Office for Nuclear Regulation

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Pile Fuel Cladding Silo Argon Inerting System – System Based Inspection at Sellafield Ltd.’s nuclear licensed site, Sellafield, Cumbria

Executive summary

Purpose of intervention

The Office for Nuclear Regulation (ONR) undertakes all regulatory interaction with Sellafield Limited (SL, the site licensee) against a strategy defined by the ONR Sellafield Programme. The inspection plan PP3 for Decommissioning sets out a programme of regulatory inspections which includes a system based inspection (SBI) of the Pile Fuel Cladding Silo (PFCS) Argon Inerting System in November 2015.

The purpose of this inspection was for ONR to consider the adequacy of implementation of the licensee’s safety case claims in respect of this system.

SL is preparing the PFCS to enable retrieval of the waste from each silo into an agreed package for interim storage. The Argon Inerting System is important for nuclear safety as it is required to maintain hydrogen concentration levels within the silo compartments below 4% to prevent a fire in the waste contained in a silo. From the system, I selected argon delivery systems and argon flow indicators for my inspection as the function of these items is particularly important to the PFCS safety case for preventing a silo fire.

Interventions Carried Out by ONR

I carried out a two day on-site SBI of the PFCS Argon Inerting System with technical support from mechanical and fault studies specialists sourced from a technical support contractor. My inspection comprised discussions with SL staff, a plant walk down and reviews of plant records and other documentation.

As part of my inspection I examined evidence for the adequate implementation of five licence conditions. These licence conditions (listed below) have been selected in view of their importance to nuclear safety and are defined within ONR’s formal process for SBI.

ONR’s process for SBI also includes LC34. LC34 requires SL to ensure that its radioactive material and radioactive waste is at all times adequately controlled and contained, and that no leak or escape of that material or waste can take place without being detected. As the Argon Inerting System does not provide any containment function, and aspects where it assists with PFCS containment by preventing a silo fire are adequately addressed through other elements of my inspection, I did not perform an explicit inspection against LC34.

Explanation of Judgement if Safety System Not Judged to be Adequate

I judged this safety system to be adequate.

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

From the evidence examined by me during this inspection, I consider that SL has adequately implemented those claims within the facility safety case that relate to argon delivery systems and argon flow indicators.

In performing this SBI, I have considered if the supporting safety case for the system requires a priority assessment of its adequacy. Based on the information gathered during this inspection, I have no reason to recommend an early assessment of this safety case.

Based on discussions with facility staff and an examination of the training records during this inspection, I consider that SL has adequate training in place to deliver an effective response to system alarms, from both a public and plant operator safety perspective. There was evidence of a good awareness of plant parameters, the means of ascertaining them, and a good level of wider understanding of which plant indications could be drawn upon with confidence in an emergency including in the case of a sustained loss of the Argon Inerting System.

All visible parts of the system appeared to be adequately maintained and in good physical condition. Components which are exposed to the marine environment are made from the appropriate grade of stainless steel and gauges and instruments are housed in weather proof enclosures.

Conclusion of Intervention

From the samples inspected, I judge that the licensee has adequately implemented the relevant claims within its safety case and I was satisfied that the formal arrangements for all the licence conditions against which I inspected are also being implemented adequately.

Although I raised no Regulatory Issues, I made a number of minor observations during my inspection. These were shared with, and accepted by, the licensee during my inspection feedback. None of these adversely affect safety.