B. Prabhakara Reddy

Enthalpies of formation of CeNi2 and CeNi5 by calorimetry

Abstract The enthalpies of formation of the intermetallic compounds, CeNi2 and CeNi5 at 298.15 K have been determined by high temperature solution calorimetry. The thermal effects of dissolution of nickel, cerium and the intermetallic compounds in liquid aluminum at 1095.15 K were determined as a function of concentration of the solutes from which the respective thermal effects of dissolution at infinite dilution were derived. The enthalpies of formation of the compounds at 298.15 K were computed from these values of thermal effects of dissolution at infinite dilution. The enthalpies of formation of CeNi2 and CeNi5, at 298.15 K thus obtained are −115.8 ± 7.3 and −201.9 ± 11.9 kJ mol−1, respectively. The present enthalpy of formation of CeNi5 is compared with the earlier literature values. In the case of CeNi2 the study provides the only experimental data for the enthalpy of formation.

PRAGAMAN: A Computer Code for Simulation of Electrotransport During Molten Salt Electrorefining

Abstract The computer code PRAGAMAN has been developed for numerical simulation of electrotransport during molten salt electrorefining of spent metallic fuels. The code is based on the thermodynamic equilibriums among pairs of elements and their chlorides that exist at the anode-electrolyte salt and cathode-electrolyte salt interfaces. It uses nonlinear and linear equations to arrive at real solutions for all 16 possible conditions that could be envisaged with respect to the solubilities of U and Pu at the anode and cathode. It can handle the electrotransport of eight elements representing typical actinides, minor actinides, and fission products, as well as potential dependent electrotransport of U and Pu.

Current status of pyrochemical reprocessing research in India

Abstract Reducing the cooling time of spent fast breeder reactor (FBR) fuel, thus reducing the doubling time and introducing metallic fuels into FBRs, is essential for meeting the increasing energy demand of India. Development of pyrochemical reprocessing technology for processing the spent FBR fuels is another prerequisite. Accordingly, studies on the molten salt electrorefining process for metallic fuels and the oxide electrowinning process for oxide fuels have been carried out at the Indira Gandhi Centre for Atomic Research, Kalpakkam. A laboratory-scale argon atmosphere facility for molten salt electrorefining process studies is operational. Using this facility, studies on all the unit operations of the process have been carried out on uranium alloys. A code, PRAGAMAN, based on thermochemical modeling has been developed to simulate the electrotransport behavior of elements during the electrorefining process. Based on our studies, the eutectic MgCl2-NaCl-KCl ternary salt has been proposed as the alternate electrolyte for the conventional 2CsCl-NaCl electrolyte for oxide processing. A facility to demonstrate the remotization of all the process steps of the molten salt electrorefining process flow sheet for metallic fuels at 1- to 3-kg scale is being set up. Basic electrochemical studies on the reduction behavior of the chlorides and oxychlorides of uranium and the lanthanides in molten salts have also been carried out. This paper describes the studies carried out so far and the plans for the near future.

Enthalpies of formation of UGa2 and UGa3 by calorimetry

Abstract Enthalpies of formation of the intermetallic compounds, UGa 2 and UGa 3 , at 298.15 K were determined by using high-temperature liquid gallium solution calorimetric measurements at 1427 K to be −40.4±6.0 and −38.3±4.4 kJ gatom −1 , respectively. The enthalpies of formation of UGa 2 at 1563 K and UGa 3 at 1038 K were determined to be −79.1±2.5 and −40.6±1.5 kJ gatom −1 by using the precipitation calorimetric method. The enthalpies of formation of UGa 3 at 298.15 and at 1038 K are found to be in agreement with each other, whereas that of UGa 2 at 1563 K is highly exothermic compared to that at 298.15 K.

Modeling the Molten Salt Electrorefining Process for Spent Metal Fuel Using COMSOL

Molten salt electrorefining process is one of the key steps of the pyrochemical reprocessing flow sheet for the spent metallic fuel from fast reactors. The electrorefining process is simulated using COMSOL Multiphysics. This involves solving multiple equations corresponding to electrochemical reactions at the electrode surfaces, mass transfer of metal ions in the electrolyte, potential distribution in the electrolyte, and overall material balance of metal ions in a coupled manner. The model is validated using the data of laboratory scale electrorefining experiments from literature. The results show a good agreement with the present experimental data, the variation being less than 10% for the U and Pu concentration changes in liquid Cd anode and molten salt, and U deposit on solid cathode.

