Romania: Applications of ASTEC Code in Relation with Hydrogen Behaviour on a Generic CANDU 6 Reactor

Under severe accident conditions in nuclear power plants, large amounts of hydrogen can be generated and released into the reactor containments. Hydrogen can be produced from oxidation of the metallic components of the core and molten core-concrete interaction (MCCI) after failure of the reactor vessel and relocation of the corium consisting of the molten reactor core and internal structures to the reactor cavity. A large amount of carbon monoxide may also be produced during MCCI in addition to hydrogen and other gases. This could potentially lead to the formation of flammable mixtures of gases in reactor containments. Combustion of these mixtures could lead to pressure and temperature levels that may jeopardize the containment integrity. Hydrogen combustion can cause containment building failure by static or quasi-static pressure loads or dynamic pressure and impulse loads, equipment failure due to temperature or pressure effects, and missile generation. The type of combustion determines local and global mechanical and thermal loads on the containment.