JPH0575359B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is for monitoring and controlling the reactor operating status to maintain safety at the start-up of a nuclear reactor in a BWR (boiling water) power plant. The present invention relates to a wide-area neutron monitoring device that monitors reactor power (approximately 10 digits) from a neutron source region to an intermediate power region using a single neutron detector.

(Prior art) Conventionally, a neutron source monitoring device (hereinafter referred to as SRM) has been used as a monitor device to monitor the reactor output during startup operation of a nuclear reactor in the neutron source region where the neutron flux level is low. It was common to use a high-level intermediate area monitoring device (hereinafter abbreviated as IRM).

FIG. 8 is a block diagram of an SRM using the conventional pulse counting method. In the figure, 1 is an ionization chamber-type neutron detector, 2 is a bias power supply for the detector, and 3
is a preamplifier that converts the minute current signal from the detector 1 into a voltage signal, 4 is an amplifier that amplifies the voltage signal from the preamplifier 3, and 5 is a pulse having energy of a predetermined level or higher from the output signal of the amplifier 4. A pulse height discrimination circuit removes pulses caused by low-energy alpha rays, gamma rays, etc. by extracting signals, and extracts only pulses caused by neutrons. 6 is the time of the number of pulses output from the pulse height discrimination circuit 5. 7 is a signal processing circuit that processes the voltage signal from the diode pump 6 and outputs it as reactor output to an external device such as a meter or recorder. In other words, SRM performs monitoring by measuring the number of incident neutrons from the count rate of the pulse signal from the neutron detector 1 and correlating it with the reactor output. An example of the recorder output in this SRM is shown in Figure 10. show.

FIG. 9 is a block diagram of an IRM using the conventional Campbell method. In the figure, 1 is an ionization box-type neutron detector, 2 is a bias power supply for the detector,
3 is a preamplifier, 8 is an amplifier that amplifies the voltage signal from the preamplifier 3 according to the gain that is manually selected by a gain switcher 9, and 10 is the root mean square of the output of the amplifier 8 (hereinafter referred to as MSV). 11 is MSV circuit that measures a value (abbreviated) and converts it to voltage.
This is a signal processing circuit that processes the voltage signal from the circuit 10 and outputs it as reactor output to an external device such as a meter or recorder. In other words, URM calculates the reactor output by measuring the number of incident neutrons from the pulsating component of the output signal from neutron detector 1, based on the Campbell method in which the MSV value of the pulsating component in the neutron detection signal is proportional to the neutron flux. Monitoring is carried out by matching the
FIG. 11 shows an example of recorder output in IRM.

However, since SRM and IRM are separate devices, the output to meters and recorders differs for each device, and adjustments, calibrations, and trip alarm settings must be made for each device, making them difficult to put into practical use. It was very complicated. Furthermore, each device requires an expensive neutron detector and special cable, leading to high costs. Furthermore, IRM requires the supervisor to manually switch the gain of the amplifier 8 according to the reactor output, which is troublesome.

Therefore, as a monitoring device that solves these problems, a single neutron detector can detect neutrons by combining the pulse counting method used in SRM and the Campbell method used in IRM to obtain a single output. There is a wide-area neutron monitoring device (Japanese Patent Publication No. 18436/1983) that monitors reactor power over a wide area of about 10 digits from the source region to the intermediate power region. The block configuration of this device is shown in FIG. 12, and an example of the recorder output is shown in FIG. 13. In Figure 12,
A detection signal from the neutron detector 1 is converted into a voltage signal by a preamplifier 3, and then applied to a pulse counting system amplifier 4 and a Campbell system amplifier 12 for amplification. Here, in the neutron source region where the neutron flux level is low, the pulse counting system output means is selected by the automatic switching circuit 13, and the output signal of the amplifier 4 is converted into a pulse signal by the pulse height discrimination circuit 5, and the pulse counting system is converted by the diode pump 6. A voltage signal corresponding to the counting rate is output and given to the signal processing circuit 14 via the automatic switching circuit 13, and becomes the reactor output. On the other hand, when the pulse counting rate exceeds a predetermined value and measurement by the pulse counting method becomes difficult (intermediate output region), the automatic switching circuit 13 switches to select the Campbell system output means. Then, the MSV value of the output signal of the amplifier 12 is obtained by the MSV circuit 10, further logarithmically converted by the logarithmic conversion circuit 15, and then converted into a voltage signal by the automatic switching circuit 13.
The signal is applied to the signal processing circuit 14 via the signal processing circuit 14, and becomes the reactor output.

