JPS5921112A - Wide band preamplifier - Google Patents

Abstract

PURPOSE:To improve the accuracy of the subsequent measuring systems, by supplying a neutron flux detecting signal of wide band detected out of a reactor pressure container to amplifiers for high frequency band, intermediate frequency band and low frequency band respectively which are connected in parallel to each other. CONSTITUTION:A wide band preamplifier 34 is connected to the output side of a neutron flux detector 30 for wide band provided in a reactor pressure container via a coaxial cable 32. An amplifier 36 for pulse system, i.e. a low input impedance type high frequency band amplifier, a low input impedance type intermediate frequency Campbell amplifier 38 and a high input impedance type low frequency Campbell amplifier 40 are connected in parallel to the amplifier 34. The output of the detector 30 is supplied to amplifiers 36, 38 and 40 respectively after separation of frequencies. In such a way, the desured amplification is carried out with three divisions of a frequency band. Thus, the accuracy of subsequent measuring systems is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a wide area preamplifier for amplifying a wide area neutron flux detection signal from within a nuclear reactor pressure vessel.

[Technical background of the invention and its problems]

Generally, the neutron flux level in a nuclear reactor pressure vessel has a wide measurement range. For example, boiling water reactors (hereinafter referred to as B
(commonly referred to as WR) has a measurement range of 11 digits, which makes it technically difficult to measure with a single measurement means. Therefore, a combination of three measuring means is generally used. (1) One of them is the low neutron flux range (
This is a measurement method based on the startup system area). In this case, since the reactor output is proportional to the counting rate, the neutron flux level is measured by determining the counting rate by pulse counting using a low range six digits.

(2) Next, there is a measurement means using the intermediate neutron flux range (intermediate system region). In this case, focus is placed on the fact that the furnace output is proportional to the root mean square value, and measurement is performed using the Campbell method. That is, it is measured according to Campell's theory using the effective value or root mean square value of the alternating current component of the detector output signal. (3) Measurement means using a high neutron flux range (output yarn range). In this case, focusing on the fact that the furnace output is proportional to direct current, the direct current from the detector is measured.

Next, the detector will be described. In a conventional BWR, there are 4 startup system detectors, 8 intermediate detectors, and 100 to 100 output system detectors.
200 of these systems are installed in the reactor core, and different types of detectors are installed for each of these systems at different positions in the reactor core to measure the neutron flux level.

In this way, the conventional BWR measures neutron flux using different detectors for each system. This will be explained below with reference to the drawings. First, the pulse measurement system counts pulses, and as shown in FIG. 1, a coaxial cable 3 is connected between the pulse measurement system detector 1 and the pulse preamplifier 2. Since the cable cannot be shortened, the cable capacity is extremely large at 2,000 to 5,000 PF. Therefore, when performing high counting rate measurements, the pulse preamplifier 2 is received by the input resistor R1 as a low input impedance. Also, if the coaxial cable 3 is long,
Since signal reflection occurs, it is necessary to match the coaxial cable 3 and the preamplifier 2.

On the other hand, in the case of an intermediate measurement system, the square of the effective value of the AC component of the input current is measured instead of counting pulses, and the signal level is very small, so low noise measurement is required.

FIG. 2 shows its configuration, in which a high input impedance type low noise Campbell preamplifier (voltage amplifier) 7 is connected to the other end of the intermediate measurement system detector 53 via an input circuit 6. This amplifier is a low noise voltage type amplifier having an input impedance of, for example, about 5 to 10 kΩ.

Therefore, as is clear from the above-mentioned differences in characteristics, it is very difficult to measure the pulse signal and the Camper signal using the same measuring device. In other words, it is technically very difficult to separate the pulse signal and camper signal while using the same detector for both systems and satisfying the measurement requirements of each system. It is difficult to get enough wrap, and it is also difficult to change the range.

In addition, the conventional wide range monitor device has a coaxial cable 3 connected to the wide range monitor detector 8 as shown in FIG.
There is also one in which one wide range preamplifier 10 is connected via an input circuit g consisting of a resistor RH and a capacitor C3.

This preamplifier 10 is of a low noise type with low input impedance.

