Study on Thermal Stratification Characteristics of a New Pressurizer Surge Line

In order to relieve the stress of the lower space arrangement in the nuclear power plant, a new pressurizer design scheme with surge line and electric heating element water tank structure is proposed in this study, and the thermal stratification characteristics of the pressurizer surge line are discussed. The new pressurizer has a new water tank located in its upper part with an inserted horizontal electric heating element, and the surge line is connected from the upper head of the pressurizer to reduce impurities into the main loop. Aiming at the in-surge and out-surge scenarios of the new pressurizer surge line, the three-dimensional flow and heat transfer simulation of surge line is carried out by using FLUENT large eddy model with the analysis results of RELAP5 system as the boundary, and the thermal stratification distribution characteristics are obtained. The results show that the thermal stratification in the vertical direction of the flow section is more likely to occur in the horizontal section of the surge line, while the thermal stratification in the horizontal direction of the flow section is easy to occur at the pressurizer outlet. In both in-surge and out-surge scenarios, the maximum temperature difference of the cross section caused by thermal stratification in the surge line is within 9K, but the phenomenon of thermal fluid deposition occurs in the in-surge condition, resulting in long-term thermal stratification, therefore, the in-surge condition deserves special attention. The results of both conditions show that the thermal stratification of the new structure has little influence.