CA1241202A - Process and apparatus for recovering metallic uranium scrap - Google Patents
Process and apparatus for recovering metallic uranium scrapInfo
- Publication number
- CA1241202A CA1241202A CA000479832A CA479832A CA1241202A CA 1241202 A CA1241202 A CA 1241202A CA 000479832 A CA000479832 A CA 000479832A CA 479832 A CA479832 A CA 479832A CA 1241202 A CA1241202 A CA 1241202A
- Authority
- CA
- Canada
- Prior art keywords
- uranium
- molten
- bath
- reservoir
- column
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- JFALSRSLKYAFGM-UHFFFAOYSA-N uranium(0) Chemical compound [U] JFALSRSLKYAFGM-UHFFFAOYSA-N 0.000 title claims abstract description 140
- 229910052770 Uranium Inorganic materials 0.000 title claims abstract description 139
- 238000000034 method Methods 0.000 title claims abstract description 19
- 150000003839 salts Chemical class 0.000 claims abstract description 42
- 238000002844 melting Methods 0.000 claims abstract description 19
- 230000008018 melting Effects 0.000 claims abstract description 18
- 229910001635 magnesium fluoride Inorganic materials 0.000 claims abstract description 13
- 239000000203 mixture Substances 0.000 claims abstract description 12
- 229910052747 lanthanoid Inorganic materials 0.000 claims abstract description 11
- 150000002602 lanthanoids Chemical class 0.000 claims abstract description 11
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 claims abstract description 4
- 229910001634 calcium fluoride Inorganic materials 0.000 claims abstract description 4
- 229910009527 YF3 Inorganic materials 0.000 claims abstract 3
- 229910001632 barium fluoride Inorganic materials 0.000 claims abstract 3
- PQXKHYXIUOZZFA-UHFFFAOYSA-M lithium fluoride Inorganic materials [Li+].[F-] PQXKHYXIUOZZFA-UHFFFAOYSA-M 0.000 claims abstract 3
- 239000012535 impurity Substances 0.000 claims description 12
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 10
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 8
- 229910052799 carbon Inorganic materials 0.000 claims description 7
- 229910010293 ceramic material Inorganic materials 0.000 claims description 7
- 238000004891 communication Methods 0.000 claims description 7
- 229910052751 metal Inorganic materials 0.000 claims description 7
- 239000002184 metal Substances 0.000 claims description 7
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 6
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 6
- 239000010936 titanium Substances 0.000 claims description 6
- 229910052719 titanium Inorganic materials 0.000 claims description 6
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 4
- 239000012530 fluid Substances 0.000 claims description 4
- 229910052757 nitrogen Inorganic materials 0.000 claims description 4
- 229910052710 silicon Inorganic materials 0.000 claims description 4
- 239000010703 silicon Substances 0.000 claims description 4
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims description 4
- 239000007787 solid Substances 0.000 claims description 3
- 229910004369 ThO2 Inorganic materials 0.000 claims 1
- ZCUFMDLYAMJYST-UHFFFAOYSA-N thorium dioxide Chemical compound O=[Th]=O ZCUFMDLYAMJYST-UHFFFAOYSA-N 0.000 claims 1
- 238000005266 casting Methods 0.000 abstract description 2
- 239000008188 pellet Substances 0.000 description 12
- 239000000463 material Substances 0.000 description 5
- 239000000919 ceramic Substances 0.000 description 4
- 229910002804 graphite Inorganic materials 0.000 description 3
- 239000010439 graphite Substances 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 239000002699 waste material Substances 0.000 description 3
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 2
- -1 Nail Chemical class 0.000 description 2
- CFQGDIWRTHFZMQ-UHFFFAOYSA-N argon helium Chemical compound [He].[Ar] CFQGDIWRTHFZMQ-UHFFFAOYSA-N 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- 229910052749 magnesium Inorganic materials 0.000 description 2
- 239000011777 magnesium Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000002901 radioactive waste Substances 0.000 description 2
- 238000011084 recovery Methods 0.000 description 2
- 238000004064 recycling Methods 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- 244000298715 Actinidia chinensis Species 0.000 description 1
- 235000009434 Actinidia chinensis Nutrition 0.000 description 1
- 235000009436 Actinidia deliciosa Nutrition 0.000 description 1
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- 241000824799 Canis lupus dingo Species 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000009933 burial Methods 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000012611 container material Substances 0.000 description 1
- 230000000994 depressogenic effect Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000000374 eutectic mixture Substances 0.000 description 1
- 230000005496 eutectics Effects 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000004636 glovebox technique Methods 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000004519 grease Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 150000004679 hydroxides Chemical class 0.000 description 1
- 238000005372 isotope separation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- ORUIBWPALBXDOA-UHFFFAOYSA-L magnesium fluoride Chemical compound [F-].[F-].[Mg+2] ORUIBWPALBXDOA-UHFFFAOYSA-L 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 238000005191 phase separation Methods 0.000 description 1
- 239000011241 protective layer Substances 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 239000012857 radioactive material Substances 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910001637 strontium fluoride Inorganic materials 0.000 description 1
- FVRNDBHWWSPNOM-UHFFFAOYSA-L strontium fluoride Chemical compound [F-].[F-].[Sr+2] FVRNDBHWWSPNOM-UHFFFAOYSA-L 0.000 description 1
- 239000001648 tannin Substances 0.000 description 1
- 229920001864 tannin Polymers 0.000 description 1
- 239000004408 titanium dioxide Substances 0.000 description 1
- 238000007514 turning Methods 0.000 description 1
- JFALSRSLKYAFGM-AHCXROLUSA-N uranium-234 Chemical compound [234U] JFALSRSLKYAFGM-AHCXROLUSA-N 0.000 description 1
- 229910052845 zircon Inorganic materials 0.000 description 1
- GFQYVLUOOAAOGM-UHFFFAOYSA-N zirconium(iv) silicate Chemical compound [Zr+4].[O-][Si]([O-])([O-])[O-] GFQYVLUOOAAOGM-UHFFFAOYSA-N 0.000 description 1
Landscapes
- Manufacture And Refinement Of Metals (AREA)
Abstract
PROCESS AND APPARATUS FOR
RECOVERING METALLIC URANIUM SCRAP
Abstract of the Disclosure There is disclosed a process and apparatus for recovering metallic uranium from scrap containing metallic uranium by introducing such metallic uranium scrap into a bath containing, in molten form, at least one member selected from the group consisting of BaF2, CaF2, MgF2, LiF, YF3, trifluorides of lanthanides and mixtures thereof, preferably with such member constituting at least 75 mole percent of the bath at a temperature aove the melting point of uranium and under an inert atmosphere and casting the purified molten metallic uranium. The bath of molten salt preferably includes means for improving contact between the molten metallic uranium scrap and the molten salt during passage of the molten uranium through the bath of molten salt.
