SIMULATION STUDY OF CONCRETE MATERIAL NUMERIC MODEL IN THE EVALUATION OF STORAGE CASK'S TIPPING OVER EVENT

Recently, at the interim storage facility of spent fuels many metal casks are used in worldwide. Generally, these metal casks are set with vertical position in the interim storage facility. In Japan, some storage casks are designed not to tip-over by the tie-down device, etc. However, in the Standard Review Plan of NRC[1], the evaluation of tipping-over of storage cask is required as a non-mechanistic event consistent with the defense-in-depth policy. The metal casks are set without shock absorbing covers during storage period, hence, in the tipping over event, the sealing part of the lid may be directly collide to the storage facilities floor. However, there are still uncertainties for the impact behaviours of the metal cask without impact limiters under such severe impact loads. The dynamic behaviour of the lid during the event greatly influences the sealing performance of the metal cask; therefore it is important to clarify the interaction of the metal cask's lid and the storage facilities floor. In this study, by using various numeric models for concrete material of the storage facilities floor, analyses of tipping over event of metal cask using dynamic analysis code LS-DYNA have been performed. The investigated cask has been designed for transport and storage of 52 BWR-type fuel assemblies with double lid structure. The target of collision of the cask is the reinforced concrete floor, and the strength of the concrete is same as a design strength of an interim storage facilities floor. And for the analytical model of the concrete material, following three material numeric models are considered. 2 (1) Concrete material model developed by CRIEPI considering strain rate dependence and multiaxial fracture (2) Pseudo tensor concrete material (3) Isotopic elastic-plastic material Furthermore, input conditions for them, such as the modification method of material properties and contact conditions for surface of concrete material have been determined from post analysis of a component test of concrete material. From the comparison with lid behaviours in tipping over event analyses with these material models, we will propose appropriate input conditions for the concrete material model when they are used for the evaluation.