APPARATUS AND METHOD FOR REMOVAL OF NUCLIDES FROM HIGH LEVEL LIQUID WASTES

A method for treating a liquid waste is provided. The method includes supplying the liquid waste to a plurality of cross flow filters from at least one high level waste tank; filtering the liquid waste via the plurality of cross flow filters to form a clarified salt solution; removing at least one radionuclide from the clarified salt solution via a plurality of elutable ion exchange columns filled with an ion exchange media to form an eluate and a decontaminated salt solution; and removing at least one radionuclide from the eluate via a first non-elutable adsorption component to form a dewatered radionuclide sorbent and a decontaminated eluate solution.

FIELD OF THE INVENTION

Embodiments of the present invention relate generally to methods and systems for treating liquid wastes having high levels of radionuclides. More specifically, embodiments of the present invention relate to methods and systems for treating liquid wastes having high levels of cesium.

BACKGROUND

As is well known, nuclear fuel produced in government facilities is processed to remove special nuclear material (SNM) such as plutonium, enriched uranium and other radionuclides of interest. SNM is recovered by dissolving the fuel in acid followed by elemental and isotopic separation of the SNM into separate streams for re-use in nuclear fuel and thermo-nuclear devices. The spent processing wastes remaining after SNM recovery contains fission products, such as strontium-90 and cesium-137, and other radionuclides, primarily lanthanides and actinides, in concentrations sufficient to generate measurable amounts of heat and be labeled as high-level nuclear waste by the US Nuclear Regulatory Commission (US-NRC). The primary non-radioactive constituents of high-level waste are sodium, potassium, aluminum, nitrates, nitrites and sulfates. Most of the high-level waste in the United States was generated by the Department of Energy (DOE) at the Hanford, Savannah River and Idaho National Laboratory sites. The high-level waste typically exists inside large storage tanks in three physico-chemical phases known as supernate, salt cake and sludge. The Hanford Site has over 53 million gallons of high-level and chemical waste that is now being stored in approximately 170 underground tanks. The Savannah River Site has over 36 million gallons of high level-waste stored in approximately 50 underground tanks. Over the years the DOE has further concentrated wastes stored in the tanks by evaporation to make room for adding more liquids and they have added significant amounts of sodium hydroxide and sodium nitrite to the tanks to maintain high pH and chemically reducing conditions that inhibit tank corrosion. These practices have led to highly concentrated chemical solutions and the precipitation of sodium nitrate/nitrite salts. When the high-level waste tanks are emptied the salt cake will have to be re-dissolved by purified water thus leading to the creation of millions of gallons of additional liquid waste requiring future treatment.

Currently, both the Savannah River Site (SRS) and Hanford Site (Hanford) have experienced delays associated with the design, installation and commissioning of equipment needed to separate strontium-90 (Sr-90) and cesium-137 (Cs-137) from the high-level waste supernate and related liquids. The inability to effectively remove Sr-90 and Cs-137 could cause the sites to miss regulatory milestones and extend the time required for the site cleanup missions thus resulting in hundreds of millions of dollars of cost overruns.

Therefore there at least remains a need in the art for methods and systems for treating liquid wastes having high levels of radionuclides such as cesium and strontium.

SUMMARY

Example embodiments of the present invention recognize and address considerations of prior art constructions and methods.

According to one aspect, an example embodiment of the present invention provides a method for treating a liquid waste having at least one radionuclide in a salt solution. The method includes supplying the liquid waste to a plurality of cross flow filters from at least one high level waste tank; filtering the liquid waste via the plurality of cross flow filters to form a clarified salt solution; removing at least one radionuclide from the clarified salt solution via a plurality of elutable ion exchange columns filled with an ion exchange media to form an eluate and a decontaminated salt solution; and removing at least one radionuclide from the eluate via a first non-elutable adsorption component to form a dewatered radionuclide sorbent and a decontaminated eluate solution.

