Thermal stratification phenomenon in a branch piping with in-leakage

A numerical analysis was performed to estimate thermal stratification phenomenon in the branch piping of nuclear power plant. Due to the turbulent penetration force by the flow in reactor coolant system piping without the valve leak, thermal stratification in the branch piping can be generated if the location of the first valve is greater than that of turbulent penetration. Even though the location of the first valve is less than that of turbulent penetration, thermal stratification can be generated by valve leak. The maximum temperature difference between top and bottom of the horizontal piping was evaluated to be about 185K when the valve leakage is about 10 times as large as the allowable value. The thermal stratification effect of the branch piping was decreased by forced convection of leak flow, however, when the valve leakage is increased to about 15 times the allowable value. Because the temperature difference depends on a number of factors such as piping layout, diameter, leak location, and wall thickness, it is recommended that specific analysis should be conducted to estimate the thermal stratification effect by valve leakage