Change in the Quantitative Composition of the NaCl–KCl–UO2Cl2–ZrCl4 Melt during Its Electrolysis

Abstract

The concentrations of ZrCl₄ and UCl₄ are studied as functions of the current density (0.08–0.63 A/cm²), the electrolysis time (1–24 h), and the initial ZrCl₄ content (0–12.3 wt %) in the (NaCl–KCl)_eq–UO₂Cl₂–ZrCl₄ melt during the formation of UO2–ZrO₂ cathode deposits. Uranium tetrachloride appears in this electrolyte due to the exchange reaction between ZrCl₄ and uranium dioxide, which forms on an electrode during the reduction of UO₂²⁺ ions. The quantitative difference between the changes in the molefraction concentrations of zirconium and uranium tetrachlorides in the salt phase is determined. This difference increases when the electrolysis time or the initial ZrCl₄ content in the electrolyte increases and the current density decreases. The mole-fraction concentration of ZrCl₄ changes more strongly than that of UCl₄. This difference is shown to be caused by the higher volatility of ZrCl₄ from the salt melt as compared to UCl₄.