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Radioiodine (129I) poses a risk to the environment due to its long half-life, toxicity, and mobility. It is found at the U.S. Department of Energy Hanford Site due to legacy releases of nuclear was...

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Radioactive iodine-129 (I-129) and technetium-99 (Tc-9(9)) pose a risk to groundwater due to their long half-lives, toxicity, and high environmental mobility. Based on literature reviewed in Moore et al. (2019) and Pearce et aL (2019), natural and engineered materials, including iron oxides, low-solubility sulfides, tin-based materials, bismuth-based materials, organoclays, and metal organic frameworks, were tested for potential use as a deployed technology for the treatment of I-129 and Tc-99 to reduce environmental mobility. Materials were evaluated with metrics including capacity for IO3- and TcO4- uptake, selectivity and long-term immobilization potential. Batch testing was used to determine IO3- and TcO4- sorption under aerobic conditions for each material in synthetic groundwater at different solution to solid ratios. Material association with IO3- and TcO4- was spatially resolved using scanning electron microscopy and X-ray microprobe mapping. The potential for redox reactions was assessed using X-ray absorption near edge structure spectroscopy. Of the materials tested, bismuth oxy(hydroxide) and ferrihydrite performed the best for IO3-. The commercial Purolite A530E anion-exchange resin outperformed all materials in its sorption capacity for TcO4-. Tin-based materials had high capacity for TcO4-, but immobilized TcO4- via reductive precipitation. Bismuth-based materials had high capacity for TcO4-, though slightly lower than the tin-based materials, but did not immobilize TcO4- by a redox-drive process, mitigating potential negative re-oxidation effects over longer time periods under oxic conditions. Cationic metal organic frameworks and polymer networks had high Tc removal capacity, with TcO4- trapped within the framework of the sorbent material. Although organodays did not have the highest capacity for IO3- and TcO4- removal in batch experiments, they are available commercially in large quantities, are relatively low cost and have low environmental impact, so were investigated in column experiments, demonstrating scale-up and removal of IO3- and TcO4- via sorption, and reductive immobilization with iron- and sulfur-based species. (C) 2020 Elsevier B.V. All rights reserved.

It is well known that radon is present in relatively high concentrations below the surface of the Earth due to natural decay of uranium and thorium. However, less information is available on the background levels of other isotopes such as 133Xe and 131mXe produced via spontaneous fission of either manmade or naturally occurring elements. The background concentrations of radioxenon in the subsurface are important to understand because these isotopes potentially can be used to confirm violations of the comprehensive nuclear-test-ban treaty during an on-site inspection. Recently, Pacific Northwest National Laboratory measured radioxenon concentrations from the subsurface at the Nevada Nuclear Security Site (NNSS—formerly known as the Nevada Test Site) to determine whether xenon isotope background levels could be detected from spontaneous fission of naturally occurring uranium or legacy 240Pu as a result of historic nuclear testing. In this paper, we discuss the results of those measurements and review the sources of xenon background that must be taken into account during OSI noble gas measurements.

