Technetium Removal Column Flow Testing with Alkaline, High Salt, Radioactive Tank Waste PDF Download
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Languages : en
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This report describes the initial work conducted at Pacific Northwest National Laboratory to study technetium (Tc) removal from Hanford tank waste supernates and Tc oxidation state in the supernates. Filtered supernate samples from four tanks were studied: a composite double shell slurry feed (DSSF) consisting of 70% from Tank AW-101, 20% from AP-106, and 10% from AP-102; and three complexant concentrate (CC) wastes (Tanks AN-107, SY-101, ANS SY-103) that are distinguished by having a high concentration of organic complexants. The work included batch contacts of these waste samples with Reillex[trademark]-HPQ (anion exchanger from Reilly Industries) and ABEC 5000 (a sorbent from Eichrom Industries), materials designed to effectively remove Tc as pertechnetate from tank wastes. A short study of Tc analysis methods was completed. A preliminary identification of the oxidation state of non-pertechnetate species in the supernates was made by analyzing the technetium x-ray absorption spectra of four CC waste samples. Molybdenum (Mo) and rhenium (Re) spiked test solutions and simulants were tested with electrospray ionization-mass spectrometry to evaluate the feasibility of the technique for identifying Tc species in waste samples.
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Languages : en
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Development of remediation technologies for the characterization, retrieval, treatment, concentration, and final disposal of radioactive and chemical tank waste stored within the Department of Energy (DOE) complex represents an enormous scientific and technological challenge. A combined total of over 90 million gallons of high-level waste (HLW) and low-level waste (LLW) are stored in 335 underground storage tanks at four different DOE sites. Roughly 98% of this waste is highly alkaline in nature and contains high concentrations of nitrate and nitrite salts along with lesser concentrations of other salts. The primary waste forms are sludge, saltcake, and liquid supernatant with the bulk of the radioactivity contained in the sludge, making it the largest source of HLW. The saltcake (liquid waste with most of the water removed) and liquid supernatant consist mainly of sodium nitrate and sodium hydroxide salts. The main radioactive constituent in the alkaline supernatant is cesium-137, but strontium-90, technetium-99, and transuranic nuclides are also present in varying concentrations. Reduction of the radioactivity below Nuclear Regulatory Commission (NRC) limits would allow the bulk of the waste to be disposed of as LLW. Because of the long half-life of technetium-99 (2.1 x 10 5 y) and the mobility of the pertechnetate ion (TcO 4 - ) in the environment, it is expected that technetium will have to be removed from the Hanford wastes prior to disposal as LLW. Also, for some of the wastes, some level of technetium removal will be required to meet LLW criteria for radioactive content. Therefore, DOE has identified a need to develop technologies for the separation and concentration of technetium-99 from LLW streams. Eichrom has responded to this DOE-identified need by demonstrating a complete flowsheet for the separation, concentration, and immobilization of technetium (and iodine) from alkaline supernatant waste.
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Languages : en
Pages : 34
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Engineering development and testing of the SRTALK solvent extraction process are discussed in this paper. This process provides a way to carry out alkaline-side removal and recovery of technetium in the form of pertechnetate anion from nuclear waste tanks within the DOE complex. The SRTALK extractant consists of a crown ether, bis-4,4'(5')[(tert-butyl)cyclohexano] -18-crown-6, in a modifier, tributyl phosphate, and a diluent, Isopar{reg_sign}L. The SRTALK flowsheet given here separates technetium from the waste and concentrates it by a factor often to minimize the load on the downstream evaporator for the technetium effluent. In this work, we initially generated and correlated the technetium extraction data, measured the dispersion number for various processing conditions, and determined hydraulic performance in a single-stage 2-cm centrifugal contactor. Then we used extraction-factor analysis, single-stage contactor tests, and stage-to-stage process calculations to develop a SRTALK flowsheet. Key features of the flowsheet are (1) a low organic-to-aqueous (O/A) flow ratio in the extraction section and a high O/A flow ratio in the strip section concentrate the technetium and (2) the use of a scrub section to reduce the salt load in the concentrated technetium effluent. Finally, the SRTALK process was evaluated in a multistage test using a synthetic tank waste. This test was very successful. Initial tests with actual waste from the Hanford nuclear waste tanks show the same technetium extractability as determined with the synthetic waste feed. Therefore, technetium removal from actual tank wastes should also work well using the SRTALK process.
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Languages : en
Pages : 5
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SuperLig(R) 639 elutable, organic resin has been selected for technetium (as pertechnetate ion) removal from Hanford Site radioactive waste samples as part of the River Protection Project - Waste Treatment Plant (RPP-WTP) design. In support of the RPP-WTP flow sheet development, column tests have been performed at the Savannah River Technology Center with SuperLig(R) 639 resin using actual Hanford Site tank waste samples. The resin was shown to be highly effective at pertechnetate removal from these caustic, high-sodium, aqueous waste samples. Pertechnetate ion was subsequently eluted from the columns with water. An additional column test conducted on a Savannah River Site waste sample revealed exceptional performance, presumably due to the fact that lower concentrations of competing anions (primarily nitrate) were present in the sample.
