Patent Number: 
Section: claims

1. A boiling water reactor core of a burner type, wherein a ratio of a number of fuel assemblies loaded on the core to a number of control rod drive mechanisms for driving control rods is at least 3, wherein a fuel of fuel rods of the fuel assemblies comprises at least one of (a) a first fuel of uranium which is an oxide of a low enriched uranium having an average enrichment for the fuel rods of the fuel assemblies of 3 to 8 wt %, (b) a second fuel of uranium and plutonium which has an average enrichment concentration of fissile plutonium for the fuel rods of the fuel assemblies of 2 to less than 6 wt %, and (c) a third fuel of uranium, plutonium and minor actinides for the fuel rods of the fuel assemblies, and wherein the fuel assemblies further include at least one water rod, characterized in that a heavy metal density is a weight of the at least one of (a) the first fuel, (b) the second fuel, and (c) the third fuel of the fuel rods of the fuel assemblies having the at least one water rod contained in a unit volume of a core area of the boiling water reactor core is 2.1 to 3.4 kg/L at a time of fuel loading of the fuel assemblies in the boiling water reactor core. 2. The BWR core according to claim 1, wherein a ratio of volume of a region of two phase flow cooling water including sub-cooled water for cooling fuel rods to a unit volume of the core is 18 to 39%, the two flow cooling phase water being present in a channel box, except for gaps between channel boxes outside of the channel boxes of the fuel assemblies, in guide members into which the control rods are inserted, and the inside of the at least one water rod. 3. The BWR core according to claim 1, wherein a ratio of volume of a region of subcooled water and saturated water to a unit volume of the core is 26 to 38%, the subcooled water and saturated water being present in gaps between channel boxes outside of the channel boxes of the fuel assemblies, in guide members into which the control rods are inserted, and the inside of the at least one water rod. 4. The BWR core according to claim 1, wherein a ratio of volume of a region of subcooled water and saturated water to a unit volume of the core is 6 to 9%, the subcooled water and saturated water being present in guide members into which control rods are inserted, and the inside of water rods. 5. The BWR core according to claim 1, wherein a ratio of volume of a region of a fuel substance to a unit volume of the core is 23 to 37%. 6. The BWR core according to claim 1, wherein a volume ratio of a volume of subcooled water and saturated water for cooling fuel rods, except for water in gaps between channel boxes outside of the channel boxes of the fuel assemblies, in guide members into which the control rods are inserted, and the inside of the at least one water rod to a volume of a fuel substance area is 0.5 to 1.8 in the reactor core area. 7. The BWR core according to claim 1, wherein a power density is 63 to 140 kW/I. 8. The BWR core according to claim 1, wherein an average of distance between channel boxes of adjoining fuel assemblies, the channel boxes facing each other, is 17 to 40 mm. 9. The BWR core according to claim 1, wherein a distance between fuel rods is 0.7 to 2.6 mm in case of a square lattice configuration or 0.7 to 3.6 mm in case of triangular lattice configuration. 10. The BWR core according to claims 1, wherein a ratio of a channel box outer width of a fuel assembly to an average fuel bundle pitch is 0.80 to 0.89. 11. The BWR core according to claim 1, wherein an active fuel length is 1.0 to 3.0 m. 12. The BWR core according to claim 1, wherein the core is configured such that the control rods are inserted into gaps between fuel assembly channel boxes, and wherein an average gap distance of the channel boxes where the control rods are inserted is larger than that where the control rods are not inserted. 13. The BWR core according to claim 1, wherein the core is constructed by fuel assemblies which have the at least one water rod whose sectional area is larger than the sectional area of a unit cell of the fuel rod lattice. 14. The boiling water reactor core according to claim 1, wherein the core is constituted by square fuel assemblies and cross-shaped control rods inserted between the fuel assemblies at a rate of one control rod per 4 fuel assemblies. 15. The boiling water reactor core according to claim 1, wherein the core is constituted by square fuel assemblies and round-shaped control rods inserted into the fuel assemblies at a rate of at least one control rod per 1 fuel assembly. 16. The boiling water reactor core according to claim 1, wherein the core is constituted by hexagonal shape fuel assemblies and Y-type control rods inserted between the fuel assemblies. 17. The boiling water reactor core according to claim 1, wherein the core is constituted by hexagonal shape fuel assemblies and round or hexagonal shaped control rods inserted into the fuel assemblies at a rate of at least one control rod per 1 fuel assembly. 