Office for Nuclear Regulation

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System Based Inspection (SBI) of Pile Fuel Storage Pond (PFSP) Containment System on Sellafield Ltd.’s nuclear licensed sites 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 Pile Fuel Storage Pond (PFSP) Containment System was planned and undertaken in February 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 PFSP pond structure, PFSP pond bunds and sumps of the under pond drainage system as well as the water ducts within the PFSP. The containment system is important to nuclear safety as it confines radioactive liquid and sludge stored in the PFSP pond. The delivery of its safety function is also important to hazard and risk reduction operations in PFSP 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. ONR’s nominated site inspector attended as an observer. I was also supported on this inspection by SL staff from its internal regulatory organisation and the Decommissioning Safety Representative. 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 PFSP Containment System. In particular, SL has undertaken a significant amount of intrusive inspection and maintenance of the pond containment to ensure its continued safe operation with suitably qualified and experienced personnel. SL also has in place a detailed inspection and surveillance regime targeted at specific locations of known weaknesses. As such I award inspection ratings of Green (No Formal Action) for LCs 10, 23, 27, and 34.

I also identified two specific areas for improvement. The first relates to operating instructions. Although SL presented some examples of good practice, ONR identified a significant shortfall in that SL failed to ensure that the maintenance of some equipment that may affect safety was carried out in accordance with the written instructions. I also identified several minor improvements that could be made. In general, there was evidence of adequate, regular and systematic examination inspection, maintenance and testing, however SL’s records of these activities were found to be inadequate.  I judge that this is a significant shortfall in the implementation of SLs arrangements. As such I award inspection ratings of AMBER (seek improvement) for LCs 24 and 28.

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 they had completed their process for the report of the annual inspection of the PFSP containment structure. Also ONR judged that the scope of the containment structure inspection could be improved.  In response to our questioning, SL was unable to provide suitable and sufficient information about the containment penetrations. However, overall, I judge these shortfalls 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 three areas where SL was unable to provide adequate evidence during the inspection. I have therefore raised 3 ONR Regulatory Issues at Level 4 to track SL’s responses to questions of detail raised in the inspection.

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