Thermophysical and mechanical properties of LaB 6 and CeB 6 synthesized through spark plasma sintering

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.