JPS5949400A - Cavitation detecting device of jet pump - Google Patents

Abstract

PURPOSE:To directly detect the generation of cavitation by providing a pressure difference detector detecting the pressure difference between the inlet side and outlet side of a diffuser, a pressure difference variation detecting circuit, and a recirculation flow detector. CONSTITUTION:When cavitation occurs in a jet pump 109, the efficiency is deteriorated, the flow in a diffuser 110 is reduced, and the pressure difference between pressures at the inlet side and outlet side is changed. This pressure difference is detected by a pressure difference detector 123 and sent to a pressure difference variation detecting circuit 126 through a calculating circuit 125 of extraction of the square root, and a signal is sent to an interlock circuit 127 when the pressure difference is changed. When the recirculation flow is constant, the interlock circuit 127 sends a signal to an alarm unit 128, thus causing it to generate an alarm that cavitation has occurred. When the recirculation flow is changed, the pressure difference in the diffuser 110 is changed and the recirculation flow signal is also changed, thereby no signal is sent out from this interlock circuit 127 and no error operation is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a device for detecting the occurrence of cavitation in a jet pump of a boiling water nuclear reactor.

[Technical background of the invention]

A general boiling water reactor is constructed as shown in FIG. That is, 1 is a nuclear reactor pressure vessel, and a reactor core 2 is accommodated in this reactor pressure vessel 1. At the bottom of this reactor pressure vessel 1 is a control rod drive mechanism 3.
... are provided, and these control rod drive mechanisms 3...
The control rods 4... are configured to be inserted into or pulled out from below into the reactor core 2, and these control rods 4...
... is configured to control the reactivity, output, etc. of the reactor core 2. Further, the coolant (light water) in the reactor pressure vessel 1 flows into the reactor core 2 from below, boils within the reactor core 2, and flows above the reactor core 2 as a two-phase flow of steam and water. This two-phase flow of steam and water is separated into steam and water by a steam separator 5, and the separated steam passes through a steam dryer 6 to remove moisture, and then passes through a main steam pipe 7 to a turbine. 8. Further, the separated water is sent to the lower part of the reactor core 2 together with the water supply by jet pumps, flows into the reactor core 21 from below, and circulates through this path. The above jet pump! ... is composed of a diffuser 10 ... and a nozzle 11 ... provided opposite to the upper end of this diffuser 10.

Further, 12.12 is a recirculation pump, and by these recirculation pumps 12.12 a part of the cooling water in the reactor pressure vessel 1 is taken out to the outside of the reactor pressure vessel 1 and pressurized, and the driving water is Nozzle 1 of jet pump 9...
It is supplied to... The drive water ejected from the nozzles 11 flows into the diffuser 10 together with the surrounding coolant, and is ejected from the lower end of the diffuser 10.

By the way, steam exists in the core 2 of such a boiling water reactor, and when the amount of this steam, that is, the void ratio changes, the amount of coolant (light water) in the core 2 changes. Since this coolant also serves as a moderator, the core 2
The output varies depending on the amount of coolant present within. Therefore, as the void fraction increases, the amount of coolant present in the core 2 decreases, resulting in a decrease in output, and as the void fraction decreases, the amount of coolant present in the core 2 increases, resulting in an increase in output. Therefore, for example, when operating in steady state, if the output of the core 2 increases for some reason, the void ratio in the core 2 increases and the output decreases. When the amount decreases, the void ratio within the core 2 decreases, and the output increases. Therefore, during steady operation, the output and void ratio of core 2 maintain a constant balance,
Stabilize the output. In addition, by changing the flow rate of coolant flowing into the reactor core 2, that is, the core flow rate, the void ratio can be changed and the output can be controlled.If the core flow rate is increased, the void ratio becomes smaller and the output increases, and the core When the flow rate is decreased, the void ratio increases and the output decreases. In boiling water reactors, output is controlled by inserting and withdrawing control rods and changing the core flow rate. The core flow rate is controlled by the recirculation pump 12.12.
This is done by changing the flow rate, that is, the recirculation flow rate.

FIG. 2 shows the relationship between the core flow rate and the core thermal output. The curve a%b in Figure 2 is a jet pump!
... is stopped and the coolant is circulated by natural convection. This is the relationship between the core flow rate and thermal output. Also, the song ii;l
b-c is the relationship between the core flow rate and thermal output when the core flow rate is changed in a state where the control rods 4... are inserted in the 100% rated pattern. Also, in song #C-d, the control rod 4.
This is the relationship between core flow and thermal output when output is controlled by insertion and withdrawal of... Further, curves d to e indicate the limits of cavitation in the jet pump, and cavitation occurs in the jet pump in the region below curves d and e. And, the control of the nuclear reactor is the above curve a--b, curve h%c, curve ic-'-
This is done within the area surrounded by the d j curve d - e.

