Empirical understanding of the dependency of hydrogen water chemistry effectiveness on BWR designs

Dependency of hydrogen water chemistry (HWC) effectiveness on plant specifi cations and operational conditions has been studied for an empirical interp retation. The HWC effectiveness was calculated exactly by employing a water radiolysis model requiring results of complex flow analysis and dose distr ibution analysis as input; in addition to the plant specifications. It was found that decrease of oxygen concentration in the reactor water in the rea ctor recirculation system could be taken as an exponential function of H-2 concentration added to the reactor water. Thus, the recombination factor rh o which was the coefficient of hydrogen concentration in the exponent could represent the recombination efficiency in the downcomer region. The rho co rresponded to the apparent reaction rate constant of the recombination reac tion of H2O2 with H-2, which included radical concentrations produced by ir radiation, multiplied by the residence time in the downcomer. The dose rate index gamma of each plant was introduced as a measure of downcomer dose ra te. Since the recombination efficiency was known to depend on the downcomer dose rate, functional dependence of rho on gamma was found to be linear. T he HWC effectiveness at the reactor pressure vessel bottom region could als o be evaluated using rho.