Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Background o the Invention
Field of the Invention
The present invention relates to a method and apparatus for sepa-
rating gaseous mixtures of substances such as, in particular, isotope mixtures.
More particularly, the inven~ion relates to new and improved apparatus and
its use having a vessel which can be evacuated and is connected to supply
devices ~or the mixture of substances as well as, optionally supplemental
gases~ as well as collecting devices for the separated substances. The
vessel contains nozzles for forming a jet of the mixture of substances ~o
be separated and a collecting device for the separated components thereof,
and is provided with window-like passages for access of an electromagnetic
radiation for exciting part of the mixture of substances according to methods
knowniper se.
Description of the Prior Art
Since the development of laser technology ~ith the possibilities
for generating a narrow-band electromagnetic wave, mvestigations have been
started on a very large scale to utilize these waves for the excitation of
~, molecules specifically for the purpose of isotope separation. Various methods
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have been proposed which are based on generating different directions and
velocities of the molecules to be separated from those which are not excited.
Such methods are described, for instance, in German Published Non-Prosecuted
Applications Nos. 23 11 584; 24 30 315; 26 59 590 as well as in United States
Patents Nos. 4,031,397; 4,032,306 and 4,119,509. It is a common feature of
all these proposals that the exci~ed particles displaced from the molecular
jet are taken to regions with the original isotope composition, so that the
; degree of enrichment attainable there is only rather small.
The problem,therefore, arises to find special devices for carrying
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out such isotope-selective enrichment methods, by means of which a consider-
ably higher degree of enrichment is attainable. The detrimental boundary
layers are also to be avoided, at least in part.
Summary of the Invention
With the foregoing and other objects in view, there is provided
in accordance with the invention an apparatus for separating isotope
mix~ures, which comprises a container which can be evacuated, two window~
like passages disposed opposite each other in the container for the passage
of an electromagnetic radiation, a slit-shaped nozzle at one side of the
path of propagation of the electro~agnetic radiation, extending parallel to
the propagation direction of the electromagnetic radiation, for forming a
gas jet of the isotope mixtura, and at the other side of the path of pro-
pagation of the electromagnetic radiation are arranged rollecting devices
for the separated components of the isotope mixture, the combination there-
:~ : with of a gas-feeding body into which said isotope mixture is fed prior to
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entering said nozzle, which gas-feeding body is also slit-shaped toward the
nozzle and arranged before the nozzle, with the slit of said gas-feeding body
~ subdivided into numerous subdivisions by a plurality of walls which are
: uniformly spaced, and are oriented perpendicularly to the propagation direct-
20: ion of the electromagnetic radiation, to form narrow outlets for the isotope
mixture, the collecting devices having numerous collecting means each provided
:with a peeler, and each collecting:meana azzociated with a narrow outlet of
:,~ the gas-feeding body~.
Although the invention is illustrated and described herein as
:~ embodied in a device for separating gaseous mixture of substances, it is
nevertheless not intended to be limlted to the details shown, slnce various
modifications may be made therein without departing from the spirit of the
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invention and within the scope and range of equivalents of the claims.
Brief Description of the Drawings
The invention, however, together with additional ob~ects and ad-
vantages thereof will be best understood from the following description when
read in connection with the accompanying drawings, in which:
~ Figure 1 schematically illustrates a top view of apparatus in
: longitudinal cross section to show a multiplicity of nozzles arranged side
by side, jets of gaseous mixtures of substances issuing from the nozzles,
laser radiation passing through a window and through the jets of gaseous
mixtures, deflection of some of the gases as shown by arrows, collectors
and a plenum for the excited gases and another plenum Eor the non-excited
gases.
Figure 2 is a cross section taken along llne LI-II of Figure 1.
Figure 3 -ls a varial~t of the apparatus in Figures 1 and 2, and
shows in vertical section a special nozzle design to improve boundary layer
conditions.
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Figure 4 is a horizontal cross section taken along line IV-IV of
Figure 3 and shows intermediate gas je~s of an inert gas between the jets of
gaseous mixtures.
Detailed Description of the Invention
A device for separating gaseous mixtures of substances, particularly
isotope mi~tures, consists of a vessel which can be evacuated and which is
connected to supply means for the mixture of subs~ances as well as, optionally,
supplemental gas. Collecting means are provided for the separated substances.
The vessel contains nozzles for forming a jet of the mixture of substances to
be separated and a collecting device for the separated components ~hereof.
