidance documents. ONR was broadly satisfied with the claims, arguments and evidence provided within the Licensee’s submission and considered that an adequate review of internal hazards for DNB PSR3 had been undertaken but noted some areas for improvement.

127. ONR sampled the overall PSR submission, but focussed primarily on the key parts of the PSR that documented the review for internal hazards, which was presented in the SF7 Report, Zonal Walkdowns and the Safety Case Health Reviews. ONR also carried out a ‘deep-slice’ review of three hazards – fire, cold gas release and missiles.

128. Overall, ONR considered the SF7 and the SCHR had; adequately reviewed the fire safety case, recognised the work that was being undertaken to develop the Long Term Fire Safety Case (LTFSC) to ensure risks are reduced ALARP and formed the basis of an adequate approach to PSR.

129. ONR noted that the SCHR at HPB / HNB challenged the validity of the modelling of cold gas releases. A condition report was raised to review the modelling at HPB / HNB and share the findings across the fleet. ONR noted that this review had been completed. ONR recommend that the review of cold gas release dispersion modelling that was planned at DNB (following the finding from HPB/HNB), should also consider whether the recent installation of the flooding protection sea wall had any impacts on the safety case.



130. Based on its sample, ONR considered the SCHR, SF7 and the zonal walkdowns adequately reviewed the Cold Gas Release hazards to ensure risks were reduced ALARP and formed the basis for an adequate approach to PSR. However, it was disappointing that there has only been one set of SCHRs and Zonal Walkdowns conducted so far at DNB, so it was not clear at this stage how effective these normal business processes will be in the longer time.

131. The SCHR had identified concerns with regards to the integrity of substantiation within the air receiver safety case arguments. The Initial judgement considered the likelihood of air receiver failure as low but recommended that the potential threat be considered further, focussing on the reactor building in general and on the Steam Release Reactor Trip (SRRT) air receivers in the boiler house in particular. The SCAP process was followed for the missile impact hazard; this resulted in an IJCO which required the installation of temporary fire protection for the SRRT air receivers within the boiler house and a commitment for permanent fire protection to remove the safety case anomaly. During a visit to DNB, ONR inspectors visited the boiler house and confirmed that the permanent fire protection had been installed which removed the safety case anomaly.

132. The SCHR stated that the effects of combined / consequential hazards arising as a consequence of fire, extreme wind, steam release, hot gas release and seismic had been considered within the relevant initiating hazard safety case. ONR confirmed that as part of its review of the LTFSC, that missile generation arising as a consequence of fire had been considered.

133. Based on its sample, ONR considered the SCHR and SF7 adequately reviewed the missile impact hazards to ensure risks were reduced ALARP and formed the basis for an adequate approach to PSR.

134. There were no category B recommendations identified at DNB that were relevant to this assessment but there were three NNBRs raised under SF7 that were considered relevant to internal hazards. In addition, a number of issues were identified by NGL via the SCHRs or zonal walkdowns that were relevant to internal hazards. These were actioned through routine NGL processes.

135. The NNBRs and other issues identified during walkdowns and SCHRs were subject to normal business processes which enable tracking to completion. ONR noted however, that they were subject to resource pressure, but considered they were being appropriately addressed. ONR gained confidence in that the Hazard Governance Board had responsibility to address shortfalls in hazard arrangements.

136. Based on its sample ONR considered the issues and recommendations had been adequately sentenced. Apart from the SCAP initiated for air receiver failure, ONR considered the other issues raised were of relatively low priority and were being addressed appropriately via normal business processes.

External Hazards (Ref. 18) 137. Overall ONR was satisfied from an external hazards perspective that the DNB PSR3

submission was adequate and supported the justification of continued safe operation of the facility for the period 2018-28.

138. ONR noted that the PSR covered the next 10 years of plant life but updates of several of the external hazard safety cases to cover this period were as yet incomplete, or not



started. ONR will monitor the progress of these safety cases through routine regulatory interactions.

