JPS62730B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides isotopic selective excitation of isotopic compounds contained in a mixture of gaseous isotopic compounds using pulsed laser light and subsequent chemical or physical separation of the isotopic compounds. Concerning an economical isotope separation method. In all such methods, only one isotopic compound is excited, so that this isotopic compound becomes a single compound, and this new compound is relatively removed from the initial mixture by conventional mechanical and chemical means. Can be easily separated. As a result, this new compound contains, inter alia, the desired isotope, such as, for example, uranium-235. Isotope separation based on this principle is particularly important industrially for uranium. This is because natural uranium contains the available fissile isotope uranium-23.
This is because 5 is originally present at only up to 0.7% and must be enriched to about 2-3% for use as a fuel material for light water reactors.

Excitation of one isotopic compound, however, ionizes it, thereby changing the dipole properties of the isotopic compound so that it can be separated by electrical means or deflected by the electric field of the laser beam itself. It is also used for Details of laser-induced isotope separation methods by physical and chemical separation can be found in German Patent Applications No. 2311584 and No.
It is described in the specification of No. 2324797. Another proposal for isotopic separation via selective excitation of molecular energy levels can be found in German Patent Application No. 2459989, which specifically describes the use of wavelengths in the infrared and ultraviolet regions. It is being

All uranium isotope separation methods start from the compound UF ₆ , which has sufficient vapor pressure to be practically a single uranium compound. However, selective excitation carried out at normal temperatures does not yield the desired enrichment values due to the superposition of absorption bands, resonance exchange and thermal activation reactions, and as a result vaporized isotopic compounds are used for improvement. It has been found desirable to expand adiabatically to a temperature below 100 K and still before condensation be irradiated by a laser beam of a suitable frequency directed into the resonator. This is described in German Patent Application No. 2447762. It has also already been proposed, instead of adiabatic expansion, to carry out cooling of the isotope mixture by means of a neutral, highly supercooled additive gas to be introduced, as can be seen in German Patent Application No. 2,651,306. .

However, the economy of these isotope separation methods is only possible when using so-called continuous wave lasers. Such devices, however, are not yet available in practice with the necessary output.

Therefore, in the current state of laser development, there is a problem in implementing isotope separation methods with pulsed lasers. Since the laser pulse of about 1 ns is very short and the pulse repetition frequency is up to about 100 Hz, conventional methods using such pulsed lasers can only excite a very small amount of material, and as a result, the method described above The use of pulsed lasers is economically disadvantageous. In that case, the gas mixture introduced must always be returned again, thus requiring an exorbitant pump power.

The object of the invention is to obtain a method which allows the use of pulsed lasers economically and which ensures that all guided mixtures are irradiated throughout and that the excitable molecules are actually excited. be.

This purpose, according to the invention, involves selectively exciting isotopic compounds of a gaseous mixture by laser pulsed light of a specific frequency and then chemically or physically separating the excited isotopic compounds from the unexcited isotopic compounds. In this method, a gaseous mixture of isotopic compounds is adiabatically expanded through a nozzle in a fixed time interval ΔT ₁ and cooled to below 100 K, the flow time ΔT ₂ being in the range of milliseconds respectively, and the nozzle The total flow time ΔT ₂
exposure to equally spaced successive pulses of n sequentially emitting lasers over a period of time, where n is the conduction time ΔT ₂
This is achieved by making the ratio equal to the residence time of the gas molecules in the irradiation path.

This method is therefore based on a combination of two features: This means that the gas mixture introduced into the isotope separation device is passed through the irradiation chamber for short flow periods at repeating intervals and is then irradiated over its entirety by a number of successively emitting laser devices, each of the same frequency. There are two things to do. This is based on the following considerations:

The results of the study showed that during dynamic cooling of the gas mixture selective excitation and separation of the desired isotopic compounds must occur over a path of about 2 cm. If the jet velocity of the material mixture entering the irradiation chamber is approximately 500 ms, the flight time of the molecules through this path is approximately 40 μs.
become. If this entire 2 cm long area is now irradiated with a laser pulse, and the next laser pulse follows after a further 40 μs, the irradiated areas of the mixed material jet will continue adjacent to each other without any gaps. Of course, this requires a laser with a pulse frequency of 25 kHz, but a laser in this desired wavelength and power range does not yet exist. The required pulse energy is around 1 Ws in the ultraviolet region (0.3 to 0.4 μm) and around 0.025 Ws in the infrared region (16 μm).

