JPH0810261B2 - Control rod withdrawal monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a control rod withdrawal monitoring device for monitoring a local output increase due to withdrawal of a control rod in a boiling water reactor.

(Prior Art) A large number of fuel assemblies are arranged in the core of a boiling water reactor, and control rods are regularly arranged between these fuel assemblies. These control rods control the chain reaction of nuclear fission, but a predetermined control rod is pulled out from a large number of control rods in order to maintain the output of the reactor at a predetermined value. When the control rod is pulled out in this way, the chain reaction near the pulled-out control rod increases and the output locally rises. If this rise in local power is too high, it may interfere with the operation of the reactor, so the local power due to pulling out the control rod is monitored.

By the way, the monitoring of the local output increase by pulling out the control rod is performed as follows. FIG. 4 is a cross-sectional view of the core of a boiling water reactor, in which an upper part shows a whole cross-sectional view and a lower part shows a partially enlarged view. Here, in order to simplify the description, description will be given with reference to a partially enlarged view. This partially enlarged view shows a cross section of coordinates (13 to 27, 9 to 23) in the core, in which the fuel assemblies 1 are regularly arranged and the control rods 2 are regularly arranged between the fuel assemblies 1. Are arranged. The neutron flux detectors 3 are arranged every two control rods 2. Therefore, four neutron flux detectors 3 are arranged so as to surround four of the control rods 2. As shown in FIG. 5, these neutron flux detectors 3 are placed inside a detecting tube 4 and each of the detectors 5-1 to 5-4.
Is provided, and each detector 5-1 to 5-
4 are arranged on the same plane as the detectors of the other neutron flux detectors 3 in the core. Then, the neutron flux detectors 3 are sent to the signal selection circuit 7 and the average power range nuclear instrumentation device 8 of the local power monitoring device 6 shown in FIG. The control rod selection signal s from the manual reactor control device 9 is input to the signal selection circuit 7, and for example, the control rod 2 at the coordinates (22,18), that is, the control rod 2a is pulled out in the core. When the control rod selection signal s indicating that the control rod is selected is input, the signal selection circuit 7 detects four neutron fluxes 3 surrounding the control rod 2a, that is, coordinates (24,20) (16,20).
The neutron flux detection signals from the (16,12) and (24,12) neutron flux detectors 3 are selected and sent to the averaging circuit 10. This averaging circuit 10 adds each neutron flux detection signal to obtain a local average value, and sends this local average value to the gain setting circuit 11.
Further, at this time, each instrumentation device 8 in the average output region adds all the neutron flux detection signals that are input to obtain an average output and sends it to the gain setting circuit 11. As a result, the gain setting circuit 11
Divides the average output value by the local average value to obtain the gain of the local average value and sends it to the trip determination circuit 12. On the other hand, the recirculation flow rate detector 13 detects the flow rate of the primary cooling water supplied to the reactor and sends the flow rate detection signal to the trip determination circuit 12. Then, the trip determination circuit 12 inputs the flow rate detection signal, creates a trip level from the flow rate, and compares the trip level with the gain-applied local average value from the gain setting circuit 11. Then, if the local average value becomes higher than the trip level by this comparison, the control rod withdrawal prevention signal g is sent to the manual reactor control device 9. As a result, when the local output becomes high, the withdrawal of the control rod is prevented.

By the way, in an actual control rod pull-out monitoring device, a dual system is constructed as shown in FIG. 7 in order to improve and ensure the reliability of monitoring. That is, each of the control rod pull-out monitoring devices 13 and 14 has the same configuration as the device shown in FIG. 6, and one control rod pull-out monitoring device 13 is, for example, an odd-numbered detector among the neutron flux detectors 3. Input the neutron flux detection signal from the other control rod pull-out monitoring device
14 inputs the neutron flux detection signal from the even-numbered neutron flux detector. Then, the control rod withdrawal prevention signals g1 and g2 output from the respective monitoring devices 13 and 14 are both sent to the reactor manual control device 9, and the reactor manual control device 9 causes the control rod withdrawal prevention signals g1 and g1. The control rod withdrawal is stopped when both g2 are input, and the control rod withdrawal is stopped when either one of the control rod withdrawal prevention signals g1 or g2 is input.

