JPH0382929A - Method and element for detecting fluid leak in radiation environment - Google Patents

Abstract

PURPOSE:To make it possible to detect the leakage of fluid stably and highly accurately in a radiation environment by arranging a plurality of conductors in close proximity, and insulating the conductors with an inorganic insulating member which has radiation resistance property and can hold and secure the fluid. CONSTITUTION:Conductors 1 and 2 are combined in a cable shape, and a detecting element is formed. The conductor 1 is a high resistance wire, and the conductor 2 is a low resistance wire. The conductors 1 and 2 are surrounded with a detecting dielectric part 3 formed of glass fiber. The glass fiber has gaps which are suitable for holding and securing fluid. The conductors 1 and 2 having the dielectric parts 3 are surrounded with a first protecting braid 4 together, and the braid 4 is further surrounded with a second protecting braid 5. Thus the conductors are protected. When a point of the high resistance wire is electrically connected to the low resistance wire 2 through leaked water and the resistivity of the water is sufficiently low, both conductors are shorted. Therefore, when the resistances of the conductors 1 and 2 are measured, the resistance which is proportional to the length of the high resistance wire 2 to the leaking point is obtained and the distance can be simply operated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a technology for detecting fluid leaks in a radiation environment such as a nuclear reactor or nuclear fuel reprocessing facility, and particularly to detect fluid leaks in fluid equipment and piping in a radiation environment. The present invention relates to a fluid leakage detection technology that can detect the occurrence and position of the pipe.

For example, the primary cooling water of a nuclear reactor has a high dose of radioactivity, and there is a risk of radioactive contamination if it leaks.

Therefore, high-dose radioactive fluids such as secondary cooling water must be closely monitored to prevent leakage.

[Conventional technology] Equipment and piping containing high temperature, high pressure, and highly radioactive fluids in nuclear power generation equipment and reprocessing facilities are required to safely shut down the reactor and reprocessing equipment before they break. It is necessary to detect leaks reliably and in a short time to prevent even the slightest leakage. 4 It is also desirable to be able to detect leak positions in order to carry out repairs and restoration measures promptly after shutdown.

Furthermore, it is desirable that the detection system be simple and that the same sensor can cover a wide detection target area.

Currently, fluid leakage detection technology in a highly radioactive environment is as follows:
Acoustic emission monitors, moisture sensing sinks 1, etc. have been developed and are in use.

However, the detection accuracy is often insufficient, and if the detection sensitivity is increased, a stop occurs due to an erroneous signal, and if the detection sensitivity is decreased, the leakage may not be detected even though it has occurred.

[Problems to be Solved by the Invention] As explained above, according to the conventional technology, detection sensitivity was not sufficient in fluid detection technology under a radiation environment.

An object of the present invention is to provide an element capable of detecting fluid leakage in a radiation environment with sufficiently excellent detection sensitivity.

It is also an object of the present invention to provide a method for detecting fluid leaks with sufficient sensitivity in a radiation environment.

Furthermore, in fluid leak detection, it is desirable that the leak position can be detected and that one sensor can cover a wide range of leak detection targets.

[Means for Solving the Problems] According to the present invention, a plurality of conductors are arranged close to each other and insulated between them by an inorganic insulating member that is radiation-resistant and capable of holding and securing fluid, so that when fluid leaks, , the fluid is held and secured by an inorganic insulating member.

[Operation] When a fluid is retained and secured in an inorganic insulating member between a plurality of conductors arranged in close proximity, the electrical characteristics between the plurality of conductors change due to the difference in dielectric properties between the fluid and air or vacuum. Fluid leaks can be detected by measuring changes in .

[Embodiment] FIGS. 1A, 1B, and 1C show a radiation-resistant fluid leak detection element according to an embodiment of the present invention.

FIG. 1(A) shows a cross-sectional view, and FIG. 1(B) shows a partially cutaway front view.

As shown in Figure 1 (A>, (B)), two conductors 1
．． 2 are combined in the form of a cable to constitute a detection element. Of the two conductors 1.2, conductor 1 is a high resistance wire and conductor 2 is a low resistance wire.

