JPS645269B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wide range monitoring device that can simultaneously and continuously measure multiple signals of neutron flux using the same detector.

Nuclear reactor neutron flux levels have a wide measurement range. For example, boiling water reactors (hereinafter referred to as BWR)
) has a measurement range of 11 digits, which makes it technically difficult to measure with a single measurement method. Therefore, a combination of three measuring means is generally used. One of them is a measurement means in the low neutron flux range (startup system region). In this case, the furnace output is proportional to the counting rate, so
The neutron flux level is measured by determining the counting rate by pulse counting using a 6-digit low range. next,
This is a measurement means in the intermediate neutron flux range (intermediate system region). In this case, focus on the fact that the furnace output is proportional to the root mean square value, and measure using the Campbell method. That is, measurement is performed according to Campbell's theory using the effective value or root mean square value of the alternating current component of the detector output signal. This is a measurement means using a high neutron flux range (output system area). 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, four startup system detectors, eight intermediate system detectors, and 100 to 200 power system detectors are installed inside the reactor core.
In addition, different types of detectors are installed for each of these systems at different locations within the reactor core to measure the neutron flux level.

In this way, conventional BWRs measure 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 and an input circuit 4 are connected between the pulse measurement system detector 1 and the pulse preamplifier 2. , since this cable 3 cannot be shortened, the cable capacity is 2000 ~
Very large at 5000PF. Therefore, when performing high counting rate measurements, the pulse preamplifier 2 is received by the input resistor R1 as a low input impedance. Further, if the coaxial cable 3 is long, signal reflection occurs, so 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 effective value of the alternating current component of the input current is measured instead of counting pulses, and the signal level is very small, so low-noise measurement is required. Figure 2 shows its configuration. A coaxial cable 3 is connected to the output side of the intermediate measurement system detector 5, and the other end of the cable 3 is connected via an input circuit 6 to a high input impedance type low noise preamplifier (voltage amplifier). )7 are connected. This amplifier 7 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 extremely difficult to measure the pulse signal and the Campbell signal using the same measuring device. In other words, it is technically very difficult to use the same detector for both measurement systems and to separate the pulse signal and the canvas signal while satisfying the measurement requirements of each system. It is also difficult to get a sufficient amount of water, and it is also difficult to switch ranges.

In addition, conventional wide range monitor devices
As shown in the figure, the wide range monitor detector 8 is connected to the coaxial cable 3, resistor RH, and capacitor C3.
There is one in which one wide range preamplifier 10 is connected via an input circuit 9 consisting of the following. This preamplifier 10 is of a low noise type with low input impedance.

By the way, this configuration has a preamplifier 10
If the input resistance of Rin is Rin, it is not possible to reduce the amplifier input equivalent noise due to the thermal noise of this input resistance Rin. Now, the input-referred noise is e _o (rms)
Then, it is expressed as e _o (rms) = √ …(1). k is Boltzmann's constant
1.3804×10 ^-23 Joul/〓, T is the absolute temperature of the resistor (〓), B is the amplifier bandwidth (Hz), and Rin is the input (signal source) resistance (Ω).

The input equivalent noise current i _o (rms) at this time is becomes. Therefore, the signal current from the detector 8 is Rin
If the value is less than the value of equation (2) determined by , separation becomes impossible and measurement becomes impossible.

Next, consider the output signal of the detector 8. When the detector 8 is a fission counter for neutron detection, its output current is generated by electrons or by ionic components. The ionic component is due to the ionization of gas in the fission counter, such as argon gas.
Although these two have the same amount of charge, their mobility in the gas is about 2000 times different, so the electron current _Ie component is a short-time pulse with a large peak current, as shown in Figure 4. The ion current I _i component becomes a long pulse of about 200 μs. Therefore, the ratio of the peak values of the electron current I _e and the ionic current I _i is about 2000 times. According to Campbell's theorem, the effective value Irms of the pile-up signal due to these pulse currents is approximately: It is. I _DC is the average direct current value, and I _p is the pulse peak current. Since I _e and I _i have the same value, the average direct current value I _DC is approximately Irms (electrons) = 45 Irms (ions) in the above example. When measuring electronic components in a pulse measurement system, B = 50MHz, Rin = 75Ω, T =
300〓, then from equations (1) and (2), e _o (rms)
= 4μV, i _o (rms) = 53nA.

In addition, when measuring ionic components with a Campbell measurement system, B = 10kHz, Rin = 5kΩ, T = 300
〓, then e _o (rms) = 0.45μV, i _o (rms) =
It becomes 0.09nA.

Comparing the two above, the noise component is Ni/
Ne=590, and Si/Se=45 for the signal component. The subscript i means current, and e means voltage component. From the above results, it can be seen that in the Campbell measurement system, it is possible to measure the ion current with a higher S/N ratio. Therefore, in the Campbell measurement system, since the square of the average value is proportional to the furnace output, it is possible to measure up to a two-digit low range in terms of furnace output.

However, it is extremely difficult to cover both ranges with a single preamplifier 10 with low input impedance and output signals in a state where signals can be separated ^as in the past. Increase the signal from detector 8 or
Alternatively, it is necessary to significantly reduce the noise of the entire measurement system, but both of these are difficult. In particular, in Fig. 3, the first-stage wideband preamplifier amplifies both the pulse signal and the canvas signal at the same time, but as mentioned above, the preamplifier 10 needs to have a low input impedance in consideration of pulse counting. As a result, this causes deterioration of S/N in the Campbell measurement system.

