JP2001153990A - System for measuring flow rate in reactor core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the flow rate in a reactor core with high accuracy without being affected by the change in the performance of a recirculation pump of a type built into a reactor. SOLUTION: The system includes a first means 37 for measuring the static pressure in a section where reactor water stagnates in the lower part of a deck of the recirculation pump 14 of a type built into a reactor, a second means 38 for measuring the static pressure in a high-speed flow section in a discharge section of the recirculation pump 14 and a means 41 that measures the pressure difference between the first and second static pressure measuring means 37 and 38, respectively. The system calculates the discharge flow rate of the recirculation pump 14 of the basis of the difference between the measured statistic pressures.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiling water reactor in which a reactor coolant is supplied to a reactor core by a reactor built-in recirculation pump (hereinafter, referred to as an internal pump). The present invention relates to a core flow rate measurement system for measuring a supply amount of material to a core without being affected by a change in performance of an internal pump.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing a conventional boiling water reactor having an internal pump.

[0003] As shown in FIG.
Is a core support plate 2 at the lower end and an upper grid plate 3 at the upper end.
Core support plate 2 and upper grid plate 3
Are fixed to a cylindrical core shroud 4. The core shroud 4 is welded and fixed to the lower mirror portion 8 of the reactor pressure vessel 7 via a shroud support leg 5 and a cylindrical shroud support cylinder 6.

[0004] A shroud head 11 having a stand pipe 9 and a steam separator 10 is provided above the core shroud 4, and a steam dryer 12 is further provided above the shroud head 11. On the other hand, an annular portion (downcomer) formed of the core shroud 4, the shroud support cylinder 6, and the reactor pressure vessel 7 is partitioned by a shroud support plate 13 below the reactor pressure vessel 7, and the shroud support plate 13 is It is fixed to the support cylinder 6 and the reactor pressure vessel 7 by welding.

Further, a plurality of internal pumps 14 are uniformly arranged on the annular portion. The internal pump 14 has a diffuser 15 as shown in FIG. 8, and the diffuser 15 is a shroud support plate 13.
And is installed on a RIP nozzle 16 provided in the lower mirror section 8 and mechanically fastened.

[0006] The internal pump 14 has an impeller shaft 17, and the impeller shaft 17 is
A motor 19 is fastened to a motor casing 18 which penetrates the P nozzle 16 and is welded and fixed to the RIP nozzle 16.

In such a structure, the reactor water in the annular portion (downcomer) above the shroud support plate 13 shown in FIG. After passing between the support legs 5, the air flows upward and flows into the core. At this time, the reactor water in the core shroud 4 is blocked by the core support plate 2, passes through the orifice of the fuel support fitting provided below the fuel 1, and is efficiently supplied to the fuel assembly.

[0008] The steam generated in the fuel assembly is separated into moisture by the steam-water separator 10 and the steam dryer 12 and supplied to a turbine (not shown). Then, the steam is condensed by a condenser, and is condensed by a condenser. The water is returned from the water supply sparger 20 installed at the upper part of the reactor pressure vessel 7 into the reactor. on the other hand,
The water separated by the steam separator 10 and the steam dryer 12 is pressurized by the internal pump 14 in the above-described path together with the water supply, and is again supplied to the core.

In such a boiling water reactor, the flow rate supplied to the core by the internal pump 14, that is, the core flow rate, is a very important management value in the burnup control of the fuel 1 and the power control of the reactor. There is a demand for high-precision measurement during plant operation.

A method of measuring a core flow rate in a nuclear reactor employing the internal pump 14 will be described below.

[0011] As shown in FIG.
On the upstream side of the core shroud 4, a static pressure hole 2
The suction side pressure of the internal pump 14 is measured by a pressure gauge (not shown) through the static pressure hole 21. A static pressure hole 22 is also provided inside the shroud support cylinder 6, and the discharge pressure of the internal pump 14 is measured by a pressure gauge (not shown) through the static pressure hole 22. That is, the two static pressure holes 21 and 22
Is connected to an external pipe via a pressure vessel penetrating nozzle (not shown), and the pressure gauge is attached to the external pipe to measure the differential pressure between them. Thereby, the differential pressure before and after the pump, that is, the differential pressure of the pump section is measured.

Here, the internal pump 14 simulates the shape of a pump installation portion before being installed in an actual reactor,
A pump performance confirmation test is performed using a test vessel capable of measuring the pump section differential pressure and the pump flow rate, and a characteristic curve of the pump flow rate and the pump section differential pressure (hereinafter, Q-Δh Characteristics). These characteristics are input to a computer for reactor operation management, and the core flow rate is calculated from the pump section differential pressure measured in actual operation.

