Dissolved Oxygen Removal from Primary Heat Transport Systems of Indian PHWRs under Nitrogen Atmosphere

摘要

A reduction in the dissolved oxygen concentration level of the primary heat transport (PHT) system was observed after a changeover from helium to nitrogen in the cover gas of the D2O storage tanks of PHT systems of Indian pressurized heavy water nuclear reactors (PHWRs).Radiolysis of the dissolved nitrogen to form atomic nitrogen and its reaction with water and OH radicals leads to the formation of NO and NH3,which results in scavenging of the dissolved oxygen.However,the concentration of corrosive nitrate formed in this process needs to be minimized.Enhancing the coolant purification flow for the removal of nitrate imposes a heat loss penalty,resulting in a reduction in power generation.On the other hand,hydrogen injection to the system,which suppresses the concentration of corrosive nitrate species,seems advantageous.Thus,a combination of nitrogen as a cover gas in the PHT heavy water storage tank with continued hydrogen injection is recommended to suppress the corrosive effects due to dissolved oxygen and nitrate while retaining the benefits due to the substitution of helium with nitrogen.