Isotope Effect in Dissociation of Uranium Hydride

Abstract

Isotope effect on dissociation behavior of uranium hydride has been studied. The equilibrium dissociation pressure of uranium protide(UH3), deuteride (UD3), and of equimolar mixture of both hydrides are measured. The dissociation pressure of deuteride is higher than that of the protide by a factor of about 2 at 400°C and mixed hydride of UH3 and UD3 has intermediate dissociation pressures. Enthalpy and entropy of formation as well as free energy of formation at 298 K obtained from the dissociation pressure are −29.9kcal/mol, −42.8 cal/K·mol and −17.7 kcal/mol for UH3, and −31.5 kcal/mol, −46.8 cal/K·mol and −17.5 kcal/mol for UD3, respectively, which are in good agreement with the values obtained from calorimetrie and heat capacity studies. Mole fractions of deuterium in the gas phase and the solid phase are determined when the mixed hydride is in dissociation equilibrium with gas mixture. In this case deuterium is found to be enriched in the gas phase and the separation factor defined by [D/H]g3S phase/[...