JRP 06-13
Partners
ContactDr. E. WielandPaul Scherrer Institut, Laboratory for Waste Management, CH-5232 Villigen PSI, Switzerland  +41 56 310 2291 
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Microscale Investigations of the Speciation and Mobility of Uranium in Cementitious MaterialsStatus
GoalsLong-term predictions of the retention of actinides, such as uranium, in the engineered barrier system are essential for the safety assessment of repositories for radioactive waste. In this project, the speciation of U(VI) in compact hydrating and fully hydrated cement will be investigated in connection with the retention and mobility of U(VI) in these systems. X-ray absorption spectroscopy (“bulk” XAS) and time-resolved laser fluorescence spectroscopy (TRLFS) measurements combined with wet chemistry experiments will be performed on uranium-doped powdered materials to determine the number of surface species and their structural arrangement in hydrated cement and cement minerals. Micro X-ray absorption spectroscopy (microXAS), micro X-ray fluorescence (microXRF) and micro X-ray diffraction (microXRD) measurements in combination with TRLFS/CLSM (confocal laser scanning microscopy) will be further applied to obtain spatially-resolved information on the distribution and speciation of U(VI) in compact cement samples. The link between U(VI) speciation and mobility in hydrated cement will be established based on in-diffusion studies. The diffusion profile in cement disks will be determined using micro laser ablation coupled with inductively coupled plasma mass spectrometry (microLIBS). The distribution of preferential sorption sites for U(VI) along diffusion paths and structural information on sorbed U(VI) will be investigated using microXRF/XAS. The overall goal of the project is to develop a novel approach to gain molecular-level information on the retention and mobility of U(VI) in compact cement matrices with the potential for future applications using other safety relevant actinides such as Np and Pu. Expected results
The proposed research aims at improving long-term predictions of the retention of actinides in the engineered barrier system in conjunction with performance assessment (PA) studies of repositories for radioactive waste. An improved mechanistic understanding of uptake processes is a first and important step towards future development of thermodynamically based retention models. The approach outlined above and developed in the frame of the project using uranium is of fundamental importance with a view to future studies under reducing conditions and using other safety relevant actinides such as Np and Pu. Reports |
