JPH07113893A - Jet pump for boiling water reactor - Google Patents

Abstract

PURPOSE:To improve safety of reactor in normal operation by selecting the outer diameter of an instrumentation pipe of jet pump so that the natural frequency of the instrumentation pipe avoids the resonance frequency zone in normal operation. CONSTITUTION:Instrumentation pipes 24 for each jet pump are fixed at welding parts 27 fillet-welded to support metals 26 of a rectangular paralelopiped on the outer surface of diffusers 20 put on a baffle plate. At the horizontal pipe 24, a plurality of pipes 24 capable of sliding to absorb the bend due to thermal expansion are supported with support metals. By selecting the outer diameter of the pipes 24 at 27, 2mm or more, the natural frequency can be avoided from the resonance frequency zone. That is, pressure pulse frequency of the natural frequency corresponding to 100% of recirculation pump revolution can be generated. Also, support part 26 suffers only stress due to forced vibration, which is kept below the fatigue limit stress and thus, damage on the welding parts 27 is prevented.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a jet pump for a boiling water reactor.

[0002]

2. Description of the Related Art A conventional boiling water reactor is constructed as shown in FIG. A shroud 3 for accommodating a core 2 is installed in a reactor pressure vessel 1, and a large number of fuel assemblies are provided between a core support plate 4 and an upper lattice plate 5 which are respectively arranged below and above the shroud 3. The body 6 is installed.

A shroud head 7 is disposed above the shroud 3, and a steam separator 9 is installed above the shroud head 7 via a stand pipe 8.
A steam dryer 10 is installed above the steam separator 9. Below the core support plate 4, a control rod guide tube 11 for accommodating a control rod (not shown) inserted into the core 2 is provided.
And a control rod drive mechanism 12 for driving the control rod.

A plurality of jet pumps 13 are provided on the side of the core 2.
The jet side of the jet pump 13 is provided with a discharge side pipe 16 of a recirculation system pipe 15 provided with a recirculation pump 14 for recirculating the cooling water in the reactor pressure vessel 1. The suction side pipe 17 of the recirculation system pipe 15 is open to the side of the jet pump 13 of the reactor pressure vessel 1.

Further, a main steam pipe 18 for guiding steam generated in the core 2 to a turbine (not shown) is opened on the side of the steam dryer 10 of the reactor pressure vessel 1, and the reactor pressure vessel 1 is further provided.
A water supply pipe 19 for supplying cooling water to the reactor pressure vessel 1 is opened on the side of the stand pipe 8.

The output of the nuclear reactor is mainly controlled by the flow rate of the cooling water to the core 2, and the control of the flow rate of the cooling water is performed by changing the number of revolutions of the recirculation pump 14 that sends water to the jet pump 13. .

The flow rate of each jet pump 13 is as shown in FIG. 9 in the upper pipe of the diffuser 20 and the baffle plate 21.
It is calculated from the calibrated differential pressure and the flow rate by measuring the differential pressure with the pressure on the lower surface of the. As for the pressure on the lower surface of the baffle plate 21, the average pressure of the entire core is taken out of the reactor pressure vessel 1 by the guide rod 22. In each jet pump 13, a pressure tap 23 is provided above the diffuser 20 so as to penetrate from the outside of the pipe to the inside of the pipe, and a pressure guiding pipe 25 called a jet pump measurement pipe 24 is connected to the pressure tap 23.
The measurement pipes 24 coming from the plurality of jet pumps 13 are bundled and taken out of the other pressure vessel 1. The measurement pipe 24 from each jet pump 13 is bent downward in the middle part of the diffuser 20 along the outer surface of the diffuser 20 from the upper part of the diffuser 20, and is laid horizontally.

As shown in a partially enlarged view of FIG. 10, the measurement pipe 24 is fixed to the outer surface of the diffuser 20 by a rectangular parallelepiped support fitting 26 and a fillet-welded weld portion 27. Further, the horizontal pipe is fixed by a support fitting (not shown) capable of supporting a plurality of slidable measurement pipes 24 so as to absorb the deflection caused by thermal expansion.

[0009]

In the reactor pressure vessel 1, a suction side pipe 17 of the recirculation system pipe 15 is opened to the side of the jet pump 13. Therefore, the blade cutting pressure pulsation of the recirculation pump 14 propagates to the side of the jet pump 13 and excites the measurement pipe 24.

