JPH0546243B2 - - Google Patents

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to an isotope separation device using a laser method, and particularly improves the utilization rate of metal vapor as a raw material and improves the separation and recovery efficiency of isotopes. The present invention relates to an isotope separation device designed to improve

(Prior art) In general, isotope separation devices using a laser method are used to extract metal raw materials containing multiple types of isotopes, such as
Uranium with mass number 235 (U-235), uranium with mass number 238 (U
The uranium metal raw material containing U-238) is heated to melt and evaporate, and the resulting metal vapor stream is irradiated with laser light to selectively cationize specific isotopes, such as U-235, in the vapor stream. It is configured to separate and collect ionized isotopes by applying an electric field to them.

Conventionally, this type of isotope separation apparatus is constructed as shown in FIGS. 6 and 7. That is, an evaporation crucible 2 containing a metal raw material 1 is installed at the inner bottom of a closed space maintained in a substantially vacuum state.

Evaporation crucible 2 has excellent thermochemical resistance,
A metal raw material 1 such as a uranium metal raw material containing a plurality of types of isotopes is housed inside. This metal raw material 1 is irradiated with an electron beam 4 emitted from an electron gun 3 and bent by a deflection magnetic field. Metal raw material 1
is heated to melt and evaporate, forming a vapor stream 5.

This steam flow 5 is sealed in a steam enclosure (not shown), and a product recovery electrode 6 is disposed above the flow of the steam flow 5.

The product recovery electrode 6 connects a plurality of positive electrodes 7 to which a positive potential is applied and a plurality of negative electrodes 8 to which a negative potential relatively lower than the potential of the positive electrodes 7 is applied.
They are constructed by facing each other substantially parallel to the flow direction and alternately arranged at required intervals. A photoreactive portion 9 is formed between each positive electrode 7 and each negative electrode 8, and each photoreactive portion 9 is provided in a direction perpendicular to the flow of the vapor flow 5 (perpendicular to the plane of paper in FIG. 7). The laser beam 10 is irradiated on each. At this time, only a specific isotope, such as U-235, in the vapor stream 5 is selectively excited and ionized to become a positive ion. The specific isotope that has become a cation is attracted toward the negative electrode 8 and separated and recovered.

On the other hand, the vapor flow containing isotopes that were not ionized by the laser beam 10 irradiation, such as U-238 and neutral metal atoms, travels straight through the electrode section without being affected by the electric field of the product recovery electrode 6. A circular arc-shaped waste collection plate 1 is disposed above the product collection electrode 6.
1 will be collected.

(Problem to be Solved by the Invention) However, in conventional isotope separation devices, the proportion of isotope atoms that participate in photoreaction with laser light among the specific isotope atoms contained in the generated vapor flow is 40. Since it is as low as ~50%, there is a problem that the isotope separation and recovery efficiency is also relatively low based on the utilization rate of the metal vapor that is the raw material. The rate at which the isotope atoms are excited and ionized varies depending on the energy level of the atoms at the operating temperature and the wavelength of the irradiated laser light, and the rate at which the isotope atoms participate in the photoreaction also changes.

Here, the process of selectively exciting and further ionizing a specific isotope in the conventional laser method will be explained with reference to FIG.

First, the isotope atom A ₀ at the ground level E ₀ is irradiated with the selective excitation laser beam 10a to raise the selective excitation level E _lb
Then, the selective excitation laser beam 10c set to a wavelength tuned to the intermediate excitation level E ₂ is irradiated to selectively excite the intermediate excitation level E ₂ , and then the transition to the ionization level E _i In order to do this, an ionizing laser beam 10d is irradiated. After the isotope atom A ₀ is selectively excited through the above three-step process,
Ionized and ionized. The laser beam 10 shown in FIGS. 6 and 7 is a combination of the selective excitation laser beam 10a, the intermediate excitation laser beam 10c, and the ionizing laser beam 10d.

