Thermal Conductivity of UO₂-BeO Pellet

Abstract

Beryllium oxide(BeO)-doped (0.3, 0.6, 0.9, 1.2 and 13.6 wt%) UO₂ pellets were fabricated to evaluate the effects of BeO precipitate shape on thermal conductivity. Precipitate distributions were of two types: BeO precipitated almost continuously along a grain boundary (designated BeO continuous type) and spherical BeO randomly dispersed within the matrix (designated BeO dispersed type). Thermal diffusivity was measured by a laser flash method and thermal conductivity was evaluated. The thermal conductivity increased with the BeO content. The thermal conductivity of the BeO continuous type was higher than that of the BeO dispersed type at lower temperatures, while their difference became smaller at higher temperatures. The thermal conductivities of UO₂-1.2 wt% BeO at 1,100K were higher than that of UO₂ by about 25 % for the BeO continuous type and by about 10 % for the BeO 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 BeO precipitates.

KEYWORDS:

• thermal properties
• thermal conductivity
• thermal diffusion
• thermal diffusivity
• laser flash method
• uranium dioxide
• beryllium oxide
• precipitation
• mixed oxide fuels
• fuel pellets
• eutectic point
• continuous phase
• dispersed phase
• shape factor