JPH0216478B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a control rod withdrawal monitoring method that monitors local output around a control rod to be withdrawn, and prevents withdrawal of the control rod when this output exceeds a predetermined set value. Regarding.

Generally, in a boiling water reactor, as shown in FIG. As shown in the figure, a reactor core 4 is arranged in a lattice shape and has a planar shape close to a circle.As shown in FIG.
is housed within. In addition, one square in FIG. 2 represents one fuel assembly 2, and each large white circle represents a control rod 1. In addition, such a core 4
There are a number of output range neutron detectors 5a..., 5b inside.
... (hereinafter referred to as LPRM detector) is provided. Note that this LPRM detector is shown as a small white or black circle in FIGS. 2 and 3. These LPRM detectors 5a...5b...
As shown in the figure, every two unit grids 3, that is, every two control rods, are arranged in a grid pattern, and as shown in FIG. It is being and these
Outputs from the LPRM detectors 5a..., 5b are processed by an average power monitor system (APRM) to detect the average power of the entire reactor core 4, and a local power monitor system (LPRM) to detect local power. When the control rod 1... is withdrawn, the local output around it is monitored, and if the local output exceeds the predetermined control rod withdrawal prevention setting value due to inappropriate withdrawal of the control rod 1... control rod withdrawal monitoring device 6 that prevents the control rod 1 from being withdrawn to ensure the integrity of the reactor if the control rod 1 is withdrawn;
is provided. For example, when the control rod 1' at the shaded position in FIG. A group of 16 LPRM detectors 5a..., 5b... are selected,
This group of LPRM detectors 5a, 5b, . . . constitutes a local output monitoring system that monitors the local output around the control rod 1'. Note that this designated control rod 1' and a group of LPRM detectors 5a..., 5b...
Fig. 4 shows the arrangement relationship with . Then, this group of LPRM detectors is further divided into a plurality of systems, for example, half each into two systems. In addition, Figures 2 to 4
Belongs to one system in the diagram (hereinafter referred to as A system)
LPRM detectors 5a... are white circles, and LPRM detectors 5b... which belong to the other system (hereinafter referred to as B system)...
is indicated by a black circle. And these LPRM detectors 5a
The average value of the output of ..., 5b... is determined for each system A and B, and if the average value of either system A or B exceeds a preset control rod withdrawal prevention setting value, the control rod will be withdrawn. A withdrawal prevention signal is sent from the monitoring device 6 to the control rod control device 7, and a signal is sent from the control rod control device 7 to the control rod drive mechanism 8 of the control rod 1 to prevent the withdrawal of the control rod 1. is configured to do so. In addition, this control rod withdrawal monitoring device 6 detects when an abnormality occurs in the LPRM detectors 5a..., 5b...
5b... is excluded or bypassed and the remaining
The average value of the outputs of the LPRM detectors 5a..., 5b... is calculated, and if an abnormality occurs in the entire A system or B system, the entire system in which the abnormality has occurred is excluded, or bypassed, and the remaining systems are monitored. It is designed to improve reliability. However, the distribution of neutron flux or power within the reactor core 4 is not uniform; for example, if the control rod 1' is pulled out halfway,
The output increases locally in the portion above the upper end of the control rod 1', and the output distribution also changes in the horizontal direction. Therefore, the changes in the signal output of each of the LPRM detectors 5a, 5b, etc. with respect to the amount of withdrawal of the control rod 1' are different. Therefore, the characteristics of the signal output with respect to the amount of control rod 1' withdrawn are different between the A system and the B system. For example, in the A system, the curve shown in Fig. 5a is
a ₁ , the B system has a characteristic as shown in the curve b ₁ in Figure 5b, and when the control rod 1' is gradually withdrawn, for example, the signal output of the B system reaches the control rod withdrawal prevention setting value L _B first. reach. Usually, the signals of this system with good response (system B in this example) are prioritized and monitored. Therefore, if the A system with poor responsiveness is bypassed, there will be no effect on the overall characteristics of the control rod withdrawal monitoring device 6, but if the B system with good responsiveness is bypassed, the A system with poor responsiveness will not be affected. Since monitoring is performed based on system signals, the control rod withdrawal monitoring device 6
The overall responsiveness deteriorated, which was unfavorable in terms of maintaining the integrity of the fuel. Also,
Although there is no bypass for the entire system, the responsiveness is extremely good.
If some of the LPRM detectors 5a..., 5b... are bypassed, the remaining LPRM detectors 5a...,
Since the outputs of 5b... are averaged, the response of system A or system B decreases as shown by curves a ₂ and b ₂ in Figure 5 a and b, and the response of the control rod withdrawal monitoring device 6 as a whole decreases. descend. In other words, the prevention of control rod withdrawal is delayed. Also, conversely, the least responsive
When the LPRM detectors 5a..., 5b... are bypassed, the responsiveness of system A or system B improves,
The overall responsiveness of the control rod withdrawal monitoring device 6 is improved.
Therefore, the system or LPRM detector 5a...,
5b... is bypassed, which system was bypassed or which LPRM detector 5a...,
Depending on whether or not the control rods 5b... are bypassed, the responsiveness of the control rod withdrawal monitoring device 6 changes, and the position at which the control rods 1'... are prevented from being withdrawn changes, resulting in a malfunction that impairs operational stability. Ta. For this reason, conventionally, for example, as shown in Fig. 4, it belongs to the A system.
Two LPRM detectors 5a... and two LPRM detectors 5b... belonging to the B system are arranged at diagonal positions in each stage,
And for each adjacent stage, these LPRM detectors 5a...,
5b... are arranged so that they are shifted by 90 degrees so that the uneven output distribution affects both systems as equally as possible, reducing the difference in response between systems A and B and improving stability. Although it is being done,
If the LPRM detector was bypassed, the instability of the system's response could not be prevented.

