Construction and application of two-dimensional axisymmetric temperature field model for high-level radioactive waste disposal repository

The long-term evolution of temperature field in high-level radioactive waste disposal repository is one of the important bases for the safety evaluation and design of buffer layer and the spatial optimization of disposal container. In this paper, a two-dimensional axisymmetric thermal analysis model with two layers of disposal unit is established to analyze the near-field temperature evolution of multi-barrier system. Firstly, the Laplace and finite Fourier sine transforms are applied to the governing equations of heat transfer to obtain the temperature solutions to the buffer layer and the surrounding rock layer in Laplace domain. Then, the corresponding solutions in time domain are obtained by numerical inversion of the Laplace domain solutions with the help of Crump method. Then, the correctness of the model is verified by comparing with the linear heat source solution and the numerical solution. The temporal and spatial distribution characteristics of the temperature field in the near-field multi-barrier system of the disposal unit are analyzed, and the effects of different parameters on the peak temperature of the buffer layer are discussed. Finally, the semi-analytical solution of the model is used to determine the minimum disposal container spacing and predict the results of the in-situ test. The results shows that the semi-analytical solution of the model is proved to be correct by comparing with the linear heat source solution and the numerical solution. The peak temperature of buffer layer is significantly affected by the tunnel spacing, container spacing, thickness of buffer layer, and the thermal conductivities of buffer layer and rock. When the tunnel spacing is 40 m, the container spacing is 7.7 m. The semi-analytical solution of the model can well predict the results of the in-situ test.