The storage tanks in nuclear facilities has a significant impact on the safety of the reactor and the radiation shielding, so its mechanical property analysis has been widely concerned in the field of engineering and scientific research. Meanwhile, the storage tank is usually filled with gas and liquid medium. In the presence of external disturbances (such as external force, displacement, earthquake etc.), the position and structure of the vessel changes, that lead to changing of the gas-liquid interface. This characteristic can make the storage tank system as a tightly fluid-structure coupling system.

In this paper, a storage tank which stored radioactive gas liquid medium is choosing to study such fluid-structure coupling system phenomenon, and a typical dynamic seismic condition is assumed. A two-way fluid-structure coupling method is used with CFD (Computational Fluid Dynamics) and FEM (Finite Element Method) numerical method. The study considered interaction between structure and two phase turbulent fluid. In FEM calculation, the time history seismic acceleration load is applied to the support of tank, and the flow loading coming from fluid medium is applied to the wall of tank which is send from CFD code. Then, the structure displacement which is calculate by FEM is transferred to CFD code. In CFD calculation, multiphase fluid numerical model is applied to simulate the flow characteristics of gas-water two phase fluid, and the turbulent properties are also considered in the calculation. Mesh deformation method is used to simulate the displacement of flow passage boundary which is send by FEM code. After CFD calculation, flow loading is transferred to the tank wall of FEM code again. Such loop of FEM and CFD calculation continues to go on with the seismic time history, the response characteristics of the tank will be solved.

In order to evaluate the difference between the above method and the traditional analysis method. An independent calculation used added mass approach is carrying out, in which the effect of steady state water is applied to the wall of the vessel, and this load will not change with the earthquake. All others load and constraint mode are same with the above method.

According to the two-way fluid-structure coupling analysis, the detailed characteristics of liquid free surface distribution and structural response of the vessel are obtained. The results show that the response vibration amplitude of the tank structure increases with the earthquake, and the response is mainly affected by the liquid sloshing. According to comparative analysis, the advantages of coupling method are proved. The method from this study can be used for the same type of analysis.

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