Since the recirculation flow rate is increased / decreased by increasing / decreasing the number of revolutions of the recirculation pump 14, the frequency f of the blade cutting pressure pulsation of the recirculation pump 14 is 0 ≦ f ≦ (maximum pump revolutions per second. Number) x number of blades [Hz].

In the conventional example, the frequency band of the pressure pulsation for exciting the device with respect to the natural frequency of the device is not taken into consideration. If the natural frequency of the equipment coincides with the above-mentioned pressure pulsation and causes a decrease in resonance, the vibration amplitude of the measurement pipe will suddenly increase (tens to hundreds of times that of forced vibration without resonance) and support it. There is a problem that stress concentrates on the root welded part of the metal fitting and the measurement pipe, and the measurement pipe breaks.

The present invention has been made to solve the above problems, and the measurement pipe of the jet pump does not resonate with the blade pulsation pressure pulsation of the recirculation pump, or even if resonance occurs, damage to the welded portion is prevented. Another object of the present invention is to provide a jet pump for a boiling water reactor which is sound and is capable of improving the safety of the reactor at normal times.

[0013]

According to the present invention, the outer diameter of the measurement pipe of a jet pump of a boiling water reactor is set so that the natural frequency of the measurement pipe is a value that avoids the resonance frequency band during normal operation. Select the natural frequency of the measurement pipe and avoid the frequency band where the blade cutting pressure pulsation of the recirculation pump is large and the frequency of use is high (long operation time) during plant operation, or occurs in the support part. It is characterized by reducing fatigue damage due to stress vibration generated in the support part by changing to a support structure or shape that reduces stress or by limiting the time of pump operation at a resonating pump speed. .

[0014]

FIG. 1 shows the relationship between the pump rotation speed and the natural frequency of the jet pump measurement pipe. A resonance phenomenon occurs under the resonance condition where the pump pressure pulsation frequency generated depending on the pump rotation speed and the natural frequency of the measurement pipe match. 75% to 95% pump speed in normal plant operation (normal operating range)
Is often used in.

In order to avoid this frequency band, if the natural frequency of the measurement pipe is increased from the frequency corresponding to 100% pump rotation speed to make it a rigid design, the blade pulsation pressure pulsation and the resonance phenomenon of the measurement pipe are avoided, and Only the stress due to the forced vibration is generated in the portion, and the fatigue limit stress value becomes less than the value, so that the damage of the welded portion can be prevented.

The pressure pulsation due to blade cutting of the recirculation pump is basically proportional to the square of the pump rotation speed from the mockup test and the actual plant measurement as shown in FIG.
If the natural frequency of the measurement pipe cannot be set higher than the frequency corresponding to 100% pump rotation speed, the natural vibration is reduced to a flexible design to reduce the excitation force, and even if it resonates, it occurs in the support part. The stress to be applied can be kept below the fatigue limit stress value, and damage to the welded part can be prevented.

The structure shown in the embodiment in which the supporting portion is described below,
Alternatively, by changing to a structure in which the exciting force does not work directly on the measurement pipe, the stress generated in the support portion even at the time of resonance can be made equal to or less than the fatigue limit stress value, and damage to the welded portion can be prevented.

Due to various conditions inside the furnace, the natural frequency of the measuring pipe is below the frequency band of the normal operating range, and there is a possibility of resonance with the pump pressure pulsation during operation. When the stress value is equal to or higher than the limit stress value, by limiting the operation time at the pump rotation speed within the operation limit range which is a resonance state, it is possible to avoid damage to the measurement pipe support portion due to fatigue during the life of the plant.

From the above, the resonance phenomenon does not occur, and
Even if it occurs, it is possible to prevent damage due to fatigue damage of the welded portion of the support point, and it is possible to improve safety during normal operation of the reactor.

[0020]

EXAMPLE A first example of a boiling water reactor jet pump according to the present invention will be described. Since the basic structure of the jet pump according to this embodiment is the same as that of the conventional example shown in FIGS. 9 and 10, the description of the specific structure is omitted, and only the parts different from the conventional example will be described.

