JP5531277B2 - Reactor startup region neutron monitoring system - Google Patents

Description

  The present invention relates to a reactor activation region neutron monitoring apparatus that measures a neutron flux in a reactor pressure vessel of an improved boiling water reactor (ABWR) and monitors an output at the time of reactor activation.

  In the reactor power monitoring of ABWR, a recent representative nuclear power plant, there are cases where the neutron flux level when the reactor starts up is low and when the neutron flux level is high enough to generate power in the turbine / generator. Two types of neutron flux monitoring are performed during the so-called reactor power operation. Instrumentation that monitors the neutron flux in a nuclear reactor is called nuclear instrumentation. A system called a startup region neutron monitor is used for nuclear instrumentation at the time of reactor startup. On the other hand, a system called a local output region neutron monitoring device is used for neutron flux monitoring during output operation.

  Here, paying attention to the point that the noise source is caused by the common mode current flowing in the signal cable, it is known to suppress the noise by suppressing the common mode current (see, for example, Patent Document 1). Specifically, noise suppression is achieved by adjusting the impedance of the loop through which the common mode current flows. The common mode loop is composed of a signal cable, stray capacitance, and ground, and has a series resonance circuit composed of stray capacitance and cable inductance. Since noise that matches this resonance point easily flows through the signal cable, the resonance frequency is shifted by changing the inductance of the signal cable so that it does not match the frequency used for neutron monitoring, or a parallel resonance circuit is added on the signal cable. Therefore, the impedance of the frequency band used for neutron monitoring is increased.

  In addition, as a countermeasure when the noise source is a power device, a return line is used to reduce the noise current flowing from the power line to the grounding system, and an inductor is added to the power line itself to reduce the noise current flowing through the power line. What is suppressed is known (for example, refer to Patent Document 2).

JP-A-7-162257 JP-A-9-2881

  Patent Document 1 is a suppression measure on the instrumentation side that is affected by noise, and Patent Document 2 is a suppression measure on the power line side that generates noise.

  In the measures on the instrumentation side disclosed in Patent Document 1, a signal line is wound around a magnetic core to achieve a desired inductance and parallel capacitance. However, signal lines that handle weak signals often have strong shields, so the signal cable itself is difficult to bend and difficult to wind tightly around the core, and it may be difficult to achieve the desired inductance or capacitance. Many.

  Further, in Patent Document 2, a large inductance is inserted in a loop through which a return line is added or a noise current flows in order to suppress a noise current on the power line side. However, in order to insert an inductance into the return line or the power line. The problem is that the construction of the project becomes a major issue.

An object of the present invention is to provide a reactor activation region neutron monitoring apparatus capable of suppressing noise that can be realized by simple means.

(1) In order to achieve the above object, the present invention provides a detector for detecting a reactor output, a coaxial cable for transmitting an output signal of the detector, and an output signal of the detector connected to the coaxial cable. A reactor activation region neutron monitoring device having a signal processing device for converting the power into a reactor output, where a stray capacitance is generated between the coaxial cable and a ground line in parallel with the stray capacitance. Thus, the first resonance suppression circuit is provided.
With this configuration, noise suppression that can be realized by simple means can be achieved.

  (2) In the above (1), preferably, the first resonance suppression circuit is provided between a shield of the coaxial cable and a ground.

  (3) In the above (1), preferably, the first resonance suppression circuit includes a series connection of a capacitance and a resistor.

(4) In the above (1), preferably, in a location where stray capacitance is generated between the power line of the power system having the control unit for controlling the drive unit and the ground line, in parallel with the stray capacitance. Thus, a second resonance suppression circuit is provided.

  (5) In the above (4), preferably, the second resonance suppression circuit is provided between the power line and ground.

(6) In the above ( 4 ), preferably, the second resonance suppression circuit includes a series connection of a capacitance and a resistor.

  (7) In the above (3) or (6), preferably, the capacitance value is a value of a stray capacitance generated for the coaxial cable or a value of a stray capacitance generated for the power line. Is bigger than that.

According to the present invention, it is possible to achieve noise suppression that can be realized by a simple means without adding significant changes to existing signal lines and power lines.

