Cermet surrogate nuclear fuels from coated powders

Abstract

• Initial coatings improve the microstructure of surrogate fuel elements. • Initial coating thickness is crucial in tuning the microstructure. • Potential for fuel elements with greater than 60 vol.% fissile fuel exists. • Higher fuel fractions would result in improved efficiency and decreased weight. Nuclear thermal propulsion (NTP), which may utilize cermet fuels, shows promise in improving the feasibility of long-distance space travel. These cermet fuels are composed of a ceramic nuclear fuel phase, such as UO 2 or UN, and a protective refractory metal (W or Mo) phase. In this work, a material system consisting of tungsten-yttria stabilized zirconia (W-YSZ) surrogate fuel elements were fabricated via spark plasma sintering . Prior to consolidation, magnetron sputtering was utilized to provide conformal W coatings to the YSZ particles, such coatings were 80 to 550 nm in thickness. These coatings, when excess W powder was added, were found to reduce the ceramic-ceramic contacts as well as improve the densification of the cermet over powders that were not coated. Furthermore, when the coating thickness was at least 350 nm, and additional W powder added to yield a metallic fraction of 32 vol.%, the ceramic-ceramic contacts remained nearly identical to higher W fractions. This suggests that conformal coated ceramic fuel particles would reduce the necessary amount of refractory metal matrix, which in turn would reduce neutron poisoning, lower fuel element weight, and increase fissile fuel content from the 60 vol.% fuel in conventional NTP cermets.