The prediction of direct containment heating

Issues on containment integrity during severe accidents

“…Intercompartment flow and intermixing of fluids could lead to a uniform composition of gases if mixing is complete, otherwise stratification could occur in a flowing state [1,3,[10][11][12][13][14]. Heat transfer to structural surfaces occurs during the course of interflows and intermixing.…”

“…For higher heating rates (typically above 0.3-0.5 Kls), the oxide layer build up is slow causing zircaloy melting and relocation to lower core region while lower heating rates prevent zircaloy relocation and causes complete oxidation in-place [1]. Zircaloy oxidation also controls total amount of hydrogen release in the vessel with little contribution of core structures and U02 because of early melting of the structures and steam exposure of U02 limiting its oxidation [7,10,11].…”

“…Other heat sources include combustion of hydrogen and carbon monoxide, and radioactive heating due to corium spread in the cavity. Heat sinks include all structural surfaces, leakages and deliberate releases from the containment volume [1,5,7,[10][11][12]14].…”

“…Severity of consequences depends largely on the melt release states from RPY. Major processes constituting various ex-vessel phenomena are containment thermohydraulics, fission products transport, and melt dispersion [1,[7][8][9][10][11][12][13][14][15][16][17][20][21][22].…”

“…Variability in structural modeling/analysis is also to be accounted. Air leakage A. In-Vessel Phenomena In-vessel phenomena for PWR can be described under general topics of thermohydraulics, oxidation of core materials, core relocation and failure of reactor pressure vessel (RPV) [7][8][9][10][11].…”