Office for Nuclear Regulation

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Dungeness B - Reactor 21 - LC28 Inspection - Structural Integrity

Executive summary

Purpose of Intervention

This report records the findings of an intervention visit to Dungeness B Nuclear Power Station (DNB) during the 2017 Reactor 21 periodic shutdown. The intervention was undertaken to confirm the adequacy of the work conducted by the licensee, EDF Energy Nuclear Generation Limited (NGL), to comply with the requirements of Licence Condition 28, examination, inspection, maintenance and testing.

Interventions Carried Out by ONR

I undertook on-site meetings and plant inspections with relevant staff from NGL and their contractors to determine the adequacy of the work being undertaken on Reactor 21 in complying with the requirements of Licence Condition 28. I concentrated my intervention on items I judged important to nuclear safety, focussed on structural integrity.

I sampled aspects of the inspection programme undertaken during the periodic shutdown on the steam and feed systems and other safety related systems external to the reactor pressure vessel. I also sampled aspects of the inspection programme undertaken on the metallic components internal to the reactor pressure vessel. 

Key Findings, Inspector's Opinions and Reasons for Judgements Made

I visited site approximately half way through the periodic shutdown. The status of the inspections showed satisfactory progress on the reactor external inspection programme, with 245 out of the 424 inspections completed at the time of my visit.

I sampled the inspection work that had been undertaken as part of the reactor external inspection programme, reviewing inspections completed and associated results. I was content that the work was progressing effectively, with inspection results sentenced appropriately. Weld and Flow Accelerated Corrosion (FAC) inspections were progressing to programme with no significant issues identified. Several areas of FAC remediation were ongoing; however these had been anticipated by DNB.

Inspection work on the boiler headers has progressed according to DNB’s plans, with no significant indications found. Emergent issues have included discovery of a socket adaptor and piece of swarf inside reheater header C4 and challenges in removing remote visual inspection equipment from reheater header D7. I consider that DNB has responded appropriately in both cases to resolve matters.

I viewed digital images from inspections of several reactor internal components and reviewed branch instructions that provided the scope of inspection. I consider that due process was being followed. No issues that could affect the planned work were apparent and no significant findings have been reported relating to the internal inspections to date.

I sampled the operation of the DNB’s Outage Assessment Panel (OAP) during my visit and by reviewing OAP minutes. I was satisfied that the OAP was following due process and that the inspection results were being reviewed appropriately.

I obtained an update on progress made at DNB in relation to their corrosion management program. I am encouraged that corrosion inspection and remediation work has continued throughout the current outage. I have requested additional information from the Corrosion Co-ordinator relating to a remediation plan for all significant corrosion (classified C1 & 2) on the most susceptible systems (known as CV1 & 2 systems), I have also requested the total number of C1 & 2 defects rectified on CV1 & 2 systems since the beginning of 2017.

I undertook a plant walk down, accompanied by the Corrosion Co-ordinator. I was able to witness planned outage related inspection and remediation activities, I was also encourage to witness ongoing inspection and remediation work as part of DNB’s corrosion management program.

I met with the System Engineer to discuss progress on inspection and repair activities associated with the Essential Cooling Water Systems. The inspections were progressing according to plan with no significant issues identified. Several examples of plant improvements and effective remediation were identified and discussed.

I discussed progress on examinations and inspections undertaken during the periodic shutdown, as required by the Pressure Systems Safety Regulations (PSSR). The PSSR Competent Person confirmed that his examinations were proceeding as planned and that station personnel had been providing effective support to his activities. He also confirmed that he was in regular communication with relevant personnel in relation to planned repairs to pressure systems. My review of the OAP minutes shows that the PSSR Competent Person regularly attends OAP meetings. No significant issues have been identified as a result of his examinations to date.

Due to challenges in gaining suitable access for inspection, I have requested further information related to condition of the gas by-pass plant filter vessels in the North Wall Plant rooms. Following my review of recommendations made from the steam and feed pipework hanger surveys I have also requested further information relating to bottomed hangers DS54, 55 & 56 associated with the dump steam pipework. DNB’s response to these requests will be assessed within my return to service assessment report.

Conclusion of Intervention

I consider that at the time of my visit to DNB power station, personnel were conducting their inspections in line with the R21 pre-outage intentions documentation and associated specifications.

In relation to DNB confirming suitable condition of the gas by-pass plant filter vessels in the North Wall plant rooms and judgements made by them regarding the bottomed dump steam pipework hangers DS54, 55 & 56, I have raised a Level 4 Regulatory Issue (number 5640) to assist in monitoring progress of commitments made by them to undertake future work.

Several minor observations have been raised with the relevant system engineers relating to corrosion management and arrangements for compliance with PSSR; these will be addressed via specific future planned ONR inspections and via DNB’s own arrangements.

I am content that the results of inspections completed on Superheater Outlet Header B8 do not challenge the claims made in NP/SC 7749, relating to the optimisation of inspection requirements on superheater outlet and reheater inlet steam side headers welds at DNB. I also consider that the recommendations made in ONR’s assessment of NP/SC 7749 remain valid.

At the time of my sample inspections and from the information that I have reviewed so far, I am satisfied that DNB’s programme for managing examination, inspection, maintenance and testing is adequate and meets the requirements of LC28.

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. I will include judgements relating to the return to service of DNB R21 within my assessment report.