JP2007108120A - Tritium monitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tritium monitor having high measurement sensitivity by having a small consumption amount of a carrier gas, dispensing with exchange working and drainage treatment of an adsorbent and simplifying maintenance working. <P>SOLUTION: The tritium monitor comprises using a highly pure nitrogen gas as a carrier gas, being discharged in the carrier gas by selectively separating steam in a sample gas 100 with a steam separator 6, interrupting the carrier gas from radon, tron, its daughter nuclide or the other gaseous radioactive substance since the carrier gas containing the discharged water vapor is introduced into a measuring ionization chamber 16 to find tritium concentration from the ionized amount. In addition, the carrier gas is dehumidified with a carrier gas dehumidifier 18 to be reproduced, so that the carrier gas of a leaked part automatically fills, and further an evaporator 29 for evaporating drain produced in a sample gas compressor 7 in exhaustion of the sample gas is provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to tritium contained in gaseous waste (sample gas) released from air or exhaust equipment in buildings such as nuclear reactor facilities, spent fuel reprocessing facilities, radioactive isotope facilities, particle beam facilities, etc. The present invention relates to a tritium monitor that continuously measures the concentration of bisphenol.

  The tritium monitor samples the air in the buildings such as nuclear reactor facilities, spent fuel reprocessing facilities, radioactive isotope facilities, and particle beam facilities, or the exhaust of exhaust equipment, and the tritium contained in the water vapor in the sample gas. The concentration is measured in a gaseous state. The radiation radiated from tritium is β-ray, and the maximum energy is as low as 18 keV. Therefore, it is necessary to measure in a gas state through a vented ionization chamber. In addition, alpha rays emitted from radon, thoron, and their daughter nuclides present in the environment as natural radionuclides generate ionization equivalent to about 1000 of the beta rays emitted from tritium, so that tritium is highly sensitive. In order to measure the concentration of tritium, it is necessary to separate and measure only tritium from the nuclide and other high energy nuclides.

  The conventional tritium monitor utilizes the property that the hollow fiber membrane selectively permeates water vapor, separates the water vapor from the sample gas, discharges it into the carrier gas flowing outside the hollow fiber membrane, and contains the separated water vapor. By introducing the carrier gas into the vented ionization chamber, the tritium concentration is measured in a state where other radionuclides are not mixed. Since the water vapor permeation effect of the hollow fiber membrane depends on the differential pressure between the water vapor of the sample gas and the carrier gas, the carrier gas is required to be a dry gas. Moreover, in order to measure the concentration of low-energy tritium, it is required not to include other radioactivity. Nitrogen gas conforms to these conditions and can be easily obtained in the form of being enclosed in a cylinder. Therefore, it is common to use nitrogen gas as a carrier gas and supply it from the cylinder.

In the conventional tritium monitor configured as described above, since the carrier gas is constantly flowing, the amount of consumption increases, and the cylinder needs to be replaced frequently. For example, when the carrier gas is used at a rate of 3 L / min, it is necessary to replace the 7 m ³ (14.7 MPa / cm ³ G) cylinder at a frequency of about 30 hours, and reducing the consumption of the carrier gas becomes an issue. It was.

In order to solve such a problem, for example, in Patent Document 1, air in the atmosphere is sucked to remove particulate matter with a filter, pressurized air is passed through a hollow fiber membrane to remove water vapor, activated carbon The tritium monitor has been proposed in which air can be used as the carrier gas by adsorbing and removing radon and thoron and purifying clean air that does not contain radioactivity.
Japanese Patent Laid-Open No. 3-189487

  However, the cylinder-free tritium monitor described in Patent Document 1 has a problem that radon, thoron, and part of their daughter nuclides adsorbed on the adsorbent are separated and discharged into the carrier gas. Further, when there is gaseous radioactivity other than tritium, radon, and thoron in the ambient air around the monitor installation place, there is a problem that they cannot be removed. Furthermore, the net current value is obtained by taking the difference between the output current from the measurement ionization chamber for measuring the tritium concentration and the output current from the compensation ionization chamber for measuring the background, and based on the result. In the measurement method for determining the tritium concentration, radon, thoron and their daughter nuclides released from the adsorbent and other gaseous radioactivity cause fluctuations in the background current value, and increase the measurement sensitivity of the tritium concentration. It was an obstacle. Further, since the adsorbent is used for the purpose of adsorbing and removing radon, thoron, its daughter nuclide, and water vapor, there has been a problem that a new maintenance work such as a replacement work of the adsorbent occurs. Furthermore, the drain generated by pressurizing the air needs to be treated as radioactive waste, and it has been a challenge to make it drainless.

  The present invention has been made to remedy the above-described problems, and consumes a small amount of carrier gas. Further, it does not require an adsorbent replacement operation or drain treatment, and maintenance work is simple. An object is to provide a tritium monitor with high sensitivity.

  A tritium monitor according to the present invention has a sample gas compressor for pressurizing a sample gas, and selectively separates water vapor in the sample gas sucked by the sampling means and sampling means for continuously sucking the sample gas. A water vapor separating means released into the carrier gas, a measuring means for measuring the tritium concentration contained in the water vapor released into the carrier gas by the water vapor separating means, and a sample gas based on the measurement result by the measuring means. Calculating means for calculating the tritium concentration, sample gas drying means for removing water vapor remaining in the sample gas from which a part of the water vapor has been separated by the water vapor separating means, and drain generated in the sample gas compressor as the sample gas Drain evaporating means that evaporates in the exhaust gas and steam separating means A carrier gas regeneration means for regenerating and circulating the carrier gas by removing the steam from the carrier gas containing the released steam is provided. The carrier gas regeneration means includes a carrier gas compressor for pressurizing the carrier gas, and a carrier gas compressor. A carrier gas dehumidifier that removes water vapor in the concentrated carrier gas is connected, and the water vapor separation means, measurement means, and carrier gas regeneration means are connected in a closed loop, and inside the closed loop while regenerating the carrier gas by the carrier gas regeneration means. While being circulated, the carrier gas is automatically replenished to the closed loop by the carrier gas replenishing means.

