In its recently published paper ‘Oxide Fuels – Credible Options’, November 2011, the Nuclear Decommissioning Authority (NDA) sets out options for the future operation of Sellafield’s Thermal Oxide Reprocessing Plant THORP. Opened in 1994 to reprocess UK’s domestic Advanced Gas Cooled (AGR) fuel and Light Water Reactor (LWR) fuel from overseas customers, the plant is currently operating years behind schedule. An estimated 400 tonnes of overseas spent fuel that should have been completed around 2004, plus some 2000 tonnes of UK AGR fuel remains to be reprocessed. These are referred to as ‘contracted fuels’.
In addition, a further 4000+ tonnes of spent AGR fuel (including the currently expected lifetime arisings from the UK’s fleet of AGR power stations) are destined either for long-term storage at Sellafield prior to disposal or for reprocessing – at the NDA’s discretion. Should 5-year extensions be granted to the AGR power stations, a further 900 tonnes of spent fuel would arise.
This CORE Briefing provides a summary of the NDA’s assessment of three Options for THORP: – 1 Complete THORP’s reprocessing contracts; 2 Close THORP early by reprocessing less than the contracted amount of spent fuel and 3 Extend THORP operations so that more than the contracted amount of spent fuel can be reprocessed.
From its assessment, the NDA has concluded that, in line with its 2011 Strategy, Option 1 is the most viable and cost-effective – with the proviso that ‘additional new and costly infrastructure can be avoided (this would include the installation of new High Level Waste tanks), and that NDA proposals for the interim storage of AGR fuel are themselves viable. After further work to underpin the strategy, and providing the provisos are met, the NDA expects to confirm Option 1 as its preferred strategic option by summer 2012.
In currently rejecting Option 3 – extending THORP operations to include more AGR fuel being reprocessed than currently contracted, and potential new business from domestic and overseas customers ‘if there were any’ – the NDA cites that:
• extended reprocessing would require multi-billion pound investment across a wide range of infrastructure at Sellafield, with major capital build projects required to support THORP’s extension beyond 2020. Such investment would divert finite resources from the NDA’s primary role of risk and hazard reduction at Sellafield, and new capital build projects would result in energy use and carbon emissions.
• extended reprocessing could potentially impact on the UK’s discharge commitments under the OSPAR treaty and could challenge the alpha and tritium target levels under the UK’s own Strategy for Radioactive Discharges.
• it would not be cost-effective to reprocess more AGR fuel in THORP than was necessary to create space for its interim storage.
• reprocessing 900 tonnes of spent fuel projected to arise from AGR power station extensions would mean THORP operating to the mid to late 2030’s and, with transport and fuel cooling period requirements, the plant could only be operated intermittently.
• there is ‘no evidence that domestic or overseas utilities are seeking to enter into new contracts for meaningful amounts of new reprocessing in THORP’ – particularly on terms and timescales that would ensure profitability to the NDA.
• no interest has been expressed by the potential operators of new-build reactors in the UK to have their spent fuel reprocessed and recycled. Even had they done so, bulk quantities of spent fuel would be unlikely to be ready for reprocessing until the mid-2030’s when THORP and associated facilities would be over 40 years old.
The NDA’s current rejection of closing THORP early under Option 2 is based on:
• the provision of additional storage capacity for AGR fuel at Sellafield to ensure that incoming fuel from the power stations – at around 180 tonnes/yr – can be managed.
• the possible need to implement alternative arrangements for overseas fuel.
• the requirement to manage spent fuels that are more susceptible to corrosion during storage.
• the resultant earlier reduction to the workforce – though this could be mitigated by redeploying workers to the high hazard reduction activities elsewhere on site.
However, the NDA nevertheless believes that the early closure option should continue to be examined because of concerns that should a number of performance risks associated with THORP and its support facilities arise, Option 1 might have to be abandoned before 2018.
These risks include the overall age and condition of the reprocessing infrastructure, further failures of Sellafield’s current suite of Evaporators which process the high level wastes produced by reprocessing – or a delay in bringing on-line of a new Evaporator in 2014/15 – and the viability of the plans to store AGR fuel. The success of these storage plans depends on the current programme to remove redundant multi-element bottles (MEB’s used to transport overseas fuel that has now been reprocessed)) from the ponds being completed on schedule, and the ponds suitably dosed with a corrosion inhibitor.
Based on THORP’s 2018 closure, an application to the Local Authority for a change of use of the ponds from buffer storage prior to reprocessing to interim storage pending disposal is expected to be made around 2016. Subject also to Regulatory approval, the NDA believes a technical and safety case for both storage and disposal of AGR fuel can be made.
In promoting what is likely to be its preferred Option 1, the NDA says that by completing THORP’s contracts in 2018, it will have honoured obligations to overseas customers (and inter-Governmental treaties); provide time to prepare facilities for the interim storage of AGR fuel and create space to receive and manage all fuel arisings from AGR stations. It would also enable fuels susceptible to corrosion to be reprocessed.
The NDA believes the costs of the next 7 years of reprocessing – taking THORP to a 2018 closure – are comparable to those of the storage and direct disposal of spent fuel – largely because the capital costs for the reprocessing infrastructure are already sunk. If this had not been the case ‘it would be more cost-effective to cease reprocessing early’.
As part of its Oxide Fuels Credible Options paper, the NDA was asked by Government to consider the wider impacts of its THORP closure decision on the potential for future reprocessing in the UK. Reviewing topics that included Fast Breeder Reactor prospects, the future use of plutonium and new-build reactor operations, the NDA concluded that the timing of THORP’s closure had little material impact on any potential future requirement to supply plutonium; that THORP’s closure would neither impact on the UK’s new-build programme nor on the long-term potential for reprocessing in the UK. Should the latter be required, a new reprocessing plant would be necessary.
It also concluded that, on a like for like basis, spent fuel storage followed by disposal ‘is currently more cost-effective than reprocessing’. This was based on an anticipated rise in costs of reprocessing and MOX fuel production in the UK, and the currently low price of uranium. Not surprisingly, all cost data was omitted from the NDA’s paper on the grounds of commercial confidentiality.