Abstract:
A vessel for both treatment of radioactive wastewater and disposal of radioactive waste contained therein. The vessel comprises a main vessel structure including a shell formed of a metal material and a liner integrally coupled to the interior surface of the shell. The liner is preferably formed of a plastic material, such as high density polyethylene. Waste treatment equipment for treatment of the radioactive wastewater is provided within the shell. Ion exchange resin is typically located in the main vessel structure which, when spent, constitutes the radioactive waste which is subject to disposal. The vessel is preferably configured to function as a High Integrity Container (HIC).

Description:
PRIORITY CLAIM 
     This application is based upon and claims the benefit of U.S. provisional application Ser. No. 61/623,240, filed Apr. 12, 2012, which is incorporated fully herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to treatment and disposal of radioactive wastewater. More particularly, the invention relates to a vessel which may be used for both treatment of radioactive wastewater and disposal of radioactive waste, including but not limited to ion exchange resin. 
     BACKGROUND OF THE INVENTION 
     As is well known, radioactive materials are used extensively in industrial, medical, agricultural, and environmental activities, among others. For example, radioactive waste is generated in all stages of nuclear reactor operations, and there are a number of liquid processes and waste streams at nuclear facilities that require treatment for removal of radioactive contaminants. Management of this waste typically includes treatment, temporary storage, and transportation of the waste to a permanent disposal site. 
     A number of processes are available for treating liquid radioactive waste. One such process is known as ion exchange, which is effective for transferring the radioactive content of a large volume of liquid into a small volume of solid. Although ion exchange processes may be implemented in a variety of ways, the most common uses of ion exchange media are as packed beds in vessels. More particularly, an ion exchange medium is typically contained inside a stainless steel pressure vessel, with an engineered inlet, outlet, and flow distribution system to allow liquid to percolate through the bed of the medium at a specified flow rate. Many types of ion exchange media are available for this purpose, including synthetic organic resins. 
     Over time, however, the ion exchange medium is spent, at which point the vessel is filled with a new medium. The spent ion exchange medium is radioactive waste, and it must either be regenerated or disposed of. During disposal, the spent ion exchange medium can be dewatered or dried and is often transferred from the vessel or an intermediate storage tank to a disposal container. The disposal container, also known as a “high integrity container” (HIC), is typically formed of ductile cast iron, concrete, steel, or high density polyethylene. Alternatively, the ion exchange vessels themselves (containing the spent ion exchange media) can be removed from service and placed in polyethylene HICs for disposal. 
     In any event, while awaiting transport to a permanent storage/burial site, the HICs are often temporarily stored at the waste processing location. Prior art polyethylene HICs require rounded shoulders at the top and bottom to absorb shocks, and thus a metal basket or nylon straps is required to lift and move the HIC for storage. Additionally, the HICs must be stacked via tables placed between each HIC. 
     Finally, when the HICs are transported to a final storage/burial site, they may be placed in protective shipping casks, which may be formed of lead or steel. 
     SUMMARY 
     The present invention recognizes and addresses disadvantages of prior art constructions and methods. According to one embodiment, the present invention provides a vessel for both treatment of radioactive wastewater and disposal of radioactive waste. The vessel comprises a shell formed of a metal material and a liner integrally coupled to the interior surface of the shell. The liner is formed of a plastic material. The vessel also comprises waste treatment equipment for treatment of the radioactive wastewater provided within the shell. In some embodiments, the plastic material may be high-density polyethylene, which may be molded to the interior surface of the shell. Preferably, the vessel may be a HIC. 
     Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended drawings, in which: 
         FIG. 1  is a flow diagram of an exemplary wastewater treatment process in which embodiments of the invention may be used. 
         FIG. 2  is an exploded view of a waste treatment and disposal vessel constructed in accordance with an embodiment of the present invention. 
         FIG. 3  is an elevation view of the waste treatment and disposal vessel of  FIG. 2 . 
         FIG. 4  is a top plan view of the waste treatment and disposal vessel of  FIG. 2 . 
         FIG. 5A  is a section view of the waste treatment and disposal vessel of  FIG. 2  shown along the line A-A in  FIG. 4 . 
