The fuel pool cooling cleanup system has a function to remove decay heat from spent fuel in the heat exchanger and the fuel cooling pool, and to desalt/filter pool water and maintain water purity and transparency. The fuel pool cooling cleanup system is designed to keep pool water tempera­ture below 52 °C in the case of the usual maximum heat load which is defined as the sum of two different decay heats: one is from the discharged spent fuel in one refueling when closing the pool gate which separates the reactor well and fuel pool and the other is from the previously discharged spent fuel. Also, the system should have sufficient cooling performance to maintain the pool water temperature below 65 °C, in combination with residual heat removal system, in the case of maximum heat load which is defined as the sum of two different decay heats: one is from the whole core at the end of cycle and the other is from the previously discharged spent fuel.