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Патент USA US3041146

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June 26, 1962
W, H, HEDLEY ETAL
3,041,136
FLAME DENITRATION AND REDUCTION OF URANIUM
NITRATE TO URANIUM DIOXIDE
Filed April 8, 1960
'
4
l
2 Sheets-Sheet l
June 26, 1962-
w.'H. HEDLr-:Y ETAL
FLAME DENITRATION AND REDUCTION OF URANIUM
,
Filed April 8, 1960
3,041,136
NITRATE TO URANIUM DIOXIDE
2 Sheets-»Sheet 2
` INVENTORS
¿Z50/avg
United States Patent O "ice
2
1
~
3,041,136
FLAME DENITRATIQN AND REDUCTION 0F
URANIUM NHTRATE T0 URANIUM DÍOXIDE
William H. Hedley, Kirkwood, and Robert I. Roehrs, St.
Louis, Mo., and Courtland MJHenderson, Xenia, Ohio,
assignors, by mesne assignments, to the United States
of America as represented by the United States Atomic
Energy Commission
Filed Apr. 8, 1960, Ser. No. 21,071
5 Claims. (Cl. 23-14.5)
The present invention `deals with a process for con
3,4l,i36
Patented .lune 26, 19562
FIGURE 1 is a diagrammatic illustration of the ap
paratus; and
FIGURE 2 is a vertical sectional view of the reaction
chamber proper.
Referring to FIGURE 1, the reaction chamber in
which the dehydration, denitrification and reduction takes
place is designated 101. A storage vessel for the aqueous
uranyl nitrate is shown as 103. Positioned just below the
reaction chamber 101 is the receiver 105. . Cyclones 107
10 and 109, to remove solid products from the gases, are
connected to the receiver 105 by pipes 106 and 108. A
verting aqueous uranyl nitrate to uranium `dioxide and
filter 111 is connected to cyclone 109 by pipeline 110.
hydrates and their solutions.
atmosphere by pipe 116.
A gas cooler 113 is connected to the outlet of the filter
an apparatus therefor. This process will hereafter be
111. The outlet of the gas cooler 113 is connected to
referred to as the “flame process.” The term “aqueous
uranyl nitrate” will -be used to cover both uranyl nitrate 15 an absorber column 115 which communicates also to the
It is an object of the invention to accomplish the
denitrification and reduction of aqueous uranyl nitrate in
a single step, decreasing the costs of the operation sub
stantially.
A rotary seal 119 communicates between the receiver
105 and a hopper 117. Similar rotary seals 121 and 123
connect the solid outlets of cyclones 107 and 109 to hop
20 per 117. A boil down tank 125 is connected to transfer
pump 127, thence to storage vessel 103.
In operation, a reducing flame is produced in the re
action chamber 101 by the incomplete combustion of a
uranium fluoride in that it reacts rapidly and completely
hydrocarbon gas such as propane. To obtain the reduc
with hydrogen fluoride to produce uranium tetrafluoride
of very high purity. This tetrailuoride is a very important 25 ing flame propane is burned in a deficiency of air. A
flame in which there is supplied less than 70% of the
intermediate material for the production of uranium
theoretically required air to burn the propane is Well
metal by reaction with calcium or magnesium. It is also
suited to the process. Aqueous uranyl nitrate is admitted
a very useful intermediate in the production of uranium
to the reaction chamber ‘101 from storage vessel 103.
hexafluoride. This is the- compound of uranium utilized
in the diffusion process of enrichment in the isotope 30 Some of the U02 produced drops into receiver 105; fur
ther amounts are separated from combustion gases by
Uz35_
cyclones 107 and 109. The last traces of U02 are re
It is also an object of this invention to produce uranium
moved by the ñlter 111. The combustion gas then is
dioxide in a form that can be stored for long periods of
cooled by the cooler 113 and nitric oxides absorbed in
time with substantially no deterioration by conversion to
higher oxides through mere contact with air at ordinary 35 the absorber column 115 before the combustion gas ex
hausts to the atmosphere.
temperatures. This occurrence would require further
Referring to FIG. 2, a tubular shell 201 is 6 feet long
reduction before conversion could be made to the fluo
and 34 inches in diameter. At the top of this shell an
ride. Otherwise there would be contamination with oxyupper flange 203 is welded extending radially outward.
fluoride and other undesirable compounds.