  According to the present invention, the carrier gas is dehumidified and regenerated by the carrier gas regenerating means and circulated in the closed loop, and the carrier gas is automatically replenished by the carrier gas replenishing means. The tritium concentration can be measured with high sensitivity in a suitable state where the daughter nuclide and other radioactivity do not exist. In addition, since the carrier gas consumption can be greatly reduced, the replacement frequency of the carrier gas cylinder can be greatly reduced, and the drain generated in the sample gas compressor is evaporated in the exhaust of the sample gas. Drain treatment such as adsorbent replacement is not required, and maintenance work can be greatly saved.

Before explaining the embodiment of the present invention, the basic principle of the present invention will be explained with reference to FIG.
The tritium monitor according to claim 1 of the present invention has a sample gas compressor 7 that pressurizes the sample gas 100 as sampling means for continuously inhaling the sample gas 100. When the sample compressor 7 operates, the sample gas 100 is sucked from the inlet valve 1 due to the negative pressure on the suction side.

  In addition, a water vapor separator 6 is provided as water vapor separation means for selectively separating water vapor in the sample gas 100 sucked by the sampling means and releasing it into the carrier gas. The tritium monitor according to the present invention uses high purity nitrogen gas as a carrier gas. As shown in FIG. 1, the water vapor separator 6 has two inlets a and c and two outlets b and d, and the sample gas 100 introduced from the inlet a is discharged from the outlet b, and the inlet c. The carrier gas introduced from is discharged from the outlet d. The steam separator 6 can be arranged on either the intake side or the exhaust side of the sample gas compressor 7, and an example is shown in which it is arranged on the intake side in the first embodiment and on the exhaust side in the second embodiment. Yes.

  Further, a measurement ionization chamber 16 and a compensation ionization chamber 28 are provided as measurement means for measuring the tritium concentration contained in the water vapor released into the carrier gas by the water vapor separator 6. Furthermore, a calculation unit 31 is provided as calculation means for calculating the tritium concentration in the sample gas based on the measurement result obtained by the measurement ionization chamber 16 and the measurement result obtained by the compensation ionization chamber 28. The details of the calculation unit 31 will be described in the section related to claim 6.

  Further, a sample gas dehumidifier 11 is provided as a sample gas drying means for removing water vapor remaining in the sample gas 100 from which part of the water vapor has been separated by the water vapor separator 6. Further, an evaporator 29 is provided as a drain evaporation means for evaporating the drain generated in the sample gas compressor 7 in the exhaust of the sample gas 100.

  Further, as carrier gas regenerating means for removing water vapor from the carrier gas containing water vapor discharged from the water vapor separator 6 and regenerating and circulating the carrier gas, a carrier gas compressor 17 for pressurizing the carrier gas, and the carrier gas compressor 17 The carrier gas dehumidifier 18 for removing water vapor in the carrier gas concentrated by the above is provided.

  Further, the tritium monitor according to the first aspect of the present invention includes a closed loop 200 that connects the water vapor separator 6, the measurement ionization chamber 16, the carrier gas compressor 17, the carrier gas dehumidifier 18, and the compensation ionization chamber 28. The inside of the closed loop 200 is circulated while the carrier gas is regenerated by the gas regeneration means, and the carrier gas is automatically replenished to the closed loop 200 by the carrier gas replenishment means. Specifically, the carrier gas is automatically supplied to the closed loop 200 from the nitrogen cylinder 21 via the constant pressure adjustment valve 22.

  As described above, according to the tritium monitor of the first aspect of the present invention, the water vapor containing tritium is selectively separated by the water vapor separator 6 and released into the carrier gas, and the carrier gas containing water vapor is removed from the ionization chamber 16 for measurement. Since the tritium concentration is measured by introducing it into the carrier, the carrier gas can be essentially shielded from radon, thoron and its daughter nuclides, and other gaseous radioactive materials, and the measurement sensitivity of the tritium concentration can be increased. Can do. In addition, since the carrier gas is dehumidified and regenerated by the carrier gas dehumidifier 18 and the leaked carrier gas is automatically replenished, the consumption amount of the carrier gas can be greatly reduced as compared with the prior art. Further, since the drain generated in the sample gas compressor 7 is evaporated in the exhaust of the sample gas 100, the drain treatment as the radioactive liquid waste and the replacement work of the adsorbent are unnecessary, and the maintenance work is greatly increased. It can save labor.

  Next, the tritium monitor according to the second aspect of the present invention is the tritium monitor according to the first aspect of the present invention, wherein the dried sample gas 100 discharged from the sample gas dehumidifier 11 which is a sample gas drying means. The other is purged of water vapor dehumidified in the sample gas dehumidifier 11, and the other is purged of water vapor dehumidified in the carrier gas dehumidifier 18, and the water vapor recovered by these purges is sampled. The gas 100 is introduced into the evaporator 29 which is a drain evaporation means.

According to the second aspect of the invention, the dry sample gas 100 discharged from the sample gas dehumidifier 11 can efficiently perform the water vapor purge of both the sample gas dehumidifier 11 and the carrier gas dehumidifier 18, Furthermore, by introducing these into the evaporator 29 as exhaust gas for the sample gas 100, a tritium monitor having a simple structure and not requiring drain treatment can be obtained.

  Next, the tritium monitor according to the third aspect of the present invention is the tritium monitor according to the first aspect of the present invention, wherein the water vapor separator 6 is the first hollow fiber membrane and the carrier gas dehumidifier 18 is the first. Sample gas dehumidifier 11 is provided with a third hollow fiber membrane, and water vapor is separated by these hollow fiber membranes. The basic structure of the water vapor separator 6, the carrier gas dehumidifier 18, and the sample gas dehumidifier 11 is the same, and the water vapor is transmitted from the gas to be processed to the purge gas side by the hollow fiber membrane having the property of selectively transmitting water vapor. Can be made.

