JPH0682587A - Control rod withdrawal monitor - Google Patents

Abstract

PURPOSE:To enhance safety in the decision of trip level by selecting intermediate values, respectively, from local output (LPRM) signals and reactor core flow rate signals detected through an average output region monitor (APRM) and employing the larger one of the LRRM signal and the smaller one of the reactor core flow rate signal in the decision for checking the withdrawal of control rod. CONSTITUTION:LPRM signals at selected positions A-D around a control rod are fed from APRM-A-D to an intermediate value selecting block 4 where two intermediate LPRM signals are selected from among four LPRM signals and thus selected LPRM signals are fed to a control rod withdrawal monitor (RBM) value selecting block 5. A larger LPRM signal is selected as an RBM value and fed to a trip level decision block 6. Similarly, a smaller reactor core flow rate signal is selected as a recirculation flow rate signal and three trip levels are set at a relatively low levels. When an RBM value is inputted depending on the selection of control rod, a decision is made whether a trip level is exceeded or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control rod withdrawal monitoring device (hereinafter referred to as "RBM") used in a nuclear power plant.

[0002]

2. Description of the Related Art Conventionally, an average value of local outputs around a control rod selected as a pulling target is obtained, and the average value is compared with a set value determined by a recirculation flow rate. RBM that outputs control rod pull-out prevention (rod block trip) signal to control rod drive control system
It has been known. In a nuclear power plant, this RBM
Thus, the control rod drive control system is controlled so that there is no fuel damage with respect to a local increase in power output of the core. Below, RB
The trip determination in M will be described using A-BWR (improved boiling water reactor) as an example.

First, in a general nuclear reactor, a large number of fuel rods are arranged in the nuclear reactor, a large number of control rods are evenly inserted between the fuel rods, and a plurality of (for example, four) neutrons are provided for each. The tubes containing the bundle detectors are evenly arranged. Further, four neutron flux detectors are arranged at different height positions A to D in each tube.

In the A-BWR system, as shown in FIG. 2, four APRM-A to APRM-D (average power range monitor) for monitoring the average power at different height positions (A to D) in the nuclear reactor. Is provided. APRM-A
Monitors the average power at the A position in the reactor by taking in the local output signal (LPRM signal) from each neutron flux detector located at the A position in each tube and further taking in the core flow rate signal. . Other APRM-B to APRM-
Similarly, for D, the LPRM signals at the corresponding height positions B to D are taken in, and the core flow rate signal is taken in to obtain the B in the reactor.
The average output in each region of -D is monitored.

Further, two RBMs 1 and 2 of A system and B system are provided, and each RBM 1 and 2 operates in the same manner. When a control rod is selected, the RBMs 1 and 2 of both the A system and the B system have respective height positions A to D around the selected control rod.
Each LPRM signal in the vicinity area is assigned to each APRM-A to
Extracted from APRM-D, A position and C of LPRM signal
Positional averaging (hereinafter referred to as "LPRM average value")
Is calculated, and the LPRM average value of the B position and the D position is calculated.

Then, the reactor average power (APRM value) obtained by the APRM is compared with the LPRM average value, and the APRM is calculated.
When the value <LPRM average value, the LPRM average value is used as the RBM value for trip determination. APRM value ≥ LPR
In the case of the M average value, the LPRM average value is gain adjusted (multiplied by the gain) to obtain APRM value = LPRM average value, and the value is set as the RBM value.

The APR to be compared with the LPRM average value
As the M value, the APRM value of APRM-A is used for the RBM1 of the A system, and the APRM value of APRM-D is used for the RBM2 of the B system.

If the APRM value to be compared is less than a certain value (usually a fixed value of 30%), "Comparison AP"
The “RM lower limit” condition is entered and the RBM is automatically bypassed. Therefore, if APRM-A is bypassed, A
The APRM outputs of PRM-B and APRM-D are to be compared.

On the other hand, in each RBM1 and 2, the recirculation flow rate signal is calculated as shown in FIG. That is, the core flow rate signal is taken in from each APRM-A to APRM-D, the average is taken, and the averaged value is used as the recirculation flow rate signal.

