The ratio of grain boundary energy to surface energy of nuclear ceramics as determined from pore geometries

Several workers have derived high grain-boundary to surface energy ratios from measurement of the geometries of pores located at grain boundaries. The values (of more than unity) are two to three times greater than those calculated from the geometries of interactions of free surfaces with grain boundaries, and, in the case of irradiates UO2, have been attributed to fission-product segregation effects. This work has confirmed previous observations of pore geometries and led to similar data for unirradiated and irradiated nuclear ceramics. It has been found that irradiation has no clear effect on pore geometries and hence it is concluded that fission-product segregation is not a significant factor. The work suggests that the theories used to derive energy ratios from pore geometries need modification. (orig.)