On the other hand, a support plate differential pressure instrumentation line 24 for measuring the vertical pressure difference is also provided at the position of the core support plate 2, and the support plate differential pressure obtained by the support plate differential pressure In a system test at the time of construction, it is calibrated based on the core flow rate obtained from the pump section differential pressure, and is used as a means for calculating the core flow rate in plant output operation.

[0014]

The above-described conventional core flow rate measuring method is a method of obtaining a core flow rate based on a pressure difference before and after the internal pump 14 is sandwiched.
For this reason, the properties of the pump water surface change over time due to the adhesion of the cladding in the furnace, erosion, etc., and the above Q-Δh
When the characteristics changed, there was a possibility that a difference might occur between the calculated flow rate from the differential pressure and the actual core flow rate. Also, regarding the support plate differential pressure, there is a possibility that an error may occur in the flow rate measurement due to the adhesion of the clad to the orifice of the fuel support fitting within the differential pressure measurement range.

The present invention has been made in view of such a conventional situation, and has a core flow rate measuring system capable of measuring a core flow rate with high accuracy without being affected by a performance change of a recirculation pump built in a reactor. The purpose is to provide.

[0016]

In order to achieve the above object, according to the first aspect of the present invention, a coolant is supplied to a core of a boiling water reactor by a recirculation pump built in the reactor, and the supply amount is reduced. In a core flow rate measuring system for measuring, first static pressure measuring means for measuring a static pressure of a reactor water stagnation section below the reactor built-in recirculation pump deck, and a discharge section of the reactor built-in recirculation pump To measure the static pressure in the high flow velocity section
Static pressure measuring means, and a differential pressure measuring means for measuring the differential pressure between the first and second static pressure measuring means, based on the static pressure difference, the discharge flow rate of the built-in recirculation pump It is characterized in that it is calculated.

According to the first aspect of the present invention, the static pressure in the reactor water stagnation section below the reactor built-in recirculation pump deck is measured by the first static pressure measuring means, while the reactor built-in recirculation pump is measured. The static pressure in the high flow velocity portion of the discharge section is measured by the second static pressure measuring means, the difference between these static pressures is calculated by the differential pressure measuring means, and the discharge flow rate is calculated based on the static pressure difference. Since the pump flow rate is directly measured by measuring the dynamic pressure at the outlet of the recirculation pump built in the furnace, the core flow rate can be measured with high accuracy without being affected by changes in the characteristics of the pump body.

According to a second aspect of the present invention, in the core flow rate measuring system according to the first aspect, there is provided a flow rate conversion means for calculating a relational expression between the static pressure difference and the discharge flow rate of the built-in recirculation pump. The core flow rate is calculated from the relational expression and the differential pressure measured during the operation of the reactor.

According to the second aspect of the present invention, a relational expression between the static pressure difference and the discharge flow rate of the built-in recirculation pump is calculated by the flow rate conversion means, and the relational expression and the differential pressure measured during operation of the reactor are calculated. By calculating the core flow rate from the above, the measurement accuracy of the core flow rate can be further improved.

According to a third aspect of the present invention, in the core flow rate measuring system according to the first or second aspect, a pump section differential pressure which is a differential pressure between a suction side pressure and a discharge side pressure of the reactor built-in recirculation pump. When there is a difference between the flow rates obtained by the measurement of the static pressure difference and the measurement of the static pressure difference, the relational expression between the pump section differential pressure and the flow rate is corrected.

According to the third aspect of the invention, when there is a difference between the flow rates obtained by the measurement of the pump section differential pressure and the measurement of the static pressure difference, the relational expression between the pump section differential pressure and the flow rate is corrected. Accordingly, the core flow rate is corrected in accordance with the secular change in the characteristics of the pump, so that stable measurement of the core flow rate becomes possible. Thereby, the number of static pressure measurement points can be reduced.

According to a fourth aspect of the present invention, in the core flow rate measuring system according to the first aspect, the second diffuser outlet is provided at a discharge part of the recirculation pump built in the reactor.
Wherein a static pressure measuring block of the static pressure measuring means is provided.

According to the fourth aspect of the present invention, since the static pressure measuring block of the second static pressure measuring means is installed at the diffuser outlet, the static pressure is measured from the stable high flow velocity position at the diffuser outlet. Therefore, measurement accuracy can be improved.

