Separating the Minor Actinides Through Advances in Selective Coordination Chemistry

This report describes work conducted at the Pacific Northwest National Laboratory (PNNL) in Fiscal Year (FY) 2012 under the auspices of the Sigma Team for Minor Actinide Separation, funded by the U.S. Department of Energy Office of Nuclear Energy. Researchers at PNNL and Argonne National Laboratory (ANL) are investigating a simplified solvent extraction system for providing a single-step process to separate the minor actinide elements from acidic high-level liquid waste (HLW), including separating the minor actinides from the lanthanide fission products

Separating the Minor Actinides Through Advances in Selective Coordination Chemistry

This report describes work conducted at the Pacific Northwest National Laboratory (PNNL) in Fiscal Year (FY) 2012 under the auspices of the Sigma Team for Minor Actinide Separation, funded by the U.S. Department of Energy Office of Nuclear Energy. Researchers at PNNL and Argonne National Laboratory (ANL) are investigating a simplified solvent extraction system for providing a single-step process to separate the minor actinide elements from acidic high-level liquid waste (HLW), including separating the minor actinides from the lanthanide fission products

Removing Phosphate from Hanford High-Phosphate Tank Wastes: FY 2010 Results

The U.S. Department of Energy (DOE) is responsible for environmental remediation at the Hanford Site in Washington State, a former nuclear weapons production site. Retrieving, processing, immobilizing, and disposing of the 2.2 × 105 m3 of radioactive wastes stored in the Hanford underground storage tanks dominates the overall environmental remediation effort at Hanford. The cornerstone of the tank waste remediation effort is the Hanford Tank Waste Treatment and Immobilization Plant (WTP). As currently designed, the capability of the WTP to treat and immobilize the Hanford tank wastes in the expected lifetime of the plant is questionable. For this reason, DOE has been pursuing supplemental treatment options for selected wastes. If implemented, these supplemental treatments will route certain waste components to processing and disposition pathways outside of WTP and thus will accelerate the overall Hanford tank waste remediation mission

Organic and Aqueous Redox Speciation of Cu(III) Periodate Oxidized Transuranium Actinides

A hexavalent group actinide separation process could streamline used nuclear fuel recycling and waste management. The limiting factor to such a process compatible with current fuel dissolution practices is obtaining and maintaining hexavalent Am, AmO₂²⁺, in molar nitric acid because of the high reduction potential of the Am­(VI)/Am­(III) couple (1.68 V vs SCE). Two strong oxidants, sodium bismuthate and Cu³⁺ periodate, have demonstrated quantitative oxidation of Am under molar acid conditions, and better than 50% recovery by diamyl amylphosphonate (DAAP) is possible under these same conditions. This work considers the use of Cu³⁺ periodate to oxidize Np­(V) to Np­(VI) and Pu­(IV) to Pu­(VI) and to recover these elements by extraction with DAAP. A metal:oxidant ratio of 1:1.2 and 1:3 was necessary to quantitatively oxidize Np­(V) and Pu­(IV), respectively, to the hexavalent state. Extraction of hexavalent Np, Pu, and Am by 1 M DAAP in n-dodecane was measured using ultraviolet–visible (PuO₂²⁺, AmO₂²⁺) and near-infrared (NpO₂²⁺) spectroscopy. Distribution values of AmO₂²⁺ were found to match previous tracer level studies. The organic phase spectra of Np, Pu, and Am are presented, and molar absorptivities are calculated for characteristic peaks. Hexavalent Pu was found to be stable in the organic phase, while NpO₂²⁺ showed some reduction to NpO₂⁺; Am was present as Am³⁺, AmO₂⁺, and AmO₂²⁺ species in aqueous and organic phases during the extraction experiments. These results demonstrate, for the first time, the ability to recover macroscopic amounts of americium that would be present during fuel reprocessing and are the first characterization of Am organic phase oxidation state speciation relevant to a hexavalent group actinide separation process under acidic conditions

Developing and Testing an Alkaline-Side Solvent Extraction Process for Technetium Separation From Tank Waste.

Engineering development and testing of the SRTALK solvent extraction process are discussed in this paper. This process provides a way to carry out alkaline-side removal and recovery of technetium in the form of pertechnetate anion from nuclear waste tanks within the DOE complex. The SRTALK extractant consists of a crown ether, bis-4,4'(5')[(tert-butyl)cyclohexano] -18-crown-6, in a modifier, tributyl phosphate, and a diluent, Isopar{reg_sign}L. The SRTALK flowsheet given here separates technetium from the waste and concentrates it by a factor often to minimize the load on the downstream evaporator for the technetium effluent. In this work, we initially generated and correlated the technetium extraction data, measured the dispersion number for various processing conditions, and determined hydraulic performance in a single-stage 2-cm centrifugal contactor. Then we used extraction-factor analysis, single-stage contactor tests, and stage-to-stage process calculations to develop a SRTALK flowsheet. Key features of the flowsheet are (1) a low organic-to-aqueous (O/A) flow ratio in the extraction section and a high O/A flow ratio in the strip section concentrate the technetium and (2) the use of a scrub section to reduce the salt load in the concentrated technetium effluent. Finally, the SRTALK process was evaluated in a multistage test using a synthetic tank waste. This test was very successful. Initial tests with actual waste from the Hanford nuclear waste tanks show the same technetium extractability as determined with the synthetic waste feed. Therefore, technetium removal from actual tank wastes should also work well using the SRTALK process

Sigma Team for Minor Actinide Separation: PNNL FY 2011 Status Report

This report summarizes work conducted in FY 2011 at PNNL to investigate new methods of separating the minor actinide elements (Am and Cm) from the trivalent lanthanide elements, and separation of Am from Cm. For the former, work focused on a solvent extraction system combining an acidic extractant (HDEHP) with a neutral extractant (CMPO) to form a hybrid solvent extraction system referred to as TRUSPEAK (combining the TRUEX and TALSPEAK processes). For the latter, ligands that strongly bing uranyl ion were investigated for stabilizing corresponding americyl ion