JPS62229098A - Control-rod drawing monitor device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention monitors the local output around a control rod that is being withdrawn, and detects when this output exceeds a predetermined set value. This relates to a control rod withdrawal monitoring #iA position that prevents control rod withdrawal.

(Prior art) In general, in a boiling water reactor (hereinafter referred to as BWR), four fuel N reactors are placed around a control rod 1 having a cross-shaped cross section, as shown in Fig. 6.
The 1s coalescence 2 is arranged to form a unit cell 3, and the unit cell 3 is arranged in a lattice shape as shown in FIG. 7 to constitute a reactor core 4 whose planar shape is approximately circular. The reactor core 4 having such a configuration is installed in a reactor pressure vessel 9 shown in FIG. Note that the square 1al in FIG. 7 indicates the fuel assembly 2, and the white circle indicates the control rod 1.

Inside the core 4, there are many power range neutron detectors (hereinafter referred to as L
PPM) 5 has been installed. These many LPs
RM5 has two unit cells 3 as shown in FIG.
In other words, every second control rod 1 is arranged, and in the vertical direction, as shown in FIG. 8, the control rods 1 are arranged in four stages.

The output from a part of the LPRM 5 is processed by an average power range monitor system (APRM) (not shown), and the average output of the entire core 4 is detected. Further, local output is detected by a local output area monitor system (LPPM) not shown. When withdrawing the control rod 1, the local output around it is monitored, and if the local output exceeds the predetermined 1160 rod handling prevention setting value due to improper withdrawal of the control rod 1, prevents handling of the control rod 1 to ensure the integrity of the reactor. The control rod monitoring system is what makes this possible! ! It is 26. For example, it is assumed that the control rod 1a at the shaded position in FIG. 7 becomes the target for the withdrawal operation. In this case, 16fl surrounding this control rod 1a
l (4 pieces x 4 stages) of LPRM detectors 5 are selected, and these 16 LPRM detectors 5 generate the local output it.
A monitor system is constructed, which monitors the local power around the control rod 1a.

Furthermore, the LPRM5 is roughly divided into two systems in order to improve its reliability. Let us assume that one system is the A system and the other system is the B system. Then, the average value of the output of LPRM5 is calculated separately for each of the A system and B system, and either the average value of the A system or the average value of the B system exceeds the preset control rod withdrawal prevention setting value. In this case, the control rod withdrawal monitoring device 6 outputs a handling prevention signal @$6 to the control rod control device 7. A signal S7 is output from this control rod operability M7 to the control rod drive mechanism 8, and thereby! ill Ill handling of rod 1 is prevented. In addition, the control rod withdrawal monitoring device 1i16 is L
If an abnormality occurs in the PRM detector 5, the LPRM detector 5 in which the abnormality has occurred is excluded, and the average value of the outputs of the remaining LPRM detectors 5 is calculated. Furthermore, if an abnormality occurs in the A system or the entire Japanese system, it has a function to exclude the system in which the abnormality has occurred and monitor the remaining systems. This is intended to improve reliability.

However, the control rod post-pulling monitoring device 6 having the above configuration is based on the assumption that only one control rod is to be pulled out, and there is a problem that good control cannot be achieved when there are multiple control rods to be pulled out. Ta. That is, in recent years, a method of controlling a plurality of control rods simultaneously has been adopted for BWR control rod operation, instead of the conventional control of one control rod at a time. This is to reduce the number of times the control rod is withdrawn, shorten the startup time, and improve control rod operability, and this type of operation is called a control rod gearing operation. Therefore, when a control rod gearing operation is performed to simultaneously pull out the control rods 1a, 1b, 1C, and 1d, which are indicated by diagonal lines in FIG. For example, one of the control rods 1a to 1d is selected and the local power distribution in the vicinity of this one control rod is monitored.

