JPH06258486A - Monitoring equipment of neutron flux in reactor - Google Patents

Abstract

PURPOSE:To obtain monitoring equipment of a neutron flux in a reactor which detects abnormality in the amount of the neutron flux in vibration modes of the same phase and a reverse phase of the neutron flux in a reactor core. CONSTITUTION:A plurality of local power region monitoring detectors 2 set dispersely inside a core, a dividing circuit 3 dividing the local power region detectors 2 into a plurality of groups so that a power average value of the local power region detectors 2 in each group may show an average power of the core as a whole, an average value calculating circuit 6 averaging output signals of the local power region monitoring detectors 2 for each group, and a disperse value computing circuit 7 determining a disperse value of each group, are provided. Moreover, a count circuit 21 counting the number of the local power region monitoring detectors 2 operating normally, a reference value storage circuit 8 storing reference values, and a comparing detecting circuit 9 comparing the average value, the disperse value and the number of the local power region monitoring detectors operating normally with the reference values and outputting signals to a reactor protecting system, are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-reactor neutron flux monitor for monitoring an abnormal change in in-reactor neutron flux of a boiling water reactor, and more particularly to a neutron flux oscillating locally in antiphase. And a neutron monitoring device in a nuclear reactor capable of detecting a fuel abnormality that occurs locally.

[0002]

2. Description of the Related Art Generally, in a boiling water reactor, a neutron flux that generates an alarm signal or a reactor scrum signal by detecting an abnormal change in the neutron flux in the reactor in order to prevent accidents such as fuel damage and nuclear runaway. A monitoring device is provided.

For example, during output operation, an average output area monitor (hereinafter referred to as APRM) is provided. This A
The PRM is composed of a plurality of channels, and each channel is, as shown in FIG.
The output signals So1 ... Son are all input to one average value calculation circuit 32, and the average value signal Sa obtained by simple average is input.
Is However, the number of LPRM signals of n: 1 channel is calculated by the equation of K: calibration coefficient.

The average value signal Sa is input to the recording indicator 33, the level high detection circuit 34 and the level lower limit detection circuit 35. On the other hand, a comparison value setting circuit 36 for storing a comparison value serving as a criterion for increasing or decreasing the neutron flux in the reactor is provided, and the comparison value signals Sb1 and Sb2 are input to the level high-high detection circuit 34 and the level low-limit detection circuit 35, and the average It is collated with the value signal Sa. When the average value signal Sa shows an abnormally high value or a low value with respect to the comparison value signals Sb1 and Sb2 as a result of the collation, the scrum signal Sc, the control rod withdrawal prevention signal Sd or the alarm from each of the detection circuits 34 and 35. A command signal such as the signal Se is issued.

Further, a counting circuit 37 for counting the number of LPRM detectors 31 operating normally in each APRM channel is provided, and the counting circuit 3 is provided.
The output signal Sf of No. 7 is input to the device inoperability detection circuit 38. Then, it is collated with the comparison value signal Sb3 which is the reference value of the normal LPRM detector 31 output from the comparison value setting circuit 36, and when the number of normal LPRM detectors is less than or equal to the comparison value, that is, Sf <Sb3, the function cannot operate. Therefore, the control rod withdrawal prevention signal Sa, the alarm signal Se, etc. are issued.

Therefore, if an accident or transient event occurs in the reactor and an increase in average neutron flux is detected, A
Based on the PRM signal, the reactor is safely scrammed, the increase of neutron flux in the core is suppressed, and the damage of fuel is prevented. In addition, even when the LPRM detector fails, the control rod is prevented from being pulled out or an alarm is issued.
Keep the reactor safe.

The APRM is usually provided with 6 to 8 channels, and the LPRM detectors 31 for each channel are evenly arranged in the core so that the neutron flux of the entire core can be monitored. 5 (a) and 5 (b) are LPRMs for one channel.
It is a figure showing an example of arrangement composition of detector 31 about a core cross section and a longitudinal section. FIG. 5 shows the planar arrangement positions of the LPRM detectors 31, and the symbols A to D attached to the planar arrangement positions of the LPRM detectors 31 are the heights in the core shown in FIG. 5 (b). Is shown.

