Modal analyses of a cylindrical structure partially submerged in a liquid sodium environment

The upper internal structure (UIS) in an SFR (Sodium cooled Fast Reactor) system is generally attached to the rotating plug of the reactor head and cantilevered downward into the reactor hot pool. The UIS is a cylindrical structure and its upper part is exposed on the cover gas but the middle and lower parts are submerged in a liquid coolant environment for a normal operating condition. Generally, the fluid contacting with the structure imposes a fluid mass on the structure and the fluid added mass may affect the dynamic characteristics of the structure. Since the UIS plays an import role in the reactor safety, its dynamic characteristics should be reflected on the component design. In this study, the modal analyses for a cylindrical structure of the UIS are carried out corresponding to the environmental conditions