The dissolution kinetics of five glasses along the NaAlSiO 4 –NaBSiO 4 join were used to evaluate how the structural variations associated with boron–aluminum substitution affect the rate of dissolution. The composition of each glass varied inversely in mol% of Al 2 O 3 (5–25 mol%) and B 2 O 3 (20–0 mol%) with Na 2 O (25 mol%) and SiO 2 (50 mol%) making up the remaining amount, in every case Na/(Al + B) = 1.0. Single-pass flow-through experiments (SPFT) were conducted under dilute conditions as a function of solution pH (from 7.0 to 12.0) and temperature (from 23 to 90 °C). Analysis of unreacted glass samples by 27 Al and 29 Si MAS-NMR suggests Al (∼98% [4] Al) and Si-atoms (∼100% [4] Si) occupy a tetrahedral coordination whereas, B-atoms occupy both tetrahedral ( [4] B) and trigonal ( [3] B) coordination. The distribution of [3] B fractionated between [3] B(ring) and [3] B(non-ring) moieties, with the [3] B(ring)/ [3] B(non-ring) ratio increases with an increase in the B/Al ratio. The MAS-NMR results also indicated an increase in the fraction of [4] B with an increase in the B/Al ratio. The 27 Al peak maxima shift to lesser values with an increase in the B/Al ratio which suggests mixing between the [4] Al and [3] B sites, assuming avoidance between tetrahedral trivalent cations ( [4] Al–O– [4] B avoidance). Unlike the 27 Al and 11 B spectra, the 29 Si spectra illustrate a subtle shift to more negative chemical shift (chemical shift range between −88 and −84 ppm) and increases in the spectral widths as the B/Al ratio increases. Raman spectroscopy of unreacted glass samples was also used to cross-check the results collected from MAS-NMR and suggested that NeB4 (the glass sample with the highest B content) may consist of B–Na enriched and Al–Si enriched micro-domains, which affected the measured dissolution rates. Results from SPFT experiments suggest a forward rate of reaction and pH power-law coefficients, η , that are independent of B/Al under these neutral to alkaline test conditions for all homogeneous glasses. The temperature dependence shows an order of magnitude increase in the dissolution rate with a 67 °C increase in temperature and suggests dissolution is controlled by a surface-mediated reaction, as indicated by the activation energy, E a , being between 44 ± 8 and 48 ± 7 kJ/mol. Forward dissolution rates, based on Na and Si release, for homogeneous glasses are independent of the B/Al ratio, whereas dissolution rates based on Al and B release are not. Normalized dissolution rates, based on B release, increase with the molar fraction of [3] B(ring). Finally in accord with previous studies, the data discussed in this manuscript suggest rupture of either the Al–O or Si–O bonds as the rate-limiting step controlling the dissolution of these glasses.

Contaminated groundwater beneath the 200 West Area at the Hanford Site in Southeast Washington is currently being treated using a pump and treat system to remove organics, inorganics, radionuclides, and metals. A granular activated carbon-based fluidized bed reactor (FBR) has been added to remove nitrate, hexavalent chromium and carbon tetrachloride. Initial analytical results indicated the microorganisms effectively reduced many of the contaminants to less than cleanup levels. However shortly thereafter operational upsets of the FBR include carbon carry over, over production of microbial extracellular polymeric substance (biofilm) materials, and over production of hydrogen sulfide. As a result detailed investigations were undertaken to understand the functional diversity and activity of the microbial community present in the FBR over time. Molecular analyses including terminal restriction fragment length polymorphism analysis, quantitative polymerase chain reaction and fluorescent in situ hybridization analyses were performed on the microbial community extracted from the biofilm within the bed and from the inoculum, to determine functional dynamics of the FBR bed over time and following operational changes. Findings from these analyses indicated: 1) the microbial community within the bed was completely different than community used for inoculation, and was likely from the groundwater; 2) analyses early in the testing more » showed an FBR community dominated by a few Curvibacter and Flavobacterium species; 3) the final sample taken indicated that the microbial community in the FBR bed had become more diverse; and 4) qPCR analyses indicated that bacteria involved in nitrogen cycling, including denitrifiers and anaerobic ammonia oxidizing bacteria, were dominant in the bed. These results indicate that molecular tools can be powerful for determining functional diversity within FBR type reactors. Coupled with micronutrient, influent and effluent chemistry evaluations, a more complete understanding of the balance between system additions (nutrients, groundwater) and biology can be achieved, thus increasing long-term predictions of performance. These analyses uniquely provide information that can be used in optimizing the overall performance, efficiency, and stability of the system both in real time as well as over the long-term, as the system design is altered or improved and/or new streams are added. « less

