Experimental study of air-water two-phase flow in an 8 × 8 rod bundle under pool condition for one-dimensional drift-flux analysis

► Adiabatic two-phase flow experiments in an 8 × 8 rod bundle were performed under pool conditions. ► An extensive database of adiabatic/boiling two-phase flows in pool rod bundle systems was collected. ► Effect of large casing on two-phase flow structure was observed in experimental data for medium 〈jg+〉 conditions. ► Existing rod bundle models were benchmarked with the present database. ► All of the void fraction prediction errors of each model are tabulated.