JP6479334B2 - Water level detection device - Google Patents

Description

  The present invention relates to a water level detection device for detecting a water level in a reactor containment vessel.

  The water level detection device in the reactor containment vessel is required to minimize expansion of pressure boundaries and increase in the amount of equipment and eliminate mechanical moving parts to reduce failure frequency and improve maintainability. . For example, Patent Document 1 discloses that a water level detection device uses an electrode type level switch, a capacitance type level switch that measures a capacitance between concentric metal probes, and a reflection time of ultrasonic waves oscillated by an ultrasonic oscillator. It is described that various water level detection devices, such as an ultrasonic type level switch, which measure the presence or absence of a water level from a difference are provided.

JP 11-118976 A

  In detecting the water level in the reactor containment vessel, it is required to be able to cope with a wide range of water quality with a simple configuration and long life. For high sensitivity detection of water level, direct current is preferable. As described above, it is necessary to prevent the elution of the probe and to improve the durability of the constituent material of the probe in order to use a direct current, and to have a long life under an environment of high temperature, high humidity and high radiation. is there. The use of a direct current in the water level detection device and the prevention of the elution of the probe are in a trade-off relationship, and it is required to satisfy both.

  Since the water level detection device in the reactor containment vessel detects the injection amount of water held for safety purposes by the power generation facility injected into the reactor containment vessel at the time of an emergency of the power generation facility, the water level is high as a change in current value. It is required to be able to detect by sensitivity. In addition, since the separation distance from the measurement point is large, it is also required to reduce the influence of noise. In order to satisfy these requirements, a direct current is used to detect the water level. As a result, for example, when water containing a large amount of electrolyte such as seawater is injected in an emergency of a power generation facility, the probe may be eluted due to the action of electrolysis.

  An object of the present invention is to provide a water level detection device for prolonging the life of a water level detection probe in a reactor containment vessel.

  In the present invention, when measuring the liquid level position of the liquid in the reactor containment vessel, a probe for water level detection provided in the reactor containment vessel, a power supply for supplying a direct current to the water level detection probe, and A current measurement circuit for measuring the DC current flowing through the water level detection probe; and a current limiting circuit for limiting the magnitude of the DC current supplied to the water level detection probe based on the concentration of the electrolyte of the liquid. It is a water level detection device including.

  Since this water level detection device uses a current limiting circuit that limits the current flowing to the water level detection probe, it is possible to suppress an excessive current from flowing to the water level detection probe. As a result, the elution of the water level detection probe used to detect the water level in the reactor containment vessel is limited, and the life can be extended.

  It is preferable that the power supply, the current measurement circuit, and the current limiting circuit be installed outside the reactor containment vessel. This makes it easy to maintain the current measuring circuit and the current limiting circuit, and has the advantage of being less susceptible to environmental deterioration inside the reactor containment vessel even during an emergency of the power generation facility.

  The current limiting circuit is preferably a circuit in which a voltage applied to both ends of the water level detection probe is adjusted when a DC current of a predetermined level or more flows through the water level detection probe. By using the electrical resistance, the current limiting circuit can be configured relatively easily.

  It is preferable that the electrode of the water level detection probe contains at least one or more of a group 4 element and a group 5 element. By doing this, the durability of the electrode can be improved.

  It is preferable that a part of the insulating material used for the water level detection probe is a ceramic. By doing this, the durability of the water level detection probe can be improved.

  In the water level detection probe, preferably, the ceramic and the electrode are joined.

  The present invention can provide a water level detection device for prolonging the life of a water level detection probe in a reactor containment vessel used in a high temperature, high humidity, and high radiation environment.

FIG. 1 is a view showing a space including a reactor vessel and its peripheral devices in a reactor containment vessel. FIG. 2a is a diagram showing an example of a current limiting circuit having a water level detection device. FIG. 2b shows another current limiting circuit with a water level detection device. FIG. 2 c is a diagram showing another current limiting circuit included in the water level detection device. FIG. 2 d is a diagram illustrating an example of another current limiting circuit included in the water level detection device. FIG. 3a shows a probe. Figure 3b is an exploded view of the probe. FIG. 3 c is a view showing an example of an electrode included in the probe.

