AbstractFracture safe design can be assured by proper application of fracture mechanics. Linear elastic fracture mechanics (LEFM) can generally be applied to a broad range of cask designs and component materials. The use of LEFM is straightforward when the linear elastic plane strain fracture toughness (K1c) of the cask material can be directly measured. When the plane strain fracture toughness cannot be directly measured, a special form of LEFM can be used. The fracture toughness can be equivalently determined through measurement of the J1c (elastic–plastic) fracture toughness. While this LEFM approach can only be used under specific conditions, such conditions are generally met by heavy-walled casks under severe loading conditions. The regulatory drop test, in which a subcritical flaw has been intentionally introduced into a prototype cask, can be used to demonstrate the suitability of applying LEFM design to a specific cask. This paper describes the LEFM design approach as applied to cask design for a ...