         FIG. 5B  is a detail view of the interface between a lid and the remainder of the waste treatment and disposal vessel as indicated in  FIG. 5A . 
         FIG. 6  is an isometric view showing exemplary internal waste treatment equipment contained within a waste treatment and disposal vessel constructed in accordance with an embodiment of the present invention. 
         FIG. 7  is an elevation view of the waste treatment and disposal vessel of  FIG. 6 . 
         FIG. 8  is a top plan view of the waste treatment and disposal vessel of  FIG. 6 . 
         FIG. 9  is a section view of the waste treatment and disposal vessel of  FIG. 6  shown along the line A-A in  FIG. 8 . 
         FIG. 10  is a perspective view of three waste treatment and disposal vessels constructed in accordance with an embodiment of the present invention which have been stacked for temporary storage. 
         FIG. 11  is a section view of a shipping cask into which a waste treatment and disposal vessel constructed in accordance with an embodiment of the present invention has been placed. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in detail to presently preferred embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Embodiments of the present invention provide a vessel which may be used for both treatment of radioactive wastewater and disposal of radioactive waste, such as ion exchange media. Some embodiments of the present invention are particularly suitable for use with ion exchange processes in a nuclear wastewater treatment environment, and the below discussion will describe preferred embodiments in that context. However, those of skill in the art will understand that the present invention is not so limited. In fact, it is contemplated that embodiments of the present invention may be used for many different applications related to the treatment of radioactive waste. 
     In this regard,  FIG. 1  is a simplified flow diagram of an exemplary wastewater treatment process  10  of the prior art which may be improved by incorporating one or more vessels in accordance with embodiments of the present invention. In particular, process  10  may be used to extract radionuclides from water used in spent nuclear fuel storage ponds. Radioactive wastewater feed may be received at a reception tank  12 , from which it is pumped via pump  14  to a series of sand pressure filters  16 . Sand pressure filters  16  may operate to remove fine particles of fuel corrosion sludge or other suspended solids in the feed. Such sludge may be stored in storage tanks  18 . After passing through sand pressure filters  16 , the wastewater feed may pass to a carbonating tower  20 . Carbonating tower  20  may be used to adjust the pH of the wastewater feed using an injection of carbon dioxide. 
     Next, the wastewater feed is pumped to two ion exchange vessels  22 ,  24  via pump  26 . Ion exchange vessels  22 ,  24 , which may comprise separate beds for cation and anion exchange or which may comprise a mixed bed system, may work in series to absorb radionuclides from the wastewater feed. When the ion exchange media in vessels  22 ,  24  becomes spent, it is hydraulically discharged to storage tanks  28 . Storage tanks  28  may also store any filter sand from pressure filters  16  which has reached the end of its useful life. After exiting ion exchange vessels  22 ,  24 , treated water may be transferred to a final tank  30 . The treated water may then be discharged via a pump  32 , such as to the sea. 
     As explained above, in the prior art, treatment vessels for treating radioactive liquids (such as ion exchange vessels  22 ,  24 ) cannot also be used to dispose of radioactive waste, such as spent ion exchange media. In the above process, for example, the spent ion exchange media is usually transferred to high-integrity containers (HICs) from intermediate storage tanks  28  for disposal. Moreover, water treatment vessels cannot be used for shipping or storage (temporary or permanent) of radioactive waste. In contrast, embodiments of the present invention comprise a waste treatment and disposal vessel which performs these and other functions. Notably, embodiments of the present invention may eliminate the need to sluice radioactive media from a wastewater treatment vessel to a storage tank, which could potentially contaminate additional equipment as well as personnel. 
     In this regard,  FIG. 2  is an exploded view of a waste treatment and disposal vessel  50  constructed in accordance with an embodiment of the present invention.  FIG. 3  is an elevation view of vessel  50 , and  FIG. 4  is a top plan view. 
     Referring first to  FIGS. 2-4 , vessel  50  has a main vessel structure which comprises a shell  52  including a body  54 , a top  56 , and a bottom  58 . In the illustrated embodiment, shell  52  is cylindrical, but in other embodiments shell  52  may take any suitable shape. Vessel  50  preferably further comprises a liner  60  and a lid  62 . Note that liner  60  is shown separated from shell  52  in  FIG. 2  solely for purposes of illustration. 
