JPH06109634A - Hydrogen detector - Google Patents

Abstract

PURPOSE:To shorten the hydrogen detecting time by constituting a hydrogen detection sensor by coiling an optical fiber, so as to detect hydrogen based upon the increase of optical transmission loss when the optical fiber absorbs hydrogen. CONSTITUTION:For a sensor part 11, the portion of an optical fiber 12 whose coating was removed is coiled up, and fixed with a coating 13 whose material is identical with the fiber 12, thus the fiber 12 is reinforced. Relating to the titled hydrogen detector, a sensor part 11 is directly provided to a fused sodium main flow channel of a fast breeder, and a laser beam source is connected to one end of the fiber 12, and an optical power meter is connected to the other end. In case a steam generator is damaged to make the fused sodium react with water to increase hydrogen in the fused sodium, the hydrogen is diffused in the fiber 12, so as to lower optical transmission efficiency. The increase of hydrogen concentration in the fused sodium is detected based upon the drop of transmission efficiency.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hydrogen detector used for detecting hydrogen dissolved in a fluid and hydrogen contained in a mixed gas.

[0002]

2. Description of the Related Art One of the applications of this type of hydrogen detector is a hydrogen detection system in a sodium cooled fast breeder reactor or the like. The steam generator of a sodium-cooled fast breeder reactor generates steam by heating a heat transfer tube through which water flows inside from outside with liquid sodium. Should this heat transfer tube break, water will gush into the sodium, causing a violent chemical reaction between the water and sodium. This phenomenon is called sodium-water reaction, and even if a small heat transfer tube is damaged in the initial stage, if left unattended, it may develop into a large-scale damage due to corrosion by reaction products, leading to an accident that generates high pressure. Are known. So as to prevent such accidents, sodium-
It is important to discover the water reaction.

For the detection of small-scale sodium-water reactions,
Conventionally, a method of detecting hydrogen gas generated by a sodium-water reaction and dissolved in molten sodium and hydrogen gas mixed in a cover gas of a steam generator has been used. The conventional hydrogen meter is designed based on a principle called a dynamic equilibrium method using a vacuum pump. FIG. 5 is a schematic view showing an example of a conventional hydrogen meter. The hydrogen meter 1 includes a cylindrical main body 2 having one end connected to a sodium flow path, a molten sodium inflow section and a decompression chamber 3 for the main body 2. And a vacuum pump 5 connected to the rear part of the decompression chamber 3
And a vacuum gauge 6 for measuring the atmospheric pressure in the decompression chamber 3, and an orifice 7 provided in front of the vacuum pump 5 for ensuring the exhaust volume.

The hydrogen meter 1 is connected to a pipe branched from a main flow path for molten sodium, and is installed so that the molten sodium flowing through the main flow path through the pipe is guided to one end of the main body 2. Hydrogen in sodium diffuses into the decompression chamber 3 through the nickel film 4, and is exhausted by the vacuum pump 5 through the orifice 7 at a constant exhaust speed. Since the diffusion amount of hydrogen and the pressure in the decompression chamber change due to the change in the hydrogen concentration in the molten sodium, the hydrogen concentration can be known from the indicated value of the vacuum gauge 6 installed.

[0005]

However, in the conventional hydrogen detection method using the hydrogen meter 1, there is a time delay due to hydrogen diffusion in the branch pipe and the nickel film, so that the hydrogen is detected when the film temperature is about 350 ° C. It took 30 seconds or more to detect the change in concentration.

The present invention has been made in view of the above circumstances, and by shortening the hydrogen detection time, in the event of a damage accident, immediately detect the occurrence of the accident and take measures to prevent the expansion of the accident. The purpose of the present invention is to provide a high-performance hydrogen detector that can improve safety. Further, the present invention is not limited to detection of hydrogen in molten sodium and cover gas, but can be applied to detection of hydrogen in other fluids and mixed gases.

[0007]

According to the invention described in claim 1, there is provided a hydrogen detection sensor section in which an optical fiber is wound in a coil shape, and the optical fiber of the hydrogen detection sensor section absorbs hydrogen. It is a hydrogen detector that detects hydrogen due to an increase in transmission loss.