Finally, it is an object of the invention to furnish an 40 Lower flange 205 is welded to the bottom of shell 201,
extending radially outward and inward therefrom. The
apparatus capable of converting aqueous uranyl nitrate to
outer
periphery of shell 201 is covered with pipe insula
uranium dioxide smoothly, completely and continuously.
tion 207. Inside of shell 201 are, in order, a first insula
The present practice for converting aqueous uranyl
nitrate to uranium dioxide normally requires three steps. 45 tor layer 209, consisting of a layer of a few inches of a
material of extra low thermal conductivity, such as high>
The usual starting material is an aqueous solution, so the
temperature service mineral wool Iblocks, a second insula
first step involves driving off sufficient water to form the
tor layer 211 consisting of a few inches of a material of
molten hydrate. Next, sufficient heat is supplied to drive
low thermal conductivity such as ñre brick or alumina
off the water of hydration and to decompose the uranium
bubbles,
and an inner refractory layer 213, made up of 6
nitrate and obtain uranium trioxide. Finally, reduction
rings of silicon carbide, one on top of the other in longi
t0 uranium dioxide is accomplished by passing either
tudinal alignment, each ring having one edge concavely
hydrogen or cracked ammonia through the heated tri
rounded and one edge convexly rounded. This construc
oxide. It is usual to perform each step in different equip~
tion is employed to retain alignment. All insulating
ment.
e
layers and the pipe insulation are supported by lower
The denitrification step may take place in a fluidized
55 flange 205. 'I'he inner layer 213 defines a reaction
bed or in a batch reaction vessel. Further, the hydrated
chamber 213a which is open at its bottom to and com
salt may be passed onto a bed of trioxide previously
It is a further object of the invention to produce a
unanium dioxide very well suited for conversion to
formed by a screw or other mechanical device. The re
municates with receiver 105 (see FIG. 1). A cylindrical
flame throat 301 is located within the upper portion of
duction also may be carried out either in a fluidized bed,
chamber 213a and is provided with a ñange 301a extend
in a mechanically agitated bed, or in a moving bed. It
60 ing outwardly therefrom near the top of the throat.
is also possible to carry out the reaction lbatchwise under
Throat 301 is coaxial with shell 201 and is formed from
static conditions using thin layers of the trioxide in a
graphite. The top of the flange 301e is flush with the
reaction vessel.
top of the shell 201. This throat 301 is secured to and
The invention herein described can accomplish all three
supported from an annular plate 303 which rests on and
steps in a single operation, but for economic reasons 65 is fastened to upper flange 203 by bolts 305 and extends
it is preferable to concentrate a uranium solution to the
from throat piece 301 to the edge of insulation 207. A,
molten hydrate stage before the process of this invention
smaller annular plate 307 rests on the larger plate 303
is applied. Therefore, the preferred embodiment of this
invention replaces only two steps of the usual process.
and is flush with the top of throat piece 301.
A burner assembly 309 comprises a double-walled
The >equipment for one workable means for effecting 70 metal cylinder 313 which` has a lower flange 315 extend
this one step reaction and the flow sheet are shown in the
ing outwardly from the base thereof, and has an air inlet
line 317 leading into the volume between the walls of
following drawings wherein:
`
3,041,136
- onrls` lf the llame is not established within that time, the
solenoid valve closes and can not be reopened for ap
proximately 30 seconds. - However, if the flame is estab
shell 313; and a gas inlet line 31.9 passing through both
l walls of shell 3ll3.l The burner assembly`3ll9 .is secured
to plates 303 and 307 `by boltsl 311 passing through ñange‘
lished the detection system is engagedl and holds lthe, feed
315. Both walls of shell 323 curve inwardly at the top.
The outer wall of shell 313 .is closed by cover 321. A 5 gas solenoid open as long as it detects a flame. An ex
cess of propane is fed .to the unit in order to simul
:llange 32la extends inwardly froml lthe inner wall of
taneously denitrate and reduce the uranyl nitrate to U02.A
shell 3213 a short distance below the point at which it
The flow of combustion gases is then increased to a
starts curving inwardly. Shell 313 is coaxial with shell
desired level and the llame is maintained automatically.
201.
