Mechanism of temperature fluctuation phenomena below steam-water interface in a pressurizer spray pipe

Abstract

In a PWR plant, a steam-water two-phase flow may exist in the pressurizer spray pipe under a normal operating condition since the flow rate of the spray water is not sufficient to fill the horizontal section of the pipe completely. Initiation of high cycle fatigue cracks is suspected to occur under such thermally stratified two phase flow conditions. Experiments for a steam-water flow have been conducted to investigate the temperature fluctuation phenomena. It has been shown that the wall temperature fluctuations were not caused by the waves on the water surface, but were caused by temperature fluctuations in water layer below the interface. An experiment with visualization test section of rectangular pipe was conducted to investigate the temperature fluctuation mechanism in water layer in this paper. The black stripe pattern was observed below the steam-water interface due to the density change. The water temperature fluctuations had the dominant frequency of about 1Hz. The Richardson number calculated with the measured temperature and velocity gradient was larger than 0.25. The dominant frequency of temperature fluctuations was nearly equal to the Brunt-Väisälä frequency. It was shown that the temperature fluctuations in water layer below the interface were caused by the internal gravity wave in the thermal stratified flow.

Keywords

• pwr plant
• pressurizer spray pipe
• thermal stratified flow
• thermal fatigue
• internal gravity wave