Study of Refractory Material Installation in the Reactor Cavity

Abstract

During a severe accident with a vessel failure, corium relocates from the vessel into the reactor cavity (PWR) or pedestal (BWR) and accumulates on top of the cavity floor to form a corium pool. This corium pool is hot enough to cause a Molten Corium-Concrete Interaction (MCCI) that can ablate the concrete structure even if water is present on top of the corium. MCCI will also produce steam and other gases that increase containment pressure as well as generate combustible gases (Hydrogen and Carbon Monoxide). Current MAAP5* calculations with conservative assumptions have shown that the ablation depth in a basemat constructed of siliceous concrete can be larger than the depth of liner, even if the reactor cavity is flooded by water. To retain the melt in the containment and to cool the corium pool before the erosion reaches the liner plate, several approaches are being considered. One of these approaches is the installation of a protective layer on top of the concrete floor to retard MCCI. The purpose of this paper is to study the performance of different protective materials under postulated severe accident conditions. The candidates for the protective materials are refractory materials and limestone/limestone-common-sand (LCS) concrete. The refractory material was chosen based on the thermal performance and dissolution rate of the refractory material calculated by analytical calculations and also by MAAP5. Adding the refractory protective material protects the underlying concrete basemat from melting temporarily, so that water ingression into the surface of the corium is not initially affected by addition of the concrete material. *MAAP5 is an integrated severe accident code owned by the Electric Power Research Institute and developed by Fauske and Associates, LLC.