KR102115139B1 - Neutron counting apparatus based on a neutron detector having dual sensitivity - Google Patents

Abstract

The present invention relates to a neutron counting device, and more particularly, to a neutron counting device applied to a neutron detector having dual sensitivity. A neutron detector-based neutron counting device having a double sensitivity according to an exemplary embodiment of the present invention includes a low concentration coefficient module connected to output terminals of a plurality of low sensitivity detectors; A high concentration coefficient module connected to the output terminals of a plurality of high sensitivity detectors; And a controller that selectively operates the low concentration coefficient module and the high concentration coefficient module according to the boron concentration of the cooling water according to the core cycle. The present invention can improve the accuracy of boron concentration measurement using a neutron detector with double sensitivity.

Description

A neutron detector-based neutron counting device with double sensitivity {NEUTRON COUNTING APPARATUS BASED ON A NEUTRON DETECTOR HAVING DUAL SENSITIVITY}

The present invention relates to a neutron counting device, and more particularly, to a neutron counting device applied to a neutron detector having dual sensitivity.

In a light-water reactor type nuclear power plant, natural boric acid water is added to the reactor coolant in order to control the long-term response to the combustion of nuclear fuel. Since the criticality varies depending on the concentration of boric acid, it is very important for the safe operation of nuclear power plants to accurately measure the concentration of boric acid in boric acid water. In order to measure the concentration of boron in the reactor coolant, nuclear power plants use an on-line chemical analysis method and an on-line neutron absorption method (boronometer method).

Boronometer generally has a larger boron concentration measurement error than of-line chemical analysis, but has the advantage of being able to measure boron concentration quickly and accurately in real time on-line. Therefore, in the currently operating nuclear power plant, Boronometer is installed in the outflow system of the Chemical & Volume Control System (CVCS) to measure the concentration of boric acid in on-line in real-time by measuring the boron concentration in the coolant from the reactor coolant system. have.

Figure 1 shows a schematic diagram of a boron concentration measuring device (Boronometer) of the neutron absorption method. In the case of a real-time boron monitoring facility currently used in nuclear power plants, a measurement method is used to measure the number of neutrons in the coolant on-line in real time and convert it to the concentration of boron. It is possible to measure the concentration of boron in real time outside the cooling line without leaking coolant such as sampling.

As shown in FIG. 1, the Boronometer is composed of three important equipments: Sampler Asembly, Electronics and Signal Procesing Drawer. Inside the sampler assembly of the Boronometer, one neutron source rod and four neutron detectors (BF3) are built in, and coolant flows into the space between them. In Sampler Electronics, the neutron generated from the source rod passes through the coolant, enters the detector, and reacts (n, alpha) with the boron in the detector. The neutrons are counted on-line in real time through the counting of ion pairs. In addition, the Signal Procesing Drawer converts the neutron coefficient into boron concentration to provide the boron concentration signal of the coolant to the operator of the main control room in real time.

Boronometer is a very important facility for the safety and operation of nuclear power plants because the operator controls the concentration of boron from reactor start to output operation and reactor stop.

Boronometer has the advantage that it can measure boron concentration quickly by continuously measuring neutron counting rate without sampling cooling water, but it has a very large error compared to chemical analysis method. The Boronometer's boron concentration measurement error based on the chemical analysis method at the nuclear power plant site has an pm error of about 80 pm and a% error of about 5%. Therefore, the Boronometer's boron concentration measurement error is very large at the nuclear power plant site, so it is not utilized for nuclear power plant operation such as fuel loading, starting operation, and control of responsiveness. When loading nuclear fuel with a high concentration of boron and when operating nuclear reactors, other measuring instruments such as the neutron monitoring facility (ENFMS) are used. In addition, at the end of the cycle where the boron concentration is low, the boron concentration measurement of the boronometer is only used to grasp the tendency of the boron concentration change.

