Modeling maximum fuel temperature in dry storage: From the CFD analysis to the engineering approach

Abstract

Dry interim storage of spent fuel has expanded significantly; as any other option it should ensure fuel rod integrity under any circumstance. This requires cooling fuel assemblies. Because major degrading mechanisms of cladding are influenced by temperature, the threshold conditions selected in most regulatory requirements is based on Peak Cladding Temperature (PCT).This paper proposes a calculation route of PCT free of the high complexity of fluid-dynamics and the long computing time burden. Based on heat transfer equations applied over conceptually suitable systems, a thermal resistance scheme is set and solved, resulting in fast and accurate estimates. Both features would enable this methodology to be coupled with fuel performance codes without overloading each single thermo-mechanical calculation. The performance of the method is illustrated through its application to a concrete and a metallic cask, both under steady and transient conditions. When compared to results from 3D-CFD calculations, the deviations observed in the PCT estimates are lower than 5%, and the time calculation saving has been estimated to be about 105 times faster. This method is planned to be extended to other variables like the minimum temperature in the cask, of utmost importance to estimate the ductile-to-brittle transition of cladding materials.