Seismic Study Of Spent Fuel Storage And Transport Basket And Internal Spent Fuel Assembly Considering Fluid-structure Coupling

The spent fuel storage and transportation basket(referred to as "basket" for short)is a new type of device for the storage and transportation of spent fuel,which is widely used internationally.The basket is immersed in a pool of spent fuel and is used for temporary storage of spent fuel,as well as for the transfer of fuel components.The structural safety of the basket under earthquake conditions is crucial for the containment of radioactive materials.The fuel components(referred to as"components")are placed in a small compartment of the basket,and the gaps between the components and the compartment wall are filled with liquid.During an earthquake,the fuel components,the basket compartment,and the fluid gaps experience strong coupled motion(i.e.fluid-solid coupling effect)and may collide.Therefore,it is necessary to conduct seismic research on the basket and fuel components under fluidsolid coupling conditions.The fluid-solid coupling effect is a key phenomenon of the basket under earthquake action.The multi-body motion of fluid-solid coupling is generally described by an additional mass matrix:the elements of the matrix can be divided into self-coupling terms and cross-coupling terms.Since the cross-coupling terms have many influencing factors and complex mechanisms,there is little research on them.Therefore,many studies only consider the self-coupling terms in fluid-solid coupling,that is,the fluid-solid coupling effect is simplified as the mass of water added to the structure.However,this method ignores the cross-coupling terms and may cause significant errors.To address the above issues,this paper uses a complete additional mass matrix to describe the fluid-solid coupling effect between the basket and the spent fuel pool,and conducts seismic analysis of the fuel components and basket under fluid-solid coupling conditions.First,based on the dynamic mesh method,a two-dimensional transient computational fluid dynamics(CFD)model is used to obtain the fluid force and additional mass matrix received by the fuel components and basket compartment.Then,using the above additional mass matrix as input parameters,a finite element model of the basket and components is established,and modal analysis is conducted to obtain the modal frequencies.The correctness of the above model is verified through experiments.Finally,based on the above finite element model,a transient analysis model of the seismic resistance of the basket and components is established using a nonlinear spring-gap element to simulate the collision between the components and the basket.The transient analysis is carried out using a sine wave pulse and the SL-2 earthquake wave at the site to obtain the displacement time history curve of the basket and the component-basket.The study found that the cross-coupling terms and self-coupling terms in the fluidsolid coupling effect between the component and the compartment are equivalent,so the influence of the cross-coupling terms needs to be considered.Under earthquake conditions.the relative displacement between the basket and the component is 5 mm,which is the same as the gap size,indicating that a collision has occurred.During the earthquake process,the basket leans on the basket and swings back and forth together.The finite element analysis model established in this paper can be used for seismic analysis of the basket and components,and provide a reference for seismic tests.