139. NGL had conducted a number of hazard review workshops to feed into a supporting information report for SF7. ONR noted that at the start of each external hazard review section those involved in the workshop were listed with some indication of their role. However, ONR recommended that the hazard review workshop process should be revised to identify the SQEP roles required for the hazard review workshops and identify who fulfils each role in each review, providing evidence for their SQEP status.

140. The PSR discussed key outcomes from the DNB post-Fukushima programme of work (Japanese Earthquake Response (JER) on the hazard reviews in order to confirm that the relevant risks were acceptable and ALARP. ONR considered the JER programme to be an example of good practice by the licensee and at a practical level the JER work clearly reduces the risks.

141. SF7 summarised the position with respect to design basis (DB) and beyond design basis (BDB) analysis of external hazards at the time of writing. ONR received updates on the current position of the analyses and noted that in general full deterministic or probabilistic assessments had not been done for BDB events, although some assessment (mainly deterministic based on the safety margins for DB events) had been done for seismic events, external flooding and industrial hazards.

142. The failure to model BDB external events was a shortfall against the ONR SAPs and ONR considered this a fleet-wide issue, which required addressing systematically in the licensee’s processes.

143. ONR noted that the HPB / HNB PSR3 recommendation on implementing the revised corrosion and ageing management technical standard (CTS/031) was also considered an applicable category B recommendation for the DNB PSR3. However ONR was concerned with the timeliness and rigour of the implementation of CTS/031.

144. ONR also noted the category B recommendation concerning three significant repair/replacement tasks which had the potential to affect the plant’s ability to withstand various external hazards such as precipitation, high winds and extreme ambient temperature (EAT). ONR observed during the 2017 statutory outage that significant repair work was ongoing to the building envelope on a number of facilities to support the integrity of facilities into decommissioning. Timely completion of these tasks was important and the licensee’s process for Cat B recommendations had ensured that this was done.

145. The PSR stated that the seismic qualification of specified tanks had been progressed as part of NGL normal business. ONR reviewed the progress to date and sampled some of the assessments. ONR found that all of the specified steel tanks had been assessed for corrosion and checked for compliance against the seismic assessment. ONR considered that NGL DNB had addressed this issue with commendable rigour.

146. The PSR noted that potentially significant cliff-edge effects arise when temperatures exceed the operating range of claimed equipment required for post-trip cooling. It stated that cliff-edge effects were mitigated by operator actions, forewarning of EAT and the thermal inertia of buildings and equipment housings which allowed sufficient time for operators to act. However a SCHR identified areas of the EAT safety case that were likely to need work when the safety case was updated to address specific concerns, principally in the areas of a lack of explicit derivation local temperatures within buildings, a lack of functional requirements of protective/ mitigating equipment



post-EAT and a reliance on operator actions without any human factors assessment. However no immediate actions were identified by the SCHR and EAT would probably not be revisited until the next cycle of SCHRs at the earliest. ONR considered that the shortfalls identified in the safety case; especially no calculation of the indoor temperatures arising from EAT should be addressed sooner, and ONR would be monitoring adequate progress through routine regulatory interactions.

Fault Studies (Ref. 19) 147. ONR judged, from a fault studies perspective, that the normal business processes

described in the submission which were claimed to fulfil the requirements of a PSR were sufficient to ensure the periodic review of the safety case and hence were in line with the requirements of LC15. These processes broadly followed the guidance presented in the ONR SAPs and TAGs, and IAEA guidance documents; however, ONR identified some shortfalls against this guidance.

148. ONR identified that no category B recommendations were relevant to this assessment, but two NNBRs were relevant and were reviewed further.

149. ONR did not find the structure and presentation of the PSR conducive to understanding how the requirements of the PSR were being met, with the arguments presented in each Safety Factor report often not specific enough to relate activities to the requirements. The assessment therefore sought evidence to provide confidence that the following activities had been adequately performed:

A review of how Deterministic Safety Analysis was performed, including the deterministic rules and computer codes and standards.

