Office for Nuclear Regulation

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Electrical Systems Based Inspection at THORP

Executive summary

Purpose of intervention

In accordance with ONR's Sellafield Strategy, ONR is assessing the adequacy of the systems at Sellafield Ltd (SL) that are most important to safety against the requirements of the relevant plant safety cases. ONR has implemented a 5 year rolling plan to ensure that these systems are inspected at least once during each 5 year period. This inspection was carried out as part of that plan, to inspect the Thermal Oxide Reprocessing Plant (THORP) electrical distribution system.

Interventions Carried Out by ONR

ONR carried out a 2 day inspection between 17 - 18 September 2014 utilising ONR specialist inspectors from the following technical disciplines:

The scope of this inspection was to identify and sample SL's arrangements for ensuring the robustness of those electrical supplies claimed within the safety case.

This involved reviewing the applicable safety case claims and sampling that they had been adequately implemented on the plant.

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

In addition I held an information-sharing session with the THORP Senior Management team to discuss areas of current regulatory focus.

Explanation of Judgement if Safety System Not Judged to be Adequate

n/a - I judge the safety system to be adequate; the issues that led to the rating of LC10 and 28 as below standard (see below) are not significant enough to imply that the THORP electrical system does not adequately fulfil the requirements of the safety case.

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

In my assessment of licence compliance I judge that compliance with LCs 23, 24 27 and 34 was adequate. However I considered that LC28 (Examination, inspection, maintenance and testing) deserved a rating of 4 - below standard due to the fact the Uninterruptable Power Systems (UPS) are generally in poor condition and replacement appears slow.

With regards to LC10 - Training - I awarded an IIS rating of 4 - below standard, due to the apparent shortfalls in training for loss of power events. However, it should be noted that this rating duplicates a rating from another recent inspection which noted similar shortfalls in emergency scheme training within THORP; this matter is being addressed via an existing Regulatory Issue.

I made a number of safety case observations during the course of my inspection, the most significant being:

The THORP management team are aware of and agree with my significant areas of regulatory concern and are committed to addressing them in a proactive way.

Conclusion of Intervention

I judge that, based on the sampling completed, the THORP electrical system adequately fulfils its safety case requirements. However I do have several observations regarding the safety case which are outside this consideration of the implementation of the extant safety case and have raised Regulatory Issues to address these. These will be progressed as part of normal regulatory business.

I am satisfied that that the rating of both LC10 and 28 as below standard relates to issues that are not significant enough to consider that the THORP electrical system does not adequately fulfil the requirements of the safety case.