1 is an overall explanatory diagram of an embodiment of the present invention in which a resonance suppression circuit is added to a power system and an instrumentation system in order to suppress noise propagating from the power system to the instrumentation system in a nuclear power plant. 2 is an equivalent circuit of noise propagation from a power system to an instrumentation system in the nuclear power plant according to the embodiment of the present invention shown in FIG. 1. It is a circuit model for calculating the characteristic which the noise which generate | occur | produced in the motive power system propagates to an instrumentation system based on the equivalent circuit of FIG. FIG. 4 is a circuit model without a resonance suppression circuit for comparison with the noise propagation characteristics of the circuit model in which the resonance suppression circuit shown in FIG. 3 exists. It is the figure which showed the common mode electric current which flows into the instrumentation cable calculated from the circuit model of FIG. 3, FIG. 4 in contrast. It is the figure which showed the common mode electric current which flows into the power cable calculated from the circuit model of FIG. 3, FIG. 4 in contrast.

Hereinafter, the configuration and operation of a reactor activation region neutron monitoring apparatus according to an embodiment of the present invention will be described with reference to FIGS.
First, the configuration of a nuclear power plant using the reactor activation region neutron monitoring apparatus according to the present embodiment will be described with reference to FIG.
FIG. 1 illustrates the configuration of a nuclear power plant that uses a reactor activation region neutron monitoring apparatus according to an embodiment of the present invention.
In the nuclear power plant 100, a reactor containment vessel 5, a preamplifier 8, and a conduit tube 7 are installed inside the reactor building 9. Further, a neutron monitoring device 10, a neutron monitoring device grounding wire 19, a power supply device 17 and a power supply device grounding wire 20 are installed at one corner of the reactor building 9. Inside the reactor containment vessel 5, there are a reactor pressure vessel 1, an instrumentation tube 2, a neutron detector 3, a detector cable 4, an electric motor 11, and an electric motor casing 12 that is a casing of the electric motor 11. And a movable cable 13 are provided.

  The neutron detector 3 is accommodated in an instrumentation tube 2 inserted into the reactor pressure vessel 1. The neutron detector 3 is a detector for a start-up region neutron monitoring apparatus. Thermal neutrons in the nuclear reactor are incident on the neutron detector 3 and a weak current is generated by an ionization action generated inside the detector. The reactor pressure vessel 1 is grounded.

  A neutron detector 3 is housed in an instrumentation tube 2 inserted into the reactor pressure vessel 1, and an ionization current corresponding to the number of incident neutrons is generated from the neutron detector 3. The neutron detector 3 is connected to the detector cable 4 via the connector 3A. A coaxial cable is used as the detector cable 4. The ionization current detected by the neutron detector 3 is transmitted via the detector cable 4. The detector cable 4 is accommodated in a conduit tube 7 and is connected to a preamplifier 8 through a penetration portion (cable penetration) 6 that is a hole for passing a nuclear instrumentation cable. The ionization current generated by the neutron detector 3 is amplified by a preamplifier 8 installed between the reactor containment vessel 5 and the wall of the reactor building 9. The amplified signal is converted into reactor power by the neutron monitoring device 10.

  On the other hand, in the reactor containment vessel 5, a large number of various electromagnetic devices such as an electric motor 11 for controlling and protecting the nuclear reactor and pumps and electromagnetic valves (not shown) are installed. These electromagnetic devices are driven by controlling supply of AC power or DC power on the power source side. That is, the power supply device 17 drives the electric motor 11 via the moving cable 13. The electric motor 11 is accommodated in the electric motor housing 12.

  A power supply ground line 20 that is a ground line of the power supply apparatus 17 and a neutron monitoring apparatus ground line 19 that is a ground line of the neutron monitoring apparatus 10 are grounded to the building ground trunk 18. As a result, the reactor pressure vessel 1 and a steel frame constituting the reactor building 9 (not shown) are also electrically connected to the building ground trunk 18.

  As described above, in FIG. 1, the power supply device 17 controls its operation by supplying power to the electric motor 11. For example, when the power supply device 17 is a single-phase AC and two-wire type, the magnitude of the current flowing into the motor 11 from one power line and the current returning from the other line to the power supply device 17 are completely the same. It is common to do. However, when an inverter is used in the power supply, the current flowing from one power line to the motor 11 and the magnitude of the current returning from the other line to the power supply device 17 are not matched by timing. There is. When the current flowing in and the magnitude of the current returning from the other line to the power supply device 17 completely match, the sum of the currents flowing through these two lines is zero, but when they do not match depending on the timing, the sum of the currents Has a significant value. The sum of the currents flowing through these two wires is a common mode current, that is, a noise current. Of the electric motors in the plant, those with large power often use three-phase alternating current. In the case of the 3-wire system, the sum of the three lines is the common mode current, and in the case of the 4-wire system, the sum of the four lines is the common mode current. If there is a common mode current, that is, a noise current, this noise current may be induced by electromagnetic induction if the signal line passes nearby, and the noise current may be transmitted to the instrumentation side via the ground wire. There is a possibility of wrapping around.

