Enhanced 99Tc retention in glass waste form using Tc(IV)-incorporated Fe minerals

Technetium (99Tc) immobilization by doping into iron oxide mineral phases may alleviate the problems with Tc volatility during vitrification of nuclear waste. Because reduced Tc, Tc(IV), substitutes for Fe(III) in the crystal structure by a process of Tc reduction from Tc(VII) to Tc(IV) followed by co-precipitation of Fe oxide minerals, two Tc-incorporated Fe minerals (Tc-goethite and Tc-magnetite/maghemite) were prepared and tested for Tc retention in glass melt samples at temperatures between 600 and 1000 °C. After being cooled, the solid glass specimens prepared at different temperatures at 600, 800, and 1000 °C were analyzed for Tc oxidation state using Tc K-edge XANES. In most samples, Tc was partially (<60%) oxidized from Tc(IV) to Tc(VII) as the melt temperature increased up to 600 °C. However, most of Tc(IV) was completely (>95%) oxidized to Tc(VII) at temperature above 800 °C. Tc retention in glass melt samples prepared using Tc-incorporated Fe minerals were slightly higher (∼10%) than in glass prepared using KTcO4 because of limited and delayed Tc volatilization

Inorganic and Radiochemical Analysis of AW-101 and AN-107 Tank Waste

This report presents the inorganic and radiochemical analytical results for AW-101 and AN-107 as received materials. The analyses were conducted in support of the BNFL Proposal No. 30406/29274 Task 5.0. The inorganic and radiochemical analysis results obtained from the as received materials are used to provide initial characterization information for subsequent process testing and to provide data to support permit application activities. Quality Assurance (QA) Plan MCS-033 provides the operational and quality control protocols for the analytical activities, and whenever possible, analyses were performed to SW-846 equivalent methods and protocols

Removal of Sulfate Ion From AN-107 by Evaporation

Hanford low-activity waste solutions contain sulfate, which can cause accelerated corrosion of the vitrification melter and unacceptable operating conditions. A method is needed to selectively separate sulfate from the waste. An experiment was conducted to evaluate evaporation for removing sulfate ion from Tank AN-107 low-activity waste. Two evaporation steps were performed. In the first step, the volume was reduced by 55% while in the second step, the liquid volume was reduced another 22%. Analysis of the solids precipitated during these evaporations revealed that large amounts of sodium nitrate and nitrite co-precipitated with sodium sulfate. Many other waste components precipitated as well. It can be concluded that sulfate removal by precipitation is not selective, and thus, evaporation is not a viable option for removing sulfate from the AN-107 liquid

The Nature of the Volatile Technetium Species Formed During Vitrification of Borosilicate Glass

Vitrification of sodium pertechnetate into borosilicate glass was performed in air at 1100 °C. A glass with a composition similar to the one developed for vitrification of the low activity waste at the Hanford site was used. A red volatile species was observed above 600 °C. The extended X-ray absorption fine structure results indicate the environment of the absorbing Tc atom consists of 2.9(6) O atoms at 1.73(2) Å, 2.2(4) O atoms at 2.02(2) Å, and 0.8(2) O atoms at 2.18(2) Å. The results are consistent with the presence of a mononuclear species with a structure closely related to TcO3(OH)(H2O)2