Office for Nuclear Regulation

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R4 Periodic Shutdown - LC28 - Structural Integrity

Executive summary

Purpose of Intervention

This report records the findings of an intervention visit to Hunterston B Nuclear Power Station (HNB) during the 2017 Reactor 4 (R4) 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 (EIMT).

Interventions Carried Out by ONR

I undertook on-site meetings and plant inspections with NGL staff and their contractors to determine the adequacy of the work being undertaken on R4 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. NGL have previously produced a safety case to justify the deferral of vessel entry inspections at this outage, therefore no inspections took place on the metallic components internal to the reactor pressure vessel.

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

I visited site on days 25 and 26 of the R4 periodic shutdown. The status of the inspections showed satisfactory progress on the reactor external inspection programme, with approximately 50% of inspections complete at the time of my visit.

I sampled the inspection work undertaken as part of the reactor external inspection programme, reviewed inspections completed and their results. I was content that the work was progressing effectively, with inspection results sentenced appropriately. Weld and Flow Assisted Corrosion (FAC) inspections were progressing to programme. Several areas of FAC had been identified and remediation was on-going; however these had generally been anticipated by the licensee. A single incident of unexpected and unacceptable degradation by FAC has been identified, for which I am satisfied that HNB has planned suitable remedial actions for R4 and will establish any potential implications for R3.

During the outage, inspection of reactor internal components is limited to remote examination by camera of two standpipes. No significant findings have been reported.

I observed the conduct of the HNB Outage Assessment Panel (OAP) during my visit and also reviewed 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 HNB in relation to their corrosion management program. I am encouraged that corrosion inspection and remediation work has continued throughout the outage and have observed good progress.

I undertook a plant walk down, accompanied by the Corrosion Co-ordinator. I observed inspection and remediation activities as part of HNB'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.

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.

Following a report of difficult access, the presence of an adverse environment and of corrosion in the Gas By-pass Plant of Dungeness B power station, I have confirmed that such conditions are not prevalent at HNB. I have sampled inspections of the system, which show no restrictions for inspection, no evidence of adverse local environment and record no significant findings.

Conclusion of Intervention

I consider that at the time of my visit to HNB power station, personnel were conducting their inspections in line with the R4 pre-outage intentions documentation and associated specifications.

In light of the unexpected FAC identified in the R4 outage and described in paragraph 5, I have raised a Level 4 Regulatory Issue (number 5799) to monitor the progress and outcome of commitments made by the licensee to address the risk of unexpected FAC in similar locations at HNB R3.

At the time of my inspection and based on the evidence I have reviewed thus far, I am satisfied that HNB's programme for managing EIMT is adequate and meets the requirements of LC28.

In my opinion, the licensee has performed EIMT 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 HNB R4 within my assessment report.