Patent Number: 
Section: claims

1. A steam separator for separating gas-liquid two-phase flow into liquid and gas, said steam separator comprising:a stand-pipe for introducing said gas-liquid two-phase flow from a lower portion thereof to an upper portion thereof;a diffuser for forming a flow path which connects to an upper end portion of said stand pipe and expands the flow path area toward the upward direction so as to be greater than that at an upper end of said stand-pipe;a first stage inner cylinder for forming a flow path being connected to an upper end portion of said diffuser;a first stage outer cylinder for forming an annular space which encloses said first stage inner cylinder;a first stage annular plate for sealing an inner peripheral edge of an upper end of said first stage outer cylinder and forming a circular hole with a diameter smaller than an inner diameter of said first stage inner cylinder;a first stage pick-off ring which has a cylindrical shape and extends from an inner peripheral edge which forms said circular hole on said first stage annular plate, and forms a flow path which passes through said circular hole;a main swirler including a hub disposed at an axial center thereof, a plurality of main swirl blades mounted radially around said hub; andan auxiliary swirler and having a plurality of auxiliary swirl blades mounted to said hub;wherein an outer edge of said main swirl blades is fixed to an inner wall of said diffuser or to an inner wall of a lower portion of said first stage inner cylinder, a main swirl flow path is formed in the space formed with said inner wall, said hub and said main swirl blades, each lower end of said plurality of auxiliary swirl blades is positioned lower than an upper end of said main swirl blades, an auxiliary swirl flow path is formed in the space along said plurality of auxiliary swirl blades formed of said hub and said plurality of auxiliary swirl blades, and an outer diameter of said auxiliary swirler is smaller than an outer diameter of said main swirler. 2. The steam separator according to claim 1,wherein a notch portion at the lower inner side of each of said main swirl blades is formed, and a number of said plurality of auxiliary swirl blades mounted to said hub is less in number than a number of said main swirl blades mountable to said hub. 3. The steam separator according to claim 1,wherein said hub is formed in a cylindrical configuration, a notch portion is formed at the inner side of each of said main swirl blade in the hollow of said hub, said auxiliary swirler is disposed in a space formed by said notch portion, and said plurality of auxiliary swirl blades and said main swirl blades are connected. 4. The steam separator according to claim 1, whereinan outer diameter of said auxiliary swirler is smaller than an inner diameter of said stand-pipe. 5. The steam separator according to claim 1,wherein a number of said plurality of auxiliary swirl blades is less than a number of said main swirl blades. 6. The steam separator according to claim 1, wherein incline slits are formed at an upper portion of said first stage inner cylinder. 7. The steam separator according to claim 1,wherein an opening is formed in said first stage annular plate, and a discharge pipe is provided to said first stage annular plate and stands upright in the opening toward an upper direction. 8. The steam separator according to claim 1,wherein when said first stage outer cylinder has a length which also encloses said diffuser, and an outer diameter of said first stage outer cylinder at a lower portion which is positioned lower than said diffuser is smaller than an outer diameter of said first stage outer cylinder at an upper portion side which is positioned above said lower portion. 9. The steam separator according to claim 1, comprising:an another stage inner cylinder for forming the flow path for the gas-liquid two-phase flow;an another stage outer cylinder enclosing said another stage inner cylinder so as to be a concentric with a space between;an another stage annular plate for sealing an inner peripheral edge of an upper end of said another stage outer cylinder and forming an another stage circular hole whose diameter is smaller than an inner diameter of said another stage inner cylinder; andan another stage pick-off ring having a cylindrical portion which extends toward lower direction from said another stage circular hole and forming a flow path which passes through said another stage circular hole,wherein a first stage steam separation section includes said diffuser, said first stage inner cylinder, said first stage outer cylinder, said first stage circular plate, said first stage pick-off ring, said main swirler and said auxiliary swirler,an another stage steam separation section includes said another stage inner cylinder, said another stage annular plate, and said another stage pick-off ring,and at least one stage of said another stage steam separation section is layered on said first stage steam separation section and connected to said first stage steam separation section as a flow path is formed. 10. A boiling water reactor comprising:a reactor pressure vessel;a core disposed in said reactor pressure vessel; and a plurality of steam separators according to claim 1 which is arranged above said core in said reactor pressure vessel. 11. A swirler assembly for being incorporated into a steam separator which separates gas-liquid two-phase flow into liquid and gas, comprising:a cylinder;a main swirler including a hub extending in an axial direction and disposed at an axial center thereof, a plurality of main swirl blades mounted radially around said hub at a same first axial position of said hub; andan auxiliary swirler having a plurality of auxiliary swirl blades mounted to said hub at a same second axial position of said hub which is spaced from the first axial position;wherein an outer edge of said main swirl blades is fixed to an inner wall of said cylinder, a main swirl flow path is formed in a space at least partially delimited by said main swirl blades and said inner wall, and said hub and said main swirl blades wherein each lower end of said plurality of auxiliary swirl blades mounted at the same second axial position is positioned lower in the axial direction of said hub than an upper end of each of said main swirl blades;wherein an auxiliary swirl flow path is formed in a space along said plurality of auxiliary swirl blades at least partially delimited by said hub and said plurality of auxiliary swirl blades; andwherein an outer diameter of said auxiliary swirler is smaller than an outer diameter of said main swirler. 12. The steam separator according to claim 1, wherein the first stage pick-off ring has the cylindrical shape which extends downwardly from the inner peripheral edge which forms said circular hole on said first stage annular plate. 13. The swirler assembly according to claim 11, wherein said cylinder has incline slits at an upper portion thereof.