The feed system is. constructed so'thateither water or
A cylindrical body 323 having an annular recirculation aqeuous uranyl nitrate can be forced through the spray
chamber‘325 therein and .surrounding a flame channel
nozzle. Common practice is to »ilow water through the
341 conforms closely to the inner‘wall of shell 313 he
system prior to introducing aqueous uranyl nitrate.
tween flange 321a and the bottom of shell 313. Ports`
There are two reasons for doing so.
327 pierce the top of body 323 and ports 329 pierce body
323 at its bottom.'
lA funnel tube 331 has its top aligned with and con
nected to the incurved end of the inner wall of shell 313
and forms a venturi 333 for the entrance of air from air
inlet 317.l The funnel. tube' 331 forms with the upper
incurving end of the inner‘wall'of the shell 313 and the
. increase toa flow rate equal to the anticipated flow of
the aqueous uranylnitrate, the unit will approach an
' equilibriuml condition and therefore the temperature in
the unit will not drop when the nitrate is introduced.
Aqueous uranyl nitrateis not allowed to .flow until the
flange 32M a gas inlet'chamber 333e` which communi» .
temperature of the exit gases at the bottom of the re
cates with gas inletl line 3119. A conical ring 335 aligned
with and connected to flange 321e forms with funnel
actor‘has reached approximately 1800° F. This tem
perature -is' experimentally,determined as being sufficient
for denitration and reduction of :uranyl nitrate to U02.
tube 331 an orifice 337 for the entrance lof gas from.
linlet 319; Air‘ignition plug 339 passes through both
It is measured with a-sheathed chromel-alumel thermo
walls of chamber member 323 into ñame channel 341
i - and when activated ignites the air-gas mixture. . The
couple.
.
.
In this process, denitration .must take place almost'in- .
continuance of the llame in channel. 341 is monitoredby '
stantly, .but reduction to U02 of the powder formed takes '
flame detector 343 essentially an ultraviolet sensitive de
- . ï vice which penetrates into chamber 341.
First, the Water
.keeps the nozzle from becoming overheated during the
preheat cycle. Second, if the flow of water is allowed to
1
place only as the particles travel down the .length of the
The function of
chamber 325 is to allowthecirculation of. the. hot com
1 reactor. This was demonstrated by some early pilot-scale
`bustion products to heat the combustion gases fed into
chamber 34d and thus facilitate their combustion. A
runs with inadequate-reduction in which the product con-`
sisted predominantly of nitrate free UaOß. `It is believed
that there :are'four main factors which affect the con
passes throughl cover 321 and ilame channel 341 to 35 version of‘aqueous uranyl nitrate to U02 bythe flame
process. They are droplet size, gas temperature, rel enter the chamber'213a. Nozzle 3fl5‘is water cooled and
ducing power of gases and residence time. Early ex
insulated (details not shown). The burner .is therefore
built around the spray nozzle and the feed is introduced \ periments` resulted in 'USOS as a product `when using. a
lliquid droplet lsize of about 4t() microns or less, a gen
along the burner axis.
‘
p
' l
l
l '
pneumatic atomizing liquid spray nozzle assembly 345
erous excess of propane, an exit gas temperature of 1800° .
Propane, vaporized‘at 50 p.s.i.g.- enters the apparatus
through inlet tube 319; air enters through its inlet 317,
F. and a reaction chamber four inches in diameter by
one foot long. Since the use of small particle size, ex
cess propane and high gas temperature alone did not
also at 50 p.s.i.g. The gases ignite and pass into the
chamber 2‘13a through the area between chamber mem
ber 323 and the spray nozzle assembly 345. Meanwhile
flame detector 343 detects the flame and releases a liquid
through spray 345. At first the liquid is ordinary water,
produce U02, it was decided that increased residence
time in the reactor would be tried. Another reaction
`chamber three feet long and live inches in diameter was
until a temperature in excess of 1500° F. is detected in
therefore constructed. Operating with this longer cham
the reaction chamber by a thermocouple (not shown).