[0008]

However, as described above, the LPRM detectors 31 are evenly arranged in the core.
A conventional neutron flux monitoring apparatus for in-reactor, which simply averages the output signal from each of the channels of the APRM, may not be able to detect the special vibration mode of the neutron flux.

That is, in general, the neutron flux distribution in the core during operation tends to be high in the central part and low in the peripheral part in the longitudinal cross section of the core, as indicated by the broken line 40 in FIG. The neutron flux distribution fluctuates with a normal output fluctuation, that is, the neutron flux oscillation tends to increase or decrease the in-phase neutron flux in the entire core, as shown by the solid lines 41 and 42 in FIG. The symbol a in the figure indicates the amplitude of the neutron flux.

If the vibration mode of the neutron flux is grasped as a time change of an arbitrary pair of LPRM output signals So1 and So2, the vibrations are in the same phase as shown in FIG. 8, and the vibration tendency is grasped by the simple average Sav. can do.

However, the oscillation phenomenon of the neutron flux in the core is not limited to the in-phase described above, but the distribution of the neutron flux is opposite to the right and left directions as shown by solid lines 43 and 44 in FIG. 7, for example. There are also cases where the phases are opposite to each other. In this case, an arbitrary pair of LPRM signals So1 ', So2'
Shows an amplitude a'of the opposite phase as shown in FIG. 9, and the output signal has a constant value in the simple average, and the fluctuation of the neutron flux in the core may be overlooked.

That is, in a phenomenon in which the neutron flux in the actual reactor core fluctuates due to a transient event or the like, it can be detected when the neutron flux vibrates in the same direction as the normal neutron flux distribution, that is, when it vibrates in the same phase. However, when the neutron flux locally oscillates in the opposite direction in the core, that is, when it oscillates in antiphase, the APRM output signal obtained by simple averaging the LPRM output signals has a constant value, and the oscillation phenomenon may not be detected. .

Further, if all the LPRM output signals are monitored at the same time, it is possible to detect vibrations in opposite phases. For example, a total of 172 LPRM detectors are installed in the core of a generator output of 1.1 million KWe class. Because it is done, 17
It is very difficult to monitor all two LPRM detectors at the same time.

Therefore, an object of the present invention is to solve such a problem, and to simultaneously and appropriately detect in-phase neutron flux oscillations and anti-phase neutron flux oscillations and to prevent fuel damage. It is to provide an in-core neutron flux monitoring device.

The existing LPR installed in the core
Since the M detector and the APRM are used, it is also an object to be able to solve the above problems with an extremely simple configuration.

[0016]

[Constitution of the invention]

[0017]

In order to solve the above problems, the in-reactor neutron flux monitoring apparatus according to the present invention is installed in a distributed manner inside the core of a nuclear reactor, and each detects the intensity of the neutron flux. A plurality of local output area monitor detectors, and the local output area monitor detectors at different positions are divided into the same group, and the output average value of the local output detectors in each group is represented so as to indicate the average output of the entire core. A division circuit for dividing the local output area detector into a plurality of groups, an average value calculation circuit for averaging the output signals of the local output area monitor detector grouped by the division circuit for each group, and the average value calculation A variance value calculation circuit for obtaining a variance value for each group from the average value of each group output from the circuit and the output signal of each local output area monitor detector belonging to each group, A counting circuit that counts the number of local output area monitor detectors that are always operating for each group, and stores the average value and dispersion value of the neutron flux and the reference value of the number of local output area monitor detectors that operate normally. A reference value storage circuit, a mean value by the mean value calculation circuit, a variance value by the variance value calculation circuit, and the number of local output area monitor detectors by the count circuit, compared with a reference value of the reference value storage circuit. However, it has a comparison detection circuit that outputs a signal to the reactor protection system when the average value or the dispersion value or the number of inoperable detectors exceeds the reference value.