The vessel lS provided with window-like passages for access of an electro-
I magnetic radiation for exciting part of the mixture of substances according
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to known methods.
In accordance with the invention, a multiplicity of jets is pro-
vided within the vessel on the one side of the propagation path of the elec~
tromagnetic wave which nozzles are arranged side by side and are connected to
supply tanks and in~which vessel a corresponding number of collecting devices
connected to plenu~s are contained on the other, opposite side. The multi-
plicity of nozzles is constructed by means of an initially slit-like base
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nozzle which is subdivided by walls perpendicular to the direction of the
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electromagnetic wave into a number of alternating narrow ou~lets for the
mixture of substances as well as, optionally, intermediate gases.
To explain this device in further detail, reference is made to the
examples shown in Figures 1 to 4. Figures 1 and 2 refer to a device accord-
;1 ing to the basic principle in which a multiplicity of nozzles are arranged
i side by side on one side of the propagation path of the electromagnetic wave
as described above. Figures 3 and 4 show a device with a special nozzle
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design for improving the boundary layer conditions.
Figure l shows a top view of a longitudinal cross section through
this device, and Figure 2 a cross section along the line II-II of Figure 1.
Laser radiation emitted by laser equipment, not shown, is provided as the
electromagnetic wave and is designated with l. This radiation enters the
device via the window 11 and passes through it along its imaginary axis 12.
The window ll is placed on the housing 6 of the device via seals. Along the
axis 12 of the laser radiation 1 are a number of individual nozzles 2 through
which the gaseous mixture of substances to be separated is expanded, for
lO instance, adiabatically. This expanded jet of the mixture of substances,
; which moves at supersonic velocity, has approximately the shape shown in
Flgure l and enters the~diffusors opposite the nozzles 2. However, due to
the deflection eect, for instance, of the magnetic field of the :Laser
radiation l ~see German Published Non-Prosecuted Application No. 24 30 315),
the 235 UF6 molecules, for instance, are excited and polarized and leave the
jet of the mixture of substances in the direction of the arrow shown. There-
fore, they no longer en~er the diffosors 4 at the same time, but enter the
spaces 5 between ~hem and go from there to a plenum 51, from which they are
drawn off. The mixture of substances, which is depleted of 235 UF6 and enters
20 the diffusors 4, gets from the latter into the plenum 41 and ls~drawll-ofE
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from there. Pumps whlch are provided for this purpose bu~ are not shown, not
only ensure the removal of the gases fed-in, but also serve in conjunction
with control devices such as valves Eor adJusting the correct pressure ratios
so that in conjunction with an appropriate design of the walls of the diffu-
sors which is known per se so-called pressure recovery takes place, as a
result oE which the gas velocity again becomes subsonic.
It is important that the gas jets 3 leaving the nozzles 2 are thin,
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~their thickness should be less than 104 - times the mean free path), in
. order to remove the 235 UF6 quickly from the gas jet with a relatively low
laser power density and not allow the collision frequency between polarized
or excited 235 UF6 with 238 UF6 to become too high on its way ~hrough the
gas jets.
The mean free path of the molecules type 1 for gas mixtures L can
be calculated according to the ~quation
L =
nr 4~A ~r ~ ~
I0 where nV~is the atom or molecule density of the particle typevv; ~ riS
the collision radius of the type 1 particles with the particle type~. M and
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M~r, respectively, are the corresponding molecular weights. The temperature
dependence of the collision radius can be taken into consideration according
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to the relation
a2 = ~2 ~ .
~,
T ~r
~;. T
where T is the absolute temperature. For estimating purposes one can set
~; al~r = al. These values and the constants a~ and T~can be found for many
gases in the book by R. Jaekel, "Kleinste Drucke" (very low pressures),
Sprlnger Verlag, Berlin l9S0, page 285. For UF6 one can set al = 1.3 x 10 15
cm2, a~ = 2.5 x 10 16 cm2 and T~= llOK.
~ With the device silown in Figures I and 2, turbulent mixing of the
: cold flow cores with the`boundary layers after they leave the nozzles at
.l the expanded gas jet 3 is difficult to avoid (by settlng a relatively low
pressure of the environment of the gas jets). These turbulent zones, however,
can fill a considerable part or the entire jet cross sectionl even more so,
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*he thinner the latter is. Due to the temperature rise connected therewith,
the selectivity of the excitation becomes poorer. Further~ore, the impulse
loss caused by the deceleration also decreases the effectiveness of the
already mentioned pressure recovery.
