The Oxidation of Uranium Oxide Spent Fuel at Low Temperatures

The expected remaining lifetime of the UK’s Advanced Gas-cooled Reactors (AGRs) will result in the generation of ~6600t of Spent Nuclear Fuel. The Nuclear Decommissioning Authority’s preferred option for this spent fuel is pre-disposal interim storage – currently in ponds at Sellafield – prior to final disposal by consignment to a geologic disposal repository in or around 2075. AGR fuel pins consist of UO2 pellets sealed inside steel cladding tubes.


Whilst in-reactor, some of the cladding can be rendered susceptible to in-pond corrosion, potentially leading to through-wall cladding failure. This may result in pond water contamination by the spent fuel (which now contains fission products and actinides as well as UO2) and inter-granular corrosion of the pellets themselves with loss of pellet integrity. Consequently, a transition to dry storage has been proposed – including the drying of wet stored spent fuel. Both actions may carry further unknown risks that need to be understood before implementation.


Using novel spent fuel simulants (SIMFUELs), we will seek to develop a molecular level understanding of the oxidation behaviour of the UO2 matrix in spent AGR fuel at low temperatures <200oC and under conditions relevant to proposed UK dry storage. Sited within Lancaster’s new state-of-the-art nuclear chemistry / chemical engineering facility (UTGARD Lab, funded by the Dept of Business, Energy & Industrial Strategy), this project will use coupled electrochemical, thermogravimetric and spectroscopic methods to elucidate the products, kinetics and thus mechanisms of the oxidation processes that obtain in both the gas an solution phase.


Academic Lead: Colin Boxhall
Researcher: Ian Robertson
Location: Lancaster University