Technischer Bericht NTB 84-05

The report presents a highly radioactive waste container concept based on the use of hot isostatically pressed aluminium oxide. The container is made of two cylindrical parts closed each at one end, which are sealed by means of a gold diffusion weld after introduction of the vitrified waste package. It is shown that the corrosion rate of the alumina material under conditions similar to those expected in Switzerland will most probably be less than 0.15 mm in 1'000 years.

The design consists of a cylinder about 2 m in length and 0.7 m in outer diameter, with hemispherical ends, ensuring that no tensional stress is present when the container is subjected to an external uniform pressure. The seal is positioned in the cylindrical part of the container, 150 mm away from the hemispherical end; in this way the stresses in the seal due to end effects and local bending can be made sufficiently small.

A stress analysis shows that for such a design a wall thickness of 60 mm is sufficient to fulfill the requirements of the stress and stability criteria even with the use of a very high safety factor, for an external pressure of 300 bar, corresponding to a repository depth of 1'200 m. For the protection of the personnel during the transport operations in the repository a metallic, temporary transport overpack is necessary; this overpack also protects the container against shocks.