Here, we will compare the case where multiple control rods are pulled out at the same time and the case where one control rod is pulled out. When multiple control rods are pulled out at the same time, compared to when a single control rod is pulled out, even if the amount of control rods pulled out is the same, the reactivity introduced into the reactor is greater, and the reactor The increase in output will also be rapid. In addition, the power output in the vicinity of the control rods that were handled also increases rapidly. In this way, when pulling multiple control rods at the same time, the output near each control rod increases rapidly compared to when pulling out a single control rod, even if the amount of control rods is pulled out is the same. There are variations depending on the control rod. Therefore, if the area near the plate control rod is arbitrarily selected and monitored as described above, the intended purpose cannot be achieved.

By the way, there is a minimum critical power ratio (hereinafter referred to as MCPR) as an index indicating the degree of heat removal from fuel to coolant. This is boiling! ! The ratio (CP/BP) between the limit CP at which heat removal from the fuel deteriorates due to changes in the mechanism and the material temperature rises, causing fuel loss, and the output BP of the fuel assembly 2 during operation. This shows the minimum +a. It is determined that this MCPR is operated with a preset limit of one or more shifts. This change in MCRP is considerably worse in the case of the above-mentioned giyoung operation than in the case of single withdrawal.

Therefore, in the case of control rod withdrawal alone, LPPM
Even if an abnormality occurs in the detector or in the entire system, it can be controlled by monitoring with the remaining LPRM detector or system that bypasses the LPPM where the abnormality occurred or the entire system. Although it was possible to prevent the reactor pressure increase due to withdrawal by preventing control rod withdrawal before fuel failure occurs, when operating the ml tIl rod gear gear young, the same control rod withdrawal prevention setting value Even if this happens, the MCPR will deteriorate significantly, so depending on how the LPRM detector or system is bypassed, fuel damage may have already occurred by the time control rod withdrawal is prevented. This will be explained in more detail with reference to FIG. In Figure 9, the horizontal axis shows the control rod withdrawal amount, and the vertical axis shows changes in the output signal and MCPR.
is the υ1 limit value of MCPR, and Lb is the control rod withdrawal prevention setting value. In addition, curve a1 is the average output signal from the LPRM detector when a single control rod is withdrawn, and the entire B system is abnormal and 4 of the 8 LPRM detectors of the A system are abnormal, so these were bypassed. It is a matter of the case. Curve a2 shows the average output during gearing operation with four control rods under the same conditions. Further, curves b1 and b2 show changes in MCPR corresponding to a1 and a2 described above. As is clear from FIG. 9, when the control rod is operated alone, when the curve al reaches Lb (when the υ1wJ pull-out prevention is applied), M CP RG, t P t and L
It never goes below a. On the other hand, in the case of four control rod gearing operation, MCPR is P2, which is less than la. As described above, conventional control rod withdrawal monitoring devices cannot monitor control rod gearing operations, and improvements have been required in order to maintain fuel integrity.

(Problems to be Solved by the Invention) As described above, the conventional control rod withdrawal monitoring system cannot monitor control rod gearing operations in which multiple control rods are withdrawn at the same time. The object of this invention is to provide a control rod withdrawal monitoring device that is capable of monitoring control rod gearing operations even in the case of control rod gearing operations.

[Structure of the Invention] (Means for Solving the Problems) That is, the control rod withdrawal monitoring device according to the present invention has a plurality of channels including a group of output WAtR neutron detectors surrounding one control ulI rod. , are these multiple channels subject to a single pull operation? It
! 1. a selection circuit that selects a channel corresponding to the control rod and selects detection signals from a group of output area neutron detectors constituting the selected channel according to a plurality of systems divided in advance for each channel; A plurality of averaging circuits are installed corresponding to the plurality of systems for each channel, and each signal selected by the selection circuit is input to each thread tube and averaged, and the signals from these plurality of averaging circuits are separately processed. A plurality of correction circuits correct the core average output by inputting the signals from the plurality of correction circuits, and a control rod withdrawal prevention signal is generated when the control rod prevention setting value is exceeded by inputting the signals from these plurality of correction circuits. and a determination circuit that outputs the information to the control rod control device.