The low resistance wire 2 is made of a low resistivity material, such as a mild steel wire, and the high resistance wire 1 is made of a relatively high resistivity material, such as a nichrome wire. Furthermore, the resistance may be increased by making the cross-sectional area of the high resistance wire 1 relatively small. Each conductor 1.2 is surrounded by a sensing dielectric 3 made of glass fiber. Glass fibers are arranged in bundles, forming gaps between them suitable for holding and securing fluids. 6 Glass generally has the property of being wet with water, but it absorbs fluids more reliably. The glass fiber surface may be subjected to a suitable surface treatment. A primary protection silk set 4 surrounds and protects the two conductors 1.2 provided with the sensing dielectric 3. This primary protective braid 4 is made of, for example, glass fiber.

A secondary protection braid 5 made of stainless steel (SUS), for example, surrounds and protects the primary protection braid 4 made of glass fiber. The primary protection braid 4 and the secondary protection braid 5 are made of a fibrous material and have a structure through which fluid can penetrate. The leaked fluid may be a gas when it leaks, but if it condenses outside and becomes a liquid, it can be detected in the same way.

The conductor 1.2 of such a detection element is highly insulating in dry conditions. That is, the conductor 1 and the conductor 2 are separated from high-resistivity air or vacuum by a high-resistivity glass fiber, and are in a highly insulated state. If, for example, water penetrates into the sensing dielectric 3, the water will replace air or vacuum. If the water that has permeated between the conductor 1 and the conductor 2 at the leakage point causes a short circuit, a state as shown in FIG. 1(C) will occur. That is, a certain point of the high resistance wire 1 is electrically connected to the low resistance wire 2 due to leaked water. If the resistivity of the water is sufficiently low, both conductors will be short-circuited.6 Therefore, if the resistance between the conductors 1 and 2 is measured, a resistance proportional to the length X of the high resistance wire 1 to the leakage point will be obtained. Now, if the high resistance wire 1 has a total length Q or a resistance R, the deviation is, if a leak occurs at the position X, the resistance up to the leakage point to be measured is R
-x/Q When leakage occurs in this way, it is possible to obtain an electrical signal according to its position. Therefore, the resistance value is calculated by measuring the voltage between the detection element lines at the time of leakage at the measurement end.
This allows the distance X to be easily calculated.

Furthermore, the structure described above is an inorganic material made of metal and glass fiber, and its properties hardly change even when exposed to high radiation. Therefore, measurements can be performed stably over a long period of time. However, with this method, if the resistivity of the leaked fluid is relatively high, the accuracy of position measurement will be poor.

FIGS. 2(A) and 2(B) show a detection apparatus using the Murray loop method using the detection elements shown in FIGS. 1(A) and 1(B).

In FIG. 2(A), the sensor 11 is shown in FIG. 1(A), (
It has the configuration shown in B), and has a low resistance wire 2 and a high resistance wire 1 inside.

Furthermore, one low-resistance heat-resistant cable is connected to the high-resistance wire 1 at its tip. This sensor 11 and one heat-resistant cable are placed at the bottom of the fluid piping 20.

The conductor 1.2 in the sensor 11 and the conductor of the heat-resistant cable 19 are connected to a signal transmission cable 13 via a connector 12.

The DC resistance bridge circuit 10 is connected in series with the high resistance wire 1 and includes a DC sliding resistor 15 forming the bridge circuit. is connected. The DC power supply 17 is connected to the sliding terminal of the DC sliding resistor 15 and the low resistance wire 2 of the sensor via the protective resistor 16. Furthermore, the sliding terminal of the DC sliding resistor 15 and the ammeter 14 are connected to an arithmetic processing unit 18 .

Now, a leak has occurred at a certain point 21 in the piping 20, and the leaked fluid has penetrated into the sensing part dielectric 3 of the sensor 11.
Assume that high resistance wire 1 and low resistance wire 2 in 1 are electrically connected. Assume that this leakage occurs at a distance X from the connecting connector 12. It is also assumed that the total length of the high resistance wire is Q. In other words, the voltage from the DC power supply 17 is supplied to a location at a distance of X from the end of the high resistance wire.