This difficulty is overcome according to the invention in that the required pulse repetition frequency is generated by successive emission of a large number of similar laser devices. However, the number of laser devices is limited, both economically and technically, since all laser devices must be arranged so that the laser beam passes through the irradiation chamber in the same path. , care is taken that the mixed substance jet passes through the irradiation chamber only during the irradiation time of the laser device to emit light sequentially. This is accomplished by connecting a valve in front of the expansion nozzle, which sends a jet of mixed material through the irradiation chamber whose length is limited at periodic intervals corresponding to the possible pulse repetition frequency of the laser. be done.

The invention will now be explained in detail with reference to the drawings.

FIG. 1 schematically shows the spatial arrangement of the irradiation chamber 3, the nozzle 2 and the valve 4. The method proceeds as follows. Mixture 46 flows into valve 4 via inlet conduit 45 . This valve 4 includes a cylindrical housing 41,
An inlet conduit 45 is connected to it on one side and an expansion nozzle 2 on the other side. Inside this housing 41, a rotor 42 with slots 43 and 44 (which are also located opposite each other on the same diameter) rotates at a constant rotational speed. The slits 43 and 44 connect the inlet conduit 45 and the nozzle 2.
A jet of mixed material of always the same length passes through the irradiation chamber 3 whenever a bond is formed between the two. The length of this irradiation chamber is designated by s. The jet velocity is
In the case of 500ms, one molecule completes this process for 40μs.
Go through it. When the front of the gas stream now leaving the nozzle arrives before the end of the irradiation chamber 3, it fires the first laser device and then, at an interval of 40 μs each, the next laser device. As a result, the irradiation area g ₁ or
A division of the mixed material jet into gn takes place. FIG. 1 shows the situation in which the last jet region gn has just been irradiated by the last, ie the nth laser device. The total length S of the mixture jet leaving the nozzle 2 at a distance is then obtained from the product of the length s of the irradiation chamber and the number n of laser devices.

FIG. 2 shows a time diagram of the switching sequence of the valve 4 and the n laser devices. Valve 4 is Δ
The channels are opened at intervals of T ₁ , where ΔT ₁ takes a value of, for example, 100 ms. The opening time of the valve, on the other hand, is, for example, 1 ms and is denoted by ΔT ₂ . During this time domain ΔT ₂ , the laser devices 1 to n emit light in sequence, and in the numerical example chosen, the emission interval between the two lasers is in each case the same as that required for one molecule to pass through the irradiation chamber 3. The time becomes 40μs.

3 and 4 schematically show examples for the introduction of light beams from different laser devices into the irradiation chamber 3. In FIG. It must be mentioned that the expansion nozzle 2 has a slit-like shape for this purpose. It has, for example, a spacing of about 0.1-0.5 mm and a width of about 1 m at its narrowest point. 3 and 4 show the nozzle 2 in plan view, ie viewed from the width side.
The number of laser devices is calculated according to the numerical example given earlier, where ΔT ₂ = 1 ms is divided by 40 μs and n =
It becomes 25. Only 10 laser devices are shown in FIG. 3 for clarity, and their light is deflected via a deflection mirror 6 onto a rotating mirror 61, which is synchronized with the repetition frequency of the individual laser devices. and rotate,
The laser beam is advanced to the irradiation chamber 3 through the same path. In the irradiation chamber 3, the light beam is reflected back and forth on the mirrored walls, so that during the duration of the laser pulse the entire material present in the irradiation chamber 3 is captured by this beam of each laser device.

As mentioned in the introduction, two frequencies can be used for excitation of the mixed material. The introduction of these two different laser beams is illustrated in FIG. This figure also shows nozzle 2 and irradiation chamber 3 with length s.
is shown in a plan view. The light beam from the laser device L shown in FIG. 3 is guided through the cylindrical lens 8 to the irradiation chamber 3, where it is reflected back and forth.

