Brittle Fracture in Transport Casks: Evaluation of Methods to Predict Crack Initiation

For the acceptance of the B(U) packages for the transport of radioactive material, the manufacturers must demonstrate their integrity for the transport of these materials. The containers· must be able to sustain the most severe drop conditions recommended by the IAEA at an ambient temperature of -40°C. This requirement implies that the absence of a risk of a sudden fracture is justified, especially for thick cast iron or forged ferritic steel containers. Recommendations concerning an elastic-plastic treatment ofthe risks of brittle fracture, i.e., taking plasticity into account in the K1 and J criteria are discussed in order to be introduced in the draft Appendix IX oflAEA Safety Guides No. 37. To assess the applicability and the validity of different evaluation methods for the risk of fracture, the lnstitut de Protection et de Surete Nucleaire (IPSN) has undertaken, with the support of the CEA/DRN/DMT mechanical engineering laboratories, a research and development program on this subject.This R&D program, which aimed to improve our knowledge ofthe mechanical behavior of a container, has now been completed. The approach adopted in this program was to carry out tests on container mock-ups and cracked rings, together with numerical simulations of tests with CASTEM-2000 finite-element codes for the static case and PLEXUS code for the dynamic case. These codes were developped at the CEA, using an elastic-plastic behavior model based on the mechanical characteristics of the material in order to establish a simplified method for J calculation. The objective is to determine the J value at the time corresponding to the initiation of the crack and to compare this value with the toughness of the material, the most significant mechanical property in this behavior.