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Contaminants disposed of at the land surface must migrate through the vadose zone before entering groundwater. Processes that occur in the vadose zone can attenuate contaminant concentrations during transport through the vadose zone. Thus, quantifying contaminant attenuation and contaminant transport processes in the vadose zone, in support of the conceptual site model (CSM) and fate and transport assessments, is important for assessing the need for, and type of, remediation in the vadose zone and groundwater. The framework to characterize attenuation and transport processes provided in U.S. Environmental Protection Agency (EPA) guidance documents was used to guide the laboratory effort reported herein.PNNL-26208 RPT-DVZ-AFRI-037 v all samples. In terms of desorption versus adsorption K d values, there was no clear trend across all of the samples.

To prevent the release of radioiodine during the reprocessing of used nuclear fuel or in the management of other wastes, many technologies have been developed for iodine capture. The capture is only part of the challenge as a durable waste form is required to ensure safe disposal of the radioiodine. This work presents the first durability studies in dilute conditions of two AgI-containing waste forms: hot-isostatically pressed silver mordenite (AgZ) and spark plasma sintered silver-functionalized silica aerogel (SFA) iodine waste forms (IWF). Using the single-pass flow-through (SPFT) test method, the dissolution rates respective to Si, Al, Ag and I were measured for variants of the IWFs. By combining solution and solid analysis information on the corrosion mechanism neutral-to-alkaline conditions was elucidated. The AgZ samples were observed to have corrosion preferentially occur at secondary phases with higher Al and alkali content. These phases contained a lower proportion of I compared with the matrix. The SFA samples experienced a higher extent of corrosion at Si-rich particles, but an increased addition of Si to the waste led to an improvement in corrosion resistance. The dissolution rates for the IWF types are of similar magnitude to other Si-based waste form materials measured using SPFT.

Revision 1 of this document includes updates to the text and added descriptions of studies that were applied to address some of the data gaps identified in Revision 0. Descriptions of the changes are provided below. Changes to Existing Sections • The summary indicates that Revision 1 contains new information and updated text. • Section 1.0 (introductory paragraph) was updated to indicate that Revision 1 contains new information and updated text. PNNL-24709, Rev. 2 RPT-DVZ-AFRI-030, Rev. 2 vi • Section 2.3.5 was added to describe the results of experiments to evaluate formation of precipitates incorporating iodate during calcite precipitation. Previous literature information about coprecipitation of iodate and calcite from Revision 0 was included in this new section. • Section 3.1.2 was added to describe the results of a vadose zone modeling analysis of the 129 I source areas for the 200-UP-1 operable unit.