ŠKODA JS has completed the development of a spent fuel storage cask for underground repository

15. 11. 2021

By producing a model of a storage packaging assembly (cask) for spent fuel from Dukovany and Temelín in the planned underground repository, ŠKODA JS a.s. has completed the development of this type of cask. The client is the Radioactive Waste Repository Authority (SÚRAO). Within the project, the optimal design of the cask was proposed and, on the basis of corrosion tests in a simulated environment of the future repository, materials with high corrosion resistance were selected which will guarantee the storage of spent fuel for hundreds of thousands of years without breaking the cask's hermeticity.

This guarantees the most important aspect, i.e. no leakage of radionuclides to the external environment. Corrosion tests of the material were carried out in cooperation with experts from the subcontractors of this project, ÚJV Řež, a.s., the University of Chemical Technology in Prague and ENERGOVÝZKUM, spol. s r.o. in Brno.

Thus designed cask consists of an outer casing made of thick-walled carbon steel tube with a diameter of 914 mm. Inside the outer casing there is a built-in structure consisting of inner shells made of thick-walled stainless steel. Each shell is designed for one fuel assembly. In the case of the VVER 440 fuel (Dukovany NPP), the cask assembly contains 7 inner shells, and in the case of the VVER 1000 fuel (Temelín NPP), the cask assembly contains only 3 shells because these fuel assemblies are larger. Both the shells and the outer casing are hermetically sealed on both sides by welded-on lids. The final welding of the lids will be carried out by welding robots in the so-called hot chambers on the site of the underground repository. The fact that each fuel assembly is hermetically sealed in a separate shell increases the safety of the fuel handling during transfer to the storage casks.

The length of the casks is determined by the type of fuel stored. For the fuel from Dukovany, the designed cask has a length of almost 4 meters and a weight of 14 tons; for the fuel from Temelín, the length is almost 5 meters and the weight is 18 tons. The diameter of both types of cask is chosen to be the same (914 mm) with a view to unification of the underground repository, in particular the handling and welding robots, transport means or the boreholes in the rock in which the casks will be embedded.

The model of the cask is made in real diameter, but in a shortened length to allow it to be placed in the planned information centre of the SÚRAO. For this purpose, the model is made with a partial cut-out to allow a view of all the details of its construction.

The development of the packaging assembly for underground repository is a logical continuation of ŠKODA JS's experience in the entire spent nuclear fuel management cycle. ŠKODA JS manufactures storage racks for pools where spent fuel is stored after being removed from the reactor. After several years of storage in the pool, the fuel assemblies are transferred to storage and transport casks, which are stored in so-called dry intermediate storage facilities in nuclear power plants. For this purpose, ŠKODA JS used to supply nuclear power plants with CASTOR casks manufactured under license from the German company GNS, and now supplies ŠKODA 1000/19 and ŠKODA 440/84 casks according to its own design. The fuel is expected to be stored in these containers for 60 years. After this time, the fuel assemblies will be transferred to the packaging assemblies for the underground repository. In thirty years, ŠKODA JS has produced almost 470 storage containers for radioactive materials, the absolute majority of them for spent nuclear fuel.