JPH0442636B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a wide range monitoring device that measures nuclear reactor power from a neutron source region to an intermediate power region using the same measurement system.

[Technical background of the invention and its problems]

The range of changes in neutron flux density during reactor startup and shutdown is extremely wide, for example, in the case of a boiling water reactor (BWR), over 11 orders of magnitude. It is very difficult to measure such a wide measurement range with one type of measurement system, so in the past, this was divided into several ranges and each range was measured as shown in Figures 1 and 2. A measurement system suitable for this purpose was installed and measurements were taken.

Figure 1 is a configuration diagram of the measurement system in the neutron source region (SRM region), and Figure 2 is the intermediate output region (IRM region).
FIG. 2 is a configuration diagram of a measurement system.

The SRM region measurement system targets the neutron region and measures the signal output from the detector as the number of pulses per unit time, that is, the frequency.
The frequency of the detector output signal in this neutron source region is a signal in the range of 0 to several hundred MHz that can be identified as a pulse, so the neutron flux level is measured by determining the counting rate by pulse counting, as shown in Figure 1. As shown, it has an SRM detector 1, an SRM preamplifier 2 that receives the output pulse signal of the detector 1, and a logarithmic count rate meter circuit 3 that receives the output signal of the preamplifier 2 and provides an SRM measurement output. An SRM preamplifier with low input impedance and high gain is used from the viewpoint of high count rate measurement of high frequency pulse signals.

On the other hand, the IRM region measurement system targets the IRM region within the intermediate output region and beyond the neutron source region. Since the detector output signal in this IRM region exhibits a waveform in which pulses are densely superimposed, it is impossible to perform pulse counting. Therefore, among the frequency components included in the detector output signal, the signal level of a specific frequency band of several hundred kHz is used, and the IRM area measurement system uses the fluctuation component of the detector output signal (Campbell signal) according to the Campbell method. The neutron flux level in the IRM region is measured by finding the root mean square value of 6
a, root mean square circuit 6b and range switch 6c
It has a linear canvas measurement circuit 6 which receives the output signal of the preamplifier 5 and provides an IRM measurement output.

The IRM preamplifier 5 includes a low frequency band amplification circuit 5a that inputs a signal of the lower limit of three digits of the Campbell signal corresponding to about six digits of reactor output, and an intermediate frequency band amplification circuit 5b that inputs the signal of the upper limit of three digits. It has a buffer amplifier 5c which selectively inputs the output of these amplifier circuits 5a or 5b by a switch and outputs it to the Campbell measurement circuit 6.

The low frequency and intermediate frequency band amplifier circuits 5a and 5b
From the perspective of improving the S/N of the IRM area measurement system,
For the low frequency band amplifier circuit 5a, one with high input impedance and low gain is used, and for the intermediate frequency band amplifier circuit 5b, the low frequency band amplifier circuit 5a and the SRM preamplifier 2 (FIG. 1) are used.
A device with an input impedance and gain between .

In this way, in the measurement of the SRM region, the frequency as the density per time of pulses is used, whereas in the measurement of the IRM region, the signal magnitude ( In conventional nuclear instrumentation, the above-mentioned
An SRM area measurement system and an IRM area measurement system were provided, respectively.

By the way, recently, a wide range monitor device as shown in Figures 3 and 4 has been proposed, which continuously measures approximately 10-digit reactor output from the SRM region to the IRM region with one type of measurement system. There is.

In Figure 3, 7 is a wide range monitoring detector (WRM detector) that detects the neutron flux level from the SRM region to the IRM region, and 8 is a wide band with low input impedance and low gain that inputs the output signal of detector 7. The preamplifiers 9a and 9b are a high frequency band amplification circuit and a low frequency band amplification circuit that separate and amplify a pulse signal component and a canvas signal component according to the frequency of the frequency component contained in the output signal of the preamplifier 8, and 10 is a high frequency band amplification circuit. A logarithmic count rate meter circuit which inputs the output of the circuit 9a and gives an IRM measurement output, 11 a logarithmic canvas circuit which inputs the output of the low frequency band amplifier circuit 9b and gives an IRM measurement output, and 12 a SRM measurement of the logarithmic count rate circuit 10. This is a coupling circuit that inputs the output and the IRM measurement output of the logarithmic Campbell circuit 11 and continuously provides a measurement value of the neutron flux level (WRM measurement output) from the SRM region to the IRM region.

