JPS63126529A - Method and device for separating isotope - Google Patents

Abstract

PURPOSE:To efficiently separate and recover the desired ionized isotope by setting the electric potential of a recovery electrode at least higher than that of the cathode of an auxiliary electrode, and forming the lines of electric force focused on the cathode of the recovery electrode. CONSTITUTION:The vapor stream 5 flowing into a photochemical reaction part 8 is irradiated by the ionization laser light 9 generated from a laser light oscillator, hence the specified isotope in the vapor stream 5 is selectively excited and then ionized. The generated ionized isotope is deflected to the cathode 7 side by the lines 18 of electric force formed between the cathode and the recovery electrode 12, separated, and recovered. The vertical diffusion of the ionized isotope generated at this times is prevented by the deflecting power of the lines 18 of electric force between the auxiliary electrodes 14 and 15, and the ionized isotope is efficiently attracted by the cathode 7 of the recovery electrode 12 along the lines 18 of electric force and recovered.

Description

[Detailed Description of the Invention] (Object of the Invention) (Industrial Application Field) The present invention relates to a method and apparatus for separating a specific isotope from a mixture containing a plurality of isotopes. The present invention relates to an isotope separation method and apparatus.

(Prior art) Uranium fuel used in nuclear fuel for nuclear reactors, etc. is separated and concentrated from a mixture of uranium isotopes to a specific uranium that causes a nuclear reaction, adjusted to a predetermined concentration, and then fed into a nuclear reactor. loaded.

Naturally occurring uranium contains approximately 0.7% uranium (hereinafter referred to as U-235), which is made up of light molecules with a mass number of 235, and the remainder is mostly uranium (hereinafter referred to as U-235), which is made up of heavy molecules with a mass number of 238. , abbreviated as U-238).

Among these, tJ-235, which causes a nuclear reaction, is separated from the above natural uranium or spent fuel, and usually 2 to 3
It is used as nuclear reactor fuel after being enriched to about 50%.

Conventionally, uranium enrichment methods for separating U-235 from a mixture containing isotopes such as Ll-235 and U-238 and increasing it to a predetermined concentration level include gas diffusion methods, centrifugation methods, laser methods, etc. In each method, separation and concentration operations are performed using differences in the chemical properties or qualitative layers of isotopes.

The gas diffusion method is a method in which a gasified isotope mixture is pumped through a diaphragm having a large number of micropores, and the isotopes are separated based on the difference in diffusion rate of each isotope passing through the diaphragm. The diffusion rate of U-235, which has a smaller and lighter atomic nucleus, is faster, and the amount of permeation is greater, so the content of tJ-235 increases slightly on the secondary side of the diaphragm. By repeating this process in multiple stages in a cascade manner, the concentration of tJ-235 is gradually increased. However, this method has the disadvantage of requiring a large-scale device with a large number of stages because the concentration rate per stage is small.

In addition, the centrifugal separation method introduces the gasified isotope mixture into a rotating cylinder and rotates it at high speed to remove heavy U-2.
38 is separated by centrifugal force, and this process is similarly repeated in multiple stages using a cascade system to increase the concentration. However, this method requires many separation steps and cascades, and requires many rotating bodies.

In addition to the above-mentioned conventional methods, isotope separation using laser light is a separation method that is particularly promising in terms of separation efficiency. This separation method is described, for example, in Japanese Patent Application Laid-Open No. 49-1050.
As disclosed in Japanese Patent Publication No. 97 and Japanese Patent Application Laid-Open No. 126895/1989, the target isotope is produced by irradiating the vapor of an isotope mixture with a laser beam having a wavelength that excites the nucleus of a specific isotope. For example, only U-235 is selectively ionized, an electric field is applied in a direction perpendicular to the vapor flow containing this ionized isotope, and only a specific ionized U-235 is deflected in a predetermined direction by this electric field. The uranium is then separated and enriched.

Next, a conventional example of an isotope separation method and apparatus using laser light will be described with reference to FIGS. 5 and 6.

FIG. 5 is a perspective view showing the configuration of an isotope separation method using Rede light used in the uranium enrichment process. below,
This will be explained using the separation of uranium isotopes as an example.

