Analysis of Hanford Cast Stone Supplemental LAW using Composition Adjusted SRS Tank 50 Salt Solution

Abstract

Vitrification is the primary disposition path for Low Activity Waste (LAW) at the Department of Energy (DOE) Hanford Site. A cementitious waste form is one of the alternatives being considered for the supplemental immobilization of the LAW that will not be treated by the primary vitrification facility. Washington River Protection Solutions (WRPS) has been directed to generate and collect data on cementitious or pozzolanic waste forms such as Cast Stone. This report documents work done to support supplemental immobilization efforts by performing testing on actual salt wastes immobilized in Cast Stone. The actual waste used in testing was a Savannah River Site (SRS) salt solution from Tank 50 H-area Tank Farm that was chemically adjusted with aluminum hydroxide, ammonium phosphate, and ammonium sulfate to represent Hanford salt waste. Radioactive Tc-99 and natural iodide-127 were also added to match previous simulant Tc-99 spike studies and to provide enough iodide for detection in the aqueous leachates. Using a chemically adjusted SRS salt waste avoided sampling, transportation and permitting issues, which would have been required for actual Hanford tank waste, while providing a readily available and representative sample for testing. Chemical adjustment of the SRS Tank 50 sample was verified by analysis showing targeted concentrations were achieved. Duplicate 2" x 4" 'baseline' monoliths were made using the adjusted Tank 50 salt solution and dry blend materials (premix) of ordinary portland cement (OPC), Class F fly ash (FA) and ground, granulated blast furnace slag (GGBFS) for a free water to premix ratio of 0.55. Three other sets of monoliths were made using various getters that included Potassium Metal Sulfide (KMS)-2 (K 2 MgSn 2 S 6), tin apatite (Sn 2 Ca 8 (PO 4) 6 Cl 2) and silver zeolite (Ag 84 Na 2 [(AlO 2) 86 (SiO 2) 106 ]•xH 2 O). The getters replaced mass from the premix, mass for mass, maintaining the effective premix ratio of 0.55. Monoliths were leach tested in reagent water using the Environmental Protection Agency (EPA) Method 1315 which is designed to provide mass transfer rates (release rates) of inorganic analytes contained in monolithic material under diffusion controlled release conditions as a function of leaching time. All initial species monolith concentrations used in the reported leachability index (LI) values are based on asbatched concentrations, i.e., no actual dissolution and characterization was performed on the monolithic cast stone matrix. As-batched species concentrations in the monoliths were based on analyzed adjusted Tank 50 supernate, previous analysis of premix components and calculated getter concentrations that are based on simple getter empirical formulas. Chemical adjustment of the SRS Tank 50 salt solution by the addition of Al, sulfate, phosphate and Tc-99 species, as well as natural iodide, met target levels as determined by chemical and radiochemical analysis. Monolith leach tests indicate no significant differences in the observed diffusivities (D obs) for these tes...

Review of recent developments in iodine wasteform production

“…Semi-dynamic leach testing of the AgZ containing wasteforms showed that in an oxidized formulation (no blast furnace slag included), no iodine was detected in the resulting leachates. This measurement was similar to another test where 5 mass% AgZ was added to a cementitious wasteform for iodine in liquid waste and on stabilizing silver alumina, silver silica gel, and AgZ in Portland cement (Mizuno et al, 1986;Lockrem, 2005;Crawford et al, 2017). This enhanced iodine retention was attributed to an Aglayer that was observed to form at the interface between the AgZ particle and matrix, see Figure 5.…”

Ultra-High-Performance Grout for Encapsulation of HEPA Filters

“…Similar to testing of 99 Tc leaching from grout, observed diffusivity for 129 I was determined for each time interval during the EPA 1315 leach testing. Figure 15(b) compares the results for the two grouts in this study and with previously reported work in Asmussen et al (2019) and Crawford et al (2017). Again, the UHPG had much lower observed diffusivity than the Baseline grout.…”

“…Observed diffusivity for 99 Tc was determined for each time interval during the EPA 1315 leach test using results from the analysis of leachate samples. Figure 15 (a) compares the results for the two grouts in this study and with work previously reported by Crawford et al (2017) Crawford et al (2017 present results from testing of grout prepared using the caststone (CS) recipe and Tank 50 liquid radioactive waste which contains a variety of radionuclides including 99 Tc and is characterized by high ionic strength and pH >14 resulting from the addition of NaOH to prevent corrosion. The UHPG had much lower observed diffusivity for both the Baseline grout was likely due to the lower porosity, Figure 8, and pore connectivity of the UHPG as shown by porosity and water retention characteristics (Figure 10 and Figure 11) as well as the ks limitations.…”