Comparison of Structural Integrity of Ductile Iron and Lead-Shielded Stainless Steel Casks for Transportation and Storage of High-Level Waste

Nine-meter (30-foot) drop simulations of three different types of transportation casks, a monolithic ductile iron (DI), a monolithic stainless steel (SS), and a lead-shielded stainless steel (SS/Pb) sandwich, were simulated using DYNA3D. The results show that the monolithic casks are much stiffer than the stainless steel/lead sandwich cask. The largest difference was observed between the DI cask and the SS/Pb sandwich cask. Although the SS/Pb cask experiences considerable plastic deformation, none of them experiences failure by rupture, and they all perform within the requirements of Regulatory Guide 7.6, Revision 1 (1978) and 1 OCFR71 (1988). To better compare the results, stress- and strain-based factors of safety were calculated for all of the simulations. These calculations show that the DI cask has a larger margin of safety than the SS/Pb sandwich cask, while the monolithic SS cask has a larger margin of safety than the monolithic DI cask. Finally, to address the concern over the brittleness of the DI casks, critical flaw sizes were calculated. All flaws required for crack propagation were larger than the detectable flaws by current inspection techniques. Overall, the results of this study indicate that DI has sufficient strength, ductility, and fracture toughness to be considered as a structural material for transport casks.