The present invention has been made in view of the above circumstances, and takes into account the conditions of the measurement system described above, and converts the neutron flux signal detected by one wide range monitoring detector into a pulse signal and a canvas signal with a good S/N ratio. The present invention provides a wide range monitor device that can separate and measure simultaneously and independently.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 5, reference numeral 20 denotes a detector for wide range monitoring, and uses, for example, a nuclear fission counter. An input circuit 22 is connected to the output side of this detector 20 via a coaxial cable 21. This input circuit 22 includes an input resistance RH, a coupling capacitor C
It has a so-called frequency filter function, which has a low input impedance circuit consisting of 4, and a high input impedance circuit consisting of an input resistor RH and a coupling capacitor C5. A pulse amplifier 23 capable of band amplification is connected, and a high input impedance type Campbell amplifier 24 capable of low noise intermediate frequency band amplification is connected to the other high input impedance circuit side.

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 input circuit 22 separates the signal into a low frequency band signal and an intermediate frequency band signal. In the pulse measurement system, only the signal components in the low frequency band are received and amplified by the pulse amplifier 23, while in the Campbell measurement system, only the signal components in the intermediate frequency band are received by the Campbell amplifier 24 with high input impedance. By amplifying it, you can increase the S/N and measure the neutron flux signal.

It is assumed that the amplifiers 23 and 24 specifically have characteristics as shown in FIG. In the figure, f _CO is the pulse signal center frequency, f _CL and f _CH are the lower and upper limits of the pulse signal frequencies, f _PO is the Campbell signal center frequency, and f _PL and f _PH are the lower and upper limits of the Campbell signal frequencies. Therefore, for example, if the coupling capacitor C4 of the input circuit 22 is determined by 1/2πf _PL ·C4=R4 from FIG. 6 in accordance with the band of the pulse signal, it can sufficiently pass the pulse signal. R4 is an input resistance of the pulse amplifier 23. At this time, since the Campbell signal (ion 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 (ion current component), and its input resistance R5 is set in advance based on R5≧(1/2πf _CO C5). If determined, the Campbell signal can be input with high impedance and the detector Campbell component (ion current component) can be separated with a good S/N ratio. The influence of noise from the pulse amplifier side is caused by the coupling capacitor C4,
This can be sufficiently removed by the frequency characteristics of the Campbell amplifier 24.

It goes without saying that the present invention is not limited to the above embodiments. That is, in the above embodiment, the measurement of pulse signals and Campbell signals was explained, but when measuring DC current in the high neutron region,
As shown in FIG. 7, a high voltage power supply HV and a DC current amplifying amplifier 25 are newly provided as the input circuit 22', and the DC current flowing from the high voltage power supply HV to the detector 20 is measured from the output of the amplifier 25. For example, direct current can be easily measured without being influenced by other signals. Further, although the above embodiment has been described with respect to the neutron flux detector 20, the present invention can be similarly applied to a detector in which the mobilities of positive and negative ionization currents are significantly different, for example.

As detailed above, according to the present invention, the output signal of a wide range monitor detector is separated into low frequency band and intermediate frequency band signals in the input circuit, and among the separated signals, the low frequency band signal is separated. The signal is amplified by a pulse amplifier, and the signal in the intermediate frequency band is amplified by a high-input-impedance canvas amplifier and output, so it is possible to measure a wide range of neutron flux levels from the output of the same wide-range monitoring detector. It can be detected in a range, and it is possible to reliably separate the pulse signal and the canvas signal with a good S/N ratio. Therefore, both signals can be measured continuously and simultaneously without particularly changing the input stage resistance.

Furthermore, if the neutron flux can be measured continuously using the same detector, it will be very advantageous in terms of the plant system in the following points. That is, the number of in-core detectors can be significantly reduced, and the accompanying guide tubes, cables, cable penetrations, etc. can be reduced, and equipment costs can be significantly reduced. In addition, if one detector breaks down, another detector can be substituted.
Greater redundancy and higher reliability can be achieved. Furthermore, it is possible to provide a wide range monitor device that is easy to maintain.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional pulse measurement system device, Fig. 2 is a block diagram of a conventional Campbell measurement system device, and Fig. 3 is a block diagram of a conventional wide range monitor device.
FIG. 4 is a state diagram of electron and ionic components of the detector output current, FIG. 5 is a configuration diagram showing an embodiment of the wide range monitor device according to the present invention, and FIG.
FIG. 7 is a block diagram showing another example of the device of the present invention. 20...Wide range monitor detector, 21...
...Coaxial cable, 22, 22'...Input circuit, 2
3...Pulse amplifier, 24...Cambell amplifier, HV...High voltage power supply, R4, R5...Amplifier input resistance.

Claims (1)

[Claims] 1 For measuring the neutron flux level of a nuclear reactor over a wide measurement range, there is a wide range monitoring detector installed at a predetermined location in the reactor core, and a sensor connected to the output side of this detector via a signal transmission cable. , an input circuit that separates the frequency band of the output signal of the detector into a low frequency band and a high frequency band, and a signal in the low frequency band of the low frequency band signal and the high frequency band signal separated by the input circuit; A wide range monitor device comprising: signal amplification/output means for amplifying the signal in the high frequency band with a pulse amplifier, and amplifying and outputting the signal in the high frequency band using a high input impedance type Campbell amplifier.