RECOVERING METALLIC URANIUM SCRAP
Abstract of the Disclosure There is disclosed a process and apparatus for recovering metallic uranium from scrap containing metallic uranium by introducing such metallic uranium scrap into a bath containing, in molten form, at least one member selected from the group consisting of BaF2, CaF2, MgF2, LiF, YF3, trifluorides of lanthanides and mixtures thereof, preferably with such member constituting at least 75 mole percent of the bath at a temperature aove the melting point of uranium and under an inert atmosphere and casting the purified molten metallic uranium. The bath of molten salt preferably includes means for improving contact between the molten metallic uranium scrap and the molten salt during passage of the molten uranium through the bath of molten salt.
Description
RECOVERING METALLIC URANIUM SCRAP
Background of the Invention . .
This invention relates to the recovery and purification of metallic scrap, and more particularly to a novel process and apparatus for the production of bulk metallic uranium from metallic uranium scrap, especially scrap of depleted uranium.
Natural uranium, i.e., the material that is mined from the earth, contains 0.005 percent uranium-234 (U234), 0.7 percent U235, and 99.295 percent U23~. Depleted uranium "DU" is a by-product of isotope separation processes, prim manly the gaseous diffusion process, through which uranium containing a higher content of the U235 isotope, referred to as enriched uranium, is produced from natural uranium. En-niched uranium is used for reactor fuels and nuclear woe-puns. DU, the residue of the enrichment process, contains only a portion of the original U235 and U234 and is there-fore "depleted" in these isotopes. The isotope distribution will vary with different enrichment goals. DU is a high density metal used as counterweights in some military and commercial aircraft, as components in some military project tiles, and as shielding material in containers in which highly radioactive materials such as Kiwi are stored and used. During production of the above items, DU scrap is produced.
The values of natural and enriched uranium metal range from $40 per pound to well over $10,000 per pound, depending upon the purity and level of enrichment. Therefore, highly efficient recovery procedures, even though very expensive, are used for the recycling of these materials. On the other hand depleted uranium is worth $0.50 to $2.00 per pound in bulk, and no economically suitable scheme has been developed for recovering and reusing this scrap. Instead, several thousand pounds per day of metallic scrap (turnings, crops, rejects, etc.) are placed in drums, packed with nonflammable material, and transported to radioactive waste dumps where the drums are buried. The burial of such radioactive waste is becoming very restricted and increasingly costly.
In "Reactor Handbook," Second Edition, Volume 1, pp.
98-104, and Volume 2, pp. 379-391, the engineering aspects of industrial and governmental uranium processing are disk closed (i.e., UF4 reduction) in essentially the same manner in which uranium processing is currently being conducted/
and in particular, identifying the importance of allowing time for phase separations of molten uranium from MgF2 or Cafe, either in derby or dingo reduction. This time for separation is achieved by preheating and by size and shape considerations only; no use is made of cleaning at tempera-lure or of eutectic mixtures. Cafe, MgF2, and various oxides are identified as liners for graphite containers.
Uranium chips along with trapped debris are pressed into briquettes prior to melting under vacuum along with other metallic uranium scrap. Oxide scums and volatile impurities are identified as sources of problems in the uranium no-melting, and it is also recognized that graphite crucibles lead to carbon pickup. Oxide scums create problems also at the metal-salt interfaces during the original reductions of UF4 by calcium or magnesium.
In "Uranium Metallurgy" by W. D. Wilkinson, there is disclosed the melting of uranium chips in crucibles lined with magnesium zircon ate covered with a protective layer of a mixture of calcium fluoride and magnesium fluoride; this melting yields ingots containing 400-600 Pam of carbon.
, A, 3L2~ 2 This large carbon addition is grossly unacceptable for much uranium recycling; it is a consequence jointly of the use of an improper salt (MgF2) together with the use of an imp proper container material (graphite).
Summary of the Invention The present invention seeks to provide a novel process and apparatus for recovering, purifying and producing bulk uranium metal from depleted-uranium scrap.