The difference between the first embodiment and the prior art is that the measuring pipe 24 itself is selected to have an outer diameter of 27.2 mm or more to avoid the natural frequency from the resonance frequency band.

The natural frequency f of the measuring pipe 24 is generally

[Equation 1] However, λ: a constant determined by the supporting condition l: distance between supporting points E: longitudinal elastic modulus of the measuring pipe I: second moment of area of the measuring pipe γ: mass density of the measuring pipe A: sectional area of the measuring pipe g: gravity Expressed in acceleration.

The measurement pipe 24 of the conventional example has a pipe outer diameter: do = 13.8 mm, a pipe plate thickness: t = 2.2 mm, and the recirculation pump has a pump speed of about 55 to 65% (power supply frequency region of 50 Hz) and about. Resonance is possible at 45-55% pump speed (60Hz power frequency region).

On the other hand, in the embodiment of the present invention, the outer diameter of the measuring pipe 24 is selected to be do ≧ 27.2 mm. As a result, the natural frequency can generate the pressure pulsation frequency corresponding to 100% of the pump rotation speed, and only the stress due to the forced vibration is generated in the supporting part, which is below the fatigue limit stress value. It is possible to prevent damage to the weld 27 shown.

Next, a second embodiment of the jet pump according to the present invention will be described with reference to FIG. ◎ Since FIG. 2 is an improvement of the part shown in FIG. 9, only the main part thereof is shown in correspondence with FIG. 10. In order to allow the measurement pipe 24 to freely rotate at the support point, the measurement pipe 24 shown in FIGS.
The support fitting 26a and the U-shaped fitting 28 shown in (d) are used.

That is, in FIG. 2 (a)-(c), the measurement piping
24 shows an example of a support structure surrounded by a quadrilateral support metal fitting 26a having a semicylindrical cross section. Note that FIG. 2B shows (a)
2C is a horizontal sectional view of FIG. 2C, and FIG. 2C is a vertical sectional view of FIG. Further, FIG. 2D shows an example of a support structure in which the metering pipe 24 is surrounded by an inverted U-shaped metal fitting 28 having a circular cross section. Figure 2
Both of the examples of (a) and (d) have a structure in which the measurement pipe 24 is supported by pins at both ends.

The supporting point of the conventional measuring pipe 24 shown in FIG. 10 is completely fixed at both ends by the welded portions 27 on the upper surface of the supporting metal fitting 26 at both ends. In the case of the conventional example, the coefficient λ of the equation (1) is 4.73. Is. On the other hand, when the support fittings 26a and 28 of this embodiment are used at both ends, the coefficient λ becomes π (= 3.14). Even if the distance l between supporting points is the same, the natural vibration coefficient is

[Equation 2] Fall to.

The exciting force F per unit length for vibrating the measuring pipe is

[Equation 3] However, P: is represented by the blade cutting pressure pulsation of the recirculation pump.

The blade cutting pressure pulsation P of the recirculation pump is shown in FIG.
As shown in, since it is proportional to the square of the rotation speed (excitation frequency) of the recirculation pump, the natural frequency decreases to 0.44 ² = 0.19 times. If there is no change in the outer diameter of the measurement pipe, the excitation force will decrease 0.19 times even if the natural frequency of the measurement pipe resonates with the blade cutting pressure pulsation of the recirculation pump. The stress σ generated in the measurement pipe is as shown in equation (3).

[0030]

[Equation 4] However, M: the bending moment acting on the beam, which is proportional to the bending moment acting on the measurement pipe, is given by the following formula under the condition of uniformly distributed load under the following supporting conditions at both ends.

・ Completely fixed at both ends

[Equation 5]

[Both ends pin support]

[Equation 6] However, W: load per unit length

Support metal fitting 26a, U-shaped metal fitting of the present invention
When 28 is used, the condition for supporting both ends of the measurement pipe 24 is changed from perfect welding fixing to pin support, the natural frequency of the measurement pipe 24 is 0.44 times that of the conventional type, and the stress generated in the measurement pipe 24 is greater than that of the conventional type.

[Equation 7] And becomes below the fatigue limit stress value.

