(19) &
(11) EP 0 984 903 B1
(12) EUROPEAN PATENT SPECIFICATION
(45) Date of publication and mention (51) Int Cl.: of the grant of the patent: C01G 43/06 (2006.01) G21F 9/00 (2006.01) 01.02.2012 Bulletin 2012/05 G21F 9/02 (2006.01) G21F 9/12 (2006.01)
(21) Application number: 98915443.0 (86) International application number: PCT/US1998/007163 (22) Date of filing: 09.04.1998 (87) International publication number: WO 1998/052872 (26.11.1998 Gazette 1998/47)
(54) REMOVAL OF TECHNETIUM IMPURITIES FROM URANIUM HEXAFLUORIDE ENTFERNUNG VON TECHNETIUMKONTAMINANTEN AUS URANHEXAFLUORID EXTRACTION D’IMPURETES DE TECHNETIUM D’HEXAFLUORURE D’URANIUM
(84) Designated Contracting States: (56) References cited: DE FR GB US-A- 3 165 376 US-A- 3 806 579 US-A- 3 848 048 US-A- 5 613 186 (30) Priority: 21.05.1997 US 860000 • SMILEY S H ET AL: "REMOVAL OF IMPURITIES (43) Date of publication of application: FROM URANIUM HEXAFLUORIDE BY 15.03.2000 Bulletin 2000/11 SELECTIVE SORPTION TECHNIQUES" TRANSACTIONS OF THE AMERICAN NUCLEAR (73) Proprietor: United States Enrichment Corporation SOCIETY, AMERICAN NUCLEAR SOCIETY, LA Bethesda, MD 20817 (US) GRANGE PARK, IL, US, 5 November 1967 (1967-11-05), page 507, XP002910084 ISSN: (72) Inventors: 0003-018X • SARACENO, Anthony, J. • SMILEY S.H. et al., "Removal of Impurities from Waverly, OH 45690 (US) Uranium Hexafluoride by Selective Sorption • BANKS, Keith, D. Techniques", TRANSACTION OF THE Lucasville, OH 45648 (US) AMERICAN NUCLEAR SOCIETY, November 1967, page 507, XP002910084 (74) Representative: Beacham, Annabel Rose et al • MILFORDR.P., "Engineering Design of Oak Ridge Dehns Fluoride Volatility Pilot Plant", INDUSTRIAL AND St Bride’s House ENGINEERING CHEMISTRY, 1958, Vol. 50, No. 2, 10 Salisbury Square pages 187-191, XP002910085 London EC4Y 8JD (GB)
Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 0 984 903 B1
Printed by Jouve, 75001 PARIS (FR) EP 0 984 903 B1
Description
[0001] This invention was made with Government support under Contract No. USEC-96-C-0001, awarded to the United States Enrichment Corporation. The Government has certain rights in this invention. 5 FIELD OF THE INVENTION
[0002] The present invention relates to methods of purifying uranium hexafluoride by removing technetium-99 impu- rities. 10 BACKGROUND OF THE INVENTION
99 [0003] Technetium-99 ( Tc) is a contaminant that is typically present in an enriched UF 6 product in low concentrations. This contaminant originates from the fission of 235uranium and is contained in reactor return uranium. Process equipment 15 99 surfaces in gaseous diffusion plants which process UF6 hold the Tc as one or more volatile compounds which are slowly released over time. As a result, the enriched UF6 product which is withdrawn from diffusion plants invariably contains low concentrations of 99Tc, due to a slow leaching from equipment surfaces. The concentrations of the99Tc impurity, although low, may easily exceed product specification limits, making the uranium hexafluoride product unac- 99 23S ceptable to fuel fabricators. Presently, the specification limit for Tc in UF6 product is only 0.2 Pg/g U or, assuming 20 5% 235U enrichment, 0.010 Pg 99Tc/g U (0.010 ppm, U basis). 99 [0004] Methods for the removal of Tc from UF6 have typically involved gas phase operation (contacting gaseous 99 UF6 with a metal fluoride, typically magnesium fluoride adsorbent). These methods are not effective at the lowTc concentrations which impact customer acceptance. For example, the lowest concentrations amenable to gas phase removal are above 0.1 Pg 99Tc/g U. Additionally, sufficient throughput must be maintained to provide adequate quantities 25 of the purified UF6. The throughput for UF6 processing which can be obtained with gas phase operations is only about 2 99 100-500 lbs/ft /hour- If the gas velocity is increased to increase UF 6 processing rates, Tc removal efficiency decreases sharply. Conversely, if gas velocity is decreased to maintain high 99Tc removal, processing rates suffer. In short, existing 99 methods (gaseous UF6 with MgF2 adsorbent) are insufficient to combine both high removal efficiency of Tc for direct control at concentrations applicable to market acceptance, and high UP6 processing rates to produce an economic 30 process without burdensome equipment size. [0005] US 3,165,376 discloses a process for the separation and recovery of technetium and nepturium fluorides from reprocessed UF6. [0006] What is needed in the art are new methods of removing 99Tc from uranium hexafluoride which overcome the problems associated with existing methods. The present invention provides such processes. 35 SUMMARY OF THE INVENTION
