Development of simplified fuel assembly model for nuclear fuel transportation

Abstract

To evaluate the integrity of spent nuclear fuel (SNF) during transportation, the vibration and drop impact analysis requires a transport cask model loaded with a significant amount of SNF and performing a dynamic analysis in the time domain. A cask model with a three-dimensional fuel assembly (FA) model requires substantial time. Therefore, simplified hexahedral-shaped FA models with equal weights have been used. However, FAs interact with the cask and account for a significant portion, affecting the mechanical response behavior of the transport cask and FA. Therefore, a dependable FA model must be used to obtain accurate cask and FA mechanical responses. Herein, we developed a simplified equivalent beam FA model to address the above issues. The guide tubes and fuel rods were modeled as a single equivalent beam, and the spacer grids were simplified to a shell shape by removing springs and dimples supporting the fuel rods. Rotational springs were implemented at the locations of spacer grids and nozzles to simulate the static bending and dynamic vibration of FA. The simplified FA model was compared with mechanical test results, and the results correlated well. Therefore, this model can be used for FA transportation and will be crucial in predicting the reliable mechanical responses of FA and transport cask.