JPH0157320B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a nuclear reactor, and in particular to a nuclear reactor having a pump (hereinafter referred to as an internal pump) having an impeller disposed inside a reactor pressure vessel as a cooling water circulation pump. It is related to furnaces.

[Conventional technology]

As a boiling water nuclear reactor equipped with an internal pump, the one described in Japanese Patent Publication No. 47239/1983 is known. In such a boiling water reactor, the reactor output can be adjusted by changing the rotational speed of the internal pump and changing the flow rate of cooling water supplied to the reactor core. In particular, load following motion of nuclear reactors has been studied recently. In this case, the reactor power varies between 100% and 50%. Such changes in output are performed by changing the amount of cooling water flowing through the core (hereinafter referred to as core flow rate). The core flow rate changes between 100% flow rate and 30% flow rate during load following motion. When adjusting reactor power by changing the core flow rate, it is necessary to accurately detect the core flow rate.

[Problem to be solved by the invention]

In a conventional boiling water reactor equipped with an internal pump, the rotation speed of the internal pump and the differential pressure at the impeller entrance and exit are measured, and water is supplied to the core based on these measured values and the Q-H curve. The cooling water flow rate, that is, the core flow rate is being determined.
However, with this method, when the core flow rate is as low as 25 to 50% or when the natural circulation flow rate is less than 25%, the impeller rotation speed decreases, resulting in poor measurement accuracy. Therefore, it becomes difficult to control the reactor power by adjusting the core flow rate in areas where the core flow rate is low.

In addition, the Karman vortex flowmeter is conventionally known as a method for measuring flow rates at low flow rates. Since the flowmeter is installed inside the reactor vessel as a flowmeter unit, the following problems arise.

(a) Increase in flow resistance It is necessary to provide a member or the like in the flow path to generate a Karman vortex, which increases flow resistance. In this regard, since the purpose is to measure flow rate at low flow rates, it is desirable to avoid an increase in flow resistance.

(b) Increased man-hours for maintenance and inspection When installed inside the reactor core, there is flow distribution between fuel channels, so trying to improve measurement accuracy would be impractical because the number of measurement points would be enormous. From the viewpoint of the number of measurement points, it is best to install it on the internal pump, but in this case, the Karman vortex flowmeter interferes with maintenance and inspection of the internal pump, which increases the number of man-hours required.

(c) Decreased safety If the flow meter should become detached, a safety problem may occur.

The purpose of the present invention is to facilitate reactor power control by applying eddy flow measurement that can improve the accuracy of flow measurement in the low core flow rate region, and to suppress an increase in flow resistance related to eddy flow measurement. The object of the present invention is to provide a nuclear reactor with a structure that is easy to maintain and inspect and has excellent safety.

[Means to solve the problem]

In order to achieve the above object, a first invention of the present invention includes a nuclear reactor vessel, a reactor core disposed within the reactor vessel, and a passageway for guiding a coolant to the core located within the reactor vessel. , a nuclear reactor comprising an impeller disposed in the coolant introduction passage, a means for rotating the impeller, and a coolant guide vane disposed in the coolant introduction passage, on the downstream side of the guide vane. Means is provided for detecting the pressure of the vortex generation part of the coolant generated in the flow rate of the coolant, and measuring the flow rate of the coolant based on the fluctuation frequency of the detected pressure, and the pressure is
The present invention is characterized in that a passage is bored inside the guide vane, and one end of the passage is detected by a pressure detection tube having a detection end formed at a downstream end face of the guide vane.

In addition to the configuration of the first invention, the second invention of the present invention further includes means for measuring the flow rate of the coolant based on the differential pressure between the upstream side and the downstream side of the impeller and the rotation speed of the impeller. When the flow rate is large, the flow rate measurement means using the differential pressure measures the flow rate, and when the flow rate is low, the flow rate measurement means is switched to the vortex flow measurement means for measurement.

[Effect]

With this configuration, the first aspect of the present invention
Alternatively, according to the second invention, a Karman vortex is generated on the downstream side of the guide vane due to the flow of the coolant,
Karman vortices occur even in low flow areas,
A vortex train is formed that periodically fluctuates in proportion to the flow rate of the coolant. This vortex train changes the coolant pressure downstream of the guide vane. This pressure change is detected by a pressure detection tube, and the flow rate of the coolant is measured based on the fluctuation frequency of the detected pressure.

