A key criterion to allow spent nuclear fuel to be safely packaged for disposal is that is conditioned such that any free moisture is limited. Residual water that is carried over in the waste container is subject to radiolysis and excess water could potentially lead to flammable atmospheres and over-pressurisation of the waste package. In principle, this should be straight-forward for spent nuclear fuels that are intact (i.e. their zircaloy or stainless-steel cladding material has not breached); however, it is much less straight-forward for failed fuels, as it is currently not possible to predict how much water remains (i.e. how much is physically/chemically entrained, how does water vapour migrate in a semi-porous, drying environment).
Recent PhD work has looked to understand the drying processes for spent fuels from first principles [1]. Separate to this finite element-based nuclear fuel performance codes, such as BISON [2] have been developed that include modelling fission gas and material release from spent nuclear fuels in accident conditions [3]. This PhD project seeks to build on this experience by applying the fundamental modelling that can be applied to existing fuel performance codes to determine the migration of water in drying environments.
[1] R. Ros Trujillo, Thermal Modelling of AGR Fuel Drying, University of Bristol, 2021–2025.
[2] Idaho National Laboratory, BISON: https://mooseframework.inl.gov/bison/
[3] M.W.D. Cooper, C. Matthews, and D.A. Andersson, Development of bubble evolution model for new mechanistic transient fission gas release capability in BISON, LA-UR-23-24769, April 2023.