JP2009198273A - Nuclear instrumentation system of reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nuclear instrumentation system which suppresses noises intruding by way of a ground loop consisting of signal cables and a building earth trunk line. <P>SOLUTION: The system comprises a structure where a power supply is composed of batteries, the system includes a charger connected to these batteries, a switching device that connects or disconnects a station power supply or an uninterruptible power supply 10 with the charger and a charge regulating circuit 36 for outputting control signals so that the charger, can be connected to the station power supply or the uninterruptible power supply by the switching device when the batteries are not used and can be disconnected when they are used and the power supply are isolated electrically from the building earth trunk line 18 to suppress noises intruding the nuclear instrumentation system by way of the ground loop. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nuclear reactor instrumentation system that is not easily affected by external noise.

  Normally, in a nuclear reactor, a radiation detector that outputs an electrical signal proportional to neutrons and gamma rays associated with nuclear fission is installed in or near the core to monitor the reactor power. In particular, in the case of a nuclear power reactor, it is necessary to accurately monitor the reactor output over a wide range of 10 digits or more. For example, in the case of a boiling water reactor, the reactor power is divided into three regions: a neutron source region, an intermediate region, and an output region. , Each is monitored individually.

  Among these, in the measurement system used in the neutron source region, a fission ionization chamber is installed in the furnace as a neutron detector, and the ionization current generated by neutron irradiation is guided outside the furnace by a metallic hard cable. This hard cable is connected to the first signal cable (coaxial cable) at the lower part of the reactor pressure vessel, and the ionization current is transmitted to the preamplifier via the signal cable.

  Since the ionization current in the neutron source region is on the order of picoamperes at the minimum, the preamplifier amplifies the signal by about 2 to 4 digits and shapes the waveform so that it can be easily processed. The output signal of the preamplifier is guided to a signal processing device built in the neutron monitoring device by a second signal cable (coaxial cable), and converted into a reactor output signal by the signal processing device. This reactor output signal is supplied to a safety protection system or the like and used for generating a scram signal.

  In such a nuclear instrumentation system, it is often a problem that external noise is induced in the first signal cable. That is, when a noise voltage is generated in the core wire and the external conductor of the first signal cable, a noise current corresponding to the potential difference between the core wire of the preamplifier input section and the external conductor flows through the preamplifier, and this current is amplified to generate a signal. Because it is transmitted to the processor, it affects the reactor output signal.

  In general, as a noise propagation path at a short distance, one based on electrostatic coupling, electromagnetic induction, and common impedance (usually a shared ground line) can be considered. As a method for suppressing noise induction due to electrostatic coupling, for example, as described in [Patent Document 1], the first signal cable is covered with a shield covering, and this shield covering is covered with the ground of the preamplifier. A method of grounding the side circuit at one point is disclosed. In addition, as a method of suppressing noise induction due to electromagnetic induction, conventionally, a signal cable and a ground are formed so that a large closed circuit (ground loop) is not formed between the signal cable and the ground so that electromagnetic induction due to interlinkage magnetic flux is not received. In addition to taking measures to ground the external conductor at one point with a signal processing device, as shown in [Patent Document 2], in order to suppress propagation of common mode noise induced in the signal cable by electromagnetic induction, Measures are taken to wind the cable around the magnetic core.

Japanese Patent No. 2877609 JP-A-7-162257

  The conventional method described in [Patent Document 2] is mainly for suppressing the influence of common mode noise induced in the ground loop by electromagnetic induction. However, noise induction by common impedance, that is, noise current is reduced. It is also effective in suppressing the influence of noise induced by sharing the grounding wire with the emitting device. For example, as shown in FIG. 5, when a noise source consisting of a motor and an inverter power source is grounded adjacent to the nuclear instrumentation system, the high frequency noise generated by the inverter is electromagnetic induction due to mutual inductance between cables, It enters the nuclear instrumentation system in two ways: direct leakage through the building's ground trunk.