CH2M HILL Plateau Remediation Company (CHPRC) is currently developing a 200-West Area groundwater pump-and-treat system as the remedial action selected under the Comprehensive Environmental Response, Compensation, and Liability Act Record of Decision for Operable Unit (OU) 200-ZP-1. This report documents the results of treatability tests Pacific Northwest National Laboratory researchers conducted to quantify the ability of selected activated carbon products (or carbons) to adsorb technetium-99 (Tc-99) from 200-West Area groundwater. The Tc-99 adsorption performance of seven activated carbons (J177601 Calgon Fitrasorb 400, J177606 Siemens AC1230AWC, J177609 Carbon Resources CR-1240-AW, J177611 General Carbon GC20X50, J177612 Norit GAC830, J177613 Norit GAC830, and J177617 Nucon LW1230) were evaluated using water from well 299-W19-36. Four of the best performing carbons (J177606 Siemens AC1230AWC, J177609 Carbon Resources CR-1240-AW, J177611 General Carbon GC20X50, and J177613 Norit GAC830) were selected for batch isotherm testing. The batch isotherm tests on four of the selected carbons indicated that under lower nitrate concentration conditions (382 mg/L), Kd values ranged from 6,000 to 20,000 mL/g. In comparison. Under higher nitrate (750 mg/L) conditions, there was a measureable decrease in Tc-99 adsorption with Kd values ranging from 3,000 to 7,000 mL/g. The adsorption data fit both the Langmuir and the Freundlich equations.more » Supplemental tests were conducted using the two carbons that demonstrated the highest adsorption capacity to resolve the issue of the best fit isotherm. These tests indicated that Langmuir isotherms provided the best fit for Tc-99 adsorption under low nitrate concentration conditions. At the design basis concentration of Tc 0.865 µg/L(14,700 pCi/L), the predicted Kd values from using Langmuir isotherm constants were 5,980 mL/g and 6,870 mL/g for for the two carbons. These Kd values did not meet the target Kd value of 9,000 mL/g. Tests conducted to ascertain the effects of changing pH showed that at pH values of 6.5 and 7.5, no significant differences existed in Tc-adsorption performance for three of the carbons, but the fourth carbon performed better at pH 7.5. When the pH was increased to 8.5, a slight decline in performance was observed for all carbons. Tests conducted to ascertain the temperature effect on Tc-99 adsorption indicated that at 21 oC, 27 oC, and 32 oC there were no significant differences in Tc-99 adsorption for three of the carbons. The fourth carbon showed a noticeable decline in Tc-99 adsorption performance with increasing temperature. The presence of volatile organic compounds (VOCs) in the source water did not significantly affect Tc-99 adsorption on either of two carbons tested. Technetium-99 adsorption differed by less than 15% with or without VOCs present in the test water, indicating that Tc-99 adsorption would not be significantly affected if VOCs were removed from the water prior to contact with carbon.« less

The uranium adsorption performance of five resins (Dowex 1, Dowex 21K 16-30 [fresh], Dowex 21K 16-30 [regenerated], Purofine PFA600/4740, and ResinTech SIR-1200) were tested using unspiked, nitrate-spiked, and nitrate-spiked/pH adjusted source water from well 299-W19-36. These batch tests were conducted in support of a resin selection process in which the best resin to use for uranium treatment in the 200-West Area groundwater pump-and-treat system will be identified. The results from these tests are as follows: • The data from the high-nitrate (1331 mg/L) tests indicated that Dowex 1, Dowex 21K 16-30 (fresh), Purofine PFA600/4740, and ResinTech SIR-1200 all adsorbed uranium similarly well with Kd values ranging from ~15,000 to 95,000 ml/g. All four resins would be considered suitable for use in the treatment system based on uranium adsorption characteristics. • Lowering the pH of the high nitrate test conditions from 8.2 to 7.5 did not significantly change the uranium adsorption isotherms for the four tested resins. The Kd values for these four resins under high nitrate (1338 mg/L), lower pH (7.5) ranged from ~15,000 to 80,000 ml/g. • Higher nitrate concentrations greatly reduced the uranium adsorption on all four resins. Tests conducted with unspiked (no amendments; nitrate at 337 mg/L and pH at 8.2) source water yielded Kd values for Dowex 1, Dowex 21K 16-30 (fresh), Purofine PFA600/4740, and ResinTech SIR-1200 resins ranging from ~800,000 to >3,000,000 ml/g. These values are about two orders of magnitude higher than the Kd values noted from tests conducted using amended source water. • Compared to the fresh resin, the regenerated Dowex 21K 16-30 resin exhibited significantly lower uranium-adsorption performance under all test conditions. The calculated Kd values for the regenerated resin were typically an order of magnitude lower than the values calculated for the fresh resin. • Additional testing using laboratory columns is recommended to better resolve differences between the adsorption abilities of the resins and to develop estimates of uranium loading on the resins. By determining the quantity of uranium that each resin can adsorb and the time required to reach various levels of loading, resin lifetime in the treatment system can be estimated.