(Operation) In other words, for all the control rods to be extracted, select a channel consisting of a group of output range neutron detectors surrounding the control rod, and divide it into a number of systems, each of which An average circuit outputs 4 average values in the thread cylinder, and this is corrected by a correction circuit, and each judgment circuit determines whether or not the value exceeds a preset control rod withdrawal prevention set value. It outputs a blocking signal.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 5. Reference numeral 101 in FIG. 1 is a control rod. Four fuel assemblies 102 are arranged around this control rod 101, forming a unit lattice 103. This unit lattice 103 is arranged in a lattice shape. As shown in FIG. 2, the reactor core 104 has a substantially circular planar shape.This core 104 is housed in a reactor pressure vessel 105 as shown in FIG. In FIG. 2, one square represents one fuel assembly 102, and a large white circle represents a control rod 101.

An LPRM 106 is installed within the reactor core 104 . This LPRM 106 has two unit cells 103 as shown in FIG. It is installed in four stages in the direction. In addition, as shown in FIG. 1, in a specific LPRM, the code (1
06ax, 106bt, 106a2.106b2)
, (106ayo, 106b3.106a4.106b
4), (106as, 106bs, 106as, 1
06bs) , (106a 7 , 106b a , 106as , 106ba ) are attached.

The nuclear control rod 101 has a control rod drive machine 4#I 10
7 are installed respectively. The control rods 101 are inserted into and withdrawn from the reactor core 104 by these control rod drive vJ structures 107. The above control rod drive machine #1107 is the control rod control device 1
Controlled by 08. Further, the LPRM detector 106
detects the local power within the reactor core 104 and outputs a signal corresponding to this.

Signals from some of these LPRM detectors 106 are output to an average output range monitor system (APRM), not shown, and are processed. Thereby, the overall average power of the reactor core 104 is detected, and based on this, it is converted into a percentage of the power during normal operation of the reactor and output. In addition, the above LPRM detector 1
The signal from 06 is output to the control rod withdrawal monitoring device W1109, and the control rod withdrawal monitoring device W1109 monitors the surroundings of the II m rod 101 for all the control rods 101 operated when withdrawing the control rods 101. detect the local output of
If the surrounding power locally exceeds the control rod withdrawal prevention setting value due to inappropriate withdrawal of the M-sagi 101, the control rod 101 is prevented from being withdrawn and the integrity of the reactor core 104 is maintained. .

Referring to FIG. 4 below, the control rod pulling technical supervisor FA device 109
The configuration will be explained in more detail. Reference numeral 110 in FIG. 4 is a selection circuit. For example, the control rod 1 shown with diagonal lines in Figure 1
When handling four control rods 01a, 101b, 1010 and 101d by control rod gearing operation, each control rod 101a.

The corresponding LPRM detectors 106 are selected for 101b, 1010, and 101d, respectively. That is, the control rod 101a has LPRM detectors 106al, 106b1 .
106a2, 106b2 are selected, and for control rod 101b, LPRM detectors 106a3, 106bs, 1
06a+ and 106b4 are selected. Similarly, for the control rod 101C, the LPRM detectors 106as, 1
06t)s.

106as and 106bs are selected, and the control rod 101d
LPRM detector 106a, 106b7.106a
8.106b6 are selected respectively.

And channels 111a, 111b, 111C respectively.
and 111d. Signals Sa, Sb, Sc and Sd are outputted to the selection circuit 110 from each of these channels 111a, 111b, 111c and 111d. On the other hand, the selection circuit 110 receives a control rod designation signal Sa that designates the four control rods 101a to 101d.
t, Stl, and SCt are input. Further, the selection circuit 110 includes the extraction control rods 101a, 101b, 10
1C and 101 (some LPPM corresponding to each of f
Each of the detector signals Sa to Sd is divided into two systems (system A and system B) of eight.

