Washing Demonstration using Nonradioactive Simulated Tank 7 Sludge-Slurry

Abstract

Tank 7 will be processed as part of the next sludge batch (Sludge Batch 3 *) in the Defense Waste Processing Facility (DWPF). Prior to processing in DWPF, a sludge-slurry must be washed to adjust the sodium content and weight percent total solids †. In typical sludge slurries, sodium is primarily soluble and easily adjusted by diluting and decanting the supernate (i.e., washing). For Tank 7, sodium adjustment is complicated by the presence of sodium oxalate which is partially soluble in aqueous solutions. To better understand how sodium oxalate would affect sludge washing, nonradioactive simulated Tank 7 sludge-slurry was prepared and washed. Soluble species (e.g., nitrate) were easily removed as expected. Sodium oxalate behaved like a partially soluble compound. As sodium concentration in wash water decreased, oxalate concentration increased until the equilibrium concentrations for sodium and oxalate were reached. Thus, sludge-slurry washing, even in the presence of sodium oxalate, is predictable. * Sludge Batch 3 for the Defense Waste Processing Facility will consist of the Sludge Batch 1B heel in Tank 51, Am/Cm and Pu/Gd slurries transferred from F and H-Areas into Tank 51, and the sludge slurry in Tank 7. However, the focus of this work is Tank 7 only; the other components of Sludge Batch 3 were not evaluated or considered. † Although weight percent total solids adjustment is an important aspect of washing, the scope of this work was sodium and oxalate adjustment/removal.

Technetium-99 Behavior in Savannah River Site High Level Waste Sludges During Waste Processing

“…This dissolution behavior has also been observed in a washing study using simulated Tank 7 sludge doped with solid Na 2 C 2 O 4 . [18] In that study the Na 2 C 2 O 4 .begin to dissolved from the solids after the Na concentration in the supernate decreased from ~4M to 2M. For the first three washes, the concentrations of all the elements in the wash solutions except U-238 decrease linearly in Figure 4-6 indicating that a constant fraction of each element is being removed by each wash solution.…”

Remediation of Spent Oxalic Acid Nuclear Decontamination Solutions Using Ozone

“…Analayzer ® with values shown by Based on the HLW system plan (Chew and Hamm, 2010), the following assumptions were used as input into creating the vitrification feed preparation (washing) tank batch preparation model. Based on previous cited SRS sludge washing studies, the effect of sludge washing on sodium concentration, the net result can be approximated by using a simple dilution model (Fowler, 1980;Wiley, 1978;Pareizs, 2002).…”

“…2) A representative initial sodium concentration of the vitrification sludge feed batch before washing is assumed to be 3.7 M. (HLW Engineering, 2008), with washing performed until the Na concentration is < 1 M (Subosits, 1994). Although, the sodium concentration of the caustic rich excess process supernatant is typically much > than 6 M , a representative Na concentration in the supernatant in the Tank Farm is 4.21 M (Pareizs, 2002), with the existing vitrification sludge feed batch sodium concentration diluted as a result of mechanical cleaning.…”

Impacts of Sodium Oxalate on High-Level Waste Processing at the Savannah River Site

“…At a volume ratio of 25:1, the oxalate concentration measured 0.177 M, which is slightly lower than the estimated maximum value of 0.250 M, based on previous testing by J. Pareiz and others. 7 ICP-ES analyses provided a list of elements detected in the wash water solutions. Appendix 2 provides a complete listing of all elements for each of the test solutions corrected for dilution and for elements found in the blank solution.…”