JPH03213127A - Method for separating isotope and heat diffusion tower therefor - Google Patents

Abstract

PURPOSE:To enhance the separation efficiency of an isotope by a method wherein the gas containing the isotope is allowed to flow between a cold wall and a warm wall to separate the isotope and, at this time, heat is applied to the warm wall to heat the same to room temp. or higher while the cold wall is cooled to room temp. or lower using a cryogen. CONSTITUTION:A reaction container 1 long in a vertical direction capable of receiving gas in a gastight state is formed from a material (e.g.; quartz glass) capable of withstanding low temp. A resistance heater 2 composed of a tungsten wire is vertically arranged at the central part of the reaction container 1 and an outer wall 3 forming a cryogen passage is provided so as to surround the reaction container 1 and a cryogen (e.g.; liquid nitrogen) is supplied to the cryogen passage from a cryogen source 8. Heat is applied to the heater 2 to heat the same to room temp. or higher and the wall of the container 1 is cooled to room temp. or less using the cryogen. Subsequently, for example, gas containing an isotope such as hydrogen containing tritium is allowed to flow to the container 1 from a treating gas access port 14 and the hydrogen gas wherein tritium is concentrated is stored in the lower part of the container 1 to be recovered.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the separation of isotopes such as tritium in hydrogen;
In particular, isotope separation using hot and cold walls arranged opposite each other (
Concentration method) and a thermal diffusion column for carrying out the method.

[Prior Art] Gas molecules (including atoms) are in thermal motion at a certain temperature. The kinetic energy Ek is Ek=(1/2) m
It can be expressed as v 2. Here, m is the mass of the molecule, and ■ is the speed of the molecule. In the case of hydrogen gas containing tritium (T), the mass m1 of the hydrogen molecule H2 is approximately 2, whereas the mass m2 of the molecule HT consisting of tritium and hydrogen is approximately 4 <
1+3=4).

Therefore, the average speed of thermal motion of H2 molecules and HT molecules at the same temperature is significantly different. Also, as the temperature changes, the average speed also changes. Therefore, when a temperature gradient is formed, gas molecules with different masses will have different distributions.

Using this phenomenon, it is possible to separate isotopes ([WI).

The isotopic content mentioned above! A thermal diffusion tower is a device that performs 4i.

A long, slender tower is erected vertically in a gravitational field, and a hot wire is placed in the center of the tower to heat it to a high temperature, while the tower wall is water-cooled to maintain a temperature around room temperature.In this way, a temperature gradient is created in the radial direction. This causes thermal diffusion and convection of gas molecules. Due to thermal diffusion under a radial temperature gradient, compared to the distribution of H2, a light molecule, HT, a heavy molecule, is depleted in high temperature areas and becomes below the average concentration, and concentrated in low temperature areas, reducing the average concentration. That's all. That is, the concentration of HT is low in the center of the tower, and the concentration of HT is high near the tower wall. High-temperature gas in the center of the tower moves upwards, and relatively low-temperature gas near the tower walls moves downwards through convection. Therefore, if the gas is collected from below, a gas with a high concentration of HT will be obtained, and the gas collected from above will contain HT.
concentration is low.

[Problems to be Solved by the Invention] Improving the efficiency of isotope separation is expected in isotope separation technology that utilizes a temperature gradient.

An object of the present invention is to provide an isotope separation method with improved isotope separation efficiency.

Another object of the present invention is to provide a thermal diffusion column that can improve isotope separation efficiency.

[Means for Solving the Problems] Conventionally, hot wires were used to form a temperature gradient, and in order to prevent the temperature of the outer wall from rising, water cooling was performed to maintain it at around room temperature.

In the present invention, the hot wall is heated to a high temperature above normal temperature, and the cold wall is cooled to below normal temperature using a cryogen.

A resistance heating element is placed in the center of the thermal diffusion tower, surrounded by a reaction vessel, a cryogen passage is formed outside the reaction vessel, and a cryogen is supplied from a cryogen source to the cryogen passage.6 [Function] Conventional The temperature gradient in the thermal diffusion column was created by heating.

