JP2011007516A - Plant with piping having branch, and boiling water nuclear power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plant with piping having branches, capable of decreasing the pressure fluctuation based on acoustic resonance.SOLUTION: A BWR plant 1 includes a main steam pipe 10 that supplies steam from a reactor pressure vessel to turbines. A branch pipe 15 with a relief safety valve 13 is joined to the main steam pipe 10. An opening is formed on the main steam pipe 10 in the joint between the main steam pipe 10 and the branch pipe 15. The branch pipe 15 is connected to the main steam pipe 10 through the opening. The diameter length of the opening formed on the main steam pipe 10 in an axial direction of the main steam pipe 10 is longer than that both in the direction perpendicular to the central axis of the main steam pipe 10 and in the direction perpendicular to the central axis of the branch pipe 15. The St number is larger than 0.6, and no feedback loops of vortexes and sounds are made in the branch pipe 15. Consequently, the pressure fluctuation based on acoustic resonance can be decreased further.

Description

  The present invention relates to a plant including a piping having a branching section and a boiling water nuclear power plant.

In a boiling water nuclear power plant (hereinafter referred to as a BWR plant) having a boiling water reactor (hereinafter referred to as a BWR) as a nuclear reactor, when the power generation capacity is increased, the pressure fluctuation increases as the main steam flow rate increases. However, there have been reports of cases leading to plant damage. In order to avoid damage to the equipment, measures are taken such as optimizing the flow path shape of the main steam system and increasing the structural strength. Such cases and countermeasures are described in G. Deboo, et al., “Quad cities unit 2 main steam line
acoustic source identification and load reduction ”, ICONE 14-89903 Proceedings of ICONE 14, (2006).

  Acoustic resonance is considered as one of the causes of pressure fluctuations in the main steam system (main steam piping or the like) in the BWR plant. In the main steam system from the steam dome of the reactor pressure vessel to the high-pressure turbine through the main steam pipe, a pressure wave is generated in the branch pipe such as the main steam relief safety valve installed in the main steam pipe, and the inside of the main steam system Propagate and reflect. As a result, a standing wave (acoustic resonance mode) having a large amplitude is formed, and the amplitude of pressure fluctuation may increase. In particular, in a BWR plant with an increased power generation capacity, fluctuations in steam pressure increase as the main steam flow rate increases, so acoustic resonance is likely to occur.

  As a method for suppressing this acoustic resonance, for example, Japanese Patent Laid-Open No. 2006-153869 discloses a method for suppressing pressure fluctuations accompanying acoustic resonance generated in the main steam system of a BWR plant using a Helmholtz resonance tube. Has been. Japanese Patent Application Laid-Open No. 2008-14458 discloses a method of suppressing pressure fluctuation associated with acoustic resonance by providing a flange member in a cavity where acoustic resonance is considered to occur. S. Ziada, et al., “Self-excited resonances of two side-branches in close proximity”, Journal of Fluids and Structures, 6, P583-601 (1992). It is disclosed that when resonance occurs, the sound pressure can be suppressed by making a difference between the lengths of adjacent branch pipes.

JP 2006-153869 A JP 2008-14458 A

G. Deboo, et al., “Quad cities unit 2 main steam line acoustic source identification and load reduction”, ICONE14-89903 Proceedings of ICONE 14, (2006) S. Ziada, et al., “Self-excited resonances of two side-branches in close proximity”, Journal of Fluids and Structures, 6, P583-601 (1992)

  Since the space inside the reactor containment vessel through which the main steam piping of the reactor is routed is limited, the method of suppressing acoustic resonance when the power generation capacity is increased is also a space-saving and compact method. I need it.

  In JP-A-2006-153869, as described above, by installing a Helmholtz pipe in the main steam pipe, the Helmholtz resonance pipe absorbs the acoustic energy in the main steam system and effectively attenuates the acoustic resonance mode. Can be made. However, Japanese Patent Laid-Open No. 2006-153869 needs to install a Helmholtz tube for each branch tube. In a BWR plant, since there are often 10 or more relief safety valves, it is necessary to enlarge the reactor containment vessel.

  Japanese Patent Application Laid-Open No. 2008-14458 also needs to attenuate the acoustic resonance mode for each branch pipe. In this case, the subject that the structure of piping becomes complicated arises.

