In the absence of experimental and measured data, a reliable numerical model is needed to predict the performance of fuel assemblies after extended storage, including acceleration and strain of fuel rods due to impact and vibration, and quantify the effects of aging (i.e., material degradation) on the risk assessment of the structural integrity of transportation casks. In this study, potential failure mechanisms of fuel-assembly components due to impact is studied. A numerical model of a transportation cask containing 32 Westinghouse 17 × 17 (WE) pressurized water reactor (PWR) optimized fuel assemblies (OFA) was simulated. The transportation cask model consists of cask body, impact limiters, neutron shield, canister, basket, spacer blocks, detailed and surrogate fuel assemblies. For the detailed fuel assembly, the fuel rods are modeled as beam elements supported at the spacer grids with nonlinear springs representing the leaf springs and dimples. The bonding of the pellets to the cladding is considered in the modeling and its effect on the dynamic response of the fuel assembly is examined. In addition, degraded models are analyzed were the stiffness of the non-linear leaf spring and dimples as well as the modulus of elasticity of the spacer straps are reduced to represent the degradation due to radiation and relaxation. The acceleration transmissibility of the cask at the level of the basket due to a 0.3 m drop above a flat unyielding and rigid horizontal surface are investigated, which results show the importance of cell location within the basket. Further, pinching forces due to the contact of the fuel rods with the leaf springs and dimples due to the impact are estimated. In this study, the leaf springs and dimples flat out due to drop and fuel rods contact the spacer grid surface, therefore the maximum pinching force of 2407 N for the initial impact is obtained.
Numerical Simulation of a Transportation Cask and Transmissibility due to 0.3 M Drop
September 13, 2019
Publication: 25th Conference on Structural Mechanics in Reactor Technology