The management of spent advanced gas-cooled reactor (AGR) fuel

Full text: In 1998 the approach to be taken by British Nuclear Fuels (BNFL) in discharging it's lifetime contracts for managing spent Advanced Gas-Cooled Reactor (AGR) fuel from British Energy's reactors was out-lined. In the first instance this was to use existing facilities and storage techniques, i.e. wet storage, but recognised that if the initial option became untenable on safety grounds the alternative of constructing a purpose built facility would be taken. The decision would then be one of either to go down the existing wet storage technology route or to a develop a variation of the Scottish Nuclear Limited (SNL) dry store concept. Since 1998 the operating climate has evolved. Changes which have impacted on the approach being taken include: - Declaration of Magnox nuclear power plant lifetimes (23 May 2000); now up to 2010. This has impacted on the availability of existing storage facilities for conversion to AGR storage only from storage in support of reprocessing. Originally the Magnox generation programme would have been completed prior to AGR storage only fuel being received to site; which provided a lead time for conversion of the site's Fuel Handling Plant. - The restructuring of British Energy plc completed 14 January 2005. For fuel loaded to reactor post restructuring, British Energy effectively lease the fuel and title for the fuel transfers to British Nuclear Group Sellafield Ltd. This changes the manner in which the spent fuel can be managed, previously this was influenced by the provisions in 'old' service contracts. - Formation of British Nuclear Group in April 2004 in readiness for the opening of UK nuclear sites to be completed; in-line with the provisions made in the Energy Act 2004. - Formation of the Nuclear Decommissioning Authority (NDA) in April 2005, under the Energy Act 2004, to take responsibility for the UK's nuclear legacy. The NDA approach with respect to AGR spent fuel management will be to establish a national review for determining the longer term options for spent fuel. In the mean time the current strategy for managing AGR spent fuel, i.e. use of Thorp Receipt and Storage, is a 'bridging' solution to maintain power generation activities pending the out-come of NDA review. - Changes in AGR station operating life, the projected Thorp end date (currently 2010/11) and site wide plant performance all impact upon the required storage capability with time; at 1 April 2004 the long-term capability need to provide storage for 3500tU. This requires flexibility in the end solution to accommodate all potential life time spent fuel scenarios. Mean while the underpining engineering and spent fuel longevity studies have also evolved in-line with the changes in the operating environment. In the near term the engineering studies are focused upon developing the Thorp Receipt and Storage asset as a 'bridging' solution to maintain AGR fuel receipts in-line with NDA requirements. These studies have established the existing plant limitations which influence key enablers such as the potential storage capability, plant longevity and the logistics of transferring from one storage environment to another. When taking into to consideration that TR and S is a production facility and a seamless transfer from one storage mode to another will be required then the extent of modifications that can be accommodated is minimal. For example, increasing the storage capability for AGR fuel is influenced by the existing plant set-up, floor loading, the 'Defence in depth' bolt and lock grid positioning system and the mechanical lifting equipment. This has lead to optimised storage system design proposals that are a variation to either the existing AGR storage skip and container and LWR Multi-element Bottle and rack designs. Currently, a 7x7x3 storage array design based upon an LWR rack is the preferred option. In terms of the spent fuel longevity studies these have focused on meeting the long term storage requirement that the primary containment barrier (fuel cladding) should have sufficient mechanical integrity after 80 years storage to enable the fuel to be removed safely for further conditioning. To date these studies have been focused on the wet storage angle as the dry storage aspects were mostly established by the Scottish Nuclear Limited dry storage project. Activities in this area have established the general corrosion rate of the cladding in the corrosion inhibitor sodium hydroxide, the evaluation of alternative corrosion inhibitors and the development of an on-line corrosion probe. To supplement the project studies aimed at underpining the 'bridging' solution, the strategic options for the longer term are being evaluated as part of the overall site strategy. The studies in the spent fuel area have re-evaluated the existing wet storage position, but have also been broadened to evaluating new build options and in particular the multitude of dry storage technologies. (author)