Radiolytic behavior and effect in nuclear reactor coolants: A focus on ammonia and hydrazine

Coolant selection is intricately linked to the design and type of the nuclear reactor. To mitigate the corrosion of structural materials, the water chemistry of the primary circuit must be carefully managed. Usually, substances such as hydrogen, ammonia, and hydrazine are employed in the reactor's primary coolant. Among these additives, ammonia and hydrazine, which are nitrogen-containing additives, undergo a series of radiolysis reactions in the reactor, and the oxidation environment of the system is altered. In this review, published studies on the radiolytic behavior of ammonia and hydrazine were summarized and analyzed. For ammonia coolants, the center dot OH radicals produced by water radiolysis react rapidly with NH3. The radiolysis product of ammonia, center dot NH2 reacted with oxidizing species such as H2O2, center dot OH, and O2. Under aerobic conditions, the radiolysis of ammonia solutions primarily led to the production of NOx-. For hydrazine coolants, NH3, H2, and N2 were formed by thermal decomposition and radiolysis. N2H4 directly inhibited the formation of H2O2 and nitrogen oxides due to its strong reducibility and ability to remove O2, center dot OH, and H2O2. As the irradiation continued, NH3 was consumed and its concentration decreased, the pH of coolant tended to decrease with further increases in absorbed dose.