According to another aspect, an example embodiment of the present invention provides a regenerable system for treating a liquid waste having at least one radionuclide in a salt solution. The system includes a plurality of cross flow filters having an inlet and an outlet, a plurality of elutable ion exchange columns in fluid communication with the outlet and comprising an eluate outlet and a decontaminated salt solution outlet, and a first non-elutable adsorption component in fluid communication with the eluate outlet and comprising a decontaminated eluate solution outlet. The plurality of elutable ion exchange columns comprises an ion exchange media.

DETAILED DESCRIPTION

Exemplary embodiments provide a regenerable system and method that can be designed, manufactured, installed, and commissioned in a short timeframe to address waste treatment and disposal issues, which, for example, would aid the DOE in meeting regulatory commitments and budgetary constraints. Of particular value is the ability to send cesium loaded non-elutable adsorption media directly to disposal, thus eliminating the need, for example, for producing “salt-only” waste canisters at SRS and for operating the High Level Waste (HLW) vitrification facility for supernate treatment at Hanford.

In one aspect, a regenerable system for treating a liquid waste having at least one radionuclide in a salt solution is provided. In general, the system may include a plurality of cross flow filters (e.g., four) having an inlet and an outlet, a plurality of elutable ion exchange columns in fluid communication with the outlet and comprising an eluate outlet and a decontaminated salt solution outlet, and a first non-elutable adsorption component in fluid communication with the eluate outlet and comprising a decontaminated eluate solution outlet. In some embodiments, the plurality of elutable ion exchange columns may comprise an ion exchange media.

In accordance with an exemplary embodiment, the liquid waste may comprise at least one radionuclide. In some embodiments, for instance, the liquid waste may comprise at least one of cesium, strontium, actinide, or any combination thereof. In further embodiments, for example, the liquid waste may comprise cesium.

FIG. 1, for example, illustrates a regenerable system in accordance with an example embodiment. As shown inFIG. 1, for instance, the regenerable system may include at least one high level waste tank101. In accordance with an exemplary embodiment and as shown inFIG. 1, for instance, the at least one high level waste tank101may comprise a mixer102and a pump103. In this regard, by utilizing the mixer102and the pump103, the at least one high level waste tank101may be configured to supply liquid waste in the form of a liquid supernate105to the plurality of cross flow filters107. In some embodiments, for example, the plurality of cross flow filters107may include standard cross flow filters, rotary microfilters and/or the like. According to certain embodiments, for instance, the plurality of cross flow filters107may be arranged in series or in parallel. Moreover, although multiple cross flow filters107are referenced herein, the system may comprise only one cross flow filter107. In addition, although cross flow filters are referenced herein, any filtration means suitable for use with the regenerable system as understood by one of ordinary skill in the art may be used. The plurality of cross flow filters107, for instance, may separate the liquid supernate105into a clarified salt solution108and a filter reject106(e.g. undissolved solids, adsorbent, etc.). The filter reject106may then be returned to the at least one high level waste tank101for future vitrification treatment. Prior to filtration by the plurality of cross flow filters107, in some embodiments, for example, the liquid waste contained in the at least one high level waste tank101may be treated with at least one targeted radionuclide adsorbent (e.g., a strontium adsorbent, an actinide adsorbent and/or the like).

Following filtration by the plurality of cross flow filters107, for instance, the clarified salt solution108may move through a plurality of elutable ion exchange columns114(e.g., Generation 3 Shielded Ion Exchange Module (SIXM3)). In some embodiments, for example, the plurality of elutable ion exchange columns may comprise a gamma dose rate reduction by a factor greater than 106. In further embodiments, for instance, the plurality of elutable ion exchange columns may comprise a maximum decay heat loading of about 3,000 W (e.g., 2,896 W). Although multiple elutable ion exchange columns114are referenced herein, the system may comprise only one elutable ion exchange column114.

