Manufacturing porous U10Zr fuels with controlled porosities by SPS and thermal properties

To accommodate the swelling of metallic fuels induced by the fission gas release for a sodium-free fuel option, advanced U-10Zr fuels with controlled porosities were designed and demonstrated by spark plasma sintering (SPS). U-10Zr fuel pellets with manufactured porosities varying from 35% up to fully dense fuel pellets have been fabricated by controlling mechanical attrition of the starting uranium powders, sintering temperature, pressure, and duration, and the correlation among the microstructure control – porosity – sintering conditions has been established. To further mimick the pore structure in irradiated fuels, different pore formers (NaCl and NH ₄HCO ₃ ) were used to control the pore size and distribution. Microstructure characterization indicates a lamellar reaction zone of enriched Zr and U composed of alpha Zr with 2 at% U and distorted alpha U with 13 at% of Zr, respectively, differing from the arc-melted U-10Zr as a result of rapid consolidation of SPS at lower temperatures and short durations. The thermal conductivity of U10Zr with different porosities were also measured. This work demonstrates the success in manufacturing new metallic fuel forms with controlled porosities and pore distribution, which can be used as model systems to investigate the thermal transfer behavior of metallic fuels in the reactor.