Which process is associated with generating hydrogen and oxygen gas in water under irradiation in a reactor coolant system?

• A. Hydrolysis
• B. Electrolysis
• C. Radiolysis
• D. Oxidation

Answer: (C)

Radiolysis is the breakdown of water molecules by ionizing radiation. In a reactor coolant system, water is continually exposed to gamma rays and fast neutrons from fission, which ionize and excite the water to produce reactive species such as hydroxyl radicals and hydrogen atoms. These species recombine and react further to form molecular hydrogen and oxygen gas (with other byproducts like hydrogen peroxide). This gas generation is a direct result of radiolysis and is distinct from hydrolysis (water splitting by chemical reaction with water, not radiation), electrolysis (splitting water with an electrical current), or oxidation (a general electron-loss process not specifically tied to radiation-induced gas production). Understanding radiolysis explains why hydrogen and oxygen can accumulate in the coolant and why gas management or recombination is important in reactor systems.