Abstract:
An apparatus and method for separating oxides of heavy isotopes of hydrogen (deuterium oxide, oxides of tritium and mixed isotope oxides) from light water (H2O) which is contaminated with these heavy hydrogen isotopes such as that currently being discharged in cooling water from nuclear power plants. A central aspect of this invention includes a plurality or bundle of elongated hollow core fibers which are positioned within an elongated enclosed housing having a feed water inlet, an exit stream outlet, and a permeate outlet. At least a portion of the hollow core fibers are at least partially filled or packed with small beads which are comprised of a porous exchange resin carrying waters of hydration. Porosity is controlled by the degree of cross-linking and bead diameter of the exchange resin which is preferably combined with aluminum sulfate or ammonium hydride to form (RSO 3 ) 3  Al or RSO 3  NH 4 . By passing the contaminated water through the bead-filled hollow core fibers within the housing, significant amounts of the oxides of heavy hydrogen isotopes remain in the hollow core fiber either combined with the resin beads or collected against the inside wall surfaces of the hollow core fibers. Some of the H2O in the contaminated water permeates out of the hollow core fibers for discharge from the permeate outlet. The water which discharges from the exit stream outlet is substantially lower in heavy hydrogen isotope content. Regeneration of the apparatus is also shown.

Description:
This is a continuation of Ser. No. 09/093,459, filed Jun. 8, 1998, which is a continuation in part of U.S. application Ser. No. 09/047,648 filed Mar. 25, 1998, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Scope of Invention 
     This invention relates generally to methods and apparatus for separating heavy isotopes of hydrogen, namely deuterium and tritium in their oxide form, from water which is contaminated with these heavy isotopes, and more particularly to an apparatus including the utilization of hollow core fiber filled with ion exchange beads as a separation medium. 
     2. Prior Art 
     Nuclear power plants must routinely deal with the replacement and disposal of contaminated water taken from the core reactor which is laden with heavy isotopes of hydrogen, namely deuterium oxides and tritium oxides. Tritium in particular is highly radioactive having a half life of about twelve and one half years emitting beta rays to form helium. 
     Periodically, the contaminated water from nuclear reactors must be replaced. It has become industry practice to dispose of the old contaminated water by simply dispersing it over adjacent ground areas. This is stressful to the environment as the deuterium oxides and tritium oxides are now known to have contaminated ground water sources. There appears to be no effective and economically practical means for otherwise disposing of this contaminated water so that this practice of ground disposal continues. 
     The present invention provides an economical alternative to ground disposal of contaminated water whereby the deuterium and tritium isotopes are held within lengths of hollow core fiber which have been filled or packed with ion exchange resin beads. Contaminated water is flowed through lengths of the filled hollow core fiber, substantially purified water discharging therefrom with the oxides of heavy isotopes of hydrogen being held or trapped within the hollow core fiber for appropriate disposal. Regeneration of the apparatus is also disclosed. This invention is equally useful for separating heavy isotopes of other smaller sized molecules such as those of oxygen and nitrogen. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention is directed to an apparatus and method for separating heavy isotopes of hydrogen (deuterium and tritium in their oxide form) from water which is contaminated with these heavy hydrogen isotopes such as that currently being discharged from nuclear power plants. A central aspect of this invention includes a single elongated length or a bundle of hollow core fibers, each which is at least partially filled or packed with small beads which are comprised of a porous exchange resin. Porosity is controlled by the degree of cross-linking and bead diameter of the ion exchange resin which is preferably combined with aluminum sulfate or ammonium hydroxide to form (RSO 3 ) 3  Al or RSO 3  NH 4  where R represents the cross linked polymer. By passing the contaminated water through the bead-filled hollow core fiber, significant amounts of the heavy hydrogen isotopes remain in the hollow core fiber for subsequent disposal, the water discharging from the exit end thereof being substantially lower in heavy hydrogen isotope content. The ion exchange beads in this invention function primarily through the exchange of waters of hydration. A method of regenerating the hollow core fiber bundle is provided, along with multi-component commercial systems. 