By the way, as mentioned above, in the conventional IRM, the operator manually switches the gain switch 9 while checking the reactor output so that the input voltage to the MSV circuit 10 can be maintained within a certain range and its accuracy can be fully demonstrated. It was necessary to switch the gain of the amplifier 8 by operating the . Therefore, in conventional wide-area neutron monitoring equipment, an automatic gain switching circuit 15 is provided to switch the gain of the Campbell system amplifier 12 based on the reactor output obtained by the signal processing circuit 14, and this function is automated. . However, in this case, MSV
Since it is determined whether or not to switch the gain of the amplifier 12 based on the output of the circuit 10, switching the gain changes the output of the MSV circuit itself, which tends to become unstable, especially when Traditional
It was technically difficult to accommodate as many as 12 stages of gain as in the case of IRM. For this reason, the above-mentioned wide-area neutron monitoring device is equipped with an automatic gain switching circuit 15 that can switch the gain of the amplifier 12 between high and low stages, and logarithmically transforms the MSV output to ensure output accuracy. .

(Problem to be solved by the invention) However, even with this method, it is undeniable that the MSV circuit output changes due to automatic gain switching, resulting in instability. Output deviations may occur at the switching point,
As a monitoring device, it had poor accuracy and reliability.

Therefore, the present invention is capable of automatically performing monitoring over a wide area using a single neutron detector during start-up operation of a nuclear reactor. The purpose is to provide a neutron monitoring device.

[Structure of the invention]

(Means for solving the problem) The first invention of the present application provides a pulse signal for obtaining a nuclear reactor output in a neutron source region by extracting a pulse signal from an output signal of a neutron detector and counting the number of pulses per unit time. A system output means, a Campbell system output means that obtains the reactor power in the intermediate power region by measuring the root mean square value of the pulsation component in the output signal of the neutron detector, and a reactor power output obtained by both of these output means. The system output selection means automatically selects one of the output signals. This device is equipped with a plurality of root mean square circuits for measuring the root mean square values of the pulsating components, and a root mean square value selection means for automatically selecting one of the outputs of these root mean square circuits as a Campbell system output. .

The second invention of the present application, in addition to the first invention,
As the system output selection means, a correction means is provided which multiplies the Campbell system output by a predetermined coefficient at a system switching point due to an increase in the reactor output, and the pulse counting system output at a system switching point due to a decrease.

(Function) In the wide-area neutron monitoring device according to the first invention, one of the MSV values for the pulsating components of the neutron detector output signal amplified with different gains is selected to output the Campbell system. Therefore, automatic gain switching will not change the output of the MSV circuit and cause the reactor output to become unstable.

Furthermore, with the wide-area neutron monitoring system adopting the second invention, the Campbell system output is corrected to match the pulse counting system output at the system switching point when the reactor power increases, and the system switching point when the reactor power decreases. In this case, the pulse counting system output is corrected to match the Campbell system output, eliminating deviation at the switching point.
A smooth single output is obtained.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block configuration diagram showing an embodiment of the present invention. This embodiment differs from the conventional device shown in FIG. The automatic switching correction circuit 20 is used as the system output switching means for switching between the output means and the output means, and the other parts are the same as those in FIG. 12, so the same reference numerals are given and detailed explanation will be omitted.

First, in the pulse counting system output means, the detector signal of the neutron detector 1, which has been converted into a voltage signal by the preamplifier 3, is amplified by the amplifier 4, and then the pulse height discrimination circuit 5
extracts pulses with energy above a predetermined value, and calculates the pulse counting rate C (cps) using the diode pump
It is determined by and output as a voltage signal V _C. At this time, the reactor power P (%) is proportional to the neutron flux, so P∝C holds true, and V _C = k ₁ × C (k ₁ is a proportionality constant), so in the pulse counting system output means, The reactor power P _C (%) can be calculated using the following equation (1).

