Hydrothermal corrosion studies on nitride fuels
Uranium mononitride (UN) has been identified as a candidate nuclear fuel for use in the current US light water reactor (LWR) fleet as well as in next generation nuclear plants (NGNP), largely due to its high uranium density and thermal conductivity. However, its hydrothermal corrosion performance in accident scenarios has not been thoroughly investigated. In this work, UN was synthesized using a hydride-de-hydride-nitride thermal synthesis route prior to sintering into dense compacts (> 90% TD). The compacts were corroded in a water filled autoclave up to 350 Celsius degrees and 125 atm. The kinetics of corrosion were characterized through phase analysis, mass loss, and microstructural analysis. The phases observed after hydrothermal corrosion correspond only to UN, UO{sub 2}, and UN{sub 2}; no U{sub 2}N{sub 3} was observed. Additionally, it appears that nitrogen uptake into the lattice of the solid product is a product of lattice strain and peak broadening, especially of the UN{sub 2} phase. UO{sub 2} appears to nucleate on the surface of the UN-UO{sub 2} monoliths and consumes the UN grain boundaries which suggests that in pure UN, UO{sub 2} formation proceeds from the surface and moves towards the core, but in samples with nominal concentrations of UO{sub 2}, oxidation from hydrolysis occurs throughout the bulk of the monoliths. Furthermore, it was demonstrated here that UN and UN-UO{sub 2} composites perform better than previously reported in the literature.