This experiment will test current theories and ideas relating to the formation of uranium hydride, which takes place in the storage of spent nuclear fuel. We will engineer an idealised mimic of the interface between the stored fuel and its environment, by growing a thin film (50nm) of uranium with an oxide (UO2) overlayer of approximately 25nm. This system will then be exposed to a 1 bar Ar/H2 atmosphere (<2% H2), using neutron reflectivity to probe the U/UO2 interfacial layer. We also intend to look at the effect of a Pd cap and the effect of a patterned oxide layer to model a real fuel surface. This will give us vital information concerning the rate at which U hydriding takes place and the way that it progresses. It will have significant impact in the commercial nuclear sector in terms of understanding safety aspects of storing and repackaging legacy nuclear waste in the UK.