JPH02227120A - Separation of isotope - Google Patents

Abstract

PURPOSE:To efficiently ionize and recover only the specified isotope component and to enhance the quality of a recovered article by simultaneously irradiating laser beams for trapping which are utilized to inhibit ionization of isotope excepting the specified isotope together with the laser beams for excitation and ionization. CONSTITUTION:When metallic uranium 1 is housed in a crucible 2 for evaporation and irradiated by the electron beams 4 emitted from a linear electron gun 3, metallic uranium 1 is heated and evaporated and vapor flow 5 is formed. The anodic electrodes 6 and the cathodic electrodes 7 are alternately provided over the crucible 2 for evaporation and the photoreaction parts 8 are provided. When pulse laser beams 10 are made incident from a laser beam irradiator 9, <235>U atom is selectively excited by absorbing them, ionized and made an ionized isotope, attracted and recovered on the surfaces of the cathodic electrodes 7. At this time, since the frequency of the pulse laser beams 10 is regulated to a wide region, <234>U is simultaneously excited and ionized. When the laser beams for trapping which are utilized to inhibit ionization thereof are simultaneously and coaxially irradiated, ionization of <234>U is inhibited and only <235>U is selectively ionized and recovered.

Description

Detailed Description of the Invention (Objective of the Invention) (Industrial Application Field) The present invention is based on an atomic method applied, for example, as a uranium enrichment method (relating to an isotope separation method, in particular isotope separation using This paper relates to an isotope separation method with improved body selection and excitation steps.

(Prior art) Generally, natural or recovered uranium includes uranium-234
(U-234>, Uranium-235 (U-235), Uranium-236 (U-236), Uranium-238 (U-2
Contains isotopic components such as 38). As is well known, U-
Natural uranium contains only about 0.7% of 235, and is enriched to about 3% to make it into fuel.

In recent years, laser isotope separation methods, particularly atomic methods, have been developed as this enrichment technology. The isotope separation method based on the atomic method heats metallic uranium in a vacuum with an electron beam to generate a uranium vapor flow, and irradiates this uranium vapor flow with laser light to selectively excite and ionize U-235. In this method, the ionized LJ-235 is recovered to an electrode. That is, by utilizing the difference in optical absorption frequency based on the energy level (isotope shift) between U-235 and other isotopes such as U-238, only U-235 is selectively excited and further ionized. It is collected and concentrated.

By the way, when uranium is enriched by such an isotope separation method, U-234 or U-236 may be ionized and recovered at the same time as U-235. Fuel containing such other isotopic components has a lower quality, and U-234 in particular is easily converted into gamma-ray emitting substances.
If this is mixed in, it will lead to an increase in shielding facilities, etc., which is undesirable from a handling and economical point of view.

Upon investigation by the inventor, U-234 or U
-236 has a light absorption frequency close to that of U-235. When uranium vapor is irradiated with LJ-235's pulsed laser beam for selective excitation and ionization, light is absorbed not only by Ll-235 but also by u-234 or U-236, which simultaneously converts energy units. It is thought that the result will be improved.

(Problems to be Solved by the Invention) In the conventional method, other isotope components whose optical absorption frequencies are close to the target isotope component are also excited and ionized, resulting in isotope recovery products. There were problems such as degrading the quality of the product.

The present invention was made in view of these circumstances, and allows efficient ionization recovery of only specific isotope components.
The purpose is to provide an isotope separation method that can improve the quality of recovered products.

[Structure of the invention]

(Means for solving the problem) The present invention heats a raw material containing multiple types of isotopes to generate a vapor flow, and uses an excitation/ionization laser to ionize only a specific isotope component in the vapor flow. In an isotope separation method in which ionized specific isotope components are collected in an electrode by irradiation with light, a trapping laser beam for preventing ionization of isotopes other than the specific isotope is combined with the excitation/ionization laser beam. It is characterized by simultaneous irradiation.

(Function) When the trapping laser beam is irradiated with the excitation/ionization laser beam at the same time, atoms of isotopes other than the specific isotope are trapped between the base degree and the trap unit, and are substantially excited into the selective excitation unit. The percentage decreases significantly. Therefore, the probability that isotopes other than the specific isotope will absorb the excitation/ionization laser light for guiding the specific isotope into ionization and become ionized is also significantly reduced.

On the other hand, since the ionization probability of specific isotopes does not decrease, only specific isotopes can be efficiently recovered.

(Example) Hereinafter, an example of the isotope separation method according to the present invention will be described with reference to the drawings.

First, this method will be schematically explained with reference to FIG.

Metal uranium 1 such as natural uranium or waste uranium produced by-product in the enrichment process is stored in an evaporation crucible 2 having excellent thermochemical resistance. Next, the electron beam 4 emitted from the linear electron gun 3 is deflected by an external magnetic field coil (not shown) and irradiated onto the metal uranium 1 in the one-shot ruppo 2 . Metallic uranium 1 irradiated by electron beam 4 has a concentration of 2500 to 3
It is heated to about 700X and evaporates to form steam 15.