This state is schematically shown in FIG. 2(B). The low resistance wire 2 is connected to the high resistance wire 1 by the leakage 21, the two parts of the high resistance wire 1 and the two parts of the sliding DC resistor 15 constitute the resistance of the bridge circuit, and the ammeter 14 is installed at the connection point. is connected. Let the ratio of the distance from the sliding terminal of the sliding resistor 15 to both ends be A:B, and the ratio of the distance from the position of the leakage point to both ends of the high resistance wire 1 be x:y as shown in the figure. do. Then, when A: y = B: x, no current flows to the ammeter, and it is possible to measure whether it is in a balanced state. At this time, A-x=B-y=B (Q-x) x=Q-B/ (A0B). Similarly, y=Q-A/(A+B).

This relationship is determined by the ratio of resistance values in the bridge circuit, and holds true regardless of the resistance value at which the low resistance line 2 and the high resistance line 1 are connected due to leakage. Therefore, detection with sufficient accuracy is possible as long as the leaking fluid is conductive.

The arithmetic processing unit 18 adjusts the sliding terminal of the sliding resistor 15 so that the ammeter 14 becomes zero, and calculates the leak point X based on the position of the sliding terminal at that time.

Note that in a state where there is no leakage, the DC sliding resistor 15, the high resistance wire 1, and the heat-resistant cable 19 form a closed loop and are at the same potential, so the needle of the ammeter 14 does not swing.

FIG. 3 shows a radiation-resistant fluid leak detection element according to another embodiment of the present invention. For example, a sensing dielectric material 32 made of glass fiber is wrapped around an inner conductor 31 made of twisted wires of mild steel. An outer braided conductor 33 made of soft copper wire surrounds the outer conductor, and an outer protective braid 34 made of glass fiber braid surrounds the conductor 33 . The sensing dielectric 32, the outer braided conductor 33, and the outer protective braid 34 are each made of a fibrous member, and are capable of permeating and permeating fluid. In a dry state, the inner conductor (*31) and the outer braided conductor 33 form a coaxial cable and have a constant characteristic impedance, such as 50Ω.

When air or a fluid having a dielectric constant different from that of vacuum penetrates from the outside and is retained and secured in the sensing dielectric 32 between the inner conductor 31 and the outer braided conductor 33, the dielectric constant changes in that part. Due to this change, the characteristic impedance of the coaxial cable changes. By detecting this change in characteristic impedance, fluid leakage can be detected. In the case of this leak detection element, detection is possible even if the fluid does not necessarily have conductivity.

FIGS. 4(A) to 4(D) show a leakage detection system using the pulse reflection method.

1. FIG. 4 (A> is a block diagram schematically showing the system configuration. 6 pulse emission detection circuit #r45 is connected to the internal conductor 31 of the sensor 42 of the fluid 8 leak detection element as shown in FIG. 3 and the connecting connector 43. , are connected via a cable 44. Also, the sensor 42 is arranged along a fluid pipe 46, and its end is grounded by a terminating resistor 41. Note that the characteristic impedance of the sensor 42 and the terminating resistor 41 are are matched so that there is no reflection. When a leak 47 occurs in the pipe 46, the impedance of the sensor 42 changes locally due to the fluid flowing out from the leak 47.

This impedance change causes the incident pulse to be reflected. If this is detected, it is possible to detect that a leak has occurred and the location of the leak.

FIG. 4(B) is a conceptual diagram showing the detection principle.

The inner conductor 31 and outer conductor 33 of the sensor 42 are connected to a pulse reflection detection circuit 45 . Further, the @ ends of the inner conductor 31 and the outer conductor 33 of the sensor 42 are matched and terminated with a terminating resistor 41. Under normal conditions, the cable of the sensor 42 has, for example, a characteristic impedance ZO=50Ω.

Suppose now that a leak 47 occurs in a part of the sensor 42.

Impedance Z decreases in a portion where fluid has permeated due to leakage. For example, when moisture penetrates, the impedance of the sensor 42 decreases significantly, typically to 40Ω or less. At this time, when a voltage pulse is emitted from the pulse emission detection port F#145, the pulse is reflected by impedance mismatching of the sensor 42 at the leakage position 47 and returns to the emission point.

