William J. Deutsch

Solubility equilibria in basalt aquifers: The Columbia Plateau, eastern Washington, U.S.A.

A speciation-solubility geochemical model, WATEQ2, was used to analyse geographically-diverse groundwater samples from the aquifers of the Columbia Plateau basalts in eastern Washington. The groundwater samples compute to be at equilibrium with calcite which provides both a solubility control for dissolved Ca and a pH buffer. Amorphic ferric hydroxide, Fe(OH)3 (a), is at saturation or modestly oversaturated in the few water samples with measured redox potentials. Most of the groundwater samples compute to be at equilibrium with amorphic silica (glass) and wairakite, a zeolite, and are saturated to oversaturated with respect to allophane, an amorphic aluminosilicate. The water samples are saturated to undersaturated with halloysite, a clay, and are variably oversaturated with regard to other secondary clay minerals. Equilibrium between the groundwater and amorphic silica presumably results from the dissolution of the glassy matrix of the basalt. The oversaturation with respect to the clay minerals other than halloysite indicates that their rate of formation lags the dissolution rate of the basaltic glass. The modeling results indicate that metastable amorphic solids limit the concentration of dissolved Si and suggest the same possibility for Al and Fe. The results also suggest that the processes of dissolution of basaltic glass and formation of metastable secondary minerals are continuing even though the basalts are of Miocene age and presumably have undergone a long history of contact with groundwaters. The computed solubility relations are found to agree with the known assemblages of alteration minerals in the basalt fractures and vesicles, if account is taken of both the difficulty of identifying amorphic phases and the slow rate of formation of clay minerals at low temperatures. Because the chemical reactivity of the bedrock will influence the transport of solutes in groundwater, the observed solubility equilibria are important factors with regard to chemical-retention processes associated with the possible migration of nuclear waste stored in the earths crust. Specifically, the occurrence of secondary minerals will enhance the sorption of dissolved radionuclides. Speciation-solubility geochemical models provide an important means of determining these solubility-equilibria relationships.

Hanford Tanks 241-C-203 and 241-C-204: Residual Waste Contaminant Release Model and Supporting Data

This report describes the development of release models for key contaminants that are present in residual sludge remaining after closure of Hanford Tanks 241-C-203 (C-203) and 241-C-204 (C-204). The release models were developed from data generated by laboratory characterization and testing of samples from these two tanks. Key results from this work are (1) future releases from the tanks of the primary contaminants of concern (99Tc and 238U) can be represented by relatively simple solubility relationships between infiltrating water and solid phases containing the contaminants; and (2) high percentages of technetium-99 in the sludges (20 wt% in C-203 and 75 wt% in C-204) are not readily water leachable, and, in fact, are very recalcitrant. This is similar to results found in related studies of sludges from Tank AY-102. These release models are being developed to support the tank closure risk assessments performed by CH2M HILL Hanford Group, Inc., for the U.S. Department of Energy.

Hanford Tanks 241-AY-102 and 241-BX-101: Sludge Composition and Contaminant Release Data

This report describes the results of testing sludge samples from Hanford tanks 241-AY-102 (AY-102) and 241-BX-101 (BX-101). These tests were conducted to characterize the sludge and assess the water leachability of contaminants from the solids. This work is being conducted to support the tank closure risk assessments being performed by CH2M HILL Hanford Group, Inc. for the U.S. Department of Energy. This is the first report of testing of BX-101 sludge and the second report of testing of AY-102. Lindberg and Deutsch (2003) described the first phase of testing on AY-102 material.

Hanford Tank 241-C-106: Impact of Cement Reactions on Release of Contaminants from Residual Waste

The CH2M HILL Hanford Group, Inc. (CH2M HILL) is producing risk/performance assessments to support the closure of single-shell tanks at the U.S. Department of Energys Hanford Site. As part of this effort, staff at Pacific Northwest National Laboratory were asked to develop release models for contaminants of concern that are present in residual sludge remaining in tank 241-C-106 (C-106) after final retrieval of waste from the tank. Initial work to produce release models was conducted on residual tank sludge using pure water as the leaching agent. The results were reported in an earlier report. The decision has now been made to close the tanks after waste retrieval with a cementitious grout to minimize infiltration and maintain the physical integrity of the tanks. This report describes testing of the residual waste with a leaching solution that simulates the composition of water passing through the grout and contacting the residual waste at the bottom of the tank.

Hanford Tank 241-C-106: Residual Waste Contaminant Release Model and Supporting Data

This report was revised in May 2007 to correct values in Section 3.4.1.7, second paragraph, last sentence; 90Sr values in Tables 3.22 and 3.32; and 99Tc values Table 4.3 and in Chapter 5. In addition, the tables in Appendix F were updated to reflect corrections to the 90Sr values. The rest of the text remains unchanged from the original report issued in May 2005. CH2M HILL is producing risk/performance assessments to support the closure of single-shell tanks at the DOEs Hanford Site. As part of this effort, staff at PNNL were asked to develop release models for contam¬inants of concern that are present in residual sludge remaining in tank 241-C-106 (C-106) after final retrieval of waste from the tank. This report provides the information developed by PNNL.

