A Long-Term Cooling Method for Research Reactors

In research reactors, a core of the reactor shall be always submerged inside water and the pool water has a role of an ultimate heat sink. In accidents, the reactor shall be immediately shut-down, and then the residual heat of the core is removed by natural circulation. The heat is transferred to the pool water and the water is evaporated continuously. So, it is very important to secure sufficient water considering an evaporation rate from a nuclear rate from a nuclear safety standpoint. In open-pool type research reactors with a down-ward flow in core, some equipment or pipes can be installed below the core due to NPSHr of pumps. If there are pipe breaks below the core, the whole pool water will be drained by siphon phenomena and the core will be exposure in the air. To limit the pool water drain a siphon breaker is installed at a height point of the main pipe. After siphon breaking the water level becomes lower by evaporation due to the residual heat of the core. If it is impossible to access and resolve this problem during several days, the pool will be empty and the reactor will have severe accidents. So, a new and simple device is developed and designed to consider the long-term cooling of research reactors. It consists of a long-term cooling dam and long-term cooling pipes in a guide wall between reactor pool and service pool. During the siphon breaking situation, the water drain from the service pool is stopped at a top of the long-term cooling dam even though the water in reactor pool is still drained. After breaking the siphon phenomena the water level of reactor pool is lower than the top of the dam and higher than the top of the core. The remained water in the service pool is passively moved into the reactor pool through the long-term cooling pipes. Therefore, this extra water supply is very helpful to remove the residual heat of the core during long time without any follow-up measures by operators