Study on flow-induced vibration of large-diameter pipings in a sodium-cooled fast reactor; Influence of elbow curvature on velocity fluctuation field

Ono, Ayako ; Kimura, Nobuyuki; Kamide, Hideki ; Tobita, Akira

The main cooling system of Japan Sodium-cooled Fast Reactor (JSFR) consists of two loops to reduce the plant construction cost. In the design of JSFR, sodium coolant velocity is beyond 9 m/s in the primary hot leg pipe with large-diameter. The maximum Reynolds number in the piping reaches 4.210. The hot leg pipe having an elbow with curvature ratio of r/D = 1.0, so-called "short elbow", which enables a compact reactor vessel. Under such a system condition, the flow-induced vibration (FIV) is concerned at the short elbow. It is significant to obtain the knowledge of the fluctuation intensity and spectra of velocity and pressure fluctuations in order to grasp the mechanism of the FIV. In this study, water experiments were conducted. Two types of 1/8 scaled elbows with different curvature ratio, r/D = 1.0, 1.5, were used to investigate the influence of curvature on velocity fluctuation at the elbow. The velocity fields in the elbows were measured using a high speed PIV method. Unsteady behavior of secondary flow at the elbow outlet and separation flow at the inner wall of elbow were observed in the two types of elbows. It was found that the growth of secondary flow correlated with the flow fluctuation near the inside wall of the elbow.