The electrochemical cell (Figure 1) was developed by a CEA group from Saclay following collaboration initiated with the SUBATECH laboratory in Nantes. The original design of this cell allows for electrochemical measurements that can be followed by X-ray absorption spectroscopy using very small solution volumes (1.5 mL maximum). The cell consisted of an inner chamber containing the solution of interest and external housing providing double containment for the study of radioactive solutions. Before use, drop tests and tests for watertightness were carried out to obtain approval by the nuclear safety authorities.
Figure 1 : Experimental set-up on the MARS beamline. Insert: inner chamber containing the solution.
For the first time on the MARS1 beamline, the reduction of a solution containing a radionuclide could be followed by X-ray absorption spectroscopy (Figure 2). We have demonstrated the formation of an uranium (IV) complex with para-coumaric acid, thus preventing the formation of uranium dioxide UO2 (s). Adjustment of the EXAFS spectrum showed, on the one hand, the monovalent coordination mode of the carboxyl groups and, on the other, that 70% of the initial uranyl had been reduced.
Figure 2 : Reduction of a solution of uranyl (VI) in the presence of para-coumaric acid, followed by X-ray absorption spectroscopy. Evolution of the XANES and EXAFS signals as a function of reaction time.
This experiment is the first in a series intended to acquire basic data on the chemistry of actinides. This study will continue with measurements on neptunium and plutonium.
1 B. Sitaud et al., J. Nucl. Mater. (2011), doi:10.1016/j.jnucmat.2011.08.017
