NRC-8, EuCheMS International Conference on Nuclear and Radiochemistry

ORAL PRESENTATION - Application of microbeam synchrotron techniques to determine the distribution and speciation of plutonium after uptake by Opalinus Clay

21 Sept 2012, 13:25

15m

Como, Italy

Oral Communications Radioactive elements in the environment, radiation archeometry and Health Physics Session 13 (cn't of Session 12) - Radioactive elements in the environment, radiation archeometry and Health Physics

Speaker

Dr Samer Amayri (Johannes Gutenberg-Universität Mainz, Institute of Nuclear Chemistry, 55099 Mainz, Germany)

Description

The synchrotron radiation based techniques X-ray fluorescence (XRF) and X-ray absorption spectroscopy (XANES: X-ray absorption near edge structure) have been used to determine the distribution and the chemical speciation of plutonium (Pu) after sorption and diffusion in Opalinus Clay (OPA, Mont Terri, Switzerland). Thin sections of OPA were contacted with 20 µM Pu(VI)-242 in OPA pore water (pH 7.6, I=0.4 M) under aerobic conditions for at least 3 days. For comparison, a OPA bore core in a diffusion cell was contacted with 20 µM Pu(VI)-242 under the same conditions for 4 weeks. The sorption and diffusion samples were investigated at the MicroXAS beamline at the Swiss Light Source, Paul Scherrer Institut, Switzerland. µ-XRF mapping has been used to determine the elemental distribution of Pu and other elements contained in OPA, e.g., Fe and Ca. Regions of high Pu concentrations were subsequently investigated by µ-XANES to identify the oxidation state of sorbed Pu on the surface of OPA. Further, µ-XRD (X-ray diffraction) was employed to gain knowledge about reactive crystalline mineral phases in the vicinity of Pu enrichments. The results of Pu L3-edge µ-XANES spectra on Pu hot spots showed that Pu(IV) is the dominating species on OPA, i.e., the highly soluble Pu(VI) was retained by OPA in the reduced and less mobile tetravalent oxidation state of Pu. µ-XRD results indicated that Pu is localized on or in the close vicinity of the Fe(II)-bearing mineral siderite and the clay mineral illite. Siderite is one of the redox-active mineral phases of OPA, which determines the speciation on Pu after uptake on OPA.