JPS6018931B2 - Leak detection device - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a leak detection device for a fluid flow path, and is particularly suitable for monitoring fluid leaks in process piping, valves, etc. that flow fluid containing radioactive materials in a plant. Regarding a detection device.

[Technical background of the invention and its problems]

For example, in the unlikely event that a defect occurs in piping or valves in a nuclear power plant or other plant, the fluid flowing through the piping or valves may leak, especially if the fluid contains radioactive materials. It is necessary to strictly monitor leaks from piping, valves, etc., as this may lead to many problems in plant management.

Conventionally, to detect leaks in pipes, valves, etc., temperature detectors are installed near the parts that require monitoring, and if a crack occurs in the pipe and fluid leaks, the temperature around the leak point will rise. Since this occurs, piping leakage is detected by detecting this. However, since this method is a measurement that depends on the enthalpy of the fluid, the amount of temperature rise varies depending on the enthalpy, and the normal temperature standards that must be determined for each plant piping and each measurement location are different. There are also problems such as the fact that measuring temperature rise is an indirect detection method, and in the case of nuclear power plants, there are hundreds of leakage measurement points in the reactor primary system per plant★
Therefore, a relatively simple measuring device was required.

[Object of the Invention] An object of the present invention is to provide a simple leakage device that can perform leakage detection at a large number of leakage monitoring points from a remote location.

[Summary of the invention]

A first aspect of the present invention is a leak detection device that detects a defect occurring in a radioactive fluid flow path by detecting the presence of radioactive fluid leaking from the defect. A detector having a radiation-sensitive optical fiber having an output part and an intermediate part disposed outside the flow path,
We provide a leakage detection device that is installed at a designated leakage monitoring point on a fluid flow path, and detects an increase in optical fiber transmission loss caused by the radioactivity of leaked fluid from a defective part that occurs in the fluid flow path.・The above objectives have been achieved.

A second aspect of the present invention is a leakage detection device that detects a defective portion occurring in a radioactive fluid flow path by detecting the presence of radioactive fluid leaking from the defective portion. A detector having a radiation-sensitive optical fiber having a part and an output part and an intermediate part placed outside the flow path is installed at a leak monitoring point determined on the flow path,
and a photoelectric converter connected to the light output section of the detector, a comparator connected vertically to the photoelectric converter and outputting when the output of the photoelectric converter exceeds a set value, and a set time. A leakage detection device is provided that includes a timer that later loses its output, and a circuit that receives the output of this timer and the output of a comparator and outputs their AND, and detects leakage from a defective part that occurs in a fluid flow path. The increase in transmission loss of the optical fiber caused by the radioactivity of the leaked fluid is compared with the set value of the comparator through the photoelectric converter, and when the set value is exceeded, a leakage signal is generated and the set time of the timer is exceeded. By blocking the output of the comparator, malfunctions due to optical fiber transmission losses that naturally increase over a long period of time are prevented, thereby achieving the above objective.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a schematic configuration diagram of an embodiment in which the leakage detection device of the present invention is applied to the instrumentation piping of a boiling water reactor. The instrumentation pipe 3 passes through a through hole 4 provided in a side wall of the reactor containment vessel 1 and is connected to a pressure detection sensor 5 .

Reference numeral 6 is a stop valve provided in the middle of the instrumentation piping 3.
In a portion of the instrumentation pipe 3 outside the reactor containment vessel 1, a detector 7 is attached to the outside of the instrumentation pipe 3, close to the through hole 4. An optical fiber cable 10 for transmission is laid from the detector 7 to the determination device 9 provided inside the central control room 8 . Note that the detector 7 and the like are generally provided with a plurality of tubes at a plurality of locations, but only one of them is shown in FIG. 2 is a detailed sectional view showing an enlarged portion of the detector 7 attached to the instrumentation piping 3 in FIG. 1, and FIG. 3 is a sectional view taken along line A-A in FIG. Show the diagram.

In FIG. 2, a cap-shaped covering part 11 whose upper end is closed is installed over the length 1 including the leak monitoring part of the instrumentation pipe 3, for example, the welded part of the pipe, and the closing part of the rising part of the covering part 11 is A land body 12 is fixed.

A connector 3 is provided on the side surface of the body 12, and both ends 14A and 14B of an optical fiber 14 having a length of several meters are optically connected to the inner end of the connector 13, respectively. Further, the intermediate portion of the optical fiber 14 is housed inside the shell 12 so as to be circulated as appropriate. The optical fiber 14 is
A material that has a high degree of disintegration when exposed to radiation is used, and for example, an optical fiber using a lead silicate chlorine glass material is suitable. At the outer end of the connector 13, a two-wire optical fiber cable 10 is connected to both ends 14A and 14A of the optical fiber 14, respectively.
14B and is optically connected. Optical fiber cable 1 The optical fiber used here has excellent radiation resistance, for example, an optical fiber made of synthetic silica material. FIG. 4 shows details of the determination device 9, in which a light emitter 15 that emits light of a constant intensity and a constant wavelength is connected to the tip of an optical fiber cable 10 connected to one end 14A of the optical fiber 14.

Further, a photoelectric converter 16 and a comparator 17 following the photoelectric converter 16 are connected to the tip of the optical fiber cable 10 connected to the other end 148 of the optical fiber 14, and output to the signal line 18. After the comparator 17, the configuration shown in FIG. 5, for example, can be used. That is, in addition to the comparator 17, a timer 19 is provided which loses its output after a set time has elapsed, and an AND circuit 20 whose inputs are the outputs of the comparator 17 and the timer 19 is connected to the output of the timer 19. Vessel 21,
and a reset switch 22 for the timer 19. Next, the operation of the leak detection device having the above configuration will be explained.

