TECHNICAL BASIS FOR EXTENDING STORAGE OF THE UK'S ADVANCED GAS-COOLED REACTOR FUEL

摘要

The UK Nuclear Decommissioning Agency has recently declared a date for cessation of reprocessing of oxide fuel from the UK's Advanced Gas-cooled Reactors (AGRs). This will fundamentally change the management of AGR fuel: from short term storage followed by reprocessing to long term fuel storage followed, in all likelihood, by geological disposal. It is estimated, based on current plans, that spent fuel stocks will rise from around 1,000-2,000 tonnes at the end of reprocessing to approximately 5,000-6,000 tonnes by 2040. There is an active, staged programme of work underway to site and build a geological disposal facility and an initial assessment of the disposability of spent AGR fuel has been completed. With a planned receipt date for spent fuel of 2075 it is anticipated that the spent fuel will need to be held in storage for many decades. Storage of spent AGR fuel in caustic dose ponds followed by reprocessing has proved an effective means of managing these fuels for up to ～20 years. Although gaps in the scientific knowledge base supporting spent fuel storage still exist, the technical underpinning is currently aligned with storage needs. The change in strategy for management of AGR fuel places new requirements on storage systems. NNL has reviewed the technical basis for available storage options to assess the adequacy of current information to support the technical case for long term storage of AGR fuel. Wet storage in caustic dosed ponds represents the most effective option for AGR fuel. Nevertheless work is required to provide reassurance that the infrastructure and fuel performance remain acceptable as storage periods increase. Further R&D into existing gaps in the scientific knowledge base relevant to spent fuel storage could increase confidence in future performance by determining whether slow degradation mechanisms, that affects a small proportion of fuel, and the effects of high burn-up are potential causes for concern. Although dry storage of large quantities of AGR fuel has been examined in the past, large scale dry storage of AGR fuel has never been deployed. To make this a credible contingency option further work would be required, particularly to establishing the required storage environment to ensure that cladding corrosion remains within acceptable limits. In the light of proposed duration of fuel storage the role of R&D in maintaining critical skills and capabilities is also highlighted.