Research On FSI Characteristics Of Spent Fuel Storage Racks Under Seismic Condition

Fuel assemblies removed from the reactor core are temporarily stored in the spent fuel storage racks(SFSRs)in spent fuel pool(SFP).The integrity of SFSR under earthquake conditions can ensure the safety of spent fuel,which is of great significance for nuclear safety.The seismic analysis of SFSR is a hot research topic in China and other countries due to the nonlinear behaviors of fluid-structure interaction(FSI),friction and collision.As shown in previous studies,there exists large uncertainty of SFSR FSI parameters(added mass and added damping),therefore,the engineering seismic analysis usually uses overconservative added mass and ignores added damping,which increases the design difficulty of SFSRs and reduces the efficiency of SFSRs.In order to reduce the excessively large margin of SFSRs design,and to obtain more accurate FSI parameters,this study carried out the research of FSI characteristics of the SFSR.The results can provide the design and analysis reference for CAP 1400 series SFSR,which is developed by China independently.As the first step in research,specific experimental rigs are built to study FSI of CAP 1400 SFSR.The FSI parameters of the rack-wall condition and rack-rack condition are measured,and the effect factors of FSI parameters are studied.Then CFD numerical simulations are carried out and compared with the experimental results to verify the reliability of numerical simulation.Moreover,a complete FSI parameter matrix by CFD method is obtained,forming the added mass matrix and added damping matrix,as the inputs for seismic analysis.In order to study the seismic response with comprehensive phenomenon such as,FSI,friction and impact,and also to verify the applicability of FSI,seismic experiments by table seismic experiment are carried out for a small-scale single-rack model and a large-scale double-rack model.The experiments can be used as a benchmark for verification of numerical simulation.Finally,the single-rack finite element method(FEM)model is established in this paper,using the input parameters of added mass matrix and damping ratio obtained by CFD method.The transient nonlinear seismic analysis is performed and compared with the results of seismic experiments.The results show that the added mass of SFSR is mainly influenced by the dimensionless gap,while the geometric scale,dynamic Reynolds number and Keulegan-Carpenter(KC)number only have limited effect.The damping ratio is determined by the dimensionless gap,the KC number and the dynamic Re number.Under different working conditions,the range of added mass is 1.5 to 3.0 times of the water mass displaced by rack,the maximum error between the experiment and numerical simulation is]5%;the damping ratio is in the range of 2%to 10%,the maximum error between the experiment and numerical simulation is 35%.The results of a comprehensive seismic experiments show that the racks slide and rock under seismic conditions,but no collision has occurred.The grid slip under seismic conditions has a large randomness,and the relative uncertainty of the maximum sliding displacement at the bottom of the grid is 15%.The tendency of results between experiment and FEM seismic analysis are consistent,however,the maximum sliding displacement of FEM method are more conservative with a margin of 30%.This shows that the added mass matrix and damping ratio calculated by CFD method can be used as the input of the SFSR seismic analysis and also meet the engineering requirements.This study carries out in-depth experiments and numerical simulations on the FSI characteristics of the CAP 1400 SFSR.The calculation methods of added mass and added damping are proposed,moreover,a process is developed to calculate the added mass matrix and the added damping ratio matrix for complex multi-body structures.These methods can provide FSI parameter input for the design and analysis of the CAP 1400 series SFSR.At the same time,a scaling analysis on seismic experiment of SFSR is proposed,moreover,seismic experimental data of single and double rack models can be the seismic analysis benchmark in the future.