Patent Number: 048470406
Section: claims

1. A nuclear power plant comprising: a gas cooled high temperature reactor exhibiting a spherical fuel element core;  a liner clad prestressed concrete pressure vessel defining a cavity surrounding said reactor;  a plurality of heat exchangers for removal of operational heat located within said cavity;  a plurality of auxiliary heat exchangers for removal of decay heat located within said cavity;  a thermal insulating layer within said cavity disposed against said liner;  a liner cooling pipe system including a plurality of liner cooling water pipes connected to said liner grouped into a plurality of liner cooling zones according to common topological location on said liner;  means for serially connecting each liner cooling zone located in an elevated topological location to at least one non-elevated liner cooling zone;  a first cooling water pump connected to a liner cooling pipe system input;  a supplemental low capacity cooling water pump connected in parallel to said first cooling water pump;  a pump bypass line connected in parallel to said first pump exhibiting a check valve responsive to said first pump;  an intermediate heat exchanger connected to said first pump located above an upper edge of said pressure vessel;  a nitrogen cushioned water reservoir connected to said line cooling pipe system input;  a vertical boiling tube connected to a liner cooling pipe system return line and located at a higher elevation than said liner cooling pipe system;  a nitrogen cushioned steam separator connected to said vertical boiling tube and said intermediate heat exchanger; and  a safety blow-off valve connected to said steam separator. 2. A nuclear power plant according to claim 1, wherein said liner cooling pipe system is arranged to increase cooling water flow by natural convection as a result of higher concrete and liner temperatures. 3. A nuclear power plant according to claim 2, wherein said liner cooling pipe system is arranged so that a high heating range is permitted for cooling water during decay heat removal. 4. A nuclear power plant according to claim 1, wherein said liner cooling pipe system, intermediate cooling loop components are arranged to minimize nominal pressure losses. 5. A nuclear power plant according to claim 1, further comprising means for directly coupling said liner cooling zones. 6. A nuclear power plant according to claim 1, further comprising means for interconnecting said liner cooling zones for decay heat removal operation by short-circuiting of zone inlet and return lines by externally accessible valves. 7. A nuclear power plant according to claim 1, wherein said check valve opens when speed of said first pump drops below a predetermined level. 8. A nuclear power plant according to claim 1, wherein said check valve is passively controlled by a pressure difference applied to said first pump wherein said check valve is closed in normal operation, and is brought open by its own weight in case of a failure of said first pump. 9. A nuclear power plant according to claim 1, wherein said check valve is passively controlled by a pressure difference applied to the cooling water pump, wherein said check valve is closed in normal operation by a difference in pressure and is opened in case of a pump failure by release of a prestressed spring. 10. A nuclear power plant according to claim 1, wherein thermal resistance of the thermal insulating layer is optimized relative to a maximum permissible temperature of the liner for a given heat removal capacity of the liner cooling system form the decay heat removal operation, affecting said fuel elements and reaction installations. 11. A nuclear power plant according to claim 10, wherein said liner cooling system is optimized in view of maximum removal of the decay heat by natural convection and minimizing of liner temperature by parameters of cooling tube diameter and spacing of the cooling pipes. 12. A nuclear power plant according to claim 1, wherein said blow-off valve has an actuating pressure correlated to pressure in said steam separator nitrogen cushion so that upon failure of said intermediate heat exchanger, removal of heat from an intermediate cooling loop to a predetermined temperature is effected in a single phase and when saturation pressure in said steam separator actuates said blow-off valve effects a two-phase cooling. 13. A nuclear power plant according to claim 12, wherein said water reservoir has an open configuration and is located geodesically high enough so that in case of a rise of pressure in the intermediate cooling loop to said blow-off valve actuating pressure, a blow-off through said water reservoir does not occur. 14. A nuclear power plant according to claim 12, further comprising a line connecting said steam separator and said reservoir wherein said water reservoir has a closed configuration and has geodesic height so that an equal water level is established in the steam separator and said water reservoir. 15. A nuclear power plant according to claim 1, wherein said liner cooling pipe system is arranged so that a high heating range is permitted for cooling water during decay heat removal. 16. A nuclear power plant according to claim 1, wherein said liner cooling system is optimized in view of maximum removal of the decay heat by natural convection and minimizing of liner temperature by parameters of cooling tube diameter and spacing of the cooling pipes.