  Furthermore, the tritium monitor according to claim 4 of the present invention is the tritium monitor according to claim 3 of the present invention, wherein the first hollow fiber membrane of the water vapor separator 6 is a non-porous ion exchange membrane, Specifically, a perfluoro sulfonic acid resin membrane is used, and a microporous membrane, specifically a polyimide membrane, is used as the second hollow fiber membrane of the carrier gas dehumidifier 18 and the third hollow fiber membrane of the sample gas dehumidifier 11. It is what was used. Perfluororosulphonic acid resin membranes have high water supply capacity and excellent water vapor separation ability, but on the other hand, with the same volume, polyimide membranes are superior in terms of water vapor separation efficiency because they can take a larger membrane area. Is possible. According to the tritium monitor according to the invention of claim 4, the water vapor separator 6 can more selectively separate the water vapor.

  Further, the tritium monitor according to claim 5 of the present invention is the tritium monitor according to claim 3 of the present invention, wherein the second hollow fiber membrane of the carrier gas dehumidifier 18 is a non-porous ion from upstream. A perfluoro sulfonic acid resin film that is an exchange film and a polyimide film that is a microporous film are connected in series in this order. As a result, even when mist is generated by the carrier gas compressor 17, it is absorbed by the non-porous ion exchange membrane, so that the amount of water vapor released from the water vapor separator 6 to the carrier gas is stably maintained high. Measurement sensitivity can be increased.

  Next, the arithmetic means of the tritium monitor according to the sixth aspect of the present invention will be described. A tritium monitor according to a sixth aspect of the present invention is the tritium monitor according to the first aspect, in which the water vapor separation measured by the water vapor density in the sample gas 100 and the ionization chamber 16 for measurement is added to the arithmetic unit 31 as the arithmetic means. Ionization amount A of the carrier gas containing water vapor discharged from the vessel 6, the water vapor density in the carrier gas containing water vapor released from the water vapor separator 6, and the regenerated carrier gas measured by the compensation ionization chamber 28 Is input respectively. Based on these data, the calculation unit 31 compensates the ionization amount B from the ionization amount A, compensates the water vapor separation efficiency based on the ratio of the water vapor density in the sample gas and the water vapor density in the carrier gas, The tritium concentration in the gas can be calculated with high accuracy. The calculation method will be described in detail in the first embodiment.

  Further, the tritium monitor according to the seventh aspect of the present invention is the tritium monitor according to the sixth aspect, wherein the carrier gas filter 26 is provided in the preceding stage of the compensation ionization chamber 28 as the background measuring means, and the ion is provided in the preceding stage. A trap 25 is provided. According to the invention of claim 6, since the charged dust and the charged mist contained in the carrier gas can be collected and removed, the compensation ionization chamber 28 and the measurement ionization chamber 16 malfunction due to the charged dust. It is possible to operate stably.

  A tritium monitor according to claim 8 of the present invention is the tritium monitor according to claim 1, wherein a steam separator 6 is disposed on the exhaust side of the sample gas compressor 7, and water vapor concentrated by pressurization is disposed. It is separated by the water vapor separator 6 and discharged into the carrier gas. According to the eighth aspect of the present invention, stable water vapor separation efficiency can be obtained in the water vapor separator 6, so that it can be always operated under suitable conditions and the measurement sensitivity can be increased. The invention according to claim 8 will be described in detail in the second embodiment below.

  Further, the tritium monitor according to the ninth aspect of the present invention is the tritium monitor according to the first aspect of the present invention, wherein a water vapor separator as a water vapor separating means is connected to a solid polymer electrolyte as shown in FIG. Electric field driven water vapor comprising a membrane 6231, catalyst electrodes provided on both sides of the solid polymer electrolyte membrane 6231, specifically an anode 6232 and a cathode 6233, and a DC power source 6234 for applying a voltage to these catalyst electrodes. A separation membrane 623 is used.

  According to the ninth aspect of the invention, when the separated water vapor is released into the carrier gas, about 25% is converted into hydrogen gas. Therefore, the humidity condition of the carrier gas in the measurement ionization chamber 16 is improved. Measurement sensitivity can be increased. The invention according to claim 9 will be described in detail in a third embodiment below.

Embodiment 1 FIG.
Hereinafter, Embodiment 1 which is a specific example of the invention of Claims 1 to 7 will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration of a tritium monitor according to Embodiment 1 of the present invention. In the first embodiment, an example in which the water vapor separator 6 is arranged on the intake side of the sample gas compressor 7 is shown.

  In the tritium monitor according to the first embodiment, when the sample gas compressor 7 which is a sampling means is operated, the suction side of the tritium monitor becomes negative pressure, so that the sample gas 100 is sucked from the inlet valve 1. From the sample gas 100 sucked from the inlet valve 1, particulate dust and radioactive substances are removed by the sample gas filter 2, and the flow rate is measured by the sample gas flow meter 3. The inlet valve 1 is provided at a measurement point (not shown) such as an exhaust pipe or a room where tritium is handled.

  Subsequently, the dew point (* 1) of the sample gas 100 is measured by the sample gas dew point meter 4 which is a sample gas water vapor density measuring means for measuring the density of water vapor, and the pressure (* 2) by the sample gas pressure gauge 5. Is measured. The sample gas 100 whose dew point has been measured is introduced into a water vapor separator 6 which is a water vapor separation means. As shown in FIG. 1, the steam separator 6 has two inlets a and c and two outlets b and d, and the sample gas 100 introduced from the inlet a is steamed in the steam separator 6. Is separated and released into the carrier gas, and the carrier gas containing water vapor is discharged from the outlet d.

  Further, the sample gas 100 discharged from the outlet b of the water vapor separator 6, that is, the sample gas 100 from which a part of the water vapor is separated by the water vapor separator 6 is sucked into the sample gas compressor 7 and pressurized. The sample gas 100 that has been pressurized and has risen in temperature is introduced into the radiator 8 and cooled, and in the mist separator 9, the mist generated by the condensation of water vapor by cooling is removed. The pressure of the wet sample gas from which the mist has been removed is measured by a pressurized sample gas pressure gauge 10, introduced into a sample gas dehumidifier 11 as a sample gas drying means, and dehumidified, and the sample gas pressure reducing valve 12 near atmospheric pressure. The sample gas 100 is dried by being reduced in pressure.

