Patent Number: 
Section: claims

1. A water-cooled reactor system for generating electricity, which includes:a water-cooled nuclear reactor that uses water as a coolant and a moderator and generates thermal energy through nuclear fission, the reactor including a reactor vessel, and a reactor core, the reactor core comprising a plurality of nuclear fuel assemblies, and one or more core baffles,the reactor core being of a shape having a hollow center portion and concentric with the reactor vessel so as to permit decay-heat removal from the plurality of nuclear fuel assemblies in the absence of the coolant;a power conversion system that is connected to the water-cooled nuclear reactor so as to indirectly receive the thermal energy generated by the reactor core of the water-cooled nuclear reactor via a heat exchanger or directly receive the thermal energy without passing through the heat exchanger, and generates electricity;a refueling water storage tank that is used when the water-cooled reactor is refueled with a nuclear fuel; anda containment that surrounds the water-cooled reactor, and the refueling water storage tank. 2. The water-cooled reactor system according to claim 1, wherein the water-cooled reactor is operated under the pressure of 1-30 MPa and has the exit temperature of 200-700° C. 3. The water-cooled reactor system according to claim 1, wherein the water-cooled nuclear reactor includes fuel rod cladding, control rod cladding, and control rod guide tube, wherein, at least one of the fuel rod cladding, control rod cladding, control rod guide tube and the core baffle is made of silicon carbide or zirconium carbide. 4. The water-cooled reactor system according to claim 1, wherein the water-cooled nuclear reactor is located in the underground. 5. The water-cooled reactor system according to claim 1, wherein the water-cooled nuclear reactor is equipped with a reactor cavity. 6. The water-cooled reactor system according to claim 5, wherein the reactor cavity is supplied with water from the refueling water storage tank actively by a pump and an AC powered valve or passively by gravity and a DC powered supply valve. 7. The water-cooled reactor system according to claim 1, wherein the refueling water storage tank is connected to the water-cooled reactor via a reactor pressure reducing line equipped with a pressure reducing valve. 8. The water-cooled reactor system according to claim 7, wherein the pressure reducing valve is opened by AC power or DC power when the pressure of the reactor reaches a set point or passively pushed open by an inner pressure and once the pressure reducing valve is opened, the pressure reducing valve is not closed again even when the pressure of the reactor drops down under the set point. 9. The water-cooled reactor system according to claim 1, wherein the refueling water storage tank supplies cooling water to the reactor through a cooling water supply line equipped with a supply valve in order to cool the reactor core. 10. The water-cooled reactor system according to claim 9, wherein the reactor core is supplied with water from the refueling water storage tank actively by a pump and an AC powered supply valve or passively by gravity and a DC powered supply valve. 11. The water-cooled reactor system according to claim 1, wherein the reactor system includes a flow path to gather water which is condensed at an inner surface of the containment into the refueling water storage tank. 12. The water-cooled reactor system according to claim 1, further comprising a reactor coolant pump (RCP) powered by AC power to circulate the coolant. 13. The water-cooled reactor system according to claim 1, wherein the refueling water storage tank comprises an opening on its side wall. 14. The water-cooled reactor system according to claim 1, wherein the containment is made of steel. 15. The water-cooled reactor system of claim 1, wherein the reactor core is square-shaped, wherein the hollow center portion is a square-shaped hollow.