Solidification of low-activity wastes with cementitious materials is a widely accepted technique that contains and isolates waste from the hydrologic environment. The radionuclides I-129, Se-75, Tc-99, and U-238 are identified as long-term dose contributors. The anionic nature of these radionuclides in aqueous solutions allows them to readily leach into the subsurface environment. Any failure of concrete encasement may result in water intrusion and consequent mobilization of radionuclides from the waste packages via mass flow and/or diffusion into the surrounding subsurface environment. Assessing the long-term performance of waste grouts for encasement of radionuclides requires understanding the: 1) speciation and interaction of the radionuclides within the concrete wasteform, 2) diffusion of radionuclide species when contacted with vadose zone porewater or groundwater under environmentally relevant conditions, and 3) long-term durability and weathering of concrete waste forms. An improved understanding of the interactions of long-lived radionuclides in cementitious matrices will improve predictions of the long-term fate of these sequestered contaminants. An integrated laboratory investigation has been conducted including a: 1) multifaceted spectroscopic investigation to interrogate the speciation and interaction of radionuclides within concrete wasteforms, 2) solubility tests to quantify the stability of solid phases identified as radionuclide-controlling phases, 3) quantify the diffusion of radionuclides from concrete wasteforms into surrounding subsurface sediment under realistic moisture contents (4%, 7%, and 15% by weight moisture content), 4) quantify the long-term durability of concrete waste forms as a function environmental parameters relevant to depository conditions, and 5) identify the formation of secondary phases or processes (microcracking) that influence radionuclide retention. Data obtained from this investigation provides valuable information for understanding the speciation, behavior, and fate of radionuclides immobilized within concrete wasteforms under vadose zone conditions and underscores the necessity for robust, multi-disciplinary performance assessments for concrete waste forms.

This report presents results from bench-scale treatability studies conducted under site-specific conditions to optimize the polyphosphate amendment for implementation of a field-scale technology demonstration to stabilize uranium within the 300 Area vadose and smear zones of the Hanford Site. The general treatability testing approach consisted of conducting studies with site sediment and under site conditions, to develop an effective chemical formulation and infiltration approach for the polyphosphate amendment under site conditions. Laboratory-scale dynamic column tests were used to 1) quantify the retardation of polyphosphate and its degradation products as a function of water content, 2) determine the rate of polyphosphate degradation under unsaturated conditions, 3) develop an understanding of the mechanism of autunite formation via the reaction of solid phase calcite-bound uranium and aqueous polyphosphate remediation technology, 4) develop an understanding of the transformation mechanism, the identity of secondary phases, and the kinetics of the reaction between uranyl-carbonate and -silicate minerals with the polyphosphate remedy under solubility-limiting conditions, and 5) quantify the extent and rate of uranium released and immobilized based on the infiltration rate of the polyphosphate remedy and the effect of and periodic wet-dry cycling on the efficacy of polyphosphate remediation for uranium in the vadose zone andmore » smear zone.« less

This report presents the results of preparation and characterization of chemical plugs based on selected Hanford Site waste simulants. Included are the results of chemical plug bench testing conducted in support of the M1/M6 Flow Loop Chemical Plugging/Unplugging Test (TP-RPP-WTP-495 Rev A). These results support the proposed plug simulants for the chemical plugging/ unplugging tests. Based on the available simulant data, a set of simulants was identified that would likely result in chemical plugs. The three types of chemical plugs that were generated and tested in this task consisted of: 1. Aluminum hydroxide (NAH), 2. Sodium aluminosilicate (NAS), and 3. Sodium aluminum phosphate (NAP). While both solvents, namely 2 molar (2 M) nitric acid (HNO3) and 2 M sodium hydroxide (NaOH) at 60°C, used in these tests were effective in dissolving the chemical plugs, the 2 M nitric acid was significantly more effective in dissolving the NAH and NAS plugs. The caustic was only slightly more effecting at dissolving the NAP plug. In the bench-scale dissolution tests, hot (60°C) 2 M nitric acid was the most effective solvent in that it completely dissolved both NAH and NAS chemical plugs much faster (1.5 – 2 x) than 2 M sodium hydroxide.more » So unless there are operational benefits for the use of caustic verses nitric acid, 2 M nitric acid heated to 60°C C should be the solvent of choice for dissolving these chemical plugs. Flow-loop testing was planned to identify a combination of parameters such as pressure, flush solution, composition, and temperature that would effectively dissolve and flush each type of chemical plug from preformed chemical plugs in 3-inch-diameter and 4-feet-long pipe sections. However, based on a review of the results of the bench-top tests and technical discussions, the Waste Treatment Plant (WTP) Research and Technology (R&T), Engineering and Mechanical Systems (EMS), and Operations concluded that flow-loop testing of the chemically plugged pipe sections would not provide any additional information or useful data. The decision was communicated through a Sub Contract Change Notice (SCN-070) that included a revised scope as follows: • Photographing the chemical plugs in the pipes before extrusion to compare the morphology of aged gels with that of fresh gels. • Setting up an extrusion apparatus and extruding the chemical plugs. • Documenting the qualitative observations on the efforts to remove the chemical plug materials from the pipe sections. • Performing X-ray diffraction (XRD) analysis of extruded gel samples to detect any crystallization of gel during storage. • Disposing of the extruded gel as a waste. • Documenting the analytical results in a test report. There were no significant morphological differences between the fresh and aged plugs except for an overgrowth of small transparent crystals on the surface of the aged NAS gel plug. An initial pressure of 15 KPa for the NAS plug and from ~2 to 6 KPa for the NAH plug. Following extrusion, the NAP plug sections were thixotropic. The bulk of all the aged gel plugs consisted of amorphous material with nitratine constituting the crystalline phase. A separate question about the whether the current in-tank waste conditions will bound the future multi-tank blended feed conditions for the Waste Treatment Plant is outside the scope of this study.« less