The present invention has been made based on the above circumstances, and its purpose is to provide a control rod that can reduce changes in response when the LPRM detector is bypassed and improve response stability. The purpose is to obtain a withdrawal monitoring method.

The present invention will be explained below with reference to an embodiment shown in FIGS. 6 to 10. Reference numeral 101 in FIG. 6 is a control rod, and four fuel assemblies 102 are arranged around the control rod 101 as shown in FIG. 6, forming a unit grid 103. These unit lattices 103 are arranged in a lattice pattern to form a core 104 whose planar shape is nearly circular as shown in FIG.
is housed within the reactor pressure vessel 105. Note that each square in Fig. 7 represents one fuel assembly 102...
, and large white circles indicate control rods 101... Inside this core 104 are power range neutron detectors 106a..., 106b... (hereinafter LPRM).
(referred to as a detector) is provided. These LPRM detectors 106a..., 106b..., as shown in FIG.
03, and at each of these two-dimensional positions, four stages are provided in the vertical direction, that is, in the insertion and withdrawal direction of the control rods 101, as shown in FIG. Note that these in Figures 7 and 8
LPRM detectors 5106a..., 106b... are indicated by small white or black circles. In addition, each of the control rods 1
Control rod drive mechanisms 107... are provided for each control rod drive mechanism 107..., and each control rod 101... is configured to be inserted and withdrawn by these control rod drive mechanisms 107.... These control rod drive mechanisms 107 are configured to be controlled by a control rod control device 108. And the above LPRM
The detectors 106a..., 106b... are configured to detect a local neutron flux, that is, a local output, within the reactor core 104, and output a signal corresponding to this. These LPRM detectors 106a..., 1
The signal from 06b... is the control rod withdrawal monitoring device 109
is configured to be sent to. This control rod withdrawal monitoring device 109 detects the local output around the operated control rod 101 when the control rod 101 is withdrawn, and detects the local output around the control rod 101 when the control rod 101 is withdrawn inappropriately. This system prevents the control rod 101 from being withdrawn when the output locally exceeds the control rod withdrawal prevention setting value, thereby maintaining the integrity of the fuel.The configuration thereof will be explained below with reference to FIG. 10. do. 1 in the diagram
Reference numeral 10 denotes a selection circuit, which is configured so that signals S _{1 . .} . from the respective LPRM detectors 106a . . . , 106b . The selection circuit 110 is also configured to receive a control rod designation signal S ₂ from the control rod control device 108 that designates the control rods 101 to be extracted. In this selection circuit 110, a group of LPRM detectors 106 surrounding the designated control rod 101...
a..., 106b... is configured to be selected. Therefore, for example, if the control rod 101' shown with diagonal lines in FIG.
The LPRM detectors 106a..., 106b... are configured to be selected. In addition, in this case, a group of
The relationship between the LPRM detectors 106a..., 106b... and the control rod 101' is shown in a perspective view in FIG. Further, in this selection circuit 110, the above-mentioned group of LPRM detectors 106a..., 106b... are connected to a plurality of systems, for example, two
The system is divided into the same number of systems, that is, eight. In addition,
In FIGS. 7 to 9, the LPRM detectors 106a belonging to one system (hereinafter referred to as A system) are indicated by white circles.
LPRM detectors 106b belonging to the other system (hereinafter referred to as B system) are indicated by black circles. And the LPRM detector 106a belonging to the A system and the B system
Two LPRM detectors 106b... are arranged in each stage, and the LPRM detectors 106a..., 106b... belonging to the same system are arranged diagonally to each other, and this arrangement is arranged at an angle of 90° between adjacent stages. They are placed staggered. Note that the control rod 101'
When a control rod 101 placed in the central part of the core 104 is specified, a total of 16 LPRM detectors 10 in four stages surround it as described above.
6a..., 106b... are selected,
Control rods 101 arranged around the core 104
If ... is specified, the total of the 3 surrounding 4 rows
A group of 8 LPRMs in total of 12 or 4 stages of 2
Detectors 106a..., 106b... are selected. This selection circuit 110 belongs to the A system.
