Office for Nuclear Regulation

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THROP cooling Water Systems Based Inspection and LC34 Compliance Inspection

Executive summary

Purpose of intervention

In accordance with our Sellafield Strategy, ONR inspects the adequacy of the systems at Sellafield that are most important to safety against the requirements of the relevant plant safety cases. ONR follows a rolling plan to ensure that these systems are inspected at least once during each 5 year period. The primary part of this intervention (in line with this rolling plan) was to inspect the Thermal Oxide Reprocessing Plant (THORP) Cooling Water system.

ONR also carries out a programme of routine Licence Condition (LC) compliance inspections to assess the implementation of Sellafield Limited’s (SL’s) arrangements.  As part of this intervention I carried out a planned inspection against LC34 – Leakage and escape of radioactive material and radioactive waste – in THORP’s feed clarification area

Interventions Carried Out by ONR

ONR carried out a 3 day inspection between 17 – 19 February 2015 utilising specialists from the following technical disciplines:

The scope of this inspection was to identify and sample SL’s arrangements for ensuring that the THORP Cooling Water system (including applicable sub-systems) is being operated as per the requirements of the safety case.

This involved reviewing the applicable safety case claims and sampling, through a combination of document reviews, discussions with operators and plant inspections, that they had been adequately implemented on the plant.

ONR assessed compliance with the following Licence Conditions (LCs) for the THORP Cooling Water system using the applicable ONR inspection guidance:

I also carried out a routine licence compliance inspection (again using applicable guidance) to assess the adequacy of SL’s compliance with LC34 – Leakage and escape of radioactive material and radioactive waste – in THORP’s feed clarification area. Here, my inspection focused on SL’s compliance with its duty to, so far as reasonably practicable, ensure that radioactive material and waste is adequately controlled or contained so that it cannot leak or otherwise escape.

Explanation of Judgement if Safety System Not Judged to be Adequate

I do not consider that the THORP Cooling Water system adequately fulfils the requirements of the plant’s safety case. SL staff were unable to fully articulate a convincing explanation of how the full requirements of the safety case had been implemented. This appeared to be, at least in part, because the safety case itself, which is spread over a large number of documents, is unclear.

There was also evidence of a lack of appropriate maintenance on some parts of the Cooling Water system due to inappropriate component safety designation. I raised specific concerns in regard to the cooling water supplies to THORP’s air compressors and potential inappropriate reliance on the plant’s Distributed Control System (DCS) to support a basket safety measure designated as a means for establishing cooling on the dissolvers.

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

In my assessment of Licence Condition compliance for the THORP Cooling Water system, I judge that compliance with LCs 10, 24, 27, 28 and 34 was adequate. However I considered that implementation of LC23 (Operating Rules) merited a rating of 4 – below standard. This was because I consider the safety case is not visible, user friendly, readily available to relevant staff and fragmented.

In regard to my separate inspection of LC34 in the feed clarification area, I judged that day-to-day management to prevent leakage and escape from sumps and vessels is executed to a high standard. However, SL does not appear to have defined and implemented an appropriate and substantiated inspection regime for in-cell Class 1 safety features, specifically the cell floor clad (including in the accountancy area). In light of this, I have awarded an IIS rating of 5 – significantly below standard – because I consider that the in-cell inspection process is “flawed such that one or more important requirements is not delivered”.

Conclusion of Intervention

In view of the finding that the THORP Cooling Water system safety case has not been adequately implemented, I have raised a Regulatory Issue for SL to resolve the significant areas for improvement; I will conduct a further intervention to ensure an appropriate resolution. I have also requested that SL writes to me to justify why it considers, given my findings on the THORP Cooling Water system, that nuclear safety at the plant is not significantly degraded.

I have also raised a Regulatory Issue to capture my findings in regard to the feed clarification area.