However, even if such a dual system is constructed, it is difficult to construct a complete dual system. The causes are as follows. First, each neutron flux detector 3 and each control rod withdrawal monitoring device 13,1
Since a metal cable is used to connect with 4,
In order to reduce the fluctuation of the signal caused by the resistance of the metal cable, it is necessary to provide a calibration variable resistor for each metal cable. Therefore, a large amount of calibration work is required using these variable resistors for calibration. Moreover, since each neutron flux detector 3 and each control rod extraction monitoring device 13, 14 are electrically connected, each neutron flux detection signal is affected by the environment and contains an error. I will end up. Further, since it has an analog circuit configuration, it is difficult to change the constant used when creating the trip level in the trip determination circuit 12, for example. Furthermore, it is difficult to easily deal with the increase or decrease in the number of control rods. In addition,
Although the calibration work can be simplified by digitizing the local output monitoring device 6 and arranging it near the neutron flux detector 3 to shorten the metal cable, the constants set in the local output monitoring device 6 can be set to the local output monitoring device 6. Since a change operation must be performed remotely from a central monitoring room or the like, there is a problem that the constant cannot be easily changed. Since the central monitoring room in which the operator is stationed is located at a predetermined distance from the core, if the local output monitoring device 6 is brought close to the detector in order to shorten the metal cable, the local output monitoring device 6 will inevitably be detected. This means that the work must be moved away from the central monitoring room, and the work of changing the constant or the configuration for it becomes complicated.

(Problems to be Solved by the Invention) As described above, it has been impossible to construct a complete dual system.

Therefore, the present invention can reduce the calibration work by the variable resistor of the metal cable that transmits the neutron flux detection signal, and can change the constant of the determination unit that executes the control rod pullout prevention determination while shortening the length of the metal cable. An object of the present invention is to provide a control rod withdrawal monitoring device that can be easily arranged in a central monitoring room and can construct a complete dual system.

[Structure of the Invention] (Means for Solving the Problem) The present invention is directed to a local problem that occurs when a control rod regularly arranged between a large number of fuel assemblies arranged in a reactor core is pulled out. In the control rod pull-out monitoring device for monitoring the output increase by receiving the neutron flux detection signal from each neutron flux detector arranged in the reactor core, the average output computing means to which each neutron flux detector is connected And a plurality of monitoring means for the dual system connected in parallel to the average output computing means. The average output calculation means digitizes and stores the neutron flux detection signals input from each of the neutron flux detectors, obtains an average output value from the stored digital neutron flux detection signals, and obtains the average output. The value and the digital neutron flux detection signal are transmitted to the monitoring means. The monitoring means receives and stores each of the digital neutron flux detection signals and the average output value transmitted from the average power calculation means, and surrounds the control rod that is extracted from the stored digital neutron flux detection signals. Select the digital neutron flux detection signal of each neutron flux detector arranged as described above to obtain a local average value, correct this local average value using the average output value, and correct this local average value and a predetermined value. Based on the result of comparison with the trip level, the local increase in output is judged.

(Operation) With the above-described configuration according to the present invention, the neutron flux detection signal from each neutron flux detector is input to the average output computing means, digitized, and once stored, the average output value is Desired. The obtained average output value and each digital neutron flux detection signal are transmitted to the monitoring means. The monitoring means stores each digital neutron flux detection signal and the average output value transmitted from the average output calculating means. Then, the digital neutron flux detection signal of each neutron flux detector, which is arranged so as to surround the control rod and is extracted from the stored digital neutron flux detection signal, is selected to obtain the local average value. This local average value is corrected using the average output value, and a local increase in output is determined based on the result of comparison between the corrected local average value and a predetermined trip level.

Therefore, the average output calculation means executes processing that requires a small constant change, such as digitalization of neutron flux detection signals and arithmetic mean of digital neutron flux detection signals, to create trip levels and change the number of simultaneous withdrawal of control rods. The monitoring means executes the control rod withdrawal prevention determination process in which various constant changes occur, and there is a high demand for constant change.

(Example) Hereinafter, one example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a control rod pull-out monitoring device. Each neutron flux detector 20 is arranged in the reactor core, and each neutron flux detection signal output from these neutron flux detectors 20 is sent to the average output computing means 21. Further, a recirculation flow rate detector 22 for detecting the flow rate of the primary cooling water supplied to the nuclear reactor is sent to the average output calculation means 21. This average power calculation means 21 is for each neutron flux detector 20
It has a function of converting each neutron flux detection signal from the above into a digital neutron flux detection signal and calculating and obtaining an average output value. Specifically, an A / D (analog / digital) converter 23 connected to each neutron flux detector 20 and an A / D converter 24 connected to the recirculation flow rate detector 22 are provided. In addition, the CPU (central processing unit) 25 is connected to the memory 27 and each I / O (input / output) port 28, 2 via the bus 26.
9,30 are connected. The I / O port 28 is connected with the A / D converter 23, and the I / O port 29 is connected with the A / D converter 24. The CPU 25 stores each digital neutron flux detection signal captured from the I / O port 28 in the memory 27 and also stores the digital flow rate detection signal captured from the I / O port 29 in the memory 27, and each stored in the memory. It has the function of calculating the average output value from the digital neutron flux detection signal.

