|Publication number||US3025143 A|
|Publication date||Mar 13, 1962|
|Filing date||Jun 9, 1959|
|Priority date||Oct 28, 1957|
|Publication number||US 3025143 A, US 3025143A, US-A-3025143, US3025143 A, US3025143A|
|Inventors||Huff John B|
|Original Assignee||Huff John B|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (2), Referenced by (3), Classifications (13)|
|External Links: USPTO, USPTO Assignment, Espacenet|
March 13, 1962 J. B. HUFF 3,025,143
SEPARATION APPARATUS Original Filed Oct. 28, 1957 IN V EN TOR. John fi. Huff BY fl w... 4 M
fitter/1e 3,825,143 Patented Mar. 13, 1962 .7 triiire 3,025,143 SEPARATHUN APPARATUS John B. Hulf, Blackfoot, Idaho, assignor to the United States of America as represented by the United States Atomic Energy Commission Original application Oct. 28, 1957, Ser. No. 692,989, now Patent No. 2,897,049, dated July 28, 1959. Divided and this application June 9, 1959, Ser. No. 819,195 3 Claims. (Cl. 23-277) This is a divisional application of application Serial No. 692,989, filed on October 28, 1957, now United States Patent No. 2,897,049, and relates to an apparatus for separating nuclear reactor waste solutions into fractions of diflerent degrees of diffioulty of decontamination and of reduced volume.
The inadequacy of existing methods for the disposal of high activity level, aqueous wastes has been generally recognized. Since it is not possible to disperse high activity level wastes to the environment, it is necessary that they be stored. It is, of course, possible to simply store the liquids in underground tanks but the constant hazard arising from the possibility of leakage and the tremendous cost of the tanks necessary makes this course of action undesirable.
Concentration of the solution to remove the Water therefrom is difficult when the solution contains large quantities of nitric acid and aluminum nitrate. Such solutions become syrupy and partial decomposition takes place. As the temperature is raised, corrosion and heat transfer problems become more serious. Removal of water, however, is essential for a long-term solution to the problem.
In addition, the nitrates present should be destroyed to leave the radioactive wastes in the form of oxides of the elements contained therein. These materials may be stored with a reasonable degree of ease. However, complete separation of the radio active constituents of the waste solution from the nonradioactive constituents would be the most desirable answer to the problem of storage of aqueous wastes since the physical volume to be stored would be reduced thereby by a factor of some ten thousand times.
A complete segregation of radioactive from nonradioactive constituents is a problem of great chemical complexity complicated by the high level of radioactivity encountered. Since aluminum nitrate makes up the great bulk of the nonradioactive constituents of the typical waste solution obtained from treatment of spent uraniumaluminum fuel elements, removal of aluminum and nitrate ions from the solution would reduce the storage problem to a more reasonable level and, in addition, would remove a prhnary source of interference in the separation of fission products.
It is accordingly an object of the present invention to develop a method of concentrating radioactive waste solutions.
it is a further object of the present invention to develop a method of handling radioactive Waste solutions to separate radioactive from nonradioactive constituents thereof.
It is a more specific object of the present invention to develop a method of vaporizing aluminum ions and nitrate ions from the radioactive waste solution obtained from processing spent aluminum-uranium fuel elements.
Another object of the present invention is to provide an apparatus by which the above objectives may be accomplished.
These and other objects of my invention are attained by my novel method wherein the highly radioactive waste solution is fed to the top of a burning mass of coke and chlorine is passed through the resulting mixture of oxides and ash to remove aluminum as the chloride.
The invention will now be described with reference to the accompanying drawing wherein the single figure illustrates a schematic view of a furnace in which my method can be carried out.
The drawing shows a retort 10 formed of firebrick. Retort it) is located in a pit 11 in the ground. Pit 11 is lined with concrete walls 12 having cooling coils 1.3 located therein. Insulating material 14, such as magnesia bricks, is located in the space between retort 10 and concrete walls 12.
Pit ll. is enlarged at 15 to provide room for two flue chambers 16 and 17 which are provided with flues 18 and 19, respectively. The enlarged portion 15 of pit i1 is also lined with firebrick. Flue chambers 16 and 17 may alternatively be placed in communication with retort 10 by operation of butterfly valves 20 and 21. Flue chambers 16 and 17 each contain a brick checkerwork heat reservoir 22 and 23, respectively, The bottom of retort llil slopes toward a discharge pipe 24.
Chlorination product recovery lines 25 and 26 afford communication between the bottom of retort 10 and the exterior and are provided with valves 27 and 28. Conduits '29 and 38 extend between flue chambers 16 and 17, respectively, and lines 25 and 26, respectively, and are provided with valves 31 and 32.
One or more liquid waste feed lines 33 penetrates the retort it near the top thereof and terminates in a sprinkler head 34 which is recessed in the firebrick. The sprinkler head 34- may be protected by a water jacket (not shown). One or more oil feed lines 35 penetrates the retort 10 just below the liquid waste feed lines 33'.