By the way, with this configuration, assuming that the input resistance of the preamplifier 10 is Rin, it is not possible to reduce the amplifier input conversion noise due to the thermal noise of this input resistance Rin.

Now, if the input conversion noise is en (rms), it is expressed as follows. k is Portzmann's constant, which is 1.380
4×10-23 joul/°K, T is the absolute temperature of the resistance (
°K), B is the amplifier bandwidth (Hz), and Rin is the input (signal source) resistance (Ω).

The input equivalent noise current in (rms) at this time is as follows. Therefore, once Rin is determined, the signal current from the detector 8 cannot be separated into S/N when it is equal to or less than equation (2), and becomes unmeasurable. This phenomenon can be explained using an example as follows. That is, since the preamplifier 10 has a low input resistance (resistance value 50Ω), the input equivalent noise current in(
rms) increases. Therefore, the S/N (RMS) characteristic is about 14 times worse than that of the conventional intermediate measurement system (input resistance value 10 kΩ). For this reason, in Campbell measurement, since the furnace power is proportional to the square of the effective value, the measurement error of the furnace power increases by 200 times.

Therefore, one low input impedance preamplifier 10
It is very difficult to cover both ranges and output signals in a state where signals can be separated. For example, if a pulse measuring meter is
It is necessary to make it possible to count more than PS, to increase the signal from the detector 8, or to significantly reduce the noise of the entire measurement system, but all of these are difficult. Especially the third
In the figure, the first-stage wideband preamplifier amplifies both the pulse signal and the Campell signal at the same time, but as mentioned above, consideration for pulse counting requires the preamplifier 10 to have a low input impedance. This causes deterioration of the S/N ratio in the system.

In order to solve these problems, the following wide range monitor devices have been developed.

In FIG. 4, reference numeral 20 denotes a detector for wide range monitoring, and uses, for example, a nuclear fission counter.

The output side of this detector 20 is connected via a coaxial cable 21 to a low input impedance type pulse amplifier 23 capable of amplifying a high frequency band and a high input impedance type Campbell amplifier 24 capable of amplifying a low noise intermediate frequency band. . A coupling capacitor C4 and an input resistor RH are connected to the input terminal of the pulse amplifier 23, and the pulse amplifier 23 is configured to receive a detection signal with a high input impedance. Further, a coupling capacitor C5 and an input resistor RH are connected to the input terminal of the Campbell amplifier 24, and is configured to receive a detection signal with a low input impedance.

According to the above device, the neutron flux signal output from the wide range monitor detector 20 is transmitted to a predetermined location via the coaxial cable 21, and then connected to the end of the coaxial cable 21. The frequency bands are divided by the input circuit 22. In the pulse measurement system, only the high frequency signal component is received by the pulse amplifier 23 at low impedance and amplified, and in the Campbell measurement system, only the intermediate frequency signal component is received and amplified by the Campbell amplifier 24 at high input impedance. Neutron flux can be measured by increasing the ratio.

It is assumed that the amplifiers 23 and 24 specifically have characteristics as shown in FIG. In the figure, fCO is the Campbell signal center frequency, fCL and fCH are the lower and upper limit frequencies of the Campbell signal, fPO is the pulse signal center frequency, and fPO and fPH are the lower and upper limits of the pulse signal frequency. Therefore, for example, if the coupling capacitor C4 of the input circuit 22 is determined according to the pulse signal band according to FIG. 5, the pulse signal can be sufficiently passed through. R4 is an input resistance of the pulse amplifier 23. At this time, since the Campbell signal (Imen current) component in the intermediate frequency band is sufficiently small, it can be sufficiently removed by pulse height discrimination.

Further, the Campbell amplifier 24 is a high input impedance type intermediate frequency band amplifier suitable for the Campbell signal (current component), and its input resistance R5 is determined by Detector Campbell component (ion current component) can be separated. The influence of noise from the pulse amplifier side can be sufficiently eliminated by the frequency characteristics of the coupling capacitor C4 and the Campbell amplifier 24.