[0007] The present invention provides processes according to claim 1 for the removal of technetium from contaminated uranium hexafluoride containing technetium, typically technetium-99 which is present in several chemical forms or 40 compounds. Some common volatile forms are pertechnetyl fluoride (TcO3F), technetium hexafluoride (TcF6) and tech- netium oxytetrafluoride (TcOF4). Less volatile forms of technetium include TCO 2 and TcF4 or TcF5. Volatility is a relative 99 property and depends upon the temperature of the process. It is generally the Tc compounds which are volatile at UF 6 handling temperatures that are present in the UF6 product. [0008] The processes of the present invention involve: 45 a) contacting contaminated uranium hexafluoride in liquid form with a solid metal fluoride, typically magnesium fluoride (MgF2), for a period of time sufficient for the technetium to become adsorbed onto the metal fluoride solid 2 thereby producing a purified uranium hexafluoride liquid wherein the rate of UF 6 processing is at least 2440 kg/m / hour (500 lbs/ft2/hour) ; and 50 b) removing the purified uranium hexafluoride liquid from the solid metal fluoride, typically magnesium fluoride solid, having adsorbed technetium.
BRIEF DESCRIPTION OF THE DRAWINGS
55 [0009]
Figure 1 illustrates a UF6 cylinder "1S" which is used in the Examples. Figure 2 shows a liquid UF6 filtering apparatus containing 8-12 mesh MgF2 as an adsorbent and a 10 micron filter.
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Figure 3 illustrates a vacuum manifold system for filtering liquid UF6 and trapping the purified UF6 in a cooled collection vessel.
DETAILED DESCRIPTION OF THE INVENTION 5 [0010] This invention disclosure describes a process modification which leads to unexpectedly large improvement in 99 99 the removal of Tc from UF 6. The process reduces Tc in UF6 to below product specification levels for UF 6 and further 99 provides high UF6 throughputs. The methods described herein can be applied to control the removal of Tc at UF6 product withdrawal stations and/or UF6 liquid transfer facilities on a scale that is attractive for installation at uranium 10 enrichment plants. [0011] As noted in the Background, existing technology employs magnesium fluoride (MgF2) in the form of pellets which are placed in a reactor. Uranium hexafluoride is passed through the reactor in the gas phase at atmospheric pressures or less. Gas chase operation in itself is inherently limiting in UF 6 throughputs or processing rates. Furthermore, this mode of operation fails to perform efficiently as99Tc concentrations decrease. The lower concentration limit for 15 useful removal and/or control of99Tc varies with gas velocity and is estimated to be above 0.1P g/g U and probably much higher. (A typical result in gas phase operation at 13.8 kPa (2 psia) is 2.2 Pg/g being reduced by 59% to 0.9 Pg/g). 2 2 It is not possible to obtain UF 6 processing rates above about 2440 kg/m /hour (500 lbs/ft /hour) at atmospheric pressure or below and still achieve acceptable reduction at concentration below 0.1 Pg/g U. [0012] The present invention is based on the surprising discovery that when liquid UF6 (rather than gaseous UF6) is 20 99 99 passed through a trap containing solid MgF2, a remarkable boost in Tc removal efficiency is realized at low Tc concentrations. As one example, at an initial concentration 0.018P g/g U, 99Tc is reduced to 0.0008 Pg/g U. In other demonstration tests, reductions to below the detection limit (0.0004 Pg/g U) are readily obtained. These high efficiencies were not expected considering the state of the art for MgF 2 trapping technology. Furthermore, UF 6 processing rates are 2 2 2 well over 14650 kg/m/hour (3000 lbs/ft2 /hour). Rates as high as 22460 kg/m/hour(4600 lbs/fts /hour) have been 25 successfully demonstrated with no apparent decrease in efficiency. These rates have considerable economic impact as 99 it is now feasible to install a reasonably sized Tc removal apparatus at any existing product withdrawal station or UF 6 99 liquid transfer facility without significantly interfering with present operations. Accordingly, direct control of Tc in UF6 product is possible and results in further cost savings due to greater flexibility of diffusion operations. The highly purified UF6 product which is obtained using the methods herein, further assures customer acceptance of the UF6 product. 30 Embodiments of the Invention
