JP2007218659A - Main steam pipe and method for operating nuclear power generation plant with boiling water reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the generation of standing waves of pressure pulsation in a main steam piping system which could be generated, according to the flow rate of main steam in a boiling water reactor. <P>SOLUTION: A main steam pipe 1 has a pipeline length changing mechanism 20 which can change the length of a pipeline according to a flow rate of main steam. A movable section 2 of the mechanism 20 has first and second parallel pipe sections 26 and 27, which are parallel to each other and a bend pipe section 28 which makes a half-turn of the direction of the pipeline, by connecting one end of the first parallel pipe section 26 to that of the second parallel pipe section 27 and is movable toward the pipeline direction of the first and second parallel pipe sections 26 and 27. In the main steam pipe 1, a first fixed pipe section 22 with a straight-line pipe section 21, which fits into the first parallel pipe section 26 so that the section 21 can slide to the section 26 and a second fixed pipe section 24 with a straight-line pipe section 23 which fits into the second parallel pipe section 27 so that the section 23 is slidable with respect to the section 27 are arranged. A pipeline connected to the first parallel pipe section 26, the bent pipe section 28, the second parallel pipe section 27 and the second fixed pipe section 24, in the order mentioned starting from the first fixed pipe section 22 is constituted. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a main steam pipe of a boiling water nuclear power plant in which pressure pulsation is suppressed and a method for operating the boiling water nuclear power plant.

  In a boiling water nuclear power plant, if the heat output is increased and the steam flow rate is increased, pressure pulsation may occur in the main steam pipe or the main steam system including the main steam pipe and the reactor internal structure. . In this case, the pressure pulsation may damage a furnace internal structure such as a steam dryer. In general, as means for suppressing pressure fluctuation, there are known a method of releasing pressure or a method of installing a Helmholtz resonator to absorb and suppress pulsation.

Such pressure fluctuation suppression means includes, for example, means for discharging steam to the water pool when the pressure rises above a certain pressure, and a buffer hole in the discharge pipe into the water in order to suppress water surface vibration during discharge. For example, in other examples, a Helmholtz resonator is installed adjacent to a pulsation source pressure vessel (see, for example, Patent Document 1).
JP-A-7-139738

  The above-described suppression by the exhaust of the prior art is provided as a means to be performed in an emergency, and if the exhaust is steadily performed, the nuclear reactor cannot be steadily operated. In addition, when installing a Helmholtz resonator, it is necessary to estimate the acoustic natural frequency of the pulsation source in advance, and to design the Helmholtz resonator accordingly, so the accuracy of estimating the natural frequency in a complex shape is improved. Was an issue. In addition, when the operating conditions change, it is necessary to readjust the natural frequency of the Helmholtz resonator to be installed, and it is also a problem to estimate various natural frequencies that are assumed in advance.

  The present invention has been made to solve the above-mentioned problems, and the standing wave of the main steam piping system pressure pulsation that can be generated according to the main steam flow rate that increases or decreases according to the change in the output of the boiling water reactor. The purpose is to prevent or suppress the occurrence.

  In order to achieve the above object, according to the present invention, in the main steam pipe for sending the main steam generated in the boiling water reactor to the steam turbine, the flow rate of the main steam in order to suppress the pressure pulsation in the main steam pipe. And a pipe length changing mechanism capable of changing the pipe length according to the above.

  In another aspect of the present invention, a main steam pipe for sending main steam generated in a boiling water reactor to a steam turbine, the main pipe going from the reactor to the steam turbine, and a branch from the main pipe In the main steam pipe having a branch pipe having a closed end at the tip, the pipe length of the branch pipe can be changed in order to suppress pressure pulsation in the main steam pipe. It is characterized by.

  According to still another aspect of the present invention, in a method for operating a boiling water nuclear power plant having a main steam pipe for sending main steam generated in a nuclear reactor to a steam turbine, pressure pulsation in the main steam pipe is suppressed. Therefore, the length of the main steam pipe is changed according to the flow rate of the main steam.