The signals from the LPRM detectors 106a... are sent to the A-system averaging circuit 111a, and the LPRM detectors belonging to the B-system
The signals from the detectors 106b... are sent to the B-system averaging circuit 11.
1b. These A-system average circuit 111a and B-system average circuit 111
b is the A-system and B-system LPRM detector 106a...,
The signal outputs of the signals 106b, . . . are averaged to calculate the average value. For example, average circuit 1 of A system
The output of 11a is sent to the A system gain adjustment circuit 112a, and the signal from the A system of the average power monitor system (APRM) described above, that is, the average output signal Sa of the reactor core 104 is input to this A system gain adjustment circuit 112a. It is configured as follows. In the A-system gain adjustment circuit 112a, the average output signal Sa
and the signal output from the A-system averaging circuit 111a, and if the level of the average output signal Sa is higher, the average output signal Sa is adjusted so that the levels of both signals match in the normal operating state of the furnace.
In the case of 100%, the gain is constantly corrected so that the signal level from the A-system averaging circuit 111a is also 100%, and when the signal output from the A-system averaging circuit 111a is larger than the average output signal Sa. teeth,
The signal output from the A-system averaging circuit 111a is directly output from the A-system gain adjustment circuit 112a. and A system gain adjustment circuit 1
The signal output from 12a is sent to an A-system correction circuit 113a, which will be described later, to be corrected and further sent to an A-system switching circuit 114a. In the A system switching circuit 114a, the circuit is disconnected when the control rod is selected, and when control rod withdrawal starts, the circuit is connected by the control rod withdrawal signal _S3 .
It is configured such that the signal output of the system correction circuit 113a is sent to the A system signal selection circuit 115a. On the other hand, the signal output from the A system gain adjustment circuit 112a is A
It is also sent to the system memory holding circuit 116a. In the A-system memory holding circuit 116a, the A-system gain adjustment circuit 112
The signal output of signal a is stored and further sent to the A-system signal selection circuit 115a. The A-system signal selection circuit 115a selects the signal output of the A-system correction circuit 113a sent via the A-system switching circuit 114a and the A-system memory holding circuit 11.
6a are compared, and the larger signal is selected and sent to the A-system determination circuit 117a. Also, the signal output of the B-system average circuit 111b is similar to that of the A-system, and the B-system gain adjustment circuit 111
2b adjusts the gain. B system gain adjustment circuit 1
The signal output of 12b is the same as the A system, the B system correction circuit 1
13b and the B-system memory holding circuit 116b.
The signal output corrected by the B system correction circuit 113b is B
The signal is sent to the system switching circuit 114b, and in the B system switching circuit 114b, like the A system, the circuit is disconnected when the control rod is selected, and when control rod withdrawal starts, the circuit is connected by the control rod withdrawal signal _S3 .
The signal output of the B-system correction circuit 113b is configured to be sent to the B-system signal selection circuit 115b. On the other hand, the signal output of the B-system memory holding circuit 116b is also sent to the B-system signal selection circuit 115b in the same way as the A-system signal, and in the B-system signal selection circuit 115b, the signal output is sent to the B-system correction circuit 11 via the B-system switching circuit 114b.
3b and the signal output of the B-system storage holding circuit 116b are compared, and the larger signal is selected and sent to the B-system determination circuit 117b. These A-system determination circuit 117a and B-system determination circuit 117b use signals from the A-system signal selection circuit 115a and B-system signal selection circuit 115b and a preset control rod withdrawal prevention setting value L _B (normally 105 % to 107%), and if the signal level from the A-system signal selection circuit 115a or the B-system signal selection circuit 115b exceeds this control rod withdrawal prevention set value L _B , a withdrawal prevention signal is generated. _S4 is sent to the control rod control device 108, and is configured to prevent the control rods 101 from being withdrawn.