[0013] In view of the above surprising discovery, the present invention provides a process for removal of technetium (99Tc), from contaminated enriched uranium hexafluoride which is withdrawn from a diffusion plant containing the tech- 35 netium. This process comprises:
(a) contacting the contaminated uranium hexafluoride in liquid form with a metal fluoride in solid form for a period of time sufficient for the technetium to become adsorbed onto the metal fluoride thereby producing a purified uranium 2 2 hexafluoride liquid, wherein the rate of UF6 processing is at least 2440 kg/m /hour (500 lbs/ft /hour); and 40 b) removing the purified uranium hexafluoride liquid from the aolid metal fluoride having adsorbed technetium.
[0014] The present invention utilizes UF6 in liquid form to achieve the significant results provided in the Examples below. Uranium hexafluoride is a volatile white crystalline solid which melts at about 64-65TC, but which sublimes at about 56-57TC under pressure of about 101 kPa (1 atmosphere). Accordingly, liquified uranium hexafluoride can be 45 obtainedunder pressure of about 152 kPa (1.5atmospheres) and at working temperatures (typically provided in cylinders). Uranium hexafluoride also reacts vigorously with water and care should be taken to remove air and moisture from the trapping system. [0015] Metal fluorides which are suitable for the removal of technetium from UF 6 are generally high melting ionic solids with very low solubility in UF6 . A particularly preferred metal fluoride is magnesium fluoride (MgF 2) which is recognized 50 for its technetium removal properties. However, other metal fluorides can also be used, such as AlF3, transition metal fluorides such as NiF2 and related high melting fluorides which are solids at temperatures at which UF6 begins to melt to a liquid. In other embodiments, the metal fluoride used in the invention can be a combination of different metal fluorides (e.g.,. a combination of MgF2 and AlF3). [0016] The method of contacting the contaminated uranium hexafluoride with a metal fluoride typically involves placing 55 a metal fluoride chemical trap in the UF6 flow line extending from the source of UF 6 to a suitable receptacle for purified UF6. Figures 1-3 provide illustrations of the types of apparatus which can be used in the present invention. One of skill in the art will understand that other apparatuses could also be used to provide the necessary contact between liquid UF6 and the metal fluoride. By allowing the contaminated uranium hexafluoride to pass through, for example, a MgF2
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chemical trap, contact is made between the MgF2 and the contaminated UF6, and technetium impurities are adsorbed onto the MgF2. Particular flow rates and contact times (between liquid UF 6 and MgF2) will be dependent on the system requirements and capabilities. The examples below provide an indication of flow rates and contact times (or residence times) for a system comprising a "2S" or "1S" feed cylinder of UF 6, a MgF 2 chemical trap constructed from a "1S" cylinder 5 body, and an attached "2S" cold trap. For this system, a flow rate of about 2.8 x 10-7 m3/s (1.0 x 10-5 ft3/sec) to about 9.9 x 10 -7 m3/s (3.5 x 10 -5 ft3/sec) is useful. These flow rates result in chemical trap residence (or contact) times of about 350 seconds to about 100 seconds. Other filters and chemical traps which operate on this same premise, including those versions which are of a larger or smaller scale and of greater or lesser trap voidage, will be known to those of skill in the art. 10 [0017] The amount and physical form (specific surface area and pellet size) of the metal fluoride used in the chemical traps will be dependent on a number of factors including the amount of UF6 to be purified, the size of the trap and the flow rate required. In one group of embodiments, the metal fluoride is MgF2 which is in the form of pellets, preferably about 0.32 cm (1/8 inch) to about 0.95 cm (3/8) inch pellets, more preferably about 0.64 cm (1/4 inch) pellets. In other embodiments, the magnesium fluoride is in the form of 6-15 mesh, preferably 8-12 mesh. The amount of magnesium 15 99 fluoride used will depend on the level of