Then aqueous uranyl nitrate is admitted under pressure
through a control valve (not shown). The droplets of
ber at the same gas and the liquid flow rates used pre
viously, it was possible to produce U02 routinely with
exit gas temperatures of approximately l800° F. In the
apparatus used introduction of the feed parallel to the
aqueous uranyl nitrate enter the zone with the com
bustion gases, and are dried, denitrated and converted to
burner axis is also important. Trial runs were made em
ploying nozzles which directed the spray into the flame
U02 by the time they reach the bottom of the chamber.
in a direction perpendicular to the flame. In these runs
It has «been found that with the pressures used, a length
55 the water was not all evaporated before it hit the opposite
of about 6 feet is sufficient to complete the reaction.
wall.
The above-described unit is capable of converting
In order to prevent freezing of the aqueous urtanyl
aqueous uranyl nitrate to the dioxide in a single step,
nitrate in the lines, Ia dilute liquid containing only 4.3
combining dehydration, denitriñcation and reduction. It
pounds of U/gallon (approximately 50 w/o uranyl ni
is also capable of converting the molten hydrate to the
dixoide in a single step. The properties of the uranium 60 trate) has been used as the -feed for most of the runs.
However, three runs have been made using concentrated
dioxide so produced are superior to those of the ordinary
liquid containing 12.0 to 13.0 pounds of uranium per
product, as will be shown later in the specification. The
gallon (uranyl nitrate hexiahydrate contains 9.75 lbs.
operation of the apparatus will now be described.
Prior to establishing a llame, nitrogen or other inert
gas is used to purge the reaction chamber. The com 65
U/gal.).
This equipment and process has been found capable
of using solutions of uranium nitrate containing up to
13 pounds of uranium per gallon. The preferred con
button on the flame detection unit. This sends current
centration is the highest concentration which can be used
to a spark plug-type ignition rod located in the com
without plugging the nozzle, because this lowers the pro
bustion area and also energizes two solenoid valves, one
in the propane line and one in the air line. Opening of 70 pane consumption per pound of uranium processed, and
also the olf-gases from the process will be licher in by~
these valves allows a predetermined mixture of propane
product nitrogen oxides which will make their recovery
and air to ñow through the burner and ignite by means
easier. The `apparatus described is able to handle 160
of the spark from the ignition rod.
bustion mixture of gases is ignited -by depressing a start
During ignition, the electronic network of the llame
detection system is `bypassed for approximately 15 sec
gal/hr. of the l0 lbs. of U/gal. liquid.
Heating and
75 reduction of this quantity requires 380 pounds of pro»
3,041,136
5
6
pane »and 6880 cu. ift. of 1‘00 p.s.i.g. fair per hour. This
TABLE III
produces a product U02 having unexpectedly desirable
Spectrographic Analysis for Trace Impimties in U02
properties.
In evaluating the product obtained by the iiarne process,
both chemical and physical properties have been rather
Flame proc-
-Fluid bed
exhaustively investigated.
ess (p.p.m.)
(p.p.m.)
(Run D-15)
EXAMPLE
A series of runs were made in the pilot scale apparatus
with 4a 3 «foot chamber length and an exit gas tempera
ture approximately 1800" P. During these runs aqueous
ur-anyl nitrate was used in ia concentration ranging from
U02 made by other processes.
TABLE I
ee
NO3
H20
<0.1
<0. 1
<0. 03
<0. 6
U02
85.6
80. 9
15
eo
<0.5
<0. 5
so
2o
<10
<10
<10
<10
4
20
1o
2o
2o
<2
<1
<2
2o
7c
3
<20
<1
<20
70
<50
(such as Cu and Zn) lare probably 'derived from com
95. 7
88. 1
Pponents `of the experimental iapparatus that require fur
ther engineering design.
30
The llame process ‘U02 contains considerably less than
the 100 ppm. iron and 75 ppm. nickel which are the
lonly limits for green salt.
Trouble is not anticipated
with any of the trace elements in this process.
In both cases efforts were made to cool the sample to
room temperature before exposing it to ai-r. Because
Reactivity with hydrogen fluoride-'liable IV shows
the HF concentrations, reaction completion times, and
reaction temperatures used for llaboratory hyidroñuorina
tion evaluation of various `oxide samples. All data listed
it is difficult to iget a sample lanalyzed without oxidation
occurring, 95% free U02 is among the highest percent
»ages ever analyzed.