P _C =k _C ×V _C (k _C is a proportionality constant) ...(1) On the other hand, the Campbell system output means is the preamplifier 3
three amplifiers 21, 22, 23 that amplify the output signal of the neutron detector 1, which is converted into a voltage signal by the
MSV circuits 24, 25, 26 provided corresponding to MSV circuits 2, 23, and MSV circuits 24, 25, 26, respectively.
The voltage comparison and selection circuit 27 compares the voltages corresponding to the MSV values obtained in step 26 and selects the optimum MSV value. In addition, each amplifier 2
It is assumed that the following relationship holds between gains G1, G2, and G3 of 1, 22, and 23.

G1:G2=1:R2 G2:G3=1: _R3 As shown in FIG. When the MSV values of are V1 _D , V2 _D V, and 3 _D , respectively, the voltage comparison and selection circuit 27 selects the optimal MSV value V _I according to the following equations (2) to (4).

If V1 _D ≧vmax/R2, then V _I = V1 _D /G1 …(2) V1 _D ＜Vmax/R2, If V2 _D ≧Vmax/R3, then V _I = V2 _D /G2 …(3) V2 _D ＜ If Vmax/R3, then V _I = V3 _D /G3...(4) However, Vmax is for each MSV circuit 24, 25, 2
This is the MSV circuit output voltage (V) when the maximum amplitude (rms) that can maintain the accuracy of 6 is input.

At this time, the reactor power P (%) is determined by Campbell's method as follows: P∝(V _I /R _I・G _P ) ² holds true, and as a result, P=k _M V _I ² (k _M is a constant), In the Campbell system output means, the reactor power P _M is determined by the following equations (5) to (7). In other words, when the MVD circuit output is expressed by equation (2), P _M =k _M (V1 _D /G1) ² ...(5), and when the MVD circuit output is expressed by equation (3), P _M =k _M (V2 _D /G1). G2) ² ...(6), and in the case of equation (4), P _M =k _M (V3 _D /G3) ² ...(7). Note that R _I is the input impedance of the preamplifier 3, and G _P is the gain of the preamplifier 3.

Now, in such a Campbell system output means, the gain ratio G1:G of each amplifier 21, 22, 23 is
2: When G3 is made small, each MSV circuit 24, 25,
Since the output voltage range of 26 becomes narrower, accuracy can be improved, but in this case, the measurable reactor power P _M
(%) range becomes narrower. for example,
G1:G2:G3=1:2:4, Vmax=10
(V), each MSV circuit 2
The output voltage range of 4, 25, and 26 is 5 to 10 (V) and can be measured with high accuracy, but each
The range that can be covered by the MSV circuits 24, 25, and 26 is as narrow as 0.6 digits each, making it impractical for a Campbell system that needs to cover approximately 6 digits.

On the other hand, the gain ratio G1:G2:G3 is 1:
If the ratio is increased to 10:1000, each MSV circuit 24, 2
The output voltage range that can be covered by 5 and 26 is 4 digits, respectively, is 0.1 to 10 (V), and with a small output of 0.1 (V), deterioration in measurement accuracy is unavoidable. Furthermore, as is clear from the above equations (2) to (7), it is convenient for G to be a multiple of 10, since it is necessary to divide G and ^G2 to obtain the reactor output. Therefore, for the above reasons, G1:G2:G3=1:10:
100 is optimal for MSV circuits 24 and 2526, and in this case, one MSV circuit can handle 2
Since it is possible to cover a reactor power range of several orders of magnitude, it is practical to use three amplifiers and an MSV circuit to cover six orders of magnitude.

Figure 3 shows the gains of amplifiers 21, 22, and 23.
An example of the reactor output P _M (%) corresponding to the MSV circuit output when G1:G2:G3=1:10:100 is shown. In the same figure, H is amplifier 2 with a gain of G3 (large).
3, M is the output of the MSV circuit 25 corresponding to the amplifier 22 with a gain of G2 (medium), and L is the output of the MSV circuit 24 corresponding to the amplifier 21 with a gain of G1 (small). This is the output.
As is clear from the figure, the output of each MSV circuit is 1
~10 (V), which is well within the practical range in terms of measurement accuracy.

