NUREG/CR-6672: RESPONSE OF GENERIC CASKS TO COLLISIONS

This paper describes the calculations performed to determine the response of four generic spent fuel casks to impact accidents that support the generic risk assessment of NUREG/CR-6672 [1]. The generic casks analyzed represent the most typical types of casks currently used in the United States to transport spent fuel: truck casks with steel-lead-steel and steel-DU-steel walls and rail casks with steel-lead-steel and monolithic steel walls. The specifications for these casks are discussed in another paper of this symposium [2]. This paper discusses the results from finite element calculations for impacts onto a rigid target in three orientations and at four velocities for the generic monolithic steel rail cask. These calculations are unique in that they modeled the entire cask, including closure bolts, and failure was directly measured by calculation of the degree of opening in the closure. In a risk assessment, as well as in the real world, most collisions do not involve impact onto a rigid target. In order to account for the energy absorbed by the target, an energy partitioning scheme was used to develop impact speeds onto yielding targets that were equivalent to the impact speeds onto the rigid target considered in the analyses. The frequency distribution of various targets is discussed in a companion paper [3]. In the transport of spent nuclear fuel, the containment boundary of the cask is not the only barrier to release. The cladding of the fuel can also provide containment. This paper also discusses the method used to determine the response of the cladding to the analyzed impacts. Knowing the response of the fuel and the response of the cask to various impacts allows rod-to-cask and cask-to-environment release fractions to be calculated. The calculations of these parameters are given in a companion paper [3].