     It is therefore an object of this invention to provide an environmentally safe alternative to the ground dispersion of water contaminated with heavy isotopes of hydrogen. 
     It is yet another object of this invention to provide means for separating heavy isotopes of hydrogen from light water (H2O). 
     It is still another object of this invention to provide a commercially viable apparatus containing a bundle of filled hollow core fiber lengths in a housing for separating heavy isotopes of hydrogen, including tritium, from contaminated water and a method for regenerating said apparatus. 
     In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified schematic view of the apparatus 10 shown in FIG. 1B, enlargements of portions thereof shown in FIGS. 1A and 1C. 
     FIG. 2 is a graphic summary or composite of the effectiveness of the invention in reducing the deuterium oxide level in contaminated water. 
     FIG. 3 is a graphic presentation of one of the performance curves of FIG. 2 for 12% cross linked (X-L) ion exchange resin loaded with aluminum. 
     FIG. 4 is a graphic presentation of another of the performance curves of FIG. 2 for 4% cross linked ion exchange resin loaded with aluminum. 
     FIG. 5 is a graphic presentation of yet another of the performance curves of FIG. 2 for 2% cross linked ion exchange resin loaded with aluminum. 
     FIG. 6 is a graphic presentation of still another of the performance curves of FIG. 2 for 2% cross linked ion exchange resin loaded with ammonia. 
     FIG. 7 is a perspective schematic view depicting one aspect of the tritium and deuterium oxide separation process of the present invention, that being permeation through the walls of the hollow core fiber. 
     FIG. 8 is a simplified schematic view of a second aspect of the invention depicting an ion exchange resin particle exchanging atoms with the contaminated water, FIG. 8A depicting the precondition to exchange, FIG. 8B depicting the post exchange molecular arrangement. 
     FIG. 9 is a simplified example of a typical set of water contaminate absorption curves with respect to both contaminant separation aspects or mechanisms of the present invention. 
     FIG. 10 is a simplified perspective view of one commercial embodiment of the invention. 
     FIG. 11 is a graphic presentation of the test performance of a prototype apparatus similar to the embodiment of the invention shown in FIG. 10 showing a graphic comparison between the feed and exit stream concentrations of D 2  O contaminated water. 
     FIG. 12 is a graphic presentation of the test performance of a prototype apparatus similar to the embodiment of the invention shown in FIG. 10 showing a graphic comparison between the feed and permeate stream concentrations of D 2  O contaminated water. 
     FIG. 13 is a graphic presentation of the test performance of a prototype apparatus similar to the embodiment of the invention shown in FIG. 10 showing a graphic comparison between the feed and exit stream concentrations of D 2  O contaminated water during a second test run after regeneration. 
     FIG. 14 is a graphic presentation of the test performance of a prototype apparatus similar to the embodiment of the invention shown in FIG. 10 showing a graphic comparison between the feed and permeate stream concentrations of D 2  O contaminated water during a second test run after regeneration. 
     FIG. 15 is a graphic presentation of a typical set of performance curves of the invention depicting the various stages of performance effectiveness of both the exit stream and the permeate. 
     FIG. 16 is one example of a typical commercial system embodying the invention. 
     FIG. 17 is an example of a commercial system for regeneration of the contaminate separation apparatus of the invention. 
     FIG. 18 is a schematic view of a commercial system for both contaminate absorption and sequential regeneration. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, the apparatus is shown generally at numeral 10 at FIG. 1B and includes a length or coil of hollow core fiber 12 which is formed of cellulose acetate and is otherwise well known in the industry. The particular features of this hollow core fiber 12 used in the experiments reported below are an inside diameter of 1.3 mm (range of 1-3 mm), a wall thickness of 0.2 mm (range of 0.05 to 0.20 mm), an outside diameter of 1.7 mm, and a density of 1.20 g/cm 3 . 
     An inlet end of the hollow core fiber length 12 is connected to a plastic feed line 18 leading to a tank 14 filled with water contaminated with heavy isotopes of hydrogen, namely deuterium oxide. This contaminated water 36 is pumped in the direction of the arrow by pump 16 through connecting plastic tubing 18 into the hollow core fiber length 12. Radioactive tritium is unavailable for routine, unregulated use, but because the tritium oxide molecule is much larger than both hydrogen oxide and deuterium oxide, the results reported herebelow for deuterium oxide separation apply at least equally well for tritium separation. 
