JP3274166B2 - Monitoring device for neutron detector output - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a neutron detector output monitoring device for monitoring an AC output in an ionization chamber type neutron detector.

[0002]

2. Description of the Related Art Ionization chamber neutron detectors are known.
It consists of a pair of electrically insulated electrodes, a neutron reactant and an ionizing gas disposed between them.
For example, in the case of fission chamber, the neutron reactant is using fission by neutrons are possible uranium or the like, when a neutron is incident into the ionization chamber, uranium and fission, by the fission fragments Ionizes ionizable gas. This ionization amount is collected by applying a voltage between the electrodes of the ionization chamber, and an output current proportional to the ionization amount, that is, the neutron flux in the ionization chamber is generated.

In order to obtain a neutron flux by measuring the output of the ionization chamber, a pulse measurement for counting current pulses generated at each fission, a direct current measurement (DC signal) obtained by measuring an average current flowing through the ionization chamber, ), Or an AC measurement (MSV measurement) obtained by measuring a root-mean-square AC in an ionization chamber in an appropriate frequency range.

In general, in a boiling water reactor, the neutron flux in the power region of the reactor is measured by a direct current. When the reactor is started, pulse measurement is performed at a low neutron flux level, and high neutrons up to the power region are measured. At the bundle level, AC measurement is adopted. As for the AC measurement, the output of the neutron detector 1 is input to the signal input device 2 to perform signal amplification and noise removal, as shown in the block diagram of FIG.

Next, the output AC signal is passed through a band-pass filter 3 (band-pass filter) in order to restrict the AC signal to a certain frequency band, and a root-mean-square circuit 4 outputs a root-mean-square output voltage ( MSV output).
Here, the frequency band of the output of the neutron detector is, as shown in the frequency band characteristic diagram of FIG. 7, the output component of the neutron detector can be formed by the movement of particles having different electrons and ions as shown by the solid characteristic curve 5. , Low frequency band 6 (for example, 0-10
kHz) and a high frequency band 7 (for example, 1 kHz to 1 MHz).

That is, in the output in the low frequency band 6, the neutron detector output component per unit frequency is larger than that in the high frequency band 7. Therefore, when an almost constant noise component (white noise) indicated by the characteristic curve 8 is added in the entire frequency band, it is better to use the output signal in the low frequency band 6 by the low frequency band pass filter 9.
Compared to using the output signal in the high frequency band 7, the ratio between the neutron detector output component and the noise component (hereinafter referred to as the S / N ratio) is improved by an amount corresponding to the larger output of the neutron detector (MSV output).

However, in this case, since a low frequency is used, the response of the output signal is reduced as compared with the case where the output signal of the high frequency band 7 by the high frequency bandpass filter 10 is used. Therefore, when AC measurement (MSV measurement) is applied to a safety protection system of a nuclear reactor or the like, a signal such as a signal (trip signal) for urgently shutting down the reactor is required to have a quick response signal. In the frequency band of the band-pass filter 3 in the conventional embodiment shown in FIG. 7, seven signals in a high frequency band are selected and processed as shown in a band-pass filter 10 shown in FIG.

[0008]

In a system that requires a fast response, only a high frequency band is used.
The S / N ratio of the obtained signal becomes worse. In addition, since the lower limit of the neutron flux measurement range of the AC measurement is determined by the S / N ratio, there is a problem that the measurement lower limit is increased and the neutron measurement range is narrowed. Conventionally, since an analog band-pass filter 3 is used for this band limitation,
The configuration of the band-pass filter 3 becomes complicated, only the frequency band of 1 or 2 can be divided, and signals other than those in the frequency band set by the band-pass filter 3 are excluded.

In the frequency band selected for this purpose,
If the frequency band of noise (external noise) that has entered from outside the device matches, an erroneous signal may be generated. In particular,
In a system requiring a quick signal response as described above, for example, a safety protection system of a nuclear reactor, the S in the measurement frequency band is required.
From the viewpoint of preventing malfunction due to poor / N ratio, there has been a demand for a monitoring device for a neutron detector output which is more excellent in noise resistance.