In particular, the guide vanes themselves are used as vortex generators,
In addition, since the detection end of the pressure detection tube is bored inside the guide vane, it is necessary to install special members such as vortex generators in the coolant flow path that can increase flow resistance. It is possible to realize a vortex flowmeter without any need. Furthermore, since the detection end is integrated with the guide vane, it does not interfere with maintenance and inspection of the internal pump, and safety is ensured since there are no detachable parts.

According to the second aspect of the present invention, a conventional flow rate measurement means using differential pressure upstream and downstream of an impeller, which has excellent accuracy in measuring large flow rates, is provided, and the method is switched between using a vortex flow measurement method and a vortex flow measurement method according to the flow rate. , it becomes possible to measure the flow rate over the entire range with high precision, making it easier to control the output of the reactor.

〔Example〕

A preferred embodiment of the present invention will be described below. Before that, an overview of a boiling water nuclear reactor with a built-in internal pump will be explained based on FIG. A reactor core in which a large number of fuel assemblies 1 are arranged exists within a reactor pressure vessel 8 . Internal shroud 1 surrounding the reactor core
1 is placed in the reactor pressure vessel 8. The lower end of the internal shroud 11 is fixed to the reactor pressure vessel 8 . A steam separator 6 is attached to the top of the internal shroud 11. A main steam pipe 7 connected to the turbine is connected to a steam dome 9 located above the cooling water level in the reactor pressure vessel 8 . Water supply pipe 1
0 is connected to an annular coolant passage 4 which is present between the reactor pressure vessel 8 and the internal shroud 11.
An impeller 3 is arranged in the annular coolant passage 4 .
A rotating shaft 12 to which the impeller 3 is attached passes through the reactor pressure vessel 8 to reach the outside, and is connected to the motor 2. The internal pump includes a motor 2, an impeller 3, and a rotating shaft 12.

When the impeller 3 rotates as the motor 2 is driven, the cooling water flowing into the annular coolant passage 4 through the water supply pipe 10 passes through the opening 14 provided at the lower end of the internal shroud 11 and flows through the lower plenum 5. is supplied to the reactor core. When the cooling water passes through the fuel assembly 1, it is heated and becomes steam. This steam is sent to the turbine through the main steam pipe 7.

FIG. 2 shows an internal pump section of a boiling water nuclear reactor which is a preferred embodiment of the present invention. The impeller 3 is arranged within the differential user 15. Diffuser 1 on the downstream side of impeller 3
A guide vane (guide vane) 16 is arranged within 5 . Guide vane 16 is attached to the inner surface of reactor pressure vessel 8 .

The core flow rate measurement device 34 includes a guide vane 16 as a Karman vortex generator, pressure detection tubes 20A and 20B, and a signal processing device 21.

The pressure detection end by Karman vortex is shown in Figures 3 and 4.
It is configured as shown in the figure. That is, the pressure detection tube 20A is installed in the differential users 15 and 16.
and 20B are provided, respectively. Passages 35A and 35
The pressure detection ports 36A and 36B of B are open at the downstream end surface of the guide vane 16. The pressure detection ports 36A and 36B detect differential pressure changes due to Karman vortices generated by the guide vane 16. The pressure detection tubes 20A and 20B penetrate the reactor pressure vessel 8 and reach the outside thereof. The signal processing device 21 includes a differential pressure transmitter 2 as shown in FIG.
3. Amplifier 24, filter circuit 25, flip-flop circuit 26, differentiation circuit 27, counter 2
8, a clock circuit 29 and an arithmetic circuit 30. Pressure detection tubes 20A and 20B are connected to differential pressure transmitter 23.

When the impeller 3 rotates and cooling water is supplied to the core, Karman vortices 31 are alternately and asymmetrically generated downstream of the guide vanes 16 as shown in FIG. Such a periodic vortex street is called a Karman vortex street. In a range where the Strouhal number takes a constant value, the frequency of vortex generation is proportional to the flow velocity. In this embodiment, the core flow rate is measured using such characteristics.

