Hanford Tank Waste Research Articles

Incorporation of trace metals in Hanford waste boehmite mineral phases and dissolution rate impacts

AbstractData from radioactive Hanford tank waste samples was analyzed to assess whether trace metals present were incorporated into the bulk boehmite matrix or were simply intermingled with the bulk material and subsequent impacts to the boehmite dissolution rate. Results suggest that chromium is primarily blended into the bulk boehmite, with a small fraction present on the surface of the solids. However, increasing the level of chromium incorporation 30‐fold decreased the dissolution rate of boehmite by only 8%, suggesting incorporation of chromium into these samples had a minimal impact on the dissolution rate. Iron was also found to be incorporated in the boehmite solids. Silicon appears to be simply intermingled and not blended into the boehmite crystals.

Automated SEM analysis of particles in Hanford tank waste

Multiple bench-scale filtration campaigns of Hanford tank waste supernatant on a backpulseable dead-end filtration skid have provided greater insight into the solids that cause fouling and reduce filter performance. The solids collected during each campaign were concentrated from the backpulse solutions and examined using automated particle analysis (APA) methods with scanning electron microscopy and X-ray energy dispersive spectroscopy to categorize particle types and their morphological characteristics. We show that with APA, thousands of particles can be analyzed to provide accurate insight into the phases that may be impacting filter performance.

The simultaneous removal of technetium and iodine from Hanford tank waste

The simultaneous removal of radionuclides technetium-99 and iodine-129 from an actual decontaminated Hanford tank waste sample (a mixture of decontaminated waste from tanks 241-AP-105 and 241-AP-107) was demonstrated for the first time in this work. A series of commercially available ion exchange resins were evaluated in batch contact tests in the tank waste, and all showed removal of both Tc and I. The highest Tc removal from the tank waste was observed for Purolite A530e while the highest iodine removal was observed for ResinTech SIR-110-MP. Isotherm tests in simulated tank waste with these two resins showed that the SIR-110-HP-MP had consistently higher Kd for both pertechnetate and iodide; with much higher Kd than previous works on Tc removal from Hanford waste. As such, the SIR-110-MP was evaluated in a dual-column (lead/lag) test processing 5.2L of the tank waste mixture showing 50 % breakthrough of Tc on the lead column and no significant breakthrough on the lag after 641 bed volumes (BV, 6 mL size) while significant iodine breakthrough (>50 %) occurred after 28 BV. The limited iodine uptake was attributed to the column conditions generating mass transfer limitations. A fraction of the Tc and I was not captured by the resin (<10 %) in either the batch tests or column tests. The iodine fraction is not iodate and is likely organo-iodide. The fraction of the Tc was identified as a non-pertechnetate species which is the first time non-pertechnetate has been identified in AP-105 and AP-107 tanks. This non-pertechnetate fraction contained Tc(I) and for the first time a stable Tc(VI) species in Hanford waste was identified..

Investigation into Na and Cs activity coefficients in high salt solutions to support Cs removal in Hanford tank waste

Abstract The treatment of Hanford tank waste is one of the most technically challenging environmental cleanup activities for the U.S. Department of Energy to date. To expedite the processing of liquid waste stored in underground tanks in southeastern Washington state, it is necessary to remove the significant dose contributor, 137Cs. Toward this effort, ion exchange with crystalline silicotitanate (CST) has been employed as part of the Tank Side Cesium Removal system. The model used to predict Cs exchange onto CST was developed using activity coefficients calculated from the Bromley equation. A series of batch contact tests that varied in [Na] were conducted to look at the impact of Na concentration on Cs distribution. Experimental distribution ratios (K d) were compared to the distribution ratios predicted using three different activity coefficient models: (1) commercially available HSC software, (2) the Bromley equation, and (3) a simplified approach adapted from Marcos-Arroyo et al. Ultimately, the Bromley method underpredicted the effect of ionic strength on the Na activity coefficient (γ Na+), HSC overestimated the impact of ionic strength on the expected performance due to the Cs activity coefficient (γ Cs+), but the simplified approach predicted the experimental K d values quite well in a binary matrix. Expansion of this approach in complex matrices is necessary for application to Hanford tank waste.

