[en] The radioactive source terms pertinent to spent fuel transport cask safety assessments are of three distinct origins; residual contamination within the cask due to previous transport and handling operations, ''crud'' deposited on the fuel rods in the course of reactor operation, and the radioactive material contained within the rods. Although the last source overwhelms the others in terms of inventory, its release into the cask, and thence into the biosphere, requires the breach of an additional release barrier, viz., the fuel rod cladding. Hence an evaluation of the fuel source term is complicated by the need to address the likelihood of fuel cladding failure during transport. A comprehensive methodology is being developed to accurately describe fuel rod response to severe impacts which includes the extent of release of radioactive material in the event of fuel cladding failure. The analysis model allows for the various levels of interaction that could occur, namely, between the cask basket and assemblies, between assemblies, and between rods. Using as-transported conditions and material properties of spent fuel, analyses have been conducted for various levels of geometric modeling details, including multi-assemblies, single assemblies, and single rod configurations. For cask design purposes, the maximum impact loading on the fuel rods that need be considered is that resulting from 0.3 meter and 9 meter drops of the loaded cask onto an unyielding target. If it is assumed that the cask body is infinitely rigid, energy absorption is limited only to the impact limiters of the cask, providing a conservative estimate of the deceleration forces imparted by the cask to its contents. 7 refs., 1 tab