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Languages : en
Pages : 5
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Highly selective ion exchange materials will be used to remove radionuclides from tank waste at the Hanford site as part of the River Protection Project. Testing in support of facility design was performed with different sizes of ion exchange columns to provide a basis for comparing results obtained using small-scale with radioactive samples and full design-height (i.e., pilot-scale) with simulant. Results indicate good comparison between small-scale radioactive tests and pilot-scale simulant tests. Because of the cost of performing radioactive tests and the unavailability of large sample volumes, understanding scale-up of performance parameters is critical to ensure that the system will perform as designed. The consistency of scale-up of ion exchange columns using SuperLig 644 and 639 resins has been demonstrated. Maintaining constant residence time, i.e., Column Volumes per hour, yields similar breakthrough profiles with resin columns ranging from 3.5 cm to 230 cm in height. Experiments performed with flow rates greatly exceeding the design parameters provided valuable information on loading and diffusion parameters. These data will be used, along with a computer model, to permit verification of design and prediction of column performance.
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Category : Environmental management
Languages : en
Pages : 972
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Languages : en
Pages : 5
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The overall goal of this research conducted under the auspices of the USDOE Environmental Management Science Program (EMSP) is to provide a scientific foundation upon which the feasibility of new liquid-liquid extraction chemistry applicable to the bulk reduction of the volume of tank waste can be evaluated. Disposal of high-level nuclear waste is horrendously expensive, in large part because the actual radioactive matter in the tanks has been diluted over 10,000-fold by ordinary inorganic chemicals. Quite simply, if the radioactive matter and bulk inorganic chemicals could be separated into separate streams, large cost savings would accrue, because the latter stream is much cheaper to dispose of. In principle, one could remove the radionuclides from the waste, leaving behind the bulk of the waste; or one could remove certain bulk chemicals from the waste, leaving behind the radionuclides. The preponderance of effort over the past two decades has focused on the former approach, which produces a high-level stream for vitrification and a low-activity stream for either vitrification (Hanford) or grout (Savannah River). At Hanford, a particular concern arises in that vitrification of a large volume of low-activity waste will be unacceptably expensive. To make matters worse, a projected future deficit of tank space may necessitate construction of expensive new tanks. These problems have raised questions as to whether a solution could be devised based on separation of sodium from the waste, resulting in the reduction of the total volume of waste that must be vitrified.
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Languages : en
Pages : 5
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Five cycles of loading, elution, and regeneration were performed to remove technetium from a Hanford waste sample retrieved from Tank 241-AW-101 using SuperLig 639 resin. The waste sample was diluted to 4.95 M Na plus and then was processed to remove 137Cs through dual ion exchange columns each containing 15 mL of SuperLig 644. To remove 99Tc, the cesium decontaminated solution was processed downwards through two ion exchange columns, each containing 12 mL of SuperLig 639 resin. The columns, designated as lead and lag, each had an inside diameter of 1.45 cm and a height of 30 cm. The columns were loaded in series, but were eluted and then regenerated separately. The average technetium loading for the cycles was 250 BV at 10 percent breakthrough. There was no significant difference in the loading performances among the five cycles. The percent removal of 99Tc was greater than 99.94 percent and the average decontamination factor (DF) was approximately 1.7 x 103. Approximately 99 percent of the 99Tc loaded on the resin was eluted with less than 15 BV of de-ionized water at 65 degrees C.
Author: Bruce A. Moyer
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Languages : en
Pages : 5
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Book Description
The overall goal of this research conducted under the auspices of the USDOE Environmental Management Science Program (EMSP) is to provide a scientific foundation upon which the feasibility of new liquid- liquid extraction chemistry applicable to the bulk reduction of the volume of tank waste can be evaluated. Disposal of high- level nuclear waste is horrendously expensive, in large part because the actual radioactive matter in the tanks has been diluted over 10,000-fold by ordinary inorganic chemicals. 1 Quite simply, if the radioactive matter and bulk inorganic chemicals could be separated into separate streams, large cost savings would accrue, because the latter stream is much cheaper to dispose of. In principle, one could remove the radionuclides from the waste, leaving behind the bulk of the waste; or one could remove certain bulk chemicals from the waste, leaving behind a mixture of radionuclides and minor inorganic salts. The preponderance of effort over the past two decades has focused on the former approach, which produces a high- level stream for vitrification and a low-activity stream for either vitrification (Hanford) or grout (Savannah River). At Hanford, a particular concern arises in that vitrification of a large volume of low-activity waste will be unacceptably expensive. To make matters worse, a projected future deficit of tank space may necessitate construction of expensive new tanks. These problems have raised questions as to whether a solution could be devised based on separation of sodium from the waste, resulting in the reduction of the total volume of waste that must be vitrified.