[0010] It is an object of the present invention is to digitize the neutron detector output is divided into three or more frequency bands, the frequency band including the noise by identifying exclusion, Roh Lee <br/>'s It is an object of the present invention to provide a monitoring device for a neutron detector output with less influence.

[0011]

According to the present invention, there is provided a signal input device for inputting an output signal of a neutron detector and performing digitization processing, and an input signal from the signal input device. Three signals in different frequency bands
The above- described band splitting device for dividing the signal, and calculating the rate of change of each signal of each frequency band divided by the band splitting device, and comparing the results with each other. And a computing device for performing a root-mean-square operation on the specified frequency band signal based on an output of the signal comparator. It is characterized by the following.

[0012]

[Action] The output signal of the neutron detector, digitize and have your <br/> to the signal input device is performed. This signal is divided into three or more frequency bands in a band division device, and signals in each frequency band are output to a signal comparator and a signal output device. The signal comparator compares the rate of change of the signal in each frequency band, and determines that a signal in a frequency band having a significantly different rate of change has added noise. Also depending on the case
Ri, neutron output distribution of each frequency band, and monitors the circuit noise, it is also possible to output an abnormality signal to detect an abnormality in the neutron detector and circuit by the change
You .

In the signal output device, neutron detection may be performed from a signal in a frequency band excluding a frequency band determined to have noise by the signal comparator and a frequency band previously determined to have a large amount of internal noise such as white noise. The output signal of the vessel can be calculated and output. For a system that requires a fast response signal, the signal output in the high response high frequency band is selected and output from the frequency bands selected as normal, while the neutron flux level is low and the detector output is low. When the signal is small, a signal in a low frequency band having an excellent S / N ratio can be output.

[0014]

An embodiment of the present invention will be described with reference to the drawings. The same components as those of the above-described conventional technology are denoted by the same reference numerals, and detailed description thereof will be omitted. As shown in the block diagram of FIG. 1, the monitoring device of the present invention includes a neutron detector 1, a signal input device 20 that receives and amplifies the output signal 1 a, and performs noise removal and digital conversion. A band dividing device 21 is provided for dividing an output signal from the signal input device 20 into signals for each frequency band.

A signal divided for each frequency band from the band dividing device 21 is inputted, and the rate of change of the signal is calculated and compared, and the signal of the frequency band whose rate of change is different from the signals of other frequency bands is input. Is the influence of noise, and the output of each frequency band is compared, that is, the frequency characteristics are monitored, and a change in the characteristics is used to diagnose an abnormality of the neutron detector 1 or the like,
A signal comparing device 23 for outputting the abnormal signal e1 is provided.

A signal divided for each frequency band in the band dividing device 21 is input, and a signal in a frequency band selected as normal is removed except for a signal in a frequency band in which a noise component is larger than a neutron output component. Of the mean square output signal and the frequency band selected as normal
If the output signal selected the signal in the high frequency band, and further, if the neutron flux level is low and the detector output is small,
And a signal output device 22 that outputs an output signal that selects a signal in a low frequency band having an excellent S / N ratio among the frequency bands selected as normal.

As shown in FIG. 2, the signal input device 20 includes a current amplifier 30 for amplifying the output of the neutron detector 1, an analog filter 31 as an anti-aging filter, and signal sampling. Sampling device 32, and A / D for converting to a digital signal
The current amplifier 30 amplifies the output signal 1a and digitizes the output.

The band dividing device 21 inputs the signal digitized by the signal input device 20, and outputs the frequency bands F1, F2,.
Fn, the signals are divided into signals f1, f2, f3... Fn as shown in the frequency band characteristic diagram of FIG.
In this method of dividing the frequency band, for example, by using a digital operation process called a known filter bank, a plurality of signals that are further finely divided can be obtained as compared with the conventional analog filter process.

In particular, when the frequency band is limited by the conventional analog, the outputs of the detectors other than the selected band are lost, and in processing a plurality of bands, the configuration of the band dividing device 3 becomes complicated. However, by dividing by digital operation, it can be used without losing all frequency bands of the neutron detector output. The signals f1, f divided by the frequency bands F1, F2, F3,.
.., Fn are output to the signal output device 22 and the signal comparison device 23.