  S. Ziada, et al., “Self-excited resonances of two side-branches in close proximity”, Journal of Fluids and Structures, 6, P583-601 (1992). It is disclosed that when resonance occurs, the sound pressure can be suppressed by making a difference between the lengths of adjacent branch pipes. However, when the branch pipe is a reactor main steam relief safety valve pedestal, a main steam relief safety valve is installed at the lower end of the branch pipe, which may interfere with other main steam pipes in some cases. there is a possibility.

  An object of the present invention is to provide a plant and a boiling water nuclear power plant including a pipe having a branching portion that can further reduce pressure fluctuations based on acoustic resonance.

The feature of the present invention that achieves the above-described object is that the opening communicated with the branch pipe is formed in the pipe at the connection between the branch pipe and the pipe through which gas flows.
The first passing length of the opening in the axial direction of the pipe is greater than the second passing length in the direction perpendicular to the central axis of the pipe and the central axis of the branch pipe. It ’s getting longer,
The first passing length is not more than 10 times the second passing length.

  Since the first passing length is longer than the second passing length, a certain vortex generated at the upstream end of the branch pipe at the connecting portion between the branch pipe and the main pipe is the branch pipe at the connecting portion. The frequency of the vortex generated in the period until it hits the inner surface of the branch pipe near the downstream end of the tube, and the sound wave generated on the inner surface of the branch pipe near the downstream end propagates in the branch pipe and A feedback loop with the frequency of the sound wave in the period until reaching the upstream end of the pipe is not formed across the branch pipe and the pipe. For this reason, the sound by the acoustic resonance which generate | occur | produces in a branch pipe can be made small, and the pressure fluctuation based on acoustic resonance can further be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the sound by the acoustic resonance which generate | occur | produces in a branch pipe can be made small, and the pressure fluctuation based on acoustic resonance can further be reduced.

FIG. 3 is an enlarged longitudinal sectional view of a branch portion of a main steam pipe and a branch pipe shown in FIG. 2. It is a block diagram of the plant (boiling water type nuclear power plant) provided with the piping which has a branch part of Example 1 which is one suitable Example of this invention. It is an enlarged view of the opening part formed in main steam piping by the connection part of the main steam piping shown in FIG. 2, and a branch pipe. It is a characteristic view which shows the relationship of the pressure fluctuation | variation represented by St number and root mean square (RMS). In a plant (boiling water nuclear power plant) having a pipe having a branch portion according to embodiment 2 which is another embodiment of the present invention, an opening formed in the main steam pipe at a connection portion between the main steam pipe and the branch pipe FIG. It is an expanded longitudinal cross-sectional view of the branch part in the plant (boiling water type nuclear power plant) provided with piping which has the branch part of Example 3 which is another Example of this invention.

  The sound generation mechanism in the branch pipe such as the main steam relief safety valve will be described below. A branch pipe that is closed by the valve body of the valve is installed in the main pipe, and gas (for example, air or steam) flows in the main pipe. At the upstream end portion of the branch pipe at the connection portion between the branch pipe and the main pipe, the gas flow flowing in the main pipe is separated, and a vortex is generated. This vortex flows downstream together with the gas, and collides with the inner surface of the branch pipe near the downstream end of the branch pipe at the connection portion. Sound waves are generated by the collision of the vortex with the inner surface of the branch pipe. The sound wave propagates through the branch pipe and is reflected by the valve body of the valve blocking the branch pipe. The reflected sound wave reaches the upstream end of the branch pipe at the connection between the branch pipe and the main pipe. For this reason, the sound wave that is reflected and reaches the connection portion works to strengthen the vortex peeled off from the main pipe. A vortex generated at the upstream end of the branch pipe at the connection between the branch pipe and the main pipe is generated in a period until it collides with the inner surface of the branch pipe near the downstream end of the branch pipe at the connection. The vortex generation frequency is close to the sound wave frequency in the period from when the sound wave generated on the inner surface of the branch pipe near the downstream end reaches the upstream end of the branch pipe. Sometimes, such a sound wave feedback loop is formed in the branch pipe and the main pipe. The formation of the vortex and sound wave feedback loop increases the intensity of the sound wave by several tens to several hundred times. The above is the sound generation mechanism by installing the branch pipe.

  In order to reduce the pressure fluctuation caused by the acoustic resonance generated in the branch pipe, the above-described vortex and sound wave feedback loop should not be formed. The pressure fluctuation accompanying the acoustic resonance generated at the branch portion which is the connection portion of the branch pipe to the main pipe is expressed by the dimensionless number called Strouhal number (St) as shown in the equation (1).

