Research activities at GRS on fuel rod behaviour during extended dry storage

As a common part of nuclear waste management strategies, used nuclear fuel is dry stored in casks. After a sufficient time of wet cooling in fuel pools, the fuel assemblies in Germany are dry stored in dual purpose casks mostly on-site until a deep geological repository will be available in the future. In the light of the extended and preliminary not foreseen timescales of up to 100 years of dry storage, open questions arise concerning the long term fuel rod behaviour. Most of these questions are linked to safety criteria e.g. the integrity and fuel encapsulation. Due to the variety of used nuclear fuels and cladding materials in Germany and the additional use of MOX fuels and very high burn-up values of 65 GWd/tHM averaged over a fuel assembly, some of the boundary conditions are unique and specific to the German situation. The GRS has a strong research program to investigate the long term behaviour of fuel assemblies under the German specific conditions of dry storage. Some aspects are presented in the following article.