[0018]

The neutron flux monitoring device in the reactor of the present invention is configured as described above, thereby increasing or decreasing the neutron flux of the entire core,
And all neutron flux oscillation modes can be detected. That is, regarding the increase or decrease of the neutron flux of the entire core, the average value of the LPRMs in the group obtained by dividing the LPRM detector arranged in the core into a plurality of groups indicates the output of the entire core, and thus the neutrons of the entire core Vibration of the neutron flux of the increase or the same phase of the flux is abnormal due to the output signal of the average value calculation circuit of the present invention, when the signal is input to the comparison detection circuit, the degree of increase, an alarm signal depending on the degree of vibration, Generates selection control rod insertion signal, scrum signal, etc.,
It is possible to prevent further increase of neutron flux and vibration. On the other hand, the neutron flux that oscillates in opposite phase can be identified as an anomaly by the signal of the dispersion value calculation circuit that calculates the dispersion value of each LPRM in the group and its average value Then, an alarm signal, a selective control rod insertion signal, a scrum signal or the like is generated depending on the degree of vibration, and further neutron flux vibration can be prevented. Moreover, the output signal of the LPRM detector is for directly detecting the increase and decrease and the vibration of the neutron flux, but the output signal may drift due to the leaf of the enclosed gas, etc., and there is a case where the true signal is not indicated. Only the output signal of the active LPRM detector should be used in the calculation. On the other hand, when the number of inoperable LPRM detectors exceeds the reference value, the comparison detection circuit can generate an alarm signal, a control rod blocking signal, etc. to prevent erroneous determination.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. This embodiment shows an in-core neutron flux monitor for a boiling water reactor. FIG. 1 shows a configuration diagram of each circuit of the in-reactor neutron flux monitoring apparatus 1 of the present embodiment.

A large number of LPRMs installed in the reactor core
The detector 2 is connected to the division circuit 3. Dividing circuit 3
Is a group designation circuit 4 and an in-core LPRM area division circuit 5
Consists of. The group designation circuit 4 is a circuit for designating the number of groups and combinations in the core region, and the LPRM detection is performed so that the intensity of the neutron flux detected by each divided group indicates the intensity of the neutron flux of the entire core. Vessel (N pieces) n
Specify to divide into groups. In-core LPR
The M region division circuit 5 outputs the output signal S from each LPRM detector 1 based on the designation signal Sp from the group designation circuit 4.
1… SN is divided into each designated group,
Group signal Sg1 each including N / n output signals
... Sgn is output.

The division circuit 3 uses the group signals Sg1 ... Sg.
It is connected to n average value calculation circuits 6 and variance value calculation circuits 7 corresponding to n. In this average value calculation circuit 6, the average value Sa1 of the N / n LPRM output signals in the group is ...
San is calculated by the following equation and output as a signal.

[0022] Here, K1: calibration coefficient Sak: average value of the kth group m: number of LPRM detectors of the kth group (= N /
n) In the variance value calculation circuit 7, the group signals Sg1 ... Sgn,
From the average value of Sa1 ... San output from the average value calculation circuit 6, the variance values Sσ ² 1 ... Sσ ² n of each group are calculated by the following equations and output as signals.

[0023] Where S σ ² k: variance value of k-th group Ski: i-th signal of LPRM detector of k-th group K1, K2: calibration coefficient m: number of LPRM detectors of k-th group Here, S σ ² as a variance value Although k 1 is calculated, in short, the variance value calculation circuit 7 only needs to calculate the deviation amount indicating the deviation from the average value.

On the other hand, comparison values α and β, which serve as criteria for determining increase and decrease of neutron flux and vibration, are set, and the comparison value signals Sα and S are set.
A reference value storage circuit 8 that outputs β is provided. The comparison value signal Sα is a reference value for the average value Sa of the LPRM signal, and the comparison value signal Sβ is a reference value for the variance value Sσ ² of the LPRM signal, each of which is determined based on actual plant data.