To avoid these disadvantages, an improvement of this device is
made in such a manner that intermediate gas jets 31 of an inert gas o~ inert
gas mixture, for instance, of rare gases, nitrogen, etc. which may be intro-
duced through stub 62 are provided between the jets 3 of the mixture of
substances which extend parallel to each other. This device variant is
shown in Figures 3 and 4. Figure ~ shows a horizontal cross section and
Figure 3 a vertical cross section. An important change of this device ~rom
that according to Figures 1 and 2 is the design of the expansion jets 2.
These are realized by means of a slit nozzle 28 ~basic nozzle) which is
mounted on a nozzle carrier 27 clamped into the housing 6. The mixture of
substances to be se~arated is fed~in via a feed member 21, the slit-shaped
exit openings of which are located shortly ahead of the constriction of the
slit-nozzle 28. Spacer webs 23 provide for this spatial relationship. This
feed member is connected to a supply tank~ not shown~ for the mixture of UF6
and supplemental gas via a connecting stub ~1, which is brought tightly
through the housing.
Divider members 22 are provided in the front discharge opening of
the feed body 21 for forming the individual nozzles 2 and thereby, the thin
jets 3 o the mixture of substances; see also Figure 4. I'he spacer webs 23
which also serve for adjusting the;posltion of the eed body 21 relative to
the nozzle 28, are arranged above and below the individual nozzles 2 formed
by the divider bodies 23 so that the inert gases or inert gas mixtures
flowing-in through the spaces between the webs 23 and the nozzle 28, after
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being expanded, likewise make thin gas jets 31 in the nozzle, which al~ernate
along the axis 12 of the laser radiation with tha jets 3 of the mixture of
substances. By the alternation of the layers of jets 3 of the mixture of
substances with those of the inert intermediate gases 31, boundary layers
between the gas jets are avoided by the special form in which they are
generated. The intermediate gas and the UF6 -containing mixture are matched
to each other with respect to molecular weight and adiabatic exponent in
such a manner that they have approximately the same velocity~ ~ithdrawal
of gas through stub 63 aids in the control of pressure in the interior. In
addition to avoiding the detrimental boundary layers between the partial
gas streams, also the pressure recovery in the diffusors 4 and 5, which are
again connected to suctioning-off chambers 41 and 51, is made possible or
improved in this manner.
As already mentloned, the boundary laye.rs between the stratiied
gas streams 3 and 31 are eliminated, but not those at the end ~ace thereof.
To make these remaining boundary layers harmless, they are separated totally
or partially from the gas stTeams 3 and 31 by a peeler 7, so that only the
selectively excited parts of the beams 3 of substance mixture enter the
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diffusors ~ and-5 with their not deflected and deflected components. The
flow is kept laminar in the vicinity of the nozzles and the diffusor entrance
by sufficiently small dimensions of the nozzle, a corresponding choice of
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the flow parameters and the composition of the gas, so as to avoid detri-
; mental mixing of the jets of substance mixture and the intermediate jets,
i.e. for instanceJ UF6 -containing and neutral gas jets. The extent of the
radiation 1 lS shown in Figure 3 by an oval. Such a radiation cross section
can be generated, ror instance, by reflection between mirrors, not shown,
the laser beam being conducted, in the case of magnetic deflection ~see
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German Published Non-Prosecuted Application No. 24 30 315) so that it yasses
through the gas jet in the same direction.
The device according to Figures 3 and 4 thus makes possible separate
feeding of the gaseous mixtures of substances as well as of the intermediate
gases to the expansion nozzle 28 subdivided illtO individual nozzles 2.
Stra~ified and adiabatically expanded gas streams 3 and 31 are formed in ~he
process, which are free of boundary layers. Dif-~usors 4 and 5 are provided
for collecting these gas streams. In the diffusor 5 are collected not only
the intermediate gas but also the 235 UF6 molecules which were de-flected, for
instance, by the magnetic field of the laser radiation, while press~lre is
being recovered, to the plenum 51 and are passed-on via the suction stub 65.
The 235 UF6-depleted gas mixture enters the plenum 41 through ~he diffusor 4,
pressure being recovered, and gets to an exhaust pump via the connecting stub
64.