A supply bin 36 is located above the top of the retort 10. The supply bin is filled with a carbonaceous material such as coke, petroleum coke or carbon black which is fed by screw conveyor 37 through an opening in the firebrick into retort 10.
The retort is operated in a two-stage cycle. In the first stage water and nitrates are expelled from the waste solution, and in the second stage aluminum chloride is volatilized. The drawing shows the apparatus set for first-stage operation.
In this stage butterfly valves 20 and 21 are alternately opened and closed, valves 27'and 28 are closed, and valves 31 and 32 are alternately opened and closed. Retort 10 is charged with carbonaceous material from bin 36 and the carbonaceous material is set on fire. Air is directed into the retort 10 through flue 18, past brick heat reservoir 22 in flue chamber 16, through conduit 29 and line 25 while off-gas passes out past brick heat reservoir 23 in flue chamber 17 to flue 19. After a short period of time, on the order of 15 minutes, the flow of air is reversed and the air in passing over the brick heat reservoir 23 becomes preheated. The off-gas passes over brick heat reservoir 22 heating it.
An air-oil mixture is passed through line 35 and the mixture burns as it enters the retort. Liquid waste solution is then introduced into the retort through line 33 and sprayed on to the top of the coke fire through sprinkler heads 34. The solution is thereby evaporated and calcined. Oxides of nitrogen obtained as a product of the calcination constitute a potentially dangerous explosion and corrosion hazard. The slightly smoky flame from the burning of the air-oil mixture reduces these to ele mental nitrogen which proceeds, along with excess air and other products of combustion, through one of the brick checkerwork heat reservoirs to its associated flue.
This procedure is continued until a considerable mass of aluminum oxide interspersed in carbonaceous material and ash is obtained. The chlorination stage is then started.
In the chlorination stage chlorine is passed into the mass from one of the lines 18 or 19 and aluminum chloride taken off through one of lines 25 and 26. Valves 31 and 32 are kept closed. A temperature of between 900 C. and 1000 C. is suitable for the chlorination stage. This temperature will be originally attained from the burning coke and will be maintained by the heat of reaction of chlorine with aluminum oxide.
The aluminum chloride is permitted to condense and is recovered. Fission product chlorides and ash remain in the retort. If any unburned carbonaceous material remains it may be burned out with oxygen. The residue is removed through ash discharge pipe 24, and the retort is then ready for a new charge of carbonaceous material.
Petroleum coke is used by preference since it is almost 100% carbon. Only a relatively small quantity of ash will be obtained therefore from a complete cycle of operations.
The mixture of ash and fission products can be stored since it is of relatively small volume or it can be processed to recover individual fission products or fractions of fission products therefrom for use as radiation sources or as tracer elements.
An elevated pressure of air or nitrogen may be supplied to the insulated space surrounding the furnace and to the coke supply bin so that any leakage will be into the system.
A furnace which is 2 meters in diameter and 6 meters in height will incinerate 1570 liters of 2.2 M aluminum nitrate solution per hour. As a chlorinator it will have a capacity of 40,000 pounds per day, equivalent to 5,670 gram mols of aluminum chloride per hour. If operated 14.9 hours as an incinerator and 9.1 hours as a chlorinator, 23,400 liters of waste solution will be processed in 24 hours. The consumption of petroleum coke for incineration is approximately 725 kilograms per hour of incineration. Chlorine is used during the chlorination cycle at a rate of about 500 kilograms per hour.
Life of the furnace is estimated at 100 days during which time it should be able to process over 2,000,000 liters of waste solution. At the end of this time it is proposed that the furnace will be filled up and abandoned as its radioactivity is so high to make it useless to salvage any of the components.
The off-gas from the incineration stage will contain all those elements volatilized in that step. This will include some radioactive material-mostly rutheniumwhich must be removed from the off-gas before it is passed to the atmosphere. This is accomplished by passing the otfgas through an oil scrubber at a temperature slightly over 100 C. The oil used can then be evaporated from the residue. Other means of decontaminating the off-gas are available. These include filtration through glass wool filters and redistillation in the presence of carbon. One or any combination of these procedures may be employed to obtain an off-gas which can be passed to the atmosphere.
The stream containing aluminum chloride can not be so simply treated. The condensate obtained by cooling this stream is highly contaiminated by Nb and Zr It is at present contemplated that this activity be handled by temporary storage of the aluminum chloride. After storage of from 2 to 4 years the activity should decrease to the point where the aluminum chloride may be released for unrestricted use.
Decontamination to comparable levels of course would be more desirable and a number of possible methods are indicated such as fractional sublimation, reduction, separation, filtration, and resublimation. The invention however is not concerned with this problem and the field is left open to other workers to develop an economically satisfactory process.