In one aspect, the invention pertains to a process for producing metallic uranium from scrap containing metallic uranium, which comprises forming in a contact zone under an inert atmosphere a bath supported on molten uranium, the bath containing, in molten form, at least one member selected from the group consisting of Cafe, Buff, MgF2, Lift YF3, trifluorides of lanthanides, and mixtures thereof, with the bath being at a temperature above the melting point of uranium and the contact zone including contact means within the bath for intimately contacting the bath and the scrap containing metallic uranium, introducing under an inert atmosphere the scrap containing metallic uranium into the bath under conditions to form molten uranium, and recovering metallic uranium from the molten uranium supporting bath wherein titanium, preferably solid titanium oxide, is present to remove carbon, nitrogen, and silicon.
The invention also pertains to an apparatus for producing metallic uranium from scrap containing metallic uranium, which comprises a reservoir means for molten uranium, with a column disposed in the reservoir for a bath of a molten salt supported on the molten uranium.
~`~
I ~Z02 pa Means provide fluid for communication between the column and the reservoir, and means maintain the column and the reservoir at a temperature above the melting point of uranium. Means are provided for introducing the scrap containing metallic uranium into the column, and means are provided for removing molten uranium from the reservoir means.
In one aspect, the apparatus includes a lip means for withdrawing the molten uranium. In another aspect, the apparatus includes piston means for displacing interracial molten metal and salt including impurities.
In a still further aspect, the reservoir and column are formed of or lined with a ceramic material including an oxide selected from the group consisting of UO2, Thou, Moo, YO-YO and trivalent oxides of the lanthanides.
More particularly, the present invention comprehends a novel process and apparatus for recovering and purify-in metallic uranium from scrap containing metallic uranium by introducing such metallic uranium scrap into a bath containing, in molten form, at least one member ~2~2~)2 selected from the group consisting of Buff, Coffey MgF2, Lift YF3, trifluorides of lanthanides and mixtures thereof, preferably with such members constituting at least 75 mole percent of the bath. The molten salt bath is under an inert `, 5 atmosphere and at a temperature above the melting point of uranium. Molten uranium is recovered after passage through the molten salt bath. The bath of molten salt preferably includes means for improving contact between the molten metallic uranium scrap and the bath of molten salt during passage of the molten uranium scrap through the bath of molten salt.
Brief Description of the Drawings Understanding of the present inventions will be facile-toted by referring to the following detailed description when taken in conjunction with the accompanying drawings wherein like numerals designate like parts throughout in which:
Figure 1 is a schematic view of the process and appear-tusk of the present invention;
Figure 2 illustrates the molten salt-molten uranium system during casting of molten uranium;
Figure 3 illustrates the molten salt-molten uranium system during removal of impurities; and Figure 4 illustrates the molten salt-molten uranium system after removal of impurities.
Detailed Description _ the Drawings Referring now to Figure 1, there is provided a uranium feed-hopper assembly and a metallic-uranium melting asset-by, generally indicated as 10 and 12 respectively. The uranium feed hopper 10 is comprised of a vacuum lock hopper system and a material-storage bin, generally indicated as 14 ~2~0;~
and 16. The vacuum lock-hopper system 14 is such as known and used by one skilled in the art and includes an inert gas inlet conduit 18 and an evacuation gas conduit 20. The material-storage bin 16 of the uranium hopper assembly 10 is provided with a ceramic conduit 22 in communication with a furnace assembly, generally indicated 24, disposed within the metallic-uranium melting assembly 12 including an outer support structure 26 comprising an inert gas inlet conduit 28 under the control of valve 30 and an outlet gas conduit 32 under the control of valve 34.
The metallic-uranium melting assembly 12 includes a column 36 formed within a suitable support structure (not shown) and disposed within a cylindrically shaped reservoir 38 including a pouring lip portion 40 all formed of or lined with a ceramic material comprised of UO2, Thou, Moo, YO-YO, or trivalent oxides of the lanthanides in which one or more of these oxides jointly make up at least 75% of the compost-lion of the resulting ceramic material. The column 36 is in communication with an end of the ceramic conduit 22 which in turn is in communication with the uranium feed hopper 10.
Surrounding the column 36 and reservoir 38, there are provided heater elements, generally indicated as 42, for maintaining the temperature above the melting point of me-talk uranium, as more fully hereinafter discussed.
Within the lower portion of the column 36 and within reservoir 38, there is provided cleaned molten uranium 44 supporting a bath 46 containing, in molten form, at least one member selected from the group consisting of Buff, Cafe, MgF2, Lift YF3, trifluorides of lanthanides and mixtures thereof, preferably with such members constituting at least 75 mole percent of the bath. The bath 46 of molten salt is I, ., 3~2~
supported as a result of the differences in the densities between the bath 46 of molten salt (approximately 3 to 4 gm/cm3) and the molten uranium (approximately 18 gm/cm3).
Thus, the uranium 44 in the column 36 is depressed by about 3/18 or 4/18 of the vertical height of the molten salt _ in the column 36 in order to support the bath 46 of molten salt on the molten uranium 44. This combination of column 36 and reservoir 38 serves as a trap through which molten uranium flows by gravity, but through which the molten salt cannot escape, except as hereinafter described with reference to removal of impurities. As a means to provide for improved contact between the bath 46 of molten salt and molten uranium descending through the column 36, the column 36 is provided with a bed of ceramic pellets, generally indicated as 48. Such pellets are more dense than the molten salt, but less dense than the molten uranium;
most of such pellets are chemically inert toward the molten salt and molten uranium and preferably of like composition to the ceramic material or liner of column 36. Further pellets of reactive titanium dioxide can be included in the pellet bed 48. The pellets either float on the molten uranium 44 in the column 36 with some pellets being forced into the upper regions of the molten uranium 44 to support the pellets above, or the pellets may rest on the solid bottom of the reservoir 36 when the volume of molten uranium is small.
