The current German waste management strategy consists of dry interim storage of spent fuel inside dual purpose casks at various sites and its subsequent direct final disposal in a deep geological repository. Interim facilities are licensed for up to 40 years of operation but this storing period will have to be extended until repository site selection and operation is concluded, potentially up to 100 years. In this context, research on long term mechanical behavior of fuel cladding and cask components during extended interim storage and transportation to a final repository are of outmost importance.

Barrier properties of the fuel cladding depend on its integrity which is affected over time by thermo-mechanical loads and by microstructure altering including potential embrittlement caused by re-oriented hydride precipitation. Experimental and numerical investigations have been performed by the international research community in order to predict the degree of cladding embrittlement against storage time. Results have shown that embrittlement of cladding materials is governed by the concentration, orientation and size of precipitated hydrides. Nevertheless, the existing variety of fuel materials and assemblies available on the market and the many parameters effecting hydride precipitation do not allow sufficient reliable safety predictions in the long term without further investigation.

Thus, knowledge on cladding integrity over storage time and during subsequent transportation is to be gained taking into consideration the relevant fuel and cladding material types as well as cladding temperatures along with peak values during cask drying and cooling rates during storage periods. Expected research results will increase the accuracy of cladding safety analysis. This paper summarizes the current German status regarding extended interim storage and how BAM is going to identify and address potential cladding integrity issues in the long term.