St = f × d / U (1)
Here, d is the length of the opening formed in the main pipe at the connection with the branch pipe in the axial direction of the main pipe (hereinafter referred to as the first length), and L is the length of the branch pipe. (The shortest distance between the connecting part of the branch pipe and the main pipe and the valve body of the valve closest to the connecting part among the valves provided in the branch pipe), U is the flow velocity of the fluid in the main pipe , F is the frequency of pressure fluctuation accompanying acoustic resonance occurring at the connection between the main pipe and the branch pipe. The passing length indicates the distance between the opposing side surfaces of the opening at the opening. For example, the passing length of the circle is equal to the diameter of the circle.

  It is known that when the St number value is in the range of 0.3 to 0.6, acoustic resonance occurs when the above-described vortex and sound feedback loop is formed in the branch pipe or the like. In particular, strong acoustic resonance occurs when the St number is around 0.4. As countermeasures for avoiding acoustic resonance, there are a method of making the St number smaller than 0.3 and a method of making the St number larger than 0.6 to avoid the formation of a vortex and sound feedback loop. When the St number at the rated operation of the plant is made smaller than 0.3, acoustic resonance at the rated operation can be avoided.

  However, since the flow rate of the gas in the main pipe at the time of starting the plant is slower than the flow rate of the gas at the time of rated operation of the plant, the St number at the start is within the range of about 0.3 to about 0.6. there is a possibility. Therefore, as a measure for avoiding substantial acoustic resonance, the St number during rated operation is set to be larger than 0.6. Therefore, based on the equation (1), the first passing length is increased. Will do. Most conventional branch pipes connected to the main pipe have a circular cross section. In order to increase the first passing length in the case where a branch pipe having a circular cross section is provided, the inner diameter of the branch pipe is increased while the cross section remains circular. The inner diameter of the branch pipe is limited by the relationship with the outer diameter of the main pipe, cannot be increased unnecessarily, and there is a limit to avoiding acoustic resonance.

  As a result of earnestly examining the solution of such a problem, the inventors have found that the opening formed in the main pipe at the connection with the branch pipe is in the direction perpendicular to the central axis of the main pipe and the center of the branch pipe. It was noticed that the passing length in the direction perpendicular to the axis (hereinafter referred to as the second passing length) did not affect the St number. Based on this new finding, the inventors have found that acoustic resonance can be avoided if the first and second passing lengths are different. In particular, since the second delivery length is restricted by the inner diameter of the main pipe, it is desirable to make the first delivery length longer than the second delivery length. In order to avoid acoustic resonance, if the first passing length is determined so that the St number is larger than 0.6 and the second passing length is shorter than the first passing length, spatial In addition, the inventors found for the first time that sound due to acoustic resonance can be actively suppressed with a compact system.

  Examples of the present invention obtained in consideration of the above examination results will be described below.

  A plant including a pipe having a branching portion, which is a preferred embodiment of the present invention, will be described below with reference to FIGS. 1, 2, and 3. The plant provided with the pipe having the branching portion of the present embodiment is a BWR plant 1. The BWR plant 1 includes a nuclear reactor 2, a main steam pipe 10, a turbine 12, a condenser (not shown), and a water supply pipe.

  The reactor 2 has a reactor pressure vessel (hereinafter referred to as RPV) 3 and a core disposed in the RPV 3. A large number of fuel assemblies (not shown) are loaded in the core. A removable lid 4 is attached to the RPV 3. In the RPV 3, a steam / water separator (not shown) is installed above the core, and a steam dryer 5 having a corrugated plate 6 is installed above the steam / water separator. The main steam pipe 10 is connected to a nozzle 9 formed in the RPV 3 and communicates with a steam dome 7 formed in the RPV 3 above the steam dryer 5. A turbine 12 is connected to the main steam pipe 10. A branch pipe 15 is connected to the main steam pipe 10, and a steam relief safety valve 13 is installed in the branch pipe 15. Although not shown, the branch pipe 15 extends to the pressure suppression chamber provided in the reactor containment vessel surrounding the nuclear reactor 2, and its tip is immersed in pool water in the pressure suppression chamber. .

