Development of retention plate which holds spent fuel cask

A method to retain a cask by a retention plate has been developed. In this method, a small fitting gap between the bottom of the cask and the circular hollow of the retention plate controls movement of the cask in the range of the circular hollow area at an earthquake. The fitting of the cask and the retention plate absorbs the seismic energy by the motion of the cask and the collision between them. Characteristics of the vibration behavior of the cask with the retention plate were analyzed by dynamic analysis. As a result of the analysis, the cask does not get out of the retention plate or fall down during an earthquake. The movement of the cask mainly consists of three basic motions, slipping motion, rocking motion, and rotating motion, and reaction force between the cask and the retention plate becomes the maximum in rocking motion. The strength integrity of the retention plate was also confirmed under condition of the maximum reaction force, and the function of the retention plate, which is to keep the cask as standing at an earthquake, was maintained. In addition, characteristics of the vibration behavior of the cask and the design of the retention plate were validated by 1/4 scale mock-up seismic test.