Note that the A-system averaging circuit 111a and the B-system averaging circuit 111b are connected to the bypassed LPRM detectors 106a..., 106b, if any.
The signals from the LPRM detectors 106a..., 106b... are excluded, and the remaining LPRM detectors 106a...,
The average value of the signals 106b, . . . is determined. Further, 118 is a circuit for determining the number of bypasses, and each circuit outputted from the selection circuit 110 is
LPRM that receives signals from the LPRM detectors 106a..., 106b... and is bypassed for each system
It is configured to detect the number of detectors 106a..., 106b... or a bypassed system. The signal from the bypass number determining circuit 118 is configured to be sent to the A-system correction circuit 113a and the B-system correction circuit 113b. And these A system correction circuits 113a and B
In the system correction circuit 113b, the bypass number determination circuit 1
Based on the signal from the A-system gain adjustment circuit 112a and the B-system gain adjustment circuit 112b, the following corrections are made to the signals from the A-system gain adjustment circuit 112a and the B-system gain adjustment circuit 112b. That is, first, a group of LPRM detectors 106 selected regardless of A system or B system.
If none of the signals a..., 106b... are bypassed, that is, in a normal state, the signal is not modified. Next, a group of LPRM detectors 106a...,
106b...If one or more of the self-systems are bypassed or other systems are bypassed, the constant C in the signals from the A-system gain adjustment circuit 112a and the B-system gain adjustment circuit 112b.
It is configured to multiply.

In one embodiment of the present invention configured as described above, the control rod 101 to be pulled out...for example, the control rod 10
1' is specified, the selection circuit 110 selects a group of 16 LPRM detectors 106a..., 106b... in total of 4 stages and 4 stages surrounding this control rod 101', and furthermore, this group of LPRM detectors 106a..., 106b... 106
a..., 106b... are divided into A system and B system. And these LPRM detectors 106a...,1
The signal from 06b... is A for each A system and B system.
System average circuit 111a and B system average circuit 111b
These average values are compared with the average output signals Sa and Sb in the A-system gain adjustment circuit 112a and the B-system gain adjustment circuit 112b, respectively, and when they are smaller than the average output signals Sa and Sb, the average output signal Sa , Sb is adjusted. When selecting a control rod, the A-system gain adjustment circuit 112a and the B-system gain adjustment circuit 112
The signal outputs of b are each sent to the A-system memory holding circuit 116.
A-system signal selection circuit 115a and B-system signal selection circuit 1 via a and B-system memory holding circuit 116b.
15b, and are further sent to the A-system determination circuit 1.
17a and B-system determination circuit 117b to monitor the local output around the selected control rod 101'. Furthermore, when control rod withdrawal is started, the signal outputs of the A-system gain adjustment circuit 112a and the B-system gain adjustment circuit 112b are changed to the A-system correction circuit 1, respectively.
13a and B system correction circuit 113b,
The A-system signal selection circuit 1 passes through the A-system switching circuit 114a and the B-system switching circuit 114b.
15a and B-system signal selection circuit 115b, and further sent to A-system determination circuit 117a and B-system determination circuit 117b, respectively, to monitor the local output around the control rod 101' being pulled out.
When the local output around the control rod 101' increases excessively due to improper withdrawal of the control rod 101', the input signals of the A system determination circuit 117a and the B system determination circuit 117b increase, and these input signals set the control rod withdrawal prevention setting. When the value L _B is exceeded, a withdrawal prevention signal is output, preventing withdrawal of the control rod 101' and ensuring the integrity of the fuel. The signals sent to the A-system determination circuit 117a and the B-system determination circuit 117b are sent to the A-system gain adjustment circuit 1, which determines when the control rod 101' is withdrawn.
12a and the B system gain adjustment circuit 112b, the responsiveness of the control rod withdrawal monitoring device 109 as a whole can be improved even if a bypass occurs in the system with better response. Deterioration is reduced. In addition, if the aforementioned modifications are made,
Since the signal that should be compared with the control rod withdrawal prevention setting value L _B in the A system judgment circuit and the B system judgment circuit is already at a high value at the time of control rod selection, the control rod withdrawal prevention may be prevented due to signal noise. Although it may happen in the past, since the A-system switching circuit and B-system switching circuit are configured to bypass the above-mentioned modification when selecting control rods, it is possible to withdraw at least one notch of control rods. . The reason will be explained below. Curve a in Figure 11 is
An example of the relationship between the amount of control rod withdrawal and the output signal of the gain adjustment circuit when the LPRM detector or other system is bypassed is shown. Further, curve b is obtained by adding the above-mentioned modification to the signal value shown by curve a. In this example, the constant C used for correction is 1.035,
L _B is a control rod withdrawal prevention setting value, which is set at 105. Normal signal noise is about 1-2%,
If the above-mentioned modification is also performed when selecting a control rod, there is a possibility that noise will prevent the control rod from being pulled out. In the present invention, when selecting a control rod, the signal is not corrected even if the LPRM detector or other system is bypassed, but the signal is corrected after starting control rod withdrawal. Blocking set value L _B
The signal to be compared with the control rod is as shown by the solid line in FIG. 11. Blocking of control rod withdrawal due to signal noise at the time of control rod selection is avoided, and the signal is corrected when control rod withdrawal is started. Therefore, conventionally, the control rod withdrawal prevention signal was issued at the position Ba, but with the modification of the present invention, the control rod withdrawal prevention signal is issued at the position Bb, which is earlier than before.