Effect of Na Concentration on Cs Distribution with Crystalline Silicotitanate in Tank Waste Simulants

Crystalline silicotitanate (CST) ion exchange media is currently utilized in the tank side cesium removal (TSCR) system on the Hanford site to remove Cs-137 from the tank waste supernate. As the main dose contributor to the liquid supernate in Hanford tank waste, it is necessary to remove the Cs-137 to expedite low activity waste processing and immobilization. Ongoing batch contact experiments with CST have been done to tease out the impact of group II metals, anions, potassium, and temperature on Cs removal to better understand bounding conditions for operations as well as aid in development of a wholesome isotherm model to predict Cs behavior in the tank waste. This paper discusses the impact of Na concentration on Cs exchange and provides insight into the challenges associated with activity coefficient estimations for modeling Cs distribution in tank waste matrices.

Optimization of Cesium Ion Exchange Performance with Hanford Tank Waste Feed Dilution

ABSTRACT Crystalline silicotitanate (CST) ion exchanger is currently used to remove cesium (137Cs) from the aqueous phase of Hanford tank wastes in preparation for vitrification at the Waste Treatment and Immobilization Plant (WTP). The CST is a non-elutable inorganic ion exchanger targeted to maintain a decontamination factor of ≥1,000 prior to the column effluent reaching a waste acceptance criterion. In an effort to reduce costs generated by ion exchange processing, system optimization of the waste treatment has been conducted. Decreasing the tank waste supernate sodium molarity prior to processing through the ion exchange columns showed that it can significantly reduce the number of columns used while maintaining the necessary sodium throughput. Optimization of this process can result in significant cost savings and ultimately result in less waste production.

Impact of gel concentration on filter fluxes in microfiltration of Hanford tank wastes and simulants

AbstractTreatment processes have been proposed that will utilize crossflow filtration to concentrate sludge waste streams at the Department of Energy's Hanford Site. Challenges associated with solid–liquid separation of the waste streams drive a necessary evaluation of available Hanford high level waste (HLW) filtration data. Limiting flux conditions during crossflow filtration are elucidated with the formation of a cake layer on the membrane surface. A mass transfer coefficient between the gel and bulk concentrations plays a critical role in determining filter flux. A correlation between the gel concentration and mass transfer coefficient is made to assist in determining filter performance of select HLW streams. As a process alternative to crossflow filtration, gravity settling of waste streams may be deployed as a solid–liquid separation technique. However, this results in a contrasting performance with the centrifuged solids concentration. A method was developed to estimate expected filtration and settling performance based on physical characterization data for Hanford tank waste samples. By assessing the estimated processing performance of HLW, technical support can be provided during flowsheet planning.

Radiobiology of Select Radionuclides in Hanford Site Tank Waste.

There are several important radionuclides involved in the "clean-up" or environmental isolation of nuclear waste contained in US Department of Energy Hanford Site underground waste tanks that drive many of the decisions associated with this activity. To make proper human health risk analyses and ensure that the most appropriate decisions are made, it is important to understand the radiation biology and the human health risk associated with these radionuclides. This manuscript provides some basic radiological science, in particular radiation biology, for some of these radionuclides, i.e., 3 H, 90 Sr, 137 Cs, 99 Tc, 129 I, and the alpha emitters 239, 240 Pu, 233,234,235,238 U, and 241 Am. These radionuclides were selected based on their designation as "constituents of potential concern," historical significance, or potential impact on human health risk. In addition to the radiobiology of these select radionuclides, this manuscript provides brief discussions of the estimated cost of planned management of Hanford tank waste and a comparison with releases into the Techa River from activities associated with the Mayak Production Association. A set of summary conclusions of the potential human health risks associated with these radionuclides is given.

