The fluid-structure interaction effect on seismic response of double CAP1400 spent fuel storage racks

Abstract The spent fuel storage racks (racks) are immersed in the spent fuel pool to storage the spent fuels temporarily. The safe and reliable operation of racks is crucial to the safety of nuclear power plants. The free-standing rack's design gradually replaces the traditional bottom-fixed design because the free-standing design uses friction and water to decrease the seismic load transfer. The fluid–structure interaction (FSI) effect, which is the key phenomenon for racks under earthquake, can be simplified as an added mass matrix among the racks and the spent fuel pool. The added mass matrix is strongly associated with the rack’s distribution and the rack’s geometry. CAP1400 (a newly designed reactor type designed by China) racks adopt end-tube-connection construction and abandon outer plates, significantly changing the FSI effect. The end-tube-connection construction’s influence on double-rack seismic response hasn’t be studied numerically. Moreover, the large uncertainties in the previous experimental response bring some difficulties in model validation. To solve the above two problems, we built two CFD models to study the influence of the rack’s outer plates on the added mass matrix. Then double-rack seismic models with /without the FSI effect are validated by the experiments of sine waves and seismic waves input. The validated model is then used to study the influence of the friction coefficient and the outer plates on the rack’s seismic response. Results show the previous experimental large uncertainties in racks’ displacement response are mainly caused by the extremely low-frequency components. Moreover, the seismic displacement response of racks without outer plates is much larger compared to racks with outer plates, which means racks’ seismic performance may be improved if an outer plate is added to CAP1400 racks.