Role of Molecular Nitrogen in the Radiolysis of the Primary Coolant of a Water-Cooled Water-Moderated Energy Reactor

Abstract

The results of simulation of radiation-chemical transformations in the primary coolant of a water-cooled water-moderated energy reactor (VVER) are presented. It has been shown that under conditions of intense irradiation, molecular nitrogen dissolved in the coolant exhibits chemical activity. The reaction of N₂ with the excited hydroxyl radical initiates the formation of ammonia and nitrous acid. Further decomposition of ammonia produces only oxidized forms of nitrogen, with N₂ acting as an intermediate product. Maintaining hydrogen and oxygen concentrations within normal limits in the ammonia water chemistry is possible only with constant dosing of NH₃ and degassing of the coolant. In the case of water chemistry with H₂ dosing (at the initial moment), on the contrary, a stationary regime is quickly established in the absence of disturbances, satisfying the requirements of VVER water chemistry standards. The difference between the two water chemistry systems is due to the presence of nitrogen in the NH₃ molecule and its transformations as an element, regardless of the initial chemical form.