Further, generally, the supporting metal fittings, the U-shaped metal fittings, and the measurement pipe 24 are installed at room temperature, and the temperature becomes high (about 270 ° C.) during the operation of the reactor. If the measurement pipe 24 and the support metal fittings are made of the same material with the same coefficient of thermal expansion, there will be a gap due to thermal expansion at the high temperature during the reactor operation, and there will be some play in the support even if the product is installed without any play. However, this may cause damage to the support portion. A material whose coefficient of thermal expansion is larger than that of the measurement pipe 24 is used as the material of the support fitting so that play does not occur in the support portion due to the difference in thermal expansion between the materials even at high temperatures.

Next, a third embodiment of the jet pump according to the present invention will be described with reference to FIG. ◎ In FIG. 4, support fittings 26, 26 for the measurement pipe 24 provided on the outer peripheral surface of the diffuser 20
At the position where the amplitude is the largest in the first natural eigenvibration (lowest frequency) mode that occurs between the points (almost the center between the support points), 29
To provide.

From equation (1), the natural frequency f of the measuring pipe is

[Equation 8] However, m is the mass of the measurement pipe, and the bending moment generated in the measurement pipe 24 is calculated from the equation (2).

[0037]

[Equation 9] The stress σ generated in the measurement pipe is calculated by the equations (3), (5) and (6).

[0038]

[Equation 10] Becomes

As an example, when the weight 29 of the measuring pipe between the support points (including the internal fluid) is installed three times, the natural frequency of the measuring pipe and the blade cutting of the recirculation pump are the same as in the above example. Even if the pressure pulsation resonates, the stress generated in the measurement pipe 24 is σ

[Equation 11] And reduce. By providing the heavy pipe 29 in the measurement pipe 24, the stress generated in the supporting portion can be made equal to or lower than the fatigue limit stress value.

The heavy weight 29 can be attached to the measurement pipe 24 integrally with the measurement pipe 24, or can be attached to the measurement pipe 24 by welding, but fine adjustment cannot be made on site. By adjusting the attachment of the heavy weight 29, it is possible to make fine adjustments on site. Further, since the heavy weight 29 is installed at room temperature and has a high temperature (about 270 ° C.) when the reactor is operating, it is possible to use a shape memory alloy for the heavy weight 29 and connect it to the measurement pipe 24 at high temperature.

Next, a fourth embodiment of the jet pump according to the present invention will be described with reference to FIG. In this embodiment, the measurement pipe 24 at the position where it is welded to the support fitting 26 is formed with a large diameter portion 31 having a locally large outer diameter so that stress concentration does not occur with the measurement pipe 24 other than the support portion. Connect with a smooth change in outer diameter. Generally, the stress σ generated in the supporting portion is expressed by the equation (3), and when the bending moment applied to the supporting portion is constant,

[Equation 12] However, di can be expressed by the inner diameter of the measurement pipe, and when the inner diameter of the measurement pipe is constant, as shown in FIG. 6, the stress generated in the measurement pipe decreases as the pipe diameter increases. For example, when the measurement pipe outer diameter do is changed to 19 mm or more, the generated stress becomes about ⅓ or less and the fatigue limit stress value or less.

Next, a fifth embodiment of the jet pump according to the present invention will be described with reference to FIG. ◎ In this embodiment, a double pipe structure is formed by welding a support pipe 30 having an inner diameter larger than the outer diameter of the measurement pipe 24 to a support fitting 26 that is taken out from the diffuser 20 at a support portion of the measurement pipe 24. Is forming.
The measurement pipe 24 is installed through the support pipe 30,
The support pipe 30 and the measurement pipe 24 are not connected.

In this embodiment, the supporting portion has a double pipe structure, and the double pipe has an air gap, and the supporting point has a flexible structure to reduce the natural frequency.
The support welded portion 27 of 30 and the measurement pipe 24 share the stress, and the stress can be reduced, and the stress generated in the support portion can be kept below the fatigue limit stress value.

Further, the inner surface of the support pipe 30 of this embodiment may be provided with a plurality of grooves in the longitudinal direction of the pipe in order to prevent clevis corrosion.

Further, the support structure and the measurement pipe 24 are installed at room temperature, and the temperature becomes high (about 270 ° C.) during the reactor operation. A material whose coefficient of thermal expansion is larger than that of the measuring pipe 24 is used as the material of the support pipe 30, and the support pipe is tightened due to the difference in the thermal expansion of the material even at high temperature, so that there is no backlash that does not require welding. Structures are possible.

