Temperature field of multi-barrier with gap layer in nuclear waste repository

A three-dimensional four-layer thermal conduction model including an air layer was developed to analyze temperature evolution in nuclear waste repository. Laplace-domain temperature solutions for each layer were obtained using finite Fourier transform and Laplace transform. The Laplace-domain solutions were transformed into time-domain semi-analytical solutions by numerical inversion. The surface temperature of central canister was obtained by superimposing the temperature increments of air and buffer layers on rock wall temperature caused by every canister in one disposal panel. The effects of the geometrical parameters, thermal parameters and nuclear waste parameters on surface temperature of canister were studied based on the obtained semi-analytical solution. The results indicate that the presence of air layer has little effect on temperature distribution in bentonite while its effect on temperature at surface of canister is significant. Thickness of air layer has a greater effect on temperature than that of its thermal conductivity. The burn-up value and cooling time also have significant influence on the temperature. Finally, the influences of repository's geometric size on temperature in this model were analyzed.