b"Figure 2. Van't Hoff analysis of U 3 Si 2hydriding behavior for various H/U ratios of U 3 Si 2 Hx with H/U ranging between 0.20 and 0.50. The figure shows similar slopes for all curves, indicating similar enthalpies of formation for the different compositions. The offsets are due to increasing formation entropy with increasing hydrogen content.of U 3 Si 2hydrided as a function ofcompositions (H/U ranging temperature helped to highlight thefrom 0.2 to 0.5) of the hydride formation of the hydride phase andphase, which are significant in confirm the PCT isotherms. understanding and modeling the From this data, a miscibility gapabsorption of hydrogen by U 3 Si 2critical temperature for hydridefuel. Figure 2 displays Van't Hoff formation was calculated to existanalysis for U 3 Si 2hydriding. It was between 350 and 400 C. Belowalso found that U 3 Si 2subjected the critical temperature, hydrideto hydride-dehydride cycles at or formation proceeds and the hydridenear the miscibility gap critical is thermodynamically stable. Abovetemperature disproportionated into this temperature, hydrogen is onlyuranium metal and silicon. This absorbed to form a solid-solutionwas confirmed using XRD and is a such that U 3 Si 2and U 3 Si 2 Hx aresignificant finding in understanding the same phase. Vant Hoff analysisU 3 Si 2fuel degradation by exposure of the PCT isotherms was usedto hydrogen.to calculate the enthalpies and entropies of formation for several 2019|AFC ACCOMPLISHMENTS 53"