In addition, instead of a local double pipe structure near the supporting portion, a double pipe structure is used throughout the measurement piping furnace
It is possible to prevent the blade cutting pressure pulsation of the recirculation pump, which is an exciting force, from directly acting on the measurement pipe, and reduce the stress generated in the measurement pipe.

Next, the sixth embodiment of the jet pump according to the present invention.
An example will be described. The measurement pipe 24 of the jet pump is about 55 to 65% of the recirculation pump 14 pump speed (power frequency 60H
There is a possibility of resonance in the z area). It always passes through the above resonable pump speed range at the time of plant startup and cycle pattern of plant operation. From the viewpoint of the soundness of the fuel and pressure vessel, the rising and falling speeds of the pump are limited and the operating procedure is determined.

Therefore, in the present embodiment, in order to minimize the operating time in the resonable region, the steady operation is not performed in this region, and the resonable region is quickly passed within the specified range. Since the resonance time is short even if the measurement pipe and the recirculation pump blade cutting pressure pulsation resonate in the resonable region, fatigue damage on the measurement pipe support can be avoided during the operating life of the plant.

The embodiments of the present invention are summarized as follows. (1) In the boiling water reactor jet pump, the natural vibration frequency between the supports of the measurement pipe has a sufficient margin from the remarkable excitation frequency in the normal operation range, and the length between the support points, the rigidity of the pipe, Adjust the support method and load mass to keep them away from each other. (2) The outer diameter of the jet pump measurement pipe of a boiling water reactor should be 27.2 mm or more. (3) In arranging the jet pump measurement pipe of the boiling reactor, it is necessary to have a plurality of support fittings that can freely rotate at the support points of the measurement pipe. (4) To have a support metal fitting made of a material having a coefficient of thermal expansion larger than that of the measurement pipe material. (5) In arranging the jet pump measurement pipes of a boiling water reactor, one or more heavy gauges should be provided in the measurement pipes between the support fittings. (6) Use of a shape memory alloy as the material of the heavy weight, or by fixing the heavy weight by shrink fitting. (7) In a jet pump measurement pipe of a boiling water reactor, a measurement pipe in which the outer diameter of the support part is locally enlarged is provided. (8) In the routing of the jet pump measurement pipe of a boiling water reactor, the support part has a double pipe structure, the outer pipe is welded to the support support, and the measurement pipe as the inner pipe penetrates through the outer pipe. (9) A plurality of longitudinal grooves are provided on the inner surface of the outer tube. (10) A supporting outer tube made of a material whose coefficient of thermal expansion is smaller than that of the measuring piping material must be provided. (11) Regarding the routing of jet pump measurement pipes for boiling water reactors, the entire routing area in the reactor shall have a double pipe structure. (12) In a boiling water reactor jet pump with a natural frequency equal to or lower than the pump pressure pulsation frequency in the normal operation range, an operation limit is set so that steady operation is not performed in the frequency range that resonates with the pump pressure pulsation. Was it.

[0050]

According to the present invention, the measurement pipe of the jet pump can avoid the resonance phenomenon with the blade cutting pressure pulsation of the recirculation pump. Further, even if the resonance phenomenon occurs, the concentrated stress value of the welded portion at the supporting point becomes equal to or less than the fatigue limit stress value, and the damage of the welded portion can be prevented. Furthermore, shortening the resonance time can prevent fatigue damage during the plant life of the weld. Therefore, it is possible to improve safety during normal operation of the nuclear reactor.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the rotational speed of a pump and the natural frequency of measurement piping for explaining the action of a jet pump.

FIG. 2A is a perspective view showing a main part of a second embodiment of the jet pump according to the present invention. (B) is a horizontal cross-sectional view of (a), (c) is a vertical cross-sectional view of (a), and (d) is a perspective view showing a main part of another example in (a).

FIG. 3 is a characteristic diagram showing the relationship between pressure pulsation applied to the measurement pipe of the jet pump in FIG. 2 and pump rotation speed.

FIG. 4 is a perspective view showing a main part of a fourth embodiment of the jet pump according to the present invention.