  If the impedance of the entire ground loop of the nuclear instrumentation system is small, the noise propagating through the ground line is propagated more to the nuclear instrumentation loop. Conversely, if the impedance of the ground loop is large, the propagating noise is suppressed. Therefore, if a magnetic core is wound around the signal cable of the nuclear instrumentation system and a large inductance component is added to this portion, the impedance against high-frequency noise increases, so that noise entering from the ground wire can be suppressed. Based on the same idea, it is also possible to increase the impedance of the ground loop by winding a magnetic core around the ground wire or power cable.

  However, these methods have two problems. First, in order to obtain a large inductance, it is necessary to increase the number of windings of the cable around the magnetic core, resulting in an increase in the size of the device. Second, even if the number of windings is increased, the distance between the cable lines is increased. It is difficult to obtain an inductance exceeding a certain level due to the effect of stray capacitance.

  Therefore, as another method for removing the influence of the ground loop, it can be considered that the ground line and the power line of the signal processing device are separated from the ground trunk of the building. Among these, since the ground line is connected only as a signal reference point, it is possible to prepare a reference point different from the ground line. On the other hand, regarding the power line, it is difficult to completely separate it from the ground trunk from the viewpoint of security in both cases where the power supply source is an in-house power source or a power source using an inverter such as an uninterruptible power supply. is there.

  As shown in FIG. 6, the impedance between both ends of the power supply device, that is, the terminal on the power supply source side and the terminal on the power supply side to the signal processing device or the like decreases substantially linearly with respect to the frequency, Since only a very small impedance is given to a high frequency, it is extremely difficult to avoid a ground loop via a power line.

  An object of the present invention is to provide a nuclear reactor instrumentation system that can eliminate a ground loop generated via a power line.

  In order to achieve the above object, the present invention comprises a power supply device that supplies power to a radiation detector, a preamplifier, and a signal processing device, which are components of a nuclear reactor instrumentation system, and is connected to these batteries. A battery charger, a switchgear that connects or disconnects the power supply electrically connected to the grounding trunk of the building, and a battery charger that connects the power supply and charger via the switchgear when the battery is not in use. A charging control circuit that outputs a control signal to disconnect the power source and the charger is sometimes provided, and the power source device and the ground trunk of the building are electrically disconnected.

  By eliminating the ground loop generated by the signal cable and the grounding trunk of the building, electromagnetic induction noise superimposed on the measurement signal of the nuclear instrumentation system via the ground loop and noise due to common impedance are suppressed.

  Each power supply device includes a plurality of batteries, and an opening / closing device installed between each battery and the power cable. The power cable is connected to the battery being charged based on a control signal from the charge control circuit. The signal cable and the grounding trunk line of the building are not electrically connected to each other via the battery being charged and its power cable. As a result, when one battery is being charged, power is supplied in a state where the remaining non-charging batteries are electrically disconnected from the building ground trunk.

  At this time, in order to increase the stability of the measurement signal, the ground line connected to the signal cable return line side of the preamplifier or the signal processing device is connected to a metal material electrically insulated from the ground trunk line of the building, The signal line is not connected to the ground trunk of the building via the ground line.

  According to the present invention, the power supply device is constituted by a battery, and the ground loop composed of the cable and the building grounding trunk line is eliminated during a period other than during charging by separating the power supply unit from the building grounding trunk line except during charging. It is possible to suppress both noise caused by electromagnetic induction and noise entering from the shared ground trunk line.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram of a nuclear instrumentation system.

  As shown in FIG. 1, an ionization current corresponding to the number of incident neutrons is generated from the fission ionization chamber 1 installed in the core 17, and this ionization current is derived to the outside of the reactor pressure vessel 16 by the hard cable 2. Is done. The first signal cable 3 stored in the conduit 15 is connected to the hard cable 2 via the connector 11 at the lower part of the reactor pressure vessel 16, and the preamplifier 4 to which the other end is connected. Transmit ionizing current to

  The preamplifier 4 amplifies the current signal and shapes the waveform, and transmits the signal to the signal processing device 7 built in the neutron flux monitoring device 6 via the second signal cable 5. The signal processing device 7 converts the amplified and shaped current signal into a reactor output, and outputs the reactor output signal to a safety protection system or the like (not shown).