  On the other hand, the water vapor separated from the sample gas 100 in the water vapor separator 6 is released into the carrier gas. The carrier gas containing the released water vapor has its dew point (* 3) measured by a carrier gas dew point meter 14 which is a carrier gas water vapor density measuring means, and its pressure is measured by a carrier gas pressure gauge 15. Subsequently, the ionization current (* 4), that is, the total of the tritium β-ray and the environmental γ-ray in the carrier gas is measured by being introduced into a measurement ionization chamber 16 as a measuring means, and tritium is measured based on this current value. The concentration is measured. The method for calculating the tritium concentration will be described in detail later.

  The carrier gas discharged from the measurement ionization chamber 16 is pressurized by a carrier gas compressor 17 which is a carrier gas regeneration means, the water vapor contained in the carrier gas is concentrated, and introduced into the carrier gas dehumidifier 18 to dehumidify the water vapor. Is done. The dehumidified carrier gas passes through the switching electromagnetic valve 19, is measured for pressure by the pressurized carrier gas pressure gauge 23, and is depressurized to near atmospheric pressure by the carrier gas pressure reducing valve 24 to become a dried carrier gas. The structures and operations of the water vapor separator 6, the sample gas dehumidifier 11, and the carrier gas dehumidifier 18 will be described later with reference to FIGS.

  The dried carrier gas is introduced into the ion trap 25, and charged dust contained in the carrier gas is collected by the electrode and removed. Charged dust is generated mainly due to wear of used members inside the carrier gas compressor 17. The charged dust collected on the electrode is discharged and adheres to the electrode, and is detached from the electrode when the particle size increases. The carrier gas filter 26 removes dust released into the carrier gas due to member wear or the like. The carrier gas from which dust has been removed is introduced into the compensation ionization chamber 28 after the flow rate is measured by the carrier gas flow meter 27, and the regenerated carrier gas ionization amount B, that is, tritium remaining in the carrier gas. The ionization current (* 5) of background radiation, which is the sum of the β rays and environmental γ rays, is measured. The carrier gas discharged from the compensation ionization chamber 28 is introduced into the inlet c of the water vapor separator 6.

  Thus, the water vapor separator 6, the measurement ionization chamber 16 and the compensation ionization chamber 28, the carrier gas compressor 17 as the carrier gas regeneration means, the carrier gas dehumidifier 18, and the like are connected by the closed loop 200. The carrier gas is circulated in the closed loop 200 while regenerating the carrier gas, and the carrier gas leaked from the closed loop 200 is automatically replenished by the carrier gas replenishing means.

  As a carrier gas replenishing means, nitrogen as a carrier gas is automatically supplied from the nitrogen cylinder 21 to the closed loop 200 via the constant pressure regulating valve 22. Further, by switching the switching electromagnetic valve 19 from open to closed and switching the purge electromagnetic valve 20 from closed to open, the carrier gas in the closed loop 200 can be replaced as necessary.

  The dried sample gas 100 dehumidified by the sample gas dehumidifier 11 and discharged from the sample gas pressure reducing valve 12 is divided into two. One purges the water vapor dehumidified by the sample gas dehumidifier 11, and the other purges the water vapor dehumidified by the carrier gas dehumidifier 18. The water vapor recovered by these purges is introduced together with the sample gas 100 into an evaporator 29 which is a drain evaporation means. The drain generated in the sample gas compressor 7 and discharged from the mist separator 9 is ejected in the form of mist in the evaporator 29, evaporates in the sample gas 100, and is discharged from the outlet valve 30 together with the sample gas 100. The structure of the evaporator 29 will be described later with reference to FIG.

  Furthermore, the tritium monitor according to the first embodiment includes a calculation unit 31 that is a calculation unit that calculates the tritium concentration in the sample gas 100 based on the measurement result obtained by the measurement ionization chamber 16. The calculation unit 31 includes a sample gas dew point (* 1) output from the sample gas dew point meter 4, a sample gas pressure (* 2) output from the sample gas pressure gauge 5, and a carrier output from the carrier gas dew point meter 14. The gas dew point (* 3), the ionization current (* 4) output from the measurement ionization chamber 16 and the ionization current (* 5) output from the compensation ionization chamber 28 are input.

  Further, the water vapor density of the sample gas corresponding to the sample gas dew point is obtained from the water vapor density table for the dew point, and the water vapor density W1 of the sample gas converted to atmospheric pressure from the sample gas pressure is obtained. Similarly, the water vapor density W2 of the carrier gas corresponding to the carrier gas dew point is obtained from the water vapor density table. Further, the difference between the ionization current measured in the measurement ionization chamber 16 and the ionization current measured in the compensation ionization chamber 28 is obtained as a net ionization current value, and the net ionization current value is multiplied by a concentration conversion coefficient, and the result Is multiplied by the water vapor density ratio W1 / W2, and the tritium concentration is calculated and output.

  A thermometer and a hygrometer may be used in place of the sample gas dew point meter 4 and the carrier gas dew point meter 14 as the sample gas water vapor density measuring unit and the carrier gas water vapor density measuring unit. In the first embodiment, the case where the output of the measurement ionization chamber 16 and the output of the compensation ionization chamber 28 are respectively input to the calculation unit 31 has been described. However, the measurement ionization chamber 16 and the compensation ionization chamber 28 are connected to each other. When a high voltage of reverse polarity is applied, the directions of the ionization currents as a result of measuring radiation are opposite to each other. By matching the respective ionization currents, a net ionization current from which background radiation has been removed is obtained. It is also possible to enter

  FIG. 2 is a diagram showing the configuration and structure of the water vapor separator 6 according to the first embodiment. In FIG. 2, arrows a, b, c and d correspond to the inlets and outlets a, b, c and d of the water vapor separator 6 shown in FIG. 1, respectively, and indicate the flow of the sample gas and the carrier gas. The sample gas (wet gas) is introduced from the dehumidified gas inlet 611 (arrow a), flows inside the numerous tubular hollow fiber membranes 612, and is discharged from the dehumidified gas outlet 613 (arrow b). On the other hand, the carrier gas (dry gas) is introduced from the purge gas inlet 614 (arrow c), flows between the outside of the tubular hollow fiber membrane 612 and the outer cylinder 615, and is discharged from the purge gas outlet 616 (arrow d). The configurations and structures of the sample gas dehumidifier 11 and the carrier gas dehumidifier 18 are also the same.