  As shown in FIG. 1, it can be seen that the signal cable 4 is connected to the building ground trunk 18 via the stray capacitance Cp. Moreover, it can be seen that the power cable 13 is connected to the building ground trunk 18 through the stray capacitance Ck. The common mode current, which is a noise source, flows through the ground via the stray capacitances Ck and Cp. In particular, since the building ground trunk 18 is realized by a thick wire or the like, the resistance itself is small, and a large common mode current is generated at a series resonance frequency composed of the inductance of the loop through which the common mode current flows and the stray capacitances Ck and Cp. There is a high possibility that it will appear as noise in the flow and instrumentation.

  As a countermeasure, in this embodiment, as shown in FIG. 1, resonance suppression circuits 15 and 16 are connected to a portion where stray capacitance is considered to occur. The resonance suppression circuit 16 is provided to reduce the noise current flowing to the instrumentation side. The resonance suppression circuit 16 is installed between the connector 3A of the neutron detector 3 and the reactor pressure vessel 1, and is installed in parallel with the stray capacitance Ck. The resonance suppression circuit 15 is provided to reduce noise generated in the power system. The resonance suppression circuit 15 is installed between the external shield of the power cable 13 in the vicinity of the electric motor 11 and the building ground trunk 18 so as to be in parallel with the stray capacitance Cp. These resonance suppression circuits 16 and 15 suppress the current during series resonance.

Next, an equivalent circuit in which the coupling of the power cable 13 and the signal cable 4 in the nuclear power plant using the reactor activation region neutron monitoring apparatus according to the present embodiment is described with reference to FIG.
FIG. 2 is an equivalent circuit diagram in which the coupling of the power cable 13 and the signal cable 4 is arranged in a nuclear power plant using the reactor activation region neutron monitoring apparatus according to the embodiment of the present invention.

  In FIG. 2, the signal cable 4 is represented by a signal cable impedance Zk. Similarly, the power cable 13 is represented by a power cable impedance Zp. The noise source exists on the power side.

  The ground trunk line is represented by five impedances Z01 to Z05. The stray capacitances of the signal cable 4 and the power cable 13 are Ck and Cp, respectively.

Next, a circuit model for calculating the common mode currents ic1 and ic2 from the generated voltage of the noise source in the nuclear power plant using the reactor activation region neutron monitoring apparatus according to the present embodiment will be described with reference to FIG.
FIG. 3 is a circuit model diagram for calculating the common mode currents ic1 and ic2 from the generated voltage of the noise source in the nuclear power plant using the reactor activation region neutron monitoring apparatus according to the embodiment of the present invention.

  In FIG. 3, the impedance of the equivalent circuit shown in FIG. 2 is represented by a series circuit of a resistor and an inductor. That is, the impedance Zk of the signal cable 4 is expressed by a series circuit of the resistor RK1 and the inductance LK1. The impedance Zp of the power cable 13 is expressed by a series circuit of a resistor RP1 and an inductance LP1.

  The impedance Z1 of the ground trunk line is expressed by a series circuit of a resistor R1 and a capacitance C1. The impedance Z2 of the ground trunk line is expressed by a series circuit of a resistor R2 and a capacitance C2. The impedance Z3 of the ground trunk line is expressed by a series circuit of a resistor R3 and a capacitance C3. The impedance Z4 of the ground trunk line is expressed by a series circuit of a resistor R4 and a capacitance C4. The impedance Z5 of the ground trunk line is expressed by a series circuit of a resistor R5 and a capacitance C5.

  Further, the resonance suppression circuit 15 is represented by a series circuit of a resistor R7 and a capacitance C7. The resonance suppression circuit 16 is represented by a series circuit of a resistor R6 and a capacitance C6.

  The noise source is represented as Vn.

Next, for comparison, a circuit model for calculating the common mode currents ic1 and ic2 from the generated voltage of the noise source when there is no resonance suppression circuit will be described for comparison.
FIG. 4 is a circuit model diagram for calculating the common mode currents ic1 and ic2 from the generated voltage of the noise source when there is no resonance suppression circuit for comparison.

  In FIG. 4, the resonance suppression circuit including the series circuit of the resistor R7 and the capacitance C7 illustrated in FIG. 3 and the resonance suppression circuit including the series circuit of the resistor R6 and the capacitance C6 are eliminated. Are the same.