That is, the selection circuit 110 selects the average circuit 1 for the signal 5aeA system.
12a and B-system averaging circuit 112b. Similarly, for sb, A-system average circuits 112a2 and 11
2b2, and the SC average circuit 112a.
3 and 112b3, and for Sd, A
It is output to system averaging circuits 112a4 and 112b+. These A-system average circuits 112at to 112a4 and B
The optical averaging circuits 112b1 to 112b+ each average the signal outputs to calculate an average value. This is then checked and output as a percentage of the reactor's normal operating output. The output signal of the A system averaging circuit 1'8112a1 is sent to the correction circuit 113at.
The output signal of the Japanese average circuit 112b1 is input to the B light correction circuit 113b. Similarly, from the A-system averaging circuit 112az to the A-light correction circuit 113a2, from the Japanese-system averaging circuit 112b2 to the B-system correction circuit 113b2, from the A-system averaging circuit 112a3 to the A-system correction circuit 113a3, and from the Japanese-system averaging circuit 112b3 to the B-system correction circuit. 113b:+, from the A system averaging circuit 112a4 to the Δ system correction circuit 113a+
, from the Japanese average circuit 112b4 to the B uncorrected circuit 113b.
4, respectively. On the other hand, the average signal 5114 of the core 104 is output from the APRM to each of the correction circuits 113ax to 113a+ and 113t to 113tl. Each of the correction circuits 113at to 113a4 and 113bl to 113b4 outputs the average signal $114.
Based on this, the signals from each averaging circuit 112at to 112a+ and 112bt to 112b+ are corrected. Then, the correction signal is sent to the A-system determination circuits 115at to 115a+.
and is output to B-system determination circuits 115th to 115b<. The A-system determination circuits 115at to 115a4 have control rod withdrawal prevention setting values (usually 105
% to 107%), the withdrawal prevention signal 511
6 is output to the control rod controller 1108. Similarly, the Japanese determination circuits 115bx to 115b+ output a withdrawal prevention signal Sgo 16 to the control rod control device 108 when the signals from the B uncorrected circuits 113bx to 113b4 exceed the υJtMI rod withdrawal prevention setting value. If the withdrawal prevention signal 5116 is output from any of the determination circuits,
A signal 8108 is outputted from the control rod control device 108 to the drive mechanisms of the four control rods that are opposed to being withdrawn, and as a result, the withdrawal of the four control rods is simultaneously prevented.

The control rod withdrawal monitoring device 109 is also equipped with a circuit diagnosis function. For example, if an abnormality occurs in multiple LPRM detectors, the occurrence of the abnormality is detected and the LPRM detector in which the abnormality has occurred is detected.
It functions to inhibit the signal from the RM detector from being output to each averaging circuit via the selection circuit 110, thereby bypassing the LPRM detector in which the abnormality has occurred. At this time, the A-system averaging circuit and the Japanese-system averaging circuit calculate the average value based on the signals from the LPRM detectors other than the LPRM detector in which the abnormality has occurred. Furthermore, even if an abnormality occurs in the A-system average circuit, the Japanese-system average circuit, etc., it functions to bypass the entire system.