  FIG. 3 is a view showing the water vapor separation operation of the hollow fiber membrane 612 constituting the water vapor separator 6. The hollow fiber membrane 612 has a property of selectively permeating water vapor, and the water vapor permeates from the dehumidified gas side (a → b) to the purge gas side (c → d). For this reason, the water vapor separator 6 can separate water vapor containing tritium from radon in the sample gas 100, the daughter nuclide of TRON, and other gaseous radioactive materials. The operation of the hollow fiber membrane 612 constituting the sample gas dehumidifier 11 and the carrier gas dehumidifier 18 is the same as this.

  Furthermore, the amount of water vapor that passes through the hollow fiber membrane 612 depends on the differential pressure at each minute portion of the hollow fiber membrane 612. Therefore, the area of the hollow fiber membrane 612, the sample gas flow rate, the pressurized sample gas pressure, the carrier gas flow rate, and the pressurized carrier gas pressure of each of the water vapor separator 6, the sample gas dehumidifier 11 and the carrier gas dehumidifier 18 are appropriately set. By setting, the humidity of the carrier gas in the measurement ionization chamber 16 can be maintained in a suitable state from the viewpoints of both insulation and measurement sensitivity. Thereby, the dehumidification efficiency can be maintained at 90% or more without generating mist due to pressurization of the carrier gas compressor 17.

  As the hollow fiber membrane 612 used for the water vapor separator 6, the sample gas dehumidifier 11, and the carrier gas dehumidifier 18, for example, a commercially available polyimide membrane manufactured by Ube Industries, Ltd. can be used. This membrane is a microporous membrane. Water vapor is dissolved in the membrane from the membrane surface on the side having a high water vapor pressure across the membrane, diffuses and moves through the membrane, and is diffused from the membrane surface on the side having a low water vapor pressure. . A difference in permeation rate occurs depending on the type of gas component, and the permeation rate of water vapor is several thousand times greater than that of air (oxygen and nitrogen) and gases other than water vapor, so that selective water vapor separation is possible. However, when mist-like water enters the polyimide film, it is discharged without passing through, so the dehumidification efficiency is lowered.

As other hollow fiber membranes 612, for example, a perfluorosulfonic acid resin membrane manufactured by Asahi Glass Engineering Co., Ltd. is commercially available. This membrane is a non-porous ion exchange membrane having a hydrophilic functional group (—SO ₃ H), and the acidity is increased by the effect of the adjacent fluorine atoms, resulting in an increase in water absorption. And has the property of adsorbing a large amount of moisture. Since this membrane has a water vapor permeation rate several hundred thousand times higher than that of air (oxygen and nitrogen), it is superior to a polyimide membrane in selective water vapor separation ability. On the other hand, since the polyimide membrane can have a larger membrane area at the same volume, the polyimide membrane is superior in terms of miniaturization or water vapor separation efficiency. Moreover, since the perfluoro sulfonic acid resin membrane has a high water absorption capacity, the water vapor separation efficiency does not decrease even when mist-like water enters. Accordingly, by using a perfluoro sulfonic acid resin membrane as the hollow fiber membrane 612 of the water vapor separator 6 and using a polyimide membrane as the hollow fiber membrane 612 of the sample gas dehumidifier 11 and the carrier gas dehumidifier 18, a water vapor separator is obtained. 6, water vapor can be more selectively separated.

  Further, when only the polyimide membrane is used as the hollow fiber membrane 612 of the carrier gas dehumidifier 18, the carrier gas compressor 17 is provided with a carrier gas so as not to lower the temperature of the pressurized carrier gas discharged from the carrier gas compressor 17 as much as possible. It is necessary to connect the dehumidifier 18 close to each other and further suppress the amount of water vapor released from the water vapor separator 6 to the carrier gas so as not to condense inside the hollow fiber membrane 612. Therefore, as the hollow fiber membrane 612 of the carrier gas dehumidifier 18, a perfluorosulfonic acid resin film and then a polyimide film are connected in series on the upstream side, so that even if dew condensation occurs in the carrier gas compressor 17, the perfluorosulfonic acid resin is used. It can be absorbed with a membrane. As a result, the amount of water vapor released from the water vapor separator 6 to the carrier gas can be increased to a humidity limit of about 50% RH for stable operation of the ionization chamber in continuous operation.

  FIG. 4 is a diagram showing the configuration and structure of the radiator 8 according to the first embodiment. The sample gas 100 introduced from the one end 81 a of the finned tube 81 dissipates heat accumulated by pressurization by the sample gas compressor 7 from the fins 81 c by blowing air from the fan 82. The sample gas 100 whose temperature has been lowered is discharged from the other end 81 b of the finned tube 81. When the temperature of the sample gas 100 is lowered, water vapor exceeding the saturated water vapor pressure at that temperature is condensed into mist-like water.

  FIG. 5 is a diagram showing the configuration and structure of the evaporator 29 which is the drain evaporation means in the first embodiment. In the figure, arrows f and g correspond to arrows f and g shown in FIG. Water vapor recovered by the purge of the sample gas dehumidifier 11 and the carrier gas dehumidifier 18 is introduced into the evaporation container 292 from the evaporation container inlet 291 together with the sample gas 100. A heater 293 is inserted into the evaporation container 292, and steel wool 294 is installed between the heater 293 and the evaporation container 292. On the other hand, the drain discharge nozzle 295 provided on the evaporation container inlet 291 side of the evaporation container 292 discharges the drain discharged from the mist separator 9 in the form of a mist, wets the steel wool 294, and heats it with the heater 293. Evaporates in the sample gas 100. The evaporated water vapor is discharged from the evaporation container outlet 296 together with the sample gas 100 and is further discharged from the outlet valve 30.