  By driving a recirculation pump (not shown), the cooling water in the RPV 3 is pressurized and ejected from a nozzle of a jet pump (not shown) installed in the RPV 3. By the jetted cooling water flow, the cooling water existing around the nozzle is sucked into the jet pump and discharged from the jet pump. The discharged cooling water is supplied to the core. The cooling water is heated by the heat generated by the nuclear fission of the nuclear fuel material in the fuel assembly while ascending the core, and a part of the cooling water becomes steam 16. Moisture contained in the steam 16 is removed by the steam separator and the steam dryer 5. The steam 16 from which moisture has been removed is guided to the turbine 12 through the main steam pipe 10 and rotates the turbine 12. A generator (not shown) connected to the turbine 12 rotates to generate electric power. The steam 16 discharged from the turbine 12 is condensed into water by a condenser (not shown). This water is pressurized as a feed water by a feed water pump (not shown), and supplied into the RPV 3 through a feed water pipe (not shown). The reactor 2 of the BWR plant is a steam generator. The water separated by the steam dryer 5 is discharged through the drain pipe 8 to a region formed between the steam-water separators below the steam dryer 5.

  In the unlikely event that the pressure in the RPV 3 becomes higher than the set value, the steam relief valve 13 is automatically opened. That is, the valve element 17 of the steam relief safety valve 13 is pushed up. The steam 16 in the RPV 3 passes through the main steam pipe 10 and the steam relief safety valve 13, is released into the pool water in the pressure suppression chamber through the branch pipe 15, and is condensed. Thereby, the pressure in the RPV 3 is suppressed to a set value or less, and the safety of the nuclear reactor 2 is ensured.

  An opening 18 is formed in the main steam pipe 10 at the connection between the main steam pipe 10 and the branch pipe 15 (see FIG. 1). The branch pipe 15 communicates with the main steam pipe 10 through the opening 18. In this embodiment, the opening 18 formed in the main steam pipe 10 has a shape as seen from directly above as shown in FIG. That is, the opening 18 has two semicircular arcs 21 that are opposed to each other in the axial direction of the main steam pipe 10, and is formed by connecting both ends of these arcs 21 with two straight lines. Has a side surface. These straight lines are parallel to each other in the axial direction of the main steam pipe 10. The passing length in the axial direction of the main steam pipe 10, that is, the first passing length 19 of the opening 18 formed in the main steam pipe 10 at the connection portion with the branch pipe 15 is the main steam of the opening 18. The passing length in the direction perpendicular to the central axis of the pipe 10 and the direction perpendicular to the central axis of the branch pipe 15, that is, longer than the second passing length 20. For this reason, the value of St number becomes large by (1) Formula, and St number becomes larger than 0.6. When the St number is larger than 0.6, the vortex generation frequency and the sound frequency are shifted as described above, and therefore, the vortex and sound (sound wave) feedback in the branch pipe 15 and the main steam pipe 10. A loop is not formed. That is, generation of a strong sound can be suppressed.

  In the present embodiment in which the first delivery length 19 is longer than the second delivery length 20, the branch pipe 15 connected to the main steam pipe 10 is between the main steam pipe 10 and the steam relief safety valve 13. It has the following configuration. The branch pipe 15 has three regions, that is, an enlarged flow path portion 23, a flow path reduction portion 24, and a circular pipe portion 25 from the main steam pipe 10 toward the steam relief safety valve 13 (see FIG. 1). The enlarged flow path portion 23 has the same cross-sectional area as the area of the opening 18 when the opening 18 is viewed from directly above, and is attached to the outer surface of the main steam pipe 10 at the position of the opening 10. The inner surface of the enlarged flow path portion 23 has the same shape as the shape of the opening 18 described above. A circular pipe portion 25 is attached to the steam relief safety valve 13. The flow path reduction part 24 is connected to the enlarged flow path part 23 and the circular pipe part 25. The flow passage cross-sectional area of the flow passage reduction portion 24 gradually decreases from the flow passage cross-sectional area of the enlarged flow passage portion 23 so as to become the flow passage cross-sectional area of the circular pipe portion 25 smaller than the flow passage cross-sectional area. ing.

  If the second delivery length 20 is equal to the first delivery length 19, the outer diameter of the branch pipe is increased. In some cases, the outer diameter of the branch pipe is larger than the outer diameter of the main steam pipe 10. . As described above, when the outer diameter of the branch pipe is larger than the outer diameter of the main steam pipe 10, the shape of the branch portion becomes complicated and it is difficult to apply to the actual machine.