Changes in pressure due to the generation of Karman vortex 31 are measured by pressure detection ports 36A and 36B. The pressure changes measured by the respective pressure detection ports 36A and 36B are transmitted to the differential pressure transmitter 23 by the pressure detection tubes 20A and 20B.
The differential pressure change signal output from the differential pressure transmitter 23 is
The signal passes through an amplifier 24 and is input to a filter circuit 25 . The pressure detection ports 36A and 36B detect not only pressure changes caused by the Karman vortex 31 but also pressure changes caused by the pulsation of the internal pump. Therefore, the output signal a of the amplifier 24 also includes pressure changes due to the pulsation of the internal pump, as shown in FIG. The frequency of the pressure change due to the pulsation of the internal pump is one order of magnitude higher than the frequency at which the Karman vortex 31 occurs, so it can be easily removed by passing it through a filter circuit (low pass filter). Signal b in Fig. 5 is
This excludes the influence of internal pump pulsation. The signal b is shaped into a square wave like the signal c by the flip-flop circuit 26, and is then shaped into a square wave like the signal c by the flip-flop circuit 26.
becomes a pulse wave d. The counter 28 repeats setting and resetting at regular intervals based on the input signal from the clock circuit 29, and receives the input pulse wave d.
Only positive pulses are counted. The positive pulses counted by the counter 28 are equal to the generation frequency f of the Karman vortex 31. This value is input to the arithmetic circuit 30, and the flow rate of cooling water supplied to the core is determined based on the relationship shown in FIG. 7 (the relationship when the Strouhal number is constant). The relationship between the Strouhal number and Reynozzle number of the guide vane 16 is determined in advance through a separate experiment. The shape of the guide vane 16 is preferably such that the Strouhal number is constant in the core flow rate measurement region. The obtained core flow rate is displayed on the display device 32.

In this embodiment, the core flow rate can be determined with high accuracy even in a low flow rate region where the core flow rate is 50% or less. In particular, even if the internal pump, which is a recirculation pump, trips and the cooling water changes from forced circulation to natural circulation (core flow rate is 25% or less), the core flow rate can be determined with high accuracy. Japanese Patent Publication 1973-
As described in Publication No. 143999 and Japanese Patent Application Laid-open No. 141990, the core flow rate at low flow rate is Since it can be measured with high precision, it is easy to accurately adjust the core flow rate without deviating from the predetermined output increase range. Therefore, the fuel rods in the reactor core will not be damaged when the power increases, improving the safety of the boiling water reactor. This also applies when power increases due to an increase in core flow rate during load following operation. On the other hand, as described in Japanese Patent Application Laid-open No. 51-141990, even when reducing the reactor power for control rod pattern replacement by lowering the reactor core flow rate, the reactor power can be adjusted accurately. , can be precisely reduced to a predetermined reactor power. This also applies when the output decreases during load following operation.

Furthermore, according to this embodiment, the guide vane 16 itself is used as a Karman vortex generator, and the pressure detection ports 36A and 36B are integrated into the guide vane 16, so there is no change in flow resistance. , no increase in pressure drop. Furthermore, the structure is simple, there are no obstacles to maintenance and inspection of the internal pump, and there are no detachable parts, so it is safe and reliable.

Another embodiment of the invention is shown in FIG. The core flow rate measuring device 37 of this embodiment is a combination of the above-described core flow rate measuring device 34 and a conventional core flow rate measuring device 38 that utilizes the differential pressure between the inlet and outlet of an impeller. A description of the core flow rate measuring device 34 will be omitted. The core flow rate measurement device 38 includes a pressure detection tube 39A that measures the pressure on the outlet side of the impeller 3, a pressure detection tube 39B that measures the pressure at the entrance and exit of the impeller, and a signal processing device 40. The signal processing device 40 determines the differential pressure between the entrance and exit of the impeller 3 determined from the pressure detection ports 39A and 39B, and determines the core flow rate based on this value and the QH curve of the impeller 3. The values of the core flow rate determined by the core flow rate measurement device 34 and the core flow rate measurement device 38 are transmitted to the display device 41 . The display device 41 displays the latter value when the core flow rate determined by the latter method exceeds 50%, and displays the former value when the core flow rate determined by the latter method is less than 50%. In this embodiment as well, the same effects as in the embodiment shown in FIG. 2 can be obtained. The measurement accuracy of the core flow rate measuring device 34 is slightly lower than that of the core flow rate measuring device 38 when the core flow rate exceeds 50%. Therefore, by dividing the measurement area of each measuring device as in this embodiment, it is possible to improve the measurement accuracy of the core flow rate in the range of 0 to 100% of the total core flow rate. The power output of the nuclear reactor can be controlled more accurately.