<1
15
<1
The differences in concentration of impurities in these
'I'hose elements
that appear to be higher in the llame process material
Percent Percent Percent Percent
Flame process (batch D-22) ........ __
Mall‘mckrodt fluid bed product ____ ._
<10
<o.10
<0.]
<1
r two samples lare small in most cases.
[Chemical Analysis]
U-H
<10
<0.1o
<o.10
<1
-
nium. Several batches were selected for tests. Since
a large number of tests were to lbe made and the tests
were lengthy, the tests were not repeated on every batch.
Comparisons were made in each case with available
«
<o.1
<10
4
<1
l5
4.2 to 13.0 lbs. uranium per gallon. Aqueous uranyl
nitrate containing 12.9 lbs. U/gal. was smoothly con
verted to \U02 iat the rate of 35.0 pounds of uranium'per
hour, using 0.225 pound of propane per pound of ura
Oxide source
4
10
U02 used to make UF4 in ia com
in this section were obtained from runs in a thermo
pletely enclosed, leakproof system would probably under
b-alance.
go less reoxidation.
TABLE IV
Stability of flame process 'U02 against atmospheric oxi
dation-_Samples of llame process U02, in layers less
Reactivity With Hydrogen Fluoride
than 1/8 inch thick, were placed in open bottles and left
exposed to the atmosphere for varying lengths of time.
The results are shown in Table II.
Hydroñuorination
reaction
45
Oxide
HF, w/o Comple- Reaction
TABLE II
Y Stability of Flame Process U02 Against Atmospheric
Oxidation
Percent
Percent
at room
U+4
free U02
temp.
° C.
50
Flame process U02 ___________________ ._
Time in Weeks
exposed to air
tion
time,
mins.
[Oxide Source: Flame Process Run 12]
temperature
Concen
tration
55
t0 U02) ____________________________ __
100
7
396~398
67
32
100
100
100
22
55
3G
<0. 7
7
390-392
398
402-405
495
504-510
100
22
498-501
100
33
506-509
Fluid bed U03 (laboratory reduced to
2
5
11
83.3
83.2
81. 9
91.9
91. 7
89.6
U03) _______________________________ ._
As shown in Table IV, the reactivity of llame process
60 material with either anhydrous HF or 70%
is ex
ceptionally good. Times vfor complete reaction for sev
eral runs with this material have ranged from 7 to ‘13
minutes using anhydrous HF at 400 C. The reactivity
of the fluid bed U02 is considered to be an average value
paratus Iduring original cooling. The oxidation which 65 for plant material run at 400° C.
took place on standing was not excessive even under these
The extreme reactivity of flame process material is
very adverse conditions. In plant practice it would not
4greatly emphasized by noting its lower completion time
be necessary to expose U02 -as thoroughly or for such
with 70% HF when compared with that of fluid bed U02
long periods as this, and thus the amount yot” oxidation
that was treated with «anhydrous HF. The 32 w/o HF
which would take place under these circumstances should 70 run with llame process U02 shows that this material can
be considerably less.
utilize HF in almost any concentration, »and that it should
U02 trace impurities-Samples of llame process U02
be compatible 'with the low excess HF process change
vThe lamount of free »U02 in the samples at time zero` is
uncertain, but is known to have been less than 95%.
This is believed to fall short of a 100% U02 product by
reason of incomplete protection in the experimental »ap
and Weldon Spring plant fluid bed U02 were «analyzed
spectrographically. The results of this analysis are listed
below:
'
being installed in the Weldon Spring plant, thus insuring
the llowest possible raw materials cost for hydrotluorina
75 tion.
3,041,136
Green salt properties-_Samples of ñame process U02
TABLE VII
and
were hydroiiuorinated
. `U02 from standard pot U03
.
P article
.
.
.
Si. e Distribution
b
with 100 w/o HF at several diiïerent temperatures. The
analyses of the green salt produced are listed in Table V.
TABLE V
Z
5
.
Mzcromero
ra h
y
t
Oxide source
g p
Diameter equal to Orlcssthan l
Green Salt Properties
.
