Sigma Team for Advanced Actinide Recycle FY2015 Accomplishments and Directions

Technical Report · Wed Sep 30 00:00:00 EDT 2015

DOI:https://doi.org/10.2172/1263841· OSTI ID:1263841

Moyer, Bruce A. ^[1]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

The Sigma Team for Minor Actinide Recycle (STAAR) has made notable progress in FY 2015 toward the overarching goal to develop more efficient separation methods for actinides in support of the United States Department of Energy (USDOE) objective of sustainable fuel cycles. Research in STAAR has been emphasizing the separation of americium and other minor actinides (MAs) to enable closed nuclear fuel recycle options, mainly within the paradigm of aqueous reprocessing of used oxide nuclear fuel dissolved in nitric acid. Its major scientific challenge concerns achieving selectivity for trivalent actinides vs lanthanides. Not only is this challenge yielding to research advances, but technology concepts such as ALSEP (Actinide Lanthanide Separation) are maturing toward demonstration readiness. Efforts are organized in five task areas: 1) combining bifunctional neutral extractants with an acidic extractant to form a single process solvent, developing a process flowsheet, and demonstrating it at bench scale; 2) oxidation of Am(III) to Am(VI) and subsequent separation with other multivalent actinides; 3) developing an effective soft-donor solvent system for An(III) selective extraction using mixed N,O-donor or all-N donor extractants such as triazinyl pyridine compounds; 4) testing of inorganic and hybrid-type ion exchange materials for MA separations; and 5) computer-aided molecular design to identify altogether new extractants and complexants and theory-based experimental data interpretation. Within these tasks, two strategies are employed, one involving oxidation of americium to its pentavalent or hexavalent state and one that seeks to selectively complex trivalent americium either in the aqueous phase or the solvent phase. Solvent extraction represents the primary separation method employed, though ion exchange and crystallization play an important role. Highlights of accomplishments include: Confirmation of the first-ever electrolytic oxidation of Am(III) in a noncomplexing aqueous solution and submission of this scientific breakthrough as a paper in Science; The first-ever co-crystallization of Am(VI) with UO₂(NO₃)₂ ∙ 6H₂O, opening the door to a new approach for separating hexavalent actinides as a group; Results showing that three potentially problematic metals will not present risk in ALSEP; Improvement in ALSEP contactor stripping kinetics to acceptable performance; A comparison of centrifugal contactors vs mixer-settlers showing the former performs better in ALSEP stripping; Synthesis of new mixed N,O-donor extractants with enhanced solubility and strength for selective trivalent actinide extraction; Development of computational methods showing promise in prediction of the selectivity of new extractants for trivalent actinides vs lanthanides; An order-of-magnitude improvement in aqueous Am/Eu complexation selectivity of an alternative macrocyclic stripping agent for ALSEP, potentially enabling an option for an Am product stream free from both Ln and Cm. An alternative aqueous combination of dipicolinate complexant and malonate buffer that may present options for ALSEP and TALSPEAK (Trivalent Actinide-Lanthanide Separations by Phosphorus-reagent Extraction from Aqueous Komplexes) type separations. The ALSEP concept is advancing toward a benchtop flowsheet demonstration planned for FY 2016, and a bench-scale test bed at Idaho National Laboratory (INL) will be employed to demonstrate at least one tandem Am oxidation and separation concept. This report outlines the goals of the STAAR, significance of achieving these goals, STAAR organization around the above aims and questions, recent highlights, and future directions. The report also includes a listing of publications, reports, patents, and dissertations.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Nuclear Energy (NE), Fuel Cycle Technologies (NE-5)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1263841
• Report Number(s): ORNL/TM-2015/586; AF5805010; NEAF315; TRN: US1601612
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
AMERICIUM
RARE EARTHS
SOLVENT EXTRACTION
PYRIDINES
MIXER-SETTLERS
OXIDATION
NUCLEAR FUELS
AQUEOUS SOLUTIONS
URANYL NITRATES
CRYSTALLIZATION
NITRIC ACID
ION EXCHANGE MATERIALS
SOLVENTS
COMPARATIVE EVALUATIONS
REPROCESSING
FUEL CYCLE
BUFFERS
AMERICIUM COMPLEXES
CALCULATION METHODS
FORECASTING
EXTRACTION APPARATUSES
KINETICS
PERFORMANCE
SYNTHESIS
TESTING