- Site: Dungeness B
- IR number: 22-009
- Date: April 2022
- LC numbers: 28
Executive summary
Purpose of Intervention
This report records the findings of an intervention at Dungeness B Nuclear Power Station during the 2021 Reactor 21 (R21) statutory overhaul inspections for the post generation period. The intervention was undertaken in response to the licensee’s (EDF Energy Nuclear Generation Limited – NGL), request to reduce or defer a number of in-service inspection (ISI) activities. These inspections are no longer considered necessary for safety demonstration in response to the recent transition for Dungeness B Nuclear Power Station from operating to end of generation activities.
ONR has already assessed and accepted the licensee’s proposals to reduce the scope of ISI activities The purpose of this intervention was to confirm that the adequacy of the work conducted by the licensee complies with the requirements of Licence Condition 28: Examination, Inspection, Maintenance and Testing (EIM&T), and has addressed the commitments made within the Engineering Change.
The intervention also provided an opportunity to get an update on the site-specific progress being made with an ONR Level 2 regulatory issue raised in respect to corrosion management, necessary to address the Level 2 Regulatory Issue actions raised from the ‘Phase 1 Benchmarking Visit to Dungeness B Power Station as Part of the Corrosion Under Insulation and Concealed Systems Intervention’.
Interventions Carried Out by ONR
I undertook numerous on-site meetings and plant inspections with relevant staff from the licensee to determine the adequacy of the work being undertaken to comply with the requirements of Licence Condition 28. I concentrated my intervention on items I judged important to nuclear safety from a structural integrity perspective and related to the actions laid down within the existing Level 2 regulatory issue.
I sampled aspects of the corrosion programme and the statutory overhaul inspections for the R21 post generation period, including Pressure System Safety Regulation (PSSR) 2000 inspections, weld inspections and other safety related systems external to the reactor pressure vessel.
Explanation of Judgement if Safety System Not Judged to be Adequate
This section is not applicable on the basis that this intervention was not a safety systems inspection.
Key Findings, Inspector’s Opinions and Reasons for Judgements Made
Based on my observations and discussions with station staff, I am content that the licensee is fulfilling the requirements of the statutory overhaul inspections proposals for the R21 post generation period. At the time of my visit, no significant emergent issues with plant material condition were raised and no deviation from expected condition of the SSCs had been reported.
I am satisfied that the Pressure System Safety Regulations 2000 (PSSR) Competent Person (CP) is providing appropriate support and oversight to the licensee, in accordance with the PSSR statutory maintenance schedule and associated Written Scheme of Examinations (WSE). From my discussion with the PSSR CP, there appears to be appropriate engagement between the two parties which facilitates inspection, sentencing and remediation in accordance with the requirements of the PSSR.
I sought further information in response to an ongoing issue related to the presence of improperly fitted Safety Relief Valve bursting discs, which has resulted in a non-compliance with PSSR. Following the provision of further evidence, it is my opinion that this does not affect the post-generation operations for the next operating period of R21. The licensee is also taking action to address these shortfalls for R22, which following consultation with other ONR specialists, I am satisfied is being resolved appropriately. I have briefed the relevant ONR inspector currently reviewing the licensee’s management of PSSR compliance on this finding.
I am satisfied that the licensee is aware of and adequately managing the risk of water hammer that may lead to pressure system failure. The licensee staff that I engaged with were well versed in the fleetwide OPEX on water hammer and could demonstrate how the risks at Dungeness B are being managed.
From the information that I sampled, the licensee has demonstrated that it is making good progress on addressing the risk of corrosion related failures on site, in line with the corrosion management programme. Work undertaken in response to address the regulatory Direction for return to service has now been complete and the site continues to address the outstanding lower-priority inspection/remediation activities and has an adequate process in place to prioritise and sentence emergent defects. I consider that, based on my observations, there is sufficient information to update the existing regulatory issue and consider re-evaluation of the current Level 2 status.
During my visit, I discussed an issue related to structural cracking identified by the licensee during routine inspection of the fuelling machine support gantry. The licensee has issued a Justification for Continued Operation (JCO), until a Category 1 safety justification is in place (expected March 2023). I have conducted a high-level review of the JCO, and I am broadly satisfied that the licensee has adequately considered key factors related to the newly discovered defects and their impact on the safety case. I am content that the licensee has provided sufficient reasoning to demonstrate that risk is reduced ALARP in the period up until the Category 1 case is issued. In my opinion, this reasoning is soundly based, underpinned by enhanced inspection coverage, metallurgical understanding of the cause of cracking to demonstrate defects are dormant or very slow moving and demonstration of sufficient redundancy in the gantry design. Overall, based on the information I have sampled, I do not consider this issue to be likely to affect post-generation operation of the fuelling machine gantry within the remaining period of validity for the JCO (March 2023). After this date, justification for operation will be provided through the planned Category 1 safety case, assessment of which will considered through ONR’s normal regulatory business.
Conclusion of Intervention
I judge that, at the time of my inspection at Dungeness B nuclear power station, personnel were conducting their inspections in line with the R21 statutory overhaul inspections proposals for post generation period.
At the time of my sample inspections and from the information that I have reviewed so far, I am satisfied that the licensee’s programme for managing examination, inspection, maintenance and testing is adequate and aligns with the requirements of LC28.
I will continue to monitor the minutes from the remaining outage assessment panel (OAP) meetings to monitor for any emerging issues from the inspections that have yet to be completed and will respond to the ONR project inspector by exception, should any later findings undermine the judgements I have made thus far.
In my opinion, the licensee has performed the examination, inspection, maintenance and testing work to an adequate standard against the requirements of LC28. I consider that, in accordance with ONR guidance on the application of inspection ratings, a GREEN rating is appropriate for this inspection, warranting no formal action as a result of my inspection.