Hydrolluorination temp. ° C. Flame
Process
AOI
Peak
Level
U02
DCI‘CCIlÉ
uns#
percent
UO from std. ot UO
2
p
3
(Run
D 22)
,
AOI,
WS.,
““““ "
In i1 fred---------- _'
UH,
50%
5%
Microns
Micrims
llíicrmis
w
»
_
15) """""""" '
10 Fluid heli
UH,
percent
95%
g1
’
_
>100'
40'
2'5
_
>100
44
4.5
“““““““““““““““““““ "
'
percent percent percent
l This signifies, for example, that 50% of Run D-15 U02 has a particle
458
422
(l O8
3. 71
73“ 0
0. 83
2“ 77
73' s
535
510
530
5(7)5
0. 05
0.06
0. 00
3. 57
73.1
74.
0
73.2
0. 3s
0‘08
0. 2ï
2. 70
4_37
4.59
73.8
72.
5
2.1i
size equal to or smaller than 2.3M.
6Go
647
0.21
L 35
7¿1_ 8
0.21
3. g5
i218
„
'
_
The above data'show that
ñamehprocess~U02 has v_irtu
ally the same particle size distribution as high fired micro»
nized material. The fluid bed U02 and the high fired U02
730
722
1. 50
1.00
75.1
2.07
4. 20
12.9
have very nearly the same particle size distributions, but
755
755
T50
1' 50
‘5-5
5-12
/4‘ ‘
both are much larger than those of micronized or flame
558
g
2.38
3.18
17-7
15
1 W.S. means water soluble and indicates UOgFs; AOI 20 process U02'
The particle Slze dlstnbutlon of flame
means ammonium oxalate insoluble and indicates unconvei-ted
PYOCCSS U02 has been nearly Constant for au funs Checked,
oxide.
with approximately 99 W/o of the material having a di.
Uranium tetratliioride is often called green salt.
The analyses show that low AOl green salt can be proamcter between ‘1/2 and l() microns.
duced on a laboratory scale from both materials at temThe average particle 4sizes of the same types of powder
peratures up to 660° C. In the hydroiluorinations at tem- 25 as determined by Fisher Sub-Sieve Sizer are listed below:
peratures of 72.2° C. and above, the AOI’s increased due
to thermal damage of the oxide. The llame process U02,
TABLE VIII
however, was less sensitive to thermal damage than was
Average Particle Size as Determined by Fisher Sub-Sieve
the standard material used for comparison. This seems
Sizer
'
s
.
Avei‘a o article
r@a so n able becau se powders compo S ed of small particle
30 Onde
Source:
me 1% 11121 icmns
tend to be less susceptible to thermal damage. The inaterial chosen for comparison is standard pot U03 which has
been laboratory reduced to U02. The indicated lower
`
D 22
o 93
F‘É‘me Proces? (Run T ) ‘‘‘‘‘‘‘‘ ‘- 0 60 1'08
susceptibility of iiame process U02 to thermal damage
Fluld b‘ed ------------ n
could ‘be of real advantage in production by reducing the 35
hlgh ñled ----------------------- “
Mlcfûmzed hlgh med -------------- _“
number of lots of green salt rejected for high AOI.
'
_2‘43
4'05
’
The results of these particle size measurements substan
. The U02 samples used in these runs contained rela-
tiate the conclusions drawn from Micromerograph meas
>tively large amounts of U2O2, probably due to partial re-
memems,
oxidation of U02 which had been exposed to the 'atmos-
Densiti'es of cold pressed and síntered U02 compacts
Phol'o before oomploto Cooling» The Presollœ of 11h15 Usos 40 Samples of several types of U02 were cold pressed to form
accounts for the relatively high water soluble contents of
the low temperature runs as compared with plant green
pellets which were ñred under a hydrogen atmosphere.
The results listed in Table IX compare the densities of
Salt. `
the pellets produced with the maximum theoretical density
v
_
_
.
Physical PFOPÚI'UGS--Tho Physlcaltpfopßrties of the
of UO2 (10.97 grains per cubic centimeter) and are the
iiame process product to be discussed include U02 X-ray 45 highest attained by this method for each powder, at the
analyses, U02 particle size, densities of cold pressed and
conditions listed.
sintered U02 compacts, U02 surface area, and tap density.
The llame process, .the micronized high-fired and the
U02 X-l'fïy ílf1f1_lyS@S~*X-fay analysis has been Used t0
standard Weldon Spring Huid-bed pellets were all fabri
determine the unit cell size, the strain, and the crystallite
cated and ñred by the same procedure; therefore, their
size for iiame process U02 and for lluid bed U02. These 50 densities should be directly comparable.
values are listed in Table VI.
