State-of-the-Art Report on Molten Corium Concrete Interaction and Ex-Vessel Molten Core Coolability

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Since 2002, the Nuclear Energy Agency (NEA) has sponsored the Melt Coolability and Concrete Interaction (MCCI) co-operative project in two phases in order to investigate ex-vessel melt coolability and concrete interaction by means of separate-effects tests and large-scale integral tests carried out at the Argonne National Laboratory (ANL). The second phase of the experimental programme was completed in March 2010. Key elements of this programme included the conduct of experiments involving real reactor material and associated analyses with the objectives of resolving the ex-vessel debris coolability issues and addressing remaining uncertainties related to long-term twodimensional molten core-concrete interactions under both wet and dry cavity conditions. It was expected that the achievement of these two objectives would demonstrate the efficacy of severe accident management guidelines for existing plants and provide the technical basis for better containment designs for the future plants. During both phases of the programme, a total of 13 separate effects tests were conducted to provide data on various core debris cooling mechanisms, including two specific tests to study mechanisms connected to new design features to enhance coolability by bottom water injection. In addition, six large-scale integral tests were conducted to provide data on long-term two-dimensional core-concrete interaction under both wet and dry cavity conditions and one specific one-dimensional large scale test was conducted to investigate the approach for augmenting ex-vessel corium coolability based on an externally-cooled surface concept. These tests provided a broad database to support the development and validation of models and codes with an aim to assess the behaviour of the full size plants under given conditions.