A review of the safety case against operating experience. A review of how safety cases were produced, controlled, and implemented

(safety case management) taking in international best practice. A systematic review of the safety case.

150. Through the review against IAEA requirements and WENRA Reference Levels, in ONR’s opinion, NGL had conducted a searching review against modern standards and met the requirements of the SAPs in relation to the deterministic safety rules; however there may be a shortfall in the nuclear safety principles (NSP) against IAEA requirements for which ONR recommended further review in this area. ONR considered that in benchmarking against Sizewell B’s nuclear safety assessment principles, and reviewing the NSPs against the WENRA Safety Objectives NGL demonstrated that reasonably practicable improvements had been sought against relevant good practice.

151. ONR judged that evidence demonstrated that the safety analysis was being reviewed with consideration of the potential for aging modelling techniques to undermine the safety case; however ONR considered that there was no evidence to suggest that reasonably practicable improvements to the modelling techniques - when compared to modern analysis techniques - had been considered.

152. ONR reviewed three processes which contribute to the review of the safety case with respect to OPEX:

Organisational Learning - Identify Relevant OPEX SCHR - Assess Impact of OPEX on the safety case SCAP - Implement Improvements



153. The review of the process specifications and evidence of their application found that the processes were generally adequate with respect to the requirements of the ONR SAPs; however an improvement to the SCHR process was recommended to require that the OPEX search was documented, so as to provide evidence that the review had been performed, and the extent of the review.

154. The lack of a clearly presented set of arguments and evidence relating to the review of the maintain design intent and modifications processes within the PSR made the assessment of this area more challenging. ONR sampled the reviews of the modifications process in a proportionate manner in order to gain some level of confidence that adequate reviews had taken place, and that the process was sufficient to ensure safety over the next PSR period.

155. From the evidence reviewed, ONR judged that the normal business reviews of the modifications process were adequately fulfilling the requirements of the PSR, and that they were sufficient to ensure safety over the next PSR period.

156. ONR reviewed NGL’s arrangements for the systematic review of the safety case (SCHR process) with the expectation that it should consider the following aspects:

The cumulative effect of modifications, Aging and degradation of the plant, Results of examination or testing, OPEX and Research findings, Modern analysis methods and best practice design.

157. Based on consideration of these, ONR expected that the reviews should consider whether the safety case, its underlying assumptions, and its associated limits and conditions remained appropriate, and whether any reasonably practicable improvements could be made.

158. ONR found evidence that the process was taking account of the cumulative effect of modifications, the aging and degradation of the plant, modern analysis techniques, and the results of examination and testing. There was also evidence that the reviews were taking account of relevant OPEX, but as noted earlier, the documentation of the extent of the OPEX search and whether it was consistently performed was lacking.

159. The SCHR process did not review the operational limits and conditions, embodied in the NGL Technical Specifications (Tech Specs), associated with the respective safety cases to ensure that they remained valid in light of any changes or challenges which the safety case may face.

160. The SF11 report recognised and discussed the shortfall and concluded that the periodic review of Tech Specs was not required as they were reviewed when they were updated. However the same document stated that 43% of the Tech Specs had not been updated since their introduction over 10 years ago but NGL also contended that there had been some generic reviews of the Tech Specs in this time, and hence no further review was required. ONR disagreed with this position, and considered that this represented a shortfall against the requirements of the SAPs and a PSR. In order to have confidence that the Tech Specs will be reviewed over the next PSR period there needed to be adequate arrangements in place to ensure that a review will take place. The following finding was raised to address this shortfall:



ONR-DNB-PSR3-09

NGL should implement adequate arrangements to ensure the periodic review of the Technical Specifications.