The plurality of elutable ion exchange columns114may include at least one ion exchange media. According to certain exemplary embodiments, for instance, the ion exchange media may comprise spherical resorcinol formaldehyde (sRF). In such embodiments, for example, the sRF may be used for over thirty loading/elution/regeneration cycles. In further embodiments, for instance, the sRF may comprise a loading cycle of about 155 bed volumes. In addition, by using sRF as the ion exchange media, for instance, the plurality of elutable ion exchange columns114may achieve high cesium decontamination factors (e.g., 5,0002) in liquid waste. Moreover, in certain embodiments, for example, eluted cesium may be adsorbed onto another sorbent ore returned to a tank as secondary liquid waste.

Moreover, in accordance with certain embodiments and as shown inFIG. 6, for instance, the plurality of elutable ion exchange columns114may comprise a lead ion exchange column610, a lag ion exchange column620, and a polishing ion exchange column630. In some embodiments, for instance, the lead ion exchange column610, the lag ion exchange column620, and the polishing ion exchange column630may be arranged in series. In other embodiments, for example, the plurality of elutable ion exchange columns114may be positioned on an ion exchange column carousel. In this regard, the plurality of elutable ion exchange columns114may be stationary or rotatable. In certain embodiments, for example, the plurality of elutable ion exchange columns114may include only a lead ion exchange column610and a lag ion exchange column620. Regardless of the arrangement of the lead ion exchange column610, the lag ion exchange column620, and the polishing ion exchange column630, the clarified salt solution108may travel through the plurality of elutable ion exchange columns114through the lead-lag-polishing configuration for cesium removal. In this regard, for instance, the clarified salt solution108may be decontaminated to form a decontaminated salt solution129and eluate solutions115. In embodiments in which the eluate solutions115result from sRF elution/regeneration, the eluate solutions115may comprise nitric acid. In such embodiments, for example, the eluate solutions115may comprise nitric acid at a concentration of about 0.2M.

According to certain embodiments, for example, the decontaminated salt solution129may then be transferred to a waste processor130. In some embodiments, for instance, the waste processor130may be in fluid communication with the decontaminated salt solution outlet of the plurality of elutable ion exchange columns114. In this regard, the waste processor130may package, stabilize, and/or treat the decontaminated salt solution129. In certain embodiments, for example, the waste processor130may scrub the decontaminated salt solution129. In some embodiments, for instance, the waste processor130may comprise a processing facility (e.g., Saltstone Processing Facility (SPF) at SRS), a direct feed low activity vitrifier (e.g., DFLAW at Hanford), a supplemental low activity vitrifier (e.g., supplemental LAW at Hanford) and/or the like. Moreover, in further embodiments, for example, the decontaminated salt solution129may be transferred to tanker trucks for off-site processing. As a result of processing by the waste processor130, packaged solids135(e.g., cement-like grout, stabilized glassified waste canisters, filters, resins, solidified concentrations and/or the like) and a scrubber condensate131may be formed. In some embodiments, for instance, the packaged solids135may be disposed via any suitable means of solid waste disposal136understood by one of ordinary skill in the art. In further embodiments, for example, the scrubber condensate131may undergo condensate treatment. For instance, the scrubber condensate131may be treated by any suitable effluent treatment means132understood by one of ordinary skill in the art. Treatment by the effluent treatment means132may form purified water137and packaged solids133(e.g., cesium-loaded non-elutable adsorbent columns, cement-like grout, stabilized glassified waste canisters, filters, resins, solidified concentrations and/or the like). The purified water137may be disposed of by any suitable water disposal means138understood by one of ordinary skill in the art. Moreover, the packaged solids133may be disposed via any suitable means of solid waste disposal134understood by one of ordinary skill in the art.