FIG. 5 is a perspective view showing a main part of a fourth embodiment of the jet pump according to the present invention.

FIG. 6 is a curve diagram showing the relationship between the stress reduction rate generated in the support part of the jet pump and the outer diameter of the support part measurement pipe in FIG.

FIG. 7 is a perspective view showing an essential part of a fifth embodiment of the jet pump according to the present invention.

FIG. 8 is a vertical sectional view schematically showing the internal structure of a conventional boiling water reactor.

9 is a system diagram showing a measurement system of the jet pump in FIG.

10 is a perspective view schematically showing a measurement pipe support structure of the jet pump in FIG.

[Explanation of symbols]

1 ... Reactor pressure vessel, 2 ... Reactor core, 3 ... Shroud, 4 ...
Core support plate, 5 ... Upper lattice plate, 6 ... Fuel assembly, 7 ... Shroud head, 8 ... Stand pipe, 9 ... Steam separator, 10 ... Steam dryer, 11 ... Control rod guide tube, 12 ... Control rod Drive mechanism, 13 ... Jet pump, 14 ... Recirculation pump, 15 ...
Recirculation pipe, 16 ... Discharge side pipe, 17 ... Suction side pipe, 18 ... Main steam pipe, 19 ... Water supply pipe, 20 ... Diffuser, 21 ... Baffle plate, 22 ... Guide rod, 23 ... Pressure tap, 24 ...
Measuring pipe, 25 ... Pressure guiding pipe, 26 / 26a ... Supporting metal, 27 ... Welding part, 28 ... U-shaped metal fitting, 29 ... Heavy weight, 30 ... Supporting pipe, 31 ... Large diameter part.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Niwa 1 Komukai Toshiba Town, Saiwai-ku, Kawasaki City, Kanagawa Prefecture Corporate Research & Development Center, Toshiba Corporation (72) Inventor Shigeru Fujimoto Komukai Toshiba, Kawasaki City, Kanagawa Prefecture Town No. 1 Incorporated company Toshiba Research and Development Center (72) Inventor Yasushi Hattori No. 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki City, Kanagawa Prefecture Incorporated company Toshiba Research and Development Center (72) Inventor Hiroshi Katayama Kanzaki Kawasaki, Kanagawa Prefecture Komukai-shi Toshiba-cho 1-share company Toshiba Research and Development Center (72) Inventor Eiji Mame Komu-shi Toshiba-cho 1-share company Toshiba Research and Development Center (72) Inventor Hideaki Takahashi 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Within the Corporate Research and Development Center, Toshiba Corporation (72) Inventor Takuya Miyakawa, Sai-ku, Kawasaki-shi, Kanagawa Komukai Toshiba Town No. 1 Incorporated Toshiba Corporation R & D Center (72) Inventor Tsuyoshi Ogiwara Komukai Toshiba No. 1 in Kawasaki City, Kanagawa Prefecture Komukai Toshiba R & D Center

Claims (5)

[Claims] 1. A measurement pipe is attached to the outer peripheral surface of a diffuser, which is located outside the core in a reactor pressure vessel and is mounted on a baffle plate, via a plurality of support fittings, and a recirculation system is provided on the inlet side. In a jet pump for a boiling water reactor in which the discharge side pipe of the pipe is opened and the suction side pipe of the recirculation system pipe is opened to the side, the outer diameter of the measurement pipe is usually the natural frequency of the measurement pipe. A jet pump for a boiling water reactor characterized by being selected so as to avoid a resonance frequency band during operation. 2. The jet pump for a boiling water reactor according to claim 1, wherein the measurement pipe has a plurality of support fittings which are freely rotatable at a support point. 3. The jet pump for a boiling water reactor according to claim 1, wherein at least one heavy weight is provided in the measurement pipe between the plurality of support fittings. 4. The jet pump for a boiling water reactor according to claim 1, wherein a large-diameter portion having a locally large outer diameter is formed in the measurement pipe at a position where the plurality of support fittings are welded. . 5. The boiling according to claim 1, wherein the measuring pipe is formed in a double structure by welding a supporting pipe having an inner diameter of an arbitrary length larger than the outer diameter of the measuring pipe to the supporting fitting. Jet pump for water reactor.