The emergency cooldown tank (ECT) is one of the major components in the passive residual heat removal system (PRHRS) of an integral reactor. It shall be designed to contain sufficient water to remove the residual heat and sensible heat from the reactor coolant system (RCS) and also to keep an immersed heat exchanger under water until safe shutdown condition is reached.
However, the water level of the ECT decreases as time goes by. When the residual heat and sensible heat from the RCS are delivered, the temperature of the coolant contained in the ECT starts to increase until it reaches the saturation temperature. Because upper part of the ECT is open to the air, loss of the coolant in the ECT by evaporation is inevitable.
In this study, the water level of the ECT will be predicted to see if it satisfies the above design requirement. And also potential provisions to extend operational period of the ECT will be presented.