Speciation of polonium released from molten lead bismuth

Abstract The alpha-emitter 210 Po is an activation product of liquid lead-bismuth, a low melting eutectic under investigation as a coolant of the next generation fast nuclear reactors. Experiments were performed to measure the gaseous polonium chemical species for assessing the radioactivity release from a Pb-Bi bath upon contact with a gas stream. The vapor pressure of lead polonide was measured over the 400-550°C temperature range and found to be in agreement with an existing correlation derived from data at higher temperatures. Also, it was experimentally confirmed that the presence of steam in the gas stream above the Pb-Bi melt substantially increases the amount of polonium released due to the formation of the volatile compound H 2 Po. The free-energy variation of the H 2 Po formation reaction was determined, permitting the calculation of the Po gas phase speciation under the experimental conditions.