JRP CALL information
Supported By

European Commission

Short description of the work
There is a general consensus that high level radioactive waste (HLW) will be disposed in deep geological formations. In clay repositories, due to the low water content, the movement of the radionuclides is driven by diffusive processes, but sorption and precipitation of newly formed phases are the key limiting processes in case of cations. Boda Claystone Formation (BCF) was selected in Hungary as potential host rock of a HLW repository. Previous combined micro-XRF measurements using 5 µm spatial resolution, on microscopically heterogeneous clay-rich rock samples originating from BCF revealed that not only the argillaceous matrix is responsible for uranium uptake, but 5-10 µm thick U-rich fringes were observed around carbonate fillings. Experiments at SLS included micro-XRF/XRD mapping at 1-2 µm resolution and U-L3 micro-XANES measurements at selected positions of thin sections treated with U(VI) solution. High-resolution micro-XRF/XRD results clearly showed that the fracture infilling region of the BCF samples contained zoned dolomite rombohedra with outer Mn-rich areas. These rhombohedra were covered with ankerite rims that showed coincidence with U enrichment. U uptake induced by ankerite would require formation of FeOOH via Fe oxidation and U reduction, however significant reduction of U could not be proved from the micro-XANES results. The investigations provided essential information to clarify the uranium uptake processes at different mineral phases in argillaceous rocks of BCF on the microscale.

Main visitor contact data
Name: Dr Janos Osan
Organisation: HAS Centre for Energy Research

JRP Identification
JRP nr: TALI-C04-12
JRP title: Micro-XAS investigation of the mechanism of uranium and thorium uptake by argillaceous rocks
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: Laboratory for Waste Management, Paul Scherrer Institute (Dr Rainer Dähn)
Other APF involved in the project:

Description of the work done at the associated pooled facility
Start date of the stay: 2/18/2015
End date of the stay: 2/24/2015
Quantity of access: 5
Access Unit: Days
Misc.: Work during week-ends

Other APF visitors of the JRP during the stay
Visitor 2: Dr Rainer Dähn (Laboratory for Waste Management, PSI)
Visitor 3: Felician Gergely (HAS Centre for Energy Research)
Visitor 4: Annamaria Keri (Laboratory for Waste Management, PSI)
Visitor 5: