Thermodynamic Properties of U, Np, Pu, and Am in Molten LiCl‐KCl Eutectic and Liquid Cadmium

Abstract

Thermodynamic property measurements for actinides in the LiCl‐KCl/Cd system have been obtained as part of the development of an electrochemical pyropartitioning process to remove actinides from PUREX waste residues. Electrochemical potential measurements and distribution ratios were employed to obtain standard Gibbs free energies of formation for actinide chlorides in LiCl‐KCl, activity coefficients of reduced actinides in Cd, and distribution coefficients for actinides in the LiCl‐KCl/Cd system relative to neodymium. The temperature‐dependent free energies of formation for U, Np, and Pu were normalΔGnormalUCl3normalo=−844.2+0.1681T false(normalkJ/normalmolfalse),normalΔGnormalNpCl3normalo=−902.9+0.1688T false(normalkJ/normalmolfalse) , and normalΔGnormalPuCl3normalo=−960.6+0.2039T false(normalkJ/normalmolfalse) when T is in K. The Gibbs free energy of formation for AmCl2 was −548.7 kJ/mol at 450°C. The activity coefficients for U and Pu in LiCl‐KCl ranged from 1 to 4×10−3 . Activity coefficients in Cd at 450°C were 15, 2.8×10−3,3.1×10−5 , and 1.1×10−4 for U, Np, Pu, and Am, respectively. The distribution coefficients between the salt and metal phases relative to Nd were 0.022, 0.056, 0.040, and 0.024 to 0.067 for U, Np, Pu, and Am in the LiCl‐KCl/Cd system at 450°C.

Method Development for Quantitative Analysis of Actinides in Molten Salts

“…Several studies used wires encased in alumina or other insulating material tubes with a known apparent surface area. 3,16,29,31,34,59 This method, however, has been shown to be ineffective in practice because the encasing material when covered in the salt becomes conductive and contributes to an error in the measurements. It is impractical to use an insulator material in the systems because undesired chemical reactions between metals and insulator material could interfere with the measurements.…”

“…The goal of the process is to maximize the separation and recovery of actinides from chlorinated fission products so that minimal amounts of actinides are lost to the process waste stream. [1][2][3][4][5] In addition to efficient actinide recovery, there is a need to address the safeguarding the recycle system. 5 Highprecision, real-time concentration measurements of actinides, present as actinide chlorides, in molten salts are required for process monitoring and control and could be used to support traditional material control and accountability techniques.…”

Analyses of Anodic Behavior of Metallic Fast Reactor Fuel Using a Multidiffusion Layer Model

“…32) These values versus the Ag/AgCl reference electrode were simply used in the following calculations. Although the standard potential for Zr(IV)/Zr(0) at 773 has not been reported, it was evaluated from the results of the emf measurements at 723 and 823 K. To discuss the anode potential during the electrorefining tests quantitatively, the iR drop of the potential due to the cell resistance should be taken into account.…”

Electrochemistry of Tm(III) and Yb(III) in Molten Salts

“…Special attention is devoted to rare earth elements (REE) mainly due to its neutronic poison effect and the high content into the spend fuel. In addition, REE have similar chemical properties [Bermejo et al, 2006[Bermejo et al, , 2007[Bermejo et al, , 2008a[Bermejo et al, , 2008bCastrillejo et al, 2005aCastrillejo et al, , 2005bCastrillejo et al, , 2005cCastrillejo et al, , 2009De Cordoba et al, 2004Kuznetsov et al, 2006;Smolenski et al, 2008aSmolenski et al, , 2008b] to those of actinides [Fusselman et al, 1999;Morss, 2008;Osipenko et al, 2010Osipenko et al, , 2011Roy et al, 1996;Sakamura et al, 1998;Serp et al, 2004Serp et al, , 2005aSerp et al, , 2005bSerp et al, , 2006Serrano & Taxil, 1999;Shirai et al, 2000] hence separation between these groups of elements is very difficult. For this reason, a good knowledge of the basic properties of REE in the proposed separation media is very important.…”