In a wide range monitor device with such a configuration, the preamplifier 8 has a low input impedance in consideration of pulse counting. In addition, since the preamplifier 8 has a low gain due to Campbell measurement considerations, the pulse signal wave height output from the preamplifier 8 becomes small, which makes it difficult to transmit the signal to the remote monitor device itself. There were drawbacks such as the influence of noise sometimes becoming a problem.

In order to overcome these drawbacks, a wide range monitor device as shown in FIG. 4 has been proposed.

In FIG. 4, 13 is a wide range monitor detector (WRM detector), 14 is a wide range monitor preamplifier (WRM preamplifier) that inputs the output signal of the detector 13, and 16 is a preamplifier 14.
This is a monitoring monitor that inputs the output signals of 1 through two signal transmission cables 15a and 15b.

The WRM preamplifier 14 has an input circuit 14a that is connected to the output side of the detector 13 and separates the output signal of the detector according to a specific frequency band of frequency components included in the output signal.

The input circuit 14a is a low input impedance circuit that passes a high-frequency signal component of the output signal of the detector 13, with one end of the resistor side of a series circuit of a capacitor _C1 and a resistor _R1 as a ground point, and the capacitor side as an input terminal. , a high input impedance circuit that passes a low-frequency signal component of the output signal of the detector 13, with one end of the resistor side of a series circuit consisting of a capacitor C ₂ and a resistor R ₂ connected to a ground point, and the capacitor side as an input terminal.

Buffer 14 on the low input impedance circuit side
A low input impedance, high gain pulse band amplification circuit 14c is connected through b, and its output is
It is sent to the monitoring monitor 16 via one signal transmission cable 15a, and is also sent to the pulse band amplification circuit 1.
It is applied to the input of an intermediate frequency band amplifier circuit 14d which has a higher input impedance and a lower gain than that of 4c.

A low frequency band amplifier circuit 14e having a higher input impedance and lower gain than the intermediate frequency band amplifier circuit 14d is connected to the high input impedance circuit side. The aforementioned pulse band amplification circuit 14c amplifies the pulse signal component with low input impedance and high gain, and the intermediate frequency band amplification circuit 14d has a higher input impedance and lower gain than the pulse band amplification circuit 14c, and amplifies a relatively of the Campbell signal components. The upper three digits of the signal level are amplified, and the low frequency band amplification circuit 14e is amplified by the intermediate frequency band amplification circuit 1.
The lower limit of three orders of magnitude of the campell signal component is amplified with a higher input impedance and lower gain than 4d. The output of the intermediate frequency band amplifier circuit 14d and the output of the low frequency band amplifier circuit 14e are level changeover switches.
The signal is selectively sent by the SW to the monitoring monitor 16 via the buffer amplifier 14f and the other signal transmission cable 15b. Note that switching of the switch SW is performed by a linear canvas circuit of the monitoring monitor 16, which will be described later.

The monitoring monitor 16 is installed in a remote central control room separately from the preamplifier 14, and is connected from the preamplifier 14 to the pulse signal component and the Campbell signal transmission cable 15a via the two signal transmission cables 15a and 15b, as described above. Been
Logarithmic count rate meter circuit 16a providing SRM measurement output
, a logarithmic canvas circuit 16b connected to the other signal transmission cable 15b, and a synthesis circuit 16c which inputs the outputs of the logarithmic count rate meter circuit 16a and the logarithmic canvas circuit 16b and provides a WRM measurement output.
and connected to the other signal transmission cable 15b.
Linear canvas circuit 1 that provides IRM measurement output
6d, and a range switch 16e for changing the range of the linear canvas circuit 16d.

According to such a configuration, a high frequency pulse signal is amplified with low input impedance and high gain,
The upper three digits of the Campbell signal with a relatively high signal level are amplified with a higher input impedance and lower gain, and the lower three digits of the Campbell signal with a lower signal level are amplified with an even higher input impedance and lower gain. will be done. As a result, although the configuration shown in FIG. 4 can improve the problems described in FIG. 3 and provide a wide range monitor device that provides good measurement results, it also has the following drawbacks.