According to a fifth aspect of the present invention, in the core flow rate measuring system according to the fourth aspect, a notch that opens downward is formed in an engagement portion of the diffuser with the block for measuring static pressure. And

According to the fifth aspect of the present invention, the notch that opens downward is formed in the engaging portion of the diffuser with the block for measuring static pressure, which hinders attachment and detachment of the diffuser. Disappears.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a core flow rate measuring system according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a core flow rate measuring system according to the present invention, FIG. 2 is an enlarged sectional view showing a static pressure measuring block of a reactor water stagnation section in FIG. 1, and FIG. FIG. 4 is an enlarged cross-sectional view showing a static pressure measurement block in a high flow velocity portion.
5 is a cross-sectional view showing the in-core instrumentation piping and instrumentation nozzle of one embodiment of the core flow rate measuring system according to the present invention, and FIG. 6 is a sectional view of the core flow rate measuring system according to the present invention. FIG. 4 is an explanatory diagram illustrating a method of correcting a Q-Δh characteristic according to an embodiment. The configurations of the boiling water reactor and the internal pump are the same as those shown in FIGS.

Referring to FIG. 1, in this embodiment, a static pressure measuring block 30 is provided at a reactor water stagnant portion below a shroud support plate 13 which is a lower portion of a deck of an internal pump 14.
On the other hand, a static pressure measurement block 31 is provided at a high flow rate portion at the outlet of the diffuser 15 which is a discharge portion of the internal pump 14. These two blocks 30, 3
1 is connected to an in-furnace instrumentation pipe 32, and the in-furnace instrumentation pipe 32 is connected to an external pipe (not shown) via an instrumentation nozzle 33. In addition, the static pressure measurement block 30 installed in the reactor water stagnation section is disposed between the installation intervals of the internal pump 14 that is not easily affected by the flow.

The inside of the static pressure measurement block 30 communicates with a static pressure hole 34 penetrating the shroud support cylinder 6 as shown in FIG. 2, and the static pressure measurement is performed at the static pressure hole 34 on the core side of the shroud support cylinder 6. Block 30 is fixed by welding, and an in-furnace instrumentation pipe 32 is fixed to the lower portion of the static pressure measurement block 30 by welding.

On the other hand, the static pressure measurement block 31 has a core side block 31a and a diffuser side block 31b as shown in FIG. 3, and the core side block 31a and the diffuser side block 31b are respectively connected to the shroud support cylinder 6. Core side and diffuser 1
5 is fixed by welding and communicates with a static pressure hole 35 penetrating the shroud support cylinder 6.

In this case, the diffuser side block 31b
Of the diffuser 15 is arranged flush with the inner surface of the outer cylinder 15a of the diffuser 15 so that a step is not formed, and the outer end of the diffuser 15 is removed so that the diffuser 15 can be removed above the reactor and reattached. A cut-out portion 36 that opens downward at an engagement portion with the diffuser-side block 31b is formed in the tube 15a.

The static pressure measuring blocks 30 and 31 are:
As shown in FIG. 4, each is drawn out of the reactor pressure vessel 7 through an in-core instrumentation pipe 32 and an instrumentation nozzle 33 having a double pipe structure, and connected to an external pipe (not shown). .

Incidentally, the static pressure in the reactor water stagnant portion obtained through the static pressure measuring block 30 is the first static pressure as shown in FIG.
The static pressure at the high flow rate portion of the discharge section of the internal pump 14 obtained through the static pressure measuring block 31 is measured by the pressure gauge 37 as the static pressure measuring means. It is measured by the pressure gauge 38.

The pressure values measured by the pressure gauges 37 and 38 are converted into digital signals by the pressure transducers 39 and 40, respectively, and then converted to a differential pressure calculator 4 as a differential pressure measuring means.
1 and the static pressure difference between them is calculated.

The signal of the static pressure difference obtained by the differential pressure calculator 41 is sent to a flow rate calculator 42 as a flow rate converter, and the flow rate calculator 42 obtains the signal of the static pressure difference. A relational expression between the static pressure difference and the discharge flow rate of the internal pump 14 is calculated, and this relational expression and the reactor (actual plant) are calculated.
The core flow rate is calculated from the differential pressure measured during operation.

Next, the operation of the present embodiment will be described.

First, a static pressure measurement block 30 installed in a reactor water stagnant section below the shroud support plate 13,
In the static pressure measurement block 31 installed at the high flow rate portion at the outlet of the diffuser 15, the static pressure is measured by pressure gauges 37 and 38 through an in-furnace instrumentation pipe 32, an instrumentation nozzle 33, and an external pipe (not shown), respectively. .