An example of monitoring using the control rod withdrawal monitoring device having the above configuration will be described with reference to FIG. This is the case where the four control rods 101a to 101d are pulled out by the control rod gearing operation as described above. In Fig. 5, the horizontal axis shows the control rod withdrawal point, and the vertical axis shows the output signal and MC.
It is a figure showing the change of PH. Also, Laa in the figure is MOP
Lbb is a limit value of R, and Lbb is a set value for preventing control rod withdrawal. In the figure, Fig. 81a shows the average output signal when one of the A system and the B system is abnormal, and the other is also abnormal and 4 out of 8 LPRM detectors are bypassed. As shown in the figure, in the case of this embodiment, control rod withdrawal is prevented when the handling amount is Ia, and the MCPR at that time is pa
It is. This Pa is not below 1aa,
Therefore, withdrawal of the control rod is prevented before the limit value 1aa is exceeded. On the other hand, in the conventional case (indicated by the broken line in the figure), when control rod withdrawal is prevented (the extraction vehicle is Ib), the MCPR is pb, and the limit value is a.
It is much lower than a. In the conventional case, even in the case of four control rod gearing operation, one control rod is surrounded by one control rod.
While monitoring is carried out by six (4 pieces x 4 stages) LPPMPP types, in this embodiment, the 64 control rods each surround the four control rods 101a to 101d that are subject to the gigang operation. (4 units x 4 stages x 4 channels) LPR
This is because the configuration is monitored by the M detector, and there are many LPRs that are operating properly even under the same bypass conditions.

According to this embodiment, the following effects can be achieved. In other words, even in the case of a four-rod control rod gearing operation, since the LPRM 106 surrounding each of the four rods is used to monitor the control rods, the control rod withdrawal is prevented before the MCPR limit value is exceeded. This makes it possible to prevent the control rod from being pulled out, thereby making it possible to prevent fuel damage due to the control rod being pulled out.

It should be noted that the present invention is not limited to the above-mentioned embodiment, and for example, the number of control rods for medium and wide objects is not limited to four.

[Effect of the invention 1] As detailed above, according to the control rod withdrawal monitoring device according to the present invention, even in the case of so-called control rod gearing operation in which multiple control rods are withdrawn at the same time, TX such as fuel damage can be avoided.
It is possible to prevent the withdrawal of the IIIt[l rod before B occurs, and this has great effects, such as maintaining the integrity of the fuel, the integrity of the reactor core, and the integrity and safety of the reactor as a whole.

[Brief explanation of drawings]

Figures 1 to 5 are diagrams showing one embodiment of the present invention.
Figure 2 is a plan view of the unit cell, Figure 2 is a plan view of the reactor core, Figure 3 is a diagram showing the configuration of the lower part of the core and reactor pressure vessel and its vicinity, and Figure 4 is the configuration of the control rod withdrawal monitoring device. The diagram shown in Figure 5 shows the signal output and MO for control and withdrawal a.
Figures 6 to 9, which show changes in PR, are used to explain the conventional example. Figure 6 is a plan view of the unit cell, Figure 7 is a plan view of the core, and Figure 8 is a diagram showing the core and FIG. 9 is a diagram showing the configuration of the reactor pressure vessel and its vicinity, and is a diagram showing changes in signal output and MCPR with respect to the amount of control rod withdrawal. 101... Control rod, 102... Fuel assembly, 103
... Unit cell, 104 ... Core, 106 ... Output vAVi neutron detection, 108 ... Control rod control device,
Upper 1L...control rod withdrawal supervisor? J! Device, 110... Selection circuit, 111a to 111d... Channel, 11
2a1-112a+, 112bt-112b+- average circuit, 113a1-113a4, 113b1-113b+
...correction circuit, 115at to 115a+. 1.15bl to 115b+...determination circuit. Applicant's agent Patent attorney Takehiko Suzue; Kura 8v? J Figure 9

Claims (1)

[Claims] Select multiple channels consisting of a group of output area neutron detectors surrounding one control rod, and a channel corresponding to the single or multiple control rods that are the target of the extraction operation from among these multiple channels. and a selection circuit that selects detection signals from a group of output area neutron detectors constituting the selected channel corresponding to a plurality of systems divided in advance for each channel; A plurality of averaging circuits are installed correspondingly and input and average each signal selected by the above-mentioned selection circuit for each system, and signals from these plurality of averaging circuits are input separately to calculate the core average output. a determination circuit that inputs signals from these multiple correction circuits and outputs a control rod withdrawal prevention signal to the control rod control device when a preset control rod prevention setting value is exceeded. A control rod withdrawal monitoring device characterized by comprising: