Finding limiting rods for dry storage analyses

Fuel rod status during reactor operation must be numerically modeled before dry storage analyses. Simulating all the rods ever irradiated in Switzerland with state-of-the-art best estimate tools would be too time consuming. The goal of this study is to develop a methodology for identifying limiting BWR rods, where the criterion of limiting is the rod internal pressure. Limiting rods are those whose parameters may challenge rod integrity during dry storage, subsequent transport, or handling. The presence of radial hydrides is of particular importance. The precipitation of radially oriented hydrides is associated with strong tensile hoop stress of the cladding. This can be a consequence of high rod internal pressure which has been chosen the limiting parameter. In the first step, the 3D core simulators provide irradiation data. Then, the core simulator results along with rod geometrical parameters are submitted to the principal component analysis. The multidimensional datasets are reduced to 2D and processed by a clustering algorithm or not, depending on the assembly design. The limiting rods are identified for each batch or cluster and simulated with the fuel performance code Falcon and the hydrogen behavior code HYPE.