Office for Nuclear Regulation

LC28 Plant inspection, corrosion focused

Executive summary

Purpose of Intervention

An inspection was carried out at Dungeness B (DNB) on the 2nd September 2020, which currently has both reactors shutdown. This was an unplanned reactive inspection, i.e. over and above the planned inspections for the year. The main purpose of the intervention was to inspect, under Site Licence Condition (LC28), Examination, Maintenance, Inspection and Testing, key areas of DNB’s corrosion management process implemented as part of its ongoing event recovery.

Interventions Carried Out by ONR

Due to the Covid-19 pandemic, a plant focussed inspection took place to maximise the benefit of a station visit, as opposed to a remote “meeting” format for the activity.

The inspection consisted of a walkdown of plant within key areas of the event recovery, discussions to understand the reasons behind recent emergent issues and the measures implemented by station to mitigate them, sampling of QA documentation associated with completed remediation, meetings with the remediation lead and a presentation relating to the ongoing phase 2 inspection activities

Explanation of Judgement if Safety System Not Judged to be Adequate

Not applicable – not a System Based Inspection.

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

All areas visited during the plant walkdown displayed good housekeeping practice, it is clear that further significant remediation work has taken place over the last 6 months. The plant observed was in good condition and where any degradation was noted, the DNB team was able to provide a verbal description of plans for its remediation. This progress is particularly encouraging when considering the Covid-19 restrictions.

Regarding recent emergent issues, I completed a review of mitigating evidence provided and am content that DNB have demonstrated a robust response to each of the recent emergent issues associated with the corrosion event recovery. In general, the cause of the issues has been attributed to errors or omissions made either immediately prior to, or in the early stages of the event recovery.

I reviewed the extent of condition report produced by the DNB Corrosion co-ordinator and consider that it represents a suitable study of the challenges posed by the emergent issues. Prior to either reactor return to service, I will record my final judgements regarding suitability of DNB’s corrosion management process as part of my future assessment of their final corrosion RTS document pack.

I am encouraged that EDF undertook a Chief Engineer review of DNB’s corrosion program and I am inclined to support its findings. The station has provided evidence to show they understand the impact of recent corrosion related emergent issues and that the time period in which they occurred has been established. Nevertheless DNB must ensure that their RTS document pack demonstrates how they understand the condition of their concealed systems and have a realistic forward plan to manage inspection and remediation of corrosion.

DNB’s corrosion defect tracker identifies a large number of corrosion related defects which need to be remediated within a maximum period of 36 months from date of discovery; this is clearly a significant ongoing challenge for the station. The defect tracker appeared current and comprehensive, containing the expected level of information. From my sample, I am content that DNB has implemented a suitable process to review the remediation of existing defects and to record resulting judgements.

For defects already remediated, I was impressed with the level of oversight and control demonstrated by the QA Engineer and the quality of the document pack sampled. I am satisfied that the corrosion project has demonstrated they hold suitable records of remediation work completed during the event recovery.

I am satisfied that the Remediation Lead and Corrosion co-ordinator were able to present and describe a reasonable remediation plan in the short term. However, a large amount of remediation remains and currently all remediation is taking place with both reactors shutdown. I reminded the remediation team of the challenge they faced to ensure appropriate remediation of corrosion defects once the reactors are operational.

I outlined my expectation that the corrosion team would continue to receive appropriate support from the Corrosion Oversight Review Board and station management, so that they are able to maintain control of the corrosion challenge at DNB and address its commitments made in response to ONR’s 2018 corrosion Direction.

In my opinion the DNB corrosion recovery phase 2 inspection program represent an area of good practice. It is clear that lessons have been learnt from the beginning of the project and that improvements implemented should result in a suitable record of the condition of the concealed systems inspected as part of phase 2.

Co-incident with planned inspection, I observed that the station had Covid-19 mitigation arrangements in place, which were being complied with.

Conclusion of Intervention

The overall conclusion of this corrosion focussed LC28 inspection at DNB is that a GREEN rating is appropriate. This is clearly a positive outcome from this inspection reflecting significant plant and process improvements witnessed, however it is worth putting into context.

Prior to return to service (RTS) of either reactor at DNB, ONR will assess the adequacy of a documentation pack that is currently being produced by EDF. This pack will aim to demonstrate that DNB understands the condition of its concealed systems and has an appropriate, resourced and realistic plan in place to continue the significant volume of inspection and remediation that remain. Our judgements will be recorded within an assessment report and used to inform the permissioning strategy for RTS at DNB. ONR will continue to maintain oversight of the progress of the corrosion event recovery.