contamination of UF6 with Tc. Typically, magnesium fluoride will adsorb up 99 to about 0.03 g Tc per g MgF2. Periodic monitoring of the chemical trap contents will determine whether the chemical trapping agent, MgF2, is in need of replacement. [0018] Following contacting the contaminated UF6 with the metal fluoride chemical trap, the resultant purified liquid UF6 is removed from the trap. Typically, in a flow-through system, the removal occurs as a matter of course as the liquid 20 UF6 (first contaminated, then purified) is pumped or transferred through the system. Accordingly, attached to the effluent port of the chemical trap is a cold trap for containing the purified UF 6. The cold trap is typically a cylinder for longer term storage of the purified UF6 which is immersed in a cold temperature bath, for example a liquid nitrogen bath (-196°C). In a flow-through system the direction of liquid flow may be vertically upward or downward. Alternative modes of liquid- solid contact are also useful, including co- current, countercurrent and unicurrent flow of the liquid and solid phases. The 25 unicurrent flow implies one of the phases is fixed, while the other is mobile. Both phases can be temporarily fixed (no flow) and either one of the two phases is then removed at a later time. [0019] The following examples are offered solely for the purposes of illustration, and are intended neither to limit nor to define the invention.
30 EXAMPLES
99 [0020] A set of tests was designed to test the removal of Tc from liquid UF 6 utilizing a MgF 2 chemical trap. The tests 99 consisted of transferring liquid UF6, containing a high concentration of Tc through a chemical trap and cold trapping the outlet of the trap. The trap contents were varied and a duplicate trap was operated for comparison. The outlet cold 35 traps were subsampled and analyzed for 99Tc and the results evaluated for 99Tc removal efficiencies.
Trap Construction
[0021] Two identical MgF 2 chemical craps were constructed using "15" cylinder bodies (see Figure 1). Both ends were 40 drilled and a 10 micron filter (see Figure 2) was silver soldered into the outlet of the traps. A cajon fitting was silver soldered to the inlet, which allowed access to the trap interior to facilitate trapping material changeouts. The 10 micron filter kept trapping material from contaminating the UF 6. The traps were pressure checked at 1380 kPa gauge (200 psig), leak checked and passivated with fluorine. The traps were wrapped with a heat tape and connected to a Variac to control temperature at -100°C. 45 Test Procedure
[0022] Testing was conducted using a vacuum manifold system typically used for liquid UF6 subsampling. The trap was connected to the cajon fitting used for subsampling UF6 cylinders. Tubing extended from the outlet end of the trap 50 to a "2S" container immersed in a liquid nitrogen bath. The liquid UF6 was supplied in "2S" containers. The following steps were used in each test conducted.
1. Liquified "2S" feed cylinder. 2. Attached cold trap "2S" to manifold 55 3. Attached liquified "2S" feed cylinder to manifold 4. pressure and leak checked apparatus 5. Applied liquid nitrogen to cold trap 6. initiated liquid UF6 flow through filter
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7. Maintained established pressure limits 8. Recorded transfer time and pressures 9. subsampled filtered UP6 99 10. Analyzed filtered (purified) UF6 for Tc. 5 Control - Filter Test
[0023] The control test is a preliminary filter test in which no MgF 2 trapping media is used. The test is used to determine the amounts of 99Tc which can be removed on a 10 micron filter in the absence of any trapping media. 10 The test was conducted on traps 1 and 2 with the feed cylinder heel. The traps were washed and the liquid was sent for 99Tc analysis.
PRELIMINARY TEST RESULTS
15 [0024]
Trap No. Tc Inlet* Concentrations Tc Outlet* Concentrations % Tc Removal Trap #1 0.488 0.429 12.1 20 Trap #2 0.560 0.510 8-9 * Pg Tc/g 235U
25 Wash Solutions Trap No. Feet "2S" Wash Filter* Wash Trap #1 0.966 1.266
30 Trap #2 1.56 0.741 * Pg Tc Total
99 [0025] As can be seen from the above data, the 10 micron filters were not effective in trapping Tc from liquid UF6. 99 99 35 The average percent of Tc removal from the liquid UF 6 was about 10 percent with equal amounts of Tc found in the filters and the feed cylinders. This indicated no selective removal of 99Tc by the filter in the empty trap.