Furthermore, by using the core flow rate measuring devices 34 and 38 together, it is possible to know the aging of the internal pump. If this correction is performed, the measurement accuracy of the core flow rate measuring device 38 can be further improved.

〔Effect of the invention〕

As explained above, according to the first aspect of the present invention, since a vortex flowmeter is applied, measurement accuracy in a low flow rate region can be improved. Thereby, the output of the nuclear reactor can be controlled more accurately.

In addition, the guide vanes themselves are used as vortex generators,
Because the detection end for pressure changes caused by vortices is formed inside the guide vane, there is no increase in flow resistance, and maintenance and inspection of the internal pump can be easily performed without being hindered, and safety can be ensured. effective.

Further, according to the second invention, in addition to the above effects,
The measurement accuracy over the entire flow range can be improved, and the reactor output can be controlled even more accurately.
The safety of nuclear reactors will be improved.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of a boiling water reactor with a built-in internal pump, Fig. 2 is a detailed view of the vicinity of the internal pump of a preferred embodiment of the present invention, and Fig. 3 is an implementation of Fig. 2. Figure 4 is an enlarged view of the downstream end of the guide vane in Figure 2. Figure 5 is a detailed diagram of the signal processing device in Figure 2. Figure 6 is the generation of Karman vortices. FIG. 7 is an explanatory diagram showing the situation, FIG. 7 is a characteristic diagram showing the relationship between the Karman vortex generation frequency and the core flow rate, and FIG. 8 is an enlarged view of the vicinity of the internal pump of a nuclear reactor according to another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Fuel assembly, 2... Motor, 3... Impeller, 4... Annular coolant passage, 8... Reactor pressure vessel, 11... Internal shroud, 12... Rotating shaft, 16... Guide vane , 20A, 20B...
Pressure detection tube, 21, 41...Signal processing device, 3
4, 38...core flow rate measuring device, 35A, 35B
...Passage, 36A, 36B...Pressure detection port.

Claims (1)

[Scope of Claims] 1. A reactor vessel, a reactor core disposed within the reactor vessel, a passageway for guiding a coolant to the reactor core present within the reactor vessel, and a passageway disposed in the coolant introduction passageway. In a nuclear reactor comprising an impeller, a means for rotating the impeller, and a coolant guide vane disposed in the coolant introduction passage, a coolant vortex generation portion generated downstream of the guide vane is provided. Means is provided for detecting pressure and measuring the flow rate of the coolant based on the fluctuation frequency of the detected pressure, and the pressure is
A nuclear reactor characterized in that a passage is bored inside the guide vane, and one end of the passage is detected by a pressure detection tube having a detection end opened at a downstream end face of the guide vane. 2. A reactor vessel, a reactor core disposed in the reactor vessel, a passageway for guiding a coolant to the reactor core present in the reactor vessel, an impeller disposed in the coolant introduction passageway, and the impeller. a means for rotating the coolant, a coolant guide vane arranged in the coolant introduction passage, a first means for measuring the flow rate of the coolant based on the differential pressure between the upstream side and the downstream side of the impeller, and the rotation speed of the impeller. A second nuclear reactor comprising a flow rate measuring means, which detects the pressure of a vortex generation part of the coolant generated on the downstream side of the guide vane, and measures the flow rate of the coolant based on the fluctuation frequency of the detected pressure. A flow rate measuring means is provided, and the pressure is detected by a pressure detection tube having a detection end formed by boring a passage inside the guide vane and opening one end of the passage to the downstream end face of the guide vane. A nuclear reactor, characterized in that a large flow rate is measured by the first flow rate measuring means, and a low flow rate is measured by the second flow rate measuring means.