Browsing by Author "Massot, L"

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    Cyclic voltammetric experiment - simulation comparisons of the complex mechanism associated with electrochemical reduction of Zr4+ in LiCl-KCl eutectic molten salt
    (The Electrochemical Society, 2012-11-29) Fabian, CP; Luca, V; Le, TH; Bond, AM; Chamelot, P; Massot, L; Caravaca, C; Hanley, TL; Lumpkin, GR
    Nuclear energy increasingly represents an important option for generating largely clean CO2-free electricity and zirconium is a fission product that is expected to be present in irradiated fuels. The present investigation addresses the electrochemical reduction of Zr4+ to Zro in LiCl - KCl eutectic molten salt in the temperature range 425–550°C using cyclic voltammetry (CV), square-wave voltammetry (SWV) and bulk electrolysis. Simulations of the CV data indicate that the initial reduction proceeds through surface confined steps: Zr4+* + 2e− ↔ Zr2+* and Zr2+* + 2e− ↔ Zr* processes (* adsorbed species) followed by a peak-shaped complex diffusion controlled step that consists of a combination of closely spaced processes associated with the reactions Zr4+ + 4e− → Zro and Zr4+ + 3e− → Zr+*. Zr+*, probably in the form of ZrCl* is then further reduced to Zro* at even more negative potentials. The simulations provide the first quantitative analysis of the thermodynamics and kinetics of the Zr4+ reduction in the LiCl-KCl eutectic. © 2012, The Electrochemical Society.
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    Reaction mechanisms of La3+ and Zr4+ in LiCl-KCl eutectic molten salt - cyclic and square wave voltammetry data simulations
    (IOP Publishing, 2011-05-01) Fabian, CP; Chamelot, P; Massot, L; Caravaca, C; Luca, V; Lumpkin, GR
    Nuclear energy increasingly represents an important option for generating clean CO2-free electricity. This has generated a nuclear renaissance with increased interest in both innovative nuclear reactors and fuel cycle technologies. The innovative reactor concepts proposed have mainly involved closed fuel cycles with implied recycling of irradiated fuel. Pyroelectrochemical processes based on a molten alkali chloride/fluoride electrolyte system show considerable promise, and as such have received considerable attention for fuel reprocessing. Lanthanum and zirconium are two fission products that are expected to be present in irradiated fuels. The present investigation addresses the electrochemical reduction of La3+ and Zr4+ in LiCl - KCl eutectic molten salt using transient techniques such as cyclic voltammetry (CV), square wave voltammetry (SWV) and chronopotentiometry (CP) from 425 to 550° C, at two concentration levels. Experimental CV data from 50 to 500 mV/sec appears to indicate that the lanthanum reaction mechanism involve a single step reduction process, i.e., La3+ + 3e- ↔ La. Hence a theoretical simulation of this experimental data should be straightforward as verification of the reaction mechanism. However, zirconium experimental CV data also from 50 to 500 mV/sec appears to indicate that its reduction proceeds through an ab initio sluggish charge-transfer step coupled with an adsorption/underpotential deposition: Zr4+ + 2e- ↔ Zr2+ followed by a second and faster step where two electrons further are transferred: Zr2+ + 2e- ↔ Zr. A theoretical simulation of the experimental voltammograms has been also conducted to verify this reaction mechanism. We show the parameter Λ in their potential separation, ∆Epp and scan rate plot to indicate the reversibility of their electrochemical process, and evaluate their standard electrochemical rate constant. Deconvolution of the SWV data for lanthanum and zirconium confirms that the reduction of La3+ proceeds through three-electron one-step reaction mechanism while that of Zr4+ proceeds through two two-electron step reactions independent of temperature and concentrations levels. © 2011 The Electrochemical Society