A NEW FRACTURE MECHANICS ASSESSMENT METHOD FOR FERRITIC STEEL COMPONENTS OF TYPE B PACKAGES

The IAEA Regulations for the Safe Transport of Radioactive Materials require the consideration of temperatures of -40 °C for Type B package designs. According to the German approval practice, this temperature shall be also taken into account during mechanical tests simulating accident situations with these packages. Therefore, the necessary safety analysis includes fracture mechanics assessments for all safety related components of the packages. ln the past, these evaluations have been performed for components manufactured from ferritic steels by methods usually used for pressure vessels. Because of the restrictions of these methods if applied to thick-walled casks and the low-temperature embrittlement of ferritic steels which is additionally increased by high impact rates during accidents, BAM as the responsible German testing authority for Type B packages required the establishment of a fracture mechanics analysis method that considers especially the test conditions for this package type. A proposal of the German cask designer GeseUschaft fiir Nuklear-Beha.lter (GNB) provides the use of a method for these analyses which bas been developed during the recent years in the European Communities for steel constructions (especially bridges) with the objective to establish an appropriate European standard. The paper discusses problems and necessary adaptions of the method if applied to Type B packages from the point of view of the testing authority.