THE CONTRIBUTION OF THERMAL-RADIATION TO THE THERMAL-CONDUCTIVITY OF POROUS UO2

The influence of cylindrical, spherical and ellipsoidal inclusions on the overall thermal conductivity was computed with the finite element technique. The results of these calculations were compared with equati ons that describe the effect of inclusions on the overall thermal cond uctivity. The analytical equation of Schulz [B. Schulz, KfK-1988 (1974 )] that describes the effect of inclusions on the overall thermal cond uctivity is in good agreement with the results of the finite element c omputations. This good agreement shows that among a variety of porosit y correction formulas, the equation of Schulz gives the best descripti on of the effect of inclusions on the overall thermal conductivity. Th is equation and the results of finite element calculations allow us to compute the contribution of radiation to the overall thermal conducti vity of UO2 with oblate ellipsoidal porosity. The present radiation ca lculations show that Hayes and Peddicord [S.L. Hayes and K.L. Peddicor d, J. Nucl. Mater. 202 (1993) 87] overestimated the contribution of th ermal radiation to the thermal conductivity.