A sensitivity analysis of direct containment heating

For some core meltdown accident sequences in light water reactors, it is possible for the primary system to remain at high pressure. Under these circumstances, as the molten core penetrates the reactor vessel, the core debris would be ejected under high pressure and, subsequently, dispersed into the containment atmosphere. During the process, thermal and chemical energies are directly transferred from the core debris to the containment atmosphere. This phenomenon has been known as direct containment heating (DCH). Since it is difficult to model mechanistically all the aspects of these physical processes, Sandia National Laboratories developed an interim DCH model (interim direct heating model (IDHM)), which treats this highly uncertain phenomenon parametrically. The IDHM was incorporated into the CONTAIN computer code system as CONTAIN Version 1.10. This paper presents a summary of the results of series of calculations performed at Brookhaven National Laboratory to provide estimates of the Zion containment pressure loadings due to DCH for a wide range of assumptions.