Thermodynamic model for uranium release from hanford site tank residual waste.

A thermodynamic model of U solid-phase solubility and paragenesis was developed for Hanford Site tank residual waste that will remain in place after tank closure. The model was developed using a combination of waste composition data, waste leach test data, and thermodynamic modeling of the leach test data. The testing and analyses were conducted using actual Hanford Site tank residual waste. Positive identification of U phases by X-ray diffraction was generally not possible either because solids in the waste were amorphous or their concentrations were not detectable by XRD for both as-received and leached residual waste. Three leachant solutions were used in the studies: deionized water, CaCO3 saturated solution, and Ca(OH)2 saturated solution. Analysis of calculated saturation indices indicate that NaUO2PO4·xH2O and Na2U2O7(am) are present in the residual wastes initially. Leaching of the residual wastes with deionized water or CaCO3 saturated solution results in preferential dissolution Na2U2O7(am) and formation of schoepite. Leaching of the residual wastes with Ca(OH)2 saturated solution appears to result in transformation of both NaUO2PO4·xH2O and Na2U2O7(am) to CaUO4. Upon the basis of these results, the paragenetic sequence of secondary phases expected to occur as leaching of residual waste progresses for two tank closure scenarios was identified.

Hanford Tanks 241-C-202 and 241-C-203 Residual Waste Contaminant Release Models and Supporting Data

As directed by Congress, the U. S. Department of Energy (DOE) established the Office of River Protection in 1998 to manage DOEs largest, most complex environmental cleanup project – retrieval of radioactive waste from Hanford tanks for treatment and eventual disposal. Sixty percent by volume of the nations high-level radioactive waste is stored at Hanford in aging deteriorating tanks. If not cleaned up, this waste is a threat to the Columbia River and the Pacific Northwest. CH2M Hill Hanford Group, Inc., is the Office of River Protections prime contractor responsible for the storage, retrieval, and disposal of Hanfords tank waste. As part of this effort, CH2M HILL Hanford Group, Inc. contracted with Pacific Northwest National Laboratory (PNNL) to develop release models for key contaminants that are present in residual sludge remaining after closure of Hanford Tanks 241-C-203 (C-203) and 241-C-204 (C-204). The release models were developed from data generated by laboratory characterization and testing of samples from these two tanks. These release models are being developed to support the tank closure risk assessments performed by CH2M HILL Hanford Group, Inc., for DOE.

Characterization of Solids in Residual Wastes from Underground Storage Tanks at the Hanford Site, Washington, U.S.A.

Solid phase physical and chemical characterization methods have been used in an ongoing study of residual wastes from several single-shell underground waste tanks at the U.S. Department of Energys Hanford Site in southeastern Washington State. Because these wastes are highly-radioactive dispersible powders and are chemically-complex assemblages of crystalline and amorphous solids that contain contaminants as discrete phases and/or co-precipitated within oxide phases, their detailed characterization offers an extraordinary technical challenge. X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS) are the two principal methods used, along with a limited series of analyses by synchrotron-based methods, to characterize solid phases and their contaminant associations in these wastes. Depending on the specific tank, numerous solids (e.g., eejkaite; Na 2 U 2 O 7 ; clarkeite; gibbsite; bohmite; dawsonite; cancrinite; Fe oxides such as hematite, goethite, and maghemite; rhodochrosite; lindbergite; whewellite; nitratine; and several amorphous phases) have been identified in residual wastes studied to date. Because many contaminants of concern are heavy elements, SEM analysis using the backscattered electron (BSE) signal has proved invaluable in distinguishing phases containing elements, such as U and Hg, within the complex assemblage of particles that make up each waste. XRD, SEM/EDS, and synchrotron-based methods provide different, but complimentary characterization data about the morphologies, crystallinity, particle sizes, surface coatings, and compositions of phases in these wastes. The impact of these techniques is magnified when each is used in an iterative fashion to help interpret the results from the other analysis methods and identify additional, more focused analyses.

Advances in Geochemical Testing of Key Contaminants in Residual Hanford Tank Waste

This report describes the advances that have been made over the past two years in testing and characterizing waste material in Hanford tanks.

Hanford Tank 241-C-103 Residual Waste Contaminant Release Models and Supporting Data

This report tabulates data generated by laboratory characterization and testing of three samples collected from tank C-103. The data presented here will form the basis for a release model that will be developed for tank C-103. These release models are being developed to support the tank risk assessments performed by CH2M HILL Hanford Group, Inc. for DOE.