Solid Secondary Waste Data Package Supporting Hanford Integrated Disposal Facility Performance Assessment

Abstract

This data package provides recommendations for waste form physical and chemical properties to support the initial analysis of Solid Secondary Waste (SSW) disposals in the 2017 Integrated Disposal Facility (IDF) Performance Assessment (PA). At this time, specific formulations have not been identified for cementitious materials that will be used to encapsulate or solidify SSW, and no IDF-specific experiments were conducted to obtain data for the PA. Thus recommended property values are provided for a range of candidate materials, and based on a review of existing literature. Four key SSW streams were identified for emphasis due to expected inventories for contaminants of potential concern (COPC): HEPA filters, ion exchange resins, carbon adsorber beds and Ag-mordenite. Based on current disposal plans, compacted HEPA filters were considered as an encapsulated waste form and the other three key waste streams were assumed to be blended and solidified in a cementitious matrix. Considerations for alternative disposal methods were also addressed. The IDF PA team identified specific COPCs expected to be the key contributors for the PA calculations: Tc-99, I-129, Cs-137, Sr-90, uranium isotopes (and total uranium), chromium, mercury and nitrate. These species are the focus of this data package.

Ultra-High-Performance Grout for Encapsulation of HEPA Filters

“…Solubility controls are not commonly ascribed to iodine in cementitious environments, and never ascribed at the very low concentrations used in these studies (Ochs et al, 2016). The 129 I Kd value for the Baseline mix sample, 103.3 ± 14.3 mL/g, is similar to that for the UHPG and is within the range previously reported by Flach et al (2016). (3.56 ± 0.49) x 10 -9 a 2 <2.81 x 10 -9 3 3.91 x 10 -9…”

“…This difference in Tc Kd values captures the expected change in Tc oxidation state from the strongly binding and low solubility nature of Tc(IV) species existing under reducing conditions, to the weakly binding and highly soluble Tc(VII) species existing under mildly oxidizing conditions. Conversely, iodine Kd value for this facility are expected to be greater in the oxidizing grout systems (2 to 8 mL/g) than reducing grout systems (0 to 2 mL/g) (Flach et al, 2016). These differences in iodine Kd values reflect the expectation that both iodine oxidation state species (iodate (IO3 -) and iodide (I -)), exist in oxidizing grouts, whereas in reducing grouts, only the poorer binding Ispecies will exist (Li et al, 2019) and (Kaplan et al, 2019).…”

“…Understanding the experimental conditions used in this study is especially important for interpreting the implications of the results because Tc and I geochemistry related to sorption is extremely sensitive to redox conditions and whether adsorption or desorption are being measured to estimate the Kd construct. For example, the Tc Kd values recommended for the IDF PA are 1000 mL/g for reducing grout, whereas under oxidizing conditions its Kd value ranges between 0.5 to 0.8 mL/g, a three order of magnitude difference (Flach et al, 2016). This difference in Tc Kd values captures the expected change in Tc oxidation state from the strongly binding and low solubility nature of Tc(IV) species existing under reducing conditions, to the weakly binding and highly soluble Tc(VII) species existing under mildly oxidizing conditions.…”

“…There were no significant differences between the average 129 I Kd values for the UHPG (114.4 ± 3.8 mL/g) and for those for the Baseline (103.3 ± 14.3 mL/g) (2-tailed t-In a review of I-grout Kd values, it was reported that they ranged from 5 to 120 mg/L (Flach et al, 2016); as such the values in Table 6 are among the larger ones in this range. They are two orders of magnitude greater than recommended IDF PA Kd values (0 to 8 mL/g).…”

Secondary Waste Cementitious Waste Form Data Package for the Integrated Disposal Facility Performance Assessment

“…Other data packages have been prepared in the past for the ILAW glass and cementitious waste forms and have recently been updated (Krupka et al 2004;Rockhold et al 2015, Last et al 2015, Pierce et al 2004, Freedman et al 2015. A separate data package is being prepared for solid secondary wastes encapsulated in cementitious waste forms (Flach et al 2016).…”