Construction of Dynamic Model of Planar and Rocking Motion for Free Standing Spent Fuel Rack

Abstract

Spent nuclear fuel is settled in racks and stored in spent fuel pool. A free standing rack (FS rack) is a type of a spent fuel rack, which is not fixed to walls unlike conventional ones. For this characteristic, movement of an FS rack during an earthquake can be reduced by fluid force and friction force. However, collision between a rack and another rack or a wall must be avoided. Therefore, it is necessary for designing an FS rack to figure out how it moves under seismic excitation. In this research, a dynamic model of FS racks is constructed considering seismic inertial force, friction force and fluid force. This model consists of two sub-models: translation model, which simulates planar translational and rotational motion; and rocking model, which simulates rocking motion. Moreover, we developed two kinds of rocking model: slide-rocking considered model, which considers the equations of both slide-rocking motion and non-slide-rocking motion; and non-slide-rocking model, which considers only the equation of non-slide-rocking motion. Then, simulations with sinusoidal inertial force input were conducted, changing values of friction coefficient. To validate this dynamic model, a miniature experiment was conducted. It is found that the non-slide-rocking model simulates movement of an FS rack well and better than the slide-rocking considered model in the aspect of translational and rocking movement. However, planar rotational movement is not simulated well with either model. Through this research, the knowledge is acquired that friction force plays a significant role in motion of an FS rack so that estimating and controlling friction coefficient is important in designing an FS rack.