A Radioactive Waste Management Overview of the Challenges Metallic Fuels and Chemically Reactive Higher Activity Wastes (HAW) Present for Geological Disposal - 22446

Metallic uranic fuel has been used in the United Kingdom's Magnox fleet of reactors since the 1950's, with the Magnox reprocessing plant at Sellafield forming a key part in the management of the spent fuel. While over 54,000 metric tonnes of metallic uranic spent fuel have been reprocessed to date, an inventory of several hundred tonnes remains to be dispositioned. This remaining metallic uranic material, arising from both the operation of the Magnox fleet and the historic Windscale Pile Reactors, has been stored for decades at facilities at the Magnox Reactor station sites and within the historic facilities at Sellafield. This is in addition to the large inventory of Magnox swarf metal waste from Magnox reprocessing operations which, since 1990, has been packaged in cement at the Sellafield Magnox Encapsulation Plant. Following the retirement of the Magnox reactor fleet and planned completion of Magnox fuel reprocessing, the UK will also possess an inventory of several hundred tonnes of metallic uranic Magnox fuel that will need to be managed and permanently disposed. These reactive metals form a significant part of the inventory to be disposed of with the UK Geological Disposal Facility and pose a range of technical challenges. These have been the subject of much consideration within the waste packaging and disposability decisions which form the basis of the Nuclear Decommissioning Authority's (NDA's) integrated waste management strategy. Due to the reactive nature of the metallic materials and the range of durations and conditions within which it has been stored, the inventory exists in a variety of states. This ranges from one extreme of corrosion products with low remaining parent metal, arising from decades of underwater storage, through to the other extreme of fully intact uranium fuel pieces and fuel debris which have been stored in nominally dry conditions in vaults and bunkers. The bulk of the inventory exists somewhere along that continuum as partially degraded Magnox swarf arising from fuel decanning including an inventory of metallic uranium 'carried over' as a result of mechanical fuel de-cladding. The varied nature of this inventory, and the high prevalence within which it is mixed with other miscellaneous Intermediate Level Wastes, has resulted in a range of solutions being implemented bespoke to the physical state of the material, the nature of the facilities in which it has been stored and the constraints of the individual nuclear licenced sites upon which it arises. The paper will discuss the variety of approaches being adopted for metallic fuel/waste material inventories across the UK including those from the Sellafield High Hazard Legacy Ponds and Silos and how these approaches balance the need for prompt remediation, reduction in overall technical risk and the requirements of ALARA to minimise risk of double handling of waste. The paper will also identify the key technical and operational risk mitigations being pursued and how these have supported the Nuclear Decommissioning Authority and its subsidiaries to work collaboratively on life cycle approaches to the management of these materials, while recognising the inherent uncertainties that will remain until a site-specific design and safety case has been developed for the UK Geological Disposal Facility (GDF). (authors)