2018 | AFC ACCOMPLISHMENTS 54 Corrosion and hydriding behavior of U3Si2 Principal Investigator: Aditya P. Shivprasad Collaborators: Joseph R.Wermer and Joshua T.White U3Si2 is a promising, high- uranium-density fuel because of its good thermal properties and performance during irradiation and has been considered as a potential replacement for UO2 in commercial light water reactors. Despite these advantages, limitations are observed when the coolant comes in contact with the fuel, e.g., breach of cladding, resulting in degradation of the fuel. Research this fiscal year (FY) focused on continuing research from FY17 by studying the hydrogen absorption of U3Si2 and relating this behavior to corrosion performance in steam. Project description Under steam and simulated pressurized water reactor (PWR) conditions, the fuel has also been observed to oxidize and potentially absorb hydrogen, after which the fuel pulverizes. Rapid pulverization of U3Si2 has been observed during exposure to both hydrogen gas mixtures, high- temperature water, and steam but is not well-understood: comparison with waterside corrosion in uranium metal showed similarities in post- corrosion microstructure, leading to the hypothesis that hydride formation occurs in U3Si2. Previous work in FY17 evaluated U3Si2 performance in hydrogenated water (5 ppm H2 at 300°C) and showed that, beyond 30 days of exposure, rapid pulverization occurred.A similar effect was observed in pure hydrogen and both were correlated to a hypothesized hydride phase observed in the microstructure. In FY18, the oxidation performance of U3Si2 in steam was evaluated using carefully-selected steam compositions and temperatures. In parallel, hydriding of U3Si2 was studied in a Sievert’s apparatus at various temperatures.The purpose of these tests was to determine the temperature regimes in which hydriding kinetics and thermodynamics were sufficient to cause pulverization of U3Si2, as well as to characterize the composition of the hydride phase that forms. Accomplishments Sintered compacts of U3Si2 were subjected to oxidation in a 75% steam/argon mixture. Using a steam furnace coupled with thermogravi- metric analysis at the Fuels Research Laboratory at Los Alamos National Laboratory (LANL). Samples were heated in argon gas maintained at Studying the mechanisms of steam oxidation and hydrogen absorption will help understand how to mitigate degradation in- reactor by these modes.