Sigma Team for Minor Actinide Separations FY2014 Accomplishments and Directions

Abstract

Significant progress including several "firsts" has been made in FY 2014 within the Sigma Team for Minor Actinide Separation (STMAS). The overarching goal of STMAS is to develop more efficient separation methods for 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. Research efforts aim in particular for a robust, more efficient separation of MAs from lanthanides, preferably as a single process. Two strategies are employed, one involving oxidation of americium to its pentavalent or hexavalent state and one that seeks to selectively complex trivalent americium. Highlighted accomplishments include: • A bench test demonstrating the first tandem oxidation of Am(III) to Am(VI) using sodium bismuthate and subsequent solvent extraction; • A breakthrough on chemical oxidation of Am(III) to Am(VI) using ozone and Ag(I) catalyst; • The first electrolytic oxidation of Am(III) in a noncomplexing aqueous solution; • A proof-of-concept test of Am(III) separation by solvent extraction using ALSEP (Actinide Lanthanide Separation); • The first test of ALSEP in centrifugal contactors; • An unprecedented ion-size based discrimination of trivalent f-elements; • New fundamental insights into TALSPEAK-like actinide separation from lanthanides; • A new design for a mixed-donor extractant for Am(III) with 108 higher extraction power; • A promising solvent system employing a bistriazinylpyridine type extractant for MAs; • Progress in developing dithiophosphinic acid extractants for highly selective MA extraction. Such accomplishments are made possible by integrated hypothesis-driven scientific research. Technology concepts emerging therefrom are being matured for potential laboratory-scale demonstrations. For example, the ALSEP concept is advancing toward a benchtop flowsheet demonstration likely in FY 2016, and a bench-scale test bed has been set up at INL for demonstrating tandem Am oxidation and separation concepts. This report outlines the goals of the STMAS, significance of achieving these goals, STMAS organization around the above aims and questions, recent highlights, and future direction.