[en] RELAP4/MOD6 is the most recent in a series of computer programs developed to describe the thermal-hydraulic conditions attendant to postulated transients in light water reactor systems. Significant new model additions include best estimate PWR reflood transient analytical models for core heat transfer, local entrainment and core vapor superheat and a new set of heat transfer correlations for PWR blowdown and reflood. These new models were used for a test prediction of the KWU three-loop PRIMAR KREISLAUF (PKL) reflood test K 5A. A brief description of the new features in RELAP4/MOD6 and comparisons of calculated test results with experimental data are presented