Modeling the Anodic Behavior of U, Zr, and U-Zr Alloy in Molten LiCl-KCl Eutectic

Abstract The DIFfusion of Actinides in EleCtrorefiner (DIFAC) computer code has been developed and is used to calculate the variation of the anode potential with time during constant current anodic dissolution of U, Zr, and U-Zr alloy in molten LiCl-KCl eutectic. A few algorithms are proposed within the framework of the DIFAC code for modeling the activation and concentration overpotentials during anodic dissolution. These algorithms are based on an iterative search procedure and would later be applied to modeling the electrorefining of a multicomponent metallic fuel system.

Evaluation of nanocrystalline hafnium nitride coating exposed to molten uranium

ABSTRACT Transition metal nitride films have a unique combination of properties and finds application as protective coatings. The present paper deals with the degradation behaviour of HfN coating deposited by reactive magnetron sputtering on high-density (HD) graphite and niobium (Nb) crucibles with molten uranium. Uranium melting experiments were carried out with uranium shots placed in HfN-coated crucibles and heated to 1573 K under ultra high purity argon gas for 25 min. The study showed delamination of HfN coating deposited on Nb and HD graphite crucibles. The degradation of HfN-coated niobium was attributed to partial melting and surface oxidation. Uranium melting of HfN-coated HD graphite crucible led to coating spallation that could be attributed to thermal expansion mismatch and also resulted in the formation of uranium–carbon mixture of unusual morphology. The paper highlights the results of the present investigation.

Experimental studies and model validation for the optimization of electrodes configuration in a molten salt electrorefiner

ABSTRACT Molten salt electrorefining is a high-temperature electrochemical process for treating the spent metallic fuel from fast reactors and is aimed at the separation of U and Pu from fission products. Potential and current distribution analysis was carried out by experimental studies as well as modelling using COMSOL Multiphysics for various electrode configurations. A 2D/2D axisymmetric geometry model was used to evaluate the potential and current distributions. The effect of the following parameters was evaluated: (1) configuration having two pairs of electrodes in parallel/staggered arrangement; (2) centre-to-centre distance between the electrodes; (3) solid cathode with and without insulation at the bottom; (4) Cd cathode and (5) cathode surface area. The resistance of the electrorefiner was calculated using COMSOL model for various electrode configurations and compared with that obtained experimentally. There was very good agreement between the experimental values and the simulation results. The computed cell resistance was also validated with published data. A sensitivity analysis was also performed to determine the parameter that more significantly influences the cell resistance. The two parameters that were varied were the electrolyte conductivity and the cell voltage. It is observed that of the two parameters the cell resistance is most sensitive to the electrolyte conductivity and there is no change in cell resistance with cell voltage.

Ultrasonic based instrumentation for measuring hygroscopic, high temperature molten salt level in an electrorefiner inside inert atmosphere glove boxes

Molten salt level measurement in the process vessels of pyrochemical reprocessing of spent metallic fuels is one of the key process parameters. Level measurement of hygroscopic and high temperature salts is a challenging task. It is proposed to use an ultrasonic based level measurement. The Commercially available ultra sonic level indicators have the limitations such as their physical dimensions, working environment, and adaptability for inert atmosphere glove boxes. Customization of molten salt level measurement technique using ultrasonic sensors in inert atmosphere glove boxes has been developed. The working principle, design concept, fabrication techniques and results have been discussed in this paper.

Preparation of (U0.55Th0.45)O2 Microspheres by Sol-Gel Process

An internal gelation process has been developed for preparing high density (U0.55Th0.45)O2 microspheres. Parameters such as concentration of gelation agents, total metal concentration etc were standardized to obtain crack free sintered microspheres of 96% theoretical density (TD). The SEM studies of the sintered spheres indicated uniform microstructure with 10-20 μm grain size. SEM-EDAX study indicated uniform distribution of uranium and thorium within the microspheres.