Office for Nuclear Regulation

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System Based Inspection (SBI) of Criticality and Leak Detection Systems on SPRS Facility on Sellafield Ltd.'s nuclear licensed site at Sellafield, Cumbria

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 the ONR Sellafield Programme.  That strategy includes a number of inspection plans, within which the requirement for a System Based Inspection (SBI) of the Sellafield Product and Residue Storage facility (SPRS) facility in February 2016 was identified.

The SPRS is a secure storage facility for Special Nuclear Material. The purpose of this inspection was for the ONR to confirm the adequacy of implementation of the safety case made for the criticality and radioactive material leakage detection system (C&LD). This system was selected due to the potential, should this system fail to deliver its safety functions, for significant contamination consequences to arise following a release event.

As part of this planned SBI, we examined SL’s compliance with the following licence conditions (LCs):

The C&LD systems were inspected against ONR guidance and the specialist inspectors’ knowledge of relevant industry good practice (RIGP).

Interventions Carried Out by ONR

We carried out a three-day, on-site, team inspection, delivered by the ONR PF&S site inspector, two ONR specialist inspectors and a representative from Sellafield Ltd Internal Regulation.  We advised the licensee that we would be examining the key hazards and related control/mitigation claims made within the safety case. In support of that aim, the licensee presented an overview of the criticality and leak detection Hazan, the key system functions, the related safety mechanisms, and the related operating documentation.

 We identified the initiating hazard defining documents, the overarching operating rules, operating instructions and maintenance procedures. We selected a number of safety systems and safety mechanisms for our sample, which, in our opinion, were associated with providing protection against those fault sequences etc. with the highest radiological consequences.

Explanation of Judgement if Safety System Not Judged to be Adequate

SPRS is a facility designed and built to modern standards. In general, it is remotely operated with a fully automatic Distributed Control System (DCS). It is our opinion that the standards of fit out and finish are exemplary and no evidence was uncovered of any issues with general plant safety or operability.

We considered the arrangements for the detection and control of both criticality and leaks of radioactive material to be adequate. Those issues that were found; the availability of certain gamma monitors and the safety classification of equipment, were not considered to be sufficiently serious to undermine the adequacy of the systems. Consequently, the criticality and radioactive material leakage detection system (C&LD) in SPRS is considered is judged to be adequate.

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

The key findings of the inspection were:

Conclusion of Intervention

The criticality and radioactive material leakage detection system (C&LD) was considered an adequate implementation of the safety case.

A Regulatory Issue has been raised to provide regulatory visibility and ensure that the concern regarding of the classification of nuclear safety equipment is adequately addressed by SL.