Contaminant Release from Residual Waste in Single Shell Tanks at the Hanford Site, Washington, USA - 9276
Determinations of elemental and solid-phase compositions, and contaminant release studies have been applied in an ongoing study of residual tank wastes (i.e., waste remaining after final retrieval operations) from five of 149 underground single-shell storage tanks (241-C-103, 241-C-106, 241-C-202, 241-C-203, and 241-S-112) at the U.S. Department of Energy’s Hanford Site in Washington State. This work is being conducted to support performance assessments that will be required to evaluate long-term health and safety risks associated with tank site closure. The results of studies completed to date show significant variability in the compositions, solid phase properties, and contaminant release characteristics from these residual tank wastes. This variability is the result of differences in waste chemistry/composition of wastes produced from several different spent fuel reprocessing schemes, subsequent waste reprocessing to remove certain target constituents, tank farm operations that concentrated wastes and mixed wastes between tanks, and differences in retrieval processes used to remove the wastes from the tanks. Release models were developed based upon results of chemical characterization of the bulk residual waste, solid-phase characterization (see companion paper 9277 by Krupka et al.), leaching and extraction experiments, and geochemical modeling. In most cases empirical release models were required to describe contaminant release from these wastes. Release of contaminants from residual waste was frequently found to be controlled by the solubility of phases that could not be identified and/or for which thermodynamic data and/or dissolution rates have not been measured. For example, significant fractions of Tc-99, I-129, and Cr appear to be coprecipitated at trace concentrations in metal oxide phases that could not be identified unambiguously. In the case of U release from tank 241-C-103 residual waste, geochemical calculations indicated that leachate concentrations of U were likely controlled by the solubility of schoepite (UO3•2H2O). Therefore, a reactive transport model based upon solubility of schoepite and the expected composition and infiltration rates of pore water could be used to simulate future release of U from this residual tank waste. In addition to the development of release models, the residual tank waste studies completed so far have provided a number of new insights that have changed our understanding of residual tank waste. For example, the release of contaminants from different tanks, although governed by the same general chemical principles, can be very different. It has also been found that significant fractions of Tc-99 and other typically highly mobile contaminants are frequently not readily released from tank residuals and occur in recalcitrant phases that are resistant to aqueous dissolution. As these studies progress, such key cross-cutting geochemical processes and solid phase characteristics important to contaminant release from residual tank waste are becoming apparent. This may allow the grouping of tanks into general categories with certain common chemical features and contaminant release characteristics – an important goal because complete characterization of residual wastes from all 149 single-shell storage tanks is not practical.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 965148
- Report Number(s):
- PNNL-SA-63383; 11694; TRN: US0903584
- Resource Relation:
- Conference: WM 2009 Waste Management for the Nuclear Renaissance, March 1-5, 2009, Phoenix, Arizona
- Country of Publication:
- United States
- Language:
- English
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Characterization of Solids in Residual Wastes from Single-Shell Tanks at the Hanford Site, Washington, USA - 9277
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Related Subjects
DISSOLUTION
LEACHATES
LEACHING
OXIDES
PERFORMANCE
REPROCESSING
SAFETY
SCHOEPITE
SOLUBILITY
SPENT FUELS
STORAGE
STORAGE FACILITIES
TANKS
TARGETS
THERMODYNAMICS
WASTE MANAGEMENT
WASTES
Residual tank waste
single-shell tank
performance assessment
Environmental Molecular Sciences Laboratory