A piston 50 under control of a hoisting and driving assembly, generally indicated as 52 is provided to effect removal of the impurities from the process, as fully herein-after discussed.
In operation, metallic uranium scrap commented into sly small pieces for ease of handling, cleaned to remove dustily and grease, generally indicated by the "x", is intro-duped into the uranium feed hopper 10. The vacuum lock-hopper assembly 14 is thereafter closed to to permit evacuation of the air in the hopper via conduit 20 followed by the introduction via conduit 18 of an inert atmosphere, such as an argon-helium mixture of like density to air to replace air which has been removed by evacuation. Such an inert atmosphere is maintained at slightly less than atoms-phonic pressure through all subsequent processing Theresa of glove-box techniques, such as are known and used by one skilled in the art. The metallic uranium scrap is passed through the furnace assembly 24 and heated to a temperature of about 1200K to about 1400K, preferably about 1300K, prior to introduction into the bath 46 con-tannins, in molten form, at least one member selected from the group consisting of Buff, Cafe, MgF2, Lift YF3, trifle-oxides of lanthanides and mixtures thereof, preferably with such members constituting at least 75 mole percent of the bath.
The molten salt is of low volatility to thereby be restricted to the bath 46 and thermodynamically stable under existing conditions so that the salt does not excessively react with molten uranium to form dilute solutions of UC13 or UF3 and dissolved metals, such as exhibited by salts such as Nail, Clue, and OF. Additionally, the salt is not hugger-scopic, since such salt tends to form molten hydroxides, which introduce hydrogen and oxygen into the uranium, and metal into the salt and vapor. Additionally, the molten salt is largely unreactive with the ceramic material or liner for the column 36. Excellent satisfaction of such 1i2 requirements is offered by a bath containing, in molten form, at least one member selected from the group consisting of Buff, Cafe, MgF2, Lift YF3, trifluorides of lanthanides and mixtures thereof, preferably with such members keenest-tuning at least 75 mole percent of the bath.
Special advantages in reducing the concentration of impurities in the molten uranium can be obtained by select-in pure salts or mixtures which melt near or below the melting point of uranium. With the list of suitable flu-oxides, MgF2 is somewhat less stable thermodynamically than would be desired. SrF2 is unsatisfactory because of unsuitable eutectic behavior and cost.
The heating elements 42 maintain the temperature of the bath 46 in the column and the uranium 44 in reservoir 38 at a temperature above the melting point of metallic urn-I'm. Preferably, the temperature at the top of the column 36 is from 50 to 125K higher than the average temperature thereof. As herein before discussed, the bath 46 of molten salt is preferably provided with a bed 48 of ceramic pellets to improve contact between the molten uranium falling through the bath 46 of molten salt to effectively remove insoluble oxides from the molten uranium whereby such impure flies move into the molten salt. If pellets of titanium oxide are included with the pellet bed 48, or if titanium is dissolved in the uranium, then carbides, nitrides and sift-aides of titanium are formed which float at the top of the molten uranium 44 within the column 36 and the uranium will thereby be purified of carbon, nitrogen and silicon; if titanium oxide is used, however, it will result in the addition of titanium to the uranium, and such titanium addition may be undesirable in some sequent uranium uses.
Lo Molten uranium overflows the pouring lip 40 and is collected in a billet mold 54 to form a billet 56.
At preselected time intervals when the removal of impurities is deemed advisable, the introduction of uranium scrap into column 36 is halted and the piston 50, referring now to Figure 2, is caused to be lowered by the hoisting and driving assembly 52. Continued downward movement of the piston 50, referring to Figure 3, causes the bath 46 of molten salt to be downwardly displaced within the column 36 until the interracial uranium and salt, including impure-ties, are caused to flow into the reservoir 38. Continued downward movement causes the interracial material, including impurities, to overflow the pouring lip 40 and into a waste billet mold 58 which has replaced uranium billet mold 54 thus to form a waste billet which is rejected and disposed of in subsequent operations (not shown).
Thereafter, the piston 50 is caused to be raised by the hoisting and driving assembly 52, referring now to Figure 4, whereby the respective liquid levels of the bath 46 ox molten salt and molten uranium 44 are lowered, with makeup salt being introduced into the column 36 concomitantly with the resumption of the introduction of uranium scrap into the process.
EXAMPLE
Operation of the process and apparatus is described in the following example which is intended to be merely thus-trative and the invention is not to be regarded as limited thereto.
600 pounds of cleaned uranium scrap is introduced into the feed assembly 10 having a volume of about 1.5 cubic feet with air being subsequently replaced by an inert atmosphere LZ~2 of argon-helium. The scrap is passed to the furnace asset-by 24 and heated to about 1300K. The heated scrap is introduced into the bath 46 of molten salt maintained at a temperature of about 1425K with a top column temperature of about 1500K. Molten uranium overflows the lip 40 and falls into the billet mold OWE
While the process of the present invention has been described with reference to the removal of impurities by use of a piston introduced into the column 36, other methods for the removal of impurities may be effected, such as introduce in an additional amount of molten salt whereby the height of the bath 46 of molten salt is raised to a point whereby such interracial molten salt is displaced from the column 36 into the reservoir 38 Additionally, a piston assembly including a piston for introduction into a much enlarged reservoir 38 may be used to facilitate uranium billet and/or waste billet formation. Still further, while the process of the present invention is described with reference to sub-staunchly continuous operation, it is understood that the present invention may be effected in operations other than continuous.