161. As raised during the previous PSR3 assessment, finding HPB HNB-PSR3-002, was

equally applicable to Dungeness B. One of the requirements for a PSR was to review the degree to which the safety case conforms to modern standards and good practices. Within the PSR3 submission, reviews had been conducted against current codes and standards and relevant good practice for many areas. However, the submission did not directly address relevant good practice in the context of the levels of safety being achieved by modern plant designs and whether it would be reasonably practicable to close or reduce any gaps.

162. Whilst reviews against modern codes and standards go some way towards this, it is not clear that they will have identified all reasonably practicable improvements. Similarly it was also acknowledged that past PSR’s would have considered this aspect to some degree; however relevant good practice has continued to develop in this respect. The following finding was raised:

ONR-DNB-PSR3-11

NGL should conduct a review of the safety performance of the plant design against the relevant good practice provided by modern plant designs to identify any further reasonably practicable improvements.

Probabilistic Safety Analysis (PSA) (Ref. 20) 163. Overall ONR was satisfied, from a PSA perspective, that the licensee had carried out

an adequate periodic safety review of the Dungeness B nuclear power station safety case to justify continued safe operations at the facility for the period 2018-28. Some gaps had been noted in the assessment compared to ONR expectations, SAPs, and the IAEA PSR guidance, although ONR did not consider these significant. ONR acknowledged that normal business arrangements through NGL’s PSA governance and oversight arrangements were adequate to close out the issues identified in the PSR.

164. Consistent with IAEA guidance the scope of the ONR assessment considered whether:

the PSAs are consistent with modern standards and adopt relevant good practice;

the PSAs reflect the actual plant and safety case; and the PSAs results indicate that risks are broadly acceptable or are tolerable if

ALARP.

165. The ONR assessment was structured around the overall claim and supporting arguments for SF6, and with the head document (Ref. 2) information that related to PSA. SF6 and all the PSA aspects of other safety factors were reviewed including an assessment of the cross-linkages to various processes discussed in other safety factors which had relevance to input data for PSAs.

166. The scope, methodologies and extent of the AGR PSAs had been reviewed in SF6 and it was clear that NGL had been making progress through the completion of ownership reports in order to gain insights from the various pilot PSA studies and to understand their implications for the AGR fleet. However, the report noted that some



ownership reports had not been completed, although they were on track to complete in the near future. NGL had not submitted these ownership reports at the time of the ONR assessment. However, ONR will track the progress of these ownership reports through normal interactions with NGL. Some of these issues were being tracked through existing ONR regulatory issues.

167. SF6 concluded that there was found to be an absence of station OPEX influencing the input data for the fuel route PSA; however NGL noted that adequate measures were in place to progress the fuel route PSA towards meeting the expectation of international guidance and NGL processes. ONR noted that the AGR fuel route PSA was in the midst of an extensive revision including upgrading the models and transferring them to a modern PSA computer code. As part of this larger programme, and as part of ongoing ONR interventions, increased use of station OPEX in the upgraded fuel route PSA was a topic that was being tracked at regulatory interactions for PSA. Thus, in ONR’s opinion, the measures that NGL noted for PSR3 were adequate to address the identified shortfalls in the fuel route PSA for DNB. When fully implemented, these measures should help to progress the fuel route PSA closer to ONR expectations.

168. ONR noted that the SF6 report provided the PSA results for the reactor, fuel route facilities and radioactive waste facilities. All the PSA results are reported to fall in the Broadly Acceptable or Tolerable if ALARP regions for each of the three PSAs.

169. ONR SAPs set the expectation of comparing risk against the numerical targets. All the results are greater than the basic safety objective (BSO), but less than the basic safety level (BSL). As per ONR SAPs, given that the risks were less than the BSL, and given that the report referred to ALARP discussions and future areas of work (e.g. hazard PSA), ONR considered that the intent of SAPs were met.