  Here, the signal processing device 7, the fission ionization chamber 1, and the power supply device 8 in the preamplifier 4 respectively include a first power supply device 26 and a second power supply device built in the neutron flux monitoring device 6. 27 and the third power supply device 28 apply an appropriate DC voltage.

  Here, in the present embodiment, two batteries are provided for each of the first, second, and third power supply devices, and the neutron flux can be monitored seamlessly even when one battery is being charged. An example is shown.

  FIG. 2 shows the configuration of the first power supply device 26. The first power supply device 26 includes two batteries 31 and is charged from the in-house power supply or the uninterruptible power supply 10 by a charger 32 connected thereto. An opening / closing device 33 is installed between the charger 32 and the in-house power supply or the uninterruptible power supply 10, and opens / closes a connection based on a control signal from the charging control circuit 36. The output of the battery 31 is connected to the signal processing device 7 in parallel via the remaining amount detector 35 and the opening / closing device 34, and a voltage is applied. The opening / closing device 34 is opened / closed by a control signal from the charge control circuit 36. The remaining amount detector 35 detects the remaining amount of the battery 31 and outputs a remaining amount detection signal corresponding to the battery voltage to the charge control circuit 36.

  FIG. 3 shows the configuration of the remaining amount detector 35. The remaining amount detector 35 includes a voltmeter 37 that measures the voltage of the battery 31, a reference voltage 38, and a voltage measured by the voltmeter 37, and an operational amplifier (also referred to as a comparator) 39 that compares both voltages. When the voltage of the battery 31 measured by the voltmeter 37 is smaller than the reference voltage 38, a remaining amount detection signal is output from the operational amplifier 39 to the charge control circuit 36. When the remaining amount detection signal is output to the charge control circuit 36, it means that charging is necessary, and is also called a charge required signal.

  When the charge control circuit 36 receives the remaining amount detection signal from the remaining amount detector 35, the charge control circuit 36 opens the opening / closing device 34 connected to the corresponding battery 31 and disconnects it from the signal processing device 7. Thereafter, the opening / closing device 33 connected to the corresponding battery 31 is closed, and charging is started from the charger 32. When the charging time elapses, the opening / closing device 33 is opened to complete charging, and then the opening / closing device 34 is closed to supply power to the signal processing device 7 again. The charging time is set to a time sufficient for charging.

  By adopting the same configuration for the second power supply device 27 and the third power supply device 28, all the ground loops generated via the power supply lines are eliminated, and electromagnetic induction noise and noise entering from the grounding trunk line of the building are eliminated. The influence of can be suppressed.

  FIG. 4 is a configuration example for increasing the stability of the measurement signal by connecting a ground line to the signal cable return line side of the signal processing device 7. An insulating material 40 is laid on the bottom of the housing of the neutron flux monitoring device 6, and a support structure 41 made of a metal material is installed on the insulating material 40.

  The signal processing device 7 is installed on the upper portion of the support structure 41, and the ground wire 42 is drawn from a terminal that is connected to the signal cable return line, and is connected to the support structure 41. Thereby, the metal material insulated from the grounding trunk line of the building can be used as a signal reference point. It should be noted that any method other than the above may be used as long as a metal bar or a metal plate is installed so as not to come into contact with the grounding trunk line of the building and the structural material conducting therewith and the grounding wire can be connected thereto.

  As described above, in the conventional nuclear instrumentation system, the power supply device and the ground wire are electrically connected to the ground trunk of the building in the vicinity of the signal processing device. According to the present embodiment, the power supply device is constituted by a battery, and the power supply device is disconnected from the ground trunk of the building except during charging, so that the cable and the building are grounded during periods other than charging. The ground loop consisting of the trunk line can be eliminated, and both noise due to electromagnetic induction and noise entering from the shared ground trunk line can be suppressed. Thereby, the noise filter and magnetic core which were added to the power supply device can be reduced.

