Maxim Erzhenkov

The electrochemical behavior of Sc(III) ions in (LiCl–KCl) _eut –ScCl ₃ (up to 2.75 mol%) melts was studied using cyclic voltammetry and chronopotentiometry at 773–873 K. It was established that the electroreduction of Sc(III) to Sc is a reversible process in the melts containing up to 0.7 mol% ScCl ₃ . The presence of nucleation/growth processes was confirmed by Sc electrodeposition on a Mo substrate. The Sc(III) diffusion coefficients were determined using a new approach considering diffusion-controlled growth of nuclei. These values (from (1.3±0.1)×10 ⁻⁵ cm ² s ⁻¹ at 773 K to (2.3±0.1)×10 ⁻⁵ cm ² s ⁻¹ at 873 K) are approximately 10% higher and 30% lower than those calculated using the Berzins-Delahay and Sand equations, respectively. The concentration dependences of the limiting diffusion current density and the Sc(III)/Sc equilibrium potential were determined. The values of the Sc(III)/Sc apparent standard potential and the Sc(III) activity coefficient were found. The prospects for using scandium as a plutonium imitator during the development of spent nuclear fuel electrorefining modes were assessed. It was showed that the equilibrium and apparent standard potentials of Sc(III)/Sc and Pu(III)/Pu at 773 K and other equal conditions coincide, while the activity coefficients of Sc(III) are 3–4 orders of magnitude lower than those of Pu(III).

Composites of (1-x)Gd₂Zr₂O₇·xMgO were prepared by mixing gadolinium zirconate with freshly precipitated Mg(OH)₂ followed by heat treatment at 1500 °C. Small concentrations of magnesium oxide dissolved in the complex oxide matrix of Gd₂Zr₂O₇. This led to decrease in the lattice parameters of the matrix phase and a complex redistribution of Gd and Zr over the A and B sublattices. According to the impedance spectroscopy results of the studied samples, for (1-x)Gd₂Zr₂O₇·xMgO (x = 0.05, 0.07, 0.10), the ionic conductivity was slightly higher than that for the undoped Gd₂Zr₂O₇. The share of dominant ion transport did not change upon doping with magnesium oxide. The composites showed chemical resistance in a lithium halide (LiCl) melt and interacted with LiCl-xLi₂O (x = 2 wt.%, 4 wt.%) melts at 650 °C with the formation of a Gd₂O₃ phase or a mixture of phases (Gd₂O₃, Li₂ZrO₃, ZrO₂, LiGdO₂, or LiGdCl₂) on the ceramic surface, respectively.

Molten fluorides of alkali metals are considered a technological medium for molten salt reactors (MSRs). However, these media are known to be extremely corrosive. The successful implementation of high-temperature technological devices using molten alkali metal fluorides requires the selection of such structural materials that have high corrosion resistance in melts with compositional characteristic of MSRs. In this research, the corrosion behavior of 12Cr18Ni10Ti steel, the alloy Ni60Cr20Mo15, and the alloy Monel 404 (Ni50Cu50) was investigated in the LiF–NaF–KF eutectic melt, containing additions of CeF₃ and NdF₃ from 0 to 5 wt.% as imitator fluorides of actinides in an inert argon atmosphere at 550 °C for 100 h. Gravimetry, energy-dispersive X-ray (EDX) microanalysis of surfaces and cross-section of samples, and ICP-MS were used to establish the corrosion behavior of the investigated alloys. Corrosion resistance of the studied materials was found to decrease in a row from Monel 404 > Hastelloy C2000 > 12Cr18Ni10Ti. The addition of cerium fluoride into the melt resulted in the additional etching of the alloy surface. The addition of neodymium fluoride resulted in the formation of the point/inter-crystalline corrosion damages in the sample bulk. The samples of steel 12Cr18Ni10Ti were subjected to local cracking corrosion. The austenitic nickel-based alloys suffered specific local corrosion with formation of subsurface voids. Excellent corrosion resistance of the Monel alloy under the test conditions was found.