Study on effect of drop attitude during 9 m slap-down drop using dynamic analysis

FEM analysis was performed using the LS-DYNA software to evaluate the effect of the secondary impact load on a slap-down drop. The finite element analysis (FEA) model, which has shock absorbers in the head and bottom, modeled a large virtual nuclear fuel transportation package that constituted a containment boundary with a primary and a secondary lid. It had a weight of 136 ton. The drop attitude angle was also considered in the slap-down drop for drop test I. The FEA model has a gap between the BWR fuel assembly and the basket lattice, and it makes a delayed drop from the BWR fuel assembly to the basket lattice. Through a case study employing 10 different drop attitude angles, the time histories of impact acceleration of representative points on the package in the drop direction and the load of both primary and secondary lid bolt shafts and basket stress were summarized.The results of the case study could not represent the maximum damage for one of the drop attitude angles for the evaluation items. By using a beam element for the bolt shafts of the FEA model, the evaluation of stress for the bolt shafts became simplified and made the computing faster than it was using solid elements.By studying these results, it was found that the drop attitude angle that produced the maximum damage was different for each evaluation item. Therefore, it was concluded that slap-down drops need to be studied with multiple angles of attitude for evaluating the structural integrity of the package.