Thermophysical and mechanical properties of LaB₆ and CeB₆ synthesized through spark plasma sintering

Abstract

Following the Fukushima Daiichi nuclear power plant accident in 2011, the development of accident tolerant fuels (ATFs) has become an integral part of the promotion of nuclear safety. Of the many design criteria, a high thermal conductivity reduces a fuel pellet's peak temperature and radial temperature gradient. Although various uranium borides such as UB₂ and UB₄ are promising ATFs that have high-temperature stability, high uranium density, and good thermal conductivity, little is known about UB₆, as it has yet to be fabricated under normal conditions. As a metal hexaboride, UB₆ may have excellent electrical conductivity, likely giving it a much higher thermal conductivity than that of UO₂. In this work, we investigate the thermophysical and mechanical properties of non-radioactive LaB₆ and CeB₆ to estimate the potential properties of UB₆, as it has yet to be successfully fabricated. The thermophysical properties of UB₆ are compared with those of UO₂, UB₂, and UB₄ to help clarify whether future attempts at fabricating UB₆ under high pressure or with other dopants are worthwhile for the development of ATFs.