Here, the occupancy P of atoms having energy level E at a certain operating temperature T is given by equation (1), where J is the composite spin of the atoms and k is Boltzmann's constant.

P∝(2J+1)e ^-E/kT ……(1) Therefore, if the temperature T of the vapor flow is 2400〓, the occupancy rate P ₀ of atoms at the ground level E ₀ where photoreactions are likely to occur is It is given by equation (2).

P ₀ = (2J+1)e ^-E ₀ ^/kT / (2J+1)e ^-Ei/kT ≒0.45...
(2) Here, 〓 ⁱ (2J+1)e ^-Ei/kT is the sum of the occupancy rates P _i of atoms at each energy level.

From equation (2), if the temperature is maintained at a high temperature of 2400㎓, only 45% of the specific isotope atoms contained in the vapor flow will participate in the photoreaction. Prove.

On the other hand, when the operating temperature T is 2400㎜, the isotope atoms are partially thermally excited to the metastable level E ₀ ^* , which has a higher energy level than the ground level E ₀ , or to its upper level. The occupancy rate P ₀ ^* of the isotope atom A ₀ ^* in this metastable level E ₀ ^* can be calculated in the same way as equation (2).
Equation (3) is obtained.

P ₀ ^* = 0.27 ……(3) In other words, a little less than 30% of the isotope atoms A ₀ ^* are collected in the waste collection plate without participating in the photoreaction, which reduces the separation and collection efficiency of product isotopes. That will happen.

As a countermeasure against this, it is also possible to separately equip a laser beam oscillation device that irradiates the selective excitation laser beam 10b to excite the isotope atom A ₀ ^* in the metastable level E ₀ ^* to the selective excitation level E _1b . Although this is being considered, it has the drawbacks of high equipment costs and complicated operation management.

Further, since conventional isotope separation apparatuses are operated under high temperature conditions, the generated vapor flow contains impurity ions and high-speed thermoelectrons generated by atomic collisions, thermal ionization, and the like. These impurity ions accompany the isotope ionized by the photoreaction and mix into the collection electrode, while thermionic electrons electrically neutralize the cationized isotope, making separation by an electric field impossible. As a result, the separation coefficient of the isotope to be recovered is reduced, causing a reduction in the purity and quality of the product.

The present invention was made in order to solve the above problems, and it initiates a photoreaction by deexciting the isotope atoms in the metastable level contained in the vapor flow to the ground level. To provide an isotope separation device that improves isotope separation and recovery efficiency by increasing the number of isotope atoms that are easy to separate, and that can obtain products of excellent quality by eliminating impurity ions mixed in a product recovery electrode. The purpose is to

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a steam generation device that generates a steam flow by heating and evaporating a metal raw material containing multiple types of isotopes, and a steam generator that generates a steam flow in parallel to the flow direction of the steam flow. A product recovery electrode formed by alternately arranging electrodes and negative electrodes, and a laser that selectively cationizes specific isotopes contained in the vapor flow by irradiating the vapor flow introduced into the product recovery electrode with laser light. Equipped with an optical oscillation device,
In an isotope separation device that applies a voltage between the product recovery electrodes to deflect a specific isotope that has been positively ionized toward the negative electrode to separate and recover it,
A de-excitation filter is disposed between the steam generation device and the product recovery electrode to transfer isotope atoms in the metastable level contained in the generated steam flow to the ground level and de-excite them. do.

(Function) According to the isotope separation device of the present invention, a deexcitation filter is disposed between the steam generation device and the product recovery electrode, and the deexcitation filter and the metastable substances contained in the vapor flow are connected to each other. Collisions with the isotope atoms at this position relax the vapor temperature, and the isotope atoms are de-excited to the ground level. The de-excited isotope atoms are ionized by being irradiated with laser beams for selective excitation, intermediate excitation, and ionization in stages, and are subjected to separation and recovery operations.

