HI-STAR 100 spent fuel transport cask analytical evaluation for drop events

Abstract

The US Nuclear Regulatory Commission (NRC) is responsible for licensing commercial spent nuclear fuel transported in casks certified by NRC under the Code of Federal Regulations (CFR), Title 10, Part 71. Both the International Atomic Energy Agency (IAEA) regulations for transporting radioactive materials (Ref. 2, paragraph 727) and 10 CFR 71·73 require casks to be evaluated for hypothetical accident conditions, which includes a 9 m (30 feet) drop impact event on a flat, essentially unyielding, horizontal surface, in the most damaging orientation. The present paper examines the behaviour of one of the NRC certified transportation casks, the HI-STAR 100, for drop impact events. The specific area examined is the behaviour of the bolted connections in the 'overpack' top flange and the closure plate, which are significantly loaded during the hypothetical drop impact event. The term 'overpack' refers to the cask that receives and contains a sealed multipurpose canister (MPC) containing spent nuclear fuel. The analytical work to evaluate the NRC certified HI-STAR 100 spent fuel transport cask for a 9 m (30 feet) drop impact event on a flat, unyielding, horizontal surface, was performed using the ANSYS and LS-DYNA finite element analysis codes. The models were sufficiently detailed, in the areas of bolt closure interfaces and containment boundaries, to evaluate the structural integrity of the bolted connections under 9 m (30 feet) free drop hypothetical accident conditions, as specified in 10 CFR 71·73. Evaluation of the cask for puncture, caused by a free drop through a distance of 1 m (40 inch) onto a mild steel bar mounted on a flat, essentially unyielding, horizontal surface, required by 10 CFR 71·73, was not included in the current work. Based on the analyses performed to date, it is concluded that, even though brief separation of the flange and the closure plate surfaces may occur, the seals would close at the end of the drop events, because the materials remain elastic during the duration of the event.