LEDA – Long-Term Experimental Dry Storage Analysis

The experimental studies will take the form of “integral effect tests”, i.e. tests and investigations on different fuel rod segments with prototypical boundary conditions for dry storage in Germany. Typical conditions are set and monitored. Furthermore, suitable investigations for the pre- and post-characterisation of the cladding tube materials are also required. The objectives of the LEDA test programme are the integral study of the behaviour of fuel rod segments representative for Germany under typical conditions of dry interim storage.

The experimental data generated in LEDA will be used to extend and validate analytical models and methods for predicting fuel rod integrity for verification purposes in line with protection goals. The previous criteria for the exclusion of systematic cladding failure and their completeness will be reviewed and analysed taking account of (long-term) hydrogen behaviour for storage times of over 40 years.

The long-term measurement campaign will be carried out with different irradiated fuel rod segments under prototypical boundary conditions. An integral approach under drying process and dry interim storage conditions is taken. The implementation of adequate pre- and post-characterisation of the fuel rod segments and the focus on hydrogen-induced effects, in combination with the use of fuel rod segments representative for Germany, in contrast to individual effect tests, allows results to be interpreted directly.

The fuel rod segments that will be studied are as similar as possible to the fuel rods used in Germany in terms of cladding tube materials, fuels and irradiation histories. This will ensure that consideration is given as far as possible to the prototypical conditions that apply to cask loads.

The tests will be carried out in the hot cells at Studsvik in Sweden in a test rig suitable for this purpose. The latter was developed and manufactured as part of the Halden Reactor Project (HRP) to investigate fuel rod behaviour under dry interim storage conditions. After the operating licence for the Halden plant expired, the Halden Board agreed to the test equipment being transported to the Studsvik laboratories in Nyköping to ensure that it could continue to be used by BGZ. A sketch of the test rig, which has been extensively modified, is shown in Figure 12. Eight fuel rod segments can be simultaneously exposed to a typical temperature transient in the test rig, varying axially and over time. Typical axial temperature profiles are set for the tests. Over a period of several months, the temperature will be successively lowered, similar to the cooling of the fuel assemblies in interim dry storage after the cask has been sealed.

At least three test campaigns with up to eight fuel rod segments each are currently planned. Each campaign includes an extensive pre- and post-characterisation phase during which mechanical and material parameters are determined. The current plans include investigations of a total of eleven fuel rod segments and ten entire fuel rods. The latter are each divided into four segments so that they can be analysed in the test stand. The segments and rods have been selected to best represent the inventory held by BGZ. The burn-up of the fuel rods and segments is between 20 and 80 GWd/tHM and the cladding tube materials consist of the alloys M5, DUPLEX, Optimized ZIRLO, Zry_-4 and Zry_-2 with and without liner.