In accordance with certain embodiments, for example, the eluate solutions115formed from the treatment of the clarified salt solution108with the plurality of elutable ion exchange columns114or from sRF elution/regeneration may be treated with an alkali116and run through a first non-elutable adsorption component117to form a decontaminated eluate solution118, which may be stored in one or more eluate tanks119. In this regard, the first non-elutable adsorption may remove cesium from all eluate and eluate related liquids (rinses, etc.) upstream of the eluate tanks119. The first (and similarly the second) non-elutable adsorption components117,120may be physically located inside at least one shielded transport cask wherein several operations involving liquid treatment and waste processing may take place prior to transporting the non-elutable adsorption components117,120. The non-elutable adsorption components117,120may be designed with remote ancillary features that allow them to be loaded with cesium, dewatered, and sealed for shipment in a safe and ALARA manner. The non-elutable adsorption components117,120may be operated in a manner that precludes the accumulation of cesium and related liquid waste radionuclides above legal cutoff limits, which makes the dewatered non-elutable adsorption components117,120candidates for disposal as low-level waste (LLW). In particular, after treatment by non-elutable adsorption components117,120, the cesium concentration in the decontaminated eluate solutions118,121may be very low, and the neutralized sodium nitrate in this stream may be at a concentration of about 0.25 M. In this regard, the decontaminated eluate solutions118,121may have low concentrations of radionuclides and salts.

In some embodiments, for instance, the one or more eluate tanks119may be in fluid communication with the decontaminated eluate solution outlet of the first non-elutable adsorption component117. Moreover, in further embodiments, for example, the one or more eluate tanks119may comprise an eluate tank outlet. According to certain exemplary embodiments, for instance, the first non-elutable adsorption component117may comprise a plurality of non-elutable adsorption columns (e.g., 3 Generation 2 Shielded Ion Exchange Modules (SIXM2)). The plurality of non-elutable adsorption columns may be arranged in series, on a carousel and/or the like. In some embodiments, for example, the first non-elutable adsorption component117may comprise at least one of chabazite zeolite, crystalline silicotitanate (CST), metal-hexacyanoferrate (FeCN), or any combination thereof. In further embodiments, for instance, the first non-elutable adsorption component117may comprise chabazite zeolite. The zeolite may provide effective removal of cesium from the eluate solution115comprising dilute sodium nitrate.

In accordance with an exemplary embodiment, the decontaminated eluate solution118may either flow through a second non-elutable adsorption component120to form a double decontaminated eluate solution121, or, in other embodiments, may flow directly to the waste processor130to be processed if the decontaminated eluate solution118comprises a low cesium concentration. In some embodiments, for example, the second non-elutable adsorption component120may be in fluid communication with the eluate tank outlet. Moreover, in further embodiments, for instance, the second non-elutable adsorption component120may comprise a second non-elutable adsorption component outlet. According to certain exemplary embodiments, for instance, the second non-elutable adsorption component120may also comprise a plurality of non-elutable adsorption columns (e.g., 3 Generation 2 Shielded Ion Exchange Modules (SIXM2)). The plurality of non-elutable adsorption columns may be arranged in series, on a carousel and/or the like. In some embodiments, for example, the second non-elutable adsorption component120may comprise at least one of chabazite zeolite, crystalline silicotitanate (CST), metal-hexacyanoferrate (FeCN), or any combination thereof. In further embodiments, for instance, the second non-elutable adsorption component120may comprise chabazite zeolite.

If the decontaminated eluate solution118flows through the second non-elutable adsorption component120to form the double decontaminated eluate solution121, for example, the double decontaminated eluate solution121may then flow through a concentrator122(e.g., sodium nitrate concentrator) to form purified water123and concentrator reject126. In some embodiments, for example, the concentrator122may be in fluid communication with the second non-elutable adsorption component outlet. In certain embodiments, for example, the concentrator122may comprise any suitable means of reverse osmosis, evaporation and/or the like as understood by one of ordinary skill in the art. Moreover, in further embodiments, for instance, the concentrator122may comprise a purified water outlet and a concentrator reject outlet. In certain embodiments, for example, the concentrator reject outlet may be in fluid communication with the waste processor130. The purified water may be stored in one or more purified water storage tanks124, which may be in fluid communication with the purified water outlet, and, in this regard, provide reclaimed water for reuse125. The concentrator reject126, however, may then flow to the waste processor130to be processed as previously described herein.