The boron dilution accident is an accident in which the reaction rate of the reactor increases due to mechanical defects of the boron system, control by human error, or boron dilution in an unplanned coolant, and accordingly, the output continuously rises to damage the nuclear fuel. In the case of fuel loading, normal temperature stop, high temperature stop, and high temperature standby condition, an alarm should be generated so that the operator can recognize the boron dilution accident about 15 to 30 minutes before reaching the threshold. In order to prevent and detect boron dilution accidents, on-line boronometers are continuously installed to monitor changes in boron concentration, but due to large measurement errors, reliable information cannot be provided to the operator, so the boron dilution accident monitoring system ( Boron Dilution Alarm System).

The nuclear reactor for light water reactor type injects a large amount of boron (5,00 pm) to maintain a critical state by compensating for a high amount of surplus reactivity at the beginning of operation, and a reactor coolant to compensate for reactivity due to combustion of nuclear fuel during output operation Reduce the boron concentration of to dilute to near 0 pm at the end of the cycle. Since the BF3 neutron detector with a single sensitivity (4 cps / nv) is used in the Boronometer to measure the broad boron concentration from 5,000 pm to 0 pm in the entire operating range, the uncertainty of the measured boron concentration is very large.

-When the boron concentration at the beginning of the cycle is very high, a lot of perturbation is caused in the signal output from the BF3 detector since the neutron flux entering the BF3 detector is very small.

-In addition, when the concentration of boron at the end of the period is very low, the neutron flux incident on the BF3 detector becomes very large, and signal line formation is deteriorated by the BF3 detector saturation (Pulse Pile-up) phenomenon.

In the case of daily load-following operation where the output fluctuation is severe, the measured value of boron concentration is not reliable due to the disadvantages of the existing WRBS. In addition, since it cannot be used as an input signal of the boron dilution warning from fuel loading to reaching the initial critical level, existing boron dilution accidents are monitored by using the starting channel of the nuclear measurement system.

Boronometer using the neutron absorption method does not generate radioactive waste and has the advantage of being able to measure boron concentration quickly in real time, but has a big disadvantage of measurement error.

1. Korean Patent Publication No. 2010-0009085 (2010.01.27), method for analyzing boron distribution of boron alloy steel

Accordingly, an object of the present invention is to provide a neutron detector-based neutron counting device having a double sensitivity capable of improving boron concentration measurement accuracy.

A neutron detector-based neutron counting device having a double sensitivity according to an exemplary embodiment of the present invention includes a low concentration coefficient module connected to output terminals of a plurality of low sensitivity detectors; A high concentration coefficient module connected to the output terminals of a plurality of high sensitivity detectors; And a controller that selectively operates the low concentration coefficient module and the high concentration coefficient module according to the boron concentration of the cooling water according to the core cycle.

Here, the low concentration coefficient module and the high concentration coefficient module can recognize a neutron pulse based on two reference voltages.

In addition, the low concentration coefficient module and the high concentration coefficient module can vary the reference voltage by varying the internal resistance.

In addition, a filter for removing DC components and noise may be included.

Also, the low sensitivity detector may be a BF3 detector.

Further, the high sensitivity detector may be a He3 detector.

The present invention can improve the accuracy of boron concentration measurement using a neutron detector with double sensitivity.

In addition, the present invention can accurately recognize a neutron pulse using two reference voltages.

In addition, the present invention can effectively remove the DC component and noise suitable for the installation environment using a variable cut-off frequency filter.