EXAMPLE 1
99 40 [0026] This example illustrates the effectiveness of a MgF 2 trapping agent in removing Tc from liquid uranium hex- afluoride.
Test Number 1
45 [0027] The chemical traps were cleaned and filled with 0.64 cm (1/4") MgF2 pellets that were manufactured at the Portsmouth Gaseous Diffusion Plant in Piketon, Ohio. The filters were evacuated to a vacuum with heat applied, then treated with fluorine several times to remove excess water. [0028] The inlet UF6 pressure was throttled at 206 kPa (30 psig).
50 RESULTS - TEST NUMBER 1
[0029]
55
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MgF2 FILTER TEST #1 Trap no. Transfer Wt. Gms. Tc Inlet* Tc Outlet* Pg Tc Removed Tc% Removal Concentrations Concentrations 5 Trap #1 1494 0.429 0.0286 20.1 93.5 Trap #2 1729 0.51 0.219 14.2 57.5 * Ug Tc/g 235U
10 [0030] As the above data indicates, the traps removed 99Tc in much greater amounts than the controls. The amounts removed in Traps #1 and #2 differed significantly, however. The inequality may have been due to the difference in weight of MgF2 in the traps.
15 EXAMPLE 2
99 [0031] This example illustrates the impact of unequal eights of MgF2 on the ability of the traps to sequester Tc. In view of the results in Example 1, this test utilized equal amounts of MgF2 in the two traps.
20 Test Number 2
[0032] Two traps were loaded equally with 40 grams of 0.64 cm (1/4") MgF2 pellets, then heated, evacuated, and fluorinated as described above. A pressure gauge was added to the outlet line of the traps. The pressure differentials were recorded to indicate any pressure drop occurring through the MgF2 trap. The flow rate of the liquid UF6 was -7 3 -5 3 25 estimated to be 4.59 x 10 m /s (1.62 x 10 ft /sec) and the residence time was about 306 seconds.
RESULTS - TEST NUMBER 2
[0033]
30 MgF2 FILTER TEST #2 Trap no. Transfer Wt. Gms. Tc Inlet* Tc Outlet* Pg Tc Removed Tc % Removal Concentrations Concentrations
35 Trap #1 2036 0.437 0.078 20.5 82.3 Trap #2 1741 0.440 0.198 11.7 55.2 * Pg Tc/g 235U
40 -7 3 -5 3 [0034] The average flow rate of the liquid UF6 was estimated to be 9.40 x 10 m /s (3.32 x 10 ft /sec) and the residence time was 150 seconds. The traps again behaved differently with resultant Tc removal very similar to the results of Test Number 1. The trap material was removed and the interior of the trap inspected by a video probe to verify that there was no difference in the trap construction. The inequality in Tc removal efficiency may be the result of the 0.64 cm (1/4") pellets allowing channelling through the 3.81 cm (1 1/2") diameter trap body. A subsequent test was established 45 to determine if a smaller mesh MgF2 would provide more consistent results.
EXAMPLE 3
99 [0035] This example illustrates the use of 8-12 mesh MgF2 for the removal of Tc from liquid UF6. 50 Test Number 3
[0036] In this test the two traps were each loaded with 106grams of 8-12 mesh MgF 2. The traps were evacuated under heat and fluorinated as described above. 55
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RESULTS - TEST NUMBER 3
[0037]
5 MgF2 FILTER TEST #3 Smaller Pellets 8 - 12 Mesh Trap no. Transfer Wt. Gms. Tc Inlet* Tc Outlet* Pg Tc Removed Tc % Removal Concentrations Concentrations Trap #1 1816 0.379 0.286 18.4 92.6 10 Trap #2 1648 0.3906 0.0174 19.6 95.6 * Pg Tc/g 238U
99 15 [0038] The increased surface area and bed density of the small mesh MgF2 produced consistent Tc trapping effi- -7 3 ciency of greater than 90 percent. The flow rates of the liquid UF6 through the traps was estimated at 8.8x 10 m /s -5 3 (3.1 x 10 ft /sec) and did not seem to be affected by the smaller mesh size of the MgF2.