In preamplifiers for wide range monitors, it is necessary to switch amplified outputs and install multiple amplifying circuits with different gains. This complicates the configuration of the preamplifier, which not only requires time and effort for gain adjustment and maintenance, but also makes it difficult to operate under harsh environmental conditions. This causes reliability problems.

The number of signal transmission cables between the wide range monitor preamplifier and the monitoring monitor is the same as in the case where the SRM area measurement system and the IRM area measurement system shown in FIGS. 1 and 2 are provided.

[Purpose of the invention]

The present invention is intended to improve the above-mentioned problems of the conventional technology.The purpose of the present invention is to provide a preamplifier with a simple configuration that does not require switching of amplified output or gain adjustment, and also to provide signal transmission between the preamplifier and a monitoring monitor. To provide a wide range monitor device that requires only one cable.

[Summary of the invention]

The features of the present invention for achieving the above object include a neutron detector, a wideband preamplifier whose input impedance and gain continuously change according to the frequency of a frequency component included in an output signal of the detector, and a wideband preamplifier whose input impedance and gain change continuously according to the frequency of the frequency component contained in the output signal of the detector. A wide range monitor device includes a single signal transmission cable that transmits an output signal, and a band amplification circuit that separates and outputs the transmission signal of the cable into a plurality of signals according to frequency bands.

[Embodiments of the invention]

FIG. 5 is a block diagram showing an embodiment of a wide range monitor device according to the present invention.

In the figure, 17 is a wide range monitor detector (WRM detector), 19 is a wide range monitor preamplifier (WRM preamplifier) that inputs the output signal of the detector 17 via a cable 18, and 21
is a monitoring monitor into which the output signal of the WRM preamplifier 19 is input via one signal transmission cable 20.

The WRM preamplifier 19 includes an input circuit 19a that receives signals with different input impedances depending on the frequency band of the frequency included in the output signal of the detector 17;
It has a wideband amplifier circuit 19b that amplifies the output of the input circuit 19a with a variable gain depending on the impedance of the circuit 19a.

The input circuit 19a has a circuit in which resistors R ₁ and R ₂ are connected in series, with one end on the resistor R ₁ side connected to the ground point, and resistor R ₂
The other end of the side is connected to the input end of the WRM preamplifier 19, and a capacitor _C3 is connected in parallel to the resistor _R2 . The resistor _R1 has a resistance value that matches the impedance of the cable 18 (for example, 5Ω) to prevent reflection of the pulse signal, and the resistor _R2 has a resistance value of about several kΩ to amplify the canvas signal with a good S/N ratio. Further, the capacitor C ₃ has a capacitance of several thousand pF, bypasses the resistor R ₂ in the high frequency pulse signal band, and provides an impedance of the same order as the resistor R ₂ in the low frequency canvas signal band.

As a result of the input circuit 19a being configured in this way,
Input impedance Zin of WRM preamplifier 19
is given by equation (1), assuming that the center frequency of the frequency band of the input signal is f=ω/2π.

Zin=1/jωC ₀ +1/jωC ₃ R ₂ +R ₁ =1/jωC ₀ +R ₂ /1+jωC ₃ +R ₁ ...(1) Therefore, the input impedance Zin of the WRM preamplifier 19 depends on the frequency included in the input signal. As a result, a distribution characteristic as shown in FIG. 6 is obtained. That is,
Input impedance Zin of WRM preamplifier 19
is determined by the resistance R ₁ in the high frequency band, and increases as the frequency decreases. The low frequency side of this characteristic curve is determined by the low frequency impedance on the high voltage power supply side, which will be described later, and falls as shown in the figure. As is clear from this characteristic curve, the high-frequency pulse signal in the detector output signal is input to the WRM preamplifier 19 with a low input impedance determined by the resistor _R1 , and as the frequency component included in the signal decreases in frequency, the The signal is input to the WRM preamplifier 19 with an input impedance that increases as the signal increases.

The amplifier circuit 19b of the WRM preamplifier 19 is a low-noise wideband amplifier circuit that can amplify from a low-frequency canvas signal of several tens of kHz to a high-frequency pulse signal of several tens of MHz band.As shown in FIG. 7, the first stage is a negative feedback amplifier circuit. including.

