Executive summary
Date(s) of inspection: December 2024
Aim of inspection
The Office for Nuclear Regulation (ONR) regulates Sellafield Site in accordance with the ONR Sellafield strategy. Two of the three key outcomes of the strategy are:
- Accelerated hazard and risk reduction across the Sellafield site.
- Evidence-based confidence that the licensee is complying with its statutory obligations and that workers and the public are protected from the hazards of the site.
Accelerated hazard and risk reduction (HRR) across the Sellafield site, targets those projects that deliver the biggest HRR. One of those projects is the retrieval of stored radioactive waste from the magnox swarf storage silo (MSSS), an intolerable risk legacy facility ONR has placed in significantly enhanced regulatory attention. The essential electrical system (EES) supports waste retrieval operations on MSSS.
This system base inspection (SBI) focused on the adequacy of Sellafield Ltd.’s implementation of the MSSS safety case as it applies to the EES. The Licence Conditions (LC) covered in the SBI were LC10 (training), LC23 (operating rules), LC24 (operating instructions), LC27 (safety mechanisms, devices and circuits) and LC28 (examination, inspection, maintenance and testing). LC34 (leakage and escape of radioactive material and radioactive waste) was omitted because there were no direct claims on the EES relating loss of containment.
Subject(s) of inspection
- LC10 - Training - Rating: GREEN
- LC10 - Training - Rating: GREEN
- LC23 - Operating rules - Rating: Not Rated
- LC23 - Operating rules - Rating: Not Rated
- LC24 - Operating instructions - Rating: Not Rated
- LC24 - Operating instructions - Rating: Not Rated
- LC27 - Safety mechanisms, devices and circuits - Rating: Not Rated
- LC27 - Safety mechanisms, devices and circuits - Rating: Not Rated
- LC28 - Examination, inspection, maintenance and testing - Rating: GREEN
- LC28 - Examination, inspection, maintenance and testing - Rating: GREEN
- LC34 - Leakage and escape of radioactive material and radioactive waste - Rating: Not Rated
- Overall Inspection Rating - Rating: GREEN
- Overall Inspection Rating - Rating: GREEN
Key findings, inspector's opinions and reasons for judgement made
The Office for Nuclear Regulation (ONR) regulates Sellafield Site in accordance with the ONR Sellafield strategy. One of the three key outcomes of the strategy requires evidence-based confidence that the licensee, Sellafield Limited, is complying with its statutory obligations and that workers and the public are protected from the hazards of the site.
The Magnox Swarf Storage Silo (MSSS) is an intolerable risk legacy facility ONR has placed in significantly enhanced regulatory attention. Sellafield Limited is implementing an extensive programme of work to address the intolerable risk by retrieving the radioactive waste for safe storage elsewhere on site prior to final disposal in the geological disposal facility. The essential electrical system EES supports safe operation including waste retrieval activities on MSSS.
This system base inspection (SBI) sampled evidence to the adequacy of Sellafield Ltd.’s implementation of the MSSS safety case as it applies to the EES. The Licence Conditions (LC) covered in the SBI were LC10 (training), LC23 (operating rules), LC24 (operating instructions), LC27 (safety mechanisms, devices and circuits) and LC28 (examination, inspection, maintenance and testing). LC34 (leakage and escape of radioactive material and radioactive waste) was omitted because the main risk is from the original building silo leakage, which has been subject to extensive ONR regulatory involvement.
The ONR inspection team consisted of me, the Legacy Silos safety inspector, an electrical engineering specialist inspector and an inspector seconded from the Japanese nuclear regulator. The SBI gained evidence from sampling key documents prior to the inspection, discussions with relevant Sellafield Limited staff, sampling documents on site, and from a guided inspection of the MSSS EES.
For LC 10, LC24 and LC28, We judged that, based on the evidence sampled, Sellafield Limited has adequately implemented the MSSS safety case as it relates to the EES. We considered that a Green rating, no formal action, is appropriate for the three LCs. Sellafield Limited provided evidence that there were no systems or components classified against LC27 on the MSSS EES. There were a small number of emergency operating rules for the system, all of which Sellafield Limited provided evidence that they were not complex or difficult to implement. From the evidence sampled, we judged that LC23 and LC27 should not be rated.
During the inspection we identified that a diesel generator system appeared not to be required, but was still available for operation and was being maintained. Sellafield Limited confirmed that the system was not required and will be permanently removed from service. We were satisfied with the licensee’s response and considered further regulatory oversight was not required in this instance
We also identified an apparent shortfall in the calibration of instruments used to inspect some EES components Subsequently, Sellafield Limited was able to provide evidence that the instruments were calibrated now and at the time of the maintenance work. We were satisfied with the licensee’s response and considered further regulatory oversight was not required in this instance.