Patent Number: 
Section: claims

1. A nuclear power plant comprising:a reactor;a reactor coolant system circulating fluid to cool the reactor, the reactor coolant system including a hot leg upstream of the reactor and a cold leg downstream of the reactor;a closed cooling circuit including a coolant including nanoparticles, the closed cooling circuit cooling at least one of the hot leg and the cold leg of the reactor coolant system via a heat exchanger in such a manner that the nanoparticles of the closed cooling circuit do not enter the fluid circulated in the reactor coolant system and the closed cooling circuit cools the reactor coolant system at least one of before the fluid enters the reactor or after the fluid exits the reactor. 2. The nuclear power plant as recited in claim 1 further comprising an emergency cooling system, the closed cooling circuit being part of the emergency cooling system. 3. The nuclear power plant as recited in claim 1 further comprising a nanoparticle supply inlet for providing nanoparticles to the coolant. 4. The nuclear power plant as recited in claim 1 wherein the closed cooling circuit is a closed cooling water system. 5. The nuclear power plant as recited in claim 2 wherein the closed cooling circuit includes at least a second heat exchanger, one of the heat exchanger and the second heater being on a hot side of the closed cooling circuit and one of the heat exchanger and the second heat exchanger being on a cold side of the closed circuit, and a pump connected to the heat exchangers. 6. The nuclear power plant as recited in claim 5 further comprising an essential service water system, the heat exchangers capable of transferring heat from the closed cooling circuit to the essential service water system. 7. The nuclear power as recited in claim 1 further comprising a nanoparticle supply inlet and a nanoparticle supply connected to the nanoparticle supply inlet. 8. The nuclear power plant as recited in claim 7 further comprising a controller controlling the nanoparticle supply to provide a setpoint concentration of nanoparticles in the coolant of the closed cooling circuit. 9. The nuclear power plant as recited in claim 3 further comprising a nanoparticle supply, the nanoparticle supply having a fill valve connected to the nanoparticle supply inlet. 10. The nuclear power plant as recited in claim 2 wherein the closed cooling circuit cools the reactor coolant system by removing heat from the emergency cooling system. 11. The nuclear power plant as recited in claim 5 wherein the nanoparticles flow between the at least two heat exchangers. 12. The nuclear power plant as recited in claim 1 wherein the closed cooling circuit increases cooling capacity during normal operation of the reactor. 13. The nuclear power plant recited in claim 1 further comprising a spray containment system, the closed cooling circuit cooling fluid entering the spray containment system in such a manner that the nanoparticles of the closed cooling circuit do not enter the fluid entering the spray containment system. 14. A nuclear power plant comprising:a reactor;a reactor coolant system circulating fluid to cool the reactor;a line supplying additional fluid into the reactor coolant system during an accident;a closed cooling circuit including a coolant including nanoparticles, the closed cooling circuit cooling the reactor coolant system by cooling the line in such a manner that the nanoparticles of the closed cooling circuit do not enter the fluid circulated in the reactor coolant system. 15. The nuclear power plant recited in claim 14 further comprising at least one of a refueling water storage tank and a containment sump, the at least one of the refueling water storage tank and the containment sump supplying the additional fluid to the line. 16. A nuclear power plant comprising:a reactor;a reactor coolant system circulating fluid to cool the reactor;a refueling water storage tank for providing water during an accident;a closed cooling circuit including a coolant including nanoparticles, the closed cooling circuit cooling the reactor coolant system via a heat exchanger in such a manner that the nanoparticles of the closed cooling circuit do not enter the fluid circulated in the reactor coolant system or water from the refueling water storage tank. 17. The nuclear power plant recited in claim 16 further comprising a spray containment system receiving the water from the refueling water storage tank during an accident, the closed cooling circuit cooling fluid entering the spray containment system in such a manner that the nanoparticles of the closed cooling circuit do not enter the water entering the spray containment system. 18. The nuclear power plant recited in claim 16 further comprising a pump providing water from the refueling water storage tank to the heat exchanger and into the reactor coolant system.