Experimental Study on Thermalhydraulics in Thermal Striping Phenomena; Comparison of Temperature Fluctuations between Sodium and Water

Kimura, Nobuyuki; Miyake, Yasuhiro*; Miyakoshi, Hiroyuki; Nagasawa, Kazuyoshi*; Igarashi, Minoru; Kamide, Hideki 

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing causes high cycle thermal fatigue in structural components, is of importance for structural integrity and reactor safety.Thermal conductivity of sodium is approximately 100 times larger than that of water. Thus, temperature fluctuation characteristics will be different between sodium, which is used as a coolant of a fast reactor, and water, which is used in general industries. In this study, a comparison of convective mixing among jets was performed in parallel triple wall jets with the same geometries between sodium and water. The discharged velocity in the sodium experiment was experimental parameter and set at the same velocity and the same Reynolds number in comparison with the water experiment. And also, the velocity ratio among the triple jets was varied to change flow pattern. It was seen that the water jets were mixed in slightly closer region to the nozzle than in sodium jets. As for the power spectrum densities (PSD) of temperature fluctuation, the PSD of sodium was similar to the PSD of water under the same discharged velocity condition. At the neighborhood of the wall, the lower frequency component in the PSD of sodium decreased in comparison with the PSD of water. It was shown that the amplitude and frequency characteristics obtained by rain-flow method, which was important to evaluate structural damage by the thermal fatigue, were identical between sodium and water overall. These experimental results show that water experiment could simulate the frequency and the amplitude in temperature fluctuation characteristics in the sodium cooled reactor.