While the invention has been described in connection with an exemplary embodiment thereof, it will be understood that many modifications will be apparent to those of ordinary skill in the art and that this application is intended to cover any adaptations or variations thereof. -
Background of the Invention . .
This invention relates to the recovery and purification of metallic scrap, and more particularly to a novel process and apparatus for the production of bulk metallic uranium from metallic uranium scrap, especially scrap of depleted uranium.
Natural uranium, i.e., the material that is mined from the earth, contains 0.005 percent uranium-234 (U234), 0.7 percent U235, and 99.295 percent U23~. Depleted uranium "DU" is a by-product of isotope separation processes, prim manly the gaseous diffusion process, through which uranium containing a higher content of the U235 isotope, referred to as enriched uranium, is produced from natural uranium. En-niched uranium is used for reactor fuels and nuclear woe-puns. DU, the residue of the enrichment process, contains only a portion of the original U235 and U234 and is there-fore "depleted" in these isotopes. The isotope distribution will vary with different enrichment goals. DU is a high density metal used as counterweights in some military and commercial aircraft, as components in some military project tiles, and as shielding material in containers in which highly radioactive materials such as Kiwi are stored and used. During production of the above items, DU scrap is produced.
The values of natural and enriched uranium metal range from $40 per pound to well over $10,000 per pound, depending upon the purity and level of enrichment. Therefore, highly efficient recovery procedures, even though very expensive, are used for the recycling of these materials. On the other hand depleted uranium is worth $0.50 to $2.00 per pound in bulk, and no economically suitable scheme has been developed for recovering and reusing this scrap. Instead, several thousand pounds per day of metallic scrap (turnings, crops, rejects, etc.) are placed in drums, packed with nonflammable material, and transported to radioactive waste dumps where the drums are buried. The burial of such radioactive waste is becoming very restricted and increasingly costly.
In "Reactor Handbook," Second Edition, Volume 1, pp.
98-104, and Volume 2, pp. 379-391, the engineering aspects of industrial and governmental uranium processing are disk closed (i.e., UF4 reduction) in essentially the same manner in which uranium processing is currently being conducted/
and in particular, identifying the importance of allowing time for phase separations of molten uranium from MgF2 or Cafe, either in derby or dingo reduction. This time for separation is achieved by preheating and by size and shape considerations only; no use is made of cleaning at tempera-lure or of eutectic mixtures. Cafe, MgF2, and various oxides are identified as liners for graphite containers.
Uranium chips along with trapped debris are pressed into briquettes prior to melting under vacuum along with other metallic uranium scrap. Oxide scums and volatile impurities are identified as sources of problems in the uranium no-melting, and it is also recognized that graphite crucibles lead to carbon pickup. Oxide scums create problems also at the metal-salt interfaces during the original reductions of UF4 by calcium or magnesium.
In "Uranium Metallurgy" by W. D. Wilkinson, there is disclosed the melting of uranium chips in crucibles lined with magnesium zircon ate covered with a protective layer of a mixture of calcium fluoride and magnesium fluoride; this melting yields ingots containing 400-600 Pam of carbon.
, A, 3L2~ 2 This large carbon addition is grossly unacceptable for much uranium recycling; it is a consequence jointly of the use of an improper salt (MgF2) together with the use of an imp proper container material (graphite).
Summary of the Invention The present invention seeks to provide a novel process and apparatus for recovering, purifying and producing bulk uranium metal from depleted-uranium scrap.
In one aspect, the invention pertains to a process for producing metallic uranium from scrap containing metallic uranium, which comprises forming in a contact zone under an inert atmosphere a bath supported on molten uranium, the bath containing, in molten form, at least one member selected from the group consisting of Cafe, Buff, MgF2, Lift YF3, trifluorides of lanthanides, and mixtures thereof, with the bath being at a temperature above the melting point of uranium and the contact zone including contact means within the bath for intimately contacting the bath and the scrap containing metallic uranium, introducing under an inert atmosphere the scrap containing metallic uranium into the bath under conditions to form molten uranium, and recovering metallic uranium from the molten uranium supporting bath wherein titanium, preferably solid titanium oxide, is present to remove carbon, nitrogen, and silicon.
The invention also pertains to an apparatus for producing metallic uranium from scrap containing metallic uranium, which comprises a reservoir means for molten uranium, with a column disposed in the reservoir for a bath of a molten salt supported on the molten uranium.
~`~
I ~Z02 pa Means provide fluid for communication between the column and the reservoir, and means maintain the column and the reservoir at a temperature above the melting point of uranium. Means are provided for introducing the scrap containing metallic uranium into the column, and means are provided for removing molten uranium from the reservoir means.
In one aspect, the apparatus includes a lip means for withdrawing the molten uranium. In another aspect, the apparatus includes piston means for displacing interracial molten metal and salt including impurities.
In a still further aspect, the reservoir and column are formed of or lined with a ceramic material including an oxide selected from the group consisting of UO2, Thou, Moo, YO-YO and trivalent oxides of the lanthanides.