On the other hand, above the evaporation crucible 2, a strip-shaped positive electrode 6 and a l
I! The electrodes 7 are arranged alternately, a photoreaction section 8 is provided on each of the electrode layers, and a pulsed laser beam 10 is incident on the photoreaction section 8 from a laser beam irradiation device 29 in the longitudinal direction. Then, the U-235 atoms are selectively excited by absorption of the pulsed laser beam 10 and are further ionized to become ionized isotopes.

Also, the positive electrode 6 and lI! A voltage is applied between the cathode 7 and the cathode 7, and LJ-235 is adsorbed and collected on the surface of the cathode 7 by the electric field formed thereby. Note that the vapor flow that has passed through the photoreaction section 8 without being ionized is suctioned and collected by a recovery plate 11 disposed on the outer edge side of the photoreaction section 8 .

FIG. 2 shows the relationship between the optical absorption intensity and the optical absorption frequency for each isotope of uranium (the numbers of atoms are expressed as being equal).

As shown in Figure 2, the peaks of the optical absorption intensity of U-234 and U-236 appear in approximately constant frequency ranges, but
In the case of Ll-235, the peaks are spread over multiple frequency ranges, and these are close to each other.

Conventionally, pulsed laser light 10 having a frequency corresponding to the light absorption frequency of U-235 was irradiated, but since the frequency of this pulsed laser light 10 was over a wide range, U-234 was also excited and ionized at the same time.

Therefore, in this embodiment, the trapping laser beam for preventing the ionization of U-234 is coaxially irradiated at the same timing as the pulsed laser beam 10.

As shown in Figure 3, the trapping laser beam is U-23
The first trapping laser beam connects only L1-234 from the ground level W1 to the selectively excited level W2, and the second trapping laser beam connects this L1-234 to the trap level W3. Note that part of the frequency components of the pulsed laser beam 10 may be substituted for the first trapping laser beam.

The first trapping laser beam has a frequency νa', while the second trapping laser beam has a frequency νb'. ) -W -(-1--1--νb'')-0 ...... (1) The following relationship is established. This relationship holds for LJ-234, but does not hold for U-235. In other words, it holds true for U-234, and U-23
5, each unit W , W ,
W and frequencies νa' and νb' are selected.

When formula (1) holds true, when the first and second trapping laser beams are irradiated, the U-234 atom is brought to the ground level W
is trapped between the trap level W3 and the selectively excited level W2.
The rate of excitation is significantly reduced. Therefore, the probability that U-234 absorbs the pulsed laser beam 10 and becomes ionized is also significantly reduced.

(Left below) Here, as shown in the following equation, when an error of δ occurs, the amount of excitation increases rapidly as shown in FIG. Therefore, each unit W, W2 . It is necessary to select W3 and frequencies νa' and νb'. Also, by setting the error δ-0 (
Equation 1) is established, and the amount of excitation of U-234 can be made substantially zero.

As described above, according to the above embodiment, by irradiating the trapping laser beam for preventing the ionization of U-234 at the same time as the pulsed laser beam 10, the ionization of U-234 is prevented and the tJ-235 Only U-234 can be selectively ionized and recovered, and a high-quality recovered product that is free from U-234 can be obtained.

In the above embodiment, the case where the ionization of U-234 is prevented is shown, but the present invention can be similarly applied to the case where the ionization of U-236 is prevented. Also,
U-234 and Ll-23 are simultaneously irradiated with a trapping laser beam for preventing the ionization of u-2j4 and a trapping laser beam for preventing the ionization of U-236.
It is also possible to prevent the ionization of 6 at the same time.

〔Effect of the invention〕

In the present invention, the trapping laser beam for preventing the ionization of isotopes other than the specific isotope is irradiated at the same time as the excitation/ionization laser beam, so that only the specific isotope component can be efficiently ionized and recovered. , the quality of recovered items can be improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining one embodiment of the present invention, FIG. 2 is a characteristic diagram showing the relationship between the optical absorption intensity and optical absorption frequency of each isotope in the above embodiment, and FIG. 3 is a diagram for explaining the above embodiment. FIG. 4 is a diagram showing the mutual relationship between the base unit, selective excitation unit, and trap unit in the embodiment, and is a characteristic diagram showing the decrease in excitation probability due to the coherent trap phenomenon in the above embodiment. 1... Metallic uranium (raw material), 5... Steam flow, 10...
...Pulsed laser light.

Claims (1)

[Claims] A raw material containing multiple types of isotopes is heated to generate a vapor flow, and this vapor flow is irradiated with excitation/ionization laser light that ionizes only specific isotope components, and the ionized specific isotope components are transferred to electrodes. An isotope separation method for recovering isotopes, characterized in that trapping laser light for preventing ionization of isotopes other than the specific isotope is irradiated simultaneously with the excitation/ionization laser light.