EXAMPLE 4
20 [0039] This example illustrates the trapping consistency of the system in Example 3, through several cylinders of UF 6.
Test Number 4
25 [0040] Testing was continued by running several "2S" containers of UF6 through trap #2 to determine consistency of 99Tc removal efficiency. It must be noted that the trap experienced a wet- air inleakage following cooldown after Test Number 3 (above). The gasket was changed and Test Number 4 was conducted.
RESULTS - TEST NUMBER 4
30 [0041]
MgF2 FILTER TEST #4 Cylinder Number Transfer W1. Tc Inlet* Tc Outlet* Pg Tc Removed Tc % Removal 35 Gms. Concentrations Concentrations 2 1690 0.219 0.039 8.61 82.5 3 1687 0.188 0.029 8.1 85.5 4 1607 0.0174 0.035 -0.85 No Removal 40 * Pg Tc/g 235U
[0042] More than 80 percent of the 99Tc was removed in two of the test cylinders. However, this amount is 10% less -6 3 -5 45 than the results seen in Test Number 3. The flow rate of the liquid UF6, was estimated at 1.03 x 10 m /s (3.65 x 10 3 ft /sec) and the residence time was 136 seconds. The wet-air inleakage may have affected the results. More UF6 may 99 have hydrolyzed on water sites of the MgF2 pellets taking up sites for Tc trapping to occur. Cylinder 4 was tested to 99 99 see how the MgF2 would remove even low level Tc from liquid UF6. The Tc outlet concentrations were the same as previous tests which was apparently due to release of material from previous tests. However, the results could indicate
50 sampling and detection errors at such low levels of technetium.
EXAMPLE 5
99 [0043] This example illustrates the removal of Tc from four cylinders of UF6 containing different concentrations of 55 the contaminant.
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Test Number 5
[0044] Test Number 5 consisted of running four more cylinders of UF6 through trap #2. The gaskets were changed as a precaution. The trap was evacuated after UF6 from each cylinder was passed through the trap. 5 [0045] Four cylinders containing several different concentrations of 99Tc were used for this test.
RESULTS - TEST NUMBER 5
[0046] 10 FILTER 2 Cylinder Number Transfer Wt. Tc Inlet* Tc Outlet* Pg To Removed Tc % Removal Gms. Concentrations Concentrations 15 6 1568 0.465 <0.02 9.6 95.8 6 1469 0.408 0.016 9.7 96.1 7 1909 0.19 <0.008 11.8 95.8 8 301 1.40 0.021 5.7 98.6 20 * Pg Tc/g 235U
99 [0047] Trap #2 removed 96% of the Tc from the four cylinders of UF 6. The flow rate of the liquid UF 6 was estimated at 9.57 x 10-7 m3/s (3.38 x 10-5 ft3/sec) and the residence time was 146 seconds. The trapping efficiency discrepancies 25 seen in earlier tests were probably a result of the wet- air inleakage experienced when the filter cooled and the aluminum gasket loosened. As a precaution the gaskets were changed and the trap was immediately evacuated and buffered with nitrogen for the remaining tests.
EXAMPLE 6 30
[0048] This example illustrates the efficiency of the present method using twelve cylinders of contaminated UF6.
Test Number 6
35 [0049] Twelve "2S" cylinders containing 1.303 Pg Tc/g 235U were trapped consecutively in this test. The trap was evacuated after each cylinder was transferred. Trap #2 was used with the same trapping media as used in the previous tests.