Impact of feed variability on cesium removal with multiple actual waste samples from the Hanford site

ABSTRACT The Tank Side Cesium Removal (TSCR) system, under development by Washington River Protection Solutions (WRPS), will send initial low-activity Hanford waste tank supernate feeds to the Hanford Waste Treatment and Immobilization Plant (WTP) Low-Activity Waste (LAW) Facility. In addition to entrained solids removal from the supernate, the primary goal of TSCR is to remove cesium-137 (137Cs) by ion exchange, allowing contact handling of the liquid effluent product at WTP. Crystalline silicotitanate (CST) ion exchange media, manufactured by Honeywell UOP (product IONSIV™ R9140-B), was selected as the ion exchange media at TSCR. This lot of material was found to have superior performance in comparison to historic batches of CST. Ion exchange column and batch contact testing with supernate from Hanford tanks AP-105, AP-107 and AW-102 was performed to assess the impact of feed variability on system performance. These tests demonstrated that batch contact measurements provide a reasonable prediction of column capacities with some deviation in performance attributed to column dynamics. In addition, the variability in CST capacity for cesium in the various actual waste samples does not track with historical understanding of the competing cations, suggesting that tank waste samples contain other components that may significantly impact cesium loading.

A newly proposed isotherm model to predict Cs exchange with crystalline silicotitanate in tank waste simulants

ABSTRACT The Zheng Anthony Miller (ZAM) computer model, a multicomponent ion exchange model used to predict the exchange of Group I metals onto crystalline silicotitanate (CST), has historically been used to predict Cs distribution coefficients from Hanford and Savannah River Site (SRS) tank waste simulants. Comparison of experimentally determined Cs distribution coefficients from tank waste simulants with ZAM isotherm model predictions indicate overprediction of Cs and K distribution coefficients for simple and complex simulants with the engineered form of CST. Additionally, recent changes in chemical composition/manufacturing of IONSIV TM R9140-B have resulted in increased Cs capacity from high-salt, highly alkaline solutions. This work served to assess different isotherm models and refine equilibrium parameters to develop a model that can be applied to Hanford and SRS tank waste Cs removal efforts. Toward this goal, the Campbell Westesen Peterson (CWP) model was developed. This model utilized the experimentally determined Cs capacity, and simplified ZAM equilibria expressions to include only the binary substitution of Cs+ or K+ on the Na+ sites. Equilibrium constants for these equations were refined using experimentally determined distribution coefficients. Overall, the CWP model significantly improved our ability to predict both Cs and K loading capacity from complex matrices.

Insight into ion exchange column dynamics through application of an analytical model of system performance

ABSTRACT The Direct Feed Low-Activity Waste flowsheet provides for the early production of immobilized low-activity waste (LAW) by feeding waste directly from Hanford tank farms to the Hanford Tank Waste Treatment and Immobilization Plant (WTP) for vitrification. Prior to the transfer of feed to the WTP LAW Vitrification Facility, tank waste supernatant will be pretreated by the Tank Side Cesium Removal (TSCR) system to meet the WTP LAW waste acceptance criteria (<3.18E-5 Ci 137Cs/mole of Na). This pretreatment will remove cesium from the waste stream using ion exchange (IX). The selected media for IX is crystalline silicotitanate (CST), product number IONSIV-R9140-B, manufactured by Honeywell UOP LLC (Des Plaines, IL). Testing was conducted to improve the understanding of the parameters that impact dynamic ion-exchange performance and to better define IX processing using Low-Activity Waste Pretreatment System (LAWPS) prototypic IX unit operations. Column testing at full height scale was conducted to gain insight into ion-exchange column dynamics and evaluate the application of an analytical model on system performance. Nominal process conditions used 5.6 M Na simulant processed in a lead/lag column format containing 1.15 L 18 × 15 mesh CST in 2.54-cm-diameter columns, 226 cm tall CST beds. Two process flowrates were tested: 1.30 and 1.82 bed volumes (BV) per hour. This work demonstrated that an analytical method can provide a reasonable estimate of the expected performance within the bounds of the assumptions employed for the analytical solution.