For example, the width is 100cm, the length is 2cm, and
With dimensions of 0.5cm thickness. Its side walls consist of a KCl or NaCl window deposited with a dielectric multilayer with 99.7% reflection at a wavelength of 0.4 μm and through which 16 μm light passes unhindered. One side of both windows 72
corresponds to a section of a cylindrical mirror with a radius of curvature of 100 cm.
With this treatment, both 16 μm light and 0.4 μm light can be
Since the ratio of the absorption capacity of UF ₆ at μm to that at 0.4 μm corresponds to the reciprocal of the optical path ratio, it is almost completely absorbed. 0.4, which is focused so that it is reflected many times in the irradiation chamber.
In contrast to the μm wavelength light, the 16 μm light is spread out to 2 cm x 0.5 cm to evenly illuminate the entire irradiation chamber. Of course, a device of this type is also suitable for processes requiring only one radiation method or only one ultraviolet quantum for excitation and separation.

If valve 4 is always open, a device with the above dimensions and data will have a temperature of 10 ⁴ when cooled to 50 K.
It has a mixed material flow rate of m ³ /h. The required pump power, on the other hand, is very high. However, in the method described above, the required pump capacity is reduced to 100 m ³ /h, which is therefore a capacity that can be obtained without great expense.

To further explain this method, the quick-open/close valve 4
Let us further discuss the size of . This valve has a width of 1 m, corresponding to a nozzle width of 1 m. In this way, uniform feeding of the nozzle 2 (viewed over its entire width) is achieved via the slots 43 and 44 of the rotor 42. At a rotation speed of 600 rpm and a rotor circumference of 20 cm, 2 for an opening time ΔT ₂ of 1 ms.
mm inlet and outlet slits 43/44
This results in a width of . The spacing between the valve housing wall and the rotor can be kept relatively small due to the low rotational speeds, so that a good seal is provided during the closing time of the valve 4.

The above-mentioned numerical example is, of course, one example, and is not limited thereto. This can be adjusted accordingly depending on other parameters such as, for example, pulse repetition frequency, number of possible lasers, etc. The work-up or the actual separation of the desired excited or enriched isotopic compounds will not be described in detail, as they are known and can be carried out in part by the methods already mentioned at the outset. It is completely irrelevant to the subject matter of the present invention.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of one embodiment of the device of the present invention, and FIG.
The figure is a diagram for explaining the operation of the method of the present invention, and FIGS. 3 and 4 are explanatory diagrams of different examples of the portion of the apparatus of the present invention that guides the laser beam to the irradiation chamber. 2...Nozzle, 3...Irradiation chamber, 4...Valve, 41
... Valve housing, 42 ... Rotor, 43, 44
... Slit, 45 ... Gas conduit, 46 ... Gas mixture, 6 ... Deflection mirror, L ... Laser device.

Claims (1)

[Claims] 1. A method of selectively exciting isotopic compounds in a gaseous mixture with laser pulse light of a specific frequency, and then chemically or physically separating the excited isotopic compounds from unexcited isotopic compounds. In,
A gaseous mixture of isotopic compounds is collected over a fixed time interval Δ
The jet is adiabatically expanded through the nozzle at T ₁ and cooled to below 100 K, and the flow time ΔT ₂ is set in the range of milliseconds, and the jet periodically exits from the nozzle over the entire flow time ΔT _2. The ipsilateral laser is exposed to continuous pulses at equal intervals from n sequentially emitting laser devices, where n is equal to the ratio of the flow time ΔT ₂ to the residence time of the gas molecules in the irradiation path. Body separation method. 2. A method according to claim 1, characterized in that the jets periodically emerging from the nozzle are exposed to laser light of different frequencies, and the same number of laser devices is used for each frequency. 3. Comprising a slit-shaped expansion nozzle 2 having a gas inlet, an irradiation chamber 3, and a plurality of laser devices L, extending across the entire nozzle width in front of the slit-shaped expansion nozzle 2 to control gas flow. A valve 4 is provided, and the valve 4 includes a cylindrical rotor 42 having two diametrically opposed longitudinal slits 43/44 and rotating at a constant speed, and a housing 41 that seals the rotor 42 inside. This housing 4 consists of
An isotope separation device characterized in that 1 is connected to an expansion nozzle 2 on one side and to a gas inflow conduit 45 on the other side diametrically opposed to the expansion nozzle 2. 4. The laser device L is arranged to face the irradiation chamber 3 by means of a deflection mirror 6, and the laser pulses emitted from the deflection mirror 6 take the same path inside the irradiation chamber 3. Apparatus according to scope 3.