  In this embodiment, the change of the root mean square (RMS), which is the strength of pressure fluctuation in the portion where the branch pipe 15 is installed in the main steam pipe 10, that is, the branch portion 11, with respect to the St number is shown in FIG. . It is known that the above-described vortex-sound feedback loop is formed and acoustic resonance occurs when the St number value is in the range of about 0.3 to about 0.6. In particular, it is known that acoustic resonance increases when the St number becomes around 0.4. In order to reduce the St number, the steam flow rate may be increased from the equation (1) or the first delivery length 19 may be decreased. Further, in order to increase the St number, it is only necessary to decrease the flow velocity of the steam or increase the first delivery length 19.

  As countermeasures for avoiding acoustic resonance, there are a method of decreasing the St number and a method of increasing the St number. When the St number during the rated output operation of the BWR plant 1 is made smaller than 0.3, acoustic resonance during the rated output operation can be avoided. However, since the flow rate of the steam in the main steam pipe 10 at the time of starting up the BWR plant 1 is slower than the flow rate of the steam at the rated output operation, the St number at the start-up is about 0.3 to about 0.6. Possible values are in range. Therefore, as a measure for avoiding substantial acoustic resonance, the St number at the rated output operation is set to be larger than 0.6. For this reason, it is necessary to reduce the steam flow velocity in the main steam pipe 10 or to increase the first delivery length 19. However, as long as the inner diameter of the main steam pipe 10 is not changed, the steam flow rate is substantially constant if the reactor power is constant. Therefore, as described above, the substantial acoustic resonance countermeasure is the first delivery length. 19 is made larger than the second delivery length 20. However, it is desirable that the first delivery length 19 is not more than 10 times the second delivery length 20.

  The BWR plant described in Japanese Patent Laid-Open No. 2006-153869 avoids acoustic resonance by providing a Helmholtz resonance pipe in a branch pipe connected to the main steam pipe. However, about 10 branch pipes are connected to the main steam pipe 10 of the BWR plant 1. In order to avoid acoustic resonance, it is necessary to install Helmholtz resonance tubes in all of these branch tubes. However, the installation of such a Helmholtz resonance tube enlarges the reactor containment vessel.

  In the present embodiment, the opening 18 formed in the main steam pipe 10 at the connecting portion between the main steam pipe 10 and the branch pipe 15 makes the first delivery length 19 longer than the second delivery length 20. Thus, acoustic resonance can be suppressed, and pressure fluctuations based on acoustic resonance can be further reduced. Furthermore, since the first delivery length 19 is longer than the second delivery length 20, it is not necessary to enlarge the reactor containment vessel.

  The BWR plant provided with the eaves member in the cavity described in Japanese Patent Application Laid-Open No. 2008-14458 needs to install eaves members in a plurality of branch pipes, and the structure is complicated. In the present embodiment in which the first delivery length 19 is longer than the second delivery length 20, the configuration of the BWR plant 1 is provided with Japanese Patent Application Laid-Open No. 2006-153869 in which a Helmholtz resonance tube is installed and a saddle member. This is more simplified than the BWR plant described in Japanese Patent Application Laid-Open No. 2008-14458.

  In this embodiment, since the first delivery length 19 is longer than the second delivery length 20, the pressure fluctuation based on acoustic resonance can be further reduced while suppressing the expansion of the containment vessel. it can. Thereby, generation | occurrence | production of the acoustic resonance in the branch part 11 can be suppressed, and the pressure fluctuation of the steam 16 which flows through the inside of the main steam piping 10 can be reduced. For this reason, the output improvement of the BWR plant 1 can be achieved easily. The improvement in the output of the BWR plant 1 is to increase the reactor core flow and increase the reactor output from the rated output (100% output). In this output improvement, the flow rate of the steam supplied to the turbine 12 is increased. In the present embodiment, the first passing length 19 is longer than the second passing length 20 to suppress the occurrence of acoustic resonance in the branch portion 11, and the pressure fluctuations of the steam 16 flowing in the main steam pipe 10. Can be reduced. For this reason, in this embodiment, the flow rate of the steam 16 supplied to the turbine 12 can be easily increased, and the output improvement of the BWR plant can be easily achieved.

  The plant provided with piping which has the branch part which is the other Example of this invention is demonstrated below using FIG. The plant provided with the piping having the branch portion of the present embodiment is a BWR plant 1A. The BWR plant 1A has a configuration in which the opening 18 formed in the main steam pipe 10 in the BWR plant 1 of Example 1 is replaced with the opening 18A. The other configuration of the BWR plant 1A is the same as that of the BWR plant 1.