Leadership and Management for Safety (LMfS), Quality and Supply Chain (Ref. 21) 170. Overall ONR was content, from an LMfS, Quality and Supply Chain perspective, that

NGL’s review of its management of safety arrangements set out in the PSR met relevant good practice and that it had taken into account relevant standards and guidance. ONR was also content that the review had been subject to appropriate due process and that there had been appropriate independent oversight throughout. ONR identified some shortfalls in NGL’s review of the effectiveness of its arrangements. In judging whether this represented a real gap ONR took cognisance of a range of ONR’s interventions which provided sufficient evidence that NGL’s arrangements were satisfactory.

171. The ONR assessment focused primarily on SF10 - Organisation, the Management System and Safety Culture and also drew on evidence from parts of SF 8 - Safety Performance.

172. The focus of PSR3, including SF10, was on the adequacy and effectiveness of normal business arrangements to ensure nuclear safety and this provided the focus for the assessment. ONR’s assessment was undertaken in accordance with the approach outlined in ONR guidance and in addition ONR sought further information and clarification during two visits to the station.

173. During the assessment ONR also utilised information from the ongoing programme of interventions with the station and the licensee’s corporate centre. It was clear from these engagements that NGL’s arrangements for the management of safety had continued to evolve since the June 2015 cut-off date for inclusion of information in the



PSR and many positive changes had been made; for example in strengthening governance and oversight arrangements at both station and fleet level.

174. ONR noted that the PSR submission included a comprehensive description of the corporate arrangements which underpinned station activities and that sufficient supporting evidence was provided to show how NGL’s corporate arrangements were implemented at DNB and how oversight was provided at both station and fleet level. Evidence was presented within SF8 to show how performance data was utilised to drive improvements. The review demonstrates that there had been a significant improvement in the overall safety performance at DNB over the last PSR period.

175. The description of NGL’s arrangements and their review of implementation in the PSR submission, together with information from ONR’s on-going engagements and visits to site to discuss arrangements, provided assurance that NGL’s arrangements for the management of safety were adequate.

176. In judging the adequacy of the PSR against relevant good practice, ONR identified some areas where it would expect more robust evidence of effectiveness. Following assessment of the HNB / HPB PSR3 report (which preceded the DNB review), a generic finding was raised by ONR relating to the presentation of evidence to demonstrate adequate and effective processes. ONR had raised a regulatory issue with respect to this finding and NGL’s progress is being monitored through ongoing PSR engagements.

177. ONR raised a recommendation relating to the identification of critical knowledge gaps and have suggested that ONR considered including ‘Operations’ resilience and the delivery and oversight of training within ‘Operations’ in the site intervention plan.

Radioactive Waste Management and Decommissioning (Ref. 22) 178. Overall ONR was satisfied that, with respect to radioactive waste management and

decommissioning aspects, the PSR3 had been conducted in accordance with relevant good practice and adequate arrangements were in place to support the continued operation of Dungeness B power station.

179. From a radioactive waste management perspective, the ONR assessment focussed on:

Adequacy of the radioactive waste management plans and arrangements to manage the radioactive waste generated;

The current condition of the radioactive waste management facilities and systems and TLMSs to enable continued safe operation for the period covered by this PSR.

180. From a decommissioning perspective, the periodic review recognised that the DNB site will transition from power generation into defuelling at the end of the 10 year periodic review period. Therefore, as part of the scope for the assessment ONR focussed on:

Establishing there were adequate arrangements in place for the review of the decommissioning strategy and decommissioning plans;

Preparations for the transition from end of generation, defuelling and into decommissioning;

181. At a corporate level, the Radioactive Waste Focus Index (RWFI) was used to monitor a range of key performance indicators related to low level waste (LLW) management, including the volumes of LLW stored on the reactor sites. The poor performance of



Dungeness B against this RWFI triggered a peer assist during 2016, which involved radwaste engineers from other reactor sites reviewing the current processes and procedures at Dungeness B to identify areas for improvements. Based on the results of this peer assist and a recent ONR compliance inspection, a twelve month improvement plan had been developed.