Therefore, the isotope atoms that were in the metastable level are transferred to the ground level where they are easily ionized by photoreaction, and the number of isotope atoms in the vapor flow that is the target of separation and recovery operations is significantly increased. It becomes possible to
As the utilization rate of metal vapor increases, the efficiency of isotope separation and recovery improves.

On the other hand, the impurity cations and thermionic electrons contained in the initial steam flow generated from the steam generator are recombined in the process of repeated collisions with the filter elements of the deexcitation filter, and the charge of the impurity cations is reduced by the thermionic electrons. electrically neutralized. Therefore, the content of impurity ions in the vapor flow introduced into the product recovery electrode becomes extremely low, and impurity ions are prevented from being adsorbed by the product recovery electrode. Therefore, the efficiency of isotope separation for the purpose of recovery is improved, and a product with excellent purity and quality can be obtained.

(Example) Next, regarding an example of the present invention, taking as an example the separation operation of uranium isotopes in the uranium enrichment process,
This will be explained with reference to the attached drawings.

FIGS. 1 and 2 are a perspective view and a sectional view showing an embodiment of an isotope separation apparatus according to the present invention. Note that the same reference numerals are given to the same components as those of the conventional example shown in FIGS. 6 and 7.

1 and 2, the isotope separation apparatus includes an evaporation crucible 2 containing a metal raw material 1 containing a plurality of uranium isotopes, and an electron beam 4 emitted from an electron gun 3 onto the metal raw material 1 contained therein. It has a steam generation device 12 that heats and evaporates the metal raw material 1 by irradiating it with water to generate a steam flow 5.

A deexcitation filter 13 is provided above the steam generator 12 . The deexcitation filter 13 is, for example, a mesh filter element 15 formed by weaving fine wires 14 of high melting point metal in the vertical and horizontal directions, as shown in FIG.
As shown in FIG. 2, these are stacked in multiple stages and housed in a housing frame 16.

Moreover, the mesh 14a of the mesh filter element 15
The opening W is set below the mean free path of the isotope molecule. Further, the meshes 14a of the mesh filter elements 15 stacked in multiple stages and facing each other are arranged alternately in the flow direction of the steam flow 5, as shown in FIG. That is, the configuration is such that the thin wires 14 of the adjacent mesh filter elements 15 are disposed at the upper and lower center of each mesh 14a.

Further, in FIGS. 1 and 2, a product recovery electrode 6 is provided on the secondary side of the deexcitation filter 13 through which the vapor flow 5 passes. The product recovery electrode 6 is formed by alternately arranging positive electrodes 7 and negative electrodes 8 substantially parallel to the flow direction of the vapor flow. A photoreaction section 9 is formed between each anode 7 and an adjacent cathode 8, and a laser beam oscillator 17 that irradiates the vapor flow 5 introduced into the photoreaction section 9 with a laser beam 10 causes a photoreaction. provided on the axial extension of the section.

Next, the effect will be explained.

In the isotope separation apparatus of this embodiment, the metal raw material 1 heated and evaporated by the steam generator 12 becomes a vapor flow 5, which is introduced into the deexcitation filter 13 while being diffused radially.

A particle of the isotopic atom A ₀ ^* in the metastable level E ₀ ^* ,
Particles contained in the vapor flow 5 such as negatively charged particles 18 such as thermoelectrons, positively charged particles 19 such as impurity cations, and electrically neutral particles 20 cause multiple collisions with the thin wires 14 of the mesh filter element 15. repeat.
Here, since the opening W of the mesh 14a of the mesh filter element 15 is set to a length equal to or less than the mean free path of the isotope molecule under operating conditions, there is a high probability that particles will collide with the thin wire 14. Moreover, the meshes 14a of the mesh filter elements 15 facing each other in the vertical direction
Since the wires are arranged alternately in the flow direction of the vapor flow, the gap formed between the opposing thin wires 14, 14 becomes narrower, increasing the scattering probability of particles and ensuring effective de-excitation and charge neutralization. It will be done.