The measured pressure values are converted into digital signals by the pressure converters 39 and 40, respectively, and the static pressure difference between them is calculated by the differential pressure calculator 41.

In this case, the dynamic pressure (p) calculated by the following equation is almost 0 because the reactor water stagnation section is not affected by the flow velocity, but the dynamic pressure (p) in the high flow velocity section depends on the flow velocity (V). Dynamic pressure occurs. Here, ρ is the density of the cooling water.

[0040]

## EQU1 ## p = 1/2 × ρV ² (1)

For this reason, the static pressure measurement blocks 30, 31
In the static pressure difference detected at the position (1), a differential pressure corresponding to the dynamic pressure of Expression (1) occurs. Here, the flow velocity (V) in the rated operation of the internal pump 14 is about 15 m / sec. In this case, a differential pressure of about 8 m head occurs, and there is no problem in detecting the differential pressure.

Then, the static pressure difference obtained as described above and the Q obtained by a pump performance confirmation test performed by simulating the shape of a pump installation portion before being installed in an actual reactor are described.
The core flow rate is calculated from the -Δh characteristic.

In the present embodiment, the differential pressure calculator 4
The signal of the static pressure difference obtained in step 1 is sent to the flow rate conversion calculator 42, where the differential pressure calculator 4
The relational expression between the static pressure difference obtained in step 1 and the discharge flow rate of the internal pump 14 is calculated, and the core flow rate is calculated from the relational expression and the differential pressure measured during operation of the reactor (actual plant).

In the core flow rate measuring system of the present embodiment, in order to accurately measure the core flow rate, the static pressure measurement blocks 30 and 31 and the differential pressure calculator 41 which measure the static pressure are used. It is necessary to strictly determine the relationship between the pressure difference and the pump discharge flow rate. For this purpose, a high-precision flow meter is provided downstream of the pump, and the internal pump 1
4 is incorporated to determine the relationship between the pump flow rate and the static pressure difference, and used for flow rate measurement in actual plant operation.

As described above, according to this embodiment, the static pressure measurement block 30 installed in the reactor water stagnant portion below the shroud support plate 13 and the static pressure measurement block installed in the high flow rate portion at the outlet of the diffuser 15 The static pressure is measured by the pressure gauges 37 and 38 through the block 31, the static pressure difference is calculated by the differential pressure calculator 41, and the discharge flow rate of the internal pump 14 is calculated based on the static pressure difference. Since the pump flow rate is directly measured by measuring the dynamic pressure at the outlet of the internal pump 14, the core flow rate can be measured with high accuracy without being affected by changes in the characteristics of the pump body.

The static pressure difference and the internal pump 1
4 is calculated by the flow rate conversion calculator 42, and the core flow rate is calculated from the relational expression and the differential pressure measured during the operation of the reactor, thereby further improving the measurement accuracy of the core flow rate. be able to.

Further, a static pressure measuring block 3 is provided at an outlet of a diffuser 15 provided at a discharge portion of the internal pump 14.
By installing 1, the static pressure is measured from the stable high flow velocity position at the outlet of the diffuser 15, so that the measurement accuracy can be improved.

The outer cylinder 15a of the diffuser 15
In addition, since the cutout portion 36 that opens downward is formed in the engagement portion with the diffuser-side block 31b, the installation and removal of the diffuser 15 is not hindered.

There is also a means for measuring the core flow rate by using both the measurement of the pump section differential pressure described in the conventional example and the measurement of the static pressure difference in the above embodiment. This will be described below as another embodiment.

In the case of this embodiment, the pump discharge flow rate is calculated from the measurement result of the pump section differential pressure, which is the differential pressure between the suction side pressure and the discharge side pressure of the internal pump 14, and the measurement result of the static pressure difference. If a difference occurs between the calculated flow rate by the former and the calculated flow rate by the latter during plant operation, it can be determined that the difference is due to a change in performance over time of the pump. Q- created by measurement
The characteristic curve of the Δh characteristic is corrected as shown in FIG. 5, that is, the relational expression between the pump section differential pressure and the flow rate is corrected, and can be applied to the next measurement of the core flow rate.

Generally, the characteristic change of the plurality of internal pumps 14 does not occur selectively in a specific pump.
Measurement of the static pressure difference by 0, 31 can be limited to the internal pump 14 at the representative position.