By the way, the jet pump mentioned above! ... is installed inside the reactor pressure vessel 1, so this jet pump
It is not possible to directly detect whether cavitation has occurred in .... Also, core flow rate and core thermal power cannot be directly detected. For this reason, conventionally, a cavitation detection device 20 as shown in FIG. 1 has been provided to prevent operation in the area below the song 9d%e. That is, No. 2 is a coolant temperature detector,
This temperature detector 21 is configured to detect the temperature of the coolant on the inlet side of the recirculation pump 12. Also, 22
is a main steam temperature detector, which is configured to detect the temperature of steam flowing in the main steam pipe 7. These coolant temperature detector 21 and main steam temperature detector 22
The signal from is configured to be sent to the arithmetic circuit 23. This arithmetic circuit 23 receives a coolant temperature signal sent from a coolant temperature detector 21 and a main steam temperature detector 22.
The main steam temperature signal sent from the jet pumps p, . The curve d - e showing the limit of cavitation is expressed as a function of core flow rate and thermal output.In addition, the relationship between coolant temperature and main steam temperature is determined according to core flow rate and core thermal output. be ridiculed.

Therefore, from the relationship between the hot coolant dust and the main steam temperature, it is possible to determine the relationship between the current reactor state and the core flow rate and thermal output, that is, whether it is in the upper region of the curve d%e or in the lower region. It can be determined whether or not it is within the range, and thereby it can be determined whether or not cavitation is occurring in the jet pump. The calculation result of the calculation circuit 23 is displayed on the meter 24, and an alarm is output from the alarm device 25 as necessary.

[Problems with background technology]

The conventional method described above indirectly detects cavitation in the dientopper 6 from the temperature of the coolant and main steam, which makes signal detection and processing complicated, resulting in a complicated structure and low accuracy. there were. Also,
Furnace equipment such as jet pumps may undergo some changes in characteristics due to long-term use, and in such cases, the relationship between the temperature of the coolant and main steam and the cavitation limit of the jet pump will change. Calibration had to be performed at regular intervals, making maintenance troublesome.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and its object is to provide a jet pump cavitation detection device that is simple in structure, highly accurate, and easy to maintain.

[Summary of the invention]

The present invention provides a differential pressure detector that detects a differential pressure between the inlet and outlet sides of a diffuser of a jet pump, a differential pressure change detection circuit that detects a change in a differential pressure signal from the differential pressure detector, and a jet pump. A recirculation flow rate detector detects the discharge flow rate of the recirculation pump that supplies drive water to the jet, and receives signals from the differential pressure change detection circuit and the recirculation flow rate detector. The jet pump is equipped with an interlock circuit that outputs a signal indicating that cavitation has occurred in the jet pump when the differential pressure between the inlet and outlet sides of the pump diffuser changes. When cavitation occurs in a jet pump, the differential pressure between the inlet and outlet sides of the diffuser changes, so by detecting a change in this differential pressure when the recirculation flow rate is constant, the jet pump The occurrence of cavitation can be directly detected. Therefore, the structure is simplified, accuracy is improved, and there is no need to perform calibration or the like, making maintenance easy.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIG. In the figure, 101 is a nuclear reactor pressure vessel, and a reactor core 102 is accommodated within this reactor pressure vessel 101. and,
A control rod drive mechanism 1 is located at the bottom of this reactor pressure vessel 101.
03... are provided, and the control rods 104... are inserted or pulled out from below into the reactor core 102 by these control rod drive 41 structures 103..., and these control rods 104... ... to control the reactivity, output, etc. of the reactor core 102. Further, the coolant (light water) in the reactor pressure vessel 101 flows into the reactor core 102 from below, boils within the reactor core 102, becomes a two-phase flow of steam and water, and flows above the reactor core 102. This two-phase flow of steam and water is separated into steam and water by a steam separator 105, and the separated steam passes through a steam dryer 106 to remove moisture, and then passes through a main steam pipe 107 to a turbine. 108. Also,
The separated water is sent to the jet pump 109 along with the water supply.
* is sent to the lower part of the reactor core 102, flows into this reactor core 102 from below, and circulates through this path. The jet pumps 709-- are composed of a diffuser 110... and a nozzle 111 provided oppositely to the upper end of the diffuser 110. Also, 112,
Reference numeral 112 denotes a recirculation pump, and C1 these recirculation pumps 112, 112 take out a part of the cooling water in the reactor pressure vessel 101 to the outside of the reactor pressure vessel 10 and increase the pressure, and the jet pump serves as driving water. 109... is supplied to the nozzle 111... and this nozzle 1
The driving water ejected from the diffuser 110 flows into the diffuser 110 along with the surrounding coolant, and is ejected from the lower end of the diffuser 110.

