Abstract: A system for the underground storage of fluids, e.g. petroleum products in rock. The system comprises a plurality of cavities excavated in the rock. Each of said cavities has a cylindrical shape with a circular or oval cross-section. Each cavity forms a storage space the walls of which are formed by the rock and directly absorb the pressure of the fluid stored in the cavity. The cavities are arranged with their center axes standing vertically, and the vertical height of each cavity is greater than or equal to the diameter of its cross-section. The distance from each cavity to adjacent cavities is equal to or greater than the diameter of the cross-section of the cavity, and the centers of the cross-sections of the cavities as seen in a horizontal cross-section of the whole system are positioned in a two-dimensional pattern.

Abstract: An underground repository for the storage of radioactive material, particularly spent fuel from nuclear reactors and radioactive wastes produced by reprocessing spent nuclear fuel. The repository comprises a hollow body of solid material for accommodating the radioactive material. The hollow body is surrounded by a shell or barrier of clay. The hollow body and the clay barrier are located in a cavity in rock, the clay filling the space between the hollow body and the inside of the rock cavity.