2. Experiment

have a number of significant advantages compared to the existing hydrometallurgical technology, which include a drastic decrease of radioactive wastes, engineering support of nonproliferation principle of using the fissile materials, and lowering cost of SNF reprocessing. Development of nonaqueous SNF reprocessing technologies allows closing nuclear fuel cycle on the basis of the expanded construction of fast reactors with inherent safety. Currently, several variants of pyrochemical technologies are under study: electrochemical technology in molten salts, fluoride volatility process, extraction of technology in molten metals, and some others. The results obtained provide evidence for both the complexity of technological processes and equipment

Electrochemical reprocessing of SNF in chloride melts is one of the most developed and promising processes. It is going to be used in the experimental industrial complex of a fast neutron reactor with the solid fuel reprocessing. The major steps of the pyrochemical technology include electrorefining or reductive extraction in molten chloride/liquid metal systems for recovering actinides, including the minor actinides, from the spent metallic or nitride nuclear fuels and high-level radioactive wastes [3, 4]. Actinides recycling by separation and transmutation are considered worldwide as one of the most promising strategies for a more efficient use of the nuclear fuel as well as for nuclear waste minimization. The goal of one of the main strategies (partitioning and transmutation) is achieving the highest possible reduction of the nuclear waste radiotoxicity in the back end of the fuel cycle. High radiation resistance of molten chlorides and the absence of neutron moderators allow reprocessing spent nuclear fuels with high fissile materials content after a short cooling time. Selectivity of hightemperature separation process taking place at the molten salt-liquid metal interface depends on different characteristics of both phases. Knowing thermodynamics of the main fission products in working media is essential for determining applicability of a particular system for

In terms of the efficiency of separating lanthanide (Ln) and actinide (An) elements, the following sequence of the low-melting metals was proposed: Al > Ga > Sn > Bi > In > Zn > Cd [5]. Cadmium is currently considered as the low-melting metal electrode for separating actinides and fission products in the pyrochemical spent nuclear fuel reprocessing. This element has the advantages of compatibility with low-carbon steels and high vapor pressure at elevated temperatures, but it is not efficient in separating lanthanides and actinides. High melting point of aluminum (933.52 K) and low compatibility with the metallic construction materials limit its application in pyrochemical technologies utilizing chloride media. Gallium is next in the row and is considered as a prospective liquid metal electrode material. Ga, however, is a trace element and therefore is rather expensive for the industrial application. Alloys of gallium with other elements, for example, aluminum or indium, can be employed instead of pure Ga. Ga-In and Ga-Al alloys are very prospective for reprocessing

The goal of this work was to investigate the effect of Al and In concentration on the thermodynamic properties of La, Nd, and U in ternary Ga-In and Ga-Al-based alloys and the separa-

tion factor of Ln/Ac couple in a "molten salt-liquid metal" system.

and their potential possibilities [1, 2].

110 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

practical application [5].

SNF [6–11].

The experiments were carried out at 723–823 K with the step 20–25 K under dry argon atmosphere in a three-electrode silica cell. All operations were performed in a SPEKS GB 02 M glovebox (< 1 ppm oxygen and <1 ppm moisture content). The electrochemical measurements were performed employing an Autolab 302 N potentiostat-galvanostat controlled by NOVA 1.11 software. Salts and metal mixtures of the required compositions were prepared from the individual components, LiCl (Sigma-Aldrich, 99.99%), KCl (Reachim, 99.9%), LaCl3 (Sigma-Aldrich, 99.99%), PrCl3 (Sigma-Aldrich, 99.99%), NdCl3 (Sigma-Aldrich, 99.99%), Ga (GA-000, 99.99%), and In (IN-000, 99.98%). Ga-Al and Ga-In alloys of the specified composition were prepared from batches of the individual metals in the inert atmosphere in glovebox. The Ga-Al and Ga-In alloys prepared were metallic, silvery liquids free from any visible oxide films. Uranium (III) ions were introduced to electrolyte by electrolysis (anodic dissolution of U metal). The amount of lanthanum or uranium in the alloys was less than 0.40 wt.%. Liquid gallium-aluminum (gallium-indium) mixture was used as cathode and placed in a beryllium oxide crucible. The dilute solutions of prepared alloys were used directly in the experiments during the electromotive force (EMF) measurements vs. the Cl�/Cl2 reference electrode. The standard construction of it was described earlier in detail [12]. The following galvanic cell was used for measuring the electrode potentials of the alloys E∗∗ Me Ga ð Þ �In :

$$(-)\text{ Me(alloy)} \mid \text{3LiCl}-2\text{KCl}, \text{Me(III)} \parallel \text{3LiCl}-2\text{KCl} \mid \text{C}\_{\text{(s)}}, \text{Cl}\_{\text{2(g)}}\text{ (+)}\tag{1}$$

The experimental procedure was the following. After preparation of the ternary alloy of a required composition, the potential-time dependence was recorded using potentiometric method at zero current at different temperatures in the experiment. The potential value of the horizontal part of the curve corresponded to the equilibrium potential of the alloy.

The lanthanide (uranium) concentrations in the chloride salts were determined by taking samples from the melts that were then dissolved in nitric acid solutions. Ln (U)-containing alloys were washed with water and then dried by ethanol. All solutions were analyzed by ICP-MS.
