Abstract: In reactor water-chemistry concepts, including boron-free reactors employing ammonia-based primary water chemistry and systems using nitrogen for pressurization, the radiation chemistry of nitrogen-containing species plays an important role in determining coolant physicochemical properties, redox conditions, corrosion-related behavior, radiolytic product distributions, and ultimately reactor operational safety. Under intense neutron and gamma irradiation, these species may interact with primary water-radiolysis products and participate in complex radical and molecular reaction networks, making their chemical evolution strongly dependent on reactor operating conditions. This review systematically summarizes the chemical characteristics of ammonia, nitrogen, and hydrazine in primary reactor coolant systems and discusses their functions and reaction mechanisms in water-chemistry control. Particular emphasis is placed on their current engineering applications, radiolytic decomposition pathways, kinetic characteristics, and potential effects on coolant performance under reactor-relevant conditions. First, the operating experience associated with three representative water-chemistry control strategies used in VVER reactors is reviewed and compared in terms of their chemical-control objectives, practical advantages, and inherent limitations. The comparison indicates that, although nitrogen-containing chemicals have been employed for coolant chemistry control and maintaining reducing conditions, their radiolysis mechanisms and quantitative modeling remain poorly understood. For aqueous ammonia systems, the effects of temperature, pressure, absorbed dose, dose rate, initial concentration, coexisting solutes, and gas-liquid conditions on radiolytic product distributions are examined. Available studies reveal substantial uncertainties arising from incomplete reaction networks, inconsistent kinetic parameters, and limited experimental validation under high-temperature and high-pressure conditions. In particular, the roles of transient nitrogen-containing intermediates and their competing reactions with water-radiolysis species have not yet been fully clarified. For nitrogen, possible pathways for radiation-induced activation and subsequent conversion into other nitrogen-containing products are discussed. However, the proposed mechanisms differ considerably among existing studies, especially regarding the formation, transformation, and ultimate fate of reactive nitrogen intermediates. Hydrazine radiolysis is likewise highly dependent on experimental conditions. Although hydrazine is widely used as a reducing and oxygen-scavenging agent in water-chemistry control, its decomposition network remains incompletely resolved, particularly with respect to short-lived intermediates, competing radical reactions, product selectivity, and the transferability of kinetic parameters obtained under different irradiation and thermohydraulic conditions. Overall, major knowledge gaps remain in obtaining reliable experimental data, confirming elementary reaction pathways, and constructing validated multiphase kinetic models for nitrogen-containing species under simultaneous high-temperature, high-pressure, and irradiation environments. Future research should therefore strengthen the integration of targeted mechanistic experiments with kinetic modeling, parameter evaluation, and sensitivity analysis, while improving the consistency and reactor relevance of thermodynamic and reaction-rate databases. Such efforts are expected to deepen the mechanistic understanding of nitrogen-species radiolysis, improve prediction of coolant chemistry evolution, and provide a more rigorous scientific basis for optimizing primary water-chemistry strategies and promoting the engineering application of nitrogen-containing chemical control in advanced reactor systems.