Office for Nuclear Regulation

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Sellafield - Essential Operations Inspection of SIXEP

Executive summary

Purpose of intervention

The Office for Nuclear Regulation’s (ONR) current regulatory strategy for Sellafield focuses on stimulating, facilitating and expediting hazard and risk reduction on the site. ONR has a number of planned interventions in place to ensure hazard and risk reduction activities are delivered safely.

The purpose of an essential operations inspection is to identify any potential shortfalls in the reliability and resilience of the functions underpinning of an operating unit that facilitates hazard and risk reduction.

This essential operations inspection focussed on Sellafield site’s Site Ion Exchange Plant (SIXEP) sea discharge treatment plant (SDTP) to support delivery of reliable and resilient hazard and risk reduction on site.

Interventions Carried Out by ONR

We undertook an essential operations inspection of the SDTP. Our inspection focused on the resilience of the SDTP and the licensee’s contingency arrangements for the unavailability or reduced operating capacity of SDTP, particularly for mitigating the impact on hazard and risk reduction.

The inspection gathered evidence from SDTP and two of its main donor plants, Magnox swarf storage silo (MSSS) and first generation Magnox storage pond (FGMSP) by meeting with key personnel and sampling supporting documentation. 

Explanation of Judgement if Safety System Not Judged to be Adequate

Not applicable; this was not a Safety System inspection.

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

The design of the current SDTP is susceptible to single points of failure that, if realised, could lead to prolonged outages with almost immediate impacts on the operations of donor plants. The licensee is aware of this and has a project, the SIXEP contingency plan, to provide long-term reliability and resilience for SDTP. This new facility is currently planned to become operational in 2024.

From the evidence presented it appeared that FGMSP and MSSS plants could manage routine operations in the event that SDTP ceased operations but that hazard and risk reduction projects would stop. There did not appear to be any reasonably practicable contingency measures that the licensee could be developing to mitigate an unplanned outage at SDTP, other than expediting the availability of SCP. However, we considered that the donor plants have a good understanding of SDTP’s requirements and could clearly articulate the options that are available if it ceased operations.

We identified that SIXEP does not appear to have sufficient quantities of spare, bespoke plant items in order to ensure prompt replacement of failed equipment. We encouraged the licensee in taking action to address this shortfall in its spares stocks to support plant reliability and resilience.

Conclusion of Intervention

Our findings were shared with, and accepted by the licensee. No ONR Regulatory Issues were raised as a result of this inspection.