     It should be noted that other water permeable membranes may be utilized, the requirement being having a pore size and molecular composition sufficient to substantially allow permeation of H2O therethrough while substantially preventing permeation of heavy isotopes of water, namely deuterium and tritium in their oxide forms. 
     The hollow core fiber 12 as best seen in FIG. 1 C is filled or packed with separate beads 28 which are formed form an ion exchange resin as described herebelow. The outlet end of the hollow core fiber length 12 is connected to a length of plastic tubing 20 which discharges the processed and purified water into a separate container 22 as it flows from the hollow core fiber 12. 
     To prevent the exchange beads 28 from being forced out of the hollow core fiber length 12, a filter or trap is connected at the discharge end thereof as shown in FIG. 1A, an enlargement of area 26 of FIG. 1B. Two spaced apart plastic tubes 30 and 32 each having a small longitudinal aperture centrally therethrough, are positioned within the outlet end of the hollow core fiber length 12. These plastic tubes 30 and 32 are spaced apart by a quantity of packed cotton 34 so that none of the exchange beads 28 will flow beyond plastic tubing member 30, yet without substantially restricting the flow of processed water flowing out of the hollow fiber core length 12 into tube 20 in the direction of the arrow. 
     EXCHANGE RESIN BEADS 
     Details of the content and method of producing the ion exchange beads formed of cross linked styrene divinyl benzene polymer are disclosed in detail in Patterson&#39;s earlier U.S. Pat. No. 5,036,031 which is incorporated herein by reference. 
     LOADING PROCEDURE FOR ION EXCHANGE RESIN BEADS 
     The procedure described herebelow was used to load cross-linked ion exchange beads with aluminum. The procedure was applied for RSO 3  H with 2%, 4% and 12% cross-linking, 60 mesh, 100-200 mesh and 200400 mesh screened for size. 
     Pretreat Beads 
     The beads were first cleaned with hydrochloric acid (2% HCl) to take out all residual cations. Ion exchange with HCl will take out Al and other metal ions which were on the beads as shown by the formula: ##STR1## The beads are then rinsed with D.I. water until the pH returns to 5-6. This will remove the XCl. 
     Load Beads with Al 
     Prepare a solution of Al 2  (SO 4 ) 3  and, preferably warmed D.I water. Apply this solution to the beads to produce this reaction: ##STR2## Rinse the loaded beads with D.I. water until the pH returns to 5-6. The beads were initially treated prior to loading into the hollow core fiber. 
     After the ion exchange beads 28 were pretreated as above described, the hollow core fiber length 12 was loaded therewith. The loaded hollow core fiber length 12 was dried in an oven at approximately 50° C. for three days in order to drive out all residual water. Three separate lengths of hollow core fiber 12 were then filled with a prepared mixture of light water (H 2  O) and deuterium oxide in a ratio of approximately 61% D 2  O by volume which was taken from a supply bottle used for the entire experiment to insure consistency. The pump rate of the deuterium oxide contaminated water was set at 2 ml per hour using a constant rate high pressure pump 16. 
     The affluent discharging into container 22 was then analyzed. This affluent was split into separate samples taken at specific time periods from the start of each experiment. These time spaced samples were taken to provide an indication of the variability of the separation capability of the apparatus 10 over time. The test data taken is shown in Table I herebelow. 
