Lead-bismuth is currently being considered as a coolant for fast reactors designed to produce low-cost electricity as well as burn actinides. Lead-bismuth 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, two-phase mixture of liquid lead-bismuth and steam in cocurrent upflow was assessed 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, but the predicted void fractions were significantly too high. For example, the Kataoka-Ishii correlation, which was the best of the available correlations, predicted void fractions that were up to 30% greater than the values from the El-Boher and Lesin correlation. Consequently, the El-Boher 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 drift flux correlation. An approach was developed so that the code's basic drift flux formulation could be used to easily implement an explicit void correlation. The predictions of the modified code were in excellent agreement with the El-Boher and Lesin void correlation.