Investigation of temperature fluctuation phenomena in pressurizer spray pipe of pressurized water reactor

Gas liquid interface is formed in a pressurizer spray pipe of a pressurized water reactor when flow rate is small at normal reactor operation. Temperature fluctuation may occur if the interface moves periodically. Measurement of inner wall and fluid temperature in the test section simulating the real pressurizer spray pipe was conducted to study mechanism of the temperature fluctuation phenomena. The effect of non-condensable gas was investigated by injecting helium gas into test section. When helium gas was injected, the condensation of the vapor was suppressed and the temperature fluctuation was reduced. Richardson number increases with the helium gas injection, which is higher than 0.25 in all conditions of the present experiment. Brunt Vaisala frequency nearly equal to the peak of temperature power spectral density. It seemed that the internal gravity waves caused temperature fluctuations in water layer below the interface. (author)