Office for Nuclear Regulation

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To conduct a planned systems inspection of the B560 containment system

Executive summary

Purpose of intervention

In accordance with ONR’s Sellafield Strategy, ONR is assessing the adequacy of the systems at Sellafield 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 as part of that plan, to inspect the THORP Receipt and Storage Pond containment system.

Interventions Carried Out by ONR

ONR carried out a 2 day inspection between 30 – 31 July 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 containment of the radiological hazard in the THORP Receipt and storage pond, focusing on the following areas which were identified following ONR’s review of 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 Receipt and storage pond containment system using the applicable ONR inspection guidance:

Explanation of Judgement if Safety System Not Judged to be Adequate

N/A - I judged the safety system to be adequate.

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

The THORP Receipt and Storage pond is a robust structure and Sellafield Limited has put in place suitable arrangements to ensure that its ongoing condition is monitored appropriately. Currently ONR has no significant concerns in relation to its integrity.

Appropriate temperature and chemical controls are in place to ensure that long term fuel clad corrosion is reduced to a minimum. It is noted that the facility roof will need to be replaced in the near future as it is approaching the end of its service life. This will help to ensure that ingress of chloride-laden rain water into the ponds due to roof leakage does not challenge SL’s chemistry control of the pond water.

Sellafield Limited has put in place suitable measures to optimise performance of the pond water containment.

I assessed that LCs 10, 23, 27, 28 and 34 were all adequately implemented with regards to the THORP Receipt and Storage containment system thereby deserving an IIS rating of 3 – Adequate.

With respect to LC 24, although I assessed that Sellafield Limited has in place suitable operating instructions which are generally to an adequate quality, I consider that improvements should be made to the standards, and to expectations regarding their use.  In particular, during this inspection ONR observed that these standards and expectations appeared to be either unclear or implemented in an inconsistent manner. As such I awarded an IIS rating of 4 – Below standard.

Conclusion of Intervention

I judge that, based on the sampling completed, the THORP Receipt and Storage containment system adequately fulfils its safety case requirements to ensure containment of the radiological inventory within it. However as identified in my assessment of LC24 – Operating instructions, I consider that the standards and expectations regarding the use of operating instructions should be improved and as such the extant Formal Regulatory Action 2382 for THORP has been updated and extended to include THORP Receipt and Storage. In addition a number of minor areas for improvement were communicated to the licensee during this inspection.