The signal comparing device 23 receives the input signals f 1,
The rate of change of f2, f3... fn is calculated and compared, and a signal whose rate of change is different from signals in other frequency bands is determined to be influenced by noise, and signals s1, s2, s3. Output to the device 22. Further, the output of each frequency band is compared, that is, the frequency characteristics are monitored, and an abnormality of the neutron detector 1 is diagnosed based on a change in the characteristics, and an abnormal signal e1 is output.

In the signal output device 22, the signal from the band splitting device 21 steadily causes the characteristic curve 11 to become smaller than the neutron output component shown in the characteristic curve 5 as shown in the frequency band characteristic diagram of FIG. The signals f1, f2 of the frequency bands F1, F2, F7, Fn-1, and Fn having large noise components are shown.
, F7, fn-1 and fn except for the frequency band F3.
, F8 ... Fn-2 signals f3 ... f6, f8 ... fn-2
And outputs a signal a1.

The signal comparing device 23 determines that there is an influence of noise, for example, the frequency bands F1, F2, F
7, F10, Fn-1 and Fn signals s1, s2, s7, s
When receiving the signals 10, s-1, and sn, the signals f3... F6, f8, f9, f11... Fn in the frequency band excluding the signals f1, f2, f7, f10, fn-1, and fn including the signal f10.
Calculates the mean square of -2 and outputs a signal a1. Further, the calculation and the signal output in the steady state in the signal output device 22 and in the signal input from the signal comparison device 23 are performed in the same manner as the signal a1 for the entire frequency band, the signal a2 limited to the low frequency band 6, and The signal a3 in the high frequency band 7 is output together.

Next, the operation of the above configuration will be described. The output signal 1a of the neutron detector 1 is
, And is converted to digital and output from the band dividing device 21. The band dividing device 21 divides an input signal into signals f1, f2, f3... Fn for a number of frequency bands F1, F2, F3.
22 and a signal comparison device 23.

The signal comparing device 23 converts the input signals f1, f2, f3,.
In particular, when noise having different intensities occurs depending on the frequency band, since the change rate of the signal in the frequency band to which the noise is added is significantly different from other bands, the frequency band is identified, and the result is output to the signal output. The signal s1,
Output as s2, s3... sn. Further, by monitoring the frequency characteristic of the output of the neutron detector 1, an abnormality of the neutron detector 1 is diagnosed, and when an abnormality occurs, an abnormal signal e1 is generated.
Is output.

In the signal output device 22, for example, as shown in the frequency band characteristic diagram of FIG. 3, the frequency bands F1 and F2 where the noise component shown in the characteristic curve 11 is larger than the neutron output component shown in the characteristic curve 5 constantly. , F7, Fn-1 and Fn excluding the frequency band F3... F6, F8.
.., F6, f8,.
And a signal a2 in the low frequency band and a signal a3 in the high frequency band. Further, the signal s1 is also applied to the frequency band determined to be affected by noise by the signal comparing device 23.
, S2, s3,..., Sn are deleted as necessary as signals containing noise, and then a root-mean-square operation is performed and output as a signal a1.

The above-mentioned root mean square calculation and its output are also performed for the low frequency band 6 and the high frequency band 7,
Signals a2 and a3 are output together. This allows
If noise, particularly noise having different intensities depending on the frequency band, is generated from the signals a1 and a2 and the signal a3 output from the neutron detector 1 by the AC measurement, the frequency to which the noise is added, that is, the signal change rate Specify a band that is significantly different from the other bands by the signal comparing device 23, and from the signals s1, s2, s3.
Omit from the output of 2 to minimize the effect of noise.

This is because, when the neutron flux which is the output signal 1a of the neutron detector 1 increases, the characteristic that the signal change rate is almost the same in all the frequency bands is usually utilized to reduce the external noise. It is to be deleted. The frequency band characteristic diagram of FIG. 4 shows a change in the frequency characteristic of the output when the sealed gas pressure in the neutron detector 1 decreases as an example. Output characteristic curve when the sealed gas pressure is lower than output characteristic curve 5 of the neutron detector 1 in a normal state
12 is the frequency band fn,
At fn + 1, an output of neutrons is generated, so that abnormality of the neutron detector 1 can be easily detected.

