(283e) First Principles Investigation of Ternary and Higher Metal Hydrides for High Temperature Tritium Sequestration Application

The U.S. Department of Energy Next Generation Nuclear Plant (NGNP) demonstration project will use a very high temperature gas-cooled reactor with helium coolant outlet temperatures in the range of 1000-1200 K. To avoid quenching this potentially industrially-useful process heat, we apply first principles methods to identify metal hydrides capable of removing the dilute tritium contaminant from the high temperature coolant. The thermodynamics of most binary metal hydrides (one metal constituent) are known, and ternary (or higher) systems are typically less thermodynamically stable than the associated binary hydrides, with exceptions for the Th-Zr-H system and complex transition metal hydrides. We first investigate the anomalous ternary interstitial Th-Zr-H system to corroborate the experimentally-observed enhanced thermodynamic stability as a proof of principle calculation for this class of materials. We compute phase diagrams using a grand potential minimization technique and account for configurational entropy effects using a cluster analysis method. We then screen a library of more than 100 complex transition metal hydrides to identify materials with enhanced thermodynamic stability relative to the associated binary hydrides and to rank candidate materials for the NGNP application.