Direct containment heating experiments for Vandellos and ASCo nuclear power plants

Abstract

The ongoing IPE studies for the Vandellos and ASCo nuclear power plants require evaluation of accident phenomena that have been perceived to potentially challenge containment integrity including direct containment heating (DCH). Analyses and scaled experiments performed to date indicated that the lower containment structures play a substantial role in mitigating the extent of DCH given a high pressure melt ejection. Since the geometry is judged to be of major importance, linearly scaled experiments were conceived and conducted to evaluate the role of such structures in the Vandellos and ASCo specific configurations. The Vandellos test configuration with an initally dry cavity and significant exhaust area for the instrument tunnel resulted in the dispersal of a majority of the debris from the instrument tunnel into the lower compartment. The test of the ASCo configuration with an initially wet reactor cavity and limited exhaust area from the instrument tunnel exhibited the retention of the majority of the debris within the instrument tunnel and reactor cavity. The observed pressure responses in these scaled experiments for the seal table room, lower containment vessel, and upper containment vessel were all less than the containment design basis pressure. These test results contribute to the existing technical basis for concluding that direct containment heating would not represent a challenge to the integrity of these containments.