While making good progress in some areas, Sellafield Ltd has made limited progress with waste and spent fuel retrievals from the legacy ponds and silos due to a combination of technical difficulties, supply chain issues and equipment reliability, according to a report from the Office for Nuclear Regulation (ONR).

Material from Dounreay has been added to Sellafield’s inventory and this has increased the overall risk and “made the totality of the remediation work more onerous”. Sellafield remains red-rated in relation to the first generation Magnox storage pond (FGMSP), Magnox swarf storage silo (MSSS) and pile fuel cladding silo (PFCS). The rest of the site is amber.

ONR says the most hazardous legacy ponds and silos and special nuclear materials areas at Sellafield “will continue to receive significantly enhanced regulatory attention for nuclear safety reasons for many years to come”.

While progress has been made with remediation of the highest hazard facilities on site, there have been a number of delays to some important hazard and risk reduction projects during the year. The most significant are the PFCS and the FGMSP.

The preparation and commissioning activities to enable export of intermediate level waste (ILW) from FGMSP have been problematic. The facility has experienced technical and supply chain difficulties, “which the licensee has struggled to resolve quickly” and which affected Sellafield’s ability to export ILW from FGMSP into a new interim storage facility. ONR is maintaining regulatory scrutiny of Sellafield Ltd’s work in this area to ensure it resolves these issues.

ONR said it took action to hold Sellafield Ltd to its legal obligations, because along with delays in safety and security improvements it faced matters of legal compliance. It applied an ‘enforcement management model’ (EMM) and captured and escalated matters through the ONR’s Issues Database. It held monthly senior level engagement meetings on performance and delivery and provided advice, guidance and expectations in relation to safety and security improvements. It said, “Sellafield Ltd recognises that there are areas of improvement and provided commitments to us that will be tracked through to completion and should performance not improve, further formal enforcement action may result.”

ONR issued an enforcement notice at the FGMSP facility requiring replacement of an inadequate fire alarm and detection system. It said, “Given the degraded condition of these facilities, containment safety functions that fall below the standards expected, and their significant radioactive inventory, these facilities will remain in ‘significantly enhanced’ attention for nuclear safety for the foreseeable future.”

Progress in places

There had been progress in several areas. ONR agreed to allow Sellafield to deploy a diver on a trial basis in PFSP bays 11 and 12. During the last 10 years, Sellafield has undertaken significant clearance work inside these two bays using a range of techniques. Good progress had been made, but the techniques have delivered diminishing returns. Sellafield completed the first dive successfully before the end of 2022 and completed the trial in March 2023 following several successful dives. The use of divers has allowed Sellafield to retrieve some of the remaining material from bays 11 and 12, which existing retrieval techniques were no longer able to do. The experience from deploying divers in the PFSP will help inform investigations into how divers might also contribute to the clean up and dewatering of nuclear ponds.

Sellafield conducted active commissioning and subsequent retrievals from MSSS Compartment 10, starting in April 2022, making good progress against the planned waste retrieval rate. It has retrieved 19 skips of miscellaneous beta gamma waste and retrievals are ongoing. It also began visual inspection of packages containing mixed oxide residues in the Mox Demonstration Facility Lab L to inform final disposition, which was completed in June 2022. Sellafield is making further progress with the assembly of the second of the three silo emptying plants, SEP1. This is in preparation for full retrievals, which are currently planned to commence in late 2025.

Leak to ground

ONR also assessed Sellafield’s responses to regulatory concerns associated with a leak to ground in the MSSS original building. This is an old facility, with historic leakage from a section of single layer containment dating back to the 1970s. Leakage had recommenced.

In its report for 2019/20, ONR required Sellafield to ensure effective management and mitigation of the leak and to review its safety case in this area. In July 2022, Sellafield provided the outcome of a review.

ONR guidance states that, in rare cases, an identified leakage and escape cannot be stopped as the required repairs are not technically feasible. This is the case for this leak. ONR said it had assessed the radiological risks to workers and the public arising from the current and postulated future leakage as low. But “Recognising the potential for leakage to continue for several decades until the bulk of waste is retrieved from the silos, the leak rate and levels of ground contamination will continue to be closely monitored and reported.” Sellafield has a programme of work associated with the leakage: inspectors identified some shortfalls with the future programme of work, which will be monitored.

The ONR has increased its scrutiny of a programme of active commissioning and early retrievals from PFCS compartment 5. It granted permission for the programme in February 2022, but during the initial stages of active commissioning, an equipment failure required an extended recovery and repair period (although it had no radiological or conventional safety consequences). Active commissioning and early retrievals were due to restart in mid 2023. ONR will monitor this “until we have confidence in the facility’s ability to retrieve”.

Sellafield Ltd is making progress in preparing for the operation of a new facility, known as the Box Encapsulation Plant Product Store/Direct Import Facility (BEPPS/DIF), for long term storage of waste from MSSS and PFCS. ONR saw delays to inactive commissioning due to technical and equipment issues but said, “We are satisfied that Sellafield Ltd is actively resolving these matters and expect the facility to request commencement of active commissioning in the mid- to late summer of 2023”.

Cyber security

Sellafield also remains red-rated for cyber security and is likely to remain so while Sellafield addresses shortfalls reported last year. But the regulator has reduced the regulatory attention level for protective security to enhanced attention and agreed a clear action plan with Sellafield Ltd that sets out the path to return to routine attention.

ONR said, “we have worked to ensure that Sellafield Ltd’s operational teams and leaders better understand their security risks and how these are effectively managed“.

Spent fuel management

With the cessation of reprocessing at the Magnox Reprocessing Facility in July 2022, regulatory effort has been targeted on the remnant Magnox fuel that was not reprocessed and the Advanced Gas-cooled Reactor operating programme, which focuses on transporting and storing the remaining spent fuel from the shutdown AGR reactors at Sellafield.

Performance of the waste vitrification plant has been affected by plant ageing and reliability issues and remains under regulatory observation.

The existing analytical services facility is now 70 years old and is suffering from the effects of ageing. ONR says enhanced attention has helped drive activities to improve the current facility structure and maintain focus on progressing a replacement facility on the Sellafield site. The work on improvements to the current facility will ensure continued safe operation until the transition into the new facility.

Industrial safety performance has been variable this year and is a “key driver for the enhanced attention level”. Formal enforcement was required: Sellafield has developed and is implementing a fire life safety improvement plan and is developing an industrial safety improvement plan, both of which are receiving targeted regulatory oversight. ONR is also increasing its focus on Sellafield’s leadership and management.

Sellafield is an extremely complex site and the legacy ponds and silos, some of which date back to the earliest days of the UK’s nuclear journey, are among the most challenging elements to resolve. Clearly, while Sellafield has made progress, technical difficulties, supply chain issues and problems with equipment reliability waste have significantly hampered their progress.