     
                                           TABLE I__________________________________________________________________________HOLLOW CORE FIBER PACKEDWITH ION EXCHANGE RESIN BEADSION EXCHANGE     VOLUME OF             ELAPSED TIME                     FREEZING                           CORRES.                                 ACCUM.RESIN     AFFLUENT (ml)             (HRS)   POINT (C.)                           % OF H.sub.2 O                                 VOL. (ml)__________________________________________________________________________(RSO.sub.3).sub.3 Al (12% x-L)     2       1       2.011 52.64 2&#34;         2       2       1.801 47.15 4&#34;         2       3       1.983 51.91 6&#34;         0.5     3 1/4   1.701 44.53 6.5(RSO.sub.3).sub.3 Al (4% x-L)     0.5     2       0.312 8.17  0.5&#34;         2       3       1.979 51.81 2.5&#34;         2       4       2.248 58.85 4.5&#34;         1       5       2.255 59.03 5.5&#34;         0.5     5 1/4   2.254 59.01 6(RSO.sub.3).sub.3 Al (2% x-L)     0.25    2       0.148 3.87  0.25&#34;         6.3     5       2.028 53.09 6.55&#34;         0.9     5 1/2   2.101 55.00 7.45&#34;         .8      6       1.856 48.59 8.25(RSO.sub.3) NH.sub.4 (2% x-L)     1       2       1.777 46.52 1&#34;         3       4       2.267 59.35 4&#34;         1.5     5       2.264 59.27 5.5__________________________________________________________________________ 
    
     GRAPHIC DISPLAY OF DATA 
     This test data is also shown graphically in FIGS. 2 to 6. FIG. 2 is a composite of all of the performance data taken, while FIGS. 3 to 6 graphically depict the performance or separation capability of each of the ion exchange resins utilized in these experiments. Again, the contaminated test water was all taken from a common prepared source. 
     The concentration of deuterium oxide is depicted as a volumetric percentage of the total affluent sample volume and is determined by carefully establishing the freezing point of each sample. The freezing point of pure light water is 0.0° C. while the freezing point of pure deuterium oxide (D 2  O) is 3.82° C. The freezing point measurements were taken utilizing an Advanced Instruments Osmometer, Model 5600. The conversion from freezing point to percent deuterium oxide is assumed to be a linear relationship. 
     In reviewing these graphic performance data shown in FIGS. 2 to 6, the 2% cross-linked sample with aluminum showed the greatest change or decrease in the deuterium oxide level from 61% by volume down to less than 4% deuterium oxide concentration in the first sample taken after two hours of system operation. Note that with respect to both the 2% and 4% cross-linked exchange resin combined with aluminum, after three to five hours of operation, the second and subsequent samples taken demonstrate substantially higher concentrations of deuterium oxide, indicating that the apparatus is most effective in removing deuterium oxide (and presumably oxides of tritium) from the contaminated water within the first period of operation. 
     Combined Exchange-Membrane Separation 
     The separation of isotopes and molecules as above described is affected by the combination of the process of selective absorption on a resin and the selective permeation through the walls of the hollow core fiber membrane. The resin particles or beads as above-described are contained within the hollow core fibers and, of particular importance, may be regenerated without the need for removal of the resin from the hollow core fibers. 
     Referring now to FIG. 7, a pictorial view of a section of hollow core fiber 12 is there shown as previously described. Water molecules HOH depicted as circled at 40 permeate through the hollow core fiber wall faster than do the tritium oxide (TOH) molecules shown as triangles at 38. A substantially higher number of water molecules 40 permeate outwardly through the hollow core fiber wall than do the larger tritium oxide molecules 38. 
     In FIG. 8, the absorption aspect of the present invention is there depicted as a second separation agent. Each of the above described resin beads or particles 28 shown in FIG. 8A include metal sites M having associated waters of hydration 42. Each resin particle also contains hydrogen H as an essential aspect of these polymer resins. When the tritium oxide molecules 44 are combined with the resin molecules 28, the absorption results are shown in FIG. 8B. In the examples shown, three tritium oxide molecules 44 are absorbed into the resin particles 28! and three water molecules 42 are released therefrom. 
     Test performance results may be generalized as shown in FIG. 9. A section of resin filled hollow core fiber 12 is shown in the insert of this graph for reference. The feed stream flows into one end while the exit stream flows out of the other end of the hollow core fiber 12 as shown. The permeate passing through the hollow core fiber walls is also shown. The feed stream has an initial and constant concentration of tritium oxide as shown by the symbols F. The typical level of tritium oxide in the permeate is shown by the letter P over time, while the concentration level of tritium oxide in the exit stream over time is shown by the letters E. Note that the tritium oxide level in the permeate P does not raise or increase to the concentration level of the feed stream F but, at some point in time, the exit stream tritium oxide concentration E exceeds that of the feed stream F. This is likely due to the fact that the resin beads 28 initially absorb and hold a high level of tritium oxide, but eventually become saturated. 