Next, the automatic switching correction circuit 20 as a system output switching means will be explained with reference to FIG.
In Fig. 4, A indicates the area covered by the reactor power P (%) by the pulse counting system output, and H
is an amplifier 23 with a gain of G3, which is a Campbell system output.
The reactor power P is determined by the MSV circuit output corresponding to
(%), M indicates the area covered by the reactor power P (%) by the MSV circuit output corresponding to the amplifier 22 with gain G2, and M indicates the area covered by the reactor power P (%) corresponding to the amplifier 21 with L gain G1. It shows the area covered by the reactor output P (%) by the circuit output. As shown in the figure, the area covered by the pulse counting system output and the Campbell system output are
There is an overlap of about one order of magnitude with the area covered by the output of the MSV circuit 26, and the counting rate at the center is assumed to be C _C (=5×10 ⁵ cps).

The automatic switching correction circuit 20 determines whether the pulse count rate is C _c at the time of reactor startup. cps), the reactor output P is the voltage signal output by the pulse system output means.
The reactor output power P _C (=k _C V _C ) corresponding to V _C is obtained. Thereafter, the automatic switching correction circuit 20 adjusts the pulse count rate to C _c
When it exceeds 100 kHz, it switches to the camber type output means. As a result, the reactor power P corresponds to the voltage signal V3 _D from the MSV circuit 26 _of the amplifier 23 with _the largest gain (G3 = 100 ₎ .
100) ² ''.

By the way, since both the pulse counting system and the Campbell system measure the same neutron flux, the outputs must match at the switching point of the systems, but the constant k _C and
k _M is a value calculated from the efficiency and degree of deterioration of the neutron detector 1, the gain of the amplifier, the band, etc.
By the automatic switching of the system described above, the reactor output P _C and
There is a risk of misalignment between PM and _M. Therefore, in this automatic switching correction circuit 20, the reactor outputs P _C and P _M of both systems are made to match around the pulse count rate C _c , that is, k _C V _C = k _M ′ (V33D/100) ² k _M ′＝αkMc ...(8) Set an arbitrary constant α (≒1) to the constant k _M so that Since we have done this, we can determine that the constant k _M is correct. Therefore, when the output of the MSV circuit 26 in the Campbell system output means is selected, the reactor output P _M corresponding to this output becomes near the switching point, and the pulse count rate increases.
When C _C is reached, the Campbell system is switched to the pulse counting system, but in order to eliminate output deviation at this time, k _C ′V _C =k _M (V3 _D /100) ² k _C ′=βk _C …… The above equation (1) is corrected by multiplying the constant k _C by an arbitrary count β so that (9) holds true.

As described above, according to this embodiment, three amplifiers 21, 22, and 23 each having a gain ratio of 10 times and three amplifiers corresponding to these amplifiers are used as the Campbell system output means.
Automatic gain switching of the amplifier that affects the output of the MSV circuit is provided by providing multiple MSV circuits 24, 25, 26 and covering a two-digit reactor output range with each pulse 24, 25, 26. Since this eliminates the need for a camber system, stable output from the Campbell system can be obtained at all times. Further, the output is corrected so that the reactor output determined by the pulse counting system and the reactor power viewing device determined by the Campbell system output do not deviate at the system switching point. Therefore, a smooth and stable single output can always be obtained over a wide range from the neutron source region to the intermediate power region, making it possible to perform highly accurate measurements with high reliability.

In the above embodiment, the voltage comparison and selection furnace 27 and the automatic switching correction circuit 20 may be processed by a microcomputer (hereinafter abbreviated as microcomputer) 30 using software. The configuration of an embodiment using this microcomputer 30 is shown in FIG. In the figure, numeral 31 is a counting rate measuring counter that measures the pulse counting rate from the pulse height discrimination circuit 5 and converts it into a digital value, and numerals 32 to 34 are analog counters that convert the output voltage of each MSV circuit 24 to 26 into digital values. It is a digital converter (hereinafter abbreviated as A/D).