By forming a temperature gradient by both heating and cooling, a temperature gradient with a large temperature difference and a low temperature can be formed. The temperature difference enters the molecules. Therefore, as the temperature of the cold wall decreases, the effect increases significantly even with the same temperature difference.

[Example] FIG. 1 shows a thermal diffusion tower according to an embodiment of the present invention.

The thermal diffusion column has a dark blue long reaction vessel 1 arranged in a vertical manner. For example, reaction vessel 1 has a diameter of approximately 1.5 CI
0 reaction vessel 1 having dimensions of 150 CI in length is made of hard glass, quartz glass, stainless steel,! ! A hot wire is arranged along the solid axis of the zero reaction vessel 1, which is an airtight tubular vessel made of a material such as oxygen steel. This hot wire is electrically connected to an upper electrode 4 and a lower electrode 5 provided on the earthen wall and the lower wall of the reaction vessel 1. In addition, the heat fIi
A weight 6 is attached to the lower end of p! Even when %R2 undergoes thermal expansion, the hot wire 2 is maintained in a stretched state. Further, a spring 7 such as a copper coil is provided under the weight 6 to absorb the shrinkage caused by the thermal expansion and contraction of the hot wire 2. Thermal fi2 is a wire made of tungsten, platinum, nichrome, etc. with a resistor, and has a resistance of 1000
It is designed to be heated above ℃. The wire has dimensions of, for example, a radius of 150 μm.

In addition, in order to arrange the hot wire 2 in the center of the reaction vessel 1,
A spacer 12 is provided along the entire length of the hot wire 2 to keep the distance between the wall of the reaction vessel I and the hot wire 2 equal. This spacer 12 is designed, for example, in the shape of a cross so as not to obstruct the flow of gas within the reaction vessel 1.

In addition, an insulating material is used at the connection between the hot wire 2 and the reaction vessel 1.
Even if the reaction vessel 1 is made of metal, the cryogen jacket 3 is made of the same material as the reaction vessel 1 and is electrically isolated from the hot wire 2. A jacket is formed between the outer wall of No. 1 and the outer wall of No. 1 to accommodate the cryogen. As the cryogen, a liquid or gas that operates at 0° C. or lower, such as liquid nitrogen, liquid air, or Freon, is used.

A cryogen inlet 9 is provided at the lower end of the cryogen jacket 3 and is connected to a cryogen source 8. Also.

A cryogen outlet 10 is provided at the upper end of the cryogen jacket 3, forming an outlet for the cryogen heated by the outer wall of the reaction vessel 1. Further, if necessary, the cryogen outlet 10 is connected to the cryogen source 8 by a cryogen circulation path 16 to circulate and reuse the cryogen.

The reaction vessel 1 is provided with a processing gas inlet/outlet 14,
A processing gas such as hydrogen containing tritium is supplied and recovered into the reaction vessel 1 through the processing gas inlet/outlet 14 .

The case where tritium-containing hydrogen gas is separated using the thermal diffusion column according to this embodiment will be described below.

A desired current is passed through the hot wire 2 through the upper electrode 4 and the lower electrode 5, and the hot wire 2 is heated to a temperature of 1000° C. or higher. In addition, liquid nitrogen is pumped from the liquid nitrogen tank 8 to fill the inside of the cryogen jacket 3 with liquid nitrogen. After the inside of the reaction vessel 1 is evacuated, hydrogen gas containing tritium is pumped into the reaction vessel 1 via a pressurizing device. The tritium-containing hydrogen gas filled in the reaction vessel 1 is diffused and separated in the radial direction due to the temperature gradient between the hot wire and the outer wall of the reaction vessel 1. Hydrogen gas with less tritium is separated near the outer wall, and hydrogen gas with more tritium is separated near the outer wall. These separated gases move up and down depending on their specific gravity depending on their thermal expansion, so hydrogen gas with less tritium accumulates in the upper part of the reaction vessel 1, and hydrogen gas enriched with tritium accumulates in the lower part of the reaction vessel 1. Accumulate. By recovering the gas accumulated at the bottom, tritium-enriched hydrogen gas can be recovered.