As mentioned above, the signal modification of the present invention can be used to compensate for the delay in preventing control rod withdrawal that occurs when a responsive LPRM detector or system is bypassed, and the signal modification is performed during control rod selection. Since there is no control rod, the control rod can be pulled out by at least one notch, there is no problem in terms of operability, and the reliability and stability of the operation of the control rod withdrawal monitoring system as a whole can be greatly improved. etc. The effect is great.

[Brief explanation of drawings]

Figures 1 to 4 show conventional examples, with Figure 1 being a plan view of the unit cell, Figure 2 being a plan view of the core, and Figure 3 being a plan view of the core.
The figure is a schematic configuration diagram, and FIG. 4 is a schematic perspective view showing the arrangement of control rods and LPRM detectors. FIG. 5 is a diagram showing the characteristics of the conventional example. 6 to 10 show one embodiment of the present invention, FIG. 6 is a plan view of a unit cell, FIG. 7 is a plan view of the core, FIG. 8 is a schematic configuration diagram, and FIG. 9 is a control rod. FIG. 10 is a block diagram of a control rod withdrawal monitoring device, and FIG. 11 is a diagram showing characteristics of a conventional example and an embodiment of the present invention. 101, 101'...control rod, 102...fuel assembly, 104...core, 106a, 106b...
...LPRM detector, 108...control rod control device,
109... Control rod withdrawal monitoring device, 110... Selection circuit, 111a, 111b... Average circuit, 113
a, 113b...correction circuit, 114a, 114b
...Switching circuit, 115a, 115b...
Signal selection circuit, 116a, 116b... Memory holding circuit, 117a, 117b... Judgment circuit, 118
...Bypass number judgment circuit.

Claims (1)

[Claims] 1. Select a group of output range neutron detectors surrounding a control rod designated for withdrawal operation, divide this selected group of output range neutron detectors into a plurality of systems, and detect abnormalities. Bypass the above output range neutron detector and the above system, calculate the average value of the output of the above output range neutron detector for each system, and determine whether one of these average values for each system is the control rod withdrawal prevention setting value. In the control rod withdrawal monitoring method that prevents control rod withdrawal if the power exceeds the limit, if there is a bypassed power range neutron detector or if there is a bypassed system, the control rod is prevented from being withdrawn. amplifying the average value of said power range neutron detector after receiving a signal indicating the start of operation, regardless of whether there is said power range neutron detector being bypassed or said system being bypassed; First, a control rod withdrawal monitoring method characterized in that the amplification is not performed before receiving the signal.