In situ studies shed light on key nuclear waste processing pathway

Nuclear energy for electricity generation offers large-scale low-carbon energy production but suffers with challenges such as the handling of radioactive waste materials. Therefore, the proper management of spent fuel arising from nuclear power production is a key issue for the sustainable development of nuclear energy 

Various advanced processes for used fuel reprocessing have been established over the last decade or two. Of these, aqueous separations processes using solvent extraction technology remain the leading option. The PUREX process is a chemical method used to purify fuel for nuclear reactors or nuclear weapons. It is an acronym standing for Plutonium Uranium Redox EXtraction. PUREX is the de facto standard aqueous nuclear reprocessing method for the recovery of uranium and plutonium from used ("spent", or "depleted") nuclear fuel. Additionally, much effort has been placed on methods to recover the minor actinides for conversion into another form and to create alternative aqueous processes to replace PUREX; for example, the “GANEX” (Grouped Actinide Extraction) process which aims to co-recover all actinides in a single process.

(a) Electrochemical cell used for experimentation on I12 at Diamond Light Source. The cell is constructed from aluminium and incorporates a “well” at the bottom of the cell. The working electrode is positioned inside the well to ensure low attenuation of the X-ray beam. Figure (b) shows the experimental setup at the I12 JEEP beamline. Only X-rays (green) which are diffracted at 4.5° are detected by the individual elements on the EDXD detector (black circles) (© Journal of Nuclear Materials)

An aluminium electrochemical cell was used to house the molten salt, and electrodes were custom built for this investigation. The electrochemical and EDXD measurements were taken at 450 °C and the results confirm that the electrochemical reduction of uranium dioxide to uranium metal seems to occur in a single, 4-electron-step, process. The rate of formation of α-uranium is seen to decrease during electrolysis and could be a result of a build-up of oxygen anions in the molten salt. Slow transport of O₂₋ ions away from the UO₂ working electrode could impede the electrochemical reduction.

Further exploration of the microstructure of working electrodes will therefore be the focus of future work. 

Read the full paper here.... 

Following the electroreduction of uranium dioxide to uranium in LiCl–KCl eutectic in situ using synchrotron radiation L.D. Brown, R. Abdulaziz, R. Jervis, V.J. Bharath, R.C. Atwood, C. Reinhard, L.D. Connor, S.J.R. Simons, D. Inman, D.J.L. Brett, P.R. Shearing. Journal of Nuclear Materials Volume 464, September 2015, Pages 256–262. http://dx.doi.org/10.1016/j.jnucmat.2015.04.037