OECD MCCI, Melt Coolability and Concrete Interaction: the OECD MCCI (Melt Coolability and Concrete Interaction) project concerns severe accidents in which the reactor core melts due to the absence of cooling, after which the reactor pressure vessel (RPV) also fails. In the reactor building, the corium reaches the concrete foundation, which should be prevented from melting through by cooling. Experiments on the coolability of corium and the interaction between corium and concrete were carried out at the Argonne National Laboratory in Chicago. In 2009, the focus was on the following work:
- In April 2009, test no. 12 in the “Small-Scale Water Ingression and Crust Strength” (SSWICS-12) series was conducted. For the first time, cooling of the heated corium was initiated by nozzles positioned on the foundation; in this case, water and nitrogen were fed in. The observed effectiveness of cooling was significantly higher than in previous tests in the SSWICS series. Data were also obtained on the dimensioning (feed pressure, flow rate) required for the cooling equipment.
- The first test in the Water-Cooled Basemat (WCB-1) series was conducted in July 2009 (duration: 230 minutes). A pipe system through which cooling water flows is located below the foundation, which is in interaction with the corium. In addition, a system is in place to trigger flooding from above with cooling water; this system was activated after the corium had heated up to about 2000°C. During the flooding phase, the temperature stabilised at about 1700°C, and the denudation of concrete on the foundation ended before the occurrence of significant damage to the cooling system located below it.