Empirical Understanding of the Dependency of Hydrogen Water Chemistry Effectiveness on BWR Designs

Dependency of hydrogen water chemistry (HWC) effectiveness on plant specifications and operational conditions has been studied for an empirical interpretation. The HWC effectiveness was calculated exactly by employing a water radiolysis model requiring results of complex flow analysis and dose distribution analysis as input, in addition to the plant specifications. It was found that decrease of oxygen concentration in the reactor water in the reactor recirculation system could be taken as an exponential function of H2 concentration added to the reactor water. Thus, the recombination factor ρ which was the coefficient of hydrogen concentration in the exponent could represent the recombination efficiency in the downcomer region. The ρ corresponded to the apparent reaction rate constant of the recombination reaction of H2O2 with H2, which included radical concentrations produced by irradiation, multiplied by the residence time in the downcomer. The dose rate index γ of each plant was introduced as a measure of downcomer dose rate. Since the recombination efficiency was known to depend on the downcomer dose rate, functional dependence of ρ on γ was found to be linear. The HWC effectiveness at the reactor pressure vessel bottom region could also be evaluated using ρ.