Office for Nuclear Regulation

Thermal Oxide Reprocessing Plant (THORP) - Planned System Based Inspection (SBI)

Executive summary

Purpose of Intervention

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 Thermal Oxide Reprocessing Plant (THORP) ventilation systems. The inspection sampled the ventilation systems, filter change systems, filter caves and the associated safety measures.

Interventions Carried Out by ONR

On the 9 - 10 October 2018, 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.

ONR assessed compliance in THORP 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

As part of routine business, SL maintains both monthly and three yearly reviews of the health of the THORP ventilation system. This process identifies a number of technical issues associated with the ventilation system. However, from my inspection, I considered that there was appropriate evidence that issues identified by the facility were being appropriately identified and acted upon. I reminded SL of the importance of continuing to do this.

Whilst some minor opportunities for improvement were identified, 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 judge that THORP 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.