By diffusing and separating the recovered tritium-enriched hydrogen gas again, the tritium concentration in the hydrogen gas can be gradually concentrated.

Here, the maximum separation coefficient (αβ) 1 maX obtained by total reflux operation of the thermal diffusion column is expressed by the following formula.

Here, the temperature of the hot wire is Th, and the temperature of the outer wall of the reaction vessel is T.
When C, ΔT=Th −Tc δ==rh/re.

rh: heat [radius of 2 rC: radius of reaction vessel 1 α■: Thermal diffusion factor (Z)=Z/rc is the bistandardized tower height.

That is, the separation coefficient αβ is exponentially dependent on ΔT/Tc. Here, if Tc is at room temperature, Tc is about 300°, and if Tc is the liquid nitrogen temperature (77°K), Tc is about 1/4 of room temperature.

FIG. 2 shows the separation coefficient with respect to gas pressure when the cold wall temperature 'rC is 77.35'' K and the temperature difference is 1000°. A maximum value of 885 is obtained as the zero separation coefficient αβ.

FIG. 3(C) shows the separation coefficient according to the conventional technology for comparison, under the same conditions except that the cold wall temperature Tc is 288.15°C. The maximum separation coefficient at this time is 63.4. In other words, in the case of this example, the separation coefficient is improved by more than one order of magnitude.If an attempt is made to achieve the same effect while keeping the temperature of the outer wall of the reaction vessel 1 at room temperature, in the above-mentioned simplified approximation, the temperature A difference ΔT=2430°K is required.

Achieving such high temperatures requires extremely limited hot wire materials and various measures for power supply, safety measures, etc. Furthermore, in practice, even if such a low temperature is used, the effect expected from a simple approximation cannot be obtained, because the value of α becomes small in the low temperature range, and αβ is used instead of the temperature of the cold wall. This is because the average temperature of the hot wall and cold wall is related, and if the temperature of the hot wall increases, the portion represented by the temperature of the cold wall in the equation also increases.

In addition, when the temperature of the outer wall is cooled using the refrigerant at the optimum pressure of the heat diffusion tower, the lower pressure becomes the optimum pressure, whereas if a temperature difference is created by increasing the temperature of the hot wall, fi31m ! The pressure is also high, and high structural strength is required.

As explained above, by heating the hot wall to a high temperature and cooling the cold wall to a low temperature, a remarkable effect that could not be obtained with the conventional technology of heating the hot wall to a high temperature while keeping the cold wall near room temperature can be achieved. can get.

Although the present invention has been described above in accordance with the examples, the present invention is not limited to these examples. For example, various modifications,
It will be obvious to those skilled in the art that improvements, combinations, etc. are possible.

[Effects of the Invention] As described above, according to the present invention, the separation coefficient can be significantly increased by employing a low temperature cooled by a refrigerant rather than room temperature as the low temperature side temperature forming the temperature gradient.

Further, it becomes easy to safely operate the thermal diffusion tower while achieving a high separation coefficient.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view schematically showing a thermal diffusion column according to an embodiment of the present invention, Fig. 2 is a graph showing an example of a separation coefficient according to an embodiment, and Fig. 3 is an example of a separation coefficient according to a conventional technique. This is a graph showing. In the figure: 1 Reaction vessel 2 Heat wire 3 Cryogen reservoir 4 Upper electrode 5 Lower electrode 0 2 4 6 Weight Spring Cryogen source Cryogen Population Cold Release Sun Spacer Processing Gas Inlet/Outlet Cryogen Circulation Router

Claims (2)

[Claims] (1) In the method of separating isotopes by flowing a gas containing isotopes between a cold wall and a hot wall, the hot wall is heated to above room temperature, and the cold wall is cooled to below room temperature using a cryogen. A gas separation method characterized by cooling. (2) a vertically long reaction vessel made of a material that can withstand low temperatures and capable of airtightly containing gas; a resistance heating element vertically disposed in the center of the reaction vessel; A thermal diffusion tower having: an outer wall surrounding a reaction vessel to form a cryogen passage; and a cryogen source supplying cryogen to the cryogen passage.