Kd values obtained on sediment samples from 200-UP-1 and 10-ZP-1 contribute to a larger Kd database that exists for other Hanford sediments, and contains significant desorption data for CCl4. Adsorption results presented here validate the use of a linear adsorption isotherm (Kd) to predict short contact time CCl4 adsorption to sediments in 200-UP-1 groundwater plume for a distinct ranges in CCl4 concentration. However, this does not imply that values of Kd will be constant if the groundwater chemical composition at 200-UP-1 changes with space or time. Additionally, results presented here suggest the potential significance of slower intraparticle diffusion on the long-term fate of CCl4 within the subsurface Hanford environment. Such behavior could afford prolonged desorption of CCl4 and serve as a long-term source of contaminant CCl4 to the aquifer. Further evaluation of possible bimodal sorption behavior for CCl4 and the mechanism of CCl¬4 sequestration should be the subject of future investigations to provide a thorough, mechanistic understanding of the retention and long-term fate of CCl4. Comparison of previous data with new results (e.g., from this study) will allow inferences to be made on how the 200-UP-1 Kd values for CCl4 may compare with sediments from other Hanford locations. This site-specific sorption data, when complemented by the chemical, geologic, mineralogic, hydrologic, and physical characterization data that are also being collected (see Sampling and Analysis Plan for the 200-UP-1 Groundwater Monitoring Well Network, DOE 2002) can be used to develop a robust, scientifically defensible data base to allow risk predictions to be generated and to aid in future remediation decisions for the 200-UP-1 and 200-ZP-1 operable units.

Environmental context. Uranium-phosphate minerals have been identified as a long-term controlling phase that limit the mobility of uranium to groundwater in many contaminated subsurface environments. Complex, coupled processes confound the ability to isolate the rates attributed to individual processes. Results of this investigation provide the necessary information to refine current prediction on the release and long-term fate of uranium in subsurface environments. Abstract. The purpose of this investigation was to conduct a series of single-pass flow-through (SPFT) tests to (1) quantify the effect of temperature (23–90°C) and pH (6–10) on meta-torbernite dissolution; (2) compare the dissolution of meta-torbernite to other autunite-group minerals; and (3) evaluate the effect of aqueous phosphate on the dissolution kinetics of meta-torbernite. Results presented here illustrate meta-torbernite dissolution rates increase by ~100× over the pH interval of 6 to 10, irrespective of temperature. The power law coefficient for meta-torbernite, η = 0.59 ± 0.07, is greater than that quantified for Ca-meta-autunite, η = 0.42 ± 0.12. This suggests the stability of meta-torbernite is greater than that of meta-autunite, which is reflected in the predicted stability constants. The rate equation for the dissolution of meta-torbernite as a function of aqueous phosphate concentration is log rdissol (mol m–2 s–1) = –4.7 × 10–13 + 4.1 × 10–10[PO43–].