Metallic uranium 1, such as natural uranium or waste uranium produced as a by-product in the enrichment process, is housed in a thermochemically resistant evaporation crucible 2. Next, the uranium metal 1 is irradiated with an electron beam 4 emitted from the linear electron gun 3. Note that the electron beam 4 emitted from the linear electron gun 3 is deflected by an external Ta field co-coil (not shown) and is directed to the evaporation crucible 2.
Metallic uranium 1 inside is irradiated. The metallic uranium 1 irradiated by the electron beam 4 is heated to about 2500-2700' and evaporated, forming a vapor flow 5. Note that the composition of the vapor flow 5 is, for example, when natural uranium is used as the metal uranium 1, U-235 is 0.7% by weight, U-2
38 is 99.3%.

On the other hand, above the evaporation crucible 2, band-shaped positive electrodes 6 and negative electrodes 7 are arranged alternately, and a photoreaction part 8 is provided between the electrodes, and the longitudinal direction of the photoreaction part 8 is to U-2
An ionizing laser beam 9 that selectively excites and ionizes only 35 is incident. The wavelength of the ionizing laser beam 9 is adjusted to the resonant ionization wavelength of U-235, and only the U-235 atoms contained in the vapor flow 5 introduced into the photoreaction section 8 resonate with the ionizing laser beam, and the wavelength remains constant. It is selectively ionized and becomes an ionized isotope with a probability of The ionized U-235 isotope is adsorbed and collected on the surface of the negative electrode 7, which serves as a collection electrode, by an electric field formed by applying a voltage between the positive electrode 6 and the negative electrode 7.

On the other hand, the mixed vapor flow of U-235 and U-238 that has passed through the photoreaction section 8 without being ionized is sucked and collected by a vapor recovery plate 10 disposed on the outer edge side of the photoreaction section 8 .

(Problems to be Solved by the Invention) According to the conventional isotope separation method, the diffusion coefficient of the ionized isotope generated in the photoreaction part is large, and a large proportion of the ionized isotope is escaped from the photoreaction part. Therefore, there was a problem in that the recovery rate of a specific isotope separated and recovered by the recovery electrode was reduced. This tendency becomes more pronounced as the operating temperature is lowered and the vapor density is increased. In other words, in order to improve the amount of isotope recovered, if the evaporation of metallic uranium is promoted and the vapor density is lowered, the density of the ionized isotopes produced will also increase, but the diffusion coefficient will also increase, so that the amount of ionized isotopes escaping from the recovery electrode will increase. The number of isotope cylinders scattered also increases.

In addition, in the pretreatment process for uranium separation operations, a powerful electron beam is irradiated to melt and vaporize metallic uranium to generate a vapor stream, so the generated vapor stream contains various impurity ions. . As impurity ions,
There are collision ionized ions of U-238 generated when the electron beam, which is a heating source for metallic uranium, collides with a steam stream, and thermoionized ions of tJ-238 and other metals generated when the vapor stream comes into contact with a high-temperature heat source. . These impurity ions are U-
Since the U-235 ions are attracted to the recovery electrode along with the U-235 ions, the separation coefficient of the target isotope decreases, and the concentration of U-235 decreases, causing a decrease in the purity quality of the recovered uranium.

The present invention was devised to solve the above-mentioned problems, and is based on the ionized isotope (U-23
By providing a mechanism to suppress the thermal diffusion of 5 ions), the ionized isotope to be recovered can be efficiently separated and recovered, and the amount of impurity ions mixed in can be reduced to improve product purity and further separation. It is an object of the present invention to provide an isotope separation method and apparatus with excellent coefficients.

[Structure of the invention]

(Means for Solving the Problems) The isotope separation method according to the first invention heats and evaporates a substance containing multiple types of isotopes to generate a vapor flow, and this vapor flow is transferred to an Ill electrode. A laser beam that selectively ionizes a specific isotope is irradiated to the vapor flow to generate ionized isotopes, and an electric field is created between the electrodes. In an isotope separation method in which specific isotopes are separated and recovered by deflecting ionized isotopes toward the recovery electrode by applying The positive electrode potential of the recovery electrode and the positive electrode potential of the auxiliary electrode are set to the same potential, while the negative electrode potential of the auxiliary electrode is set to at least a higher potential than the negative electrode potential of the recovery electrode. Forms electric lines of force that are focused on the electrode, prevents the diffusion of specific ionized isotopes by the deflection force of the lines of electric force, and collects the ionized isotopes behind the electrode! It is characterized by focusing at the pole.

