Field assisted sintering of CeO₂, UO₂ and mixed (U,Ce)O₂ pellets

Robert W. Harrison1

J. Morgan, J. Buckley1, T. Abram1, D. Pearmain3, S. Bostanchi3, C. Green, R. White, D. Goddard2, N. Barron2

1University of Manchester, 2UK NNL and 3Lucideon Ltd


Field assisted sintering (FAS) techniques such as spark plasma sintering (SPS) and flash sintering (FS) have received increasing attention for the manufacture of uranium-based nuclear fuels over the last decade. Conventionally, UO2 is manufactured by cold uniaxial pressing followed by pressure-less sintering in a reductive atmosphere at hold temperatures of ~1700°C for 5-10 hours to achieve the required density, microstructure and stoichiometry. SPS and FS offer the possibility to dramatically decrease the sintering hold time and temperatures required to produce dense fuel pellets. The reduced sintering temperatures and times make these techniques of interest to mixed uranium-plutonium oxide (MOx) fuels for thermal and fast reactors. However, there are still challenges to address with both techniques to demonstrate controllability, repeatability and scale-up as well as understanding the effect of shorter hold times and sintering temperatures on the plutonium distribution in the MOx fuel, which has consequences on fuel performance and reprocess-ability of the fuel.

To examine the effects of the shorter hold times and sintering temperature on the pellet microstructure and “Pu distribution” in MOx fuel we have manufactured UO2 and (U0.93,Ce0.07)O2 as a MOx fuel surrogate using FS, SPS and conventional sintering at the Nuclear Fuels Centre of Excellence (NFCE). This has involved collaborative work with the National Nuclear Laboratory (NNL) and Lucideon Limited to develop, install and commission a bespoke uranium active FS furnace at the NFCE. Lucideon have employed their nonlinear real time FS control software to solve homogeneity and reliability in CeO2 as a fuel surrogate, and its benefit is demonstrated, as utilised here for uranium active materials. The optimisation of this novel active FS system for UO2 pellet manufacture together with how the FS control mechanisms monitor the thermal and electrical behaviour of the material (pellet) to ensure homogeneity in surrogate/uranium-based fuels will be presented. Alongside this, results of the effect of sintering technique/parameters on the pellet microstructures and chemical homogeneity from XRD, SEM-EDS and Raman microscopy characterisation will be presented with an outlook for exploiting the benefit of FS and other FAS techniques for the manufacture of uranium oxide bearing fuels.

Event Timeslots (1)

Tuesday – 14th September 2021
Robert W. Harrison