JPH06121915A - Tritium-hydrogen gas separation membrane - Google Patents

Abstract

PURPOSE:To obtain a gas separation membrane with which light hydrogen, heavy hydrogen, and tritium can be separated at one time by blending partially dithiocarbamated polyvinyl chloride with acrylonitrile-butadiene rubber (NBR) and then effecting photobromination in an inhomogeneous system. CONSTITUTION:This gas separation membrane is used for separation and concentration of light hydrogen, heavy hydrogen, and tritium. In this case, the gas separation membrane is obtd. by blending partially dithiocarbamated polyvinyl chloride with acrylonitrile-butadiene rubber (NBR) and effecting photobromination in an inhomogeneous system to give antiradiation property to the membrane. In order to measure the permeation coefft., for example, a measuring device equipped with various instruments such as gas permeation cell 1, gas supply manometer 2, pressure measuring head 3, Pirani gauge 13, and electric pressure sensor 14 is used. Thereby, the obtd. gas separation membrane is used to separate and concentrate light hydrogen, heavy hydrogen and tritium at one time.

Description

Detailed Description of the Invention

The present invention relates to a radiation-resistant separation membrane for separating and concentrating gaseous light hydrogen, deuterium and radioactive tritium (tritium).

[0002]

[Industrial application] The main sources of tritium are nuclear reactors (light water reactors, fast reactors and heavy water reactors) and fusion experiments. On the other hand, the environmental release standard of tritium is determined by law to be the concentration limit in air of 2 × 10 ⁴ Bq / cm ³ (gas) or less, and the release to the external environment is significantly restricted. In order to minimize the release of tritium generated in the fuel reprocessing plant, heavy water reactor, etc., it is necessary to separate tritium from light hydrogen or deuterium. Considering the abundance in the natural world, when deuterium is separated from light hydrogen, the abundance of deuterium is 1.5 × 10 5.
^Although it is low as ^-4 , it is difficult, but in the case of tritium, an abundance of about 10 ^-11 is expected, and therefore separation is more difficult.

As nuclear power generation grows rapidly in the future,
As a result, tritium produced and released by nuclear power generation, especially tritium generated during reprocessing of spent fuel in a power generation reactor, becomes extremely large, and has recently attracted attention as a tritium problem. However, the problems of tritium are more serious in that it is technically difficult to establish an appropriate method for removing tritium, and that there are few concrete methods for controlling tritium contamination at present.

On the other hand, apart from the problem of decontamination, the purpose of the isotope separation of hydrogen, in other words, the use of the separated and concentrated and purified isotope of hydrogen, is roughly two. One is the use of heavy water for nuclear power and the demand for tritium fusion. Others include application to instrumental analysis using heavy water, which is a stable isotope like carbon, oxygen, nitrogen, and sulfur, and in research fields centered on science and engineering and life science using tritium as a radioactive isotope. Demand.

Generally, isotope separation is used when separating stable isotopes from each other and separating radioactive isotopes concerned from other elements. Isotopes are generally difficult to separate to near 100%, and strictly defined are enrichments.

[0006]

2. Description of the Related Art The separation of hydrogen isotopes has a long history, deuterium concentration was industrialized from an early stage, and heavy water and compounds containing a large amount of deuterium are now commercially available and used for various purposes. ing. Demand for heavy hydrogen in heavy water reactors is expected to increase in the future, and the need for recovery of tritium from heavy water reactors and nuclear fuel waste is increasing. In order to realize a fusion reactor in the future, it is essential to establish a technology for recovering tritium.

First, from a general viewpoint of isotope separation,
Isotope separation can be divided into individual separation method and statistical separation method. In the individual separation method, the separation coefficient of a unit stage is ideally close to infinity, and there are an electromagnetic separation method, an optical separation method (laser separation method), and the like. On the other hand, in the statistical separation method, the separation coefficient of the unit stage is extremely poor except when hydrogen is used.
Close to. This method includes a chemical exchange method as a reversible separation method,
There is a fractional distillation method, and the irreversible separation method includes a gas diffusion method, a centrifugal separation method, a thermal diffusion method, a nozzle separation method, a molecular distillation method, an electrolysis method, an electrophoresis method, and the like.

Examples of the deuterium concentration method include a water distillation method, a chemical exchange method (a process in which a water / hydrogen exchange reaction and water electrolysis are combined (CECE)), and a double temperature exchange method. When comparing the economics of these separation processes, the separation factor is one measure, but the problem of energy consumption is also important. To briefly describe the features of these concentration methods,
The electrolysis method (CECE) has a large separation coefficient, but consumes a large amount of energy unless there is a method using hydrogen as a by-product.
The dual temperature exchange method has a relatively low separation factor and consumes a large amount of energy. Moreover, it is necessary to use hydrogen sulfide, which has a bad odor and is highly corrosive. As described above, the conventional method has an advantage that it consumes a large amount of energy as a whole and can be carried out on a large scale, but at the same time has a drawback that the construction cost, that is, the initial capital investment becomes large.