According to a second aspect of the present invention, the hydrogen detection sensor portion is formed by winding an optical fiber around the outer periphery of the quartz rod to fuse and integrate the optical fiber, and thinning the cladding of the optical fiber by etching. Is.

According to a third aspect of the present invention, there is provided a conductor comprising SiO ₂ doped with GeO ₂ or TiO ₂ on a substrate, extending from the incident end and the emission end in a double spiral shape and connected at the end. A waveguide is formed and the waveguide is made of SiO ₂
Is a hydrogen detector including a hydrogen detection sensor unit covered with a thin film made of, and detecting hydrogen by an increase in optical transmission loss when the waveguide of the hydrogen detection sensor unit absorbs hydrogen.

According to a fourth aspect of the invention, the metal coated fiber is stripped of the metal coating to expose the bare optical fiber, and the metal coating on both sides of the exposed portion is held by a reinforcing member having a liquid passage hole. A hydrogen detector that forms a hydrogen detection sensor part and that detects hydrogen due to an increase in optical transmission loss when the optical fiber of the hydrogen detection sensor part absorbs hydrogen.

[0011]

In the hydrogen detector according to the present invention, an optical fiber or a waveguide is used in the hydrogen detection sensor section. If hydrogen exists around the optical fiber or the waveguide, hydrogen diffuses into the optical fiber or the waveguide. The detection principle is the property that hydrogen reacts chemically with these materials and the optical transmission efficiency of the optical fiber or the waveguide decreases. Since these hydrogen detection sensor parts can be easily downsized and can be used at high temperatures,
It is possible to install the sensor part in the main flow path in the fluid,
By making the branch pipe unnecessary and increasing the temperature of the sensor unit, the diffusion speed is increased and the detection time can be shortened.

[0012]

1 shows a first embodiment of a hydrogen detector according to the present invention, in which reference numeral 11 denotes a hydrogen detection sensor section (hereinafter abbreviated as a sensor section). The sensor portion 11 has a structure in which the coating removed portion of the optical fiber 12 is wound in a coil shape and is fixed with a coating 13 made of the same material as the optical fiber 12. This coating 13 is for reinforcing the fiber which is easily broken in the bare wire state. To exemplify the method of manufacturing the sensor unit 11, the core diameter is 40 μ
A bare fiber having a diameter of about 50 m and a fiber diameter of about 50 μm is spun, wound around a 10 mmφ quartz rod (or quartz pipe), covered with a thin quartz tube having an inner diameter of 11 mm and an outer diameter of 12 mm, and then a glass lathe and an oxyhydrogen torch are used. It is manufactured by performing collapse and integrating. Alternatively, the spun fiber may be wound around a 10 mmφ quartz rod (or a quartz pipe), plastically deformed in a high temperature furnace at about 1000 ° C., and then covered with a thin quartz pipe (without collaps).

In this hydrogen detector, the sensor unit 11 is directly installed in the molten sodium main flow path of the fast breeder reactor, the laser light source is connected to one end of the optical fiber 12, and the other end is connected to the optical power meter. It is installed and puts in laser light from one end and monitors the output at the other end. If the steam generator is damaged and hydrogen increases in the molten sodium due to the reaction between the molten sodium and water, hydrogen diffuses into the optical fiber 12 in the sensor unit 11 and the material and hydrogen Chemically react with each other to increase the optical transmission loss of the optical fiber 12 and reduce the optical transmission efficiency. Due to this decrease in light transmission efficiency, an increase in hydrogen concentration in molten sodium is detected.

The diameter of the coil of the sensor section 11 can be set to about 1 cm, so that what was conventionally installed outside the main flow path of molten sodium using a branch pipe is directly installed in the main flow path. It is possible to eliminate the detection delay due to the use of the branch pipe. Furthermore, by installing the sensor unit 11 in the main flow path, the temperature of the sensor unit 11 can be set to 400 to 450 ° C., and the diffusion rate of hydrogen into the optical fiber 12 of the sensor unit 11 can be increased. Therefore, the detection time delay due to the hydrogen diffusion delay can be improved. Therefore, with this hydrogen detector, it is possible to shorten the hydrogen detection time compared to conventional products, and if a damage accident occurs, immediately detect the accident occurrence and take measures to prevent the accident from spreading. The safety can be improved.

