Izuo Aya

Fluid and pressure oscillations occuring at direct contact condensation of steam flow with cold water

Abstract Pressure and fluid oscillations at pressure suppression containment and cold leg flow oscillations at Emergency Core Cooling Water Injection in water-cooled nuclear power reactors are studied concerning flow oscillations occuring at direct contact condensation of steam flow with cold water. Classifications and mechanisms of these oscillation patterns are presented. Linear frequency analyses are developed in explaining the oscillation frequency and oscillation threshold of both condensation oscillation and plug oscillation. Oscillation frequencies at chugging and at ON-OFF oscillation are examined with analytical models developed for such large amplitude oscillations. Analytical results with these models are compared with the data by simulation experiments. Discussions are made focusing on the applicability of the analyses.

Evaluation of heat-transfer coefficient at direct-contact condensation of cold water and steam

The estimation of the heat transfer coefficient at the direct-contact condensation of cold water and steam is a very hard task since the phenoma are essentially undsteady and the interface motion is so complicated that an exact estimation of its area is almost impossible. The present study shows the heat transfer coefficient evaluated experimentally by assuming simple interface shapes for complicated surfaces and estimated those through comparison of the numerical analyses to the data of experiments related to the loss of coolant accidents of light water reactors. At chugging, the heat transfer coefficient reached up to 2 × 106W/(m2 K). At condensation oscillation, it ranged between 105–106 W/(m2 K). At a jet region of cold water injected into the steam flow in a pipe or the stationary steam in a vessel, the value was around 2 × 105W/(m2K), and at the surface of stratified flow, it was between 3 × 103–3 × 104W/(m2K).

Pressure and Fluid Oscillations in Vent System due to Steam Condensation, (I): Experimental Results and Analysis Model for Chugging

Pressure and fluid oscillation in vent tubes and a header induced by steam condensation were measured with a test apparatus. Pressure oscillation consists of low-, middle- and high-frequency components. The frequencies measured in the present apparatus are around 2–8Hz, 15 Hz and 100–150 Hz for low, middle and high frequency respectively. The chugging phenomenon occurs in a certain range of steam flow rate. When the amplitude of fluid oscillation becomes maximum, the amplitude of pressure oscillation in the header also becomes maximum. High frequency component is predominant in the pressure oscillation in vent tubes. When the temperature of pool water becomes lower, the amplitude becomes larger. As the temperature of pool water gets higher, high-frequency component of pressure oscillation disappears, and middle, low frequency in order. Based on the experimental facts mentioned above, the theoretical analysis was conducted by considering the header as one volume and by modeling chugging as one-dimensional ...

Natural circulation of integrated-type marine reactor at inclined attitude

A steady-state single-phase natural circulation test was performed to clarify the effect of inclination by using a model of an integrated-type marine reactor. It was found that several types of flow pattern occur in the natural circulation loop corresponding to the range of inclination angle. Stable flow rates are sustained up to near 90° because of the occurrence of a driving force arising from those sections of the facility which were horizontal before the inclination. It was found that the temperature distribution in the steam generator at inclined attitude depends essentially only on the elevation z. The applicability of a one-dimensional analytical model was examined. It was clarified that employment of detailed U-turn flow paths, their correlation, and temperature-distribution function of core is essential for improvement.

Occurrence threshold of pressure oscillations induced by steam condensation into pool water.

蒸気をサブクール水中で凝縮させる際発生する圧力振動は、プール水温の上昇とともに高周波振動成分、低周波振動成分の順に消滅する。これらの圧力振動の発生限界を、高周波成分に対しては蒸気泡を、低周波成分に対してはヘッダまで含めた大きな蒸気空間をそれぞれのコントロール容積と考え、気液界面の平衡位置からの微少変動が発散するか否かの限界として線形安定論から求め、従来得られている小規模実験データを説明した。