When the bypassed APRM exists, the average value of the core flow rate signals of the remaining APRMs is used as the recirculation flow rate signal. Further, the core flow rate signals are compared with each other, and when the difference exceeds a certain value (usually a fixed value of 10%), a control rod withdrawal prevention signal is output.

Each of the RBMs 1 and 2 multiplies the recirculation flow rate signal obtained as described above by inclining and applying a bias to calculate three trip levels associated with the flow rate as shown in FIG. The three trip levels consist of "level positive position" which is the threshold of the upper level alarm, "level intermediate" which is the threshold of the intermediate level alarm, and "level low" which is the threshold of the lower level alarm.

The RBMs 1 and 2 compare the above-mentioned RBM value with each trip level, and when the RBM value exceeds the trip level, output a control rod withdrawal inhibition signal to the control rod drive control system 3. There is.

However, the conventional RBM simply adds the LPRM signals from the APRM-A to APRM-D when calculating the LPRM average value. Therefore, AP
In the case where any one of the LPRM signals from the RM-A to APRM-D is shifted (A
If the abnormality does not reach the PRM unit abnormality, but the abnormality occurs due to some cause, etc.), the LPRM average value calculated by the RBM includes a large error. Especially when the LPRM signal is deviated to a lower level,
It is not preferable because the rod block is difficult to hang.

Further, when the recirculation flow rate signal is calculated by the RBM, since the core flow rate signals from the APRM-A to APRM-D are simply added as described above, the APRM is calculated.
If even one of the core flow rate signals from -A to APRM-D deviates, the calculated recirculation flow rate signal deviates significantly from the true value. Particularly, when the core flow rate signal is deviated to a higher level, the rod block becomes difficult to hang, which is not preferable.

[0015]

As described above, the conventional R
BM is LPRM from each APRM-A to APRM-D
Since the signal and the core flow rate signal were simply added to obtain the LPRM average value and the recirculation flow rate signal used for trip determination, when either APRM failed, the LPRM average value or the recirculation flow rate signal was changed from the true value. There is a possibility that the rod block will be greatly displaced and it will become difficult to hang the rod block.

Therefore, the present invention has been made in view of the above-mentioned circumstances, and L having a low reliability that deviates from the true value.
The PRM signal or core flow signal can be excluded from the calculation of the LPRM mean value or recirculation flow signal, and the safety side L
It is an object of the present invention to provide a control rod withdrawal monitoring device capable of making a trip determination using a PRM signal or a true furnace flow rate signal and having improved safety.

[0017]

In order to achieve the above object, the control rod pull-out monitoring apparatus of the present invention uses a local output signal around the control rod selected as a pull-out target as an average output at various places in the reactor. In the case of taking in from multiple average output area monitors, which are respectively shared, and performing pull-out prevention determination of the selected control rod by using each local output signal around the control rod that has been taken in, from each average output area monitor A plurality of intermediate-valued local output signals are selected from the acquired local output signals, and the larger local output signal is used for the extraction prevention determination.

Further, the control rod withdrawal monitoring device of the present invention is
Core flow rate signals are respectively captured from multiple average power range monitors that monitor the average output at each location in the reactor, and the recirculation flow rate signal is obtained from each of the captured core flow rate signals. In the determination of pulling out prevention of the control rod using the circulation flow rate signal, a plurality of intermediate value core flow rate signals are selected from among the core flow rate signals captured from the average output area monitors, and the smaller one of them is selected. The core flow rate signal is configured to be used for the withdrawal prevention determination.

[0019]

In the control rod pull-out monitoring device of the present invention, the local output signal around the selected control rod is taken in from each of the plurality of average output area monitors. Then, a plurality of intermediate-value local output signals are selected from the fetched local output signals, and the local output signals greatly deviated from the true value are excluded. Further, the larger local output signal is selected from the selected plurality of intermediate values, that is, the local output signal that is most likely to be applied by the rod block is selected from the intermediate values, and the pull-out prevention determination is performed.

Further, in the control rod pull-out monitoring device of the present invention,
A core flow rate signal is acquired from each average power range monitor. A plurality of intermediate-value core flow rate signals are selected from the taken-in core flow rate signals, and low-reliability signals that largely deviate from the true values are excluded. Then, the smaller core flow rate signal is selected as the recirculation flow rate signal from the selected plurality of intermediate values. That is, the core flow rate signal that is most likely to be applied to the rod block is selected from the intermediate values and used for the withdrawal prevention determination.

