Office for Nuclear Regulation

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System Based Inspection (SBI) of SPP 1 containment on Sellafield Ltd.'s nuclear licensed sites 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's Sellafield Programme. In accordance with that strategy, a system based inspection (SBI) of the confinement of radioactive substances provided by various containment features within the Sludge Packaging Plant 1 (SPP1) facility was planned for July 2016. The purpose of this inspection is for ONR to examine whether SL's safety case claims in respect of this system important to safety (i.e. containment) have been adequately implemented on plant.

This planned inspection activity targeted the tank and sump level monitoring system containment features within the SPP1 because the function of this facility is to contain a significant radiological inventory, and failure of the SPP1 containment has the potential to lead to a significant radiological release. This system essentially comprises the level monitoring system in the three Bulk Storage Vessel (BSV) tanks and the Effluent Collection Vessel (ECV) tank as well as the SPP1 building and tank sumps. The pulse-jet mixers although fitted in SPP1 are not is use and were not included in the scope of this inspection.

Our system based inspection process examines evidence to determine the compliance status against six key licence conditions (LCs). These licence conditions (listed below) have been selected in view of their importance to nuclear safety and in supporting 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 a two-day, on-site, system based inspection of the tank and sump monitoring system containment features associated with the SPP1 facility. I was assisted by technical support from one specialist with expertise in the fields of electrical engineering and control and instrumentation engineering. The inspection comprised discussions with SL staff, physical viewing and inspections of targeted structures, systems and components, and reviews of Sellafield Ltd.'s records and other safety documentation.

Explanation of Judgement if Safety System Not Judged to be Adequate

The system was judged to be an adequate implementation of the safety case.

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

From the areas I targeted and evidence I examined during this inspection, I consider that SL has implemented adequately those safety case claims that relate to the containment features within the SPP1 facility. In particular, SL described good evidence of training and continuous assessment of supervisors' competencies, and SL's staff demonstrated good process and plant knowledge and a good safety culture. I have, however, identified two minor areas for improvement, one relates to improving the clarity of the control and supervision interface between SPP1 and the First Generation Magnox Storage Pond (FGMSP) in the SPP1 operating instructions, the other to the provision of a sump level monitoring capability in the SPP1 sump room. SL had already started a review and update of its operating instructions and the procurement of a suitable sump level monitoring system that will address these minor shortfalls. There are no operating rules in SPP1, consequently, LC23 was not assessed.

It is my opinion that a rating of GREEN (No Formal Action) is appropriate for compliance against LCs 10, 24, 27, 28 and 34.

Conclusion of Intervention

Overall, I consider that the system has generally met relevant good practice with only minor shortfalls when compared with appropriate benchmarks, and I consider that an overall rating of GREEN (No Formal Action) is merited.

I consider that the Licensee has a good knowledge of the physical condition of these structures, systems and components relating to containment, and has in place appropriate management controls to ensure on-going safety.

I have, however, identified two minor areas for improvement and I will track SL's progress regarding these through my normal regulatory interactions.