  During operation of the tritium monitor, the switching solenoid valve 19 is closed and the purge solenoid valve 20 is opened, whereby the constant pressure adjusting valve 22 is operated to automatically supply nitrogen gas from the nitrogen gas cylinder 21 to the closed loop 200. Air is replaced by the carrier gas. When the replacement of the nitrogen gas in the closed loop 200 is completed, the switching solenoid valve 19 is opened, the purge solenoid valve 20 is closed, and the operation is started. After the operation is started, the constant pressure adjusting valve 22 is adjusted so that the pressurized carrier gas pressure gauge 23 has a predetermined pressure. Next, the carrier gas pressure reducing valve 24 is adjusted so that the carrier gas pressure gauge 15 has a predetermined pressure. Subsequently, the sample gas pressure reducing valve 12 is adjusted so that the pressurized sample gas pressure gauge 10 has a predetermined pressure. Finally, the instruction of the sample gas flow meter 3 is checked to confirm that the sampling is normally performed. Similarly, the instruction of the carrier gas flow meter 27 is checked to confirm that the carrier gas is normally circulated.

The carrier gas leaked during operation is automatically replenished only by the amount reduced from the nitrogen gas cylinder 21 by the operation of the constant pressure regulating valve 22. It is easy to suppress the leakage amount to 0.1 cm ³ / sec or less with normal piping connection. In contrast to the case where nitrogen gas is supplied without regeneration when the carrier gas flow rate is 3 L / min, the consumption of nitrogen gas when the carrier gas is recycled in the first embodiment can be reduced to 2/100 or less. The 7m ³ (14.7 MPa / cm ³ G) cylinder was changed in 30 hours, but it can be extended to about 2 months.

  As described above, according to the first embodiment, high-purity nitrogen gas is used as the carrier gas, and the water vapor in the sample gas 100 is selectively separated by the water vapor separator 6 and released into the carrier gas. Since the carrier gas containing the released water vapor is introduced into the ionization chamber 16 for measurement and the tritium concentration is measured from the ionization amount, the carrier gas is radon, thoron and its daughter nuclide, and other gaseous radioactive materials. The substance can be essentially blocked from the substance, and the measurement sensitivity can be increased.

  Further, the carrier gas dehumidifier 18 dehumidifies and regenerates the carrier gas, and only the amount reduced by leakage is automatically replenished, so that the consumption of nitrogen gas can be greatly reduced compared to the conventional case. As a result, the replacement frequency of the nitrogen gas cylinder can be reduced from the conventional daily unit to the monthly unit, so that the maintenance work can be greatly saved.

Further, the sample gas 100 dehumidified and dried by the sample gas dehumidifier 11 is diverted, the water vapor dehumidified in the sample gas dehumidifier 11 and the carrier gas dehumidifier 18 is purged, and the water vapor recovered by these purges Is introduced into the evaporator 29 together with the sample gas 100, and the drain is evaporated and returned to the exhaust of the sample gas 100. Therefore, the drain treatment as the radioactive liquid waste and the replacement work of the adsorbent are unnecessary, and the maintenance work Can greatly save labor.
As described above, according to the first embodiment, the consumption of nitrogen gas can be greatly reduced, and the drain process is not required, so that a portable tritium monitor equipped with a small cylinder can be easily realized. .

  Further, the carrier gas filter 26 is provided at the front stage of the compensation ionization chamber 28 and the ion trap 25 is provided at the front stage thereof, and charged dust and charged mist contained in the carrier gas are collected and removed by the electrode, and the carrier gas filter is obtained. 26, the compensation ionization chamber 28 and the measurement ionization chamber 16 do not malfunction due to charged dust, and can be operated stably.

  In addition, a perfluororosulphonic acid resin membrane that is a non-porous ion exchange membrane is used as the hollow fiber membrane 612 of the water vapor separator 6, and the porous fiber membrane 612 of the sample gas dehumidifier 11 and the carrier gas dehumidifier 18 is microporous. By using the polyimide membrane of the membrane, the hollow fiber membrane 612 of the water vapor separator 6, the sample gas dehumidifier 11 and the carrier gas dehumidifier 18 is more selective than the case of using a microporous polyimide membrane. Water vapor can be separated. Further, as the hollow fiber membrane 612 of the carrier gas dehumidifier 18, by connecting in series from the upstream, a perfluorosulfonic acid resin membrane that is a non-porous ion exchange membrane, followed by a polyimide membrane of a microporous membrane, Even if mist is generated by the carrier gas compressor 17, it is absorbed by the perfluoro sulfonic acid resin film having a high water supply capacity, so that the amount of water vapor released from the water vapor separator 6 into the carrier gas can be stabilized by the continuous operation. It is possible to increase the humidity limit for operation to about 50% RH, and the measurement sensitivity can be increased.

Embodiment 2. FIG.
Next, a second embodiment which is a specific example of the invention of claim 8 will be described with reference to the drawings. In the first embodiment, the case where the water vapor separator 6 is connected to the intake side of the sample gas compressor 7 has been described, but in the second embodiment, the water vapor separator 6 is connected to the exhaust side of the mist separator 9. Will be described with reference to FIG. FIG. 6 is a diagram partially showing the configuration of the tritium monitor according to the second embodiment of the present invention. In the figure, the same and corresponding parts are denoted by the same reference numerals. In FIG. 6, symbols h, i, j, k, and m attached to the arrows respectively correspond to the portions with the same symbols in FIG. 1.