[0021]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 shows an RBM according to an embodiment of the present invention.
The functional blocks of are shown. Note that this embodiment is A
Although there are two systems of RBMs, a system and a system B, both have the same configuration and operate in the same manner, so only the system RBM will be described in detail.

The RBM of the present embodiment is the LPR at each of the positions A to D around the control rod selected as the extraction target.
The M signal is input to the intermediate value selection block 4 from each of the APRM-A to APRM-D. The intermediate value selection block 4 has a function of selecting two LPRM signals as intermediate values from the four LPRM signals input from APRM-A to APRM-D. This intermediate value selection block 4
The two LPRM signals of the intermediate value selected in step 1 are output to the RBM value selection block 5. RBM value selection block 5
Is the two LPRMs input from the intermediate value selection block 4.
It has a function of selecting the larger LPRM signal of the signals as the RBM value. Then, the RBM value selected by the RBM value selection block 5 is input to the trip level determination block 6.

The RBM of this embodiment is the above-mentioned APRM.
The core flow rate signals from -A to APRM-D are input to the flow rate signal intermediate value selection block 7. This flow signal intermediate value selection block 7 has a function of selecting two core flow signals of intermediate values from the core flow signals from APRM-A to APRM-D. The selected two core flow rate signals are further input to the recirculation flow rate signal selection block 8.
The recirculation flow rate signal selection block 8 selects the smaller core flow rate signal of the two core flow rate signals input from the flow rate signal intermediate value selection block 7 as the recirculation flow rate signal. The recirculation flow rate signal output from the recirculation flow rate signal selection block 8 is the trip level determination block 6
Entered in.

The trip level judgment block 6 calculates the above-mentioned three trip levels from the recirculation flow rate signal input from the recirculation flow rate signal selection block 8 and compares each trip level with the RBM value to make a trip. It has the function of making a judgment.

In the present embodiment configured as described above, when a control rod is selected, LPRM signals at positions A to D around the selected control rod are changed to APRM-A.
Input from APRM-D to the intermediate value selection block 4. Then, in the intermediate value selection block 4, two LPRM signals with intermediate values are selected from the four LPRM signals. Here, when the LPRM signal for one channel is largely deviated from the other LPRM signals due to some cause, although the APRM unit is not abnormal, the deviated LPRM signal
The two LPRM signals containing the signal will be excluded.

In this way, the two LPRM signals from which the LPRM signals that are largely deviated from the true value are reliably excluded are given to the RBM value selection block 5. This RBM
The value selection block 5 selects the larger LPRM signal of the two LPRM signals as the RBM value and outputs it to the trip level determination block 6.

Since the larger LPRM signal selected by the RBM value selection block 5 is closer to the trip level than the other LPRM signal, by setting the larger LPRM signal to the RBM value, it is possible to obtain 4 as in the conventional case. LPR
Compared with using the average value of the M signal for rod block trip determination, the system can be reliably operated in the direction in which the rod block is easily engaged.

On the other hand, each APRM-A to APRM-D is A
The core flow rate signal used to calculate each average power from position D to position D is the flow signal intermediate value selection block 7 of the RBM.
Entered in. In the flow rate signal intermediate value selection block 7, two intermediate flow rate signals having intermediate values are selected from the four input core flow rate signals.

As a result, even if one of the APRMs is abnormal and the core flow rate signal from that APRM deviates greatly from the true value, the core flow rate signal greatly deviated from the true value is included. Two core flow signals
It will be excluded from the determination of the recirculation flow signal.

Then, the two core flow rate signals selected by the flow rate signal intermediate value selection block 7 are input to the recirculation flow rate signal selection block 8, where the smaller core flow rate signal of the two core flow rate signals is recirculated. Selected as a flow signal.

Here, by determining the trip level using the smaller core flow rate signal, the trip level is set to a lower level, so that the system is easy to engage with the rod block.

The recirculation flow rate signal selected by the circulation flow rate signal selection block 8 is input to the trip level determination block 6, and three trip levels are set based on the recirculation flow rate signal. The trip level is set lower.

