A Review of Surge Line Thermal Stratification

摘要

the paper presents a literature review of thermal stratification phenomena in surge line. It focuses on the history of thermal stratification in surge line, the range of operating conditions, factors affecting the thermal stratification phenomena, and thermal stratification effects. In case of fluid a hot layer resides over a cold layer due to density difference forming a top to bottom temperature differential making the flow stratified and phenomena is known as thermal stratification. The most important loading on the surge line is thermal stratification. The reactor coolant temperature difference between the pressurizer and hot leg is in the range of 110 to 180 °C during reactor heat up phase and 30 to 50 °C during reactor normal operation. Whereas the surge line velocity is in the order of mm/s to cm/s during in-surge or out-surge. The contributing factors of thermal stratification are temperature differential between pressurizer and hot leg, surge line velocity and surge line layout. During heat up phase there is almost a constant out surge flow, whereas during normal operation both in-surge and out-surge flows take place. Hence the surge line is extremely prone to constant and subsequently cyclic thermal loads. These thermal loads results in thermal stratification and assist thermal fatigue. A good amount of research work has been conducted to calculate the effects of thermal stratification. A major change to the of surge line layout has been noticed in the design of AP1000.