18. The boiling water reactor core according to claim 14, wherein at least one of a water removal plate and a water removal rod is disposed in gaps between the channel boxes or in the at least one water rod, at least one of the removal plate and removal rod being able to be withdrawn during operation of the core. 19. The boiling water reactor core according to claim 14, wherein a water removal plate is disposed adjacent the control rods, the water removal plate being detachable and being withdrawable from the core during operation of the core. 20. The boiling water reactor core according to claim 15, wherein a water removal rod of round or hexagonal shape is disposed adjacent the control rods, the water removal rod being withdrawable from the core during operation of the core. 21. A boiling water reactor core of a burner type, wherein a ratio of a number of fuel assemblies loaded on the core to a number of control rod drive mechanisms for driving control rods is at least 3, and an effective water-to-fuel volume ratio of at least 1 at the time the reactor is operated at at least 50% of rated power, the fuel assemblies including at least one water rod and at least one of (a) a first fuel of uranium of fuel rods of the fuel assemblies, (b) a second fuel of uranium and plutonium of the fuel rods of the fuel assemblies, and (c) a third fuel of uranium, plutonium and minor actinides of the fuel rods of the fuel assemblies, characterized in that a heavy metal density is a weight of the at least one of (a) the first fuel, (b) the second fuel, and (c) the third fuel of the fuel rods of the fuel assemblies having the at least one water rod contained in a unit volume of a core area of the boiling water reactor core is 2.1 to 3.4 kg/L at a time of fuel loading of the fuel assemblies in the boiling water reactor core. 22. The BWR core according to claim 21, wherein a ratio of volume of a region of two phase flow cooling water including subcooled water for cooling fuel rods to a unit volume of the core is 18 to 39%, the two phase flow cooling water being present in a channel box, except for water in gaps between channel boxes outside of the channel boxes of the fuel assemblies, in guide members for inserting control rods thereinto, and the inside of the at least one water rod. 23. The BWR core according to claim 21, wherein a ratio of volume of a region of subcooled water and saturated water to a unit volume of the core is 26 to 38%, the subcooled water and saturated water being present in gaps between channel boxes outside of the channel boxes of the fuel assemblies, in guide members for inserting control rods thereinto, and the inside of the at least one water rod. 24. The BWR core according to claim 21, wherein a ratio of volume of a region of subcooled water and saturated water to a unit volume of the core is 6 to 9%, the subcooled water and saturated water being present in guide members into which control rods are inserted in channel boxes, and the inside of the at least one water rod. 25. The BWR core according to claim 21, wherein a ratio of volume of a region of a fuel substance to a unit volume of the core is 23 to 37%. 26. The BWR core according to claim 21, wherein a ratio of a volume of the two phase flow cooling water including sub-cooled water for cooling the fuel rods, except for water in gaps between channel boxes outside of the channel boxes of the fuel assemblies, in guide members into which the control rods are inserted, and the inside of the at least one water rod, to a volume of a fuel substance area is 0.5 to 1.8. 27. The BWR core according to claim 21, wherein a power density is 63 to 140 kW/I. 28. The BWR core according to claim 21, wherein an average of distance between channel boxes of adjoining fuel assemblies, the channel boxes facing each other, is 17 to 40 mm. 29. The BWR core according to claim 21, wherein a distance between fuel rods is 0.7 to 2.6 mm in case of a square lattice configuration or 0.7 to 3.6 mm in case of triangular lattice configuration. 30. The BWR core according to claim 21, wherein a ratio of a channel box outer width of a fuel assembly to an average fuel bundle pitch is 0.80 to 0.89. 31. The BWR core according to claim 21, wherein an active fuel length of fuel is 1.0 to 3.0 m. 32. The BWR core according to claim 21, wherein the core is configured such that the control rods are inserted into gaps between fuel assembly channel boxes, and wherein an average gap distance of the channel boxes where the control rods are inserted is larger than that where the control rods are not inserted. 33. The BWR core according to claim 21, wherein the core is constructed by fuel assemblies which have the at least one water rod whose sectional area is larger than the sectional area of a unit cell of the fuel rod lattice. 34. The boiling water reactor core according to claim 21, wherein the core is constituted by square fuel assemblies and cross-shaped control rods inserted between the fuel assemblies at a rate of one control rod per 4 fuel assemblies. 35. The boiling water reactor core according to claim 21, wherein the core is constituted by square fuel assemblies and round-shaped control rods inserted into the fuel assemblies at a rate of at least one control rod per one fuel assembly. 36. The boiling water reactor core according to claim 21, wherein the core is constituted by hexagonal shape fuel assemblies and Y-type control rods inserted between the fuel assemblies. 37. The boiling water reactor core according to claim 21, wherein the core is constituted by hexagonal shape fuel assemblies and round or hexagonal shaped control rods inserted into the fuel assemblies at a rate of at least one control rod per 1 fuel assembly. 38. The boiling water reactor core according to claim 34, wherein at least one of a water removal plate and a water removal rod is disposed in gaps between channel boxes or in the at least one water rod, the at least one of the removal plate and removal rod being withdrawable during operation of the core. 39. The boiling water reactor core according to claim 34, wherein a water removal plate is disposed adjacent the control rods, the water removal plate being detachable. 40. The boiling water reactor core according to claim 35, wherein a water removal plate is disposed adjacent the control rods, the water removal plate being detachable.