  In yet another aspect of the present invention, a main steam provided with a main pipe for sending main steam generated in a nuclear reactor to a steam turbine, and a branch pipe branched from the main pipe and having a closed end at the tip. In a method of operating a boiling water nuclear power plant having a pipe, the pipe length of the branch pipe is changed in order to suppress pressure pulsation in the main steam pipe.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the standing wave of the main steam piping system pressure pulsation which can generate | occur | produce according to the main steam flow volume which increases / decreases according to the change of a reactor output can be prevented or suppressed.

  Hereinafter, various embodiments of a main steam pipe of a boiling water nuclear power plant according to the present invention will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 1 and FIG. 2 are schematic longitudinal sectional views showing the vicinity of the pipe length changing mechanism of the first embodiment of the main steam pipe according to the present invention, and FIG. 1 shows a state in which the pipe length is shortened. FIG. 2 is a diagram showing a state in which the pipe length is increased. The main steam pipe 1 has a function of connecting a reactor (not shown) and a steam turbine and sending main steam generated in the reactor to the steam turbine. As shown in the figure, a pipe length changing mechanism 20 capable of changing the pipe length is provided in the middle of the main steam pipe 1. That is, a first fixed tube portion 22 including a first straight tube portion 21 having an open end is provided in the middle of the main steam pipe 1, and the first fixed tube portion 22 is separated from the first fixed tube portion 22. A second fixed tube portion 24 including the opened second straight tube portion 23 is provided.

  The U-shaped movable tube portion 2 is arranged so as to connect the first straight tube portion 21 of the first fixed tube portion 22 and the second straight tube portion 23 of the second fixed tube portion 24. . The movable tube portion 2 includes a first parallel tube portion 26, a second parallel tube portion 27 parallel to the first parallel tube portion 26, a first parallel tube portion 26, and a second parallel tube portion 27. And a curved pipe portion 28 that changes the direction of the pipe line by 180 degrees. The first parallel tube portion 26 of the movable tube portion 2 is disposed so as to cover the first straight tube portion 21 of the first fixed tube portion 22 and slides in the pipe line direction of the first straight tube portion 21. The second parallel tube portion 27 of the movable tube portion 2 is arranged so as to cover the second straight tube portion 23 of the second fixed tube portion 24, and the conduit of the second straight tube portion 23 is possible. It can slide in the direction.

  A driving device 5 is provided to slide the movable tube portion 2 in the pipe line direction of the first straight tube portion 21 and the second straight tube portion 23. Leakage of main steam occurs in the sliding portion between the first straight tube portion 21 and the first parallel tube portion 26 and in the sliding portion between the second straight tube portion 23 and the second parallel tube portion 27. A sealing mechanism 3 is provided for preventing and suppressing the above.

  A pressure sensor 6 is attached to a fixed portion of the main steam pipe 1 so that a pressure fluctuation in the main steam pipe 1 can be detected. A strain gauge 7 is attached to the outer surface of the fixed portion of the main steam pipe 1 so that vibration of the main steam pipe 1 can be detected. The outputs of the pressure sensor 6 and the strain gauge 7 are input to the measurement data processing device 8, processed, and the output is input to the control device 9.

  The control device 9 drives the drive device 5 to avoid resonance when the vibration of the main steam pipe 1 is generated based on the output of both or one of the pressure sensor 6 and the strain gauge 7 or the main steam pipe 1. Adjust the pipe length.

  In determining the mounting position of the pressure sensor 6, acoustic analysis of the main steam piping system is performed in advance, and when the pressure vibration of the main steam piping system resonates, the vicinity of the antinode where the amplitude of the pressure vibration increases is selected. Is preferred.

  According to this embodiment, when the main steam flow rate is changed by changing the reactor output, the resonance of the main steam piping system is avoided by changing the length of the main steam line along with this. Can do. Further, even when pressure vibration or main steam pipe vibration occurs, resonance can be suppressed by detecting this and changing the length of the main steam pipe.

