Remodeling of the Oxidant Species During Radiolysis of High-Temperature Water in a Pressurized Water Reactor

The production of radiolytic species in a pressurized water reactor has been calculated for various initial hydrogen and boron concentrations. The concentration of oxidants decreases with increasing hydrogen concentration, but the decrease is <20% when [H₂] is increased from 5 to 50 Ncm³/kg (N refers to normal conditions, i.e., 0°C, 1.013 bar). The concentration of oxidants is reduced ∼35% when the boron concentration is reduced from 340 to 0 ppm. The reduction is caused by a decrease in linear energy transfer (LET) of the mixed radiation. An increase in LET results in lower radical yields and higher molecular yields. For a hydrogen concentration of 15 Ncm³/kg and a boron concentration of 800 ppm, the highest H₂O₂ concentration —17 ppb —is found at the highest dose rate in the fuel channel. The highest oxygen concentration — 0.7ppb — is found at the entrance to the downcomer. The highest concentration —0.5 ppb —is found in the fuel channel. Of these species, may be expected to have the highest rate constant in oxidation processes. At a hydrogen concentration of 5 Ncm³/kg, the oxidant concentrations are only slightly higher than the preceding values. A decrease in hydrogen concentration is supposed to be beneficial in decreasing the risk of primary water stress corrosion cracking of the steam generator alloy 600 material.