Structural drivers controlling sulfur solubility in alkali aluminoborosilicate glasses

AbstractIf the direct feed approach to vitrify the Hanford's tank waste is implemented, the low activity waste (LAW) will comprise higher concentrations of alkali/alkaline‐earth sulfates than expected under the previously proposed vitrification scheme. To ensure a minimal impact of higher sulfate concentrations on the downstream operations and overall cost of vitrification, advanced glass formulations with enhanced sulfate loadings (solubility) are needed. While, the current sulfate solubility predictive models have been successful in designing LAW glasses with sulfate loadings &lt;2 wt.%, it will be difficult for them to design glass compositions with enhanced loadings due to our limited understanding of the fundamental science governing these processes. In this pursuit, this article unearths the underlying compositional and structural drivers controlling the sulfate solubility in model LAW glasses. It has been shown that the preferentially removes non‐framework cations from the modifier sites in the silicate network, thus, leading to the polymerization in the glass network via the formation of ring‐structured borosilicate units. Furthermore, though the sulfate solubility slightly decreases with increasing Li+/Na+ in the glasses, the prefers to be charge compensated by Na+, as it is easier for to break Na–O bonds instead of Li–O bonds.

Crystallization of rhenium salts in a simulated low‐activity waste borosilicate glass: Erratum

Corresponding author: Brian Riley; email id: [email protected] There is a typographical error in the introduction of this paper. The volume of the Hanford tank waste is 55 million gallons, which should be listed as “2.1 × 105 m3” instead of “2.1 × 1011 m3.”

A history of Hanford tank waste, implications for waste treatment, and disposal

AbstractMore than 40 years of plutonium processing have left almost 56 million gallons of mixed radioactive waste sequestered in 177 underground tanks on the Hanford Site. Three different processing technologies were employed for plutonium purification in addition to uranium scavenging and fission product removal from the tank waste. All of these chemical processes have contributed to a complex waste stream that varies from tank to tank that presents downstream processing challenges to render the waste into a safe form for long‐term storage. The current disposition pathway for Hanford tank waste is vitrification. To maximize waste loading and minimize the number of high‐level waste canisters stored in a geologic repository, pretreatment of the waste is required. Both pretreatment and vitrification operations are impacted by the waste composition.

Small to Full-Height Scale Comparisons of Cesium Ion Exchange Performance with Crystalline Silicotitanate

ABSTRACT Crystalline silicotitanate (CST) ion exchanger is planned for use in the removal of cesium (137Cs) from the aqueous phase of Hanford tank wastes in preparation for vitrification at the Waste Treatment and Immobilization Plant (WTP). Batch contact testing was conducted to assess cesium exchange kinetics at four different CST particle-size distributions. Column testing was conducted at three column sizes, small (2.5% full height), medium (12% full height), and full height, to assess Cs loading performance behavior. Testing at the small scale was compared to actual Hanford tank waste testing to verify the validity of simulant tests to reflect full-height column performance. CST particle size adjustment was essential in scaling the column dynamics down from full scale to medium and small scales. The mean (d 50) CST particle size needed to be reduced from 633 microns to 567 and 542 microns, respectively, to achieve appropriately scaled results. Based on these results, a determination of intraparticle and film-diffusion impacts on overall mass-transfer coefficients will allow future modeling of the breakthrough performance at a range of process conditions.

Identification and Quantification of Technetium Species in Hanford Waste Tank AN-102.