     Shell  52  may preferably be formed of a suitable high-strength material such as carbon steel, stainless steel or alloy steel. For example, shell  52  may be formed via a  3 -piece welded construction, wherein top  56  and bottom  58  are welded with body  54  to form shell  52 , although in other embodiments top  56  and bottom  58  may be integrally formed with or attached to body  54  using any suitable method. In a preferred embodiment, shell  52  of vessel  50  is constructed to meet applicable requirements regarding the construction of pressure vessels, such as the requirements defined in the American Society of Mechanical Engineers Boiler and Pressure Vessel Code, Section VIII (incorporated herein by reference in its entirety). 
     As can be seen most clearly in  FIG. 3 , shell  52  may further comprise a plurality of lift lugs  64  having a base portion  65  coupled with body  54 . As shown, for example, shell  52  comprises four lift lugs  64  disposed perpendicularly to top  56  and which are equally spaced around the circumference of body  54 . Each lift lug  64  may preferably also comprise a top portion  67  which extends above top  56  of shell  52 . Further, top portion  67  preferably defines a narrower width than base portion  65  such that the radial distance between the longitudinal axis of shell  52  and top portion  67  is greater than the radial distance between the longitudinal axis of shell  52  and bottom portion  65 . The difference between these distances preferably defines a gap G as shown in  FIGS. 3 and 4  and as discussed in more detail below. Additionally, each lift lug  64  may define an aperture  69  therethrough to facilitate the attachment of rigging for lifting and handling of vessel  50 . 
     Referring also to  FIG. 5A , which is a section view of vessel  50 , and  FIG. 5B , which is a detail view of the interface between lid  62  and shell  52 , shell  52  also preferably defines an opening  66  in top  56 . Further, a rim  68  preferably depends from top  56  coincident with the circumference of opening  66 . A flange  70  is preferably coupled with rim  68  and extends perpendicularly about its circumference. Flange  70  may define a plurality of apertures  72  (which, as shown, may be threaded) via which lid  62  may be coupled with shell  52 . 
     Notably, vessel  50  is preferably a HIC. Thus, vessel  50  is preferably constructed in accordance with governmental regulations governing HICs. For example, vessel  50  preferably has sufficient mechanical strength to withstand specified horizontal and vertical loads during disposal, will withstand at least 30′ drop test, allows free liquid within the container to be removed to less than 1% by volume within the container, has a design life of at least 300 years, and limits gas generation. HIC requirements are well-known to those skilled in the art and are delineated at 10 CFR  61 . 
     Moreover, in a preferred embodiment, liner  60  is formed of a polyethylene material, such as high density cross-linked or linear polyethylene, which resists corrosion, damage from certain chemicals, and biodegradation. Notably, liner  60  may be spin-molded or rotomolded in shell  52  such that it tightly adheres to the interior of shell  52 . Those of skill in the art will appreciate that other methods of manufacturing liner  60  are within the scope of the present invention, including injection molding and heat welding, among others. 
     Because liner  60  may be molded to the interior of shell  52 , the thickness of liner  60  may be less than that of standalone polyethylene HICs, which may have a wall thickness of ½″. For example, in one embodiment, liner  60  may define a thickness of ⅜″ or less. Additionally, because large, rounded shoulders are not required for liner  60  (as they may be with standalone HICs) and because liner  60  is manufactured to tightly adhere to the interior of shell  52 , liner  60  (and thus, vessel  50 ) may store a larger volume of waste than a traditional HIC of the same diameter and height. 
     Similar to liner  60 , lid  62  is preferably formed of a polyethylene material, although other suitable materials may be used. In one embodiment, lid  62  may define threads which engage corresponding threads on rim  68  or flange  70  of shell  52 . In other embodiments, lid  62  may be heat welded with liner  60 . In another embodiment, as shown in FIGS.  2  and  5 A- 5 B, liner  60  may preferably define a lip  74  which at least partially surrounds flange  70  of shell  52 . Lip  74  defines apertures  76  aligned with apertures  72  of flange  70 . Similarly, lid  62  preferably defines apertures  78  aligned with apertures  76 ,  72 . Thereby, lid  62  may also be secured with shell  52  and liner  60  via suitable fasteners. In some embodiments, a gasket material may be provided in apertures  78  or between lid  62  and lip  74 . 
