Computer Models Needed to Analyze the Hazard of Direct Containment Heating (DCH)

Abstract

Accidents at Three Mile Island and at Chernobyl heightened the public awareness and at the same time changed the industry’s perception of nuclear safety; core melt accidents are no longer considered incredible for nuclear reactor plants, although the probability for such accidents is still believed to be very low. One of the safety issues that is currently under extensive investigation is direct heating and pressurization of the reactor containment atmosphere by molten core materials ejected from the reactor vessel under pressure. Direct containment heating (DCH) is of concern because of its potential for early failure to the reactor containment that provides the last barrier against the release of radionuclides to the environment. DCH involves many complicated processes: an unsteady, compressible, and turbulent flow of multi-phase and multi-component fluids; chemical reactions; heat transfer; jet disintegration; debris- structure interactions; etc. Several research activities are ongoing in an attempt to quantify the effects of DCH. Extrapolation of test results is difficult because of the lack of a scaling law. A more suitable approach is the development of analytical models of the associated phenomena and the computation of the extent of DCH using an integrated containment response code. The models needed for such analyses, and their relative importance are discussed.