  FIG. 1 is a view showing a space 10 including a reactor vessel 2 in a reactor containment vessel and peripheral devices thereof. The inside of the reactor containment vessel 19 is a sealed space, and the water level in the containment vessel rises by injecting water from the outside.

  In the space 10 in the reactor containment vessel, a detection point of the water level is set in the containment vessel in order to monitor the rise of the water level to be injected when the power generation apparatus is in an emergency. In order to measure the water level in the space 10 in the reactor containment vessel, a pair of water level detection probes (hereinafter appropriately referred to as probes) 15 of the water level detection device 14 are installed. By providing the probe 15 at the position of the upper limit water level 12, it is possible to monitor the important equipment installed in the reactor containment vessel 19 from being submerged. Also, by providing a probe 15 in a space lower than the bottom surface of the reactor vessel 2 and adding a detection point of the water level as the lower water level 13, a means for directly monitoring the flooded state of the melted fuel is provided. It can also be provided. The pair of probes 15 may be installed to measure a plurality of locations for the purpose of monitoring the rise of the water level.

  The water of the reactor containment vessel 19 is secured in the path from the lower floor of the reactor containment vessel 19 to the containment vessel recirculation sump. The amount of water injected into the space 10 in the reactor containment vessel is measured indirectly by determining the integrated value of the containment vessel recirculation sump water level meter 11 or a flowmeter installed in the water injection path into the containment vessel. Since it is possible to estimate the water level, it is possible to grasp the water level in the reactor containment vessel 19 using these. Furthermore, even during an emergency of the power generation facility, the water level of the space 10 in the reactor containment vessel is directly monitored, and the water level also exceeds the measurement range of the existing water level gauges such as the containment vessel recirculation sump water level gauge. The water level detection device 14 is provided so that it can monitor.

  The water level detection device 14 includes a pair of probes 15, a water level measurement circuit 16, a current limiting circuit 17, and a DC power supply 18. In order to minimize expansion of the pressure boundary and increase in the amount of equipment, the water level detection device 14 is provided with a probe 15 in the reactor containment vessel 19, and the water level measurement circuit 16, the current limiting circuit 17 and the DC power supply 18 are central. It is provided in the operation room 20. The water level measurement circuit 16 may be connected to the device 21 that displays the water level state, or may be connected to a recording device.

  The current limiting circuit 17 may be realized using, for example, a transistor such as an IGBT (insulate gate bipolar transistor), a MOSFET (metal oxide semiconductor field effect transistor) or a bipolar transistor, or is electrically equivalent to the transistor or the like. It may be realized by a circuit.

  FIG. 2a shows an example of a current limiting circuit 17 having a water level detection device. FIG. 2b shows another current limiting circuit 17a having a water level detection device. FIG. 2 c is a diagram showing another current limiting circuit 17 b included in the water level detection device. FIG. 2 d is a diagram showing an example of another current limiting circuit 17 c included in the water level detection device.

The current limiting circuit 17 shown in FIG. 2a is a circuit in which an electric resistance 31 is provided between the water level measuring circuit 16 and the DC power supply 18 so that a current of a predetermined value or more does not flow to the probe 15. Of the liquid that may exist between the probes 15 and 15, the electric resistance value of the electric resistance 31 is R2, and the electric resistance value of the liquid having the smallest electric resistance value is R2. When the liquid with the smallest electric resistance value described above is present in the pair of probes 15, 15, the DC power supply 18, the electric resistance 31, the water level measurement circuit 16 and the probe 15, the liquid with the smallest electric resistance value and the closed circuit with the probe 15. Is formed. Assuming that the voltage between terminals of the DC power supply 18 is V, the current I flowing through the current limiting circuit 17 can be obtained by the equation (1).
I = V / (R1 + R2) · · · (1)

When it is desired to limit the current I flowing through the current limiting circuit 17 to I_lim or less, R1 is expressed by the equation (2) using the equation (1). Assuming that the liquid having the smallest electric resistance value among the liquid that may exist between the pair of probes 15, and by defining the upper limit value I_lim of the current flowing to the probes 15, the equation (2 The electric resistance value R1 of the electric resistance 31 can be obtained from By using the electric resistance 31 having the electric resistance value R1 obtained in this manner, the current limiting circuit 17 can limit the current I flowing through the probes 15, 15 to the upper limit value I_lim or less.
R1> V / Ilim-R2 (2)