     In any event, the mechanism by which lid  62  is secured with shell  52  and liner  60  preferably facilitates simple, rapid installation and removal, either manually or using remote and/or automated tooling. Moreover, lid  62  may include a passive vent or filter to prevent overpressurization of vessel  50 . According to a further embodiment, vessel  50  may include a cover over lid  62 . The cover may be coupled with opening  66  in top  56  of shell  52  and may preferably be formed of carbon steel. It will be appreciated that the carbon steel material of shell  52  and the cover (if provided) provides a measure of fire resistance to vessel  50 . 
     Embodiments of the present invention are preferably compatible with and may include waste treatment equipment, such as piping suitable for use in an ion exchange vessel. In this regard, one example of waste treatment equipment which may be used with some embodiments of the present invention is discussed below with reference to  FIGS. 6-9 .  FIG. 6  is an isometric view of a waste treatment and disposal vessel  100  in accordance with the present invention that includes internal waste treatment equipment  102 . Vessel  100  may preferably be analogous to vessel  50  described above and thus may comprise a shell  104 , a rim  106 , and lift lugs  108 .  FIGS. 7-9  are respective elevation, plan, and section views of vessel  100 . As shown in  FIG. 9 , vessel  100  also preferably includes a liner  110  and a lid  112 . In  FIGS. 6-8 , shell  104  of vessel  100  is shown in broken lines to facilitate illustration of waste treatment equipment  102 . 
     More particularly, in the illustrated embodiment waste treatment equipment  102  may comprise a plurality of filter layers  114 ,  116 ,  118 ,  120 , and  122 . Depending on the waste treatment process involved, those of skill in the art will appreciate that more or fewer than five filter layers may be provided. Each filter layer preferably comprises a manifold  124  which extends transversely across the interior of shell  104 . 
     In fluid communication with and extending normally from each manifold  124  are a plurality of conduits  126 . As shown, each manifold  124  is in fluid communication with ten such conduits  126 , although this number may vary depending on the application, as noted above. Conduits  126  may preferably be configured to introduce influent evenly across the transverse area of the interior of shell  104 . Further, conduits  126  may each comprise a filter element  128  to capture undissolved solids in the influent and effluent. In one embodiment, filter elements  128  may comprise a 0.5 μm depth filter. 
     Supporting each of filter layers  114 - 122  is a support structure  130 . As shown, support structure  130  is a frame-like structure which may rest on the bottom of the interior of shell  104 . Also, support structure  130  may be coupled with the terminal ends of each conduit  126 . In a preferred embodiment, support structure  130  may be formed of a lightweight plastic material suitable for use in a waste treatment environment, such as PVC. In other embodiments, however, support structure  130  may be formed of steel. 
     Waste treatment equipment  102  may further comprise a connection plate  132  ( FIG. 9 ) for facilitating connections between each filter layer  114 - 122  and external equipment. Connection plate  132  may comprise a transverse plate coupled with and depending from rim  106 . Connection plate  132  includes a plurality of upper connectors  134  and lower connectors  136  equally spaced along its length. In one embodiment, connectors  134 ,  136  may comprise camlock fittings. Preferably, the number of upper and lower connectors  134 ,  136  corresponds to the number of filter layers of waste treatment equipment  102 . Thus, as shown, five each of upper and lower connectors  134 ,  136  are provided. Notably, upper connectors  134  are located below the opening so that they will not interfere with attachment of the lid in the manner described above. 
     Correspondingly, each filter layer  114 - 122  may comprise a connector  138  in fluid communication with each manifold  124 . Connectors  138  may likewise comprise camlock fittings. A hose may be releasably connected between the connector  138  of each filter layer  114 - 122  and one of lower connectors  136  to provide fluid communication between external equipment connected to each upper connector  134  and each filter layer  114 - 122 . Similarly, external equipment, such as a fillhead or a dewatering pump, may comprise one or more hoses which releasably couple with upper connectors  134 . Those of skill in the art are familiar with hoses suitable for waste treatment processes. 
