Study of Thermal Stratification for Pressurizer Surge Line of Pressurizer Water Reactor /

Abstract

Pressurizer water reactor is commonly used operating nuclear power plant. Thermal stratification is common issue in almost in every PWR. Thermal stratification is formation of layer in fluid due to density difference which results in thermal and fatigue stresses. In current work thermal stratification is studied using ANSYS CFX for conjugate heat transfer analysis. Three different turbulence models have been compared to analyze the temperature trend along the pressurizer surge line. The effect of different flow velocity and over all downward slope of 5 degree is considered for stratification effect. The heat up rate affects the thermal stratification phenomenon, at very low flow velocities of the order of 0.05 m/sec the top to bottom temperature difference increases and later with increase in flow velocity this difference decreases. Overall, the increase in heat up rate reduces the tendency of thermal stratification phenomenon. The RNG K-E and SST turbulence models can be used to analyze the behavior of flow in pressurizer surge line for thermal stratification condition. The well established and most widely validated standard k-ε turbulence model does not predict well due to its moderate agreement in unconfined flows, curved boundary layers and swirling flows. The overall downward slope in the pressurizer surge line affects the flow field and reduces the maximum top to bottom temperature difference along the pressurizer surge line especially in regions near pressurizer end.