In order to simultaneously output a signal in the low frequency band 6 having a good S / N ratio characteristic and a signal in the high frequency band 7 having a good signal response from the signal output device 22, a signal a2 having an excellent S / N ratio is provided. At the same time, a signal a3 having a fast response suitable for a trip signal or the like can be output at the same time. That is, compared to the measurement of only the high frequency band as in the above-described conventional example,
As for the response, the same response is obtained because the same high frequency band is used as before, and at the same time, the signal in the low frequency band is also output, so that the S / N ratio characteristic is improved, and it is possible to measure even lower neutron flux levels. Become.

As described above, noise generated in a specific frequency band is automatically deleted from the frequency band of the root-mean-square operation, and a root-mean-square output signal proportional to the neutron flux level unaffected by the noise is obtained. Further, since an abnormality in the neutron detector 1 can be detected at an early stage, occurrence of an erroneous signal due to a failure of the neutron detector 1 can be prevented. Further, a signal having a fast signal response and a signal having a good S / N ratio can be obtained. The neutron flux range can be expanded while maintaining a high signal response as compared with the related art in order to output the signals with distinction.

FIG. 5 is a block diagram of another embodiment of the present invention, in which the output of the signal comparing device 23 is used for adjusting the gain of the current amplifier 34 of the signal input device 24. The signal measured when no voltage is applied to the neutron detector 1 is a white noise component mainly generated by the resistance of the input stage. If the resistance of the input stage is the same, the magnitude of the component is determined by the current amplifier 34. This is due to the difference in the amplification in the following circuits.

Therefore, by measuring the white noise component, that is, by measuring the noise component in an appropriate frequency band and adjusting the gain of the current amplifier 34, the amplification degree can be automatically calibrated. Further, even during the neutron flux measurement, by using a signal in a frequency band of an output component due to neutrons, such as a signal in each frequency band fn shown in FIG. 3,
Since the degree of amplification or the operation state of the circuit can always be verified, the reliability is improved.

[0032]

As described above, according to the present invention, noise generated in a specific frequency band is not affected by the calculation result by automatically deleting the frequency band from the frequency band of the root mean square calculation. Noise characteristics are improved. Also , sometimes
In addition, since the neutron output and the frequency characteristics of the white noise of the circuit can be measured, abnormality of the neutron detector and the circuit can be detected at an early stage, and occurrence of an erroneous signal due to failure of the neutron detector and the monitoring device can be prevented. In addition, if
More can be output to distinguish good signal early signal and the S / N ratio of the signal response, as a result, while maintaining a fast signal response, Ru can expand the measurement range of the neutron flux.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a detailed configuration diagram of a signal input device according to one embodiment of the present invention.

FIG. 3 is a frequency band characteristic diagram of an output signal of a neutron detector according to one embodiment of the present invention.

FIG. 4 is a frequency band characteristic diagram of an output signal of the abnormal neutron detector according to one embodiment of the present invention.

FIG. 5 is a block diagram of another embodiment of the present invention.

FIG. 6 is a block diagram of a conventional neutron detector output monitoring device.

FIG. 7 is a frequency band characteristic diagram in a conventional neutron detector output monitoring device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Neutron detector, 1a ... Output signal, 5 ... Characteristic curve of neutron output component, 6 ... Low frequency band, 7 ... High frequency band,
11: noise component characteristic curve, 12: neutron abnormal output component characteristic curve, 20, 24: signal input device, 21: band splitting device,
22: signal output device, 23: signal comparison device, 30, 34: current amplifier, 31: analog filter, 32: sampling device,
33 ... A / D converter.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01T 3/00

Claims (1)

(57) [Claims] 1. A signal input device for inputting an output signal of a neutron detector and performing a digitization process, and a signal input from the signal input device having different frequencies.
A band dividing device that divides the signal into three or more signals of several bands, and calculates a rate of change of each signal of each frequency band divided by the band dividing device and compares the results with each other. A signal comparator that excludes signals in different frequency bands and specifies signals in the remaining frequency bands; and an arithmetic device that performs a root mean square operation on the specified frequency band signals based on an output of the signal comparator A device for monitoring the output of a neutron detector, comprising: