Office for Nuclear Regulation

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System Based Inspection (SBI) of First Generation Magnox Storage Pond (FGMSP) Containment System at Sellafield

Executive summary

Purpose of Intervention

The Office for Nuclear Regulation (ONR) undertakes all regulatory interaction with the Sellafield site licensee (Sellafield Limited, SL) against a strategy defined by ONR's Sellafield Programme. In accordance with that Strategy, a System Based Inspection (SBI) of the First Generation Magnox Storage Pond (FGMSP) Containment System was planned and undertaken in May 2017. The purpose of this inspection is for ONR to examine whether the licensee's safety case claims in respect of this system important to safety have been adequately implemented.

This scope of this inspection activity comprised the civil, structural and architectural aspects of the FGMSP pond structure, FGMSP pond bunds and sumps of the drainage system. The containment system is important to nuclear safety as it confines fuel, radioactive liquid and sludge stored in the FGMSP pond. The delivery of its safety function is also important to hazard and risk reduction operations in FGMSP and across the site more generally.

ONR's SBI process examines evidence to determine compliance against six key licence conditions (LCs). These licence conditions (listed below) have been selected in view of their relevance to ensuring nuclear safety and in providing a structured approach to determining whether the safety case has been implemented adequately through the system being inspected.

Interventions Carried Out by ONR

I carried out this SBI over the course of two days. I was assisted by two ONR specialist inspectors with expertise in the field of civil engineering and fault studies respectively. I was also supported on this inspection by SL staff from its internal regulatory group. The inspection comprised discussions with SL staff, physical viewing and inspections of targeted structures, systems and components, and review of SL's records and other safety documentation.

Explanation of Judgement if Safety System Not Judged to be Adequate

I judge the safety case supporting this system to be adequately implemented.

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

From the areas I targeted and the evidence I examined during this inspection, I consider that SL has adequately implemented those safety case claims that relate to the FGMSP Containment System. In particular, SL has undertaken a significant amount of work to maintain and improve the continued safe delivery of the bulk containment function of the FGMSP operation with suitably qualified and experienced personnel. I also identified several minor improvements that could be made. On balance, I award inspection ratings of Green (No Formal Action) for LCs 10, 23, 24 and 27.

I also identified two specific areas for improvement. SL has in place a detailed inspection and surveillance regime targeted at specific locations of known weaknesses. Although SL presented some examples of good practice of inspection, ONR identified a significant shortfall in that SL failed to ensure that the inspection comprehensively covered the FGMSP containment boundary. I also identified several minor improvements that could be made. In general, there was good evidence of bulk containment but in one case ONR judged that SL was able to do more to ensure the pond water was contained so that it cannot leak or otherwise escape from the FGMSP containment. I judge that this is a significant shortfall in the implementation of SLs arrangements. On balance, I award inspection ratings of AMBER (seek improvement) for LCs 28 and 34.

In the course of my inspection I did not identify any significant concerns with the adequacy of the licensee's safety case for this system that would necessitate an earlier than planned assessment by ONR.

During the course of the inspection SL was unable to provide adequate evidence that the sampled staff had completed all their required training but committed to do so post inspection. However, overall, I judge this shortfall to be minor.

Conclusion of Intervention

I consider that the licensee has a good knowledge of the physical condition of the structures, systems and components reviewed during this inspection and have in place appropriate management controls to ensure on-going safety.

I have, however, identified two specific areas for improvement, which require appropriate attention from the licensee. I have therefore raised two ONR Regulatory Issues at Level 3.

I have also identified that SL has not yet closed out its own recommendations for improving FGMSP containment. I have therefore raised an ONR Regulatory Issue at Level 4 to track SL's progress of these matters.

Overall, on balance therefore, I consider the safety case supporting this system to be adequately implemented.