Dependencies of radiolytic aspects on geometric and operational conditions of boiling water reactor (BWR) primary systems were studied for normal operation or for hydrogen alternate water chemistry (HAWC) by using a computer simulation code AQUARY. Statistical regression analyses were applied to those calculated results and a great many close correlations were found among radiolytic concentrations. In the course of the study, it was discovered that residence time and energy deposition rate in the downcomer had a critical effect on HAWC. A set of simple estimation formulas for radiolytic conditions was proposed for normal BWR operation, and the following prediction formulas were proposed for the oxygen gas release rate and oxygen concentration in the recirculation line under HAWC: .