It will be noted that I have outlined a process which results in the transformation of aluminum nitrate wastes into three fractions. That portion vaporized in the incineration stage, is as described, easily decontaminated. The aluminum chloride fraction may be stored for a few years before it can be used unrestrictedly. A few years storage represents a practical solution to the problem as opposed to storage of the entire waste solution which may have to be for centuries and therefore represents only a stopgap solution.
The fission product fraction will have to be separated into its components or stored indefinitely. This can be done since the volume is relatively small and the material is in an easily stored form.
It will also be noted that difiiculty in evaporating aluminum nitrate solutions is obviated according to this invention. The solution is sprinkled onto burning coke and is immediately evaporated and calcined to the oxide. The oxides appear as fine particles interspersed with ash which make them easily susceptible to chlorination in the chlorination stage.
Details of a preliminary laboratory experiment will now be described. A retort was fabricated from Vycor glass and connected to a Pyrex condenser by a ball joint. The retort was heated to 900 C. by a furnace having Nichrome heating elements.
To 10 grams carbon black was added 4.5 grams liquid waste. This liquid waste was obtained by dissolving in nitric acid a uranium fuel element clad with aluminum. The fuel element had been irradiated in a neutronic reactor and had been allowed to undergo radioactive decay for several weeks to reduce its radioactivity. The solution had a specific gravity of 1.29 and was 1.6 M in aluminum, about 5.8 M in nitrates and 1 M in ammonium ion. It had an activity equivalent to 67 curies/liter. The solution was heated in the retort to 900 C. in a nitrogen atmosphere. The off-gas was condensed at 0 C. and the condensate redistilled in the presence of carbon. A series of these redistillations indicated that ruthenium could be removed in this fashion. A number of tests on the off-gas indicated that it can be scrubbed to pass maximum permissible concentration.
Chlorine gas was passed at 900 C. through the carbon aluminum oxide mixture remaining in the retort. The vaporized constituents were permitted to condense and consisted primarily of aluminum chloride. Tests on this condensate indicated that complete decontamination of the aluminum chloride would be very difficult. Since it is economically possible to hold the material for long enough so that the material becomes decontaminated by the passage of time, these tests were not continued.
It was thus shown that the process of this invention is technically possible. Additional tests were made in a furnace which had an opening 10 cm. square and 46 cm. high and was lined with firebrick. A coke fire was started in the furnace and compressed air supplied through a hose. An aluminum. nitrate solution was fed at 5 liters per hour. The best efficiency obtained in these experiments showed that .97 liter of 2.2 M aluminum nitrate Was converted to ash for each pound of coke burned. Cost of fuel is therefore estimated to be on the order of one cent per liter.
It will be understood that this invention is not to be limited to the details given herein but that it may be modified within the scope of the appended claims.
What is claimed is:
1. An apparatus for treating an aqueous waste solu tion from a nuclear reactor, comprising an elongated vertical retort, a firebrick lining for the retort, a plurality of flue chambers above and in communication with the top of the retort, a like plurality of lines leading upward, one from each of said flue chambers, a like plurality of independently operated valves between the flue chambers and the top of the retort, each valve in its closed position shutting off the retort from one of the flue chambers whereby a stream of combustion gas may be led upward out of the retort through only one of the flue chambers sequentially, a charging chute adapted to carry solid dry carbonaceous material and entering the retort adjacent its top, a nuclear-reactor liquid-waste-carrying line entering the retort adjacent its top and below the entry of the charging chute, liquid spraying means in communication With said nuclear-reactor-liquid-wastecarrying line, an air-oil-mixture-carrying line adapted to produce a reducing flame and entering the retort adjacent its top at a region substantially spaced below the entry of the nuclear-reactor-liquid-waste-carrying line, a plurality of ohlorination-product-recovery lines equal to the plurality of flue chambers and entering the retort adjacent its bottom at a region substantially spaced below the entry of the nuclear-reactor-liquid-waste-canrying and air-oil-mixture-oarrying lines, said chlorination-productrecovery lines being adapted to carry liquid chlorination products away from the bottom of the retort by gravity, a second equal plurality of downcomer lines adapted to carrying heated air and chlorine gas and connecting said 20 flue chambers with said chlorination-product-recovery lines, valves in said downcomer lines near the connections with said chlorination-product-recovery lines, and valves in said chiorination-product-recovery lines at regions more remote from said retort than said connections with said downcomer lines, and means for discharging ash at the bottom of the retort.
2. The apparatus of claim 1 where the liquid spraying means is a sprinkler head.
3. The apparatus according to claim 1 where its supporting structure from beneath and laterally in all directions up to the level of the top of the flue chambers is the ground.
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|U.S. Classification||422/159, 422/206, 266/139, 422/232, 432/96, 976/DIG.380, 266/186, 432/101, 432/100|
|International Classification||G21F9/14, G21F9/06|