Further, 41 is a monitoring means, which monitors each digital neutron flux detection signal obtained by the average output computing means 21,
Upon receiving the average output value and the digital flow rate detection signal, the digital neutron flux detection signal of each neutron flux detector arranged so as to surround the control rod to be extracted is selected to obtain the local output value. The local output value and the average output value Also, it has a function of determining a local output increase based on the digital flow rate detection signal. Specifically, it has a configuration in which a memory 33, a display 34, a function key 35, and each I / O port 36, 37 are connected to the CPU 31 via a bus 32. Then, the I / O port 36 and the I / O port 30 of the average output calculation means 21 are connected via the transmission devices 38 and 39, respectively, and the I / O port 37 is connected to the reactor manual control device 40. There is. The CPU 31 has various functions as shown in FIG.
31-1 has a function of selecting each digital neutron flux detection signal of each of the four neutron flux detectors arranged so as to surround the control rod to be pulled out, and a local average calculating means 31-
2 has a function of adding and averaging the selected digital neutron flux detection signals to obtain a local average value, and the gain setting means 31-3 further calculates the local average value from the local average value and the average output value. It has a function of obtaining a gain and multiplying this gain by a local average value. And
The trip determination means 31-4 obtains a trip level from the digital flow rate detection signal, compares the trip level with the local average value obtained by the gain setting means 31-3, and controls if the local average value is higher than the trip level. It has a function of transmitting a bar pull-out prevention signal.

Next, the operation of the apparatus configured as described above will be described.

Each neutron flux detection signal output from each neutron flux detector 20 is digitally converted by the A / D converter 23 and sent to the I / O port 28. Further, the flow rate detection signal of the primary cooling water output from the recirculation flow rate detector 22 is digitally converted by the A / D converter 24 and sent to the I / O port 29. At this time, CPU25 is I / O
Each digital neutron flux detection signal is scanned and taken in from the port 28, these digital neutron flux detection signals are sequentially stored in the memory 27, and the digital flow rate detection signal is taken in from the I / O port 29 and stored in the memory 27. And then
The CPU 25 reads, for example, each digital neutron flux detection signal stored in the memory 27 for each scanning of the I / O port 28 and adds them to obtain an average value, that is, an average output value. Next, the CPU 25 reads out the digital neutron flux detection signal, the average output value and the digital flow rate detection signal from the memory 27 and transmits the signal to the transmission device.
Send to 39. As a result, the transmission device 39 converts the digital neutron flux detection signal, the average output value and the digital flow rate detection signal into a serial signal and transmits the serial signal to the monitoring means 41.

In the monitoring means 41, when the transmitter 38 receives the digital neutron flux detection signal, the average output value and the digital flow rate detection signal, the CPU 31 stores the digital neutron flux detection signal, the average output value and the digital flow rate detection signal in the memory 33.
To memorize.

In this state, when the control rod selection signal is taken in from the reactor manual control device 40 through the I / O port 37, the signal selection means 31-1 of the CPU 31 determines the position of the control rod to be pulled out from this control rod selection signal. Then, each of the four neutron flux detectors surrounding this control rod is judged. Then, the signal selection means 31-of the CPU 31
1 reads each digital neutron flux detection signal of these neutron flux detectors from the memory 33. Next, the local average calculation means 31
For -2, these read digital neutron flux detection signals are added to calculate an average value thereof, and this value is set as a local average value. Then, the gain setting means 31-3 of the CPU 31 operates as the memory 3
The average output value is read from 3, the average output value is divided by the local average value to calculate the gain of the local average value, and this gain is multiplied by the local average value. Here, the gain of the local average value represents the ratio of the local average value in the local area surrounding a certain control rod to the average output value of the entire reactor. Since the reactor power has a characteristic that the central part is high in the horizontal cross section of the reactor and decreases as it approaches the peripheral part, the output in the horizontal cross section of the reactor is calculated by multiplying the gain by the local average value. The top can be treated as uniform. On the other hand, the trip determination means 31-4 reads the digital flow rate signal from the memory 33 and creates a trip level from this flow rate value. Then, the trip determining means 31-4 compares the trip level with the local average value obtained by the local average calculating means 31-2 and multiplied by the gain in the gain setting means 31-3, and the local average value is calculated. If it is higher than the trip level, a control rod pull-out prevention signal is sent. Then, this control rod withdrawal prevention signal is sent to the reactor manual control device 40 through the I / O port 37. As a result, the withdrawal of the control rod is stopped.

By the way, when a double system is constructed by using the above-mentioned devices, the structure is as shown in FIG. That is, the monitoring means 41 and 42 having the same structure as the monitoring means 41 shown in FIG. 1 are commonly connected to the average output calculation means 21, and the monitoring means 41 and 42 and the reactor manual control device 40 are connected between them. The control rod selection signal and the control rod pull-out prevention signal are transmitted and received. However, each monitoring means 41, 42
May receive neutron flux detection signals from all neutron flux detectors 20, respectively, also each monitoring means 41, 4
In step 2, the neutron flux detectors of odd number and even number may be separately captured.