In addition, the isotope separation device according to the second invention includes a steam generation device that generates a vapor flow by heating and vaporizing a substance containing multiple types of isotopes, and positive electrodes and negative electrodes that are arranged side by side alternately. The isotope recovery device has a recovery electrode that is formed as a vapor flow and is arranged approximately parallel to the flow direction of the vapor flow, and the vapor flow that has flowed into the isotope recovery device is irradiated with a laser beam of a predetermined wavelength to collect a specific isotope. A selectively ionizing laser beam oscillation device is provided, and auxiliary electrodes that form lines of electric force that are focused on the negative electrode of the recovery electrode are arranged adjacent to the steam inlet side and the steam outlet side of the recovery electrode, respectively. shall be.

<Function> According to the isotope separation method and separation device according to the present invention,
Auxiliary electrodes are provided on the steam inlet side and the steam outlet side of the recovery electrode, and by applying voltage to these auxiliary electrodes, lines of electric force are formed that converge on the negative electrode of the recovery electrode. Since thermal diffusion of the ionized isotope is effectively prevented by the deflection force of , the amount of ionized isotope recovered at the negative electrode is increased.

In addition, an auxiliary r! provided on the steam inlet side! By the action of the electric field formed by the i-electrode, impurity ions contained in the vapor flow are collected and removed in advance before they flow into the collection electrode. Therefore,
The recovery electrode can be supplied with a vapor stream that is free of impurity ions and consists of electrically neutral isotopes.

Therefore, the amount of impurity ions attracted to the collection electrode is small, the target isotope is collected with a high separation coefficient, and a product with excellent purity and quality can be obtained.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings, taking as an example an operation for separating uranium isotopes in a uranium enrichment process.

FIG. 1 is a perspective view showing an embodiment of an isotope separation apparatus according to the present invention. Note that the same components and parts as in the conventional example shown in FIGS. 5 and 6 are given the same reference numerals.

The isotope separation device includes an evaporation crucible 2 containing uranium metal 1, and irradiates the uranium metal 1 contained in the evaporation crucible 2 with an electron beam 4 generated from a linear electron gun 3 to heat and evaporate the uranium metal 1. Steam generation v producing steam stream 5
11 is provided. An isotope recovery device 13 having a recovery electrode 12 formed by alternately arranging positive electrodes 6 and negative electrodes 7 is provided above the steam generation device 11 .

each! A photoreaction section 8 is formed between the i12 electrode 6 and the cathode 7, and a laser beam oscillator 16 that irradiates the vapor 21!5 flowing through the photoreaction section 8 with an ionizing laser beam 9 is connected to the photoreaction section 8. It is provided on the axial extension of.

Further, auxiliary electrodes 14.15 are provided on the vapor inlet side and the vapor outlet side of the recovery electrode 12, respectively, and the auxiliary electrode 14 on the vapor inlet side is further arranged adjacent to the lower edge of the recovery electrode. It is composed of an electrode 14a and a negative electrode 14b. On the other hand, the auxiliary electrode 15 on the vapor outlet side is further composed of a positive electrode 15a and a negative electrode 15b, which are placed adjacent to the upper edge of the recovery TIl electrode 12.

Next, the voltage applied to each electrode, the lines of electric force generated, etc. will be explained. FIG. 3 is an enlarged cross-sectional view of a part of the photoreactive portion in FIGS. 1 and 2. FIG.

The positive electrode 6 of the recovery electrode 12 and the positive electrodes 14a and 15a of the auxiliary electrodes 14.15 are electrically connected to each other and a voltage Va is applied thereto, and the negative electrode 7 of the recovery electrode 12 is grounded and set to zero potential. has been done. On the other hand, the negative electrodes 14b and 15b of the auxiliary electrodes 14 and 15 are both set to the voltage vb.

The relationship between voltage Va and voltage vb is as shown in equation (1).

Va > V b > O--(1) At this time, in the photoreaction section 8, an equipotential layer 1a shown by a solid line is formed along the flow direction of the vapor flow 5, as illustrated in FIG. At the same time, the positive electrode 6 and the auxiliary electrode 14 of the recovery electrode 12
．． Electric lines of force 18 converging from the 15 positive electrodes 14a, 15a toward the negative electrode 7 of the recovery electrode 12 are formed as shown by broken lines. Electric lines of force 18 are also formed between the positive and negative electrodes of each auxiliary electrode 14, 15.

