Patent Number: 
Section: claims

1. A jet pump comprising:a nozzle apparatus for ejecting a motive fluid; a throat for passing the motive fluid and a sucked suction fluid in a direction from an upper end portion to a lower end portion of the throat; and a diffuser into which the lower end portion of the throat is inserted;wherein the nozzle apparatus is disposed above a bell mouth installed on the upper end portion of the throat, apart from the bell mouth, the nozzle apparatus has a nozzle base member disposed above the bell mouth, and a plurality of nozzles installed to the nozzle base member, protruded from an undersurface of the nozzle base member toward the bell mouth and forming a plurality of narrowing portions, in which a fluid passage cross-sectional area of a motive fluid passage formed in the nozzle is reduced; andwherein a cross-sectional area of a fluid passage formed in the throat diminishes toward the lower end portion of the throat which is inserted into the diffuser. 2. The jet pump according to claim 1, wherein, when a water head of the jet pump is H, measured in Pascals; a jet pump flow rate is Q, measured in cubic meters per second; and a density of fluid flowing in the jet pump is ρ, measured in kilograms per cubic meters, an inner diameter D2, measured in meters, of the lower end portion of the throat is (8 ρQ2/πH)0.25 or more, and smaller than an inner diameter D1, measured in meters, of the throat at a position where a cross-sectional area of the fluid passage in the throat starts to diminish. 3. The jet pump according to claim 1, wherein the lower end portion of the throat which is inserted into the diffuser, has a thickness which a greater than a thickness of a portion of the throat disposed above an upper end of the diffuser. 4. The jet pump according to claim 3, wherein a plurality of grooves extending in a circumferential direction of the throat are arranged in an axial direction of the throat and the plurality of grooves are formed on a surface of the greater thickness portion of the throat facing the diffuser. 5. The jet pump according to claim 1, wherein each of the nozzles has a first nozzle straight-tube portion, a first nozzle narrowing portion, a second nozzle straight-tube portion, a second nozzle narrowing portion, and a nozzle lower end portion; an ejection outlet is formed at a lower end of the nozzle lower end portion and communicated with the driving motive passage; and the first nozzle straight-tube portion, the first nozzle narrowing portion, the second nozzle straight-tube portion, the second nozzle narrowing portion, and the nozzle lower end portion are disposed in this order from the nozzle base member to the ejection outlet. 6. The jet pump according to claim 5, wherein a narrowing angle of the second nozzle narrowing portion is larger than that of the first nozzle narrowing portion. 7. A jet pump comprising:a nozzle apparatus having a header portion disposing a first pipe member forming a suction fluid passage for introducing a suction fluid, inside the header portion, and including an annular passage, which surrounds the first pipe member, for introducing a motive fluid, and a nozzle portion installed to the header portion, surrounding the first pipe member, and forming an ejection outlet, which is communicated with the annular passage formed in the header portion, for ejecting the motive fluid;a throat for passing the motive fluid ejected from the ejection outlet and the sucked suction fluid in a direction from an upper end portion to a lower end portion of the throat;a diffuser into which the lower end portion of the throat is inserted; anda second pipe member, one end of which is connected to the nozzle apparatus, forming a motive fluid passage for introducing the motive fluid to the annular passage in the header portion;wherein the nozzle apparatus is disposed above a bell mouth installed on the upper end portion of the throat, apart from the bell mouth;wherein the first pipe member is disposed inside the motive fluid passage formed in the second pipe member through the one end of the second pipe member, and an opening for the suction fluid passage is formed on an outer surface of the second pipe member and opened toward outside of the second pipe member;wherein the motive fluid passage is formed in a way that the motive fluid flowing toward the one end of the second pipe member hits the first pipe member diagonally in the axial direction of the first pipe member; andwherein a cross-sectional area of a fluid passage formed in the throat diminishes toward the lower end portion of the throat which is inserted into the diffuser. 8. The jet pump according to claim 7, wherein the second pipe member is curved into an inverted U-shape. 9. The jet pump according to claim 7, wherein the jet pump has a fluid-adjusting member installed in the second pipe member along a central axis of the second pipe member. 10. The jet pump according to claim 9, wherein the fluid-adjusting member is disposed at a position above the first pipe member. 11. A jet pump comprising:a nozzle apparatus for ejecting a motive fluid;a throat for passing the motive fluid ejected from the nozzle apparatus and a sucked suction fluid in a direction from an upper end portion to a lower end portion of the throat; anda diffuser into which the lower end portion of the throat is inserted;wherein the nozzle apparatus is disposed above a bell mouth installed on an upper end portion of the throat, apart from the bell mouth;the nozzle apparatus has a first tubular member; a second tubular member disposed in the first tubular member, apart from the first tubular member; a fluid passage forming member disposed in the first tubular member, and installed to an upper end portion of the second tubular member; a plurality of passage members fixing one end portion and an other end portion to the first and the second tubular members; the plurality of passage members being disposed in a circumferential direction of the nozzle apparatus; and an annular ejection outlet is formed between a lower portion of the first tubular member and a lower portion of the second tubular member;a suction passage formed in each of the passage members, for introducing the suction fluid from outside of the nozzle apparatus to inside of the passage members, communicates with an inner region formed in the second tubular member,an annular motive fluid passage for introducing the motive fluid, across which each of the passage members is disposed, is formed between the first tubular member, and the second tubular member and the fluid passage forming member, and communicated with the annular ejection outlet,an ejection outlet-side portion of the driving fluid passage slopes inward toward a lower end of the nozzle apparatus, and,wherein a cross-sectional area of a fluid passage formed in the throat diminishes toward the lower end portion of the throat which is inserted into the diffuser. 12. The jet pump according to claim 11, wherein the passage member slopes toward a lower end of the nozzle apparatus as approaching the inner region. 13. The jet pump according to claim 11, wherein a cross section of the passage member, perpendicular to an axis of the passage member is an oval shape. 14. The jet pump according to claim 13, wherein the passage member is disposed in a way that a major axis of the oval shape follows an axial direction of the nozzle apparatus. 15. The jet pump according to claim 11, wherein a surface of the fluid passage forming member, facing the inner region is a curved surface curved from an outlet of the suction passage to a lower end of the fluid passage forming member. 16. The jet pump according to claim 15, wherein a cross-sectional area of a fluid passage inside of the fluid passage forming member decreases toward a lower end of the fluid passage forming member in a portion where a curved surface of the fluid passage forming member is formed. 17. The jet pump according to claim 11, wherein a cone member in which a cross-sectional area decreases upward is disposed on an upper end of the fluid passage forming member. 18. A boiling water reactor having a reactor vessel and a plurality of jet pumps installed in the reactor vessel, which jet pumps are for feeding coolant to a core formed in the reactor vessel,wherein each of the jet pumps comprise:a nozzle apparatus for ejecting a motive fluid; a throat for passing the motive fluid and a sucked suction fluid in a direction from an upper end portion to a lower end portion of the throat; and a diffuser into which the lower end portion of the throat is inserted;wherein the nozzle apparatus has a nozzle base member, and a plurality of nozzles installed to the nozzle base member and forming a plurality of narrowing portions, in which a fluid passage cross-sectional area of a motive fluid passage formed in the plurality of nozzles is reduced; andwherein a cross-sectional area of a fluid passage formed in the throat diminishes toward the lower end portion of the throat which is inserted into the diffuser.