Motion Model of Free-Standing Racks Considering Two-Dimensional Gap Flow

The spent fuel pool of a nuclear power plant is a huge water tank with a vertical and horizontal depth of more than a dozen meters, and multiple box-shaped spent fuel racks in which spent nuclear fuel is stored are lined up in the pool. A free-standing (FS) rack is considered one of the means to improve the earthquake resistance of the spent fuel pool. The rack is not fixed to the floor so that it can move in the pool. Therefore, the inertial force due to an earthquake can be reduced by the frictional force with the floor and the fluid force from the surrounding water, and improvement in earthquake resistance can be expected. In this study, to evaluate the fluid force more precisely, the flow between the racks and the one between the racks and pool wall is treated as a two-dimensional gap flow, and the pressure loss coefficient at the flow path junction and the top of the flow path was estimated based on the steady computational fluid dynamics (CFD) calculation and incorporated into the motion model.