Framework for dynamic analysis of radioactive material transport packages under accident drop conditions

Abstract

Radioactive material transport packages for certain forms of radioactive materials are designed to withstand a 9-meter accident drop onto an essentially rigid surface in accordance with the IAEA regulations SSR-6. This study presents a framework for dynamic analysis of transport packages under accident drop and impact conditions. To evaluate structural behavior and performance of the transport packages with large deformation occurring in a very short duration, material models incorporated in the dynamic analysis framework are established with four key aspects: 1) true stress and strain are used to describe characteristics of large deformation of materials; 2) effect of strain rate is included to reveal dynamic response of materials to high-energy impact loads; 3) material constitutive models are established to capture realistic mechanical behaviour of materials under highly triaxial stress states; and 4) stress triaxiality-dependent damage and fracture criteria of materials are incorporated to limit the plastic deformation to material fracture and to safeguard the containment boundary of the Dry Storage Container (DSC) that contains the used (i.e., irradiated) fuel or other forms of radioactive materials. Critical material and model parameters and properties associated with the material constitutive models, true stress-strain relationships, strain rate effect, and damage and fracture criteria are appropriately determined based on experimental results or theoretically derived based on observed material behavior in elementary stress states. The implementation of the proposed analysis framework is demonstrated by a case study for a Type B(U) transport package, with results to predict the maximum true plastic strain, strain rate, and damage condition of the materials of the package. Since the proposed analysis framework is comprehensive enough to cover necessary aspects to complete an advanced analysis, and the critical material and model parameters are properly determined within this framework that can be readily implemented, the proposed analysis framework is capable of addressing high-energy accident drop scenarios and impact conditions of radioactive material transport packages and containers to meet the nuclear licensing requirements.