  The current limiting circuit 17 a shown in FIG. 2 b is a circuit in which a variable electrical resistance 33 is provided between the water level measuring circuit 16 and the DC power supply 18. When this current limiting circuit 17a is used, for example, the operator 32 reads the current value of the water level measurement circuit 16 in the control room, and changes the electrical resistance value of the variable electrical resistance 33 if the current value exceeds the upper limit value I_lim. Do. By doing this, the amount of current flowing through the pair of probes 15 is made to be constant and not exceed the upper limit value I_lim. Further, the variable electric resistance 33 may be automatically adjusted by the signal from the water level measurement circuit 16 so as not to exceed the upper limit value I_lim.

  In this case, for example, the control device 30 sets the variable resistance 33 so that the difference between the current value Ic detected by the water level measurement circuit 16 and the target current value Ip of the current flowing through the current limiting circuit 17a becomes zero. Feedback can be controlled. The target current value Ip is set to the upper limit value I_lim or less. By doing this, the current limiting circuit 17a can limit the current I flowing through the probe 15 to the upper limit value I_lim or less.

  In the current limiting circuit 17b shown in FIG. 2c, an npn transistor 36 is provided between the water level measuring circuit 16 and the DC power supply 18, the variable power supply 34 and the electric resistor 35 are provided at the base of the npn transistor 36. It is a circuit in which a DC power supply 18 is provided on the collector side. Although control by the method using the variable electrical resistance 33 of the current limiting circuit 17a shown in FIG. 2b is easy, since power is consumed by the variable electrical resistance 33, consumption of the DC power supply is large. The current limiting circuit 17 b shown in FIG. 2 c can suppress the consumption of the DC power supply 18 by controlling the variable power supply 34 different from the DC power supply 18. The variable power supply 34 feeds back the current value measured by the water level measurement circuit 16 to adjust the current I flowing through the probe 15 by the npn transistor 36 through the electric resistor 35. The operation for adjustment may be performed automatically or manually by an operator.

  In the current limiting circuit 17c shown in FIG. 2d, a pnp transistor 39 is provided between the water level measuring circuit 16 and the DC power supply 18, the diode 38 is at the base of the pnp transistor 39, and the electric resistor 37 is the emitter of the pnp transistor 39. It is a circuit connected to

Since the maximum value of the voltage drop in the forward direction of the diode 38 is determined by the physical properties of the material constituting the diode 38, the maximum value of the voltage flowing through the electric resistance 37 is the forward voltage drop of the diode 38. Even when the electrical resistance between the pair of probes 15 and 15 is below a certain level, the current I does not exceed the value determined by the equation (3). I_lim is the upper limit value of the current flowing through the probe 15, Vd is the forward voltage drop of the diode 38, and R is the electric resistance value of the electric resistance 37. Thus, the current limiting circuit 17c can limit the current I flowing through the probe 15 to the upper limit value I_lim or less by setting the electric resistance value R of the electric resistance 37 to an appropriate value.
I_lim = Vd / R (3)

  FIG. 3 a shows the probe 15. FIG. 3 b is an exploded view of the probe 15. The probe 15 includes an electrode 28, a cap 29, a sleeve 24A, an adapter 24B, an annular member 23, and a part 22 having an insulating function including titanium. The electrode 28, the cap 29, the sleeve 24A, and the annular member 23 are titanium or a titanium alloy in the present embodiment, but may contain at least one or more of a group 4 element and a group 5 element. The annular member 23 is also titanium or a titanium alloy in the present embodiment, but may contain at least one or more of a group 4 element and a group 5 element. The MI (Mineral Insulator) cable coating 25 and the adapter 24B are, for example, an iron-based alloy. The MI insulator 26 is, for example, magnesium oxide.