182. Overall, whilst there were shortfalls identified in SF14 in relation to the management of radioactive waste these had been captured by the improvement plan developed to support an extant regulatory issue.

183. As part of the site visit, NGL provided a detailed update of the planned improvements to the liquid radioactive waste systems, including work which had been completed and planned timescales for the future work. From the facility walkdown it was clear that improvement works had progressed since the production of the PSR3 documentation.

184. Based on the evidence sampled, it was ONR’s opinion that should the work described within the TLMS and system review be completed as planned, and there was continued review of the condition of the active effluent treatment plant in line with the existing arrangements, then adequate arrangements were in place to enable the continued safe operation of the liquid radioactive waste facilities for the period covered by the PSR.

185. Whilst there were a number of shortfalls identified in relation to the decontamination centre and the management of LLW, ONR recognised that there was an appropriate improvement plan in place which was managed through a regulatory issue. Therefore, based on the evidence sampled ONR considered that NGL had provided an adequate demonstration that the solid radioactive waste management facilities and systems had adequate arrangements in place to enable continued safe operation for the period covered by the PSR.

186. In preparation for decommissioning, NGL had established two project teams at a corporate level; the end of generation project team is tasked with optimising fuel use and developing the safety case strategy for shutdown and defueling. A second project team is focussed on the deconstruction covering the post-operational clean out and decommissioning requirements. DNB is currently planned to be one of the later AGR stations to enter into defuelling and decommissioning and will therefore benefit from the experience gained from other AGRs. From a site perspective, current arrangements require a Site Decommissioning Group (SDG) to be established at least 3 years in advance of end of generation.

187. NGL recognised the potential for a Non-Elective Closure (NEC) prior to the establishment of comprehensive decommissioning plans. Operational processes will be adopted across site to ensure the safe state of the site is maintained until the appropriate decommissioning arrangements are in place. Through the maintenance of the NEC arrangements by the NGL corporate body, and the formation of SDG to support the preparations at the end of planned generation, it was ONR’s opinion that adequate arrangements were in place to manage the site in a NEC.

188. Based on the evidence sample, ONR considered that there were adequate arrangements in place for the review of the decommissioning strategy and decommissioning plans. ONR noted that preparations for the transition from end of generation, defuelling and into decommissioning was predominantly at a corporate level. However, taking into account that DNB is currently planned to be the last AGR station to shutdown, ONR considered this to be appropriate at this stage.



Radiological Protection (Ref. 23) 189. Overall ONR judged, from a radiological protection perspective, there to be sufficient

evidence within PSR submissions, supporting documentation, responses to queries and visits to station and Barnwood to be able to support acceptance of PSR3 for DNB for the period until January 2028.

190. As part of their PSR review the licensee identified a number of recommendations, which were classified based on their safety significance now and through the next PSR period. None of these related to radiological protection and ONR was content with this conclusion.

191. While ONR noted the improvement in terms of the presentation of evidence for PSR3 of DNB, ONR found that the information analysed and presented continued to be primarily focussed on corporate radiological protection arrangements and lacked sufficient information specific to DNB. ONR was able to ascertain the station specific information from visits to station and Barnwood.

192. Overall, ONR judged that the process, approach and scope applied for SF15 of DNB was adequate but that improvements in the presentation of the evidence gathered and conclusions reached were required in future PSRs.

193. Based on the assessment ONR was satisfied that sufficient evidence was provided to demonstrate the adequacy and effectiveness of arrangements for radiological protection until the next PSR or end of life.

194. Although not discussed in the SF15 report there were a number of areas that were likely to have significant implications for RP at DNB over the remaining lifetime of the station and which were identified in other sections (SFs) of the PSR3 report. NGL RP fleet management provided assurances that, although the RP implications of these areas were not specifically covered in the PSR3 documentation, they had been considered and it was concluded that they would be accommodated within routine operational arrangements.

