JPH0820545B2 - Core flow measurement device - Google Patents

Description

The present invention relates to a core flow rate measuring device for measuring a core flow rate of a boiling water reactor equipped with an in-reactor recirculation pump,
In particular, the present invention relates to a core flow rate measuring device for measuring a differential pressure between a pump suction side and a pump discharge side and detecting a pump rotation speed to obtain a core flow rate.

(Prior Art) Generally, an improved boiling water reactor is equipped with an in-reactor recirculation pump that circulates reactor water as a coolant to the core.

6 and 7 are sectional views showing an example of the improved boiling water reactor. Reactor pressure vessel (hereinafter referred to as RPV)
A core shroud 2 is integrally provided in the core shroud 1, a core support plate 3 is horizontally fixed to the core shroud 2, and a core (not shown) is provided on the core support plate 3.
Further, a reactor pressure vessel skirt 5 is integrally provided on the side wall 4 of the RPV 1 (hereinafter referred to as the RPV wall).

A plurality of in-reactor recirculation pumps 6 are provided so as to penetrate through a reactor pressure vessel lower mirror (hereinafter referred to as RPV lower mirror) 7 forming the bottom of the RPV 1. Each in-reactor recirculation pump is provided with a core shroud 2 and an RPV. It has an impeller 11 for circulating the reactor water from the downcomer portion 8 between the walls 4 to the lower plenum 10 through the shroud support leg 9, and a motor portion 12 for rotationally driving the impeller 11. Further, a diffuser 13 is fixedly provided on the pump deck 14 on the downstream side of the impeller 11, and the reactor water fed from the impeller 11 is diffused and fed to the lower plenum 10.

When the in-reactor recirculation pump 6 is operated, the reactor water in the downcomer unit 8 is sucked by the suction force generated by the rotation of the impeller 11, is pushed out by the impeller 11, and is further diffused by the diffuser 13.
It is sent to the lower plenum 10 from between the shroud support legs 9.

The reactor water sent to the lower plenum 10 enters the core (not shown) through the gap between the reactor water support plates 3, absorbs the heat of the core and part of the reactor water becomes steam, and is guided to a steam separator (not shown). It On the other hand, the reactor water that has not been vaporized and the water separated by the steam separator return to the downcomer unit 8 and are sent again to the core by the in-reactor recirculation pump 6.

By the way, the flow rate of reactor water as a coolant fed to the core, that is, the core flow rate, has a close relationship with the reactor output, the fuel burnup, etc., and is the basis for calculating the reactor output, the fuel burnup, etc. Therefore, the core flow rate is measured by the core flow rate measuring device.

Conventionally, a pump deck differential pressure measurement system utilizing the pump characteristics of the recirculation pump 6 in the reactor has been used as a core flow rate measuring device. The principle of the pump deck differential pressure measurement system is as follows.

First, in a pre-delivery test of an actual reactor or the like, a relationship between a pump deck differential pressure and a pump flow rate is obtained in advance by using the pump rotation speed of the internal reactor recirculation pump 6 as a parameter.
The pump deck differential pressure is the difference between the measured water pressure on the upstream side and the measured water pressure on the downstream side of the pump deck 14. Further, when the pump rotation speed is 0, that is, when the forward flow or the backward flow flows into the pump in the stopped state, the relationship between the pump deck differential pressure-forward flow rate and the pump deck differential pressure-backflow rate is similarly obtained.

Then, in the actual operating state, the rotational speed of each pump and the pump deck differential pressure are measured. When all of the in-reactor recirculation pumps 6 are operated, the pump flow rate of each pump is obtained from the previously obtained relationship between the pump deck differential pressure and the pump flow rate, and the core flow rate is obtained from the sum.

When a part of the plurality of in-reactor recirculation pumps 6 is operated, the pump flow rate of each pump is calculated in the same manner as described above for the operating pumps, and the sum of the pump flow rates is first calculated. Next, the backflow rate is obtained from the relationship between the pump deck differential pressure during backflow and the backflow rate obtained in advance for the stopped pump, and the total backflow rate of the stopped pumps is obtained. Then, the core flow rate is obtained by subtracting the reverse flow rate of the pump that is stopped from the total pump flow rate of the pump that is operating. When all of the in-reactor recirculation pumps 6 are stopped, the sum of the forward flow rates of all the pumps is calculated from the previously determined relationship between the pump deck differential pressure during forward flow and the forward flow rate. Calculate the core flow rate from the sum.

