Quality assurance aspects in using ductile cast iron for transportation casks

There has been an interest in recent years to assess the suitability of using ductile cast iron (DCI) as the structural containment boundary material for nuclear material transportation casks. This interest is based on the ability to cast to nearly final dimensions and to cast monolithic casks which eliminate welds in the containment boundary. Also, the low material and fabrication costs provide added incentive for evaluating DCI for cask construction. To date, ferritic materials (including DCI) have not been certified for this application. The principal issue in using ferritic materials is that they can (under certain combined mechanical and environmental conditions) fail in a low energy, brittle type fashion, particularly in the vicinity of a flaw. Also, for thick-walled castings, inevitable variability in material microstructure results in mechanical property variability. To qualify this material for use in transport casks, it is necessary to demonstrate not only that the possibility of brittle fracture is precluded but also that the results are repeatable. That is, the development approach (design, fabrication, and testing) used for a prototype cask for proof tests must be transferable to each production cask