  In addition, each power supply unit is equipped with multiple batteries, disconnecting the battery being charged from the power line, and supplying power with a battery that is electrically disconnected from the rest of the building ground line, making it impossible to measure while charging the battery The period can be eliminated. In addition, even if the in-house power supply is lost, the normal operation of the nuclear instrumentation system can be ensured, so that the configuration of the uninterruptible power supply currently used in the nuclear instrumentation system can be simplified.

  Measurements can be made without creating a ground loop by adding a ground wire to the signal cable return line side of the preamplifier or signal processor to connect a metal material that is electrically insulated from the ground trunk line of the building. The reference point of the signal can be obtained, and the stability of the measurement signal can be increased.

  In addition to nuclear instrumentation systems, there is a possibility that it can be applied to all measurement systems that use weak signals in plants where inverter devices are being introduced.

It is a block diagram of the nuclear instrumentation system which is one Example of this invention. It is a block diagram which shows an example of a 1st power supply device. It is a block diagram which shows an example of a residual amount detector. It is a longitudinal cross-sectional view of the neutron flux monitoring apparatus which shows an example of the earthing | grounding to the insulated metal material from the grounding trunk line of a building. It is a figure explaining the noise penetration | invasion via a ground loop. It is a figure explaining the noise penetration | invasion via a ground loop.

Explanation of symbols

1 fission ionization chamber 2 hard cable 3 first signal cable 4 preamplifier 5 second signal cable 6 neutron flux monitoring device 7 signal processing device 8 preamplifier power supply 9 power supply 10 in-house power supply or uninterruptible power supply 11 connector 12 detector guide tube 13 penetrating portion 14 reactor containment vessel 15 conduit 16 reactor pressure vessel 17 core 18 building grounding main line 19 fission ionization chamber power wire 20 preamplifier power wire 21 inverter power source 22 motor 23 motor housing 24 stray capacitance 25 magnetic core 26 first power supply device 27 second power supply device 28 third power supply device 29 mutual inductance 30 metal material 31 battery 32 chargers 33 and 34 switching device 35 remaining amount detector 36 charge control circuit 37 Voltmeter 38 Reference voltage 39 Operational amplifier 40 Insulating material 41 Metal support structure 42 Ground wire

Claims (4)

  A radiation detector that is installed in or near the reactor and converts the radiation dose generated by the nuclear reaction in the reactor into an electrical signal, a preamplifier that amplifies the signal detected by the radiation detector, and the radiation detection A first signal cable for connecting a reactor and a preamplifier, a signal processing device for inputting a signal amplified by the preamplifier and outputting a reactor output signal, the preamplifier and the signal processing device, A second signal cable for connecting the signal processing device, a first power supply device for operating the signal processing device, a second power supply device for applying a voltage to the preamplifier, and applying a voltage to the radiation detector A third power supply device, the first, second and third power supply devices and signal processing device, a power cable connecting the preamplifier and the radiation detector, and the first, second and third power supply devices Connection of the building provided in the power supply Batteries electrically insulated from main lines, chargers connected to these batteries, switchgears for connecting or disconnecting power supplies and chargers electrically connected to ground trunks of buildings, and the power supplies And a charging control circuit for outputting a control signal so that each charger is connected by the switchgear when the battery is not used and is not connected when the battery is used.   The first, second and third power supply devices each have a plurality of batteries and an opening / closing device installed between each battery and the power supply, and based on a control signal from a charge control circuit, The nuclear reactor instrumentation system according to claim 1, wherein the battery being charged is disconnected from the power cable.   Each of the batteries includes a remaining amount detector that detects a remaining amount of the battery and outputs the detected amount to a charge control circuit, and the charge control circuit generates a control signal for a switching device connected to each battery based on the remaining amount of the battery. The nuclear reactor instrumentation system according to 1 or 2.   The nuclear reactor instrumentation system according to claim 1, wherein a ground line connected to a signal cable return line side of the preamplifier or the signal processing apparatus is connected to a metal material electrically insulated from a ground trunk line of the building. .

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