  The probe 15 is connected to the end of the MI cable. The electrode 28 penetrates the part 22 and is firmly bonded within the adapter 24B. The MI cable side end face of the electrode 28 is joined to the core 27 of the MI cable by welding or brazing. Also, the electrode 28 is joined to the cap 29 by welding or brazing. The part 22 is made of a material having an insulation and water resistance function, and is firmly adhered to the annular member 23 by brazing. Since the part 22 is made of ceramic, it is provided in contact with the cap 29 and the sleeve 24A, and adheres to these parts by welding or brazing with the annular member 23. The core material 27 and the electrode 28 are fixedly filled with a ceramic insulator 26 so as not to contact the cable coating 25, the adapter 24B, the sleeve 24A, and the upper annular member 23.

  The probe 15 is made of, for example, titanium and ceramics (alumina) having water resistance. In addition, a combination of Kovar and ceramics having water resistance may be used. The non-conductive material used for the probe 15 may be a resin material (eg, polyimide or aromatic ether) other than ceramics (eg, alumina or magnesium oxide) depending on heat resistance and radiation resistance in the installation environment. Ketone, epoxy, etc.) may be used.

  In the present embodiment, the current flowing through the probe 15 is limited using the current limiting circuits 17, 17a, 17b, 17c. As a result, it is possible to suppress the flow of an excessive current to the probe 15, so it is possible to suppress the elution of the probe due to the electric corrosion and to prolong the life of the probe 15 in the reactor containment vessel 19.

  FIG. 3 c is a view showing an example of the electrode 28 included in the probe 15. The electrode 28 includes an electrode plate 28b opposed at the time of assembly. The shape of the electrode plate 28b is a circle, an ellipse, a rectangle, a square, a bar, or the like, and the areas of the opposing electrode plates are preferably equal but may be different. By the presence of the electrode plates 28b opposed to each other, the contact area of the probe 15 with water can be expanded, and the sensitivity as a sensor can be improved.

  The present invention is not limited by the contents described in the embodiments. In addition, constituent elements of the embodiment include those which can be easily conceived by those skilled in the art, those substantially the same, and those within the equivalent range. Furthermore, the components described in the embodiments can be combined as appropriate. In addition, various omissions, substitutions, or modifications of the components can be made without departing from the scope of the embodiment.

2 reactor vessel 10 space in the reactor containment vessel 11 containment vessel recirculation sump water gauge 12 upper limit water level 13 containment vessel water level 14 water level detection device 15 water level detection probe (probe)
16 Water level measurement circuit 17, 17a, 17b, 17c Current limiting circuit 18 DC power supply 19 Reactor containment vessel 20 Central control room 21 Equipment 22 Parts 23 Annular member 24A Sleeve 24B Adapter 25 Cable coating 26 Insulator 27 Core 28 Electrode 28b Electrode Board 29 Cap 30 Controller 31 Electric resistance 33 Variable electric resistance 34 Variable power source 35 Electric resistance 36 npn type transistor 37 Electric resistance 38 Diode 39 pnp type transistor

Claims (4)

In measuring the liquid level position of the liquid in the reactor containment vessel,
A probe provided in the reactor containment vessel;
A power supply for supplying a direct current to the probe used for water level detection;
A current measurement circuit that measures the DC current flowing through the probe;
A current limiting circuit which limits the magnitude of the direct current supplied to the probe based on the concentration of the electrolyte of the liquid;
Including
The electrode contained in the probe contains at least one or more of a group 4 element and a group 5 element, and is a cylindrical adapter formed in a rod shape and having an end face penetrating a ceramic part to interiorize the part Inside is joined to the core of the end of the cable, the adapter is connected to the end of the cable sheath of the cable and formed of an alloy together with the cable sheath, and the electrode and the core are insulating of ceramic A water level detection device that is insulated from other parts by the body. Electrode included before Symbol probe comprises an electrode plate opposite at a gap during assembly, is equal to the area of the opposing electrode plates, the water level detecting device according to claim 1.   The water level detection device according to claim 1, wherein the power supply, the current measurement circuit, and the current limiting circuit are installed outside the reactor containment vessel.   The water level detection device according to any one of claims 1 to 3, wherein the current limiting circuit is a circuit whose electric resistance is changed when the DC current of a predetermined level or more flows through the probe.

Images