Office for Nuclear Regulation

PMF(N) Glove box and Cell Pu Leak Detection Systems (SBI)

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.  The inspection plan PP1 for the plutonium finishing and storage facilities (PF&S) details a strategic programme of regulatory inspections which includes a System Based Inspection (SBI) of the Plutonium Management Facility (North) (PMF(N)) Finishing Line 5 (FL5) Glove Box and Into Cell Plutonium Leak Detection Systems.

FL5 is the plutonium finishing line that takes the Pu enriched nitric acid feedstock from the Magnox Reprocessing Facility and produces pure powdered PuO2 in cans for storage.

The purpose of this inspection was for the ONR to confirm the adequacy of implementation of the safety case made for the plutonium leak detection system. This system is responsible for detecting any leakage of plutonium from the plant into a glove box or into the cell areas outside of the glove boxes before sufficient material can collect to cause a criticality. A criticality is a spontaneous fission event that gives rise to a burst of neutron radiation which would be fatal to anyone in the vicinity. The protection systems that guard against this are therefore very important to nuclear safety.

Interventions Carried Out by ONR

We carried out a two and a half day, on-site team inspection, delivered by the ONR site inspector, and three specialist Technical Support Contractors (TSC’s).

As part of this SBI, we examined SL’s compliance against ONR guidance for the following licence conditions (LCs):

The inspection included a general discussion of the requirements set out for the system in the facility safety case and relevant safety documentation, a plant walk down and individual discussions with relevant plant safety case and operational personnel.

Explanation of Judgement if Safety System Not Judged to be Adequate

The overall safety system was judged to be adequate. However there was evidence of specific procedural and safety case weaknesses that will be addressed as regulatory issues.

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

The key findings of the inspection are:

Conclusion of Intervention

The conclusion of the intervention was that the protection system for controlling the risks of leakage and escape of nuclear material met the requirements specified for it in the safety case.

However, the inspection revealed that there were a few specific fault sequences in the safety case where the specified arrangements were considered to be below an adequate standard. Sellafield were informed of this at the close out meeting. These issues will be raised as regulatory issues and assessed by ONR specialist inspectors. These fault sequences detailed relatively low probability events and, additionally, as the plant is shut down for an extended outage, they were not considered to require immediate regulatory intervention.

 If necessary, subject to the results of the ONR assessment, suitable improvements will be implemented as appropriate to ensure continued safe operation of the facility following the outage.

A number of other minor issues relating to procedural improvements were raised with Sellafield and will be addressed as part of the continuing regulatory inspection programme.