     Based on the above, waste treatment equipment  102  may be used for a number of different waste treatment processes. For example, waste treatment equipment  102  may be used in an ion exchange process to treat radioactive wastewater. In this case, vessel  100  may include a bed of ion exchange material. A fillhead may be coupled with one or more of upper connectors  134  to introduce wastewater into vessel  100  at a predetermined flow rate. Via hoses extending between lower connectors  136  and connectors  138  on one or more of filter layers  114 - 120 , the wastewater may be distributed over the bed of ion exchange material. Filter layer  122 , located at the bottom of shell  104 , may be used to capture effluent, which then passes via a hose to a lower connector  136  and upper connector  134 . Treated effluent then exits vessel  100 . 
     Those of skill in the art will appreciate that other embodiments of the present invention may include additional or different waste treatment equipment and may be used with different waste treatment processes than those mentioned above. For example, vessel  100  may be used as a filter to remove undissolved solids from a waste stream. Alternatively, waste treatment equipment  102  may be used in a “buffering” or “bulk” ion exchange treatment process, wherein used or partially spent media which retains some capacity for ion exchange is sluiced into vessel  100 . In this process, the partially spent media may form a portion of a waste feed which also comprises a large amount of water, and thus an upper filter layer, such as filter layer  114 , may be used to decant the water as the media is sluiced into vessel  100 . After a predetermined amount of partially spent media is introduced into vessel  100 , wastewater may be flushed through the media as discussed above as an initial or final treatment process. 
     Further, waste treatment equipment  102  may be used in a dewatering process to remove water from radioactive waste in vessel  100  prior to storage or shipment. For example, dewatering equipment may be connected with one or more of upper connectors  134 . Depending on the application, dewatering equipment may include a source of compressed air or a dewatering vacuum pump, as those of skill in the art are aware. 
     Referring now to  FIGS. 10-11 , and as noted above, embodiments of the present invention comprise features which facilitate storage and transport of waste treatment and disposal vessels  150 . Waste treatment and disposal vessels  150  are preferably analogous to vessels  50 ,  100  discussed above. Thus, vessels  150  preferably comprise a shell  152  having a body  154 , a top  156 , and bottom  158 . Further, vessels  150  preferably comprise a plurality of lift lugs  160  defining a gap G. 
     Lift lugs  160  are preferably constructed to accommodate the maximum allowable load of vessels  150 , which allows vessels  150  to be lifted and stacked even when full. Also, vessels  150  are preferably constructed to have a mating configuration between the top  156  of one vessel  150  and the bottom  158  of another vessel  150  to facilitate stacking. Lift lugs  160  may act as a guide during the stacking process. Further, because vessels  150  are constructed to meet applicable requirements regarding the construction of pressure vessels, vessels  150  may be stacked at least 3 high (as shown in  FIG. 10 ). Finally, gap G of lugs  160  allows lugs  160  to be used to tie down vessels  150  even when vessels  150  are stacked. 
     Additionally, vessels  150  are preferably constructed in accordance with applicable governmental regulations and requirements regarding shipping of radioactive material. For example, in one embodiment vessels  150  may be a Type A Shipping Package. Correspondingly, vessels  150  may be sized to fit within various-sized transport casks  162 . As those of skill in the art are aware, casks  162  may be placed on a truck for transport to a disposal or burial site. After arrival at the site, vessel  150  may be removed from cask  162  for burial. 
     Thus, embodiments of the present invention provide a high-integrity container capable of both treating radioactive wastewater and disposing of radioactive waste, including meeting applicable regulations for shipping and storage of such waste. Moreover, as explained above, sluicing or transferring waste media from a wastewater treatment vessel can be hazardous, can cause personnel radiation exposure or other safety concerns, and may cause expensive repairs. Importantly, however, in embodiments of the present invention it is not necessary to sluice or transfer waste media from the wastewater treatment vessel. 
     While one or more preferred embodiments of the invention have been described above, it should be understood that any and all equivalent realizations of the present invention are included within the scope and spirit thereof. The embodiments depicted are presented by way of example only and are not intended as limitations upon the present invention. Thus, it should be understood by those of ordinary skill in this art that the present invention is not limited to these embodiments since modifications can be made. Therefore, it is contemplated that any and all such embodiments are included in the present invention as may fall within the scope and spirit thereof.