Further, since the detection sensitivity of the sensor section 11 is proportional to the optical path length, this hydrogen detector also has a feature that the detection sensitivity can be arbitrarily adjusted by the number of turns of the coil.

As the composition of the optical fiber 12 used in this hydrogen detector, a GeO ₂ --P ₂ O ₅ --SiO ₂ based optical fiber is suitable. That is, in this type of optical fiber, H ₂ gas permeates and diffuses into the glass and combines with non-bridging oxygen in the glass to generate an OH group, which causes O 2 in the optical fiber.
The H absorption peak increases and the loss increases. The optical fiber having the above composition has the highest rate of reaction for producing OH groups.

FIG. 2 shows a second embodiment of the hydrogen detector according to the present invention, in which reference numeral 21 is a sensor portion of the hydrogen detector. In this sensor portion 21, a quartz optical fiber bare wire 23 is wound around a quartz rod 22 while being plastically deformed by a burner so as to be fused and integrated with the outer circumference of a quartz rod 22. Clad thickness 10μm
It will be thinned to a certain degree. The bare silica optical fiber 23 used here is a GeO ₂ -doped SiO ₂ core, which is used in the ordinary optical communication field, and S.
What is composed of an iO ₂ clad is used.

In the hydrogen detector according to this embodiment, the sensor portion 21 can be directly installed in the main flow path, like the previous embodiment, and the detection delay due to the use of the branch pipe can be eliminated. In addition, since the temperature of the sensor can be increased to increase the diffusion rate of hydrogen, the hydrogen detection time can be shortened. Safety can be improved by taking measures to prevent expansion. Further, since the ordinary core / clad type optical fiber is used and the cladding is thinned to shorten the hydrogen diffusion distance to the core, the response speed of hydrogen detection can be increased. Further, the hydrogen sensor unit can be configured by using an ordinary optical fiber, which is excellent in compatibility with existing light sources and photodetectors, and can be easily connected to these devices.

FIG. 3 shows a third embodiment of the hydrogen detector according to the present invention, in which reference numeral 31 is a sensor portion of the hydrogen detector. The sensor unit 31 is made of SiO ₂ doped with GeO ₂ or TiO ₂ on a substrate 32 made of quartz or silicon, and extends from the incident end 33 and the emitting end 34 in a double spiral shape and is connected at the end. The waveguide 35 is formed, and the waveguide 35 is covered with a thin film (not shown) made of SiO ₂ . The thickness of this coating is 5
About μm is sufficient. To form the waveguide 35, a GeO ₂ -doped SiO ₂ film having a shape as shown in FIG. 3 is formed on a quartz substrate.
Of SiO _{2 on the} waveguide formation surface.
Is uniformly deposited with a thickness of about 5 μm. Incident end 33 and exit end 34 of the waveguide 35
An optical fiber 36 is connected to each.

Since the hydrogen detector according to this embodiment can increase the response speed of hydrogen detection in the same manner as in the previous embodiment, when a damage accident occurs, the accident occurrence is immediately detected. The safety can be improved by taking measures to prevent the accident from spreading.

FIG. 4 shows a fourth embodiment of the hydrogen detector according to the present invention. This hydrogen detector is configured by forming one or a plurality of sensor units 42 on a metal-coated fiber 41 and connecting an OTDR (not shown) to one of the metal-coated fibers 41. In this sensor section 42, the metal coating 44 of the metal coated fiber 41 is peeled off by a predetermined length to expose the bare optical fiber 43, and the metal coating 43 on both sides of the exposed portion is reinforced with a liquid passage hole 45.
It is configured by being gripped with and reinforced. For the coating material of the metal-coated fiber 41 and the reinforcing member 46, a metal material that does not react with the fluid to be measured is used.