At this time, the ratio of the output fluctuation amount σs to the magnitude S of the Campbell system output signal, that is, the fluctuation rate I' is determined as follows. In equation (3), r is a first-order delay constant of a circuit connected to the subsequent stage, and Nn is a pulse rate (CPS) due to neutrons. Then, in equation (3), fCL=
1kHz, fCH=10kHz, first-order lag time constant r
1msec, 10msec, 0.1sec, 1sec
FIG. 6 shows the characteristics of the fluctuation rate I' with respect to the pulse rate Nn (CPS). As can be seen from FIG. 7, in order to maintain the fluctuation rate I' below about 2%, the r should be set to 0.
It can be seen that it is necessary to perform measurements with a longer response time of 1 sec or more.

However, when the above-mentioned r is set to 0.1 sec or more, the pulse rate Nn (CPS) increases, making it impossible to perform measurements in the short response time required when the furnace output increases rapidly.

As mentioned above, in the first device, that is, the device using a wideband amplifier in the first stage, the S/
This has the drawback that the N characteristic deteriorates, and the overlapping region of the measurement ranges of the pulse system and the Campbell system becomes narrow, resulting in a lack of reliability. In addition, in the second device, which uses a bandpass filter in the first stage to separate the frequency bands of the pulse system and the Campbell system, the response time in the Campbell region becomes long, and the short response time required when generating a high pulse rate increases. It was not possible to measure the response time.

[Purpose of the invention]

An object of the present invention is to provide a wide-range preamplifier that can frequency-separate a wide-range neutron flux detection signal detected from inside a nuclear reactor pressure vessel and perform amplification that satisfies the required conditions within each band. It's about doing.

[Summary of the invention]

The wide-band preamplifier according to the present invention has a low input impedance type high frequency band amplifier, a low input impedance type intermediate frequency band amplifier, and a high input impedance type low frequency band amplifier connected in parallel to each other, Wide-area neutron flux detection signals detected from inside the reactor pressure vessel are input to these.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIGS. 7 and 8. In FIG. 7, reference numeral 30 denotes a wide-area neutron flux detector installed in the reactor pressure vessel, and this detector 30 uses, for example, a nuclear fission counter. A wide area preamplifier 34 is connected to the output side of the detector 30 via a coaxial cable 32.

This wide range preamplifier 34 includes a pulse system amplifier 36 which is a low input impedance type high frequency range amplifier;
An intermediate frequency Campbell amplifier 38, which is a low input impedance type intermediate frequency band amplifier, and a low frequency Campbell amplifier 40, which is a high input impedance type low frequency band amplifier, are connected in parallel with each other.

Each of these amplifiers 36, 38, and 40 is configured to receive a detection signal from the detector 30.

A coupling capacitor C6 (capacitance: c6) and an input resistor R6 (resistance value: r6) are connected to the input terminal of the pulse system amplifier 36.
are connected in series. If the input impedance value due to these capacitor C6 and resistor R6 is Z6, then Z6
becomes (j2=-1, ω=2πf, f: frequency). The resistance r6 and the capacitance c6 are set so that Z6 is the minimum in the high frequency band of f≧1MHz, that is, Z6≒r6, and r1 is set so as to match the characteristic impedance value of the coaxial cable 32. ing.

Similarly, coupling capacitors C7 and C8 (capacitances: c7 and c8, respectively) are also connected to the input terminals of the intermediate frequency Campbell amplifier 38 and the low frequency Campbell amplifier 40.
and input resistors R7 and R8 (resistance values: r7 and r8, respectively)
are connected in series. Assuming that the input impedance value of the amplifier 38 is Z7 and the input impedance value of the amplifier 40 is Z8, Z7 and Z8 are calculated in the same manner as in equation (4) above. And the resistance value r7 and capacitance c7 are f≒10
Z7 is set to be minimum in the intermediate frequency band of 0 kHz. In addition, the resistance value r8 and the capacitance c8 are 1kHz.
Z8 is set to be minimum in the low frequency band of ≦f≦10kHz.

A band amplifier 4 is provided after each of the amplifiers 36, 38, and 40.
A pulse measuring thread 50, a Campbell measuring system 52 for an intermediate frequency band, and a Campbell measuring system 54 for a high frequency band are connected via lines 2, 44, and 46, respectively.

The effects of the embodiment configured as described above will be explained.