RESULTS - TEST NUMBER 6 40
[0050]
Cylinder Transfer Wt. Tc Inlet* Tc Outlet* Pg 99Tc Percent
45 Number grams Concentrations Concentrations Removed Removal 9 1213 1.303 0.011 47.2 99.2 10 1449 1.303 0.011 56.3 99.2 11 1187 1.303 0.015 46.0 98.9 50 12 1248 1.303 0.013 48.4 99.0 13 1132 1.303 0.018 43.8 98.6 14 2181 1.303 0.009 85.0 99.3
55 15 1195 1.303 0.020 48.1 98.5 16 1352 1.303 0.009 52.7 99.3 17 1199 1.303 0.009 46.7 99.3
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(continued)
Cylinder Transfer Wt. Tc Inlet* Tc Outlet* Pg 99Tc Percent Number grams Concentrations Concentrations Removed Removal 5 18 1160 1.303 0.025 44.6 98.1 19 1799 1.303 0.031 68.8 97.6 20 1542 1.303 0.016 59.7 98.8
10 16,657 645.3
[0051] The 12 test cylinders used in this test had ≈99% of the 99Tc removed. The results were consistent at the 98-99% -6 3 removal efficiency for the total 16,659 grams of UF 6. The flow rate of the liquid UF 6 was estimated to be 1.17 x 10 m /s (4.13 x 10-5 ft3/sec) and the residence time was 120 seconds.. 15 [0052] The total 99Tc contained in chemical trap #2, after a total of 20 "25" cylinders were filtered, was theoretically 718 Pg Tc. The high percentage removal of Tc indicates that saturation was not approached. These results further indicate that UF6 contact with MgF2 is more important than flow rates and residence time within the boundaries of our tests. This series of tests has demonstrated that with the 8-12 mesh MgF2 and a trap bed of 106 grams in the 7 x 3.81 99 cm (1 1/2 inch) chambers in excess of 28 Kg of UF6, were successfully stripped of Tc. 20 [0053] Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.
25 Claims
1. A process for the removal of technetium from contaminated enriched uranium hexafluoride which is withdrawn from a diffusion plant containing said technetium, said process comprising:
30 (a) contacting said contaminated uranium hexafluoride in liquid form with metal fluoride in solid form for a period of time sufficient for said technetium to become adsorbed onto said metal fluoride thereby producing a purified 2 2 uranium hexafluoride liquid, wherein the rate of UF 6 processing is at least 2440 kg/m /hour (500 lbs/ft /hour); and (b) removing said purified uranium hexafluoride liquid from said metal fluoride having adsorbed technetium.
35 2. A process in accordance with claim 1, wherein said technetium is technetium-99.
3. A process in accordance with claim 1, wherein said metal fluoride is magnesium fluoride in the form of pellets.
4. A process in accordance with claim 1, wherein said metal fluoride is magnesium fluoride in the form of 0.32 cm to 40 0.95 cm (1/8" to 3/8") pellets.
5. A process in accordance with claim 1, wherein said metal fluoride is magnesium fluoride in the form of 8-12 mesh pellets.
45 6. A process in accordance with claim 1, wherein said metal fluoride is present in a trap and is treated with fluorine prior to said contacting step (a).
2 2 7. A process in accordance with claim 1, wherein the rate of UF 6 processing is at least 14650 kg/m /hour (3000 lbs/ft / hour). 50 2 2 8. A process in accordance with claim 1, wherein the rate of UF 6 processing is at least 22460 kg/m /hour (4600 lbs/ft / hour).
9. A process in accordance with claim 1, wherein said purified uranium hexafluoride liquid contains less than about 55 0.1 Pg technetium/g uranium.
10. A process in accordance with claim 1, wherein said purified uranium hexafluoride liquid contains less than about 0.01 Pg technetium/g uranium.
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11. A process in accordance with claim 1, wherein said purified uranium hexafluoride liquid contains less than about 0.001 Pg technetium/g uranium.
5 Patentansprüche
1. Verfahren zum Entfernen von Technetium aus verunreinigtem angereichertem Uranhexafluorid, welches aus einer Diffusionsanlage entnommen wird, die das Technetium enthält, wobei das Verfahren Folgendes umfasst:
10 (a) In-Kontakt-Bringen des verunreinigten Uranhexafluorids in flüssiger Form mit Metallfluorid in fester Form für eine ausreichende Zeit, damit das Technetium auf dem Metallfluorid adsorbiert wird, wodurch eine gereinigte Uranhexafluorid-Flüssigkeit erzeugt wird, wobei die Geschwindigkeit der UF6-Verarbeitung mindestens 2.440 kg/m2/Stunde (500 lb/ft2/Stunde) beträgt; und (b) Entfernen der gereinigten Uranhexafluorid- Flüssigkeit von dem Metallfluorid, welches das adsorbierte Tech- 15 netium aufweist.
2. Verfahren nach Anspruch 1, wobei es sich bei dem Technetium um Technetium-99 handelt.
3. Verfahren nach Anspruch 1, wobei es sich bei dem Metallfluorid um Magnesiumfluorid in Form von Pellets handelt. 20 4. Verfahren nach Anspruch 1, wobei es sich bei dem Metallfluorid um Magnesiumfluorid in Form von Pellets der Größe 0,32 cm bis 0,95 cm (1/8 Inch bis 3/8 Inch) handelt.