The microcomputer 30 is programmed to execute the flowchart shown in FIG. That is, first, in step ST1, the count rate is read from the count rate measurement counter 31, and the A/D3
The output voltage of each MSV circuit 24-26 is read from 2-34. Next, as ST2, the voltage comparison and selection circuit 27 described in the previous embodiment is applied to the collected data.
The calculations similar to those performed by the automatic switching correction circuit 20 and the automatic switching correction circuit 20 are executed, and the selection processing of the MSV circuit output and the selection correction processing of the pulse counting system and the Campbell system are performed, and as ST3, the reactor output P (% ). After that, in ST4, abnormality determination and output processing to a recorder etc. are performed, and then the process returns to data collection processing.

In this way, if the device uses the microcomputer 30, the level will be determined by software at the time of output from the recorder and the range of the recorder will be automatically changed. It becomes possible to obtain a linear output. Further, in this case, since the output of the pulse counting system and the output of each Campbell system are taken in and processed at the same time, even if an abnormality occurs in any one system, it can be adequately dealt with.

〔Effect of the invention〕

As described in detail above, according to the first and second inventions of the present application, in a system that can automatically perform monitoring during startup operation of a nuclear reactor over a wide area using one neutron detector, the reactor output It is possible to provide a wide-area neutron monitoring device that can improve accuracy and reliability.

[Brief explanation of the drawing]

1 to 4 are diagrams showing one embodiment of the present invention, in which FIG. 1 is an overall block configuration diagram, FIG.
The figure shows an example of the reactor output by the Campbell system output means, FIG. 4 is an explanatory diagram of the operation of the system output automatic switching means, and FIGS. 5 to 7 are diagrams showing embodiments in which a microcomputer is applied to the present invention. , FIG. 5 is a block configuration diagram, FIG. 6 is a flowchart showing the operation of the microcomputer, FIG. 7 is a diagram showing an example of output, and FIGS. 8 to 13 are diagrams showing conventional examples. The figure is a block diagram of SRM, Figure 9 is a block diagram of IRM,
Figure 10 is a diagram showing an example of output in SRM, Figure 11 is a diagram showing an example of output in IRM,
FIG. 2 is a block diagram of a conventional wide-area neutron monitoring device, and FIG. 13 is a diagram showing an example of the output of the conventional device. 1...neutron detector, 3...preamplifier, 4,
21, 22, 23... Amplifier, 5... Wave height discrimination circuit, 6... Diode pump, 20... Automatic switching correction circuit, 24, 25, 26... MSV (root mean square) circuit, 27... Voltage comparison selection Circuit, 30...
Microcomputer (microcomputer).

Claims (1)

[Claims] 1. A pulse system output means for obtaining a reactor output in a neutron source region by extracting a pulse signal from an output signal of a neutron detector and counting the number of pulses per unit time, and the neutron detector a Campbell system output means that obtains the reactor output in the intermediate power range by measuring the root mean square value of the pulsation component in the output signal of the output signal, and a system that automatically selects one of the reactor outputs obtained by both of these output means. output selection means, and the Campbell system output means includes a plurality of amplifiers that amplify the output signals of the neutron detector with different gains, and a root mean square value of the pulsating components of the output signals amplified by these amplifiers. A wide-area neutron monitoring device comprising: a plurality of root mean square circuits for measuring each of the root mean square circuits; and root mean square value selection means for automatically selecting one of the outputs of the root mean square circuits as a Campbell system output. . 2. The wide-area neutron monitoring device according to claim 1, wherein each of the plurality of amplifiers has a gain ratio that differs by a factor of 10. 3 pulse system output means for obtaining the reactor output in the neutron source region by extracting a pulse signal from the output signal of the neutron detector and counting the number of pulses per unit time; It is equipped with a Campbell system output means for obtaining a reactor output in an intermediate power range by measuring the root mean square value, and a system output selection means for automatically selecting one of the reactor outputs obtained by both of these output means. , the Campbell system output means includes a plurality of amplifiers that amplify the output signals of the neutron detector with different gains, and a plurality of amplifiers that respectively measure the root mean square value of the pulsating components of the output signals amplified by these amplifiers. It is equipped with an average circuit and a root mean square value selection means for automatically selecting one of the outputs of these root mean square circuits as a Campbell system output, and the system output selection means is configured to automatically select one of the outputs of these root mean square circuits as a Campbell system output, and the system output selection means 1. A wide-area neutron monitoring device comprising a correction means for multiplying a Campbell system output and a pulse counting system output by a predetermined coefficient at a system switching point due to descent.