Drying of Spent Advanced Gas Reactor Fuel for Storage and Disposal

In 2012 the Nuclear Decommissioning Authority took the decision to cease reprocessing spent Advanced Gas-cooled Reactor fuel, with any fuel arisings beyond the contracted amount to be stored pending a decision on whether to classify the fuel as waste for disposal. If the fuel is deemed waste then it will be sent to the high heat generating part of the UK’s Geological Disposal Facility (GDF), expected to be in 2075. The current strategy till then is to use extended wet storage while work is being conducted to support dry storage as an alternative and as a pre-treatment for final disposal. The aim of the drying process is to prevent radiolysis of any water left in or on the fuel pin which could lead to both hydrogen and hydrogen peroxide in either the dry store or the GDF. With hydrogen and hydrogen being of particular concern due to hydrogen being explosive and hydrogen peroxide being corrosive. Regarding wet storage the primary concern is that water may seep through the cladding of any failed fuel with stress corrosion cracking the likely cause of this failure. This mechanism causes highly tortuous and branched cracks making characterisation difficult. This work aims to produce a process model to be used to inform the conditions for a future drying procedure. To achieve this two work streams have been set up. The first beign the computational side where the flow through the cracks in the cladding is being modelled and the second, the experimental side, aiming to produce representative crack to aid in validating the process model. Current progress and results will be presented here.