In accordance with certain embodiments, for example, sodium hydroxide may be added to the decontaminated eluate solution118and/or the double decontaminated eluate solution121, and the treated decontaminated eluate solutions118,121may be transferred to a holding tank or to one or more of the high level waste tanks101. In such embodiments, for instance, the decontaminated eluate solutions118,121may be an 0.2M solution of sodium nitrate having a pH greater than 12 or any other suitable alkaline pH value. In this regard, the treated decontaminated eluate solutions118,121may be reused in salt dissolution.

The system described above may be used until the lead ion exchange column610requires regeneration. The method of regenerating the lead ion exchange column610is discussed in more detail below. However, to accomplish regeneration, one or more reagents110(e.g., sodium hydroxide, sodium nitrate and/or the like) may be stored in one or more reagent tanks109. The reagents110and reclaimed water111may flow to one or more eluent tanks112to form eluent solutions113. The eluent solutions113may then be utilized in the regeneration of the lead ion exchange column610. In this regard, the elution/regeneration cycle may be counter-current from oldest to the most recently eluted ion exchange column such that freshly eluted and regenerated ion exchange columns114will be placed on-line in the polishing position630and then sequenced forward as upstream columns610,620experience cesium breakthrough.

In accordance with certain embodiments, for example, the system may operate at a treatment rate from about 1 gallon/min. to about 100 gallons/min. In other embodiments, for instance, the system may operate at a treatment rate from about 3 gallons/min. to about 50 gallons/min. In further embodiments, for example, the system may operate at a treatment rate from about 5 gallons/min. to about 25 gallons/min. In some embodiments, for instance, the system may operate at a treatment rate from about 7 gallons/min. to about 12 gallons/min. In certain embodiments, for example, the system may operate at a treatment rate of about 10 gallons/min. As such, in certain embodiments, the system may operate at a treatment rate from at least about any of the following: 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 gallons/min. and/or at most about 100, 75, 50, 40, 30, 25, 20, 15, 12, 11, and 10 gallons/min. (e.g., about 8-75 gallons/min, about 10-100 gallons/min., etc.).

In accordance with certain embodiments, for instance, the system may operate at a temperature from about 10° C. to about 60° C. In other embodiments, for example, the system may operate at a temperature from about 20° C. to about 50° C. In further embodiments, for instance, the system may operate at a temperature from about 30° C. to about 40° C. In certain embodiments, for example, the system may operate at a temperature of about 38° C. As such, in certain embodiments, the system may operate at a temperate from at least about any of the following: 10, 15, 20, 25, 30, 35, and 38° C. and/or at most about 60, 55, 50, 45, 40, and 38° C. (e.g., about 30-50° C., about 20-60° C., etc.).

In another aspect, a method for treating a liquid waste having at least one radionuclide in a salt solution is provided. In general, the method may include supplying the liquid waste to a plurality of cross flow filters from at least one high level waste tank; filtering the liquid waste via the plurality of cross flow filters to form a clarified salt solution; removing at least one radionuclide from the clarified salt solution via a plurality of elutable ion exchange columns filled with an ion exchange media to form an eluate and a decontaminated salt solution; and removing at least one radionuclide from the eluate via a first non-elutable adsorption component to form a dewatered radionuclide sorbent and a decontaminated eluate solution. Moreover, any and all disclosures made in relation to the system also apply to the method as described herein.

