Abstract
Polonium is formed in relatively large quantities in lead-bismuth eutectic (LBE) cooled nuclear systems. Because of its radiotoxicity and volatility, a good understanding of the chemical equilibria governing polonium release from LBE is required. In this work, a set of thermochemical data is derived for the chemical species involved in the equilibrium between a solution of polonium in LBE and its vapor in inert conditions. The data were obtained by matching thermochemical models with experimental vapor pressure measurements and ab initio results. The dilute-limit activity coefficient of dissolved polonium in LBE is estimated, as well as the solubility of solid lead polonide in LBE. The results indicate that polonium evaporates from LBE according to the experimentally determined Henry’s law, up to dissolved polonium concentrations well above that expected in LBE cooled nuclear systems.
Highlights
IntroductionIn safety evaluations used for design and licensing of lead-bismuth eutectic (LBE) cooled nuclear systems, it is required to assess polonium release by evaporation from LBE in various reactor operation and accidental conditions
The presently derived set of thermochemical data for polonium species involved in the equilibrium between a solution of Po in lead-bismuth eutectic (LBE) and its vapor is consistent with primary experimental vapor pressure measurements, contrary to earlier evaluations
The dilutelimit activity coefficient of dissolved Po in LBE and the solubility of solid PbPo(s) in LBE indicates that polonium is fully dissolved in the coolant in operating LBE cooled reactors
Summary
In safety evaluations used for design and licensing of LBE cooled nuclear systems, it is required to assess polonium release by evaporation from LBE in various reactor operation and accidental conditions. We first revisit the vapor pressure of pure metallic polonium, and provide a set of thermodynamic data that is consistent with primary experimental measurements and recent ab initio data. Because of its potentially important role in chemical equilibria with polonium in LBE, the thermochemical properties of solid lead polonide are estimated. Based on this new information, the validity of Henry’s law for polonium in LBE is examined and its expected range of applicability determined
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