  As a modification of the first embodiment described above, instead of being arranged so that the parallel tube portions 26 and 27 of the movable tube portion 2 are outside the straight tube portions 21 and 23 of the fixed tube portion 22, the movable tube The parallel tube portions 26 and 27 of the portion 2 may be structured so as to be inside the straight tube portions 21 and 23 of the fixed tube portion 22.

[Second Embodiment]
3 and 4 are schematic longitudinal sectional views showing the vicinity of the pipe length changing mechanism of the second embodiment of the main steam pipe according to the present invention, and FIG. 3 shows a state in which the pipe length is lengthened. FIG. 4 is a diagram showing a state in which the pipe length is shortened.

  In this embodiment, a plurality of branch pipes having different pipe lengths are arranged in the middle of the main steam pipe 1, and the branch pipes are selected by switching the valve. It changes the length. More specifically, the U-shaped pipe portion 10 is disposed as a part of the pipe length changing mechanism 30. And there is a branch part in the middle of the U-shaped pipe part 10, and a part of the U-shaped pipe part 10 is provided with a plurality (two in the example of FIGS. 3 and 4) of short-circuit pipes (bypass pipes) 12a and 12b. Can be short-circuited. Short-circuit valves 11a and 11b are arranged in the short-circuit lines 12a and 12b, respectively.

  The control device 9 opens and closes the short-circuit valves 11a and 11b to avoid resonance when vibration of the main steam pipe 1 occurs based on the output of either or one of the pressure sensor 6 and the strain gauge 7 or the main steam. The pipe length of the pipe 1 is adjusted.

  In the state of FIG. 3, both the short-circuit valves 11 a and 11 b are closed, and all the main steam flowing through the main steam pipe 1 passes through the longest flow path of the U-shaped pipe portion 10. In the state of FIG. 4, since the short circuit valve 11a is opened and the short circuit valve 11b is closed, the main steam flowing through the main steam pipe 1 flows through both the longest flow path of the U-shaped pipe section 10 and the short circuit pipe 12a. . Thereby, the substantial length of the main steam pipe 1 can be changed.

  According to this embodiment, the length of the main steam line can be changed with changes in the reactor power and the main steam flow rate, thereby avoiding resonance between the main steam pipe and the reactor internal structure. Can do.

[Third Embodiment]
5 and 6 are schematic longitudinal sectional views showing the vicinity of the pipe length changing mechanism of the third embodiment of the main steam pipe according to the present invention, and FIG. 5 shows a state in which the pipe length is shortened. FIG. 6 is a diagram showing a state in which the pipe length is increased.

  In this embodiment, a pipe length changing mechanism 35 that can change the pipe length is disposed in the middle of the main steam pipe 1. As a part of the pipe length changing mechanism 35, a first straight pipe portion 36 and a second straight pipe portion 37 that are parallel to each other are arranged. Each of the first straight tube portion 36 and the second straight tube portion 37 has a plurality of branch portions (three portions in FIGS. 5 and 6), and the first straight tube portion 36 and the second straight tube portion. Branch pipes 38a, 38b, and 38c that connect the 37 branch portions to each other are disposed.

  The first straight tube portion 36 and the second straight tube portion 37 are formed with female threads 13a and 13b, respectively, and the first valve body 39 and the second valve body 40 are respectively formed with male threads. Are inserted into the female threads of the first straight tube portion 36 and the second straight tube portion 37 by screwing. The first valve body 39 and the second valve body 40 are joined to the first drive device 41 and the second drive device 42, respectively, and are rotated by the rotation of the first drive device 41 and the second drive device 42, respectively. The first valve body 39 and the second valve body 40 are driven in the pipeline direction inside the first straight pipe section 36 and the second straight pipe section 37 while rotating. Thereby, the first valve body 39 and the second valve body 40 partially close or open the first straight tube portion 36 and the second straight tube portion 37.

