Dynamic structural response of reinforced concrete dry storage casks subjected to impact considering material degradation

Abstract

The performance of vertical concrete casks (VCC) for storage of spent nuclear fuel (SNF) under hypothetical accident conditions is of particular importance given the planned extensions of service-lives of such structures in the absence of a permanent disposal solution. Numerical models are created in this paper to simulate the structural response of a generic VCC in the cases of end-drop (handling drop) and tip-over considering material degradation. A concrete damage plasticity model (CDP) was calibrated using standard material tests to capture the non-linear behavior of concrete. Similarly, the steel properties and the properties of the soil supporting the cask foundation were based on material test data. The finite element models (FEM) were validated using experimental data from end-drop and tip-over tests of a 1/3-scale VCC performed by the same authors and reported elsewhere. The numerical results are compared with the experimental measurements in terms of velocity, acceleration, damage, and failure modes to gain confidence in the numerical results. Thereafter, a push-over analysis method was proposed and performed on the VCC for the first time to investigate the effect of different levels of material degradation on the structural response of VCC. The reduction in the concrete reinforcing steel area and bond degradation due to corrosion, and concrete strength reduction due to effects such as alkali-silica reactivity were considered as the variables for the parametric analysis. The results are interpreted to understand the changes in the performance of VCC in the long-term when subjected to hypothetical accident conditions in comparison to intact as built conditions.