FIG. 4(C) shows an example of the waveforms of the emitted pulse and the reflected pulse. When a rectangular emitted pulse 48 is emitted, it is reflected by leakage and the waveform of the returning pulse changes as shown in 48. There is. In Figure 4 (D>), if the time required for the pulse to return after being emitted is reflected as T1,
The location of the leak can be detected from this time. Furthermore, the leakage range can be read from the reflected pulse waveform. Figure 4 (
D) is an example of this waveform. After the pulse is emitted, there is a reflected pulse after 3 T1, and the range of the reflected pulse is T.
2, the sensor signal propagation delay time T O
Since (n5ec/11) is constant, the distance from the pulse emission point to the leakage position and the leakage range can be calculated.

In the leak detection system described above, all the sensors are made of inorganic materials, and the sensor has high radiation resistance and high heat resistance, so it maintains stable properties even in high temperature and high radioactivity environments. Further, when a leak occurs, if the leaked fluid is a liquid, measurement can be performed in that state. temperature 150-20
Even if the leaked fluid is steam, such as cooling water at 0°C, it will be cooled by the outside air and will extend to 11m, and the external protection l# string 3
4. Penetrates and passes through the external braided conductor 33 to form the sensing dielectric 3
2, the impedance of the sensor in that part decreases compared to the steady state, and the reduced impedance part causes impedance mismatching with other parts of the sensor, making detection possible. When a pulse enters the mismatching section from the pulse emission detection circuit, the pulse is reflected by the mismatching section 4, and the reflected pulse is detected by the pulse emission detection circuit. Using the time difference between the emitted pulse and the reflected pulse, the arithmetic circuit performs calculations to detect the leakage position and leakage range.

In the embodiments described above, the sensing portion dielectric is made of glass fiber, but other materials such as ceramic fiber can also be used. It is important to use an inorganic material with high radiation resistance.

Although the present invention has been described above with reference to practical examples, the present invention is not limited to these examples.

For example, it will be obvious to those skilled in the art that various changes, improvements, combinations, etc. are possible.

[Effects of the Invention] As described above, according to the present invention, fluid leakage can be detected stably with high accuracy in a radiation environment.

In addition, by making the detection element into a cable-like form,
Leakage can be detected over a wide range using the same detection element.

Since the sensor is manufactured from an inorganic material that is heat-resistant and radiation-resistant, it can stably detect leaks over a long period of time without changing over time, even in high-temperature conditions in radiation environments.

[Brief explanation of drawings]

FIGS. 1(A), (B), and (C) show a radiation-resistant fluid leak detection element according to an embodiment of the present invention, FIG. 1(A) is a sectional view, and FIG. 1(B) is a partially broken view. Front view, Fig. 1 (C) is an equivalent circuit diagram, Fig. 2 (A) and (B) show a detection device using Murray loop method, Fig. 2 (A) is a block diagram showing the configuration, Fig. 2 (B) is an equivalent circuit diagram of the main part, FIG. 3 shows a fluid leakage detection element according to another embodiment of the present invention, FIG. 3(A) is a sectional view, and FIG. 3(B) is a partially broken view. Front view, Figures 4(A) to (D) show a leakage detection system using the pulse reflection method, Figure 4(A) is a block diagram showing the system configuration, and Figure 4(B) explains the detection principle 6. FIG. 4(C) is a diagram showing the waveforms of the emitted pulse and reflected pulse, and FIG. 4(D) is a diagram showing the detected waveform of the detection signal. In the figure, 0 1 2 3 4 5 Conductor (high resistance wire) Conductor (low resistance wire) Sensing part dielectric (glass fiber) Primary protection braid (glass m fiber) Secondary protection braid DC resistance bridge circuit internal conductor sensing part Dielectric (glass fiber) External braided conductor External protection braid Pulse emission detection circuit

Claims (2)

[Claims] (1) a set of a plurality of conductors arranged in close proximity, and an inorganic insulating member with radiation resistance that insulates between the plurality of conductors and can retain and secure the fluid when the fluid comes into contact; A fluid leak detection element for use in a radiation environment, characterized by having an electrode. (2) In a radiation environment, the fluid leak detection element according to claim 1 is disposed near equipment/piping containing fluid, and when fluid leaks from the equipment/piping, inorganic insulation of the fluid leak detection element is provided. A method for detecting fluid leakage in a radiation environment, comprising: detecting leakage of the fluid by measuring electrical characteristics between the plurality of conductors when the fluid is held and secured in a member.