  The tritium monitor according to the second embodiment introduces the sample gas 100, which is pressurized by the sample gas compressor 7 and cooled by the radiator 8 and from which the mist is removed by the mist separator 9, into the water vapor separator 6, and is concentrated. The water vapor is separated by the water vapor separator 6 and released into the carrier gas. Since other configurations are the same as those in the first embodiment, description thereof is omitted.

  The water vapor separation efficiency depends on the water vapor density (water vapor pressure) of the sample gas 100. For this reason, in the case of the first embodiment, when the water vapor density in the sample gas 100 becomes low in winter, the amount of water vapor that is separated by the water vapor separator 6 and released into the carrier gas decreases. On the other hand, in the second embodiment, the sample gas 100 is pressurized by the sample gas compressor 7 and the mist is removed by the mist separator 9 and then introduced into the water vapor separator 6. The density can be stably maintained at a high level. For this reason, according to the second embodiment, high-sensitivity measurement is possible even when the water vapor density of the sample gas 100 at the measurement point is low.

  However, if the humidity becomes too high, the leakage current of the ionization chamber increases and the measurement sensitivity deteriorates. For this reason, it is necessary to adjust the carrier gas flow rate so that the inside of the closed loop 200 is in a predetermined humidity range. When the water vapor separator 6 is connected to the intake side of the sample gas compressor 7 as in the first embodiment, it is necessary to finely adjust the carrier gas flow rate. There is an advantage that it is difficult. On the other hand, when the water vapor separator 6 is connected to the exhaust side of the sample gas compressor 7 as in the second embodiment, water is deposited on the water vapor separator 6 so that cleaning maintenance is required, but the water vapor separation efficiency is stable. Therefore, frequent flow rate adjustment is unnecessary, and it is possible to always operate under suitable conditions.

Embodiment 3 FIG.
Next, a third embodiment which is a specific example of the invention of claim 9 will be described with reference to the drawings. In the first embodiment and the second embodiment, a non-porous ion exchange membrane or a microporous membrane is used as the hollow fiber membrane 612 for the water vapor separator 6, the sample gas dehumidifier 11 and the carrier gas dehumidifier 18, Although the water vapor is separated by using the water vapor differential pressure between the membrane surfaces as the driving force, in the third embodiment, the water vapor is separated by using the electric field generated by the DC voltage applied to the electrodes on both surfaces of the solid polymer electrolyte membrane as the driving force. An example will be described with reference to FIGS.

  FIG. 7 is a diagram showing the configuration of the water vapor separator 6a according to Embodiment 3 of the present invention, and FIG. 8 shows the operation of the electric field driven water vapor separation membrane 623 used in the water vapor separator 6a in Embodiment 3. FIG. In FIG. 7, arrows a, b, c, and d attached to the water vapor separator 6a correspond to the inlets and outlets a, b, c, and d of the water vapor separator 6 shown in FIG. Shows the flow. Since the configuration of the tritium monitor in the third embodiment is the same as that of the first embodiment except for the configuration of the water vapor separator 6a, the description will be made with reference to FIG.

  As shown in FIG. 7, the sample gas 100 is introduced into the dehumidification chamber 622 from the dehumidification chamber inlet 621 of the water vapor separator 6a (arrow a), and a part of the water vapor is separated by the electric field driven water vapor separation membrane 623, so that the dehumidification chamber is obtained. It is discharged from the outlet 625 (arrow b). On the other hand, the carrier gas is introduced into the humidification chamber 624 from the humidification chamber inlet 626 (arrow c), and the water vapor released from the electric field driven water vapor separation membrane 623 into the carrier gas is purged and discharged from the humidification chamber outlet 627 (arrow). d).

As shown in FIG. 8, the electric field driven water vapor separation membrane 623 used in the water vapor separator 6a in Embodiment 3 includes a solid polymer electrolyte membrane 6231, an anode 6232, a cathode 6233, and a DC power source 6234. The anode 6232 and the cathode 6233 are porous catalyst electrodes. The water vapor of the sample gas is adsorbed by the anode 6232 and electrolyzed, and the generated oxygen is released as oxygen gas into the humidification chamber 624. Hydrogen ions (H ⁺ ) and tritium ions (T ⁺ ) are accompanied by about two water molecules, and are driven by an electric field by a DC voltage applied between an anode 6232 and a cathode 6233 by a DC power source 6234 to be a solid polymer. The inside of the electrolyte membrane 6231 moves to the cathode 6233 side. At the cathode 6233, hydrogen ions become hydrogen gas, and tritium ions (T ⁺ ) are combined with hydrogen ions (HT) and are discharged from the humidification chamber outlet 627 together with the accompanying water vapor.

  The water vapor and hydrogen gas released into the carrier gas are introduced into the measurement ionization chamber 16, and then pressurized and concentrated by the carrier gas compressor 17, and the water vapor and hydrogen gas are separated by the hollow fiber membrane 612 of the carrier gas dehumidifier 18. Removed. Since the hollow fiber membrane 612 of a microporous polyimide membrane has a property of permeating hydrogen like water vapor, the carrier gas can be recycled.

  According to the third embodiment, by using the electric field driven water vapor separation membrane 623 in the water vapor separator 6a, about 25% is converted into hydrogen gas when the separated water vapor is released into the carrier gas. Therefore, the humidity condition of the carrier gas in the measurement ionization chamber 16 is improved. The humidity limit for stable operation of the ionization chamber in continuous operation is about 50% RH. However, when the electric field driven steam separation membrane 623 is used, the humidity is 62.5% (50% + 50% × 0.25 = 62.5%), the conditions are the same as when the hollow fiber membrane 612 is operated at a humidity of 50%, and therefore it is possible to measure with high sensitivity even at high humidity.

