EFFECT OF HEAT-UP TRANSIENT CONDITION ON THE THERMAL STRATIFICATION IN NUCLEAR POWER PLANT SURGELINE

During operating transients of the pressurizer, thermal stratification effect may occur especially in the horizontal parts of surge line. Generally, the fatigue usage factor of surge line is comparative high, due to its operating temperature and pressure transients and its thermal stratification loads. Traditional 2-D finite clement model (FEM) for thermal stratification analysis has excessive conservativeness. To reduce such an excessive conservativeness, 3-D numerical analysis model for fluid-structure interaction (FSI) problem in the surgeline and some parametric FSI analyses were performed with different heat-up temperature rate and flow rate in the inlet of surgeline during plant heat-up. Based on these FSI analysis results, an efficient condition to reduce the excessive conservativeness in surgeline stratification analysis could be proposed in terms of heat-up rate and flow rate.