In this hydrogen detector, a metal-coated fiber 41 having a plurality of sensor portions 42 is laid in the main flow path of the fluid to be measured, and measurement light is incident from one side of the fiber to OT.
The DR method enables multipoint measurement of loss increase in the length direction of the fiber. Sensor part 4
The principle of hydrogen detection in 2 is the same as in each of the previous embodiments,
The fluid to be measured is in contact with the bare optical fiber 43 through the through hole 45 of the reinforcing member 46, and if hydrogen is present in the fluid to be measured, the hydrogen diffuses into the bare optical fiber 43, and the material of the optical fiber becomes Hydrogen chemically reacts to increase the optical transmission loss of the optical fiber and reduce the optical transmission efficiency. This decrease in light transmission efficiency is measured by OTDR to detect an increase in hydrogen concentration in the fluid.

The hydrogen detector according to this embodiment has the same effects as those of the previous embodiments, and also has a metal-coated fiber 41.
Since a plurality of sensor parts 42 are formed at intervals in the main flow path of the fluid to be measured and OTDR is used to perform multipoint measurement in the length direction, it is possible to perform multipoint measurement along the main flow path. The measurement can be performed at the same time, and the shortening of the hydrogen detection time can be further improved.

[0024]

As described above, the hydrogen detector of the present invention uses an optical fiber or a waveguide in the hydrogen detection sensor section, and uses an optical fiber or a waveguide when the hydrogen detection sensor section absorbs hydrogen. Since hydrogen is detected by increasing the transmission loss, it is easy to downsize the hydrogen detection sensor part and it can be used at high temperature, so it is possible to install the sensor part in the main flow path of the fluid to be measured. In addition, the branch pipe is not required, and the temperature of the sensor portion is increased to increase the diffusion rate and shorten the detection time. Therefore, according to this hydrogen detector, the detection time of hydrogen can be shortened as compared with the conventional product. If this is applied to a liquid metal cooled fast breeder reactor, in the unlikely event of a damage accident, it is possible to improve safety by immediately detecting the occurrence of the accident and taking measures to prevent the expansion of the accident.

[Brief description of drawings]

FIG. 1 is a perspective view of essential parts showing a first embodiment of a hydrogen detector of the present invention.

FIG. 2 is a main part perspective view showing a second embodiment of the hydrogen detector of the present invention.

FIG. 3 is a main part plan view showing a third embodiment of the hydrogen detector of the present invention.

FIG. 4 is a side view of essential parts showing a fourth embodiment of the hydrogen detector of the present invention.

FIG. 5 is a schematic configuration diagram showing a conventional hydrogen meter.

[Explanation of symbols]

11, 21, 31, 42 ... Hydrogen detection sensor section, 12 ...
… Optical fiber, 13… Coating, 22… Quartz rod, 2
3 ... Silica-based bare optical fiber, 32 ... Substrate, 33 ...
Input end, 34 ... Emission end, 35 ... Waveguide, 41 ... Metal coated fiber, 43 ... Bare optical fiber, 44 ... Coated, 45 ... Liquid passage hole, 46 ... Reinforcing member.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Sanada 1440 Rokuzaki, Sakura City, Chiba Prefecture, inside the Sakura Factory, Fujikura Electric Wire Co., Ltd.

Claims (4)

[Claims] 1. A hydrogen detector which comprises a hydrogen detection sensor unit in which an optical fiber is wound in a coil shape, and which detects hydrogen due to an increase in optical transmission loss when the optical fiber of the hydrogen detection sensor unit absorbs hydrogen. 2. The hydrogen detection sensor unit is characterized in that an optical fiber is wound around the outer circumference of a quartz rod to be fused and integrated, and the cladding of the optical fiber is thinned by etching. Hydrogen detector. 3. A waveguide made of SiO ₂ doped with GeO ₂ or TiO ₂ is formed on the substrate, the waveguide extending from the entrance end and the exit end in a double spiral shape and connected at the end, and the waveguide is formed. A hydrogen detector comprising a hydrogen detection sensor unit whose waveguide is covered with a thin film made of SiO _2, and which detects hydrogen due to an increase in optical transmission loss when the waveguide of the hydrogen detection sensor unit absorbs hydrogen. 4. A hydrogen detection sensor portion is formed on a metal-coated fiber by exposing the bare optical fiber by stripping the metal coating and gripping the metal coating on both sides of the exposed portion with a reinforcing member having a liquid passage hole. A hydrogen detector that detects hydrogen due to an increase in optical transmission loss when the optical fiber of the hydrogen detection sensor unit absorbs hydrogen.