Suppression of thermal stratification in gravity driven water pool of an advanced reactor using shrouds

Advanced and innovative reactor systems are considering the use of large pools as heat sink for various safety functions like decay heat removal or containment cooling. These designs generally have heat exchangers immersed in the pool. For enhanced safety and reliability, preferred heat transfer mode is considered to be passive so that heat sink availability is maintained even in failure of power supply and active components. However, heat transfer by natural convection in large pools poses a problem of thermal stratification. As a result of natural convection, hot layers of water may accumulate over the relatively cold one and in turn inhibit the natural convection itself. Not only the heat transfer performance may get deteriorated but some structural parts of the pool like concrete wall may be subjected to high temperature which is not desirable. In this paper, a new concept of employing shrouds around the heat source is proposed. These shrouds provide multiple natural circulation loops around the heat source, thereby facilitating mixing of hot and cold fluid, which eliminate stratification. The concept has been applied to the Gravity Driven Water Pool (GDWP) of Advance Heavy Water Reactor (AHWR) in which Isolation Condensers (ICs) tubes are submerged for decay heat removal of AHWR using ICS and thermal stratification phenomenon was predicted without and with ICS. Results indicate that the shrouds have application in elimination of thermal stratification in GDWP.