195. From the sampling exercise performed, ONR’s assessment of NGL’s consideration of and ability to deal with RP challenges at DNB in the future was that they had been considered by various different methods and that robust measures were in place to manage them.

196. Whilst ONR recommended that additional evidence be included within the approach taken to provide evidence from a radiological protection perspective in future PSR3s, ONR was content that this did not fundamentally undermine the PSR nor its conclusion that an adequate basis for continued operation had been presented.



Table 1 - DNB PSR3 Category B Recommendations

Safety Factor Recommendation Number

Title Planned completion

2 - Actual Condition of Plant Important to Safety

SF2 Rec 001 As part of both the TLMS and PLEX processes a review was carried out on the condition of safety related buildings. The most significant issues are listed below. All of the work is captured in the MTP or PLEX investment lists. 1. Repair / replace the Reactor Building Annulus Roof (DoN 351762). 2. Replace high level glazing on various buildings (DoN 351733). 3. Repair / replacement of internal & external cladding of the reactor building (DoN 351764).

End 2020

4 – Ageing & Lifetime Management

SF4 Rec 001 The DNB Autoclaves are used to provide corrosion monitoring for steel specimens representing components in the boilers. The autoclaves availability has been low during the PSR3 review period and the specimens have been exposed to lower durations of reactor operating conditions than the actual reactor running time. Additionally the autoclave controls are ageing and obsolete which is adding to the reliability issues and may lead to safety case challenges in the future.

January 2018

SF4 Rec 002 The POLARIS data logging system is used for the temperature monitoring of both reactor vessels and their internal components. The nuclear safety duty of POLARIS relates to compliance with Tech Spec temperature limits derived from plant design temperature/life usage considerations, monitoring functions in support of multi-legged safety case arguments, and operator trend displays of reactor parameters. In all cases the safety significance is considered to be sufficiently low that the POLARIS hardware and software design is adequate for the application; monitoring requirements can be satisfied by manual data collection albeit very labour intensive. The AIC data logging system forms part of the Alternative indication centre which allows plant monitoring from a single location in the event of the CCR being put out of service. The data logging system acts as a diverse source of key indication provided by the hardwired instrumentation. It also provides supplementary indications which are less important to safety. The POLARIS and AIC systems are obsolete. All the computer hardware and associated network interfacing are not only no longer produced, but are now no longer supported by any third party. The software is also no longer supported.

End 2020

SF4 Rec 003 The reliability of the EDG has been monitored over the last PSR period and with the implementation of various modifications and maintenance strategy changes the

End 2020





reliability has improved to 94.85%. To further improve reliability the focus is now shifting to replacement/refurbishment of the obsolete Engine Control and AVR panels. The cubicles and their contents are obsolete with extremely limited spares availability (only that which is on stock).

SF4 Rec 4 PSR2 raised concerns over the reliability of the MG sets, however, the original MG Sets and their control equipment remain installed and in operational use. The maintenance and operational procedures were enhanced within the PSR period to ensure increased reliability and therefore availability, following a reliability investigation carried out in 2006 (as detailed in ACIN 625493). Following a recent increase in the failure rate, a further ACIN (983301) has been completed to review the MG Set reliability. This investigation has identified that further enhancements are required to reduce the increased failure rate, including the reinstatement of a Condition Monitoring routine and requests for further operator training. The investigation also showed that the MG Sets and their control gear have now reached the point where they require upgrading/replacing in the next few years This shortfall refers to the following MG sets. a) 110V Safety Supplies MG Sets b) 110V Guaranteed Supplies MG sets and controls c) 415V Guaranteed Supplies MG Sets & Control gear

End 2019

SF4 Rec 005 As part of PSR2 concerns were raised against the reliability of the 275kV breakers as a result of two disruptive failures in the external electrical supply industry of Reyrolle OBR 60, 300kV Air blast circuit breakers. Personnel protection has been in place in the grid substation throughout the period however the review of the April 2014 phase imbalance event (See PSR3 Safety Factor 8, Section 5.4.3.3) by the Inspector General, noted the response to operating experience to be insufficiently rigorous and there were signs of insufficient general awareness of the links between outside grid disturbances and nuclear safety. This increased the focus on the vulnerability to loss of offsite power (LOOP) on station. The 2014 event also showed a need for a negative phase sequence alarm system.