First, when the frequency band of the signal output from the detector 30 is approximately 1 MHz or more, most of the detected signal is input to the pulse system amplifier 36, which has the minimum input impedance value in such a high frequency band. become. At this time, the coaxial cable 32 and the amplifier 36 are impedance matched in a frequency band of 1 MHz or more. Therefore, generation of reflected waves is prevented and an output waveform without distortion can be obtained.

Next, the frequency band of the signal output from the detector 30 is 1
In the case of approximately 00 kHz, most of the detection signal is input to the intermediate frequency band Campbell amplifier 38, which has the minimum input impedance value in such an intermediate frequency band. In such a case, the Campbell amplifier 38 inputs the detection signal with a low input resistance value r7, which deteriorates the S/N characteristic, but since the frequency band of the detection signal is high, about 100 kHz, the response time is short and the fluctuation is suppressed. It is possible to send out an output signal with a small rate.

Further, when the frequency band of the signal output from the detector 30 is from about 1 kHz to about 10 kHz, most of the detected signal is transferred to the low frequency band Campbell amplifier 40, which has the minimum input impedance value in such a low frequency band. will be input. In such a case, Campbell amplifier 4
0 inputs the detection signal with a high input resistance value r8, so S
Campbell measurement can be performed with improved /N characteristics. Therefore, even when the magnitude of the output signal of the detector 30 is small, it can be amplified with sufficient accuracy. Therefore, the measurement range of the pulse measurement system 50 and the measurement range of the low frequency band Campbell amplifier 54 can be sufficiently overlapped to improve the reliability of measurement.

FIG. 8 shows the fluctuation rate I' of the output signals of the intermediate frequency band Campbell measurement system 52 and the low frequency band Campbell measurement system 54 when the above-mentioned wide range preamplifier 34 is used.
The characteristics of input pulse rate N (CPS) are shown below.

Input pulse rate N (CPS) from 103CPS to 10
It can be seen that input signals up to 7 CPS are input to the Campbell amplifier 40 for the low frequency band, and input signals of 107 CPS or more are input to the Campbell amplifier 38 for the intermediate frequency band. Therefore, measurement can be performed with sufficient accuracy even at low input pulse rates, and furthermore, at high input pulse rates, Campbell measurement with a small fluctuation rate I' can be performed with a short response time.

〔Effect of the invention〕

According to the present invention, the wide-range neutron flux detection signal from inside the reactor pressure vessel can be divided into three frequency bands and amplification can be performed that satisfies the required conditions within each region. be.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional pulse measurement system, Figure 2 is a configuration diagram of a conventional Campbell measurement system, Figure 3 is a configuration diagram of a conventional wide range monitor, and Figure 4 is a configuration diagram of a conventional wide range monitor. A configuration diagram showing another example of the monitor device, FIG. 5 is a diagram showing the amplifier characteristics of FIG. 4, and set 6 is a characteristic showing the fluctuation rate of the output signal with respect to the input pulse rate N of the device shown in FIG. 4. 7 is a block diagram showing an embodiment of the present invention, and FIG. 8 is a characteristic diagram showing the fluctuation rate I' of the output signal with respect to the input pulse rate N of the device shown in FIG. 30... Wide area neutron flux detector, 32... Coaxial cable, 34... Wide area front value amplifier, 36... High frequency band amplifier, 38... Intermediate frequency band amplifier,
40...Low frequency band amplifier, C6, C7, C8.
...Coupling capacitor, R6, R7, R8...Input resistance. Applicant's agent Patent attorney Takehiko Suzue M1 Figure 4 fCL feo CH' fPIL fF'
o fPH river fatigue (H2)

Claims (2)

[Claims] (1) A low input impedance high frequency band amplifier, a low input impedance intermediate frequency band amplifier, and a high input impedance low frequency band amplifier are connected in parallel, and each amplifier is connected to the reactor pressure. A wide area preamplifier characterized by inputting a wide area neutron flux detection signal detected from inside a container. (2) Each of the frequency band amplifiers has a coupling capacitor and an input resistor connected in series to the input terminal, and the input signal is frequency-separated by selecting the capacitance of the coupling capacitor and the resistance value of the input resistor. A wide area preamplifier according to claim (1), characterized in that: