- Site: Sellafield
- IR number: 21-142
- Date: December 2021
- LC numbers: 10, 23, 24, 27, 28, 34
Executive summary
Purpose of Intervention
In accordance with the Office for Nuclear Regulation’s (ONR’s) Sellafield Ltd’s Strategy, each year ONR performs a series of planned System Based Inspections (SBIs) targeted on key safety significant systems. The purpose of this particular intervention was to undertake a SBI of the Thermal Oxide Reprocessing Plant (THORP) Shield Doors to confirm the adequacy of the implementation of the safety case, inspection of evidence to support the claims made in the safety case and to ascertain compliance against Licence Conditions 10, 23, 24, 27, 28 and 34.
Interventions Carried Out by ONR
We, the Site Inspector for THORP and Fuel Storage, a Fault Studies Inspector and an Electrical, Control and Instrumentation Inspector undertook a planned two day inspection of the THORP Shield Doors on 15 and 16 December 2021.
In order to determine the adequacy of the Licensee’s implementation of the safety case claims in respect of these systems, we examined evidence to verify the adequacy of the implementation of Sellafield Ltd’s arrangements for six pre-defined Licence Conditions (LCs), as listed at Paragraph 5. 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 evidence to determine compliance against the selected LCs at the facility. This was achieved through a combination of document reviews, plant inspections and discussions with operators, training and maintenance staff.
We assessed compliance against the following LCs by using the applicable ONR inspection guidance documents:
- LC10 – Training (NS-INSP-GD-010)
- LC23 – Operating rules (NS-INSP-GD-023)
- LC24 – Operating instructions (NS-INSP-GD-024)
- LC27 – Safety mechanisms, devices and circuits (NS-INSP-GD-027)
- LC28 – Examination, inspection, maintenance and testing (NS-INSP-GD-028)
- LC34 – Leakage and escape of radioactive material and radioactive waste (NS-INSP-GD-034)
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
From the evidence sampled we found that the Operating Rules were an accurate reflection of the safety case, and that they had been appropriately implemented into the working level documentation such that they were visible and usable by the operators, and that the operating instructions were clear in providing a means to comply with the Operating Rules. We did identify one Operating Rule that had been amended by a management decision and potentially weakened and have raised a Level 4 (lowest level) regulatory issue to address this. This is not an immediate safety concern as the underpinning arrangements are robust and maintain the integrity of the original intent.
We found that the Shield Doors and associated equipment have been adequately maintained and tested to meet the claims in the safety case and supporting safe operations for related activities. We identified several areas for improvement in relation to the approach to calibration testing and the proactive management of system health for key equipment and have raised two Level 4 regulatory issues in these areas.
We also found both maintenance and operations staff at THORP were knowledgeable, having a good understanding of the safety case and the Shield Doors. However, we did identify that there is no written evidence to support the safety requirements related to the Shield Doors in the training package for the Duly Authorised Person, and we have raised a further Level 4 issue to address this.
We identified that one condition report related to the Shield Doors had not been processed fully in accordance with the Sellafield Ltd LC7 (Incidents on the site) arrangements and we gave regulatory advice over this matter.
Consequently, it is our 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.
Our findings from the intervention were presented to and accepted by the Sellafield Ltd Deputy Head of Operations for THORP on completion of the inspection.
Conclusion of Intervention
From the evidence sampled during the inspection, we judge that Sellafield Ltd has adequately implemented the relevant claims safety case for the Shield Doors at THORP and that the formal arrangements for LCs 10, 23, 24, 27, 28 and 34 are being adequately implemented. Three Level 4 (lowest level) regulatory issues have been raised in relation to shortfalls in the implementation of the arrangements at THORP and we have raised a further regulatory issue to address the calibration concern at a corporate level; in addition, we gave regulatory advice in relation to the implementation of the Sellafield Ltd LC7 (Incidents on the site) arrangements.
Overall, we judge that the safety system is adequate and fulfils the requirements of the safety case.