Office for Nuclear Regulation

LC28 Plant inspection

Executive summary

Purpose of Intervention

An inspection was carried out at Dungeness B on the 2nd of July 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 (EMIT)), the newly discovered corrosion under insulation of concealed systems and newly discovered corrosion of recently mitigated corroded pipework, associated with nuclear related plant. Also, the inspection included the on-going work to improve the maintenance and reliability of the extant Emergency Nitrogen Injection Plant, in readiness for return to front line service, when the reactors at back at power. While at the station, the opportunity was also taken to inspect the installation of the new Automatic Boiler Emergency Depressurisation (ABED) system, which supports the station’s new boiler tube leak safety case.

Interventions Carried Out by ONR

Due to the Covid-19 pandemic, as much information as possible was reviewed ahead of the station visit. This was to maximise the time available on station to inspect plant and equipment.

This allowed the maximum time available to physically inspect relevant plant associated with the newly discovered corrosion of concealed safety systems and the extant Emergency Nitrogen Injection Plant, against the legal requirements of LC28 (EMIT). While at the station, the opportunity was taken to carry out a limited inspection of the newly installed ABED system, in support of the station’s new boiler tube leak safety case.

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

With regard to the newly found corrosion, I found that the extent of condition plant inspections and remediations in progress were thorough and systematic. I also noted that improvements in standards by System Engineers had been implemented, including the use of Operational Experience. However, the station should have adequate arrangements in place which effectively monitor configuration control of safety related systems, structures and components and replace safety related items as necessary. Those arrangements should recognise and assess the longer term impact on safety related systems, structure and components, and take due consideration of asset management requirements (e.g. ageing, degradation, obsolescence). The newly discovered corrosion under insulation and recently mitigated corroded pipework suggests the station’s arrangements are not effective. The station’s investigations into the root causes, extent of condition and appropriate corrective actions are on-going.  I judged that improvement in the station’s arrangements for the management of concealed safety related systems was needed and rated this element of the inspection as Amber.  There is already an ONR Regulatory Issue covering the wider and on-going corrosion issues across the station. ONR will review the outcome of the station’s investigations into this newly found corrosion of concealed safety systems before considering any further amendments to the existing regulatory issue.

With regard to the extant Emergency Nitrogen Injection Plant, I found that maintenance and testing of the plant had commenced in February this year and has gradually improved the condition and reliability of the plant, albeit with the close monitoring and intervention of Suitably Qualified and Experienced Persons during testing. I found the application of the station’s Technical Fault Finding process to be focused, systematic and particularly effective. The required plant performance for front line emergency duty had almost been achieved at the time of the inspection. The station and EDF Independent Nuclear Assurance (INA) were confident that the required reliability could be achieved by the end of July 2020, well ahead of return to service of the reactors. Assurance was obtained that the extant nitrogen plant would continue to be maintained and regularly tested to ensure consistent and sustained reliability. I therefore rated this element of the inspection as Green.

Overall, the LC28 inspection was given an Amber rating, due to the newly discovered corrosion of concealed safety systems.

With regard to the newly installed ABEDs system, the pre-inspection review of the documentation associated with the new installation indicated it to be comprehensive, however I found that not all required entries had been completed. On the station, my inspections were carried out from the Boiler Emergency Depressurisation valves in the boiler annexe to the Main Control Room (MCR). However, due to the limited access, mainly due to Confined Space access, only a small part of the route could be inspected with regard to separation and segregation of the cabling from extant plant systems. The cable junctions in the associated switch room and the new cabinets in the Instrument Room adjacent to the MCR were examined, and found to be in good order.

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 conclusion of my LC28 intervention was that an Amber rating was appropriate, i.e. that ONR seeks improvement. This was associated with the newly found corrosion of concealed safety related systems. ONR will review the outcome of the station’s investigations into root causes, extent of condition and corrective actions before considering any amendments to the existing regulatory issue on the topic.

The inspection associated with the extant Emergency Nitrogen Injection Plant found the plant maintenance and reliability has improved in recent months and is expected to meet the necessary level of reliability soon, ahead of return to service of the reactors. On-going maintenance and testing will be requirement to ensure consistent and sustained reliability, and assurances were given by the station.

From the limited sampling and inspection of the installation of the new Automatic Boiler Emergency Depressurisation system, I judged that the system installation indicated that legal requirements had been met.