JPS61191978A - Measurement for concentration of tritium in gaseous phase - Google Patents

Abstract

PURPOSE:To enable highly accurate measurement, by selectively separating tritium and hydrogen from a sample while water type tritium condensable at the normal temperature is converted into a chemical form of hydrogen molecule non-condensable at the normal temperature followed by introducing into a radiation detector. CONSTITUTION:A gas sample containing tritium of various chemical forms is passed through a reactor 1 to convert tritium and hydrogen contained in the sample into chemical forms of water (H2O, HTO and T2O) to be introduced into an electrolytic cell 2. Then, the water (H2O, HTO and T2O) in the gas sample introduced into a cell 2 is electrolyzed selectively with an anode to form an oxygen atom (O2) and hidrogen ion (H<+> or T<+>) and the oxygen atom is exhausted together with other components in the gas sample. The hydrogen ion is moved to an cathode through a solid electrolyte to form an hydrogen atom (H2, HT or T2) continuously and selectively with the cathode. The hydrogen atom containing tritium generated on the cathode side is introduced to a radiation detector 4 through a hydrogen flowmeter 3 to detect the concentration of tritium.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a method for measuring the concentration of tritium contained in a gas sample. Because it is a nuclide with a long half-life even if its concentration is low, it is necessary to measure and monitor it at extremely low concentrations to protect against environmental pollution. Furthermore, tritium
Because it is a radioactive isotope of hydrogen, which is one of the basic constituent elements of organic compounds that make up living organisms, it is an important measurement target for medical, biological applications, and nuclear safety. In general, it is desirable for tritium measurement methods to have high sensitivity, no contamination of the detection part, good stability, and the possibility of continuous measurement0 [Prior art and its problems] Number of radioactive substances Tritium (T) is usually found in water-type tritium (HTO) in the exhaust gas from facilities that handle water or in the environment.
,T2O) Although it is possible to measure, (1)
Detection sensitivity is insufficient Q (2) Background increases due to adsorption and occlusion of water-type tritium (HTO, T2O), etc. to the detection part.

(3) Corrosion and contaminants (e.g. HCl) to the detection part.

There are also drawbacks such as a decrease in stability due to the contamination of SOx (...).In addition, there is also a method of measuring the tritium concentration using a liquid scintillator after condensing and collecting the tritium water contained in the gas sample. Yes, the detection sensitivity is high, but (1) a condensation process is required, making continuous measurement difficult.

(2) The measurement operation is complicated (3) There are disadvantages such as the fact that radioactive waste containing tritium remains.

Furthermore, as another measurement method, tritium water is condensed and collected, and then electrolyzed using an electrolytic cell made of a proton-conductive polymer electrolyte membrane, resulting in hydrogen molecules (H2, HT).
, T2) There is a method to detect the tritium concentration in
Although it is possible to reduce the background of the detection part and remove corrosion and contaminants, it has drawbacks such as the difficulty of continuous measurement because it requires a condensation process.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a highly sensitive and stable method for continuously measuring tritium concentration without contaminating the detection section.

[Key points of the invention]

The present invention involves converting tritium in a gaseous sample, which is contained in various chemical forms, into the chemical form of water (H2O, HTO, T2O), and then continuously converting the tritium in a gaseous state in an electrolytic cell made of a proton-conducting solid electrolyte. And try to measure the tritium concentration in the gas sample by selectively electrolyzing and converting it into the chemical form of hydrogen molecules (Hz, HT, T2) and then guiding it to a radiation detector to detect tritium. 0 However, the present invention involves the following steps: (1) converting tritium (T) into water (HTO, 'r2o);
Hydrogen molecules (HT, T2) or hydrocarbons (CH3T...
Tritium (T) in samples containing various chemical forms such as
) and hydrogen (H) once in the gas phase with water (H2O.

a first step of converting into the chemical form HTO,'r,o);
(2))! A second step in which water containing lithium is continuously supplied in a vapor state from the anode side to the solid electrolyte of an electrolytic cell made of a proton-conductive solid electrolyte with electrodes bonded to both sides, (3) electrodes; A voltage is applied between them, and hydrogen molecules (
(4) a fourth step of continuously guiding the generated tritium-containing hydrogen molecules to a radiation detector to measure the tritium concentration. In the present invention, citritium (T) and hydrogen (H) are selectively separated from a sample, and water-type tritium, which condenses at room temperature, is separated from hydrogen molecules, which do not condense at room temperature. Since it is continuously introduced into the radiation detector after being converted into a chemical form, a concentration effect is also obtained, and the drawbacks of the prior art as described above can be eliminated. [Detailed Description of the Invention] Below, A specific example of the measuring method of the present invention will be described with reference to the drawings.

Example 1 FIG. 1 is a schematic diagram of a specific example of an apparatus used for carrying out the measuring method of the present invention. In order to carry out the measuring method of the present invention with such an apparatus, first, tritium is Tritium (T) and hydrogen (I All water (H2O, HTO
, T2O) and then introduced into the electrolytic cell 2. The electrolytic cell 2 is made of sinate glass such as P2O5-BaO or 8rCel-x Mx 0a-a (x=0.
05~0.1; M=Yb, Sc, Y, Mg
A solid electrolyte 21 having proton conductivity such as a perovskite-type oxide with a composition and an outer tube such as an alumina tube or a quartz tube have a double structure. are joined. The electrolytic cell 2 is heated by a heater (not shown).

