Simulating Hydrogen Diffusion in ZrH Moderator and its Impact on Coupled Neutronic-Thermal Simulation of a Heat Pipe Microreactor

Abstract

Metal hydride moderators are a common material choice for moderating compact reactor designs, as their high thermal limits and high density of hydrogen make them favorable for operation. One additional attribute of metal hydrides, zirconium hydride in particular, is the relatively large mobility of hydrogen within the metal lattice, especially at high temperatures and under large thermal gradients. As hydrogen’s spatial distribution directly impacts neutron thermalization in the system, and therefore power shape, changes in hydrogen concentration of the moderator may be important to analyze. This work couples OpenMC and MOOSE in order to solve the feedback loop of the coupled power distribution-thermal distribution-hydrogen migration without relying on mesh discretization. Functional expansions are used extensively as a method of transferring spatial information, and continuously varying material tracking is used in the neutronic solver to represent the change in hydrogen concentrations. The resulting hydrogen redistribution is highlighted, as well as the resulting neutronic and thermal impact of this redistribution.