As described above, according to the present embodiment, the above-described static pressure measurement blocks 30 and 31 are installed only in the representative internal pump 14, and the pump discharge flow rate is obtained. When a difference from the obtained flow rate occurs, the core flow rate can be measured stably by correcting the Q-Δh characteristic so that the latter flow rate matches the former flow rate. Thereby, the number of static pressure measurement points can be reduced.

[0053]

As described above, claims 1 and 2
According to the described invention, since the pump flow rate is directly measured by measuring the dynamic pressure at the outlet of the pump, the core flow rate can be measured with high accuracy without being affected by the change in the characteristics of the pump main body.

According to the third aspect of the present invention, since the conventional Q-.DELTA.h characteristic due to the differential pressure of the pump section is corrected in accordance with the characteristic change of the pump over time, a stable measurement of the core flow rate becomes possible. Become. As a result, the number of pumps on which the static pressure measuring means is installed can be reduced to specific pumps.

According to the fourth aspect of the present invention, since the static pressure measuring block of the second static pressure measuring means is installed at the diffuser outlet, the static pressure can be reduced from the stable high flow velocity position at the diffuser outlet. Since measurement is performed, measurement accuracy can be improved.

According to the fifth aspect of the present invention, since the notch which opens downward is formed in the engaging portion of the diffuser with the block for measuring static pressure, there is no problem in attaching and detaching the diffuser. Will not come.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a core flow rate measurement system according to the present invention.

FIG. 2 is an enlarged sectional view showing a static pressure measurement block of a reactor water stagnation section in FIG. 1;

FIG. 3 is an enlarged cross-sectional view showing a static pressure measurement block of a high flow velocity section in FIG.

FIG. 4 is a sectional view taken along line AA of FIG. 3;

FIG. 5 is a sectional view showing an in-core instrumentation pipe and an instrumentation nozzle of one embodiment of the core flow rate measuring system according to the present invention.

FIG. 6 is an explanatory diagram showing a method of correcting a Q-Δh characteristic showing one embodiment of a core flow rate measuring system according to the present invention.

FIG. 7 is a sectional view showing the internal structure of a conventional general boiling water reactor.

FIG. 8 is a cross-sectional view showing an internal pump in the internal structure of a conventional general boiling water reactor.

[Explanation of symbols]

7 Reactor pressure vessel 13 Shroud support plate (reactor built-in recirculation pump deck) 14 Internal pump (reactor built-in recirculation pump) 15 Diffuser 15a Outer cylinder 30 Static pressure measurement block 31 Static pressure measurement block 31a Core side block 31b Diffuser side block 32 In-core instrumentation pipe 33 Instrumentation nozzle 34 Static pressure hole 35 Static pressure hole 36 Notch 37 Pressure gauge (first static pressure measurement means) 38 Pressure gauge (second static pressure measurement) Means) 39 Pressure transducer 40 Pressure transducer 41 Differential pressure calculator (Differential pressure measurement means) 42 Flow rate conversion calculator (Flow rate conversion means)

Claims (5)

[Claims] In a core flow rate measuring system for supplying a coolant to a core of a boiling water reactor by a built-in recirculation pump and measuring the supply amount, the reactor built-in recirculation pump deck is provided. First static pressure measuring means for measuring the static pressure of the lower reactor water stagnant portion, second static pressure measuring means for measuring the static pressure of the high flow rate portion of the discharge section of the built-in recirculation pump, A differential pressure measuring means for measuring a differential pressure between the first and second static pressure measuring means, and calculating a discharge flow rate of the reactor built-in type recirculation pump based on the static pressure difference. Core flow measurement system. 2. The reactor core flow rate measuring system according to claim 1, further comprising a flow rate conversion means for calculating a relational expression between the static pressure difference and a discharge flow rate of the recirculation pump inside the reactor. A core flow rate measurement system, wherein a core flow rate is calculated from a differential pressure measured during operation. 3. The core flow rate measuring system according to claim 1, wherein a difference between a suction side pressure and a discharge side pressure of the built-in reactor type recirculation pump is measured, and the static pressure difference is measured. A flow rate measurement system for a core, wherein a relational expression between the pump section differential pressure and the flow rate is corrected when there is a difference between the flow rates obtained by the measurement of the core flow rate. 4. The reactor core flow rate measuring system according to claim 1, wherein a static pressure measuring block of said second static pressure measuring means is installed at a diffuser outlet provided at a discharge part of said reactor built-in recirculation pump. A core flow measurement system, characterized in that: 5. The core flow rate measuring system according to claim 4, wherein a notch that opens downward is formed in an engaging portion of the diffuser with the static pressure measuring block. .