That is, while multiple collisions are repeated in the mesh filter element 15, the vapor flow temperature is relaxed, and the isotope atoms A ₀ ^* at the metastable level E ₀ ^* are de-excited and transition to the ground level E ₀ .

On the other hand, thermionic electrons and impurity cations recombine during repeated collisions, resulting in electrically neutral neutral particles 20
becomes.

Isotope atom A ₀ generated by transitioning to ground level E ₀
The neutral particles 20 generated by the recombination pass through the mesh 14a together with other metal vapors, flow out from the upper surface of the deexcitation filter 13, and flow into the photoreaction section 9 of the product recovery electrode 6.

Irradiation of the vapor flow introduced into the photoreaction section with laser light and other separation operation procedures are the same as in the case of the conventional apparatus.

According to this example, the isotope atoms A ₀ ^* in the metastable level E ₀ ^* contained in the generated initial vapor flow 5 are:
The ground level can be effectively reduced by the deexcitation filter 13.
Isotope atom deexcited to E ₀ and at ground level E ₀
After transitioning to A ₀ , it easily reacts with the laser beam 10 and becomes ionized. Therefore, it becomes possible to significantly increase the number of isotopic atoms in the vapor stream that is the target of separation and recovery operations.

Therefore, the utilization rate of the raw metal vapor is 20
This increases by approximately 30%, greatly improving isotope separation and recovery efficiency. In addition, by providing the deexcitation filter 13, isotope atoms in the metastable level E ₀ ^*
A laser beam oscillation device that oscillates the selective excitation laser beam 10b for exciting A ₀ ^* to the selective excitation level E _1b is not required, the manufacturing cost is reduced, and the operation and operation can be simplified.

Further, according to this embodiment, the steam flow 5 at the initial stage of generation
The impurity cations and thermionic electrons contained in the product are removed by the deexcitation filter 13 before being introduced into the product recovery electrode 6. That is, during repeated collisions within the deexcitation filter 13, both atoms recombine and become neutral atoms. Therefore, the ions adsorbed to the product recovery electrode 6 are only specific isotopes excited and ionized by the laser beam 10.

Therefore, impurity ions are less likely to be entrained and adsorbed by the product recovery electrode 6 and reduce the isotope separation efficiency or degrade the purity and quality of the product, unlike in the prior art.

Next, another embodiment of the present invention will be described with reference to FIG.

This embodiment is characterized by being equipped with a power supply device 21 that applies a negative potential to the mesh filter elements 15 stacked in multiple stages within the deexcitation filter 13.
As shown in FIG. 4, the mesh filter element 15, which is applied with a negative potential, collects hot electrons contained in the vapor flow 5 and high-speed electrons emitted from the electron beam recoil on the molten liquid surface of the evaporation crucible. negatively charged particles 18
It has the function of electrically reflecting the negative charge particles 18
This prevents the substances from entering the photoreaction area. That is, recombination of the ionized isotope and thermionic electrons generated by the photoreaction is prevented. Therefore, the separation and recovery efficiency of a specific isotope in the product recovery electrode 6 is improved.

Furthermore, if the negative potential applied to each mesh filter element 15 is set so that the absolute value of the potential gradually decreases from the steam generator side to the product recovery electrode side, a potential gradient is formed within the deexcitation filter 13. be done. Therefore, the positively charged particles 19 such as various impurity cations contained in the vapor flow 5 are deflected or captured between the mesh filter elements 15, as shown in FIG.

Therefore, impurity ions, etc. are removed from the product recovery electrode 6.
The concentration of impurities contained in the recovered product is reduced, and an isotope product with excellent purity quality can be obtained.

In the embodiment shown in FIG. 1, the deexcitation filter 13 is constructed by stacking mesh filter elements 15 in multiple stages within the housing frame 16. 1
It is also possible to have a simple structure by filling the inside of 6.