Such a nuclear reactor is equipped with a cavitation detection device 120 according to an embodiment of the present invention, and the configuration thereof will be described below. In the figure, reference numerals 121 and 121 are pressure take-off pipes, which communicate with the inlet side and the outlet side 1 of the diffuser 110 of the jet pump 109. These pressure outlet pipes 12 and 1'21 are connected to a differential pressure detector 123, and this differential pressure detector 123 measures the differential pressure between the static pressure on the inlet side and the static pressure on the outlet side of the diffuser 110. Configured to be detected. Excellent recirculation pump 11
A recirculation flow rate detector 124 is provided on the discharge side of the pump 2, and the recirculation flow rate detector 124 is configured to detect the discharge amount of the recirculation pump 112, that is, the recirculation flow rate. The differential pressure signal from the differential pressure detector 123 is sent to a square root calculation circuit 125 to find the square root, and is converted into a signal corresponding to the flow velocity in the diffuser 110. Next, the signal from this square root calculation circuit 125 is sent to a differential pressure change detection circuit 126. This differential pressure change detection circuit 126 is configured to differentiate the signal from the square root calculation circuit 125 and detect whether the differential pressure within the diffuser 110, that is, the flow velocity has changed. This differential pressure fecalization detection circuit 126 and the recirculation flow rate detector 124
The signal from the interlock circuit 127 is configured to be sent to the interlock circuit 127. When the signal from the recirculation flow rate detector 124 is constant, that is, when the recirculation flow rate is constant, this interlock circuit 127 connects the differential pressure change detection circuit 12
The alarm 128 sends a signal indicating that cavitation has occurred only when a signal indicating that the differential pressure has changed is sent from the alarm 128.
The alarm device 128 is configured to issue an alarm to the effect that cavitation has occurred.

In one embodiment of the present invention configured as described above, when cavitation occurs in the jet pump 109, the efficiency decreases.
The flow rate inside the diffuser 1 θ decreases, and as a result, the differential pressure between the pressure on the inlet side and the pressure on the outlet side of the diffuser 110 changes. This differential pressure is detected by a differential pressure detector 123 and sent to a differential pressure change detection circuit 126 via a square root calculation circuit 125, and if there is a change in differential pressure, a signal is sent to an interrotter circuit 127. The interlock circuit 127 sends a signal to the alarm 128 when the recirculation flow rate is low, and generates an alarm indicating that cavitation has occurred. Therefore, as shown in FIG. 4, cavitation occurs in the jet pump 109 even when the output is changed from the state of point F to the state of point G without changing the core life. In this case, the alarm will definitely be output.

Note that when the recirculation flow rate is changed, the differential pressure within the child isouser 110 changes accordingly, but in such a case, the recirculation flow rate detector 124 sends the recirculation flow rate to the interlock circuit 127. Since the circulating flow rate signal also changes, no signal is output from the ink clock circuit 127, and therefore no malfunction occurs.

Note that the present invention is not limited to the above embodiment.

For example, it is not necessary to provide a square root calculation circuit.

In addition, since jet pumps with the same characteristics are used, it is not necessary to provide such a cavitation detection device for all jet pumps, and it is not necessary to provide such a cavitation detection device for one or more jet pumps. If so, the occurrence of cavitation can be detected. Of course, such a cavitation detection device may be provided for all jet pumps.

〔Effect of the invention〕

As described above, the present invention includes a differential pressure detector that detects the differential pressure between the inlet and outlet sides of a jet pump diffuser, a differential pressure change detection circuit that detects a change in the differential pressure signal from the differential pressure detector, A recirculation flow rate detector detects the discharge flow rate of the recirculation pump that supplies drive water to the jet pump, and signals from the differential pressure change detection circuit and recirculation flow rate detector are received when the recirculation flow rate is constant. The jet pump is equipped with an interlock circuit that outputs a signal indicating that cavitation has occurred in the jet pump when the differential pressure between the inlet side and the outlet side of the diffuser of the jet pump changes.

When cavitation occurs in a jet pump, the pressure difference between the inlet side and the outlet side of the diffuser changes according to Roy's law, so when the recirculation flow rate is constant, by detecting the change in the pressure of this difference, it is possible to It is possible to directly detect the occurrence of cavitation in the pump. Therefore, the structure is simple, the accuracy is improved, and there is no need to perform calibration, etc., and maintenance is easy, which has great effects.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a conventional example. Further, FIG. 2 is a diagram showing the relationship between the core flow rate and the core thermal output. FIG. 3 is a schematic configuration diagram of an embodiment of the present invention, and FIG. 4 is a diagram showing the relationship between core flow rate and thermal output. 101...Reactor pressure vessel, 102...Reactor core, 10
9... Jet pump, 110... Diffuser,
123... Differential pressure detector, 124... Recirculation flow rate detector, 126... Differential pressure change detector, 127... Interlock circuit.

Claims (1)

[Claims] A differential pressure detector that detects the differential pressure between the inlet and outlet sides of the diffuser of the jet pump, a differential pressure change detection circuit that detects changes in the differential pressure signal from the differential pressure detector, and a drive water a recirculation flow rate detector that detects the discharge flow rate of the recirculation pump that supplies the recirculation flow rate, and a recirculation flow rate detector that receives signals from the differential pressure change detection circuit and the recirculation flow rate detector that detects the discharge flow rate of the jet pump when the recirculation flow rate is constant. 1. A jet pump cavitation detection device comprising: an interlock circuit that outputs a signal indicating that cavitation has occurred in the jet pump when the differential pressure between the inlet side and the outlet side of the jet pump changes.