Comparison of the Elastic and Elastoplastic Approaches for Brittle Fracture Assessment

In general, TRANSNUCLEAIRE uses a dedicated forged carbon steel (SA 350 grade LF 5) to manufacture the body of large casks for spent fuel transport. Thick-walled bodies ensure the main biological protection and the confinement of radioactive materials. For transport safety as required by the lntenational Atomic Energy Agency Regulations (lAEA 1990, Safety Series no. 6) for type B packagings, the steel confinement should provide sufficient structural resistance during drop tests, including at low temperature ( -40°C), which implies the justification of the absence of brittle fracture. Risk of brittle fracture in this carbon steel is mainly related to the presence of initial flaws similar to cracks, to the stress intensity during impacts, and to the low temperature. To reduce this risk, preventive measures during design and manufacturing have to be taken. During manufacturing, an ultrasonic examination is performed to detect flaws with a minimum size of 6 nun ( 1/4 inch). The body is rejected if such flaws are detected. Then, to prove that flaws of equal or smaller size are acceptable from the brittle fracture point of view, specific studies using a Finite Element method are achieved, taking into account cracks of 6 nun length.