Here, the potentials Va and Vb to be set at each electrode are determined from the kinetic energy possessed by charged particles such as thermoelectrons, ionized isotopes, and impurity ions at the operating temperature.

The kinetic energy Ei of the impurity cations contained in the steam flow 5 has a value comparable to the kinetic energy of thermionic electrons, and the operating section IIT is set to 2700', and the Boltz v constant k is set to 8.
When it is set to 617×10 −5 eV/′, the equation (2) is obtained.

1-kT -8,6t7x 10-5 (eV/"K) x2700
"K-0,23(eV)...(2)
The above kinetic energy E1 is not the same value for all impurity ions (it exhibits a certain probability distribution based on the above value. Therefore, in order to adsorb impurity cations in advance at the negative electrode 14b of the auxiliary electrode 14, It is necessary to set the voltage difference between the auxiliary electric currents 8i14 to be at least higher than the voltage corresponding to the kinetic energy Ei. That is, it may be set so as to satisfy equation (3).

e (Va-Vb) >>E i = (3) Here, e is the charge of the impurity ion.

Therefore, from equations (1), (2), and (3), generally Va-
It is preferable to set it to about 100 (V), Vb-50 (V).

Next, the effect will be explained.

In the isotope separation method and apparatus configured as described above, the metallic uranium 1 heated and vaporized by the steam generator is vaporized in the vapor stream 5.
As such, it is first introduced between the auxiliary electrodes 14 on the steam inlet side.

At this time, the thermal lightning beam and impurity ions contained in the vapor flow 5 are attracted toward the respective electrodes by the electric lines of force 18 formed between the auxiliary electrodes, and are removed from the vapor flow 5.

Therefore, the vapor flow 5 flowing into the photoreaction section 8 does not contain any charged particles as impurities and is composed only of electrically neutral components.

Next, the vapor flow 5 that has entered the photoreaction section 8 is irradiated with an ionizing laser beam 9 oscillated from a laser beam oscillator, and a specific isotope in the vapor flow 5 is selectively excited. Furthermore, it becomes an ionized isotope. The generated ionized isotopes are deflected toward the negative electrode 7 by the electric lines of force 18 formed between the collection electrodes 12 and separated and collected. At this point, the generated ionized isotope is prevented from diffusing in the vertical direction by the deflection force of the electric lines of force 18 formed between the auxiliary electrodes 14 and 15, and is moved along the lines of electric force 18 to the recovery electrode 12.
The static electricity remover 447 efficiently sucks and collects the static electricity.

Therefore, according to this embodiment, impurity ions and the like in the vapor stream 5 are removed before being introduced into the photoreaction section 8, and only the clean vapor is subjected to the subsequent separation step. Therefore, it is possible to significantly reduce the impurity (1) that was conventionally attracted to the recovery electrode along with the isotope to be recovered.

In addition, the ionized isotopes that are selectively excited and generated in the photoreaction section 8 are prevented from diffusing by the electric lines of force 18 formed between the auxiliary electrodes 14 and 15, and are dissipated in the vertical direction of the photoreaction section 8. It is prevented from doing so. Therefore, the isotope recovery efficiency at the recovery electrode 12 is improved, and i1m?
The overall isotopic separation factor is significantly improved.

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

FIG. 4 is an enlarged cross-sectional view of a part of the electrode section of the isotope separation device, similar to FIG. 3.

In this embodiment, an equal voltage Va is applied to all the positive and negative electrodes of the auxiliary electrodes 14.15 and the positive electrode 6 of the recovery electrode 12,
Only the negative electrode 7 of the recovery electrode 12 is configured to have a ground potential.

In this case, electric lines of force 18 formed between each electrode
As shown in FIG. 4, the focusing density of the recovery electrode 12 in the direction of the negative electrode 7 becomes high. Further, the equipotential 1i117 is formed concentrically with both ends of the cathode 7 as starting points.

Therefore, the action of deflecting and recovering the ionized isotope generated in the photoreaction part 8 to the cathode 7 is strengthened, and the efficiency of isotope separation and recovery is further improved.

