ON THE BEHAVIOUR OF CAVITIES IN A VISCOPLASTIC MEDIUM WITH APPLICATION TO UNDERGROUND REPOSITORIES OF RADIOACTIVE WASTE IN SALT DOMES

摘要

A cavity in a viscoplastic material will shrink if the surrounding medium is exposed to an external pressure. This shrinkage is greatly influenced by the temperature of the material, because of an Arrhenius-type material law for the creep behaviour. If the temperature is also time-dependent thermal expansion will, in addition, affect the volume change of the cavity. Rock salt behaves like a viscoplastic material. In salt domes used as underground repositories for radioactive waste, temperature differences of about 200 degrees C can arise in the salt. For a safety analysis of the repository it is of great interest to know the shrinkage of the cavities, called the convergence. The convergence behaviour is investigated in the case of a hollow sphere and a hollow cylinder. A viscoplastic material with variable time-dependent temperature is assumed. The problem leads to a nonlinear integro-differential equation which is solved analytically in simplified cases and numerically in the general case. The numerical solution shows good agreement with experimental results. An approximate solution for the general case is proposed. [References: 15]