March 2018



Table 2 – HNB/HPB PSR3 Category B Recommendations Applicable to DNB



1 - Plant Design SF1 Rec 001 The ongoing fleet implementation of the SCHR process requires appropriate process governance arrangements to be established

Closed by time of DNB PSR3 submission

2 - Actual Condition of Plant Important to Safety

SF2 Rec 001 Corrosion management is identified as an issue across the fleet. A new Company Technical Standard - Corrosion and Ageing Management (CTS/031) has been issued but is not yet implemented by stations, demonstrating a gap to this standard.

Awaiting agreement from Corrosion and Ageing Steering Group and the Corrosion and Ageing Working Group that CTS/031 is appropriately implemented at stations

3 – Equipment Qualification

SF3 Rec 001 The ongoing implementation of the Zonal Walkdowns and Zonal Based Views requires effective process governance and oversight arrangements to be established

Closed by time of DNB PSR3 submission

4 – Ageing & Lifetime Management

SF4 Rec 5 The recently implemented obsolescence strategy is relatively immature and requires increased focus.

28 June 2018



Table 3 – ONR DNB PSR3 Assessment Findings

ONR Finding Detail

ONR-DNB-PSR3-01 General Issues Database Number: 6109

NGL should review their SCHR process to ensure it is adequate to support the requirements of a PSR

ONR-DNB-PSR3-02 Civil Engineering Issues Database Number: 6110

NGL should carry out sample visual inspections of the rubber bearings that support the Pre-stressed Concrete Pressure Vessels, or provide an adequate ALARP justification for the current lack of such inspections.


NGL should clarify how the Equipment Reliability process is applied to the management of Civil Structures and should identify and rectify any compliance gaps.


NGL should develop a site-specific ageing management programme for safety significant civil structures that takes account of relevant good practice in IAEA Safety Guide ND-G-2.12.


NGL should develop and implement a lifetime strategy and ageing management programme for the Fuel Pond. The work should identify all relevant ageing and degradation mechanisms, review available options to address ageing and degradation, and define any reasonably practicable improvements to the inspection, monitoring, maintenance and repair regimes. Where appropriate, the programme activities should be included in the Maintenance Schedule.

ONR-DNB-PSR3-06 General Issues Database Number: 6114

NGL should ensure timely implementation the PLEX-identified boiler tube failure protection modifications.

ONR-DNB-PSR3-07 Graphite Issues Database Number: 6115

NGL should re-review the long-term steady-state temperatures in the graphite core and ensure that they continue to be reviewed with sufficient regularity to ensure that any unexpected trend is identified early.

ONR-DNB-PSR3-08 Graphite Issues Database Number: 6116

NGL should: - Provide a shorter term seismic safety justification for the graphite core. This should consider stress margins, particularly in the key/keyway area, and ensure no control rod control rod obstructions could occur within a current period of operation of the reactors. - Inform ONR of the time necessary to produce a safety case that includes full whole core modelling and associated stress analysis for DNB.



ONR Finding Detail

ONR-DNB-PSR3-09 Fault Studies Issues Database Number: 6117

NGL should implement adequate arrangements to ensure the periodic review of the Technical Specifications.

ONR-DNB-PSR3-10 Structural Integrity Issues Database Number: 6118

NGL to review the oversight arrangements for managing plant ageing (i.e. corrosion, particularly corrosion under insulation) on the Dungeness B site.

ONR-DNB-PSR3-11 Fault Studies Issues Database Number: 6119

NGL should conduct a review of the safety performance of the plant design against the relevant good practice provided by modern plant designs to identify any further reasonably practicable improvements.