EXAFS/XANES studies of plutonium-loaded sodalite/glass waste forms

A sodalite/glass ceramic waste form is being developed to immobilize highly radioactive nuclear wastes in chloride form, as part of an electrochemical cleanup process. Two types of simulated waste forms were studied: where th e plutonium was alone in an LiCl/KCl matrix and where simulated fission-pro duct elements were added representative of the electrometallurgical treatme nt process used to recover uranium from spent nuclear fuel also containing plutonium and a variety of fission products. Extended X-ray absorption fine structure spectroscopy (EXAFS) and X-ray absorption near-edge spectroscopy (XANES) studies were performed to determine the location, oxidation state, and particle size of the plutonium within these waste form samples. Pluton ium was found to segregate as plutonium(IV) oxide with a crystallite size o f at least 4.8 mn in the non-fission-element case and 1.3 nm with fission e lements present. No plutonium was observed within the socialite in the wast e form made from the plutonium-loaded LiCl/KCl eutectic salt. Up to 35% of the plutonium in the waste form made from the plutonium-loaded simulated fi ssion-product salt may be segregated with a heavy-element nearest neighbor other than plutonium or occluded internally within the socialite lattice. ( C) 2001 Elsevier Science B.V. All rights reserved.