A conceptual design study of the sodium-cooled fast reactor (JSFR) is in progress in "Feasibility Study on Commercialized Fast Reactor Cycle Systems". The cooling system of the reactor is composed of two loops in order to reduce plant construction cost. According to reduction of loop number, large diameter pipings are adopted in the primary cooling system, and the average sodium velocity in the piping increases to 9 m/s level. One of issues for piping design is to confirm hydraulic and flow-induced vibration behaviors of the piping under high Reynolds number (10^7 order level) conditions. Then, a flow-induced vibration test facility which simulates a hot leg piping with 1/3 scale has been fabricated. As a first step of the test series, this report describes outline of flow visualization test results.