The high-iired `screwereactor powder which had not
TABLE VI
been micronized was not iired as long nor at as high a
temperature as the other samples. A longer, higher~
~
U02 X-Rfly Analysis
temperature ñring of the material would be expected to
55 increase the density of the product slightly, but not to the
Flam@
process
U 02 (Run
.
extent that it would equal the micronized screw-reactor
Fluid
_
Bed U02
"22)
Unit ceu size A ______________________________ __
Strain, diinensionless_-_
Crystaiiite size A ____________________________ -_
5.4084
Nono
1,150
.
material, or llame-process material. The pellets evaluated
were cyiindiical in shape (0.4” in diameter by 0.4" high).
5. 40s G0
0. 055
TABLE IX
_ ~
800
`
Denszties of cold pressed and szntered U02 c0mpacts.--
The unit cell size of both «flame process U02 and fluid
commu Percent
bed U02 are the same within the limits of measurement.
_
U02
The composition
can definitelyofvbethe
established
main phase
as being
of thebetween
flame process
UOMO 65
Firing Finne
Onde Source
mangi'
tion
Ofmfix.
máis/m
sq. in. density
and U02_01, probably closer to U02'20.
A statistical analysis of the X-ray data shows that the
ä/iëilln@ igrßâßïlëîIí-ï--d-«î ------ »strain trapped in the lattice of llame process U02 is not
*
different from zero within 95% confidence limits. Based 70 Stälìlâlard Weldon Sprintr Iluid~
on this saine analysis, the crystallite size is 1150i10()
angstrorn units within 95% confidence limits.
20
20
2O
1y 700
17700
1 0
16
m2352222.“ggg;"r2-„55657155“
mlßl‘OlllZlDs) ----------------- --
50
50
96.1
95.1
’7 0
50
92'2
1,635
100
91.7
U02 particle size-«The Microinerograph particle size
distribution of U02 producgd by Various methods is Shown
.
in Table VII.
1 The 'temperatures listed were obtained by means of an optical pyrom»
eter which had been sighted on the molybdenum bout in which the
75 pellets were fired.
‘
3,041,136
10
by this flame process. Analytical results are not yet avail
Pellets produced yfrom lflame process U02 are slightly
more dense than those produced from micronized high
tired U02 and yet `did not require the further expensive
particle size reduction.
able, but X-ray analysis indicates that the product from
thorium nitrate is Th02 with no other phases detected.
It will be understood that this invention is not to be
limited to the details given herein, but that it may be
modiiied Within the scope of the appended claims. In
particular the apparatus portion of the invention is not
limited to the device described in detail. For example,
it may be desirable to use multiple spray nozzles operat
ing parallel to each other; it might also, under some cir
cumstances, be advantageous to spray countercurrent to
The cost of micronizing one ton of U02 at a rate of 25
pounds per hour has been estimated at $1,466.26. While
this cost might be lowered considerably if the rate could
be increased »to 50 or 75 pounds of U02 per hour, the
cost of micronizing would still be many times larger than
the flame process cost of converting uranyl nitrate l-iquor
to U02. This cost could be completely saved in cases
Where flame process U02 could be successfully substituted
for micronized U02 in ceramic applications.
U02 surface area-Table X shows .the surface area of
several U02 powders.
v
TABLE X
the hot combustion gases.
with a pressure atomizing nozzle, but a pneumatic atom
15 izing nozzle could eliminate this need for high pressure.
In general an apparatus for the process must include,
for satisfactory operation:
U02 Surface Area
BET surface area
OXlde SOUICSÍ
sq. meters/ gram
Flame process (Run D-22) ______________ __ 2.6
Fluid bed
____
High pressure would be re
quired to form liquor droplets of sufficiently small size
_
3.14
Normal screw _________________________ _.-
1.38
High tired _____________________ __ _____ __
0.57
(1) A feed system;
(2) An insulated tubular reactor;
20 (3) A spray nozzle positioned parallel to the axis of the
reactor;
(4) A burner for continuously burning a fuel gas-air
mixture with less than the stoichiometric amount of
Micronized high fired ___________________ __ 2.19
air to produce hot reducing gases;
The surface area (as determined by lthe BET krypton 25 (5) An ignition system;
(6) A llame detection system;
method) is approximately 2.6 -square meters per gram lfor
(7) Devices for collecting the products.