Next, calculation results of the common mode currents ic1 and ic2 in the nuclear power plant using the reactor activation region neutron monitoring apparatus according to the present embodiment will be described with reference to FIGS.
FIG. 5 is a calculation result diagram of the common mode current on the instrumentation side in the nuclear power plant using the reactor activation region neutron monitoring apparatus according to one embodiment of the present invention. FIG. 6 is a calculation result diagram of the power-side common mode current in the nuclear power plant using the reactor activation region neutron monitoring apparatus according to the embodiment of the present invention.

  5 and 6, the horizontal axis indicates the frequency (MHz), and the vertical axis indicates the noise current (dB).

  FIG. 5 shows the result of calculating the common mode current ic2 on the instrumentation side using FIG. 3 and FIG.

  As shown in FIG. 4, when the instrumentation-side resonance suppression circuit 15 is not provided, resonance peaks of noise current occur at two frequencies. The low frequency peak occurs around 40 kHz, and the high frequency peak occurs around 400 kHz.

  On the other hand, as shown in FIG. 3, when the instrumentation-side resonance suppression circuit 15 is provided, a sharp resonance peak is eliminated, noise is reduced, and noise is suppressed.

  Here, in the resonance suppression circuit (resonance suppression circuit 15 on the instrumentation side in FIG. 1) composed of a series circuit of the resistor R7 and the capacitance C7 in FIG. 3, the value of the resistor R7 and the value of the capacitance C7 are as follows. It is set as follows. That is, the value of the capacitance C7 is increased with respect to the value of the stray capacitance Ck. For example, when the stray capacitance Ck is several hundred pF, the value of the capacitance C7 is several nF. Since the stray capacitance Ck and the capacitance C7 are connected in parallel, increasing the value of the capacitance C7 with respect to the value of the stray capacitance Ck makes it easier for the current to flow toward the capacitance C7. And since the electric current which flows through the electrostatic capacitance C7 is converted into heat energy and consumed by the resistor R7, noise can be suppressed. The value of the resistor R7 is about several tens Ω to several hundreds Ω.

  Conventionally, it has been necessary to insert a parallel resonant circuit or a resonant frequency shift circuit into the common mode loop, and as a result, existing signal lines and power lines have to be modified. On the other hand, in this embodiment, since the resonance suppression circuit is connected to the existing signal line or power line in parallel, only the terminal to be connected is necessary, but the existing signal line or power line itself is hardly used. There is no need to add. In the resonance suppression circuit, the capacitance of the capacitor to be connected is made larger than the stray capacitance so that a large amount of noise current flows to the suppression circuit side, and the noise current is converted into heat by a resistor connected in series with the capacitor. Thereby, in the conventional method, the resonance frequency is shifted to a low frequency by increasing the inductance of the existing signal line or power line, whereas in this embodiment, the steep resonance peak itself can be eliminated.

  FIG. 6 shows the result of calculating the common mode current ic1 on the power supply side using FIG. 3 and FIG.

  As shown in FIG. 4, when the power supply side resonance suppression circuit 16 is not provided, a resonance peak of noise current occurs at one frequency. The frequency of this peak is about 40 kHz.

  On the other hand, as shown in FIG. 3, when the power source side resonance suppression circuit 16 is provided, a sharp resonance peak is eliminated, noise is reduced, and noise is suppressed.

  Here, in the resonance suppression circuit (resonance suppression circuit 16 on the power source side in FIG. 1) composed of a series circuit of the resistor R6 and the capacitance C6 in FIG. 3, the values of the resistor R6 and the capacitance C6 are as follows. It is set like this. That is, the value of the capacitance C6 is increased with respect to the value of the stray capacitance Cp. For example, when the stray capacitance Cp is several tens of nF, the value of the capacitance C6 is set to several hundreds nF. Since the stray capacitance Cp and the capacitance C6 are connected in parallel, increasing the value of the capacitance C6 relative to the value of the stray capacitance Cp makes it easier for the current to flow toward the capacitance C6. The current flowing through the capacitance C6 is consumed by the resistor R6, so that noise can be suppressed. The value of the resistor R6 is about several tens of ohms to several hundreds of ohms.

  In both FIGS. 5 and 6, the common mode current value, which is noise, is smaller when there is no resonance suppression circuit at some frequencies. Normally, noise is a problem because noise sensitivity is high, and it is effective in that the maximum value of noise sensitivity can be lowered.