     A commercially viable embodiment of the invention is shown generally at numeral 50 in FIG. 10. This commercial module 50 includes an elongated tubular housing 52 having a header 58 sealingly connected at each end thereof which supports an inlet tube 54 and an outlet tube 56, respectively. Positioned within the housing 52 is a bundle of elongated hollow core fibers 60, each of which is filled with ion exchange resin beads as previously described. This bundle of hollow core fibers 60 is held together by header 62 at each end thereof and positioned within housing 52. The feed stream enters the device 50 at inlet 54 in the direction of arrow E, while the exit stream flows into the direction of arrow F from outlet 56. Headers 62 insure that all of the feed stream liquid flows through and not outside of the hollow core fiber members 60. Separately, permeate flows from permeate outlet 64 in the direction of arrow G to a condenser 66. 
     The experimental test results reported herebelow utilize this experimental module in developing the data shown in FIGS. 11 to 14. The test module 50 includes thirty two such hollow core fibers 60 filled with ion exchange resin particles 61. Each of the fibers were eight feet in length. The feed stream had a D 2  O concentration of 4.85 percent by weight within water. The experimental results are described more fully herebelow. 
     Still referring to FIG. 10, the apparatus 50 may be regenerated when the ion exchange resin bead 61 packed within each hollow core fiber member 60 becomes saturated as previously described in FIG. 9. Saturation may be determined by sensing the D2O and/or the TOH concentrations in the exit stream. To regenerate the resin, the feed stream is interrupted and, preferably, the apparatus 50 is emptied of fluid. Thereafter, a stream of hot air is forced into inlet 68 in the direction of arrow H. Inlet 54 and outlet 56 are closed during this regeneration process so that the heated air (at approx. 70° C., for example) would be fed into housing 52 through inlet 68. The heat releases waters of hydration TOH and H2O. When the humidity of the heated air exiting the housing 52 at outlet 64 reaches a predetermined humidity level, the exit gas would flow to a separate high capacity condenser (not shown in FIG. 10) to condense the maximum amount of water from this exit airstream. 
     Referring now to FIGS. 11 and 12, the above described module 50, having thirty two columns of hollow core fiber members 60 longitudinally arranged and packed therein, were test run utilizing a feed stream of light water contaminated with 4.85% D2O by weight. The D2O concentration of the exit stream was monitored and is shown in FIG. 11 with respect to the exit stream flow shown by weight (g) over time. 
     In FIG. 12, during the same experiment, the concentration of the permeate as a function of total permeate flow by weight (g) is there shown. With respect to both the exit stream and the permeate, the D2O concentrations were initially very low indicating a very high efficiency in D2O separation from water which gradually decreased over time. 
     Referring now to FIGS. 13 and 14, the same experiment utilizing the same module 50 having thirty two columns of hollow core fiber members filled with the same ion exchange resin was retested. Prior to this retest, the airflow regeneration process above described was completed. 
     In comparing the test results of the first run to the second run after regeneration, it is noted that, with respect to the exit stream concentrations shown in FIGS. 11 and 13, the greatest reduction in D 2  O was 90% on the first run, increasing to virtually 100% in the second run after regeneration. Likewise, comparing FIGS. 12 and 14, the permeate concentration on the first run showed a maximum near test onset of 55%, increasing to above 60% D2O reduction in the initial sampling after regeneration. 
     Commercial System 
     To commercialize the present invention, it is useful to divide the separation performance curves with respect to both the exit stream and permeate into sections or segments as shown in FIG. 15. With respect to the exit stream, the first exit product with the highest reduction in heavy water concentration ends at time S. Second exit product and third exit product stages end at times T and U, respectively. After time U, it is recommended that each module be taken out of service and regenerated as above described. 