As already mentioned, the thickness o the substance mixture jets
3, is less than 104-times tbe mean free path and is preferably in the order
of magnitude of the mean free path for collisions of the UF6 molecules among
each other. At a partial UF6 pressure of lO 3 mb and a temperature of lOK
this mean free path is about 0.3 mm. Further characteristic data for the
operation of such a separating device for separating UF6 are listecl below in
tabular form:
Mixing ratio UF6 : Ar l:100
Input pressure 1 bar
Input temperature 330 K
Width of nozzle neck 0.02 mm
Final nozzle width 3 mm
~ Layer thickness of the UF6-
;~ containing gas jets 0.3 mm
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Layer thickness of the UF6-
free gas jets 0.3 mm
Pressure at peeler ~0.2 mb
Pressure behind diffusor <14 mb
With the magnetic deflection assumed here (German Published Non-
Prosecuted Application No. 23 11 584) and 10 - fold transversal in the same
direction and phase of a linearly polarized laser beam, the laser power is
of the order of 20 kW for radiation into the Q-branch of the small ~3 vibra~
tion of the 235 UF6.
10As a further example ~or the application of this device~ a sepa-
ration method will be named which is described in detail in German Published
Non-Prosecuted Application No. 26 59 590. According to the methods described
there, UF6 is mixed with a supplemental gas such as argon, where by appropri-
ate flow parameters this mixture is condensed without excitation and further-
;; more, the temperature drops below lOOK, so that selective excitation of the
UF6 is possible.
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By exciting the 235 UF6, it is selectively prevented from being
condensed. The mean thermal velocity V of the UF6 molecules is then V = 1.46
x 104 ~ cm/sec, where T stands for the absolute temperature and M for the
molecular weight. Because of the larger mass of the condensed particles
their velocity is smaller and their thermal motion is slower, while their
directional velocity is nearly equal to the jet velocity. The excited parti-
cles therefore, move out of the gas jet more rapidly, be it by collision-
free motion or by diffusion. Added to this is further the energy gain of the
excited UF6 monomers with inelastic scattering. The laser power density is
chosen so high that the 235 UF6 molecules are excited rapidly enough, i~e.
before being condensed, and that losses of the excitation energy, which can
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be produced, for instance, by scatter processes and resonance transition, are
made up again rapidly~ In order to prevent non-selective condensation to a
large degree, the laser beam ext~nds into the nozzle up to the regions of
appreciable condensation till shortly before the collector or diffusor. This
can be achieved readily through beam formation by known optical means.
The data regarding the device and the procedur~ suited for this
case are listed below:
Mixture NuF6 Ar
Input pressure PO - 2 bar
Input temperature To = 300 K
Width of nozzle gap 0.02 mm
Final nozzle width 1.3 mm
Nozzle wall of polychlorotri-
fluoroethylene ~CF2 - CPCl~n
Layer thickness of the UF6-
containing gas jet layers 0.3 mm
Layer thicXness of UF6-free
gas jet layers 0.3 mm
Pressure at the peeler ~5 mb
, 20 Pressure behind diffusor <150 mb
Wave number of the laser at about 628 cm
(~3-Q-branch of the
235 UF6)
Laser power density approximately 200 W/cmZ
with one-time beam trans-
versal. It can be
reduced further through
i repeated beam transversal
(forward and back).
It should be noted that the presentation of the device examples is
~j of a schematic nature and that these can be modified or adapted dependin~ on
-, the method to be carried out thereby, such as was mentioned already at the
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outset and in the Examples. Thus, it is, for instance, not all~ays necessary
to take the adiabatic expansion down to temperatures beLow lOOK, for instance,
in the separation of boron isotopes. The shape of the nozzle and the oper-
ating conditions can then be chosen accordingly. This applies also to the
; choice and manner of conducting the electromagnetic wave, which in general
is a laser radiation. With mirror systems, not shownJ this radiation can
pass through the irradiation chamber several times~ for instance, in the
same direction or in opposite directions or also as a standing wave. It is,
of course, also possible to introduce a combined wave, for instance, of
ultraviolet and infrared radiation, into this device. In all cases the
advantage of the separation or enrichment methods carried out by means of
the device according to the invention consists in that the detrimental in-
fluence of the boundary layer is largely eliminated and, in particular, that
the separated particles alone or together w;th a neutral intermediate gas
are collected so that no substantial weakening of the enrichment or separation
process due to the method can occur via the output substance xixture.
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