Assessment of the ATHENA code for calculating the void fraction of a lead-bismuth/steam mixture in vertical upflow

Lead-bismuth is currently being considered as a coolant for fast reactors d esigned to produce low-cost electricity as well as burn actinides. Lead-bis muth fluid properties have been added to the ATHENA code so that it can be used in the thermal-hydraulic analysis of lead-bismuth-cooled reactors. The capability of ATHENA to calculate the void fraction of a two-component, tw o-phase mixture of liquid lead-bismuth and steam in cocurrent upflow was as sessed using the El-Boher and Lesin void correlation. The assessment showed that the drift flux correlations currently available in the code predicted trends that were in reasonable agreement with the El-Boher and Lesin void correlation, bur the predicted void fractions were significantly too high. For example, the Kataoka-Ishii correlation, which was the best of the avail able correlations, predicted void fractions that were up To 30% greater tha n the values from the El-Boher and Lesin correlation. Consequently the El-B oher and Lesin correlation was implemented in a modified version of ATHENA. The implementation was complicated by the fact that the El-Boher and Lesin correlation was an explicit correlation for void fraction rather than a dr ift flux correlation. An approach was developed so that the code's basic dr ift flux formulation could be used to easily implement an explicit void cor relation. The predictions of the modified code were in excellent agreement with the El-Boher and Lesin void correlation.