  An opening 18A is formed at the connection between the main steam pipe 10 and the branch pipe 15 in the present embodiment (see FIG. 5). The branch pipe 15 communicates with the main steam pipe 10 through the opening 18A. In the present embodiment, the opening 18A formed in the main steam pipe 10 has an elliptical shape as viewed from directly above as shown in FIG. Also in the opening 18A, the first delivery length 19A is longer than the second delivery length 20A.

  Also in this embodiment, each effect produced in the first embodiment can be obtained.

  The plant provided with the piping which has a branch part which is another Example of this invention is demonstrated below using FIG. The plant provided with the piping having the branching portion of the present embodiment is a BWR plant 1B. The BWR plant 1B has a configuration in which the branch pipe 15 is replaced with the branch pipe 15A in the BWR plant 1 of the first embodiment. The other structure of the BWR plant 1B is the same as that of the BWR plant 1.

  The opening 18 formed in the main steam pipe 10 at the connecting portion with the branch pipe 15A has the same shape as the opening 18 formed in the main steam pipe 10 in the first embodiment. The branch pipe 15 </ b> A has a circular cross section at the end connected to the steam relief safety valve 13, and the other end connected to the main steam pipe 10 surrounds the opening 18. The inner surface of the end portion of the branch pipe 15A connected to the steam relief valve 13 has a circular cross section, and the inner surface of the other end portion connected to the main steam pipe 10 has the above-described shape of the opening 18 ( (See FIG. 3).

  Also in this embodiment, the first delivery length 19 is longer than the second delivery length 20 as in the first embodiment. For this reason, the value of St number becomes large by (1) Formula, and St number becomes larger than 0.6. When the St number is larger than 0.6, as described in the first embodiment, a deviation occurs between the vortex generation frequency and the sound frequency, and the vortex and sound (sound wave) is generated in the branch pipe 15 and the main steam pipe 10. ) Feedback loop is not formed. That is, this embodiment can suppress the generation of a strong sound.

  Also in this embodiment, each effect produced in the first embodiment can be obtained.

  Each of the embodiments described above includes a pressurized water nuclear plant having a steam pipe connecting the steam generator (steam generator) and the turbine, a thermal power plant having a steam pipe connecting the boiler (steam generator) and the turbine, and the like. It can apply to the plant provided with piping which has a branch part of this and gas (steam, air, etc.) flows. Moreover, each above-mentioned Example is applicable also to the heating system which has the steam piping connected to a steam generator.

  The present invention can be applied to plants such as nuclear power plants and thermal power plants having steam pipes.

  DESCRIPTION OF SYMBOLS 1,1A, 1B ... Boiling water type nuclear power plant, 2 ... Reactor, 3 ... Reactor pressure vessel, 10 ... Main steam piping, 15, 15A ... Branch pipe, 13 ... Main steam relief safety valve, 11 ... Branch part, 18 , 18A ... opening.

Claims (7)

It is equipped with a pipe to which a branch pipe is connected and gas flows inside.
An opening connected to the branch pipe is formed in the pipe at a connection portion between the branch pipe and the pipe,
The second span of the opening in the direction perpendicular to the central axis of the branch pipe and the first span in the axial direction of the pipe is perpendicular to the central axis of the pipe Longer than the length,
A plant comprising a pipe having a branching section, wherein the first delivery length is 10 times or less of the second delivery length. The branch pipe is provided with a valve;
The pipe having a branch portion according to claim 1, wherein a flow passage cross-sectional area of the branch pipe decreases from the pipe toward the valve in at least a part of the branch pipe between the pipe and the valve. With a plant.   The plant provided with a pipe having a branch part according to claim 1 or 2, wherein the pipe is a steam pipe connected to a steam generator.   The said plant is either a nuclear power plant or a thermal power plant, The plant provided with piping which has a branch part of any one of Claim 1 thru | or 3.   The plant provided with piping which has a branching part given in any 1 paragraph of Claims 1, 3 and 4 with which a valve is provided in said branching pipe. A reactor and a steam pipe connected to the reactor to guide the steam generated in the reactor and connected to a branch pipe;
An opening communicated with the branch pipe is formed in the steam pipe at a connection portion between the branch pipe and the steam pipe,
The first span length of the opening in the axial direction of the steam pipe is a second length in the direction perpendicular to the central axis of the steam pipe and in the direction perpendicular to the central axis of the branch pipe. It is longer than the delivery length of
A boiling water nuclear plant comprising a pipe having a branching portion, wherein the first delivery length is 10 times or less of the second delivery length.   The boiling water nuclear plant according to claim 6, wherein a steam relief safety valve is provided in the branch pipe.

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