[en] The properties of high-level wastes disposed of in geological formations after solidification with vitreous and pyroceramic materials, the behaviour of these wastes under high temperatures and the effects of ionizing radiation are discussed. With strontium-90 serving as an example, the variations in maximum leaching rates are estimated with different compositions of material in interim storage conditions. The temperatures occurring in boreholes, each of which is filled with different types of solidified waste, are given for different borehole diameters and thermal conductivities of the ground. Leaching mechanisms with various types of disposal condition are discussed. (author)