Radiolysis in a reactor coolant system primarily leads to the production of which gas, saturating the system?

• A. Hydrogen
• B. Oxygen
• C. Nitrogen
• D. Methane

Answer: (A)

Radiolysis of water in the reactor coolant system produces hydrogen and oxygen as ionizing radiation breaks water molecules into reactive fragments, which eventually form diatomic hydrogen and diatomic oxygen. The overall reaction 2 H2O -> 2 H2 + O2 shows hydrogen is generated in gaseous form alongside oxygen. Hydrogen tends to saturate the system because it is produced directly and has relatively low solubility in water, so it readily escapes into the gas phase. Oxygen can also form but is often consumed or dissolved more readily in the coolant or via recombination, so hydrogen is the gas that predominantly saturates the system. Nitrogen and methane are not produced in meaningful amounts by this radiolysis process.