More particularly, the present invention comprehends a novel process and apparatus for recovering and purify-in metallic uranium from scrap containing metallic uranium by introducing such metallic uranium scrap into a bath containing, in molten form, at least one member ~2~2~)2 selected from the group consisting of Buff, Coffey MgF2, Lift YF3, trifluorides of lanthanides and mixtures thereof, preferably with such members constituting at least 75 mole percent of the bath. The molten salt bath is under an inert `, 5 atmosphere and at a temperature above the melting point of uranium. Molten uranium is recovered after passage through the molten salt bath. The bath of molten salt preferably includes means for improving contact between the molten metallic uranium scrap and the bath of molten salt during passage of the molten uranium scrap through the bath of molten salt.
Brief Description of the Drawings Understanding of the present inventions will be facile-toted by referring to the following detailed description when taken in conjunction with the accompanying drawings wherein like numerals designate like parts throughout in which:
Figure 1 is a schematic view of the process and appear-tusk of the present invention;
Figure 2 illustrates the molten salt-molten uranium system during casting of molten uranium;
Figure 3 illustrates the molten salt-molten uranium system during removal of impurities; and Figure 4 illustrates the molten salt-molten uranium system after removal of impurities.
Detailed Description _ the Drawings Referring now to Figure 1, there is provided a uranium feed-hopper assembly and a metallic-uranium melting asset-by, generally indicated as 10 and 12 respectively. The uranium feed hopper 10 is comprised of a vacuum lock hopper system and a material-storage bin, generally indicated as 14 ~2~0;~
and 16. The vacuum lock-hopper system 14 is such as known and used by one skilled in the art and includes an inert gas inlet conduit 18 and an evacuation gas conduit 20. The material-storage bin 16 of the uranium hopper assembly 10 is provided with a ceramic conduit 22 in communication with a furnace assembly, generally indicated 24, disposed within the metallic-uranium melting assembly 12 including an outer support structure 26 comprising an inert gas inlet conduit 28 under the control of valve 30 and an outlet gas conduit 32 under the control of valve 34.
The metallic-uranium melting assembly 12 includes a column 36 formed within a suitable support structure (not shown) and disposed within a cylindrically shaped reservoir 38 including a pouring lip portion 40 all formed of or lined with a ceramic material comprised of UO2, Thou, Moo, YO-YO, or trivalent oxides of the lanthanides in which one or more of these oxides jointly make up at least 75% of the compost-lion of the resulting ceramic material. The column 36 is in communication with an end of the ceramic conduit 22 which in turn is in communication with the uranium feed hopper 10.
Surrounding the column 36 and reservoir 38, there are provided heater elements, generally indicated as 42, for maintaining the temperature above the melting point of me-talk uranium, as more fully hereinafter discussed.
Within the lower portion of the column 36 and within reservoir 38, there is provided cleaned molten uranium 44 supporting a bath 46 containing, in molten form, at least one member selected from the group consisting of Buff, Cafe, MgF2, Lift YF3, trifluorides of lanthanides and mixtures thereof, preferably with such members constituting at least 75 mole percent of the bath. The bath 46 of molten salt is I, ., 3~2~
supported as a result of the differences in the densities between the bath 46 of molten salt (approximately 3 to 4 gm/cm3) and the molten uranium (approximately 18 gm/cm3).
Thus, the uranium 44 in the column 36 is depressed by about 3/18 or 4/18 of the vertical height of the molten salt _ in the column 36 in order to support the bath 46 of molten salt on the molten uranium 44. This combination of column 36 and reservoir 38 serves as a trap through which molten uranium flows by gravity, but through which the molten salt cannot escape, except as hereinafter described with reference to removal of impurities. As a means to provide for improved contact between the bath 46 of molten salt and molten uranium descending through the column 36, the column 36 is provided with a bed of ceramic pellets, generally indicated as 48. Such pellets are more dense than the molten salt, but less dense than the molten uranium;
most of such pellets are chemically inert toward the molten salt and molten uranium and preferably of like composition to the ceramic material or liner of column 36. Further pellets of reactive titanium dioxide can be included in the pellet bed 48. The pellets either float on the molten uranium 44 in the column 36 with some pellets being forced into the upper regions of the molten uranium 44 to support the pellets above, or the pellets may rest on the solid bottom of the reservoir 36 when the volume of molten uranium is small.
A piston 50 under control of a hoisting and driving assembly, generally indicated as 52 is provided to effect removal of the impurities from the process, as fully herein-after discussed.
In operation, metallic uranium scrap commented into sly small pieces for ease of handling, cleaned to remove dustily and grease, generally indicated by the "x", is intro-duped into the uranium feed hopper 10. The vacuum lock-hopper assembly 14 is thereafter closed to to permit evacuation of the air in the hopper via conduit 20 followed by the introduction via conduit 18 of an inert atmosphere, such as an argon-helium mixture of like density to air to replace air which has been removed by evacuation. Such an inert atmosphere is maintained at slightly less than atoms-phonic pressure through all subsequent processing Theresa of glove-box techniques, such as are known and used by one skilled in the art. The metallic uranium scrap is passed through the furnace assembly 24 and heated to a temperature of about 1200K to about 1400K, preferably about 1300K, prior to introduction into the bath 46 con-tannins, in molten form, at least one member selected from the group consisting of Buff, Cafe, MgF2, Lift YF3, trifle-oxides of lanthanides and mixtures thereof, preferably with such members constituting at least 75 mole percent of the bath.
The molten salt is of low volatility to thereby be restricted to the bath 46 and thermodynamically stable under existing conditions so that the salt does not excessively react with molten uranium to form dilute solutions of UC13 or UF3 and dissolved metals, such as exhibited by salts such as Nail, Clue, and OF. Additionally, the salt is not hugger-scopic, since such salt tends to form molten hydroxides, which introduce hydrogen and oxygen into the uranium, and metal into the salt and vapor. Additionally, the molten salt is largely unreactive with the ceramic material or liner for the column 36. Excellent satisfaction of such 1i2 requirements is offered by a bath containing, in molten form, at least one member selected from the group consisting of Buff, Cafe, MgF2, Lift YF3, trifluorides of lanthanides and mixtures thereof, preferably with such members keenest-tuning at least 75 mole percent of the bath.
Special advantages in reducing the concentration of impurities in the molten uranium can be obtained by select-in pure salts or mixtures which melt near or below the melting point of uranium. With the list of suitable flu-oxides, MgF2 is somewhat less stable thermodynamically than would be desired. SrF2 is unsatisfactory because of unsuitable eutectic behavior and cost.
The heating elements 42 maintain the temperature of the bath 46 in the column and the uranium 44 in reservoir 38 at a temperature above the melting point of metallic urn-I'm. Preferably, the temperature at the top of the column 36 is from 50 to 125K higher than the average temperature thereof. As herein before discussed, the bath 46 of molten salt is preferably provided with a bed 48 of ceramic pellets to improve contact between the molten uranium falling through the bath 46 of molten salt to effectively remove insoluble oxides from the molten uranium whereby such impure flies move into the molten salt. If pellets of titanium oxide are included with the pellet bed 48, or if titanium is dissolved in the uranium, then carbides, nitrides and sift-aides of titanium are formed which float at the top of the molten uranium 44 within the column 36 and the uranium will thereby be purified of carbon, nitrogen and silicon; if titanium oxide is used, however, it will result in the addition of titanium to the uranium, and such titanium addition may be undesirable in some sequent uranium uses.
Lo Molten uranium overflows the pouring lip 40 and is collected in a billet mold 54 to form a billet 56.
At preselected time intervals when the removal of impurities is deemed advisable, the introduction of uranium scrap into column 36 is halted and the piston 50, referring now to Figure 2, is caused to be lowered by the hoisting and driving assembly 52. Continued downward movement of the piston 50, referring to Figure 3, causes the bath 46 of molten salt to be downwardly displaced within the column 36 until the interracial uranium and salt, including impure-ties, are caused to flow into the reservoir 38. Continued downward movement causes the interracial material, including impurities, to overflow the pouring lip 40 and into a waste billet mold 58 which has replaced uranium billet mold 54 thus to form a waste billet which is rejected and disposed of in subsequent operations (not shown).
Thereafter, the piston 50 is caused to be raised by the hoisting and driving assembly 52, referring now to Figure 4, whereby the respective liquid levels of the bath 46 ox molten salt and molten uranium 44 are lowered, with makeup salt being introduced into the column 36 concomitantly with the resumption of the introduction of uranium scrap into the process.
EXAMPLE
Operation of the process and apparatus is described in the following example which is intended to be merely thus-trative and the invention is not to be regarded as limited thereto.
600 pounds of cleaned uranium scrap is introduced into the feed assembly 10 having a volume of about 1.5 cubic feet with air being subsequently replaced by an inert atmosphere LZ~2 of argon-helium. The scrap is passed to the furnace asset-by 24 and heated to about 1300K. The heated scrap is introduced into the bath 46 of molten salt maintained at a temperature of about 1425K with a top column temperature of about 1500K. Molten uranium overflows the lip 40 and falls into the billet mold OWE
While the process of the present invention has been described with reference to the removal of impurities by use of a piston introduced into the column 36, other methods for the removal of impurities may be effected, such as introduce in an additional amount of molten salt whereby the height of the bath 46 of molten salt is raised to a point whereby such interracial molten salt is displaced from the column 36 into the reservoir 38 Additionally, a piston assembly including a piston for introduction into a much enlarged reservoir 38 may be used to facilitate uranium billet and/or waste billet formation. Still further, while the process of the present invention is described with reference to sub-staunchly continuous operation, it is understood that the present invention may be effected in operations other than continuous.
While the invention has been described in connection with an exemplary embodiment thereof, it will be understood that many modifications will be apparent to those of ordinary skill in the art and that this application is intended to cover any adaptations or variations thereof. -
Claims (6)
1. A process for producing metallic uranium from scrap containing metallic uranium, which comprises:
(a) forming in a contact zone under an inert atmosphere a bath supported on molten uranium, said bath containing, in molten form, at least one member selected from the group consisting of CaF2, BaF2, MgF2, LiF, YF3, trifluorides of lanthanides, and mixtures thereof, said bath being at a temperature above the melting point of uranium and said contact zone including contact means within said bath for intimately contacting said bath and said scrap containing metallic uranium;
(b) introducing under an inert atmosphere said scrap containing metallic uranium into said bath under conditions to form molten uranium; and (c) recovering metallic uranium from said molten uranium supporting bath wherein said bath includes solid titanium oxide to remove carbon, nitrogen, and silicon.
