Patent Number: 
Section: claims

1. A method of operating a nuclear plant having (a) a closed loop main power system comprising a pebble bed nuclear reactor, which reactor has a sphere outlet and a sphere inlet, an electrical generator, a turbine drivingly connected to the electrical generator, and a high pressure compressor and (b) a fuel handling and storage system for handling and storing fuel spheres and moderator spheres, which system comprises a network of pipes that defines a sphere flow path having a sphere inlet connected to the sphere outlet of the reactor and a sphere outlet connected to the sphere inlet of the reactor, the sphere flow path extending from the sphere outlet of the reactor to the sphere inlet of the reactor, which method includes:receiving heated coolant gas from the reactor;cooling the heated coolant gas to a temperature that is lower than the temperature inside the reactor which inhibits plate out of radio-nuclides in the fuel handling and storage system;introducing such cooled coolant gas from a position downstream of the high pressure compressor into the sphere flow path at a pressure sufficient that the pressure at the sphere inlet of the sphere flow path is higher than the pressure at the sphere outlet of the reactor and the pressure at the sphere outlet of the sphere flow path is higher than the pressure at the sphere inlet of the reactor, thereby to create a leak flow from the fuel handling and storage system to the reactor; andflowing the cooled coolant gas along the sphere flow path to convey spheres along the sphere flow path from the sphere outlet of the reactor to the sphere inlet of the reactor. 2. A method as claimed in claim 1, in which the introducing such cooled coolant gas includes feeding coolant gas from the main power system into the fuel handling and storage system in an amount sufficient to replace gas leaked from the fuel handling and storage system into the reactor. 3. A method as claimed in claim 1, in which the main power system further comprises a recuperator having a high pressure side including an inlet that is in communication with the outlet of the high pressure compressor and the introducing such cooled coolant gas includes feeding gas from the main power system from a position between the outlet of the high pressure compressor and the inlet of the high pressure side of the recuperator. 4. A method as claimed in claim 1, which includes dampening the transmission of pressure fluctuations in coolant of the reactor to the fuel handling and storage system. 5. A method as claimed in claim 1, which includes checking the integrity of the fuel spheres in the sphere flow path and removing damaged fuel spheres from the sphere flow path. 6. A method as claimed in claim 5, wherein the checking the integrity of the fuel spheres includes determining whether or not a fuel sphere is suitable for a further pass through the reactor and separating spent fuel spheres from used fuel spheres which are still capable of producing useful energy. 7. A method as claimed in claim 1, in which the sphere flow path has a gas inlet and a gas outlet and which includes feeding gas from an outlet of a blower to the gas inlet and feeding gas from the sphere flow path through the gas outlet to an inlet of the blower to create a flow of gas along the sphere flow path from the gas outlet towards the sphere inlet of the reactor. 8. A method as claimed in claim 7, in which the gas inlet is spaced from the sphere inlet of the sphere flow path outlet and fuel spheres and moderator spheres entering the sphere flow path move under the influence of gravity from the sphere inlet of the sphere flow path to the gas inlet. 9. A method as claimed in claim 1, in which the introducing such cooled coolant gas includes feeding gas from the main power system from a position where the gas in the main power system is at its highest pressure and lowest temperature.