〔Effect of the invention〕

According to the isotope separation device according to the present invention, the deexcitation filter is disposed between the steam generation device and the product recovery electrode, and the collision of vapor flows within the deexcitation filter and the relaxation of the vapor flow temperature are prevented. Therefore, the isotope atoms in the metastable level contained in the vapor flow are de-excited to the ground level. Therefore, the number of isotope atoms at the ground level, which are easily ionized by photoreaction, increases significantly. Therefore, the utilization rate of the metal vapor used in the separation operation is increased, and the isotope separation and recovery efficiency is improved.

On the other hand, the impurity cations and thermionic electrons contained in the initial steam flow generated from the steam generator are recombined in the process of repeated collisions in the deexcitation filter, and the charge of the impurity cations is electrically transferred by the thermionic electrons. is neutralized by Therefore, impurity ions are prevented from being adsorbed on the product recovery electrode, the efficiency of isotope separation for recovery is improved, and a product with excellent purity and quality can be provided.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the isotope separation device according to the present invention, and FIG.
3 is an enlarged perspective view of the mesh filter element shown in FIG. 2, FIG. 4 is a sectional view showing the behavior of atoms in the vapor flow in the laminated mesh filter element, and FIG. FIG. 6 is a perspective view showing the configuration of a conventional isotope separation device, and FIG. 7 is a sectional view taken along the - arrow in FIG. 6. 1...metal raw material, 2...evaporation crucible, 3...
Electron gun, 4...electron beam, 5...vapor flow, 6...
...Product recovery electrode, 7... Positive electrode, 8... Negative electrode,
9...Photoreaction part, 10...Laser light, 10a, 1
0b... Selective excitation laser beam, 10c... Intermediate excitation laser beam, 10d... Ionization laser beam, 11... Waste collection plate, 12... Steam generator, 13... Deexcitation filter, 14... Thin wire, 14a...mesh,
15...Mesh filter element, 16...Accommodating frame, 17...Laser beam oscillation device, 18...Negatively charged particles, 19...Positively charged particles, 20...Neutral particles,
21... Power supply, A ₀ ... Isotope atom at ground level, A ₀ ^* ... Isotope atom at metastable level,
E ₀ ... ground level, E _1a , E _1b ... selectively excited level, E ₂
... intermediate excited level, E _i ... ionization level, W ... mesh opening.

Claims (1)

[Scope of Claims] 1. A steam generation device that generates a steam flow by heating and vaporizing a metal raw material containing multiple types of isotopes;
A product recovery electrode is formed by alternately arranging positive and negative electrodes parallel to the flow direction of the vapor flow, and a laser beam is irradiated onto the vapor flow introduced into the product recovery electrode to identify the vapor contained in the vapor flow. and a laser beam oscillation device that selectively cationizes the isotope, and by applying a voltage between the product recovery electrodes, the cationized specific isotope is deflected toward the cathode to separate and recover it. In an isotope separation device, a deexcitation filter is placed between the vapor generation device and the product recovery electrode to transfer isotope atoms in the metastable level contained in the generated vapor flow to the ground level and deexcite them. An isotope separation device characterized by: 2. A patent claim in which the deexcitation filter is constructed by stacking mesh filter elements in multiple stages formed by weaving fine wires vertically and horizontally, and the opening of the mesh of the mesh filter element is set to be equal to or less than the mean free path of the isotope molecule. The isotope separation device according to item 1. 3. The isotope separation device according to claim 2, wherein the meshes of the opposing mesh filter elements are arranged alternately in the flow direction of the vapor flow. 4. The isotope separation device according to claim 2, wherein the deexcitation filter is equipped with a power supply device that applies a negative potential to the mesh filter element. 5. The isotope separation device according to claim 4, wherein the negative potential applied to each mesh filter element is set such that the absolute value thereof gradually decreases from the steam generation device side toward the product recovery electrode side.