However, in this case, since the same voltage ya is applied to both the positive electrode 14a and the negative electrode 14b of the auxiliary cylinder 1414, no electric field is formed between the auxiliary electrodes 14, so that impurity ions are removed. The action doesn't work. Therefore, it is not suitable when the vapor flow 5 contains many impurity ions.

Therefore, it is desirable to appropriately select and use the embodiment shown in FIG. 3 and the embodiment shown in FIG. 4 depending on the amount of impurity ions contained in the vapor flow 5. That is, in FIG. 3, impurity ions are removed by fixing the voltage ■a applied to the positive electrode and adjusting the voltage vb applied to the negative electrode of the auxiliary electrode as appropriate in accordance with the amount of impurity ions generated. Operating conditions that maximize the sum of the effects and the effects of recovering ionized isotopes can be easily set.

〔Effect of the invention〕

As explained above, according to the isotope separation method and apparatus according to the present invention, auxiliary electrodes are installed on the vapor inlet side and the outlet side of the recovery electrode, and lines of electric force are formed at the auxiliary electrodes. Since the diffusion of ionized isotopes is effectively prevented by the action of , the amount of ionized isotopes recovered at the recovery electrode increases, and the isotope separation coefficient is significantly improved.

In addition, impurity ions contained in the vapor flow are removed in advance by the action of an electric field formed between auxiliary electrodes provided on the vapor inlet side of the recovery electrode. Therefore, less impurity ions a are attracted and collected by the collection electrode, and a valuable product with excellent purity and quality of the target isotope can be provided.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of an isotope separation apparatus for carrying out the isotope separation method according to the present invention, FIG. FIG. 4 is an enlarged sectional view of a part of the photoreactive part shown in FIG. 2; FIG. 4 is an enlarged sectional view of a part of the photoreaction part according to another embodiment;
The figure is a perspective view showing the configuration of a conventional isotope separation device, and FIG. 6 is a sectional view taken along the line Vl-vr in FIG. 1...metallic uranium, 2...evaporation crucible, 3...
Linear electron gun, 4...electron beam, 5...vapor flow,
6... Positive electrode, 7... Negative electrode, 8... Photoreactive part,
9... Laser beam for ionization, 10... Steam recovery plate, 11
...Steam generation bag d112...Recovery electrode, 13...
Isotope recovery device, 14... Auxiliary electrode, 14a... Positive electrode, 14b... Negative electrode, 15... Auxiliary electrode, 15
a... Positive electrode, 15b... Negative electrode, 16... Laser beam oscillation device, 17... Equipotential lines, 18... Lines of electric force, ■... Operation temperature, Ei...・Kinetic energy of ionized ions, e...Charge of impurity ions, Va, Vb
···Voltage. Representative Patent Attorney Nori Chika Yushu Hiroshi Mitsumata Fumizuru 2 times

Claims (1)

[Claims] 1. A vapor flow is generated by heating and evaporating a substance containing multiple types of isotopes, and this vapor flow is introduced into a recovery electrode formed by alternately arranging positive and negative electrodes. After that, the vapor flow is irradiated with a laser beam that selectively ionizes a specific isotope to generate ionized isotopes, and an electric field is applied between the electrodes to deflect the ionized isotopes toward the recovery electrode. In an isotope separation method that separates and recovers a specific isotope, auxiliary electrodes are installed adjacent to the vapor inlet and vapor outlet sides of the recovery electrode, and the positive electrode potential of the recovery electrode and the positive electrode potential of the auxiliary electrode are are set to the same potential, and on the other hand, the negative electrode potential of the auxiliary electrode is set to at least a higher potential than the negative electrode potential of the collection electrode to form lines of electric force that are focused on the negative electrode of the collection electrode. An isotope separation method characterized by preventing the diffusion of specific ionized isotopes using a deflection force and focusing the ionized isotopes on a negative electrode of a recovery electrode. 2. A steam generation device that heats and evaporates substances containing multiple types of isotopes to generate a vapor flow, and a positive electrode and a negative electrode that are alternately arranged in parallel and arranged approximately parallel to the flow direction of the vapor flow. and a laser beam oscillation device that selectively ionizes a specific isotope by irradiating a vapor flow flowing into the isotope recovery device with laser light of a predetermined wavelength, An isotope separation device characterized in that auxiliary electrodes that form lines of electric force that are focused on the negative electrode of the recovery electrode are arranged adjacent to the vapor inlet side and the vapor outlet side of the recovery electrode, respectively.