DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document. Executive SummaryResearch at Pacific Northwest National Laboratory (PNNI,)@) has probed the physical mechanisms and waste properties that contribute to the retention and release of flammable gases fiom radioactive waste stored in underground tanks at Hanford. This study was conducted for Westinghouse Hanford Company as part of the PNNL Flammable Gas Project. The wastes contained in the tanks are mixes of radioactive and chemical products, and some of these wastes are known to generate mixtures of flammable gases, including hydrogen, nitrous oxide, and ammonia. Because these gases are flammable, their retention and episodic release pose a number of safety concerns.Previous investigations of bubble retention focused on bubbles retained in settled solids that are submerged beneath a supernatant liquid layer. This configuration is typical of waste stored in double-shell tanks (DSTs). In this situation, when the retention of bubbles causes the solids to become buoyant, the waste undergoes a buoyancy-induced rollover. While the rollover gas release mechanism in DSTs is well documented, the mechanism of bubble retention is not as well understood. In single-shell tanks (SSTs), in contrast, the settled solids are often not completely submerged, and buoyant rollovers similar to those in DSTs are not possible. For SST waste, neither the mechanisms of bubble retention nor those of bubble release are well understood.The objective of this study is to quantify the pertinent mechanisms of bubble retention and release by measuring and observing bubble retention both in actual waste samples and in simulated wastes. M a x i m u m gas retention and release data were obtained fiom actual waste samples fiom the SST 241-S-102 (S-102) and the DST 241-SY-103 (SY-103), both of which are on the Flammable Gas Watch List. In addition to the retentiodrelease studies, the ability of waste particles to armor and stabilize gas bubbles was investigated using an SY-103 waste sample.The simulants studied in this work were chosen to mimic the behavior of actual SST waste. SST wastes have a wide range of physical properties that range fiom clay-like, plastic sludges to hard salt cake. In this work, experiments focusid on fine-particle simulants composed of bentonite clay and water, because these are believed to mimic the sludge-like waste contained in SSTs. Because the actual properties of SST waste are not well-known, simulants with a wide range of strengths were prepared and tested. The experimental results quantified the ability of these simulants to retain gas and indicated how the gas is released. For comparison-with these simulants, some previously reported results for particulate simulants were reevaluated. In addition, new gas retention results were obtained for partially drained particulate simulants to aid in our understanding of gas retention in SSTs that have been salt-well pumped. Together, th...

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Approximately 190 kg of 2 μm‐diameter zero‐valent iron (ZVI) particles were injected into a test zone in the top 2 m of an unconfined aquifer within a trichloroethene (TCE) source area. A shear‐thinning fluid was used to enhance ZVI delivery in the subsurface to a radial distance of up to 4 m from a single injection well. The ZVI particles were mixed in‐line with the injection water, shear‐thinning fluid, and a low concentration of surfactant. ZVI was observed at each of the seven monitoring wells within the targeted radius of influence during injection. Additionally, all wells within the targeted zone showed low TCE concentrations and primarily dechlorination products present 44 d after injection. These results suggest that ZVI can be directly injected into an aquifer with shear‐thinning fluids to induce dechlorination and extends the applicability of ZVI to situations where other emplacement methods may not be viable.

