- Site: Sellafield
- IR number: 21-182
- Date: March 2022
- LC numbers: 10, 23, 24, 27, 28, 34
Executive summary
Purpose of Intervention
In accordance with the Office for Nuclear Regulation’s (ONR’s) intervention strategy for Sellafield Ltd, 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 an SBI of the Thermal Oxide Reprocessing Plant (THORP) Nuclear Fire Protection System to confirm the adequacy of the implementation of the safety case with respect to nuclear fire safety, inspection of evidence to support the claims made in the safety case in this context, 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, an Internal Hazards Inspector and an Electrical, Control and Instrumentation Inspector undertook a planned two-day inspection of the THORP Nuclear Fire Protection System on 9 and 10 March 2022. In attendance for the first day was a trainee Nuclear Fire Safety Inspector.
In order to determine the adequacy of the Licensee’s implementation of the safety case claims in respect of the system, 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 case, the nuclear fire safety assessment 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, safety case personnel 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
We found that THORP has adequately implemented the limits and conditions within the safety case for high consequence faults that could be impacted by a fire; instructions to operators are sufficiently clear and unambiguous and records show that there has been adequate control of the limits and conditions as the risk profile at THORP reduces as the facility enters Post Operational Clean Out (POCO).
We also found that safety equipment has been identified and examination, inspection, maintenance and testing has been completed. Where defects were identified by THORP, these were understood, recorded and controlled, and records provided us with evidence that earlier reported defects had been repaired.
We were satisfied that the training records demonstrated that the personnel whose records were sampled had received training in relation to fire protection activities, and we also found that the personnel were aware of the potential for the escape of radioactivity as a result of fires, including fire-fighting water, and that any potential contaminated waste has been considered and mitigation is in place.
We identified that the Nuclear Fire Safety Assessment (NFSA), although implemented is starting to diverge from the remainder of the safety case and provided regulatory advice to THORP that this should be updated as the facility transitions through POCO and that THORP should consider developing a fire safety strategy similar to those developed elsewhere on site.
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 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 in the safety case for the nuclear fire protection system at THORP and that the formal arrangements for LCs 10, 23, 24, 27, 28 and 34 are being adequately implemented. No regulatory issues were raised; however, we gave regulatory advice in relation to THORP updating its nuclear fire safety assessment at an appropriate time in the transition through POCO into Surveillance and Maintenance so that it better reflects the facility’s hazards and risks during those phases, and that THORP should consider developing a fire safety strategy similar to those developed elsewhere on site.
Overall, we judge that the safety system is adequate and fulfils the requirements of the safety case.