(a) forming in a contact zone under an inert atmosphere a bath supported on molten uranium, said bath containing, in molten form, at least one member selected from the group consisting of CaF2, BaF2, MgF2, LiF, YF3, trifluorides of lanthanides, and mixtures thereof, said bath being at a temperature above the melting point of uranium and said contact zone including contact means within said bath for intimately contacting said bath and said scrap containing metallic uranium;
(b) introducing under an inert atmosphere said scrap containing metallic uranium into said bath under conditions to form molten uranium; and (c) recovering metallic uranium from said molten uranium supporting bath wherein said bath includes solid titanium oxide to remove carbon, nitrogen, and silicon.
2. A process for producing metallic uranium from scrap containing metallic uranium, which comprises:
(a) forming in a contact zone under an inert atmosphere a bath supported on molten uranium, said bath containing, in molten form, at least one member selected from the group consisting of CaF2, BaF2, MgF2, LiF, YF3, trifluorides of lanthanides, and mixtures thereof, said bath being at a temperature above the melting point of uranium and sai.d contact zone including contact means within said bath for intimately contacting said bath and said scrap containing metallic uranium;
(b) introducing under an inert atmosphere said scrap containing metallic uranium into said bath under conditions to form molten uranium; and (c) recovering metallic uranium from said molten uranium supporting bath wherein titanium is present to remove carbon, nitrogen, and silicon.
(a) forming in a contact zone under an inert atmosphere a bath supported on molten uranium, said bath containing, in molten form, at least one member selected from the group consisting of CaF2, BaF2, MgF2, LiF, YF3, trifluorides of lanthanides, and mixtures thereof, said bath being at a temperature above the melting point of uranium and sai.d contact zone including contact means within said bath for intimately contacting said bath and said scrap containing metallic uranium;
(b) introducing under an inert atmosphere said scrap containing metallic uranium into said bath under conditions to form molten uranium; and (c) recovering metallic uranium from said molten uranium supporting bath wherein titanium is present to remove carbon, nitrogen, and silicon.
3. An apparatus for producing metallic uranium from scrap containing metallic uranium, which comprises:
a reservoir means for molten uranium;
a column disposed in said reservoir for a bath of a molten salt supported on said molten uranium;
means to provide fluid communication between said column and said reservoir;
means for maintaining said column and said reservoir at a temperature above the melting point of uranium;
means for introducing said scrap containing metallic uranium into said column; and means for removing molten uranium from said reservoir means wherein said apparatus includes a lip means for withdrawing said molten uranium.
a reservoir means for molten uranium;
a column disposed in said reservoir for a bath of a molten salt supported on said molten uranium;
means to provide fluid communication between said column and said reservoir;
means for maintaining said column and said reservoir at a temperature above the melting point of uranium;
means for introducing said scrap containing metallic uranium into said column; and means for removing molten uranium from said reservoir means wherein said apparatus includes a lip means for withdrawing said molten uranium.
4. An apparatus for producing metallic uranium from scrap containing metallic uranium, which comprises:
a reservoir means for molten uranium;
a column disposed in said reservoir for a bath of a molten salt supported on said molten uranium;
means to provide fluid communication between said column and said reservoir;
means for maintaining said column and said reservoir at a temperature above the melting point of uranium;
means for introducing said scrap containing metallic uranium into said column; and means for removing molten uranium from said reservoir means wherein said apparatus includes piston means for displacing interfacial molten metal and salt including impurities.
a reservoir means for molten uranium;
a column disposed in said reservoir for a bath of a molten salt supported on said molten uranium;
means to provide fluid communication between said column and said reservoir;
means for maintaining said column and said reservoir at a temperature above the melting point of uranium;
means for introducing said scrap containing metallic uranium into said column; and means for removing molten uranium from said reservoir means wherein said apparatus includes piston means for displacing interfacial molten metal and salt including impurities.
5. An apparatus for producing metallic uranium from scrap containing metallic uranium, which comprises:
a reservoir means for molten uranium;
a column disposed in said reservoir for a bath of a molten salt supported on said molten uranium;
means to provide fluid communication between said column and said reservoir;
means for maintaining said column and said reservoir at a temperature above the melting point of uranium;
means for introducing said scrap containing metallic uranium into said column; and means for removing molten uranium from said reservoir means wherein said reservoir and column are formed of or lined with a ceramic material including an oxide selected from the group consisting of UO2, ThO2, MgO, Y2O3 and trivalent oxides of the lanthanides.
a reservoir means for molten uranium;
a column disposed in said reservoir for a bath of a molten salt supported on said molten uranium;
means to provide fluid communication between said column and said reservoir;
means for maintaining said column and said reservoir at a temperature above the melting point of uranium;
means for introducing said scrap containing metallic uranium into said column; and means for removing molten uranium from said reservoir means wherein said reservoir and column are formed of or lined with a ceramic material including an oxide selected from the group consisting of UO2, ThO2, MgO, Y2O3 and trivalent oxides of the lanthanides.
6. The apparatus as defined in Claim 5 wherein said oxide forms at least 75 percent of the ceramic material.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000479832A CA1241202A (en) | 1985-04-23 | 1985-04-23 | Process and apparatus for recovering metallic uranium scrap |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000479832A CA1241202A (en) | 1985-04-23 | 1985-04-23 | Process and apparatus for recovering metallic uranium scrap |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1241202A true CA1241202A (en) | 1988-08-30 |
Family
ID=4130333
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000479832A Expired CA1241202A (en) | 1985-04-23 | 1985-04-23 | Process and apparatus for recovering metallic uranium scrap |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1241202A (en) |
-
1985
- 1985-04-23 CA CA000479832A patent/CA1241202A/en not_active Expired
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