Also, the platinum electrode n is kept at a constant temperature in the range of °C.
Water (H 2 O
, HTO, T2O) are selectively electrolyzed at the anode as shown in reaction formula 1, and oxygen molecules (02) and hydrogen ions (H"IT") are generated. H2O (HTO,
T2O) → 2H"CT+) 20g+2e...
・■ The oxygen molecules generated here are absorbed by other components in the gas sample (e.g. nitrogen, corrosion/contaminants (HC4SOx...), etc.)
The zero hydrogen ions (H+, T+) that are exhausted along with the reaction move to the cathode side in the solid electrolyte, and hydrogen molecules (H2, HT, T2) are continuously and selectively generated at the cathode as shown in reaction formula (■). .

2H+(T+)+2e-+H2(HT, T2)...
......■Hydrogen molecules containing tritium generated on the cathode side are guided to the radiation detector 4 through the hydrogen flow meter 3, and the tritium concentration is detected. The tritium concentration in the sample can be determined by multiplying the detected value by the value obtained by the hydrogen flowmeter 3.Also, the same effect can be obtained by flowing the gas sample outside the proton conductive solid electrolyte tube. Of course, this can be obtained.

Example 2 FIG. 2 is a modification of the electrolytic cell used in Example 1, in which a test tube type solid electrolyte with one end closed is used.

In Fig. 2, 31 is a sample introduction tube made of alumina or quartz provided in the solid electrolyte 21, 32 is an outer cylinder made of alumina, etc., and the electrolytic cell is heated to a constant temperature within the range of 500 to 1000°C using a heater. keep it. A is a backing made of graphite or the like 0 When the reactor 1 shown in FIG. Here, if a constant voltage is applied so that the inside of the solid electrolyte 21 is positive (anode) and the outside is negative (cathode), water (H2O, HTO) in the gas sample will be absorbed while rising inside the solid electrolyte tube.

T2O) is electrolyzed, and oxygen (0□) is continuously and selectively generated on the anode side and hydrogen molecules (H2, HT, T2) on the cathode side. Oxygen generated on the anode side is exhausted together with unelectrolyzed components in the gas sample. A constant flow rate of carrier gas (for example, nitrogen, argon, etc.) is allowed to flow inside the outer cylinder 32, and hydrogen molecules containing tritium generated on the cathode side are guided to a radiation detector to detect tritium and detect the presence of tritium in the gas sample. Measure tritium concentration.

By using such an electrolytic cell, it is possible to preheat the gas sample before electrolysis, thus increasing the flow rate of the gas sample and electrolyzing a large amount of water in the gas sample in a short period of time. be able to. Moreover, it becomes possible to downsize the device.

Example 3 FIG. 3 shows a unit electrolytic cell of a laminated electrolytic cell, which is another modification of the electrolytic cell used in Example 1 and uses a plate-shaped solid electrolyte.

In Figure 3, A is an air-permeable current collector that electrically connects the DC power source and the platinum electrode and allows gas to pass through.The measurement method of the present invention is carried out using such an electrolytic cell. In order to do this, the unit electrolytic cells shown in Fig. 3 are constructed to have a multilayer structure, and a gas sample containing water-type tritium that has passed through the reactor 1 shown in Fig. 1 is continuously applied to the anode side of each unit electrolytic cell. A carrier gas (for example, nitrogen, argon, etc.) is flowed on the cathode side. Next, the tritium concentration is measured in the same manner as in Example 1.

By using this electrolytic cell, the flow rate of the gas sample can be increased, a large amount of water in the gas sample can be electrolyzed in a short time, and the apparatus can be made smaller.

〔Effect of the invention〕

According to the present invention, tritium contained in a gaseous sample in various chemical forms is once converted into the chemical form of water (H2O, HTO, T2O), and then remains in a gas phase in an electrolytic cell made of a proton-conducting solid electrolyte. to continuously and selectively electrolyze hydrogen molecules (H2, HT).

After converting to the chemical form of citritium (T2), it is introduced into a radiation detector to detect tritium and measure the tritium concentration.
) and hydrogen (H:) can be selectively separated, and water-type tritium, which condenses at room temperature, can be converted into the chemical form of hydrogen molecules, which does not condense at room temperature, and can be continuously introduced into the radiation detector.

For this reason, (i) No condensation step is required.

(11) Preventing background increase due to adsorption of water-type tritium onto radiation detectors.

(iii) Corrosion and contaminants can be removed before the radiation detector.

Gv) 0 which is stable because it uses a solid electrolyte
(■) It is possible to concentrate tritium, which results in the following effects: (1) Continuous measurement is possible (2) Background is reduced (3) Stability is improved (4) Detection sensitivity is improved 0

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a specific example of an apparatus used for carrying out the measurement method of the present invention. FIGS.
0 1... Reactor, 2... Electrolytic cell, 3... Radiation detector, 21... Solid electrolyte, n...・Platinum electrode banquet 1 so

Claims (1)

[Claims] 1) A method for measuring tritium concentration in a gas phase, which comprises the following steps. (1) Tritium (T) and hydrogen molecules (HT, T_2),
Water (HTO, T_2O) or hydrocarbons (CH_3T, ・
Tritium (T
) and hydrogen (H) to water (H_2O, HTO, T_2O)
(2) A gaseous sample containing tritium (T) in the chemical form of water (H_2O, HTO, T_2O) is electrolyzed using a proton-conductive solid electrolyte with electrodes bonded to both sides. The second step is to supply water to the electrolyte from the anode side of the cell.
_2), and (4) hydrogen molecules containing tritium (T) generated on the cathode side (H_2, HT,
A fourth step of introducing T_2) into a radiation detector and measuring the tritium concentration. 2) In the measurement method described in claim 1, hydrogen molecules (H_2) containing tritium (T) generated on the cathode side
, HT, T_2) into a detector together with an inert carrier gas.