The methods currently considered as the separation method of tritium are 1) water / hydrogen sulfide exchange reaction, 2) water / hydrogen exchange reaction, 3) hydrogen rectification, 4) vacuum distillation of water, and 5) gas. -Solid chromatography, 6) electrolysis, 7) thermal diffusion,
8) solvent extraction, 9) LIS (laser separation method) and the like.

As described above, the separation of tritium, generally speaking, the separation of isotopes is carried out by utilizing a slight difference in the isotope effect. There are roughly three methods that utilize the difference of physical isotopes [3), 4), 5), 7), 8),
9)] and methods utilizing chemical differences [1), 2),
6)]. From a different point of view, they are divided according to the physical properties of isotopes and the difference in reaction mechanism.

[0011]

DISCLOSURE OF THE INVENTION The present invention overcomes the drawbacks of the conventional method, such as high energy consumption, complexity, corrosiveness, and harmfulness, and can be variously changed depending on the scale with a simple device and simple operation. The purpose of the present invention is to provide a gas separation membrane for simultaneous separation and concentration of light hydrogen, deuterium and tritium, which is advantageous for energy-saving, continuous, and industrial implementation. Until now, various methods using physical or chemical isotope effects have been studied and implemented as methods for separating and concentrating deuterium and tritium from light hydrogen. However, unlike the membrane separation method according to the present invention, there was no method capable of simultaneously separating and concentrating light hydrogen, deuterium and tritium. Further, in the membrane separation method of the present invention,
One of the major characteristics is that the concentrated product can be taken out as a pure simple substance gas.

[0012]

Means for Solving the Problems As a result of earnest studies on the material for a gas separation membrane of hydrogen isotope, the present inventor has found that partially dithiocarbamated polyvinyl chloride (PV
If a membrane prepared by blending C) with acrylonitrile-butadiene rubber (NBR) and performing photobromination in a heterogeneous system can be used, it is possible to separate and concentrate light hydrogen, deuterium and tritium gas by a membrane separation method. They have found the present invention and made the present invention.

[0013]

The separation membrane of the present invention is characterized by having the characteristics of a gas separation membrane of hydrogen isotope and being durable against tritium which is a radioactive isotope. This is because the separation membrane of the present invention uses partially dithiocarbamate-converted PVC as a component polymer, and thus has a radiation durability function due to the unstable radical scavenging property of dithiocarbamate. Since the separation membrane of the present invention is basically a polymer alloy composed of PVC resin and NBR rubber, it is a combination of low-priced materials and is therefore economically excellent as a material. In addition, it has excellent melt flowability and therefore excellent moldability. As for the film forming method, not only the solution casting method adopted in the present invention but also the thermal compression method by hot pressing can be applied. In other words, this separation membrane is made of a polymer alloy material having a multi-function excellent in economical efficiency and film forming processability in addition to the function of a hydrogen isotope gas separation membrane having radiation resistance.

[0014]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited thereto.

Example 1 Prior to subjecting an acrylonitrile-butadiene copolymer (NBR) having an acrylonitrile content of 41 wt% to the reaction, purified 1,4-purified 1,4-to remove unreacted monomers and impurities during polymerization. What was once dissolved in dioxane to form a solution was gradually added dropwise to methanol for reprecipitation purification, and subsequently vacuum dried. For film formation, make a dry NBR 1,4-dioxane solution, cast it on a glass plate floated on mercury in a petri dish, cover it with air and let it dry naturally, and finally vacuum. It went dry.

Prior to the reaction, polyvinyl chloride (PVC) was purified by dissolving and reprecipitating it with 1,4-dioxane and methanol, and dried under vacuum. A purified N, N-dimethylformamide (DMF) solution of PVC is prepared, and separately, a DMF solution of sodium N, N-dimethyldithiocarbamate corresponding to ½ mol of this PVC is prepared.
Both solutions were placed in a flask equipped with a thermometer, a reflux condenser and a stirrer, and reacted at 55 ° C for 5 hours. After reaction water
The reaction solution was added dropwise to the methanol mixed solution to precipitate the polymer. This was filtered off, washed and dried to give N, N
-Dimethyldithiocarbamate PVC (PMD).

80% of this PMD and the previously purified NBR
Dissolve in DMF at a ratio of 20 (weight ratio) and mix to give 1
A 0% blended polymer solution was made. This solution was cast on a glass plate, and when drying proceeded to a certain extent, the solution was transferred to a heating vacuum dryer heated to 50 ° C. to continue drying.

The blended film was not peeled off from the glass plate, and 1c below the liquid surface of a petri dish containing saturated bromine water (3.46%).
Hold horizontally at 10 m from the blend film
Immediately, ultraviolet rays were irradiated from a low pressure mercury lamp (615 V, 25 mA) placed at a distance of 1 to start the photobromination reaction. The irradiation time was usually 1 hour. After the reaction, the product was thoroughly washed with water to finally obtain a photobrominated blend film.

