In the present invention, a recuperator is used in a refrigerant cycle to make a heat exchange between a refrigerant generated in a condenser and a refrigerant before flowing into a compressor, thereby supercooling the refrigerant to minimize the quality of the refrigerant introduced into an evaporator, elevating temperatures at an inlet and an outlet of the compressor, and increasing condensed heat of the condenser. In the present invention, a recuperator is used to increase condensed heat of the condenser, leading to increasing the heat which circulation water circulating in a steam producing cycle receives from the condenser, whereby steam production efficiency can be improved.

A coolant recirculation system of a nuclear power plant is provided that may include: a reactor vessel configured to accommodate a reactor core and a reactor coolant therein; a steam generator configured to transfer a gas, converted from a liquid phase to a gaseous phase by exchanging heat with the reactor coolant, to a turbine system; a pressurizer configured to control pressure of the reactor coolant in the reactor vessel; a primary system pressure reducing valve located above the pressurizer and configured to open at a predetermined pressure to discharge the reactor coolant into a containment building for rapid depressurization; and a moisture separator connected to the primary system pressure reducing valve to separate moisture. The moisture separator may separate the reactor coolant into a gaseous phase and a liquid phase. Then, the liquid phase reactor coolant may be returned to the reactor vessel to be recirculated.

In the present invention, a recuperator is used in a refrigerant cycle to make a heat exchange between a refrigerant generated in a condenser and a refrigerant before flowing into a compressor, thereby supercooling the refrigerant to minimize the quality of the refrigerant introduced into an evaporator, elevating temperatures at an inlet and an outlet of the compressor, and increasing condensed heat of the condenser. In the present invention, a recuperator is used to increase condensed heat of the condenser, leading to increasing the heat which circulation water circulating in a steam producing cycle receives from the condenser, whereby steam production efficiency can be improved.