Beryllium oxide(Be0)-doped (0.3, 0.6, 0.9, 1.2 and 13.6 wt%) UO, pellets were fabricated to evaluate the effects of Be0 precipitate shape on thermal conductivity. Precipitate distributions were of two types: Be0 precipitated almost continuously along a grain boundary (designated Be0 continuous type) and spherical Be0 randomly dispersed within the matrix (designated Be0 dispersed type). Thermal diffusivity was measured by a laser flash method and thermal conductivity was evaluated. The thermal conductivity increased with the Be0 content. The thermal conductivity of the Be0 continuous type was higher than that of the Be0 dispersed type at lower temperatures, while their difference became smaller at higher temperatures. The thermal conductivities of U0,-1.2 wt% Be0 at 1,100 K were higher than that of UO, by about 25 % for the Be0 continuous type and by about 10 % for the Be0 dispersed type. The thermal conductivities of both types were expressed by a semi-empirical equation as a function of volume fraction and shape of the Be0 precipitates.F~x +81-29423-6621, pellets were provided for this study; one had Be0 precipitating almost continuously along grain boundaries, while fine spherical precipitates were randomly dispersed within the matrix in the second type. The thermal conductivity was evaluated in terms of the volume fraction and shape of Be0 precipitates.
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