Office for Nuclear Regulation

Sizewell B - SBI 11 inspection

Executive summary

Purpose of Intervention

The purpose of this intervention was to undertake a system based and licence condition (LC) compliance inspections at EDF Energy Nuclear Generation Limited’s (NGL) Sizewell B Power Station, in line with the ONR’s Operational Facilities Division intervention strategy. The intervention was carried out by the ONR site inspector, supported by a number of specialist inspectors.  

Interventions Carried Out by ONR

We carried out a system based inspection of the station’s high head safety injection system and refuelling water storage tank. These systems structures and components (SSCs) form part of Sizewell B emergency core cooling systems installed to provide diverse and redundant means to cool the reactor during fault conditions.  This inspection was undertaken by the ONR site inspector and a specialist inspector.  During this intervention we examined the licensee’s compliance against the following nuclear site licence conditions (LCs), which are applicable provisions of the Energy Act 2013:

LC10 (Training);

We also carried out an intervention to review the progress of NGL’s programme to evaluate material condition of the station’s tanks, vessels and buried pipework.

The ONR site inspector also conducted a licence condition 26 (Control and Supervision) compliance inspection, evaluating arrangements for controlling mode change during outage and the use of a proprietary risk monitoring tool.

The intervention was performed in line with ONR's guidance requirements (as described in our technical inspection guides) in the areas inspected.

Explanation of Judgement if Safety System Not Judged to be Adequate

Not applicable.

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

For the SBI - We judged that appropriate limits and conditions for operation of the system had been adequately defined within the Station’s technical specifications. Operational documentation sampled provided satisfactory evidence of compliance with these limits. Based on our sample inspection, we judged that the licensee has developed and implemented an appropriate preventative maintenance regime for the high head safety inspection system. We walked down a sample of the equipment and found it to be in an acceptable condition. No significant compliance shortfalls were identified and we judged that Green inspections ratings were appropriate for the following licence conditions: LC10, LC23, LC24, LC27, and LC28. 

Tanks, vessels and buried pipework - In summary, we were satisfied that the licensee is maintaining its systems appropriately from a plant material condition perspective. We were also satisfied with the upfront communication on the Condensate Storage Tank issues by the system engineers, which enabled the intervention to be focused. There are several areas where we require more clarity, we have therefore requested this in the form of programmes/plans for future work, particularly on the Condensate Storage Tanks, Reserve Ultimate Heat Sink and the overall corrosion management programme, a regulatory  issue has been raised to ensure this information is received in a timely fashion. There is also some follow up work required to determine whether the licensee  has suitably addressed recommendations from the Engineering Advice Note on buried pipework. We were satisfied that there is still suitable control of the licensee’s corrosion management programme.

Control of mode change during outage - The LC26 inspection provided confidence that adequate control and supervision is in place to manage the plant when safety equipment is unavailable.  This was demonstrated by the licensee’s  maintenance operations at-power, mode changes and when planning outages.  Systematic review processes are in place with management sign-off at appropriate levels. The use of risk information from RiskWatcher was  positive, noting the current limitations of the method to Level 1 Probabilistic Safety Analysis (core damage frequency).  The station staff interviewed understood how to use the output from RiskWatcher.  In particular to interpret the significance of any risk increases predicted by RiskWatcher, and how to identify equipment that becomes risk significant following the unavailability of other equipment.  It was clear that these insights were used to consider Operational Risk Mitigations, Minimum Essential Equipment Lists and contingency plans as input into its As Low As Reasonable Practicable decisions. No significant compliance shortfalls were identified for the LC26 compliance inspection and we judged that Green inspections rating was appropriate.

Conclusion of Intervention

One minor regulatory issue has been raised to track its progress by the station. There are no findings from this inspection that could significantly undermine nuclear safety.  At present, no additional regulatory action is needed over and above the planned interventions at Sizewell B Power Station.