The signal output from the average value calculation circuit 6 is input to the average output detection circuit 10 in the comparison detection circuit 9,
The reference value signal Sα output from the reference value storage circuit 8 is compared and collated. When the neutron flux in the reactor increases as a whole or oscillates in the same phase as shown in FIG. 2, the average value calculation circuit 6
Output signal Sa1 ... San increases and Sai> Sα with respect to the comparison value signal Sa, and it is determined that the fluctuation of the neutron flux is abnormal. Here, Sai indicates the average value of the i-th group.

The comparison value α which gives the comparison value signal Sα is defined as α1, α2 ... According to the degree of increase of the neutron flux, and Sa
1 ... If the San signal exceeds each comparison value α, the warning signal 11, the scrum signal 12, the selection control rod insertion signal 13 and the like are instructed to the reactor protection system according to each step.

Here, FIG. 2 shows a case where the neutron flux oscillates in the same phase, the horizontal axis represents the distance from the center of the core of the nuclear reactor, and the vertical axis represents the amount of neutron flux. In the case shown in FIG. 2, the amount of neutron flux fluctuates in the same phase throughout the reactor core according to the output of the reactor. The solid lines 15 and 16 show the amounts of high-level and low-level neutron flux, respectively, and the broken line 17 shows the average value thereof.

Next, the output signal Sσ ² 1 of the variance value calculation circuit 7
... S σ ² n is the local output detection circuit 1 in the comparison detection circuit 9.
4 and is compared and collated with the reference signal Sβ output from the reference value storage circuit 8. When the neutron flux in the reactor oscillates in the opposite phase where the increase and decrease of neutrons are locally reversed as shown in FIG. 3, the output signal Sσ ² 1 ... Sσ of the dispersion value calculation circuit
^{When 2} n increases and Sσ ² n> Sβ, the fluctuation of the neutron flux is determined to be abnormal. Comparison value β giving comparison value signal Sβ
Is defined as β 1, β 2 ... According to the degree of increase of neutron flux, and if Sσ ² 1 ... Sσ ² n exceeds each comparison value, an alarm signal 11, a scrum signal 12, a selection control rod insertion signal are obtained according to each step. 13 and other commands to the reactor protection system.

Here, FIG. 3 shows the case where the neutron flux oscillates in the opposite phase with respect to the center of the core, the horizontal axis represents the distance from the center of the reactor core, and the vertical axis represents the neutron flux. The amount is shown. FIG. 3 shows a case where the reaction of the fuel is locally biased during the transition period of the output of the nuclear reactor and the amount of neutron flux is large on one side of the core and small on the other side. Solid line 1
Reference numerals 8 and 19 represent neutron flux quantities that oscillate in opposite phases with respect to the core center, and a broken line 20 represents an average value of the neutron flux quantities. It varies in the same phase throughout the reactor core with respect to the average value. The solid lines 15 and 16 show the amounts of high-level and low-level neutron flux, respectively, and the broken line 17 shows the average value thereof.

It is assumed that the LPRM detectors 2 in each group divided into areas by the dividing circuit 3 are operating normally, and if there is a signal from the defective LPRM detector 1, average value calculation and dispersion calculation are performed. Need to be excluded from.

The counting circuit 21 counts the number of LPRM detectors 1 which are operating normally and outputs the signal SQ.
Is output to the average value calculation circuit 6 and the variance value calculation circuit 7, and the signal of the LPRM detector 1 used for the calculation is only the signal from the normal detector.

The reference value Sγ output from the reference value storage circuit 8 is an allowable value for the number of inoperable LPRM detectors 1 and is connected to the inoperable detection circuit 22. The reference value Sγ is compared with the output signal SQ of the counting circuit 21, and if it exceeds the reference value Sγ, it is determined that the function cannot be operated, and the alarm signal 11, the scrum signal 12, the control rod withdrawal prevention signal 13 and the like are issued.

