Patent Number: 
Section: claims

1. A plant with piping,wherein said piping includes a main pipe connected to a turbine and which introduces steam to said turbine, said main pipe having a nozzle portion as a joint portion to a vessel and a branch portion of said main pipe connected with a branch pipe having a steam safety relief valve attached thereto, said branch pipe being said branch portion of said main pipe extended from said main pipe; andwherein an enlarged passage portion of said main pipe is formed at said branch portion of said main pipe at the connection with said branch pipe having said steam safety relief valve attached thereto and which extends from said main pipe, and a passage sectional area of said enlarged passage portion of said main pipe at said branch portion is larger than a passage sectional area of said main pipe at an upstream side and at a downstream side of said enlarged passage portion of said main pipe, and said branch pipe having said steam safety relief valve attached thereto and which extends from said main pipe is connected to said enlarged passage portion of said main pipe at said branch portion of said main pipe. 2. The plant with piping according to claim 1,wherein a center axis of said enlarged passage portion of said main pipe is in alignment with a center axis of said main pipe at the upstream side and at the downstream side of said enlarged passage portion of said main pipe. 3. The plant with piping according to claim 1,wherein said enlarged passage portion of said main pipe includes a plurality of steam paths connected to said main pipe. 4. The plant with piping according to claim 1,wherein said main pipe is a steam pipe connected to said vessel which is a steam generator. 5. The plant with piping according to claim 1,wherein said plant is one of a reactor plant and a thermal power plant. 6. The plant with piping according to claim 1,wherein said enlarged passage portion of said main pipe formed at said branch portion of said main pipe enables a reduction in flow of steam thereat and decrease of fluctuation pressure at said branch portion with suppression of occurrence of acoustic resonance. 7. A boiling water reactor plant comprising:a nuclear reactor; anda main steam pipe having a nozzle part connected to said nuclear reactor and introducing steam generated in said nuclear reactor to a turbine which is connected to said main steam pipe, and a branch portion of said main steam pipe is connected with a branch pipe having a steam safety relief valve attached thereto, said branch pipe being said branch portion of said main steam pipe extended from said main steam pipe,wherein an enlarged passage portion of said main steam pipe is formed at said branch portion of said main steam pipe at the connection with said branch pipe having said steam safety relief valve attached thereto, and a passage sectional area of said enlarged passage portion of said main steam pipe at said branch portion is larger than a passage sectional area of said main steam pipe at an upstream side and at a downstream side of said enlarged passage portion of said main steam pipe, and said branch pipe having said steam safety relief valve attached thereto is connected to and extended from said enlarged passage portion of said main steam pipe at said branch portion. 8. The boiling water reactor plant according to claim 7, whereina center axis of said enlarged passage portion of said main steam pipe is in alignment with a center axis of said main steam pipe at a downstream side of said enlarged passage portion of said main steam pipe. 9. The boiling water reactor plant according to claim 7,wherein said enlarged passage portion of said main steam pipe includes a plurality of steam paths connected to said main steam pipe. 10. The boiling water reactor plant according to claim 7,wherein said enlarged passage portion of said main steam pipe formed at said branch portion of said main steam pipe enables a reduction in flow of steam thereat and decrease of fluctuation pressure at said branch portion with suppression of occurrence of acoustic resonance. 11. A plant with piping,wherein said piping includes a main steam pipe which introduces steam to a turbine connected to said main steam pipe, said main steam pipe having a nozzle portion as a joint portion to a vessel and a branch portion connected with a branch pipe having a steam safety relief valve attached thereto, said branch pipe being a branch portion of said main steam pipe extended from said main steam pipe; andwherein an enlarged passage portion of said main steam pipe is formed at said branch portion, and a passage sectional area of said enlarged passage portion at said branch portion is larger than a passage sectional area of said main steam pipe at a downstream side of said enlarged passage portion of said main steam pipe. 12. The plant with piping according to claim 11,wherein a center axis of said enlarged passage portion is in alignment with a center axis of said main steam pipe at the downstream side of said enlarged passage portion of said main steam pipe. 13. The plant with piping according to claim 11,wherein said main steam pipe is connected to a steam generator as said vessel. 14. The plant with piping according to claim 11,wherein said plant is one of a reactor plant and a thermal power plant, andwherein said enlarged passage portion of said main steam pipe formed at said branch portion of said main steam pipe enables a reduction in flow of steam thereat and decrease of fluctuation pressure at said branch portion with suppression of occurrence of acoustic resonance. 15. A boiling water reactor plant comprising:a nuclear reactor; anda main steam pipe connected to a turbine, said main steam pipe having a nozzle part connected to said nuclear reactor and introducing steam generated in said nuclear reactor to said turbine, said main steam pipe having a branch portion connected with a branch pipe having a steam safety relieve valve attached thereto, said branch pipe being said branch portion of said main steam pipe extended from said main steam pipe;wherein an enlarged passage portion is formed of said main steam pipe at said branch portion at the connection with said branch pipe having said steam safety relieve valve attached thereto, and a passage sectional area of said enlarged passage portion of said main steam pipe at said one of said nozzle portion and said branch portion is larger than a passage sectional area of said main steam pipe at least at a downstream side of said enlarged passage portion of said main steam pipe. 16. The boiling water reactor plant according to claim 15, whereina center of said enlarged passage portion is in alignment with a center axis of said main steam pipe at the downstream side of said enlarged passage portion of said main steam pipe. 17. The boiling water reactor plant according to claim 15,wherein said enlarged passage portion includes a plurality of steam paths connected to said main steam pipe. 18. The boiling water reactor plant according to claim 15, wherein said enlarged passage portion of said main steam pipe formed at said branch portion of said main steam pipe enables a reduction in flow of steam thereat and decrease of fluctuation pressure at said branch portion with suppression of occurrence of acoustic resonance. 19. The boiling water reactor plant according to claim 15, wherein said nozzle portion forms another enlarged passage portion of said main pipe. 20. The boiling water reactor plant according to claim 15, wherein said enlarged passage portion of said main steam pipe is formed at said branch portion at the connection with said branch pipe and has the passage sectional area which is larger than the passage sectional area of said main steam pipe at both of the downstream side and an upstream side of said enlarged passage portion of said main steam pipe, said enlarged passage portion of said main steam pipe enabling a reduction in flow of steam thereat and decrease of fluctuation pressure with suppression of occurrence of acoustic resonance.