When the RBM value described above is input to the trip level judgment block 6 in which such a trip level is set in correspondence with the selection of the control rod, it is judged whether or not the RBM value exceeds the trip level, and the RBM value is exceeded. When the value exceeds the trip level, the control rod pull-out drive control system 3
A control rod pull-out prevention signal is output to.

According to the present embodiment as described above, since the intermediate value selection block 4 selects two LPRM signals having intermediate values, an abnormality occurs in a certain APRM and the APR is abnormal.
Even if the LPRM signal from M is largely deviated from other LPRM signals, the deviated LPRM signal can be excluded from the calculation of the RBM value. Therefore, even if a low-reliability LPRM signal that largely deviates from the true value is input, the trip determination can be performed based on the RBM value that does not include an error due to the low-reliability LPRM signal.

Further, since the larger LPRM signal of the two LPRM signals of the intermediate value selected by the intermediate value selection block 4 is set as the RBM value, as compared with the case of using the average value of the four LPRM signals, It is possible to have a system configuration in which the rod block is easily hooked.

Further, according to the present embodiment, the two intermediate flow rate core flow rate signals are selected by the flow rate signal intermediate value selection block 7, so that there is an APR error due to an APRM abnormality or the like.
Even if the core flow rate signal from M greatly deviates from other core flow rate signals, the deviated core flow rate signal can be excluded from the calculation of the recirculation flow rate signal. Therefore, even if an unreliable core flow rate signal that largely deviates from the true value is input, the trip level can be determined by the recirculation flow rate signal that does not include an error due to the unreliable signal.

Further, the smaller core flow rate signal of the two core flow rate signals selected in the flow rate signal intermediate value selection block 7 is selected as the recirculation flow rate signal to determine the trip level, so that the four core flow rates are determined. Since the trip level is set lower than the case where the trip level is determined by the recirculation flow rate signal obtained by adding and averaging the signals, the system configuration in which the rod block is easily engaged can be achieved.

In the above embodiment, the LPRM signal intermediate value selection block 4 and the flow signal intermediate value selection block 7 are composed of separate blocks, but both blocks are 4 blocks.
It suffices to have a function of selecting two intermediate-valued signals from one input signal, and thus a single block having such a function may also be configured to be used in common. The present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

[0040]

As described in detail above, according to the present invention, a low-reliability LPRM signal or core flow signal deviating from the true value can be excluded from the calculation of the LPRM average value or the recirculation flow signal. It is possible to always make a trip determination by using the LPRM signal or the true furnace flow rate signal on the safety side, and it is possible to provide a control rod withdrawal monitoring device with improved safety.

[Brief description of drawings]

FIG. 1 is a functional block diagram of a control rod pull-out monitoring device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an LPRM average value calculation function in a conventional control rod pull-out monitoring device.

FIG. 3 is a diagram showing a recirculation flow rate calculating function in a conventional control rod pull-out monitoring device.

FIG. 4 is a diagram showing a concept of setting a trip level in a conventional control rod pull-out monitoring device.

[Explanation of symbols]

4 ... LPRM signal intermediate value selection block, 5 ... RBM value selection block, 6 ... Trip level determination block, 7 ... Flow signal intermediate value selection block, 8 ... Recirculation flow rate selection block.

Claims (2)

[Claims] 1. A local output signal around a control rod selected as an extraction target is taken in from a plurality of average output area monitors which share and monitor the average output in each area in the height direction of the reactor, In a control rod pull-out monitoring device that performs pull-out prevention determination of the selected control rod by using each local output signal around the fetched control rod, in the local output signals fetched from each average output area monitor A control rod pull-out monitoring device, characterized in that a plurality of local output signals having different values are selected, and the larger local output signal is used for the pull-out prevention determination. 2. A core flow rate signal is respectively acquired from a plurality of average power range monitors which respectively monitor the average power in each range in the reactor, and a recirculation flow rate signal is obtained from each of the acquired core flow rate signals. In the control rod pull-out monitoring device that determines the pull-out prevention of the control rod by using the obtained recirculation flow rate signal, the core flow rate of the intermediate value from the core flow rate signals captured from the average output range monitors A control rod withdrawal monitoring device characterized in that a plurality of signals are selected and the smaller core flow rate signal is used for the withdrawal prevention determination.