1 shows a schematic view of a boron concentration measuring device (Boronometer) of the neutron absorption method.
Figure 2 shows a schematic structure of a sampler assembly (Sampler Assembly) in the boron concentration measuring device (Boronometer) of the neutron absorption method.
3 shows a functional block diagram of a neutron counting device according to a preferred embodiment of the present invention.
4 shows an example of a circuit diagram of the main amplifier of FIG. 3.
5 shows simulation results for evaluating the filtering characteristics of the filter unit 312a of FIG. 4.
6 shows a simulation result for explaining the effect of the feedback capacitor.
Fig. 7 shows the final input / output waveform of the main amplifier of 4.
FIG. 8 shows an example of the delimiter circuit of FIG. 3.
9 shows simulation results for explaining the effect of removing noise by a filter on a delimiter.
10 is a view for explaining a method for recognizing a neutron pulse using a Schmitt trigger circuit.
11 is a view for explaining the experimental results of comparing the noise canceling performance of the existing comparator and Schmidt trigger.
12 shows a circuit diagram for explaining the operating principle of the Schmitt trigger circuit of FIG. 8.
13 shows an example of a multivibrator & line driver circuit diagram.
14 shows a diagram that proves that the pulse width is adjusted through simulation.

The present invention can be applied to various changes and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

In describing each drawing, similar reference numerals are used for similar components. In the description of the present invention, if it is determined that a detailed description of known technologies related to the present invention may obscure the subject matter of the present invention, the detailed description will be omitted.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from other components.

For example, the first component may be referred to as a second component without departing from the scope of the present invention, and similarly, the second component may be referred to as a first component.

The term and / or includes a combination of a plurality of related described items or any one of a plurality of related described items.

When an element is said to be "connected" or "connected" to another component, it is understood that other components may be directly connected to or connected to the other component, but there may be other components in between. It should be.

On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that no other component exists in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention.

Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, terms such as “include” or “have” are intended to indicate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains.

Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

Hereinafter, a neutron detector-based neutron counting device having a double sensitivity according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

Figure 2 shows a schematic structure of a sampler assembly (Sampler Assembly) in the boron concentration measuring device (Boronometer) of the neutron absorption method. Referring to FIG. 2, the sampler assembly is cylindrical, the side is stainless steel, and is airtight and has a neutron source at its center. In addition, six detectors are positioned at the same distance apart from the neutron source. The detector includes a plurality of low sensitivity detectors (100, Low sensitityty detector) and a plurality of high sensitivity detectors (200, High sensitivity detector). FIG. 2 illustrates the case where the four low sensitivity detectors 100 and the case where the two high sensitivity detectors 200 are illustrated. In order to evenly detect the concentration of boron in the cooler evenly inside the sampler assembly, it is preferable that the detectors 200 are spaced apart and installed at the same intervals. A cooler inlet (not shown) is installed on one side of the sampler assembly, and a coolant outlet (not shown) is installed on the other side, and a neutron corresponding to the concentration of boron on the coolant flowing through the coolant inlet can be detected through the detector. .

A method of measuring boron concentration in a boronmometer is to convert the neutrons emitted from a neutron source located in the center of the bolometer to a boron concentration by counting with a neutron proportional counter. A certain amount of neutron emitted from the source is changed when it enters the detector due to the boron concentration of the coolant filled inside the bolometer assembly, so the neutron coefficient measured by the detector can be converted to boron concentration by using an appropriate conversion formula. Do. Each event pulse generated by the neutron incident to the detector is a mixture of ambient noise and gamma background signal. The neutron counting circuit primarily amplifies the pulse signal generated by the detector through a preamplifier. The amplified neutron pulse signal signal compares a reference voltage value through a discriminator, and generates an output pulse by removing background noise caused by noise. The output pulse signal maintains a characteristic pulse shape and improves the signal-to-noise ratio to output a TTL signal for easy counting.

3 shows a functional block diagram of a neutron counting device according to a preferred embodiment of the present invention.

The neutron counting device 300 may include a low concentration counting module 310 and a high concentration counting module 320.

The low concentration coefficient module 310 may include a low concentration preliminary amplifier 311, a main amplifier 312, a delimiter 313, a multivibrator & line driver 314.

The input terminal of the low concentration preliminary amplifier 311 may be connected to the output terminals of the plurality of low sensitivity detectors 100. The output terminals of the plurality of low-sensitivity detectors 100 may be connected in parallel with the input terminals of a single low-concentration coefficient module 310 to compensate for the limit of the detection area of the single detector 100. The low-concentration preamplifier 311 may amplify the input voltage at a lower amplification ratio than the main amplifier 312. A BF3 detector may be used as the low sensitivity detector 110. The sensitivity of the BF3 detector can be 4.0 cps / nv.