The gas permeability of hydrogen and deuterium was measured by the high vacuum method. By measuring the pressure increase of the gas that permeates the membrane from the high pressure side into which a gas of 10 cmHg to 80 cmHg is introduced to the low pressure side held in a high vacuum of 10 ⁻⁵ to 10 ⁻⁶ mmHg, the following formula (1) is obtained. The permeation coefficient (P) of hydrogen and deuterium was determined. The pressure of the permeated gas was measured by a device with a recorder attached to a Baratron vacuum gauge (electrical pressure sensor).

[0020] Here, V is the low-pressure side volume (cm ³ ), T is the room temperature (° C.) at the time of measurement, p is the high-pressure side gas pressure (cmHg), A is the permeable membrane area (cm ² ), and dp / dt is the low-pressure side. Pressure change (m
mHg It was cm ² . The permeation coefficient (permeation rate) was measured three times under the same conditions, and the average value was shown. The film thickness is 1 /
It was measured with a micrometer having an accuracy of 100 mm. The actual film thickness was 62 μm and 85 μm.

A special cell manometer for measuring tritium was used to measure the permeability coefficient of tritium gas. The tritium gas used for the measurement was carrier free.
The gas supplied in the form enclosed in an ampoule tube with a breakable joint was used as the gas. Two isotopes having an isotope abundance ratio of 90% or more and a radioactivity quantity of 1 Ci (37 GBq) were used.

After welding the ampoule tube filled with tritium to the supply side of the upper cell, the photobrominated blend film to be measured is attached to the cell, and the upper cell and the lower cell are fastened and joined with bolts and nuts, The gas supply side and the permeation side are evacuated with a vacuum pump for a long time. After the inside of the system has been sufficiently deaerated under vacuum, the system is closed and the movement of the mercury column of a compact mercury manometer is observed with a 1/100 mm precision reading microscope. There is no leakage or deaeration within the expected measurement time. Make sure that.

When the preparation is completed, the breakable joint is broken to introduce tritium gas into the membrane surface on the supply side, and the measurement of the permeation coefficient is started. The permeation coefficient of tritium was obtained by using the above equation (1) by reading the pressure increase of tritium permeating to the permeation side through the membrane from the temporal change of the height of the mercury column.

Before conducting the measurement experiment of the permeation coefficient of tritium, as a preliminary experiment, light hydrogen having the same pressure as tritium was introduced into the same special cell manometer to measure the permeation coefficient of hydrogen, and the apparatus of the special cell manometer was measured. Was calibrated.

In this experiment, in order to prevent radiation contamination and ensure safety, the entire special selmanometer was put in an airtight glove box made of an acrylic plate, and even if tritium gas leaks, the contamination will spread further. The experiment was carried out by taking measures to prevent this.

With the separation membrane of the present invention, light hydrogen (H 2
₂ ), the permeation coefficient of deuterium (D ₂ ) and tritium (T ₂ ) was measured, and the results shown in Table 1 were obtained. Further, the ideal separation coefficient was determined from the value of the transmission coefficient and is shown in Table 1. The unit of the transmission coefficient used here is cc (STP) cm / c.
It is m ² · sec · cmHg.

Table 2 shows the separation membrane of the present invention at ⁶⁰ C.
The gas generation amount obtained by irradiating γ-rays from o with 6.5 Mrad (65 KGy) was measured, and the experimental results are shown.

[0028]

As shown in Table 1, obtained from the results of the permeation coefficient of light hydrogen, deuterium and tritium obtained at room temperature by the photobrominated blend separation membrane of the present invention and the value of the permeation coefficient. From the ideal separation factor of the transmission coefficient c. g.
s. The unit is 10 ^−9, which is sufficiently large and the ideal separation coefficient between deuterium and tritium with respect to light hydrogen obviously differs by a factor of 1/1000. Therefore, the gas separation method using the separation membrane of the present invention is performed. By doing, deuterium and tritium can be separated and concentrated.

From the experimental results of the gas generation amount shown in Table 2, as compared with PVC which is a component material of the blend, the generated amount of decomposed gas of the blend film of the present invention is remarkably small and the radiation resistance is clearly high. It is shown. That is,
A feature of the separation membrane of the present invention is that it can sufficiently withstand a long-term tritium treatment.

[Brief description of drawings]

FIG. 1 shows an example of a measuring device used for measuring a transmission coefficient in the present invention.

[Explanation of symbols]

 1 ... Gas permeation cell 2 ... Gas supply manometer 3 ... Pressure measuring head 4 ... Constant temperature water tank 5 ... Sensitive relay 6 ... Diffusion pump 7 ... Oil rotary pump 8 ... Cold trap 9 ... Macleod gauge 10 ... Gas reservoir 11 ... Glass cock 12 ... Spare gas reservoir 13… Pirani gauge 14… Paratron pressure gauge

Claims (1)

[Claims] 1. A partially dithiocarbamate-modified polyvinyl chloride is added to an acrylonitrile-butadiene rubber (NB
Radiation resistant tritium, deuterium and hydrogen gas separation membranes blended with R) and photobrominated in a heterogeneous system.