  For example, in the state shown in FIG. 5, the first valve body 39 and the second valve body 40 are inserted to the back of the first straight tube portion 36 and the second straight tube portion 37, and as a result, the branch tube 38b, 38c is closed, and the flow path of the main steam pipe 1 is only through the branch pipe 38a. Accordingly, the main steam pipe 1 at this time has a short pipe length. In the state shown in FIG. 6, the first valve body 39 and the second valve body 40 are pulled out from the first straight tube portion 36 and the second straight tube portion 37 as compared with the state in FIG. 5. In this case, the flow path of the main steam pipe 1 includes any of the branch pipes 38a, 38b, and 38c. Thereby, the substantial length of the main steam pipe 1 can be changed.

  According to this embodiment, the length of the main steam line can be changed with changes in the reactor power and the main steam flow rate, thereby avoiding resonance between the main steam pipe and the reactor internal structure. Can do.

  In the example shown in FIGS. 5 and 6, the number of branch pipes 38a, 38b, and 38c is three, but the number can be arbitrarily selected from two or more.

  Further, as a modification of the third embodiment, instead of linearly moving the valve bodies 39 and 40 by screws while rotating the valve bodies 39 and 40, piston-like (columnar) valve bodies are directly connected in the straight pipe portions 36 and 37. It is also possible to drive linearly.

[Fourth Embodiment]
FIG. 7 and FIG. 8 are schematic longitudinal sectional views showing the vicinity of the branch pipe line of the fourth embodiment of the main steam pipe according to the present invention, and FIG. 7 is a view showing a state in which the pipe line length is shortened. FIG. 8 is a diagram showing a state in which the branch pipe length is increased.

  The main steam pipe 1 has a main pipe 50 heading from the reactor to the steam turbine, and a branch pipe 51 branched from the main pipe 50 and closed at the tip. In the middle of the branch pipe 51, for example, a measuring instrument such as a pressure gauge, a relief valve that is normally closed (not shown), and the like are attached.

  Such a branch pipe 51 may become a resonance source. Therefore, in the present embodiment, the length of the branch pipe 51 can be adjusted to avoid resonance. That is, the branch pipe 51 covers the outer side of the fixed branch pipe part 52 while sliding with respect to the fixed branch pipe part 52 and the fixed branch pipe part 52 fixed to the main pipe 50 and having the open end. And a movable closing pipe portion 53 arranged at the bottom. The driving device 5 is attached to the movable closing tube portion 53, and the movable closing tube portion 53 is driven. A seal mechanism 3 is provided at a sliding portion between the fixed branch pipe portion 52 and the movable closing pipe portion 53, and leakage of main steam in the main steam pipe 1 is prevented or suppressed.

  A pressure sensor 6 is attached to the main pipe 50 so that the pressure fluctuation in the main steam pipe 1 can be detected. A strain gauge 7 is attached to the outer surface of the main pipe 50 so that vibration of the main steam pipe 1 can be detected. The outputs of the pressure sensor 6 and the strain gauge 7 are input to the measurement data processing device 8, processed, and the output is input to the control device 9.

  The control device 9 drives the drive device 5 to avoid resonance when the vibration of the main steam pipe 1 is generated based on the output of one or both of the pressure sensor 6 and the strain gauge 7, and the branch pipe 51 Adjust the pipe length.

  In determining the mounting position of the pressure sensor 6, acoustic analysis of the main steam piping system is performed in advance, and when the pressure vibration of the main steam piping system resonates, the vicinity of the antinode where the amplitude of the pressure vibration increases is selected. Is preferred.

  According to this embodiment, when the main steam flow rate is changed by changing the reactor power, the length of the branch pipe 51 is changed accordingly, thereby avoiding resonance of the main steam piping system. Can do. Even when pressure vibration or main steam pipe vibration occurs, resonance can be suppressed by detecting this and changing the length of the branch pipe 51.

  As a modification of the fourth embodiment described above, it is also possible to slide the movable closing tube portion 53 inside the fixed branch tube portion 52. In this case, you may comprise like the piston which slides the inside of the fixed branch pipe part 52 by making the movable closing pipe part 53 into a solid.

[Fifth Embodiment]
FIG. 9 and FIG. 10 are schematic longitudinal sectional views showing the vicinity of the branch pipeline of the fifth embodiment of the main steam pipe according to the present invention, and FIG. 9 is a diagram showing a state in which the branch pipeline length is shortened. FIG. 10 is a diagram showing a state in which the branch pipe length is increased.

