Sintering of CaF 2 pellets as nuclear fuel analog for surface stability experiments

To enable a detailed study of the influence of microstructure and surface properties on the stability of spent nuclear fuel, it is necessary to produce analogs that closely resemble nuclear fuel in terms of crystallography and microstructure. One such analog can be obtained by sintering CaF ₂ powder. This paper reports the microstructures obtained after sintering CaF ₂ powders at temperatures up to 1240°C. Pellets with microstructure, density and pore structure similar to that of UO ₂ spent nuclear fuel pellets were obtained in the temperature range between 900°C and 1000°C. When CaF ₂ was sintered above 1100°C the formation of CaO at the grain boundaries caused the disintegration of the pellet due to hydration occurring after sintering. First results from a novel set-up of dissolution experiments show that changes in roughness, dissolution rate and etch pit shape of fluorite surfaces are strongly dependent on the crystallographic orientation of the expose surface. Consequently, the differences observed for each orientation will affect the overall dissolution rate and will lead to uncertainties in the estimation of dissolution rates of spent nuclear fuel.