According to the in-reactor neutron flux monitoring apparatus shown in the above embodiments, it is possible to detect a local increase in neutron flux and vibration of an antiphase neutron flux which cannot be detected by the simple average of the conventional LPRM detection signal. Highly accurate neutron flux monitoring is possible. Further, since the existing LPRM detector can be used as it is, the equipment can be used rationally. Furthermore, it is needless to say that the present invention can be applied to various reactors other than boiling water reactors.

[0034]

As is apparent from the above description, the neutron flux monitoring apparatus in the present invention has a plurality of LPRM detectors distributed in the reactor and a dividing circuit for dividing the LPRM detectors into groups. And an average value calculation circuit for calculating the average value of the LPRM signals of each group, and the LPR of each group
A dispersion value calculation circuit for calculating a dispersion value of the M signal, a count circuit which operates normally, a reference value storage circuit for storing a reference value for each output value, and a comparison detection circuit for comparing the output value with the reference value are provided. Since it has, the detectors in the reactor are divided into a plurality of groups, the average value of the signal of each detector and its dispersion value are obtained, and by comparison with a predetermined reference value, the increase or decrease of the neutron flux and the vibration Anomalies can be detected, vibrations of antiphase neutron flux that could not be detected in the past can be easily detected, neutron flux in the reactor can be monitored with higher accuracy, and fuel damage can be prevented. . In addition, the neutron flux monitoring apparatus of the present invention can reasonably utilize existing equipment by utilizing the existing LPRM detector.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a neutron flux monitoring device in a nuclear reactor of the present invention.

FIG. 2 is a diagram showing an in-phase vibration mode of a neutron flux.

FIG. 3 is a diagram showing an antiphase vibration mode of a neutron flux.

FIG. 4 is a diagram showing a configuration of a conventional neutron flux monitoring device in a nuclear reactor.

FIG. 5 is a view showing vertical and radial arrangement positions of a local output area monitor detector.

FIG. 6 is a diagram showing in-phase vibration modes of neutron flux.

FIG. 7 is a diagram showing an antiphase vibration mode of a neutron flux.

FIG. 8 is an explanatory diagram showing the operation of a conventional neutron flux monitoring device in a nuclear reactor with respect to the in-phase oscillation mode of neutron flux.

FIG. 9 is an explanatory view showing the action of the conventional neutron flux monitoring device in a nuclear reactor with respect to the antiphase oscillation mode of neutron flux.

[Explanation of symbols]

 1 in-reactor neutron flux monitor 2 LPRM detector 3 division circuit 4 group designation circuit 5 in-core LPRM region division circuit 6 average value calculation circuit 7 variance value calculation circuit 8 reference value storage circuit 9 comparison detection circuit 10 average output detection circuit 14 local output detection circuit 21 count circuit 22 inoperability detection circuit

Claims (1)

[Claims] 1. A plurality of local output area monitor detectors, which are installed in a distributed manner inside the core of a nuclear reactor and detect the intensity of neutron flux, respectively, and the local output area monitor detectors at different positions are in the same group. And a division circuit that divides the local power area detector into a plurality of groups so that the average output value of the local output detectors of each group indicates the average output of the entire core, and the division circuit is divided into groups. An average value calculation circuit for averaging the output signals of the local output area monitor detector for each group, an average value for each group output from the average value calculation circuit, and an individual local output area monitor detector belonging to each group A variance value calculation circuit that obtains the variance value for each group from the output signal of the, and a counter that counts the number of normally operating local output area monitor detectors for each group. Circuit, a reference value storage circuit that stores the average value and the dispersion value of the neutron flux, and the reference value of the number of local output area monitor detectors that operate normally, and the average value and the dispersion value by the average value calculation circuit. The variance value by the value calculation circuit and the number of local output area monitor detectors by the count circuit are compared with the reference value of the reference value storage circuit, and the average value or variance value or the number of inoperable detectors exceeds the reference value. And a comparison detection circuit that outputs a signal to the reactor protection system in the event of a failure.