Key Findings and Remaining Questions in the Areas of Core-Concrete Interaction and Debris Coolability

摘要

The reactor accidents at Fukushima Daiichi have rekindled interest in late-phase severe accident behavior involving reactor pressure vessel breach and discharge of molten core melt into the containment. Two technical issues of interest in this area are core-concrete interaction and the extent to which the core debris may be quenched and rendered coolable by top flooding. The Organisation for Economic Co-operation and Development-sponsored Melt Coolability and Concrete Interaction programs at Argonne National Laboratory included the conduct of large-scale reactor material experiments and associated analysis with the objectives of resolving the ex-vessel debris coolability issue and addressing remaining uncertainties related to long-term two-dimensional molten core-concrete interactions under both wet and dry cavity conditions. These tests provided a broad database to support accident management planning as well as the development and validation of models and codes that can be used to extrapolate the experimental results to plant conditions. This paper provides a high-level overview of the key experimental results obtained during the program. A discussion is also provided of the technical gaps that remain in this area, several of which have arisen based on the sequence of events and operator actions during Fukushima.