In Fig. 7, IN is an input terminal for inputting the output signal of the WRM detector 17, and a resistor _R2 and a resistor _R2 having a capacitor _C3 connected in parallel with a capacitor C0 are connected.
Broadband amplifier circuit 19b via the series circuit of _R1
is connected to the (-) input terminal of the first stage amplifier circuit 19b-1. The first stage amplifier circuit 19b-1 has a feedback impedance Zf between its output terminal OUT and its (-) input terminal, and its (+) input terminal is connected to a ground point.

Resistors R ₁ and R ₂ and capacitors C ₃ and C ₀ are the same functional elements that perform the same functions as those with the same reference numerals in FIG. According to such a configuration, the first stage amplifier circuit 19
The gain A of b-1 is given by equation (2) using the feedback impedance Zf and the above-mentioned input impedance Zin.

A=Zf/Zin (2) Therefore, when Zf is constant, the gain A has characteristics as shown in FIG. 8 depending on the frequency of the detector output signal. In other words, the gain increases as the frequency increases, and the gain is low for a Campbell signal where the frequency components included in the detector output signal are low in frequency, and the gain is low for a Campbell signal where the frequency components included in the detector output signal are high in frequency. High gain amplification is possible for pulse signals.

In addition, capacitor C ₀ of WRM preamplifier 19
is the WRM detector 1 from the high voltage power supply for the detector described later.
The high voltage bias voltage applied to the amplifier circuit 19
This is to prevent input to b.

The monitoring monitor 21 connected to the WRM preamplifier 19 having the above configuration via a single signal transmission cable 20 has a high frequency band amplification circuit 21a and a low frequency band amplification circuit 21b connected to the signal transmission cable 20, and a high frequency band amplification circuit 21b connected to the signal transmission cable 20. A logarithmic count rate meter circuit 21c that receives the output signal (pulse signal) of the band amplification circuit 21a and provides an SRM measurement output, a logarithmic Campbell circuit 21d that receives the output signal (Cambell signal) of the low frequency band amplifier circuit 21b, and the logarithm Count rate meter circuit 21c and logarithmic Campbell circuit 21
a synthesis circuit 21e that receives each logarithmic output of d and provides a WRM measurement output; and the low frequency band amplification circuit 21.
It has a linear canvas circuit 21f that receives the output signal of the output signal B and provides an IRM measurement output, and a range switch 21g that switches the range of the linear canvass circuit 21f. In addition, 21h is a low voltage power supply that supplies operating power to the WRM preamplifier 19, and 21i is a low voltage power supply that supplies operating power to the WRM preamplifier 19.
This is a high-voltage power supply for the WRM detector 17 that supplies a high-voltage bias voltage.

In the configuration shown in FIG. 5 described above, as is clear from the above description of the configuration, unlike the conventional configuration shown in FIG. It is configured to input and amplify output with the optimal input impedance and gain according to the frequency, and
Both the pulse signal of the preamplifier 19 and the cabel signal are connected to the monitoring monitor 2 using the same signal transmission cable 20.
1, and further configured to provide a monitoring monitor 2
1, the pulse signal and the canvas signal are separated by band amplification circuits 21a and 21b.

According to the wide range monitor device having such a configuration, the output signal of the WRM detector 17 is inputted by the WRM preamplifier 19 at an impedance corresponding to the frequency of the frequency component included in the signal, and is It will be amplified and output using the gain. In other words, the high frequency pulse signal component in the detector output signal is amplified and output with low input impedance and high gain, and the intermediate frequency and low frequency Campbell signal components are amplified and output with high input impedance and low gain according to their frequency. and sent to the monitoring monitor 21 via a single signal transmission cable 20. In the monitoring monitor 21, the signal is separated into a pulse signal and a canvas signal by band amplification circuits 21a and 21b.
Logarithmic count rate meter circuit 21c, logarithmic Campbell circuit 2
1d and a combining circuit 21e provide a WRM measurement output.

By the way, when configuring a wide range monitor device, the count rate characteristics of the pulse signal are good, the S/N ratio of the Campbell signal is good, and the output linearity on the lower limit side extends to the low neutron flux level, and the SRM It is necessary to have sufficient overlap between the measurement output and the IRM measurement output.

