SummaryAssessing long-term performance of Category 3 waste cement grouts for radionuclide encasement requires knowledge of the radionuclide-cement interactions and mechanisms of retention (i.e., sorption or precipitation); the mechanism of contaminant release; the significance of contaminant release pathways; how waste form performance is affected by the full range of environmental conditions within the disposal facility; the process of waste form aging under conditions that are representative of processes occurring in response to changing environmental conditions within the disposal facility; the effect of waste form aging on chemical, physical, and radiological properties; and the associated impact on contaminant release. This knowledge will enable accurate prediction of radionuclide fate when the waste forms come in contact with groundwater. Numerous sets of tests were initiated in fiscal years (FY) 2006 through2009 to evaluate 1) diffusion of iodine (I) and technetium (Tc) from concrete into uncontaminated soil after 1 and 2 years, 2) I and rhenium (Re) diffusion from contaminated soil into fractured concrete, 3) I and Re (set 1) and Tc (set 2) diffusion from fractured concrete into uncontaminated soil, 4) the moisture distribution profile within the sediment half-cell, 5) the reactivity and speciation of uranium (VI) [U(VI)] compounds in concrete porewaters, 6) the rate of dissolution of concrete monoliths, and 7) the diffusion of simulated tank waste into concrete.In FY 2008, concrete-soil half-cells initiated during FY 2007 using fractured concrete prepared with and without metallic iron, half of which were carbonated, were sectioned to evaluate the diffusion of I and Re in the concrete part of the half-cell. Probit plots were constructed from this data set.A second set of diffusion experiments, which had been initiated during FY 2007 using concrete-soil half-cells containing Tc, was sectioned in FY 2008 to measure the diffusion profile in the soil half-cell. These half-cells were prepared with and without metallic iron (Fe) and set up under unsaturated conditions (4%, 7%, and 15% moisture content by weight). Probit plots were constructed from this data set. In FY 2008, a set of concrete-soil half-cells were initiated. The half-cells were sectioned in FY 2009 to measure the diffusion profile in the concrete half-cell. Concentration and probit analysis was performed on the half-cells.A study was initiated during FY 2004 to better understand the reactivity of limited solubility U(VI)-bearing compounds in Portland cement grout specimens. The U(VI) nitrate-spiked specimens were aged for various time spans ranging from 2 weeks to 1 year. The uranium phases in these specimens were identified to be soddyite, becquerelite, uranophane, and autunite. Reliable thermochemical data are not available for these phases under conditions present in concrete waste forms. Therefore, to gather such data, synthetic routes were developed for the precipitation of pure uranium phases. From FY 2007 to FY 2008, the solubility meas...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.