The output terminal of the low concentration preamplifier 311 may be connected to the main amplifier 312. 4 shows an example of a circuit diagram of the main amplifier of FIG. 3. Referring to FIG. 4, the main amplifier 312 may include a filter unit 312a and an amplifier unit 312b.

The filter unit 312a includes C1 connected to the + input terminal of the amplifying unit 312b and R1 connected in parallel to C1. C1 and R1 act as a high pass filter and can function to block DC components.

5 shows simulation results for evaluating the filtering characteristics of the filter unit 312a of FIG. 4.

Referring to FIG. 5, the red color (input) has an offset of about 0.3 V DC component. As the DC component is blocked while passing through the filter unit 312a, it can be seen that the waveform is located on the y-axis (voltage) 0 level. In FIG. 5, the red waveform is a waveform before the DC component is filtered, and the green waveform represents a waveform after the DC component is filtered. When setting the discriminator level, this offset is a disturbing factor, so it is preferable to remove it through the filter unit 312a.

Referring to FIG. 4 again, the amplifying unit 312b may be designed as a non-inverting amplifier. The amplifying unit 312b may amplify the input signal of the + input terminal. The input signal is applied to the non-inverting input terminal (+) and can be amplified compared to the voltage of the inverting input terminal (-) and output. The output can be returned to the inverting input terminal after the voltage drop. The input / output relationship may be as follows.

Vout = (1 + R4 / R2) Vin, Vout / Vin = 1 + R4 / R2

Here, R2 is actually a variable resistor, and the amplification degree of the circuit may vary according to the value of R2. C3 is a feedback capacitor. This is to secure a phase margin to reduce noise filtering and signal distortion. 6 shows a simulation result for explaining the effect of the feedback capacitor. In FIG. 6, the red waveform is a waveform when there is no feedback capacitor, and the blue waveform represents a waveform when there is a feedback capacitor. Fig. 7 shows the final input / output waveform of the main amplifier of 4. In FIG. 7, the red waveform is an input waveform to the main output device, and the green waveform indicates an output waveform from the main output device. It can be seen that the noise larger than the main signal was mostly removed and the signal itself was amplified. The output of the main amplifier 312 may be connected to the input of the delimiter 313.

8 shows an example of the circuit of the delimiter 313 of FIG. 3. A Schmitt trigger circuit was used as a disc limiter. Discriminator amplifies by comparing input voltage and voltage of other reference power. A diode was used at the input to prevent the signal from the main amplifier from being saturated with sound, and a filter was designed to remove noise. In addition, a buffer circuit is inserted in the output stage to obtain a fast output response speed. As a result, the Rising and Failling Time of the output signal is improved and it is easy to transmit the signal to a farther place. C13 D1 is a capacitor / diode for input protection. U7A is an inverter (buffer) for output boards. The existing delimiter sets only one reference voltage (LLD, Low Limit of Detection) to count only voltages above LLD and does not count voltages below. Setting LLD is the most important factor to control the linearity of pulse output. When using only a single reference voltage, the passive element value that determines the time constant is fixed and the cutoff frequency of the low pass filter is fixed. For this reason, the graph of the coefficient value according to the surrounding environment such as the noise level and the inflow amount leads to different characteristic results each time. In addition, if the LLD is increased, the sensitization of the pulse may not be counted by the neutron, and when the LLD is lowered, unnecessary noise is counted, and the output tends to saturate and output linearity is greatly lost. Severe JITTER is likely to occur due to one comparative voltage source, which has a problem of being directly connected to counting error. The present invention can use two reference voltages using a Schmitt trigger circuit. By setting two reference voltages (UTP (Upper Trigger Point) and LTP (Lower Trigger Point)), only the voltage above UTP is counted, and only the voltage below LTP has a LOW value. Maintain the existing value for intermediate voltage changes. The disc limiter 313 may have an active low pass filter on the input end side. This low pass filter may be implemented as R14 and C13 in FIG. 8. R14 may be a variable resistor. The low pass filter may be capable of actively filtering noise according to a noise environment. By adjusting the resistance of R14, the time constant of the variable filter can be adjusted to actively remove the DC component and inflow noise. Accordingly, it is possible to improve the system performance in a subsequent signal processing process by improving the filtering function against the instantaneous change due to noise. By setting the upper trigger point (UTP) and lower trigger point (LTP) of the Schmitt trigger circuit to improve the filtering function against the instantaneous change due to noise, the system performance can be improved in the subsequent signal processing.

