Patent Number: 053923260
Section: claims

1. A boiling water reactor comprising: a reactor pressure vessel accommodated in a reactor containment vessel in a vertical fashion;  a core disposed at a low portion in the reactor pressure vessel, said core being composed of a plurality of fuel assemblies arranged with spaces from each other;  a plurality of control rods to be inserted from an upper side of the core into the spaces between the fuel assemblies and withdrawn therefrom upwardly;  a shroud surrounding the fuel assemblies so as to define the core and having an upper end opening;  a shroud head which closes the upper end opening of the shroud and through which said control rods are inserted or withdrawn;  a separator means standing upward from the shroud head to carry out gas-water separation of steam generated from the core;  a fixing pedestal disposed above the separator means and provided with a steam flow hole through which steam separated by the separator means passes;  a control rod driving mechanism located within the reactor pressure vessel mounted on the fixing pedestal and adapted to drive the control rods;  a drier means arranged along an upper inner wall surface of the reactor pressure vessel; and  a jet pump means disposed in a space between an outer surface of the shroud and an inner wall surface of the reactor pressure vessel. 2. A boiling water reactor according to claim 1, wherein said drier means comprises a plurality of drier elements arranged annularly along the upper inner wall surface of the reactor pressure vessel, drain receiving vessels disposed at lower end portions of the drier elements and drain tubes extending downward from the drain receiving vessels. 3. A boiling water reactor according to claim 2, wherein each of said drier element is composed of a metal plate formed with a number of punched holes. 4. A boiling water reactor according to claim 1, wherein said reactor pressure vessel has an upper end opening closed by a cover to which are provided a plurality of cable protection tubes through each of which a plurality of cables for measurement in a bundle extend outward from an inside of the reactor pressure vessel. 5. A boiling water reactor according to claim 1, wherein each of said control rods is provided with a magnet coupling on the way of the control rod so as to separate the control rod at a portion at which the magnet coupling is mounted. 6. A boiling water reactor according to claim 1, wherein said control rod driving mechanism is provided with a drive means composed of electromagnetic coils. 7. A boiling water reactor according to claim 6, wherein said electromagnetic coils are formed as metal insulated cables to which metal coating ceramics insulation is effected. 8. A boiling water reactor according to claim 1, wherein said control rod driving mechanism is provided with a drive means composed of an electromagnetically driven motor. 9. A boiling water reactor according to claim 1, wherein said separator means comprises a plurality of cylindrical bodies standing upward from the shroud head, a plurality of cross-shaped control rod guide tubes to be inserted into a space between adjacent fuel assemblies and a support plate for supporting the cylindrical bodies standing upward vertical attitude. 10. A boiling water reactor according to claim 9, wherein each of said cross-shaped control rod guide tubes is formed with a portion through which a control rod driving shaft penetrates and to which a labyrinth is formed to prevent a coolant from rising. 11. A boiling water reactor according to claim 1, wherein each of said control rods has a vertical length substantially equal to a vertical length of the core and a vertically moving length of a control rod driving shaft is substantially equal to the vertical length of the core. 12. A boiling water reactor according to claim 1, wherein said jet pump means comprises a plurality of jet pumps arranged with equal spaces from each other and annularly along the inner wall surface of the reactor pressure vessel. 13. A boiling water reactor according to claim 12, wherein each of said jet pumps comprises first and second stage nozzles, first and second stage throats and a diffuser connected to the second stage throat. 14. A boiling water reactor according to claim 12, wherein said jet pump means is driven by a plurality of jet pump driving pumps. 15. A boiling water reactor according to claim 12, wherein said jet pump means is driven by a plurality of steam injectors. 16. A boiling water reactor according to claim 1, wherein said jet pump means is operated so that a flow rate ratio of a driving water with respect to a driven water is at least more than 6. 17. A boiling water reactor according to claim 1, wherein the control rod drive mechanism is removed together with the fixing pedestal out of the reactor pressure vessel. 18. A boiling water reactor according to claim 1, wherein each of the fuel assemblies has a longitudinal length longer than twice a conventional fuel assembly. 19. A boiling water reactor according to claim 1, wherein the control rods have a cross-shaped cluster structure. 20. A boiling water reactor according to claim 1, wherein a channel box is formed with vertical grooves along which the control rods move.