  In this embodiment, instead of the branch pipe 51 that can change the pipe length in the fourth embodiment (FIGS. 7 and 8), the pipe length is changed by a screw in the third embodiment (FIGS. 5 and 6). The mechanism method is applied. That is, a branch pipe 55 having a closed tip branches off from the main pipe 50. A female screw 56 is formed inside the branch pipe 55, and a valve body 57 having a male screw that is screwed into the female screw 56 is inserted into the branch pipe 55. The driving device 5 is joined to the valve body 57, and the valve body 57 is rotationally driven by the driving device 5, whereby the valve body 57 moves in the branch pipe 55 in the pipe line direction. Thereby, the pipe line length of the branch pipe 55 can be changed.

  According to this embodiment, the length of the branch pipe 55 can be changed with changes in the reactor power and the main steam flow rate, thereby avoiding resonance between the main steam pipe and the reactor internal structure. it can.

  As a modified example of the fifth embodiment described above, instead of linearly moving the valve body 57 with a screw while rotationally driving the valve body 57, a piston-like (columnar) valve body is directly linear in the fixed branch pipe 55. It is also possible to drive it.

  As still another modification, the end of the fixed branch pipe is opened, a male screw is formed on the outside of the fixed branch pipe, and a movable closed pipe portion having a female screw threadedly engaged with the male screw is provided outside the fixed branch pipe. It is also possible to displace the movable closing tube and move it in the axial direction. In this case, it can also be said that the movement of the movable closing tube portion 53 of the fourth embodiment (FIGS. 7 and 8) is changed to a screw system.

[Sixth Embodiment]
FIG. 11 and FIG. 12 are schematic longitudinal sectional views showing the vicinity of the branch pipeline of the sixth embodiment of the main steam pipe according to the present invention, and FIG. 11 is a diagram showing a state in which the branch pipeline length is shortened. FIG. 12 is a diagram showing a state in which the branch pipe length is increased.

  In this embodiment, the method of changing the branch pipe length in the fourth embodiment (FIGS. 7 and 8) or the fifth embodiment (FIGS. 9 and 10) is changed.

  In this embodiment, a branch pipe 60 whose tip is closed branches off from the main pipe 50. Two valves 61 and 62 are disposed in series in the middle of the branch pipe 60. In FIG. 1, since the valve 61 on the side close to the main pipe 50 is closed, the effective length of the branch pipe 60 at this time is the shortest. In contrast, in FIG. 2, since both the valves 61 and 62 are open, the effective length of the branch pipe 60 at this time is the longest. Although illustration is omitted, when the valve 61 is open and the valve 62 is closed, the effective length of the branch pipe 60 is intermediate between that in FIG. 11 and that in FIG. In this way, the effective pipe length of the branch pipe 55 can be changed.

  According to this embodiment, the length of the branch pipe 60 can be changed with changes in the reactor power and the main steam flow rate, thereby avoiding resonance between the main steam pipe and the reactor internal structure. it can.

  In this embodiment, the number of valves provided in the branch pipe 60 can be any number of one or more depending on the design.

[Other Embodiments]
Although various embodiments have been described above, these are merely examples, and the present invention is not limited to these embodiments.

  For example, in the above description, the vibration length is detected by the output of the pressure sensor 6 or the strain gauge 7, and the length of the main steam pipe or the branch pipe is changed. Based on the flow rate or the like, the pipe length may be changed to prevent resonance.

  Furthermore, it can also be implemented by combining a plurality of characteristic portions of the above embodiments or their modifications.