5. Verfahren nach Anspruch 1, wobei es sich bei dem Metallfluorid um Magnesiumfluorid in Form von Pellets der 25 Größe 8 bis 12 Mesh handelt.
6. Verfahren nach Anspruch 1, wobei das Metallfluorid in einer Falle vorliegt und vor dem Schritt (a) des In-Kontakt- Bringens mit Fluor behandelt wird.
30 2 7. Verfahren nach Anspruch 1, wobei die Geschwindigkeit der UF6-Verarbeitung mindestens 14.650 kg/m /Stunde (3.000 lb/ft2/Stunde) beträgt.
2 8. Verfahren nach Anspruch 1, wobei die Geschwindigkeit der UF6-Verarbeitung mindestens 22.460 kg/m /Stunde (4.600 lb/ft2/Stunde) beträgt. 35 9. Verfahren nach Anspruch 1, wobei die gereinigte Uranhexafluorid- Flüssigkeit weniger als ungefähr 0,1 Pg Techne- tium je g Uran enthält.
10. Verfahren nach Anspruch 1, wobei die gereinigte Uranhexafluorid-Flüssigkeit weniger als ungefähr 0,01 Pg Tech- 40 netium je g Uran enthält.
11. Verfahren nach Anspruch 1, wobei die gereinigte Uranhexafluorid- Flüssigkeit weniger als ungefähr 0,001 Pg Tech- netium je g Uran enthält.
45 Revendications
1. Procédé de retrait de technétium d’hexafluorure d’uranium enrichi contaminé qui est extrait d’une usine de diffusion gazeuse contenant ledit technétium, ledit procédé comprenant : 50 (a) la mise en contact dudit hexafluorure d’uranium contaminé sous forme liquide avec un fluorure métallique sous forme solide pendant une période de temps suffisante pour que ledit technétium soit adsorbé sur ledit fluorure métallique pour obtenir ainsi un liquide d’hexafluorure d’uranium purifié, la vitesse de traitement de 2 2 l’UF6 étant d’au moins 2440 kg/m /heure (500 lbs/ft /hour) ; et 55 (b) le retrait dudit liquide d’hexafluorure d’uranium purifié dudit fluorure métallique comprenant le technétium adsorbé.
2. Procédé selon la revendication 1, dans lequel ledit technétium est du technétium-99.
10 EP 0 984 903 B1
3. Procédé selon la revendication 1, dans lequel ledit fluorure métallique est du fluorure de magnésium sous la forme de pastilles.
4. Procédé selon la revendication 1, dans lequel ledit fluorure métallique est du fluorure de magnésium sous la forme 5 de pastilles de 0,32 cm à 0,95 cm (1/8" à 3/8").
5. Procédé selon la revendication 1, dans lequel ledit fluorure métallique est du fluorure de magnésium sous la forme de pastilles de 8-12 mesh.
10 6. Procédé selon la revendication 1, dans lequel ledit fluorure métallique est présent dans un piège et est traité avec du fluor avant ladite étape de mise en contact (a).
2 7. Procédé selon la revendication 1, dans lequel la vitesse de traitement de l’UF6 est d’au moins 14 650 kg/m /heure (3000 lbs/ft2/hour). 15 2 8. Procédé selon la revendication 1, dans lequel la vitesse de traitement de l’UF6 est d’au moins 22 460 kg/m /heure (4600 lbs/ft2/hour).
9. Procédé selon la revendication 1, dans lequel ledit liquide d’hexafluorure d’uranium purifié contient moins d’environ 20 0,1 Pg de technétium/g d’uranium.
10. Procédé selon la revendication 1, dans lequel ledit liquide d’hexafluorure d’uranium purifié contient moins d’environ 0,01 Pg de technétium/g d’uranium.
25 11. Procédé selon la revendication 1, dans lequel ledit liquide d’hexafluorure d’uranium purifié contient moins d’environ 0,001 Pg de technétium/g d’uranium.
30
35
40
45
50
55
11 EP 0 984 903 B1
12 EP 0 984 903 B1
13 EP 0 984 903 B1
14 EP 0 984 903 B1
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.
Patent documents cited in the description
• US 3165376 A [0005]
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