Numerical analysis of the effect of gap-filling options on the maximum peak temperature of a buffer in an HLW repository

Abstract The gaps around the buffer in a high-level waste (HLW) repository have a significant influence on the temperature of the buffer and its long-term performance. This study carried out numerical simulations to analyze the effect of void and filling options on the peak temperature in the buffer. The presence of void inner and outer gaps around the buffer greatly raised the peak temperature of the buffer. However, this high peak temperature was lowered by fillings (bentonite pellets) into the outer gap, and it also decreased with the increase in the dry density and degree of saturation of fillings and the decrease in outer gap spacing. On the other hand, for the inner gap, it was advantageous to leave it empty in lowering the peak temperature of the buffer. The peak temperature compared to the void inner gap, when also considering the effect of radiation, showed only a very minor reduction when the average temperature in the gap, gap spacing, and the emissivity of the copper canister surface decreased. Based on the results of the above numerical simulations, this study also proposed a buffer-gap system that minimizes the peak temperature of the buffer.