Generation of hydrogen

4.156. Hydrogen and oxygen are generated during normal operation of a plant as a result of the radiolysis of water in the core. After a LOCA, a mixture of hydrogen and air might be formed in the containment atmosphere as a consequence of:

— Radiolysis of the water in the core,

— Radiolysis of the water in the sump or the suppression pool,

— Metal-water reactions in the core,

— Chemical reactions with materials in the containment,

— Degassing of hydrogen dissolved in the primary coolant,

— Releases from the hydrogen tanks used for control of the primary coolant chemistry.

All these contributions to the generation of hydrogen should be evaluated.

4.157. The amount of hydrogen generated should be calculated for normal operation and for LOCA conditions. The uncertainties in the various possible mechanisms for hydrogen generation should be taken into account by the use of adequate margins.