As described above, in the above-described embodiment, the neutron flux detection signals from the neutron flux detectors are input, and the average output value is calculated from each digital neutron flux signal digitized to obtain each monitor for the dual system. Sending to the means, in these monitoring means, the digital neutron flux detection signal of each neutron flux detector arranged so as to surround the control rod to be extracted is selected to obtain the local average value, and this local average value is compared with the trip level. Since the local increase in output is determined based on the result, a complete dual system can be constructed, and both monitoring means can be used.
In 41 and 42, it is possible to determine the local increase in output by using the total neutron flux detection signal, which enables more accurate monitoring and improves the monitoring accuracy. In this case, the monitoring accuracy does not decrease even if either one of the monitoring means 41 or 42 cannot be used.

Furthermore, the monitoring means 41 and 42 having completely the same configuration can
Since the heavy system is constructed, if the calculation results in the monitoring means 41 and 42 do not match, it is possible to clearly determine that there is an abnormality. Also, in order to prevent erroneous determination, it is necessary to make each monitoring means of the same configuration a dual system.

In addition, the digitization of each neutron flux detection signal makes it less susceptible to external influences, and the speed at which each digital neutron flux detection signal is taken in is increased to shorten the determination cycle in the trip determination means 31-4. Can be easily accommodated.

Further, when a plurality of control rods are pulled out at one time, it can be easily dealt with by repeating the operation of each means 31-1 to 31-4 in each monitoring means 41, 42.

In addition, the function keys 35 can be used to easily change, for example, set values when creating a trip level.

However, because of the above, this device is a perfect 2
A duplication system can be built.

Further, in the present apparatus, it is possible to display a cross-sectional view of the reactor as shown in FIG. 4 on the display 34, show the control rod when pulling out the control rod, and display the local output at that time with numerical values or the like. .

It should be noted that the present invention is not limited to the above-mentioned embodiment, and may be modified within a range not departing from the gist thereof. For example, each of the transmission devices 38 and 39 may be an optical transmission device, in which case the average output calculation means 21 and the monitoring means 41 can be electrically insulated completely. Further, a plurality of average output calculation means 21 may be provided, and a repeater may be provided in the transmission line between the average output calculation means 21 and the monitoring means 41. Further, the monitoring means 41 may include an analog circuit.

[Advantages of the Invention] As described in detail above, according to the present invention, it is possible to reduce the calibration work of the variable resistor of the metal cable that transmits the neutron flux detection signal, and to prevent the control rod from being pulled out while shortening the length of the metal cable. It is possible to provide a control rod pull-out monitoring device that can arrange a determination unit that performs determination in a central monitoring room where the constant can be easily changed, and can build a complete dual system.

[Brief description of drawings]

1 to 3 are views for explaining one embodiment of a control rod pull-out monitoring device according to the present invention, FIG. 1 is an overall configuration diagram, and FIG. 2 is a functional block diagram of monitoring means, FIG. 3 is a block diagram of a double system, FIG. 4 is a cross-sectional view of a boiling water reactor, FIG. 5 is an external view of a neutron flux detector, and FIGS. 6 and 7 explain conventional equipment. FIG. 20 ... Neutron flux detector, 21 ... Average power calculation means, 22 ...
… Recirculation flow rate detector, 23,24 …… A / D converter, 25 …… CP
U, 27 …… Memory, 41 …… Monitoring means, 31 …… CPU, 33 ……
Memory, 34 ... Display, 35 ... Function keys, 3
8,39 …… Transmission device, 40 …… Reactor manual control device.

Claims (1)

[Claims] 1. A local power increase caused when a control rod regularly arranged between a plurality of fuel assemblies arranged in a reactor core is pulled out is arranged in the reactor core. In the control rod withdrawal monitoring device for monitoring by receiving the neutron flux detection signal from each neutron flux detector, the average output calculation means to which each neutron flux detector is connected, and is connected in parallel to the average output calculation means And a plurality of monitoring means for the dual system, the average output computing means digitizes and stores the neutron flux detection signals input from the neutron flux detectors, and stores the stored digital neutrons. An average output value is obtained from the flux detection signal, and the obtained average output value and each of the digital neutron flux detection signals are transmitted to each of the monitoring means, wherein the monitoring means is the average output calculation means. Receiving and storing the transmitted each digital neutron flux detection signal and the average output value, of each neutron flux detector arranged to surround the control rod that is extracted from the stored digital neutron flux detection signal Select a digital neutron flux detection signal to obtain a local average value, correct the local average value using the average output value, and output the local value by comparing the corrected local average value with a predetermined trip level. A control rod pull-out monitoring device characterized by making a rise determination.