It is a figure which shows the structure of the tritium monitor concerning Embodiment 1 of this invention. It is a figure which shows the structure and structure of the water vapor separator concerning Embodiment 1 of this invention. It is a figure which shows operation | movement of the water vapor | steam separation of the water vapor separator concerning Embodiment 1 of this invention. It is a figure which shows the structure and structure of the heat radiator concerning Embodiment 1 of this invention. It is a figure which shows the structure and structure of the evaporator concerning Embodiment 1 of this invention. It is a figure which shows partially the structure of the tritium monitor concerning Embodiment 2 of this invention. It is a figure which shows the structure of the water vapor separator concerning Embodiment 3 of this invention. It is a figure which shows operation | movement of the electric field drive water vapor separation membrane used for the water vapor separator concerning Embodiment 3 of this invention.

Explanation of symbols

1 Inlet valve, 2 sample gas filter, 3 sample gas flow meter,
4 Sample gas dew point meter, 5 Sample gas pressure gauge, 6, 6a Water vapor separator,
611 Dehumidified gas inlet, 612 hollow fiber membrane, 613 Dehumidified gas outlet,
614 purge gas inlet, 615 outer cylinder, 616 purge gas outlet,
621 Dehumidification chamber inlet, 622 Dehumidification chamber, 623 Electric field driven water vapor separation membrane,
6231 solid polymer electrolyte membrane, 6232 anode, 6233 cathode,
6234 DC power source, 624 humidification chamber, 625 dehumidification chamber outlet, 626 humidification chamber inlet, 627 humidification chamber outlet, 7 sample gas compressor,
8 radiator, 81 finned tube, 82 fan,
9 Mist separator, 10 Pressurized sample gas pressure gauge, 11 Sample gas dehumidifier,
12 sample gas pressure reducing valve, 13 dry sample gas flow meter,
14 carrier gas dew point meter, 15 carrier gas pressure gauge, 16 ionization chamber for measurement,
17 carrier gas compressor, 18 carrier gas dehumidifier, 19 switching solenoid valve,
20 Purge solenoid valve, 21 Nitrogen gas cylinder, 22 Constant pressure adjustment valve,
23 Carrier gas pressure gauge, 24 Carrier gas pressure reducing valve, 25 Ion trap, 26 Carrier gas filter, 27 Carrier gas flow meter, 28 Ionization chamber for compensation,
29 Evaporator, 291 Evaporation container inlet, 292 Evaporation container, 293 Heater,
294 Steel wool, 295 Drain blow nozzle, 296 Evaporator outlet,
30 outlet valve, 31 computing unit, 100 sample gas, 200 closed loop.

Claims (9)

A sampling means having a sample gas compressor for pressurizing the sample gas and continuously sucking the sample gas;
Water vapor separation means for selectively separating water vapor in the sample gas sucked by the sampling means and releasing it into the carrier gas;
Measuring means for measuring the tritium concentration contained in the water vapor released into the carrier gas by the water vapor separating means;
Calculation means for calculating the tritium concentration in the sample gas based on the measurement result by the measurement means,
Sample gas drying means for removing water vapor remaining in the sample gas from which a part of water vapor has been separated by the water vapor separation means,
Drain evaporation means for evaporating the drain generated in the sample gas compressor in the exhaust of the sample gas, and removing the water vapor from the carrier gas containing the water vapor released from the water vapor separation means, thereby regenerating and circulating the carrier gas Comprising carrier gas regeneration means,
The carrier gas regeneration means includes a carrier gas compressor that pressurizes the carrier gas, and a carrier gas dehumidifier that removes water vapor in the carrier gas concentrated by the carrier gas compressor, the water vapor separation means, the measurement means, and The carrier gas regeneration means is connected in a closed loop, circulated in the closed loop while regenerating the carrier gas by the carrier gas regeneration means, and the carrier gas is automatically replenished to the closed loop by the carrier gas replenishment means. Tritium monitor featured. 2. The tritium monitor according to claim 1, wherein the dried sample gas discharged from the sample gas drying means is divided into two, one purges water vapor dehumidified in the sample gas drying means, and the other A tritium monitor characterized by purging water vapor dehumidified in the carrier gas dehumidifier and introducing the water vapor recovered by these purges into the drain evaporation means together with the sample gas. 2. The tritium monitor according to claim 1, wherein the water vapor separation means is a first hollow fiber membrane, the carrier gas dehumidifier is a second hollow fiber membrane, and the sample gas drying means is a third hollow fiber membrane. A tritium monitor comprising a membrane and separating water vapor by these hollow fiber membranes. 4. The tritium monitor according to claim 3, wherein a non-porous ion exchange membrane is used as the first hollow fiber membrane, and a microporous membrane is used as the second hollow fiber membrane and the third hollow fiber membrane. Tritium monitor characterized by using 4. The tritium monitor according to claim 3, wherein the second hollow fiber membrane is connected in series in the order of a non-porous ion exchange membrane and then a microporous membrane from upstream. . 2. The tritium monitor according to claim 1, wherein the calculation means includes: a water vapor density in the sample gas; and an ionization amount A of a carrier gas containing water vapor released from the water vapor separation means measured by the measurement means; The water vapor density in the carrier gas containing the water vapor released from the water vapor separation means and the ionization amount B of the regenerated carrier gas measured by the measurement means are inputted, respectively, and the ionization amount is based on these data. A tritium monitor that compensates for the ionization amount B from A, calculates the tritium concentration in the sample gas by compensating the water vapor separation efficiency based on the ratio of the water vapor density in the sample gas and the water vapor density in the carrier gas . 7. The tritium monitor according to claim 6, wherein a carrier gas filter is provided in the preceding stage of the measuring means for measuring the ionization amount B of the regenerated carrier gas, and an ion trap is provided in the preceding stage. 2. The tritium monitor according to claim 1, wherein the water vapor separation means is disposed on the exhaust side of the sample gas compressor, and the water vapor concentrated by pressurization is separated by the water vapor separation means and released into the carrier gas. A tritium monitor characterized by that. 2. The tritium monitor according to claim 1, wherein as the water vapor separating means, a solid polymer electrolyte membrane, catalyst electrodes provided on both sides of the solid polymer electrolyte membrane, and a voltage is applied to these catalyst electrodes. A tritium monitor using an electric field driven water vapor separation membrane composed of a DC power source.

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