Office for Nuclear Regulation

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Hunterston B System Based Inspection of the Buffer Storage Facility (Decay Stores)

Executive summary

Purpose of intervention

The purpose of this intervention was to undertake a system based inspection at EDF Nuclear Generation Limited's (NGL's) Hunterston B power station in line with the planned inspection programme contained in the Hunterston B Integrated Intervention Strategy (IIS) for 2016/17.

The inspection was undertaken by a fuel performance inspector and nominated site inspector and concentrated on the Buffer Storage Facility. The aim of the inspection was to confirm that the Buffer Store, with its associated operating instructions and maintenance schedule, is able to meet the safety case functional requirements.

Interventions Carried Out by ONR

The system based inspection of the Buffer Store was conducted against compliance with the following licence conditions:

The inspections were based on sampling the implementation of the arrangements in place against each licence condition. Pre- and post- inspection meetings with the site personnel were held and the main findings were communicated.

Although aspects of CO2 leakage and management were considered the extent of the inspection did not enable adequate coverage to provide a rating against LC34: Leakage and Escape of Radioactive Material and Radioactive Waste.

Explanation of Judgement if Safety System Not Judged to be Adequate

Based on the sample made during this inspection I judged that the Buffer Store adequately meets the requirement of the safety case.

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

The training records of a number of fuel route staff, who work on the buffer store, were sampled against their role profile. Two instances of non-compliance with essential training requirements were identified. However, the licensee's training department tracks compliance as an indicator and has a generally adequate performance (99.7% compliance) and in one of the two cases appropriate measures were in place for training renewal. The Fuel Route Manager was advised to review the extent of condition for the fuel route. Notwithstanding, I consider that it is appropriate to rate LC 10 as 'Green'.

The licensee's "Living Safety Case" documentation for the Buffer Store was reviewed in conjunction with the relevant operating procedures, technical specifications and check sheets. The procedures and critical steps were also talked through with a Duly Authorised Person (DAP) from the operations team and discussed on plant with fuel route operatives.

Post-fault actions were discussed with the DAP particularly with regard to loss of gas pressure. This discussion went through station operating manuals (SOMs) and emergency procedures in the event of failure to recover pressure and hence cooling. The documentation was generally in good order with line of sight to the living safety case. It was identified that use of SOMs is no longer the company practice, though this is not specifically non-compliance.

The fuel route operatives had an in-depth knowledge of the equipment and associated procedures and demonstrated an understanding of the important control measures and hold points in the process. Procedures and check-sheets for the ongoing operation were completed as required. However, one verification check was identified not to be signed off correctly and was raised with the Fuel Route Manager for corrective action.

Based on the sample inspections completed I consider a rating of 'Green' to be appropriate for LC 23 and LC 24.

Relevant system health review documentation and system health metrics were reviewed with the system owner. Overall the plant condition and reliability was found to be adequate based on the system health evidence and plant walk-down inspection. Improvements in foreign material exclusion practices brought about by trends in minor issues had been implemented. Furthermore, obsolescence issues with instrumentation had been identified by the licensee and are being actioned through an investment plan.

Several Condition Reports concerning adverse conditions on the buffer store were considered during the inspection and the licensee was able to demonstrate adequate closure and follow up through their internal processes. Evidence of how Hunterston B have learnt from a specific safety event at Hinkley Point B (HPB) in March 2015 was requested and later provided to an adequate standard. Accordingly, I consider a rating of 'Green' to be appropriate for LC 27.

The station's maintenance inspection and testing (MIT) records were sampled via its Asset Management System (AMS) for three SSCs (structures systems and components) claimed within the living safety case. There is satisfactory evidence from this sample that maintenance on the buffer store system is being carried out in accordance with the requirements of the plant maintenance schedule. However the information gathered suggests that the backlog of scanning and overall records management, previously captured under regulatory issue 3237, raised in February 2015, is more acute in Fuel Route.

I judge that the compliance with LC 28 for the buffer store is adequate and requires no formal follow up actions at this time. This is notwithstanding the ongoing backlog of MITs check-sheets which continues to be managed under an existing Level 4 regulatory issue. Accordingly, I consider a rating of 'Green' to be appropriate for LC 28.

Conclusion of Intervention

From the evidence gathered during this intervention, I do not consider there to be any matters that have the potential to impact significantly on nuclear safety. Several low level items were identified for follow up by the nominated site inspector as part of normal regulatory business. However, at present, no additional formal regulatory action is needed over and above the planned interventions of Hunterston B power station as set out in the Integrated Intervention Strategy.