     With respect to the permeate, there is also a high efficiency time period ending at time R during which the contaminant reduction is at a maximum. During the second permeate stage between time R and U, the decrease in contaminate removal is generally steady and of a very useful nature. Obviously, although the permeate would continue to be at a contaminate level below that of the feed stream, the module should be regenerated because the exit stream would then contain a higher contamination level than that of the feed stream. 
     Putting these concepts of stages into effect, referring to FIG. 16, one example of a commercial system is shown generally at numeral 70 The feed stream enters a stage 1 absorber 72, the exit stream therefrom being monitored for contamination level at sensor/valve 74. The first exit product will be directed to a clean water product tank 76. When the sensor/valve 74 indicates that the contaminate removal level is declining as after time S in FIG. 15, the exit stream will then be redirected as a second exit product to a stage 3 absorber at 78. When the sensor 74 detects a contaminate concentration level at time T in FIG. 15, the exit stream is again redirected into a stage 2 absorber 80. 
     The permeate from the stage 1 absorber 72 will be directed into a stage 1 condenser 82. Condensed liquid will pass through sensor 84 which will direct the first permeate having a relatively low level of contamination up to time R as shown in FIG. 15 into, for example a stage 8 absorber 86. At time R, when the concentration of contaminates begins to rise, the second permeate will then be redirected into a stage four absorber 88. 
     A typical plant or commercial facility of this nature may have between five and fifteen absorber stages, each of which will receive different specified amounts of contaminate concentration for further processing or use as desired. 
     Regeneration 
     In a typical regeneration process shown in FIG. 17, each stage or module in a typical system like that shown in FIG. 16 is shown typically at numeral 92. During regeneration, the feed and exits are closed and hot air from a hot air generator 94 is directed into the module 92 as shown by the arrows. Hot air flowing through the module 92 will remove the liquid within the exchange resin of each of the hollow core fiber members by releasing waters of hydration H2O, HTO, D2O, and HDO which are carried from the module 92 into a regeneration condenser 96. The liquid condensed and discharging from regeneration condenser 96 during the initial time portion of the regeneration cycle will have the least amount of contaminants in this first regeneration stream and may be returned to the system 70 of FIG. 16 for reprocessing. The second regeneration stream carrying higher amounts of contaminants would be collected at 98, while the third or last regeneration condensate stream would likely be carrying the greatest amount of contaminants such as tritiated water and would be directed to storage tank 100 for appropriate disposal. 
     To further distinguish the contaminant levels of each of these permeate condensate regeneration streams, the temperature of the air exiting the hot air generator 94 may be gradually increased and/or pressure reduced in steps to provide a greater driving force for contaminant removal. 
     The regenerated resin and fiber system is returned to the absorption cascade and is rehydrated by the feed stream. The absorption and regeneration cycles are repeated as desired. 
     Referring lastly to FIG. 18, an overall system for both deuterium and tritium removal from the water contaminated with same is there shown. This system 100 may include prefilters 102 and 104 in the form of either commercial reverse osmosis units or deionization units for pretreating the feed stream entering the stage 1 contaminate separating module 106. Its exit stream enters the stage 2 module 110 and so forth in upward cascade fashion until the final feed stream exits into a container 122 which collects the purest of the processed contaminated water. Permeate from each of the modules is typically collected at condenser 108 and then collected into condensed permeate tank 112 or exiting from 114 or 116 as other stages of contaminated permeate previously described. 
     Each of the modules may be selectively bypassed as the exit stream contamination level reaches the contamination level of the feed stream for regeneration. Undisconnected from the system 100, a typical hot dry air feed 118 forces hot air directly into each bypass module during the regeneration cycle previously described. 
     To further decontaminate the condensed permeate collecting in each tank 112, it may be reintroduced at 120 into the feed stream between adjacent modules 110 according to the contamination level of the permeate condensate. 
     While the instant invention has been shown and described herein in what are conceived to be the most practical and preferred embodiments, it is recognized that departures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein, but is to be afforded the full scope of the claims so as to embrace any and all equivalent apparatus and articles.