  As can be understood by comparing FIG. 5 and FIG. 6, on the instrumentation side shown in FIG. 5, when there is no resonance suppression circuit, noise peaks occur at two locations near 400 kHz and 40 kHz, as shown in FIG. On the power side, when there is no resonance suppression circuit, a noise peak occurs in the vicinity of 40 kHz. Here, when the mode is converted from the common mode to the normal mode, the influence of noise on the high frequency side is larger. Therefore, among the two noise peaks shown in FIG. 5 and the one noise peak shown in FIG. 6, the influence of the noise peak around 400 kHz shown in FIG. 5 is large.

  Therefore, in the example shown in FIG. 1, the instrumentation-side resonance suppression circuit 15 is particularly effective because the instrumentation-side resonance suppression circuit 15 includes the high-frequency noise and the noise in the vicinity of 40 kHz. Is. When noise suppression is not sufficient only by the instrumentation-side resonance suppression circuit 15, there is also an influence of power-side noise. Therefore, by providing the power-side resonance suppression circuit 16, noise can be suppressed more effectively.

  As described above, according to the present embodiment, it is possible to suppress the noise current flowing in the signal line, particularly the noise current at the resonance point in question, and the maximum value of the noise current can be suppressed. It is effective.

  In addition, the noise current flowing through the power line can be suppressed, and the maximum value of the noise current can be suppressed, which is effective for noise suppression. If the noise current on the power side, that is, the noise generation side is large, the instrumentation may be affected by electromagnetic induction, which is effective for noise suppression.

  Furthermore, since a resonance suppression circuit for noise suppression is added in parallel with the common mode loop through which the noise current flows, not only the work for noise suppression is simplified, but also a large core, a long return line or A special power supply line to which a return line is added becomes unnecessary, and it is not necessary to use expensive parts.

  As described above, since the resonance suppression circuit is added in parallel to the common mode loop through which the noise current flows, it is not necessary to modify the signal lines and the power lines themselves, and noise countermeasures can be easily implemented.

Note that the present invention can be applied not only to a nuclear power plant but also to thermal power having a low ground impedance and noise reduction of a chemical plant.

DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel 2 ... Instrumentation tube 3 ... Neutron detector 4 ... Signal cable 5 ... Reactor containment vessel 6 ... Penetration part 7 ... Conduit 8 ... Preamplifier 9 ... Reactor building 10 ... Neutron monitoring device 11 ... Motor 12 ... Motor casing 13 ... Power cable 14 ... Penetration parts 15 and 16 ... Resonance suppression circuit 17 ... Power supply device 18 ... Building ground trunk 19 ... Neutron monitoring device ground wire 20 ... Power device ground wire 100 ... Nuclear power plant

Claims (7)

A reactor having a detector for detecting a reactor output, a coaxial cable for transmitting an output signal of the detector, and a signal processing apparatus connected to the coaxial cable and converting the output signal of the detector into a reactor output A launch region neutron monitor,
Reactor start-up region neutron monitoring device comprising a first resonance suppression circuit at a location where stray capacitance is generated between the coaxial cable and a ground line in parallel with the stray capacitance . In the reactor activation region neutron monitoring apparatus according to claim 1,
The reactor start-up region neutron monitoring apparatus, wherein the first resonance suppression circuit is provided between a shield of the coaxial cable and a ground. In the reactor activation region neutron monitoring apparatus according to claim 1,
The reactor start-up region neutron monitoring apparatus, wherein the first resonance suppression circuit comprises a series connection of a capacitance and a resistance. In the reactor activation region neutron monitoring apparatus according to claim 1 ,
A second resonance suppression circuit is provided in parallel with the stray capacitance at a location where stray capacitance is generated between the power line of the power system having the control unit for controlling the drive unit and the ground line. A reactor start-up region neutron monitoring device characterized by the above. In the reactor activation region neutron monitoring apparatus according to claim 4,
The reactor start-up region neutron monitoring apparatus, wherein the second resonance suppression circuit is provided between the power line and ground. In the reactor activation region neutron monitoring apparatus according to claim 4 ,
The reactor start-up region neutron monitoring apparatus, wherein the second resonance suppression circuit comprises a series connection of capacitance and resistance. In the reactor start-up region neutron monitoring apparatus according to claim 3 or claim 6,
The reactor activation region neutron monitoring apparatus, wherein the capacitance value is larger than a stray capacitance value generated for the coaxial cable or a stray capacitance value generated for the power line.

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