Fuel performance modeling of used nuclear fuel transfer between storage pools and its impact on dry storage

The transfer of fuel in dry casks between the storage pools at the Swiss nuclear power plant Gösgen is known as the Wet-To-Dry-To-Wet (W2D2W) transfer procedure. The process is associated with vacuum drying, transfer to an external storage pool and reflooding. The high cladding temperature and stress during the drying and transport in combination with quick reflooding can lead to precipitation of radial hydrides and deterioration of the cladding mechanical properties. In this report, the impact of the drying, transfer and reflooding periods on the concentration and distribution of radial hydrides is studied. The most limiting rods are identified based on the criteria proposed in this work and submitted to multiple scenarios considering various durations of the W2D2W stages. The results show the impact of different phases and reveal that the reflooding speed/rate has the biggest influence on the hydrogen behavior. The analysis of the simulated dry storage scenarios shows that the maximum temperature obtained at the end of drying governs the hydrogen migration into the liner.