FIG. 3 is a schematic longitudinal sectional view showing the vicinity of the pipe length changing mechanism of the first embodiment of the main steam pipe according to the present invention, and showing a state in which the pipe length is shortened. It is a typical longitudinal section showing the pipe length change mechanism neighborhood of a 1st embodiment of main steam piping concerning the present invention, and is a figure showing the state where pipe length was lengthened. It is a typical longitudinal section showing the pipe length change mechanism neighborhood of a 2nd embodiment of main steam piping concerning the present invention, and is a figure showing the state where pipe length was lengthened. It is a typical longitudinal cross-sectional view which shows the pipe line length change mechanism vicinity of 2nd Embodiment of the main steam piping which concerns on this invention, Comprising: The figure which shows the state which shortened the pipe line length. It is a typical longitudinal cross-sectional view which shows the pipe length change mechanism vicinity of 3rd Embodiment of the main steam piping which concerns on this invention, Comprising: The figure which shows the state which shortened the pipe line length. It is a typical longitudinal section showing the pipe length change mechanism neighborhood of a 3rd embodiment of main steam piping concerning the present invention, and is a figure showing the state where pipe length was lengthened. It is a schematic longitudinal cross-sectional view which shows the branch pipeline vicinity of 4th Embodiment of the main steam piping which concerns on this invention, Comprising: The figure which shows the state which shortened the branch pipeline length. It is a typical longitudinal cross-sectional view which shows the branch pipeline vicinity of 4th Embodiment of the main steam piping which concerns on this invention, Comprising: The figure which shows the state which lengthened the branch pipeline length. It is a typical longitudinal cross-sectional view which shows the branch pipeline vicinity of 5th Embodiment of the main steam piping which concerns on this invention, Comprising: The figure which shows the state which shortened the branch pipeline length. It is a typical longitudinal cross-sectional view which shows the branch pipeline vicinity of 5th Embodiment of the main steam piping which concerns on this invention, Comprising: The figure which shows the state which lengthened the branch pipeline length. It is a schematic longitudinal cross-sectional view which shows the branch pipeline vicinity of 6th Embodiment of the main steam piping which concerns on this invention, Comprising: The figure which shows the state which shortened the branch pipeline length. It is a typical longitudinal cross-sectional view which shows the branch pipeline vicinity of 6th Embodiment of the main steam piping which concerns on this invention, Comprising: The figure which shows the state which lengthened the branch pipeline length.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Main steam piping, 2 ... Movable pipe part, 3 ... Sealing mechanism, 5 ... Drive apparatus, 6 ... Pressure sensor, 7 ... Strain gauge, 8 ... Measurement data processing apparatus, 9 ... Control apparatus, 10 ... U-shaped pipe part 11a, 11b ... short-circuit valve, 12a, 12b ... branch pipe (bypass pipe), 13 ... female screw, 20 ... pipe length changing mechanism, 21 ... first straight pipe section, 22 ... first fixed pipe , 23 ... second straight pipe part, 24 ... second fixed pipe part, 26 ... first parallel pipe part, 27 ... second parallel pipe part, 28 ... curved pipe part, 30 ... pipe length change Mechanism: 35 ... Pipe length changing mechanism, 36 ... First straight pipe section, 37 ... Second straight pipe section, 38a, 38b, 38c ... Branch pipe, 39 ... First valve element, 40 ... Second Valve body 41... First drive device 42. Second drive device 50. Main pipe 51. Branch pipe 52. Fixed branch pipe 53 53 Movable closed pipe 55 Branch pipe, 56 ... male screw, 57 ... valve body, 60 ... branch pipe, 61, 62 ... valve

Claims (15)