9 shows simulation results for explaining the effect of removing noise by a filter on the delimiter 313. In FIG. 9, the red waveform is an input waveform to the delimiter 313, and the green waveform represents an output waveform. 9, it can be seen that the Rising / Falling time has been improved and the noise removal capability.

10 is a view for explaining a method for recognizing a neutron pulse using a Schmitt trigger circuit.

As is well known, the Schmitt trigger has a hysteresis characteristic in which the output state changes at different trigger voltage values of the upper trigger point (UTP) and the lower trigger point (LTP). That is, when a potential higher than UTP is applied, the upper limit state is maintained, and the upper limit state value is maintained until the potential falls below LTP. By using this, it is possible to prevent the output voltage from easily changing to a high or low limit for a small input change near the threshold. In addition, the pulse level dropped below the LTP is maintained at a low value regardless of any change in the middle as long as it does not rise above the UPT again. Therefore, when the output value of the Schmitt trigger is in the upper limit, it is regarded as a normal pulse corresponding to the neutron, and outputs a pulse signal in the form of a TTL (Transistor Transistor Logic). Can be ignored without.

11 is a view for explaining the experimental results of comparing the noise canceling performance of the existing comparator and Schmidt trigger. In FIG. 11, red represents an input (simulated input), green represents an existing comparator output, and blue represents an output of a Schmitt trigger. Noise is included in the simulated input. The simulated signal contains noise in three neutron signals. Referring to FIG. 11, since the existing comparator uses one reference voltage, a total of 6 pulses are output. This is because signals above LLD (Low Limit of Detection) are all determined as neutron signals. Thereby, it can be confirmed that incorrect count information (six pulse signals) in which noise signals are mixed is output instead of the correct neutron signal (three pulse signals). On the other hand, when the Schmitt trigger circuit of FIG. 8 is used, it can be seen that the designer can set the range of UTP / LTP under the same input condition, and no output error occurs even in the case of an intermediate noise change. In other words, if the signal does not fall below the LTP even when the signal is confirmed to be above UTP, it is regarded as a normal neutron pulse and the rest of the signals are considered noise, so only three pulse signals are regarded as correct neutron signals.

12 shows a circuit diagram for explaining the operating principle of the Schmitt trigger circuit of FIG. 8.

Applying Kirchhoff's Current Low on V2 node,

It has two thresholds depending on the output voltage. The two output states are as follows.

That is, UTP and LTP can be set by adjusting only the resistance values R1, R2, and R3.

The output of the delimiter 313 is supplied to the multivibrator & line driver 314.

13 shows an example of a multivibrator & line driver circuit diagram.

Referring to FIG. 13, as a multivibrator, a mono-stable multivibrator SN7412 may be used, and as a line driver, a MAX41147 that is resistant to external noise and can be driven to a high frequency may be used. The MAX41147 may include an output stabilization buffer 7404. The output pulse width of the Schmitt trigger output signal is adjusted through the monostable multivibrator (SN74121N). 14 shows a diagram that proves that the pulse width is adjusted through simulation. In FIG. 14, red represents an input pulse, green represents a pulse width control output, and blue represents a line driver output. It can be seen from the following equation that the calculated output and the simulation result are almost identical.

