Equilibrium Evaporation Behavior of Polonium and Its Homologue Tellurium in Liquid Lead-Bismuth Eutectic

Experimental study using the transpiration method investigates equilibrium evaporation behavior of radionuclide polonium ( 210 Po) generated and accumulated in liquid lead-bismuth eutectic (LBE) cooled nuclear systems. The experiment consists of two series of tests: preliminary evaporation tests for homologue element tellurium (Te) in LBE, and evaporation tests for 210 Po-accumulated LBE in which test specimens are prepared by neutron irradiation. The evaporation tests of Te in LBE provide the suggestion that Te exists in a chemical form of PbTe as well as the information for confirming the validity of technique and conditions of Po test. From the evaporation tests of 210 Po in LBE, we obtain fundamental data and empirical equations such as 210 Po vapor concentration in the gas phase, 210 Po partial vapor pressure, thermodynamic activity coefficients, and gas-liquid equilibrium partition coefficients of 210 Po in LBE in the temperature range from 450 to 750°C. Additionally, radioactivity concentration of 210 Po and 210m Bi vapor in a cover gas region of a typical LBE-cooled nuclear system is specifically estimated based on the obtained experimental results, and the importance of 210 Po evaporation behavior is quantitatively demonstrated.