In the main steam pipe for sending the main steam generated in the boiling water reactor to the steam turbine,
A main steam pipe having a pipe length changing mechanism capable of changing a pipe length in accordance with a flow rate of the main steam in order to suppress pressure pulsation in the main steam pipe. The pipe length changing mechanism is
First and second parallel parts parallel to each other, and a curved pipe part that connects one end of each of the first and second parallel pipe parts and changes the direction of the pipe line by 180 degrees, A movable pipe portion movable in the pipe direction of the first and second parallel pipe portions;
A first fixed tube portion having a straight tube portion that fits slidably with respect to the first parallel tube portion and extends in the direction of the first parallel tube portion;
A second fixed tube portion having a straight tube portion that fits slidably with respect to the second parallel tube portion and extends in the direction of the second parallel tube portion;
Have
The first fixed pipe section constitutes a pipe line sequentially connected to the first parallel pipe section, the curved pipe section, the second parallel pipe section, and the second fixed pipe section. Item 4. The main steam pipe according to item 1.   The pipe length changing mechanism includes a plurality of branch pipes having different inlets and outlets and having different lengths, and valves arranged in the branch pipes. Main steam piping as described. The pipe length changing mechanism is
A first straight tube portion having a plurality of branch portions;
A second straight tube portion having a plurality of branch portions;
A plurality of branch pipes connecting the respective branch parts of the first straight pipe part and the second straight pipe part;
The first straight pipe section and the second straight pipe section are inserted into at least one of the first straight pipe section and are slidable along the pipeline, and the first or second straight pipe section is branched by the sliding. A valve body that can be opened and closed,
The main steam pipe according to claim 3, wherein   The valve body is formed with a male screw, and the first or second straight tube portion into which the valve body is inserted is formed with a female screw that is screwed with the male screw, and the valve body is rotated. The main steam pipe according to claim 4, wherein the valve body is configured to move in a pipe line direction of the first or second straight pipe section. A pressure sensor for detecting pressure fluctuations in the main steam pipe;
Means for controlling the pipe length changing mechanism to change the pipe length so as to suppress pressure fluctuations in accordance with the output of the pressure sensor;
The main steam pipe according to any one of claims 1 to 5, further comprising: A strain gauge attached to the surface of the main steam pipe for detecting strain fluctuations on the surface of the main steam pipe;
Means for controlling the pipe length changing mechanism to change the pipe length so as to suppress the strain fluctuation according to the output of the strain gauge;
The main steam pipe according to any one of claims 1 to 6, further comprising: A main steam pipe for sending main steam generated in a boiling water reactor to a steam turbine, a main pipe going from the reactor to the steam turbine, and a branch pipe branched from the main pipe and having a closed end at the tip In the main steam pipe having
A main steam pipe, characterized in that the pipe length of the branch pipe can be changed to suppress pressure pulsation in the main steam pipe. The branch pipe is
A fixed branch pipe part branched from the main pipe and having an open end at the tip;
A movable closing pipe portion slidably fitted to the open end and having a closed end at the tip;
The main steam pipe according to claim 8, characterized by comprising: The branch pipe is
A fixed branch pipe portion branched from the main pipe;
A valve body that is slidable within the fixed branch pipe part and capable of closing a pipe line of the fixed branch pipe part;
The main steam pipe according to claim 8, characterized by comprising:   The valve body is formed with a male screw, the fixed branch pipe portion is formed with a female screw that is screwed with the male screw, and the valve body is rotated by the rotation of the valve body. The main steam pipe according to claim 10, wherein the main steam pipe is configured to move in a pipe line direction. A pressure sensor for detecting pressure fluctuations in the main steam pipe;
Control means for changing the pipe length of the branch pipe so as to suppress pressure fluctuation in accordance with the output of the pressure sensor;
The main steam pipe according to any one of claims 8 to 11, further comprising: A strain gauge attached to the surface of the main steam pipe for detecting strain fluctuations on the surface of the main steam pipe;
In accordance with the output of the strain gauge, control means for changing the pipe length of the branch pipe so as to suppress the strain fluctuation;
The main steam pipe according to any one of claims 8 to 12, further comprising: In a method for operating a boiling water nuclear power plant having a main steam pipe for sending main steam generated in a nuclear reactor to a steam turbine,
A method for operating a boiling water nuclear power plant, wherein the length of the main steam pipe is changed in accordance with the flow rate of the main steam in order to suppress pressure pulsation in the main steam pipe. Operation of a boiling water nuclear power plant having a main steam pipe having a main pipe for sending main steam generated in a nuclear reactor to a steam turbine and a branch pipe branched from the main pipe and having a closed end at a tip. In the method
A method for operating a boiling water nuclear power plant, wherein a pipe length of the branch pipe is changed in order to suppress pressure pulsation in the main steam pipe.

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