Office for Nuclear Regulation

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System Based Inspection of the Special Nuclear Materials South (SNM(S)) Thorp Product Store

Executive summary

In accordance with the Office for Nuclear Regulation’s (ONR’s) Sellafield Strategy, each year ONR performs a series of planned system based inspections (SBIs) targeted on key safety significant systems. The purpose of this particular inspection was for ONR to determine the adequacy of implementation of Sellafield Ltd.’s (SL’s) safety case claims for the Special Nuclear Materials (SNM) South Thermal Oxide Reprocessing Plant (THORP) Product Store. The inspection focussed on the ventilation system for the store itself. This provides a cooling, containment and indirectly a control (criticality) fundamental safety function. The safety function of the product packages contained within the store was excluded. 

Interventions Carried Out by ONR

On the 29 and 30 October 2019, ONR carried out a planned two day inspection of the THORP ventilation system utilising specialists from the following technical disciplines:

In order to determine the adequacy of the licensee’s implementation of the safety case   claims in respect of these systems, ONR examined evidence to verify the adequacy of the implementation of SL’s arrangements for six pre-defined licence conditions (LCs), as listed below. These LCs have been selected in view of their importance to nuclear safety and are defined­ within ONR’s formal process for SBIs.

The inspection involved reviewing the applicable claims in the safety cases and then sampling suitable evidence to determine compliance against the selected LCs on the plant. This was achieved through a combination of document reviews, plant inspections and discussions with operators and maintenance staff.

I inspected compliance in the THORP Product Store against the following LCs by using the current versions of the applicable ONR inspection guidance documents:

Explanation of Judgement if Safety System Not Judged to be Adequate

This safety system is judged to be adequate.

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

Evidence was seen that SL is subjecting the THORP Product Store to an adequate level of Examination, Maintenance, Inspection and Testing (EMIT). As is not unusual, this process had identified some technical issues associated with the ventilation system. However, from the inspection, I considered that there was evidence that the matters were being appropriately identified by SL and that SL was committed to acting upon the findings. I reminded SL of the importance of continuing to do this.

From the evidence sampled, I judged that SL had adequately implemented the safety case limits and conditions specified within the safety case. Furthermore, I was satisfied that the facility adequately understood the limits and conditions and their importance in the safety case. 

Whilst SNM(S) operate the THORP Product Store, THORP Operational Services support the operation and EMIT of the store ventilation. In light of the end of reprocessing within THORP I encouraged SL to define and document the strategy for the longer term management of the TPS ventilation systems and the operating philosophy.

Whilst some minor opportunities for improvement were identified resulting in the raising of four level four issues, overall, I found LCs 10, 23, 24, 27, 28 and 34 to be adequately implemented in relation to the systems inspected. Consequently, it is my opinion that for this system based inspection a rating of GREEN - No formal action is appropriate for LCs 10, 23, 24, 27, 28 and 34.  

Conclusion of Intervention

From the evidence sampled during the inspection, I judged that SNM(S) has adequately implemented the relevant claims in the safety case and that the formal arrangements for LCs 10, 23, 24, 27, 28 and 34 are being adequately implemented. Overall, I judge that the safety system adequately fulfils the requirements of the safety case.