Technetium-99 (Tc), a high yield fission product generated in nuclear reactors, is one of the most difficult contaminants to address at the U.S. Department of Energy Hanford, Savannah River, and other sites. In strongly alkaline solutions typifying Hanford tank waste, Tc exists as pertechnetate (TcO4-) (oxidation state VII) as well as in reduced forms (oxidation state < VII), collectively known as non-pertechnetate (non-TcO4-) species. Designing strategies for effective Tc management, including separation and immobilization, necessitates understanding the molecular structure of the non-TcO4- species and their identification in actual tank waste samples. Identification of non-TcO4- species would facilitate the development of new treatment technologies effective for dissimilar Tc species. Toward this objective, a spectroscopic library of the Tc(I) [fac-Tc(CO)3]+ and Tc(II, IV, V, VII) compounds was generated and applied to the characterization of the actual Hanford AN-102 tank waste supernatant, which was processed to adjust Na concentration to ∼5.6 M and remove 137Cs by spherical resorcinol-formaldehyde (sRF) ion-exchange resin. Post 137Cs removal, the cesium-loaded sRF column was eluted with 0.45 M HNO3. As-received AN-102, Cs-depleted effluent, and sRF eluate fractions were comprehensively characterized for chemical composition and speciation of Tc using 99Tc nuclear magnetic resonance spectroscopy and X-ray absorption spectroscopy. It was demonstrated for the first time that non-TcO4- Tc present in the AN-102 tank waste is composed of several low-valent Tc species, including the Tc(I) [fac-Tc(CO)3]+ and Tc(IV) compounds. This is the first demonstration of multiple non-TcO4- species co-existing in the Hanford tank waste, highlighting their importance for the waste processing.

Elemental characterization of crystalline silicotitanate following Hanford tank waste processing

ABSTRACT To expedite vitrification of low activity waste at the Hanford Site, a Tank-Side Cesium Removal system, using crystalline silicotitanate (CST) as the ion exchange media, is being evaluated. Laboratory scale testing of Cs removal by CST from Hanford tank waste supernates has been conducted by Pacific Northwest National Laboratory. Selectivity and partitioning of analytes on spent CST, specifically RCRA hazardous metals, selected +2 cations, and transuranic elements, were characterized through the complete digestion of CST. The CST was shown to adsorb a relevant fraction of Ca, Cd, Pb, Sr, U, Pu, Np, Am, and potentially Fe by IX and/or other mechanisms.

RETRACTED ARTICLE: Direct quantification of iodine in nuclear wastes using DRC-ICP-MS

A method was developed for the direct quantification of iodine in Hanford tank waste using inductively coupled plasma mass spectrometry coupled with a dynamic reaction cell. The following parameters were optimized to lower the 129 m/z background signal and minimize iodine carryover effects: diluent, oxygen gas flow rate, radiofrequency voltage applied to the dynamic reaction cell, and rinse times. The concentration of 129I was 23 ± 1 µg/mL (n = 4, ± 1σ) in the Hanford waste tank 241-AP-107; to our knowledge this work constitutes the first report of iodine concentration in the tank waste.

Optimizing radionuclide sequestration in anion nanotraps with record pertechnetate sorption

The elimination of specific contaminants from competitors poses a significant challenge. Rather than relying on a single direct interaction, the cooperation of multiple functionalities is an emerging strategy for adsorbents design to achieve the required affinity. Here, we describe that the interaction with the target species can be altered by modifying the local environment of the direct contact site, as demonstrated by manipulating the affinity of pyridinium-based anion nanotraps toward pertechnetate. Systematic control of the substituent effect allows the resulting anion nanotraps to combine multiple features, overcoming the long-term challenge of TcO4− segregation under extreme conditions of super acidity and basicity, strong irradiation field, and high ionic strength. The top material exhibits the highest sorption capacity together with record-high extraction efficiencies after a single treatment from conditions relevant to the used nuclear fuel (Hanford tank wastes, 95%) and legacy nuclear wastes (Savannah River Sites, 80%) among materials reported thus far.

Cesium removal from AP-105 Hanford tank waste using spherical resorcinol formaldehyde resin

ABSTRACTSpherical resorcinol formaldehyde (SRF) resin is planned for use in removing cesium (137Cs) from Hanford tank waste supernates in preparation for waste vitrification at the Waste Treatment and Immobilization Plant. The results of six complete load/elute cycles using 12 L of Hanford tank waste supernatant collected from Tank AP-105 are provided. Testing exposed SRF to the combined sources of chemical degradation, physical stresses, and radiolytic exposure. Decreased flowrates and increased elution volumes improved performance. Increased cycling decreased performance; increased flowrate increased mass transfer zones; Cs leakage into ensuing cycle increased with decreased eluate volume, and analyte mass fractionation were examined.