FIG. 9 shows each measurement output characteristic of the configuration shown in FIG.
IRM measurement output characteristics, c is logarithmic Campbell circuit 2
IRM measurement output characteristics of 1d, (d) is composite circuit 21e
This is the WRM measurement output characteristic of

As is clear from FIG. 9, according to the configuration shown in FIG. 5, the count rate characteristic of the pulse signal is good, the SRM measurement output characteristic a extends to a high neutron flux level, and
As shown by the IRM logarithm measurement output characteristic c, the lower limit side of the Campbell signal extends to the low neutron flux level, and it can be seen that there is sufficient overlap between the two.

Such characteristics can be obtained with the SRM preamplifier 19 for pulse signal components in the high frequency band.
This is because the signal is amplified with a low input impedance and a high gain, and the Campbell signal component is amplified with a high input impedance and a low gain according to its frequency band. As a result, it becomes possible to amplify the Campbell signal component in the low frequency band with a good S/N. In other words, the preamp S/
When the input signal level S is constant, the N ratio is mostly determined by the preamplifier input equivalent noise Nv, and Nv
is expressed by the following equation.

Nv=N _F・√4... _IN ...(3) In equation (3), K is Boltzmann's constant, T is the absolute temperature of the resistor, B is the amplifier band amplification, R _IN is the input resistance,
_NF is a noise figure. The input current equivalent noise Ni at this time is expressed by the following equation using equation (3).

Ni=Nv/R _IN =N _F・√4・・_IN …(4) Therefore, when the amplifier bandwidth B is constant, the larger the input resistance R _IN is, the smaller the input current equivalent noise is, and the lower the frequency It becomes possible to amplify signal components with good S/N ratio.

According to the wide range monitor device configured as described above, there is no need to switch the amplification output related to the Campbell signal in the WRM preamplifier as shown in the conventional configuration shown in FIG. It can be constructed without level shifting between logarithmic outputs, and the construction of a logarithmic canvas circuit becomes easy. In the conventional configuration shown in FIG. 4, since the amplification output of the Campbell signal is switched in the WRM preamplifier, the level of the logarithmic output must be shifted between the lower three digits and the upper three digits of the Campbell signal.

〔Effect of the invention〕

As explained above, according to the present invention, the input impedance and gain change continuously according to the frequency of the frequency component included in the detector output signal.
A WRM preamplifier is installed, and the pulse signal component and the canvas signal component are sent to the monitoring monitor in a superimposed manner via a single signal transmission cable, eliminating the need for range switching and gain adjustment in the WRM preamplifier. In addition, it is possible to provide a wide range monitor device in which only one signal transmission cable is required between the WRM preamplifier and the monitoring monitor, and cable installation is facilitated.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional SRM area measurement system, Figure 2 is a configuration diagram of a conventional IRM area measurement system, Figure 3 is a configuration diagram of a conventional wide range monitor device, and Figure 4 is a configuration diagram of a conventional wide range monitor device.
5 is a block diagram showing an embodiment of the wide range monitor device according to the present invention. FIG.
Figure 7 is a diagram showing the input impedance frequency dependence characteristics of the WRM preamplifier; FIG. 9 is a diagram showing each measurement output characteristic of the configuration of FIG. 5. 17... Detector for wide range monitor (WRM detector), 19... Preamplifier for wide range monitor (WRM preamplifier), 19a... Input circuit, 19b
... wideband amplifier circuit, 20 ... signal transmission cable, 2
1... Surveillance monitor, 21a... High frequency band amplification circuit,
21b...Low frequency band amplifier circuit.

Claims (1)

[Claims] 1. A neutron detector; In the case of SRM measurement, which targets high-frequency pulses among the detection signals of this neutron detector, the detection signal of the neutron detector has a low input impedance and a high gain. In the case of IRM measurement that targets a frequency band of several hundred kHz among the included frequency components, the input impedance and gain change continuously according to the output signal of the detector to achieve high input impedance and low gain. A single signal transmission cable that transmits the output signal of the preamplifier, and a band amplification circuit that separates and outputs the transmission signal of the cable into multiple signals according to frequency components. Wide range monitor device.