(Problems to be Solved by the Invention) In a conventional pump deck differential pressure measuring system, a pump deck differential pressure measuring device 16 is provided to measure the pump deck differential pressure. The pump deck differential pressure measuring device 16 detects the pump suction side pressure from the pump suction side pressure hole 17 provided on the upstream side of the pump deck 14 through the pump suction side pressure guiding pipe 18 as shown in FIG. From the pump discharge side pressure hole 19 provided on the downstream side of the pump deck 14 to the pump discharge side pressure guide tube 20.
The pressure on the discharge side of the pump is detected via, and the pressure difference between the pressure on the discharge side of the pump and the pressure on the suction side of the pump is determined.

The pump suction side pressure hole 17 of the conventional pump deck differential pressure measuring device 16 is located between the pump deck 14 and the upper end of the diffuser 13, as shown in FIG.
Is located between the pump deck 14 and the lower end of the diffuser 13. Further, as shown in FIG. 7 in plan view, the pump suction side pressure hole 17 is located between the diffuser 13 and the core shroud 2, and the pump discharge side pressure hole 19 is the core shroud 2.
And shroud support leg 9 in the area surrounded by RPV wall 4
Located above.

However, as shown in FIGS. 8 and 9, a secondary flow B other than the main flow A that is sucked into the pump impeller 11 is generated in the upper part of the pump deck 14, and due to the change in the operating state of each pump, this secondary flow B Changes subtly.

Also, as shown in Figs. 10 and 11, the pump deck
A secondary flow B other than the main flow A discharged to the opening of the shroud support leg 9 is generated in the lower portion of the shroud support leg 9, and the secondary flow B is subtly changed due to a change in the operating state of each pump.

Subtle changes in pressure due to such changes in the secondary flow B are caused by the pump suction side pressure hole 17 and the pump discharge side pressure hole 19.
Is detected, and as a result, the pump deck differential pressure becomes unstable, and an accurate pump deck differential pressure cannot be measured.

Generally, in an improved boiling water reactor having a plurality of in-reactor recirculation pumps 6, various operation modes can be considered between the pumps. Therefore, when the pump deck differential pressure cannot be accurately measured due to the secondary flow B that varies in each operation mode, the core flow rate cannot be accurately measured, and the operating margin of the plant cannot be accurately grasped. Not only that, it will result in a deterioration in fuel economy.

The present invention has been made in consideration of the above circumstances, and by obtaining an accurate pump deck differential pressure without being affected by the secondary flow in each operation mode of a plurality of in-reactor recirculation pumps, the core An object of the present invention is to provide a core flow rate measuring device capable of improving flow rate measurement accuracy.

[Structure of Invention]

(Means for Solving the Problem) The present invention measures the differential pressure between the pressure on the pump suction side and the pressure on the pump discharge side in a nuclear reactor equipped with an internal reactor recirculation pump, and In the core flow rate measurement device that detects the core flow rate by detecting it, the pressure detection end on the pump suction side is installed in the downcomer part at about 1.5 m or more upstream from the pump deck, while the pressure detection end on the pump discharge side is located inside the core shroud. It is provided in the plenum.

(Operation) Even if the recirculation pump in the nuclear reactor is operated and a secondary flow occurs near the pump, the fluctuation of the suction side pressure due to the secondary flow is a pump provided at least 1.5 m upstream from the pump deck. It is not detected at the pressure detection end on the suction side.

Also, the fluctuation of the pressure on the pump discharge side due to the secondary flow is
Since it does not reach the lower plenum inside the core shroud, the pressure detection end on the pump discharge side is not affected by the pressure fluctuation due to the secondary flow.

Therefore, even in various operation modes of a plurality of in-reactor recirculation pumps, an accurate pump deck differential pressure can be obtained without being affected by the secondary flow, and the accuracy of core flow rate measurement can be improved. .

(Example) An example of the core flow rate measuring device according to the present invention will be described with reference to the drawings.

1 and 2, the reactor pressure vessel (hereinafter
A core shroud 2 is integrally provided in an RPV (1), a core support plate 3 is horizontally fixed to the core shroud 2, and a core (not shown) is provided on the core support plate 3. In addition, the side wall 4 of RPV1 (hereinafter referred to as RPV wall)
A reactor pressure vessel skirt 5 is provided integrally therewith.

Further, a plurality of reactor pressure vessel lower mirrors (hereinafter referred to as RPV lower mirrors) forming the bottom of the RPV 1 are provided with a plurality of reactor internal recirculation pumps 6, and each reactor internal recirculation pump 6 circulates reactor water. It has an impeller 11 for making it rotate, and a motor unit 12 for driving the impeller 11 to rotate.

A diffuser 13 is fixedly provided on the pump deck 14 on the downstream side of the impeller 11, and the diffuser 13 diffuses the reactor water sent from the impeller 11 and sends it to the lower plenum 10 from between the shroud support legs 9. It has become.

The core flow rate measuring device according to the present invention is provided with a pump deck differential pressure measuring device 16, a pump suction side pressure hole 17 as a pressure detection end for detecting the pressure on the upstream side of the pump deck 14, and the pump deck 14. A pump discharge side pressure hole 19 as a pressure detecting end for detecting the pressure on the downstream side is provided.

The pump deck differential pressure measuring device 16 receives the pump suction side pressure detected by the pump suction side pressure hole 17 via the pump suction side pressure guiding pipe 18, and the pump discharge side detected by the pump discharge side pressure hole 19. The pressure is received via the pump discharge side pressure guiding pipe 20, and the differential pressure between the pump discharge side pressure and the pump suction side pressure is obtained as the pump deck differential pressure.

By the way, when the recirculation pump 6 in the reactor is operated, a secondary flow B different from the main flow A of the reactor water is generated as shown in FIG. As shown in FIG. 4, the pressure fluctuation does not occur above 1.5 m from the upper surface of the pump deck 14.

That is, the horizontal axis in FIG. 4 shows the pressure fluctuation as a relative value (dimensional pressure fluctuation) when the maximum pressure fluctuation is 1, and the vertical axis shows the distance from the upper surface of the pump deck 14 to the upstream side of the pump. Is shown.

As described above, since there is little fluctuation in pressure due to the secondary flow B above about 1.5 m from the upper surface of the pump deck 14,
In the present embodiment, the pump suction side pressure hole 17 is provided in the outer wall of the core shroud 2 in the downcomer portion above the upper surface of the pump deck 14 by about 1.5 m. The suction side pressure hole 17 may be provided in the RPV wall 4 of the downcomer portion 8.

Further, the reactor water sent from the impeller 11 to the diffuser 13 is diffused by the diffuser 13 and then sent to the lower plenum 10 through between the shroud support legs 9, so that the pressure in the lower plenum 10 is stable. Therefore, the influence of the secondary flow B is not exerted. Therefore, the pump discharge side pressure hole 19 of this embodiment is provided in the inner wall of the core shroud 2 above the shroud support leg 9 in the lower plenum 10.

On the other hand, regarding the planar positional relationship, as shown in FIG. 2, the pump suction side pressure hole 17 and the pump discharge side pressure hole 19 are provided.
Both of them are located in the vicinity of the recirculation pump 6 in each reactor. In this embodiment, the downcomer section 8 between the in-reactor recirculation pumps 6 is divided into four equal parts by a line drawn from the center 22 of the RPV 1, and the areas close to the in-reactor recirculation pumps 6 among these areas. The pressure holes 17 and 19 are provided in a range that does not exceed. This is because the area near the middle of each reactor recirculation pump 6 is
This is because, depending on the operating states of both in-reactor recirculation pumps 6, pressure fluctuations due to the adjacent in-reactor recirculation pumps 6 may be affected.

In the above embodiment, since the pump discharge side pressure hole 19 and the pump suction side pressure hole 17 are provided at positions that are not easily affected by the pressure fluctuations due to the secondary flow B, various operations of the multiple recirculation pumps 6 in the reactor are performed. Even in the mode, the accurate pump deck differential pressure can be stably measured without being affected by the secondary flow B, and the measurement accuracy of the core flow rate can be improved.

Improving the accuracy of core flow rate measurement will significantly improve the operability of the plant because the reactor output can be calculated accurately.
It also contributes to the improvement of fuel economy.

FIG. 5 is a diagram showing the relationship between the core flow rate measurement accuracy and the fuel cycle cost. The horizontal axis shows the measurement error in% when the rated flow rate is 100%, and the vertical axis shows the fuel burnup.
The calculation error when the value is 100% is expressed in% as the increase / decrease in fuel cycle cost.

That is, if the core flow rate measurement accuracy is poor, the burnup of the fuel cannot be calculated accurately, so the fuel must be exchanged before the fuel is sufficiently burned, which increases the fuel cycle cost. On the other hand, if the core flow rate measurement accuracy improves, the burnup of the fuel can be accurately calculated, and the fuel can be replaced at an appropriate time. Therefore, the fuel cycle cost can be reduced and the economic efficiency can be improved. it can.

〔The invention's effect〕

In the core flow rate measuring device according to the present invention, the pump suction side pressure detection end is provided in the downcomer portion on the upstream side of about 1.5 m or more from the pump deck, while the pump discharge side pressure detection end is provided in the lower plenum portion inside the core shroud. Therefore, the core flow rate measurement accuracy can be improved by obtaining the accurate pump deck differential pressure without being affected by the secondary flow in each operation mode of the plurality of in-reactor recirculation pumps. Therefore, the operability of the plant is improved and the economical efficiency of the fuel is improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing a state in which an embodiment of the core flow rate measuring device according to the present invention is incorporated in a general improved boiling water reactor, and FIG. 2 is a view taken along the line II-II in FIG. FIGS. 3 and 4 are enlarged views of the pump deck portion in the above embodiment, and FIG.
The figure shows the relationship between the pressure fluctuation and the distance from the upper surface of the pump deck. Fig. 5 shows the relationship between the core flow rate measurement accuracy and the increase / decrease in fuel cycle cost. Fig. 6 shows the conventional core flow rate measuring device. Sectional view showing a state of being incorporated in a general improved boiling water reactor, Fig. 7 is a view taken along the line VII-VII in Fig. 6, and Fig. 8 is a secondary flow occurring on the upstream side of the pump deck. Sectional view near the pump deck, Fig. 9 is in Fig. 8
IX-IX line arrow view, Figure 10 is a sectional view near the pump deck showing the secondary flow occurring on the downstream side of the pump deck, and Figure 11 is the
FIG. 11 is a view taken along the line XI-XI in FIG. 1 ... Reactor pressure vessel, 2 ... Core shroud, 4 ...
Reactor pressure vessel wall, 6 ... Recirculation pump in reactor, 8 ...
... Downcomer part, 9 ... Shroud support leg, 10 ...
… Lower plenum, 11 …… impeller, 13 …… diffuser, 14 …… pump deck, 16 …… pump deck differential pressure measuring instrument, 17 …… pump suction side pressure hole, 19 …… pump discharge side pressure hole.

Claims (2)

[Claims] 1. A core flow rate for determining a core flow rate by measuring a differential pressure between a pressure on a pump suction side and a pressure on a pump discharge side in a nuclear reactor equipped with an in-reactor recirculation pump In the measuring device, the pressure detection end on the pump suction side is provided in the downcomer part on the upstream side about 1.5 m or more from the pump deck, while the pressure detection end on the pump discharge side is provided in the lower plenum part inside the core shroud. Core flow rate measuring device. 2. The pressure detection end on the pump suction side is provided on the outer wall of the core shroud above each in-reactor recirculation pump or the inner wall of the reactor pressure vessel, and the pressure detection end on the pump discharge side comprises: The core flow rate measuring device according to claim 1, which is provided on the inner wall of the core shroud above the shroud support leg for each in-reactor recirculation pump.