Thermodynamic assessment of solubility and activity of iron, chromium, and nickel in lead bismuth eutectic

Abstract

Lead–Bismuth Eutectic (LBE) is a heavy liquid alloy used as a coolant for the Lead-Cooled Fast Reactors and spallation target for Accelerator Driven Systems. LBE is also considered in sodium fast reactor designs as coolant in secondary circuit to avoid any occurrence of the reaction between sodium and water in steam generators. Even if this coolant presents many advantages due to its thermophysical properties, corrosion towards structural materials remains one of the major issues of LBE. Because corrosion in LBE is partly driven by dissolution processes, the solubility and chemical activity of the main elements of the alloy are the key parameters to model the related corrosion processes.Using the Calphad method and the Thermo-Calc software, a thermodynamic database was developed to assess the interaction between Cr–Ni–Fe alloys and LBE. The current thermodynamic data on the Cr–Fe–Ni+Bi–Pb quinary system was reviewed and the Bi–Cr and Cr–Pb binary phase diagrams were assessed. Fe, Cr and Ni solubilities (in at. fraction, T in K) at LBE composition were calculated:Fe solubility at LBE composition:log10(SFe)=0.5719-4398.6T(399–1173K)Cr solubility at LBE composition:log10(SCr)=-0.2757-3056.1T(399–1173K)Ni solubility at LBE composition:log10(SNi)=2.8717-2932.9T(528–742K)log10(SNi)=0.2871-1006.3T(742–1173K)Then, the thermodynamic assessment performed in this study was used to predict more accurately the Fe, Cr and Ni activities and solubilities in the case of four austenitic model alloys also studied in the framework of corrosion tests [1]. The calculated activities and solubilities provide thermodynamic data to better understand dissolution or precipitation phenomena observed during LBE corrosion processes.