(GRS-856) SPIZWURZ Benchmark Phase 1 - Blind Benchmark Report (Version 1)

In-house research project RS1586A

The originally licensed dry storage period of 40 years for spent nuclear fuel requires ex tension due to the lack of a duly available final disposal facility in Germany. The assess ment of fuel rod integrity at the end of extended storage periods relies heavily on numer ical predictions. Therefore, the development, verification, and validation of reliable fuel performance codes are essential to allow for a robust safety assessment of long-term dry storage operation. Within the framework of the SPIZWURZ project, the SPIZWURZ bundle experiment at KIT was conducted to provide an experimental basis for model development and valida tion. In this test, a fuel rod bundle was subjected to a gradual cooling transient over a period of 250 days, with an average cooling rate of approximately 0.95 °C per day. The experiment generated integral measurement data on cladding creep deformation and hydrogen behavior under conditions representative of dry storage. This report documents the results of a blind benchmark exercise performed to assess the capability of existing fuel performance codes to predict the thermo-mechanical and hydrogen-related phenomena occurring during a long-term cooling transient. The bench mark results provide insight into the current predictive capabilities and limitations of the applied models and contribute to their further improvement for safety assessments of extended dry storage.