As in the above equation, the width of the pulse can be adjusted with a capacitor and a resistor. This can also be designed to be adjustable during operation using a variable resistor. C36 is a pulse width adjustment capacitor, and the remaining capacitors are power supply smoothing capacitors.

Referring back to FIG. 3, the high concentration coefficient module 320 may include a high concentration preliminary amplifier 321, a main amplifier 322, a delimiter 323, a multivibrator & line driver 324.

The input terminal of the high concentration preliminary amplifier 311 may be connected to the output terminals of the plurality of high sensitivity detectors 200. The output terminals of the plurality of high sensitivity detectors 200 may be connected in parallel with the input terminals of a single high concentration coefficient module 320 to compensate for the limit of the detection area of the single detector 200. The high concentration preliminary amplifier 321 may amplify the input voltage at a lower amplification ratio than the main amplifier 322. The He3 detector may be used as the high sensitivity detector 200. The He3 detector may have a sensitivity of 11.3 cps / nv.

The output terminal of the high concentration preliminary amplifier 321 may be connected to the main amplifier 322. The structure / function / operation of the main amplifier 322, the delimiter 323, the multivibrator & line driver 324 is the main amplifier 312, the delimiter 313, the multivibrator & line driver 314 seen above. ).

The controller 400 can control the overall operation of the neutron counting device. The controller 400 operates the high concentration counting module 320 and the low concentration counting module 310 at the same time to compensate for the low neutron flux in a section having a high boron concentration, such as an initial and middle section of the core cycle, and a core cycle having a low boron concentration. In the horse section, pulse saturation of the detection module can be eliminated by turning off the high concentration counting module 320 and operating only the low concentration counting module 310. To this end, the controller 400 drives and controls the counting modules 310 and 320 to be turned on and off, but counts each counting module 310 according to the core cycle based on the core cycle information stored in advance in the memory (not shown). 320) can be controlled to operate automatically ON / OFF operation.

100: low sensitivity detector
200: high sensitivity detector
300: neutron counting device
310: low concentration coefficient module
320: high concentration coefficient module
400: controller

Claims (6)

A low concentration coefficient module connected to output terminals of a plurality of low sensitivity detectors;
A high concentration coefficient module connected to the output terminals of a plurality of high sensitivity detectors; And
A controller for selectively operating the low concentration coefficient module and the high concentration coefficient module according to the concentration of boron in the cooling water according to the core cycle,
The low concentration coefficient module includes: a low concentration preliminary amplifier connected to the output terminals of the plurality of low sensitivity detectors; And
It includes; a main amplifier connected to the output terminal of the preliminary amplifier for low concentration;
The high concentration coefficient module includes a high concentration preliminary amplifier for connecting the output terminals of the plurality of high sensitivity detectors; And
Includes; main amplifier connected to the output terminal of the high-concentration pre-amplifier,
The low concentration coefficient module and the high concentration coefficient module,
A delimiter connected to the output terminal of the main amplifier to set an upper triggering point and a lower triggering point of the Schmitt trigger circuit to filter the instantaneous change due to noise; And
A neutron detector-based neutron counting device having a double sensitivity, comprising a multivibrator & line driver connected to the output terminal of the delimiter to adjust the output pulse width of the delimiter with a capacitor and a variable resistor.
According to claim 1,
The low-concentration counting module and the high-concentration counting module recognize a neutron pulse based on two reference voltages. According to claim 1,
The low-concentration counting module and the high-concentration counting module are neutron detector-based neutron counting devices having a double sensitivity, characterized in that the reference voltage can be varied by varying the internal resistance. According to claim 1,
A neutron detector-based neutron counting device having a double sensitivity, comprising a filter for removing DC components and noise. According to claim 1,
The low sensitivity detector is a neutron detector-based neutron counting device having a double sensitivity, characterized in that the BF3 detector. According to claim 1,
The high sensitivity detector is a neutron detector-based neutron counting device having a double sensitivity, characterized in that the He3 detector.

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