Reactor water 2A accommodated inside the pressure vessel 2 is transferred to the instrumentation piping 3.
The pressure reaches the pressure detection sensor 5 through the reactor water 2A, and detects the pressure of the reactor water 2A. Although the reactor water 2A contains radioactive materials, the radiation exposure of the optical fiber 14 housed in the detector is extremely small and can usually be ignored due to the shielding effect of the down pipe of the pipe 3. be. Therefore, the light is emitted from the light emitter 16, and the path of the optical fiber cable 10, the optical fiber 14
, and the light intensity received by the photoelectric converter 16 via the return path of the optical fiber cable 10 maintains a substantially constant value over a long period of time. Here, a break such as a crack occurs in the section where the covering part 11 of the instrumentation piping 3 is installed, and the reactor water 2A
When leakage occurs, the reactor water 2A is at high temperature and pressure, so it turns into steam and fills the inside of the casing 12, and the optical fiber 14 is exposed to this radioactive reactor water vapor.

Since the optical fiber 14 has the property of increasing transmission loss with respect to the exposure radiation dose illustrated in FIG. 6, the amount of light received by the photoelectric converter 16 decreases. Since the reference value of the comparator 17 is set, for example, to the output value of the photoelectric converter 16 in the case of the transmission loss Fo shown in FIG. 6, the signal line 18 as shown in FIG.
A leak alarm signal is generated, and a leak in the pipe 3 can be detected. Next, the operation of the configuration shown in FIG. 5 will be explained.

As long as the Xuling piping 3 is healthy, the radiation exposure of the optical fiber 14 will be minimal, but over a long period of time, the accumulated radiation dose will finally reach Ro in Figure 6, and in that case, even though there is no leakage, There is a risk of generating a false alarm signal. However, since the set time of the timer 19 is set so that the cumulative dose at the location where the detector 7 is installed is shorter than the predicted time when the cumulative dose reaches Ro in Fig. 6, the output generated on the signal line 18 within this set time produces the output of the AND circuit 20 to allow detection of a genuine leak in the instrumentation piping 3. When the set time is exceeded, the output of the timer 19 disappears, so even if the product dose reaches Ro and an output is generated on the signal line 18, no output is generated on the logic circuit 20. At the same time, the display 21 indicates that the output of the timer 19 has disappeared, thereby prompting replacement of the optical fiber 14. timer 19
If the reset switch 22 is activated, time measurement can be started again. FIG. 8 shows the relationship among the outputs of the comparator 17, the timer 19, and the AND circuit 20 described above. This circuit configuration is particularly effective when a certain leakage radiation intensity is generated from the fluid flow path. [Effects of the Invention] As detailed above, according to the first aspect of the present invention, it is possible to realize a small, simple and robust detector, so that a large number of leakage points can be monitored from a remote location in a favorable environment. A detection device can be obtained.

Further, according to the second aspect of the present invention, it is possible to obtain a leakage detection device that can prevent malfunctions for a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment in which the present invention is applied to the instrumentation piping of a boiling water reactor, and FIG. 2 is a detailed cross-sectional view showing an enlarged portion including the detector in FIG. 1. Figure 3 is A- in Figure 2.
4 is a connection diagram showing details of the determination device shown in FIG. 1, FIG. 5 is a circuit diagram showing a modification of the comparator shown in FIG. 4, and FIG. 6 is a diagram showing a modification of the comparator shown in FIG. Figure 7 is a diagram showing the relationship between exposure radiation dose and transmission loss, Figure 7 is a diagram showing the relationship between glass fiber transmission loss and comparator output, and Figure 8 is a diagram showing the relationship between transmission loss of the glass fiber and comparator output.
FIG. 3 is a diagram showing the interrelationship between the comparator output, the timer output, and the AND circuit output in the figure. 3...Instrumentation piping, 7...Detector, 14
...Optical fiber, 14A, 14B...
End of optical fiber, 16...Photoelectric converter, 17
... Comparator, 19 ... Timer, 20.
...Logic product circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Scope of Claims] 1. In a leakage detection device that detects a defect occurring in a radioactive fluid flow path by detecting the presence of the radioactive fluid leaked from the defect, both ends thereof are connected to a light input portion and an output portion, respectively. 1. A leakage detection device comprising: a detector having a radiation-sensitive optical fiber having a central portion and an intermediate portion disposed outside the flow path, and installed at a leak monitoring point determined on the flow path. 2. The leak detection device according to claim 1, wherein the light guide material of the radiation-sensitive optical fiber is lead silicate-based. 3. In a leak detection device that detects a defect occurring in a radioactive fluid flow path by detecting the presence of the radioactive fluid leaked from the defect, both ends are used as an input part and an output part for light, respectively, and an intermediate part A detector having a radiation-sensitive optical fiber with a portion disposed outside the flow path is installed at a leak monitoring point determined on the flow path, and a photoelectric fiber is connected to the light output portion of the detector. a converter, a comparator that is cascaded to this photoelectric converter and outputs an output when the output of this photoelectric converter exceeds a set value, a timer that loses its output after a set time, and a comparator that outputs an output when the output of this photoelectric converter exceeds a set value; What is claimed is: 1. A leakage detection device comprising: a circuit that receives an output and an output and outputs a logical product thereof. 4. The leak detection device according to claim 3, wherein the light guide material of the radiation-sensitive optical fiber is lead silicate-based.