SummaryAt the Hanford Site in southeastern Washington State, contaminated groundwater discharges to the Columbia River after passing through a zone of groundwater/river water interaction at the shoreline (i.e., the hyporheic zone). In the hyporheic zone, river water may infiltrate the riverbank during periods of high-river stage and mix with the approaching groundwater. Contaminants carried by groundwater may become diluted by the infiltrating river water, thus reducing concentrations at locations of exposure, such as riverbank springs and upwelling through the riverbed. There have been limited studies of contaminant concentrations, physical properties, or the extent of the hyporheic zone near the Hanford Site's 300 Area, yet this zone is a major interface for discharge of groundwater contamination into the Columbia River.The Remediation Task of the Remediation and Closure Science Project conducts research to meet several objectives concerning the discharge of groundwater contamination into the river at the 300 Area of the Hanford Site in Washington State. This report documents research conducted to meet these objectives by developing baseline data for future evaluation of remedial technologies, evaluating the effects of changing river stage on near-shore groundwater chemistry, improving estimates of contaminant flux to the river, providing estimates on the extent of contaminant discharge areas along the shoreline, and providing data to support computer models used to evaluate remedial alternatives. This report summarizes the activities conducted to date, and provides an overview of data collected through July 2006. Recent geologic investigations (funded through other U.S. Department of Energy [DOE] projects)have provided a more complete geologic interpretation of the 300 Area and a characterization of the vertical extent of uranium contamination. Extrapolation of this geologic interpretation into the hyporheic zone is possible, but little data are available to provide corroboration. Penetration testing was conducted along the shoreline to develop evidence to support the extrapolation of the mapping of the geologic facies. While this penetration testing provided evidence supporting the extrapolation of the most recent geologic interpretation, it also provided some higher-resolution detail on the shape of the layer that constrains contaminant movement. Information on this confining layer will provide a more-detailed estimate of the area of riverbed that has the potential to be impacted by uranium discharge to the river from groundwater transport.Water sampling in the hyporheic zone has provided results that illustrate the degree of mixing that occurs in the hyporheic zone. Uranium concentrations measured at individual sampling locations can vary by several orders of magnitude depending on the Columbia River and near-shore aquifer elevations. This report shows that the concentrations of all the measured constituents in water samples collected from the hyporheic zone vary according to the ratio of groundwater and C...

range from 70 to 85 wt%; the reported water content is somewhat higher in Tank T-111 (85 to 90 wt%) and lower in a few samples from T-201 (~65 wt%). Most of the data for bulk solids samples, a matrix of waste solids and interstitial liquid, show bulk densities of 1.15 to 1.30 g/mL, and the density generally increases with decreasing water content. The shear strength estimates obtained from the extrusion methods were compared with the water content and bulk density of waste samples from the same core segments. The shear strength and, to a lesser extent, the density show some tendency to decrease with increasing water, but significant scatter exists in the data. The physical properties of in situ and diluted SST TRU waste described in this report and summarized in the discussion above are tabulated in Table ES.1. In many cases, the expected range of properties is estimated from limited data. However, in those instances where data are available for many tanks and multiple locations within tanks, the data do not indicate major differences among individual tanks. Therefore, it appears reasonable to treat individual tank results as typical of Hanford SST TRU waste. Table S.1. Expected Range of Physical Properties of In Situ and Diluted SST TRU Waste Property Expected Range Comments Shear strength 200 to 2,000 Pa (majority of waste) 0 to 4,000 Pa (range, including liquid) Estimated from data obtained from core extrusions (Sections 3.1 and 3.2) and reported shear vane measurements (Section 4.1). Viscosity 2 to 25 cP at 10 s-1 2 to 15 cP at 100 s-1 Results for 1:1 dilution with water; higher viscosities expected for waste diluted less and at lower strain rates. Waste exhibited pseudoplastic rheology. Section 4.1. Waste settling ~0 vol% free liquid (1 G) 2 to 40 vol% free liquid (>1000 G, 1 hr) Undiluted waste, >200 Pa shear strength. Weaker waste (liquid in the extreme) is expected to produce more free liquid on settling. Section 4.2. Waste settling 5 to 25 vol% free liquid (1 G, ~2 days) 40 to 60 vol% free liquid (>1000 G, 1 hr) 1:1 diluted waste, >200 Pa shear strength prior to dilution. See comment above. Section 4.2. Waste settling 40 to 65 vol% free liquid (1 G, ~2 days) 70 to 85 vol% free liquid (>1000 G, 1 hr) 3:1 diluted waste, >200 Pa shear strength prior to dilution. See comment above. Section 4.2. Particle size, mean 7 to 70 µm (volume density) < 2 µm (number density) Section 4.3. Water content 70 to 85 wt% (majority of waste) 65 to 90 wt% (range) Section 5.1. Liquid Density ~1.05 g/mL Section 5.2 Bulk Density 1.15 to 1.3 g/mL (majority of waste) 1.1 to 1.4 g/mL (range) Section 5.2 vii