FIGS. 2-5, for example, illustrate the method in accordance with example embodiments. As shown inFIG. 2, for instance, the method may comprise supplying the liquid waste to a plurality of cross flow filters from at least one high level waste tank at operation210; filtering the liquid waste via the plurality of cross flow filters to form a clarified salt solution at operation220; removing at least one radionuclide from the clarified salt solution via a plurality of elutable ion exchange columns filled with an ion exchange media to form an eluate and a decontaminated salt solution at operation230; and removing at least one radionuclide from the eluate via a first non-elutable adsorption component to form a dewatered radionuclide sorbent and a decontaminated eluate solution at operation240. The method may also include an optional step of eluting the lead ion exchange column at operation250, which is described in greater detail in relation toFIG. 4herein.

As shown inFIG. 3, for example, removing at least one radionuclide from the eluate via a first non-elutable adsorption component to form a dewatered radionuclide sorbent and a decontaminated eluate solution at operation310may be followed by one or more of disposing the dewatered radionuclide sorbent at operation320a,packaging at least one of the decontaminated salt solution, the decontaminated eluate solution, a concentrator reject, or any combination thereof via a waste processor to form packaged solids and a condensate at operation320b,and/or removing at least one radionuclide from the decontaminated eluate solution via a second non-elutable adsorption component to form a double decontaminated eluate solution at operation320c.As further shown byFIG. 3, operation320bmay be followed by disposing the packaged solids at operation330aand/or treating the condensate at operation330b. Moreover, if operation320cis used, then operation320cmay be followed by concentrating the double decontaminated eluate solution to form purified water and the concentrator reject at operation340. Following operation340, the method may start at operation320band proceed through at least one of operations330aand330b.

As shown inFIG. 4, for example, eluting the lead ion exchange column may comprise displacing the lead ion exchange column at operation410, rinsing the lead ion exchange column with water at operation420, neutralizing the lead ion exchange column, eluting the lead ion exchange column with an acid (e.g., nitric acid) at operation430, rinsing the lead ion exchange column with water at operation440, regenerating the ion exchange media to a sodium form via, e.g., sodium hydroxide, at operation450, and replacing the polishing ion exchange column with the lead ion exchange column at operation460.

In this regard, in certain embodiments, for example, the elution/regeneration method may last from about 12 hours to about 48 hours. In other embodiments, for instance, the elution/regeneration method may last from about 18 hours to about 40 hours. In further embodiments, for example, the elution/regeneration method may last from about 20 hours to about 30 hours. In certain embodiments, for instance, the elution/regeneration method may last about 24 hours. As such, in certain embodiments, the elution/regeneration method may last for a time from at least about any of the following: 12, 15, 18, 20, 21, 22, 23, and 24 hours and/or at most about 48, 45, 40, 35, 30, 29, 28, 27, 26, 25, and 24 hours (e.g., about 18-26 hours, about 21-30 hours, etc.).

Moreover, according to certain embodiments, for example, the sRF may go through an elution/regeneration cycle after treating from about 25,000 gallons to about 75,000 gallons. In other embodiments, for instance, the sRF may go through an elution/regeneration cycle after treating from about 40,000 gallons to about 60,000 gallons. In further embodiments, for example, the sRF may go through an elution/regeneration cycle after treating about 50,000 gallons. As such, in certain embodiments, the sRF may go through an elution/regeneration cycle after treating a number of gallons of liquid waste from at least about any of the following: 25,000; 30,000; 35,000; 40,000; 45,000; and 50,000 gallons and/or at most about 75,000; 70,000; 65,000; 60,000; 55,000; and 50,000 gallons (e.g., about 40,000-65,000 gallons, about 50,000-75,000 gallons, etc.). In this regard, each elution/regeneration cycle may generate about 6,200 gallons of cesium-laden eluate and regeneration chemicals (i.e. eluent solutions113) to be transferred to the one or more eluate tanks119.

As shown inFIG. 5, for example, treating the condensate may comprise scrubbing the condensate to form an effluent at operation510, purifying the effluent to form purified water and packaged solids at operation520, and disposing the purified water and the packaged solids at operation530.

While one or more example 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. In addition, 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.