JRP CALL information
Supported By

European Commission

Short description of the work
Speciation of neptunium along diffusion pathways in Opalinus Clay using μ‐XAFS and μ‐XRF

Samer Amayri1, Jonathan Rosemann1, Jakob Drebert1, Ugras Kaplan1,3, Daniel Grolimund 2, Tobias Reich1

1 Institute of Nuclear Chemistry, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany
2 Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
3 Present address: Institute of Nuclear Waste Management, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany

Neptunium, together with other actinides, plays an important role in the disposal of nuclear waste because of its long half-life (2.14×106 a) and high radiotoxicity. Argillaceous rocks are under consideration as potential host rock formation for the construction of high-level nuclear waste repositories in several European countries. For the safety assessment, it is of fundamental relevance to study the interaction of Np with clays on a molecular scale. Therefore, a combination of spatially-resolved synchrotron based techniques, i.e., micro X-ray fluorescence (µ-XRF) and micro X-ray absorption near edge structure (µ XANES) were used at the MicroXAS Beamline at the Swiss Light Source (Paul Scherrer Institut, Villigen, Switzerland) to study the distribution and speciation of Np(V) on Opalinus Clay (OPA, Mont Terri, Switzerland) after diffusion processes. Using the advantage of a microfocus beam for X-ray spectroscopy, it was possible to determine the Np speciation along its diffusion pathway, despite the diluted concentrations. µ-XRF maps showed the distribution of Np and other elements contained in OPA (i.e., Ca, Fe). Np LIII-edge µ-XANES spectra on several Np hot spots showed that Np(IV) is the dominating species on OPA after the diffusion process. Highly soluble Np(V) is reduced progressively along its diffusion path and in progress of time to the less mobile Np(IV), which is a positive result for the safety assessment of radioactive waste disposal in argillaceous host rocks. Furthermore, the combination of spatially-resolved X-ray microprobe methods is a powerful tool to determine the transport pattern of actinides in heterogeneous natural systems.

Main visitor contact data
Name: Dr Samer Amayri
Organisation: Institute of Nuclear Chemistry, Johannes Gutenberg-Universität Mainz

 

JRP Identification
JRP nr: TALI-C01-15
JRP title: Speciation of neptunium along diffusion pathways in Opalinus Clay using μ‐XAFS and μ‐XRF
JRP scope: Scope 2: Actinide in the geological environment

Visited Associated Pooled Facility
Visited APF during the stay: PSI - MicroXAS Beamline
Name of the APF Contact Person: Dr Daniel Grolimund

Other APF and organisation involved in the JRP
Other organisations involved:
Other APF involved in the project: PSI - MicroXAS Beamline

Description of the work done at the associated pooled facility
Start date of the stay: 10/9/2013
End date of the stay: 10/12/2013
Quantity of access: 12
Access Unit: Shifts
Misc.: Work during week-ends

Other APF visitors of the JRP during the stay
Visitor 2: Prof. Tobias Reich (Gutenberg-Universität Mainz)
Visitor 3: Prashanta Jonathan Benjamin Rosemann (Gutenberg-Universität Mainz)
Visitor 4: Dr Ugras Kaplan (Gutenberg-Universität Mainz)
Visitor 5: Jakob Drebert (Gutenberg-Universität Mainz)