Patent Number: 
Section: claims

1. A nuclear reactor comprising:a pressure vessel that includes a coolant inlet nozzle and a coolant outlet nozzle at an upper portion thereof;a core barrel being disposed in the pressure vessel;a core being disposed in the core barrel;a lower plenum being partitioned by the pressure vessel and a bottom portion of the core barrel; anda downcomer portion being partitioned by the pressure vessel and a side wall of the core barrel, and being connected to the coolant inlet nozzle and the lower plenum;a lower core support plate provided at the lower portion of the core barrel;a plurality of columns suspended from the lower core support plate; anda straightener member including an upper straightening ring and a lower straightening ring, the upper straightening ring and the lower straightening ring being connected by the columns to be disposed in the lower plenum, to form two vortex suppressing rings, wherein the lower straightening ring includes a lower outer ring, a lower inner ring, and a plurality of lower spokes disposed radially between the lower outer ring and the lower inner ring,the upper straightening ring includes an upper outer ring, an upper inner ring, and a plurality of upper spokes disposed radially between the upper outer ring and the upper inner ring, andthe plurality of columns suspended from the lower core support plate are connected to the upper outer ring and the lower outer ring, and are arranged in the circumferential direction of the upper outer ring and the lower outer ring. 2. The nuclear reactor according to claim 1, wherein an intermediate ring intersecting with the straightening spokes is provided between the outer ring and the inner ring. 3. The nuclear reactor according to claim 1, wherein an outer diameter of the upper ring is set larger than an outer diameter of the lower ring. 4. The nuclear reactor according to claim 1, wherein the straightening spokes arranged in the upper ring and the straightening spokes arranged in the lower ring are disposed to be shifted in a circumferential direction. 5. The nuclear reactor according to claim 1, further comprising a straightening auxiliary member arranged towards the inner surface of the pressure vessel from an outer peripheral portion of the upper outer ring. 6. The nuclear reactor according to claim 5, wherein the straightening auxiliary member is in a ring shape and supported by the outer peripheral portion of the upper outer ring with a plurality of connection members. 7. The nuclear reactor according to claim 5, wherein an upper surface of the upper outer ring is placed higher than an upper surface of the straightening auxiliary member. 8. The nuclear reactor according to claim 5, further comprising a wall member on an upper surface of the outer peripheral portion of the upper outer ring. 9. The nuclear reactor according to claim 1, further comprising:a plurality of additional columns suspended from the lower core plate, the additional columns being connected to the upper and lower spokes; anda vortex elimination member having a ring shape provided on an outer peripheral portion of the additional columns. 10. The nuclear reactor according to claim 1, further comprising a vortex elimination member provided on both sides of the upper straightening spokes in a lengthwise direction of the upper straightening spokes. 11. The nuclear reactor according to claim 1, further comprising:an upper core plate in an upper portion of the core barrel in the pressure vessel; andan instrumentation guide tube that penetrates the upper core plate from the upper portion of the pressure vessel. 12. The nuclear reactor according to claim 1, further comprising a vortex elimination member having a larger outer diameter than a width of the upper and lower spokes, in a vertical direction, the vortex elimination member being connected to the upper and lower spokes. 13. The nuclear reactor according to claim 1, wherein the upper straightening ring includes an upper outer ring, an upper inner ring, and a plurality of upper spokes disposed radially between the upper outer ring and the upper inner ring. 14. The nuclear reactor according to claim 1, wherein the pressure vessel includes further coolant inlet nozzles, and the plurality of lower spokes is arranged I the circumference direction of the lower straightening ring at regular intervals, such that one of the lower spokes is arranged between adjacent two of the inlet nozzles, and two of the lower spokes are arranged between separated two of the inlet nozzles. 15. The nuclear reactor according to claim 1, wherein the columns are arranged at the same position of the upper spokes and the lower spokes.