the three samples of flame process U02 evaluated thus far.
e value determined for the fluid ybed U02 is slightly
It is intended that the invention include all variations in
higher than that of ñame process U02 even though its
methods of assembling the apparatus.
agglomerates are much larger than those of the llame 30
What is claimed is:
process material. This is probably due to a large amount
1. A process for converting uranyl nitrate solution to
of surface area inside the ñuid ybecl U02 agglomerates, but
uranium dioxide comprising spraying fine droplets of
the reason why ñuid bed U02 reacts so much more slowly
aqueous uranyl nitrate solution into a high temperature
than flame process U02 is unknown.
35 hydrocarbon llame, said ñame being deficient in oxygen
Tap Densiiy-(a)-U02.-The tap densities of several
approximately 30%, retaining the feed in the llame for a
types of U02 are listed in Table XI.
siu‘îicient length of time to reduce the nitrate to the diox
ide, and recovering uranium dioxide.
TABLE XI
U02 Tap Density
Oxide source:
2. A process according to claim 1 wherein the reduc
40 ing flame is formed by air and an excess of propane.
Tap density, gJcc.
3. A process according to claim 2 wherein the feed is
introduced axially of the llame.
4. A process according to claim 3 wherein the flame
is maintained at such a temperature that the temperature
Flame process ______________________ __ 1.5-3.6
Fluid bed
_____ __
~4.5
Micronized high fired ______________ __ 2.74-3.50
oi the exit gases is at least 1800° F.
5. A process according to claim 4 wherein the droplets
of aqueous uranyl nitrate solution are no greater than 40
microns in diameter.
High fired ________________________ __ 4.3-4.42
These numbers express the range of values which have
been obtained for each material. The tap densities of
the recently produced ilame process U02 have all been
at the high end of the range listed. In recent experi- .
ments, it has been possible to raise the tap density of 50
flame process U02 by changing operating conditions, and
it is believed -that the upper limit has not yet been reached
for this material.
(b)-UF4.--Green salt was prepared by hydrolluori 55
nating llame process U02 with 100i w/o HF batchwise
in a laboratory furnace. The range of tap densities for
this material and for plant UF4 are listed below:
TABLE XII
Green Salt Source:
2,267,720
2,613,137
2,735,745
2,737,445
2,757,072
2,761,767
2,903,334
60
Tap Density of Green Salt
'
References Cited in the rile of this patent
UNITED STATES PATENTS
-Cyr ________________ __ Dec. 30,
Hellwig _____________ __ Oct. 7,
Flook et al. __________ __ Feb. 21,
Nassen ______________ __ Mar. 6,
Kapp et al. __________ __ July 31,
Perieres _____________ __ Sept. 4,
Buckingham __________ __ Sept. 8,
1941
1952
1956
1956
1956
1956
1959
FOREIGN PATENTS
density of
661,685
Great Britain _______ ___ Nov. 28, 1951
U 4, gms/cc.
707,389
Great Britain ________ __ Apr. 14, 1954
'l‘a
Flame Process U02 (laboratory hydrofluori
nated to U'F4) ___________________ -_ 1.7-2.3
Screw Reactors _____________________ __ 3.1-3.8
65
OTHER REFERENCES
Ser No. 379,872, Ebner (A.P.C.), published Apr. 27,
1943.
_
The recent values of tap density for llame process ma
Katz: “The Chemistry of Uranium,” 1st edition, pages
terial have been at the high end of the range quoted.
303, 304, 307, McGraw-Hill Book Co., New York, N.Y.
However, as in the case of tap density for iiame process
U02, this is not considered to be the maximum attainable 70 (1951).
Johnson et al.: “Ceramic Bulletin,” vol. 36, No. 3, page
value.
Further experiments have been made in which thorium
nitrate, thorium-uranium (5 weight percent uranium) ni
trate and aluminum nitrate solutions have been treated
116 (1957).
MCW-1429, pages 57-75, May 1, 1959.
Y
V
Hedley et al.: MCW-l45‘1, pages 19-24, Aug. l, 1960.
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