A core catcher is a device provided to catch the molten core material (corium) of a nuclear reactor in case of a nuclear meltdown and prevent it from escaping the containment building. A core catcher is a device provided to catch the molten core material (corium) of a nuclear reactor in case of a nuclear meltdown and prevent it from escaping the containment building. A core catcher is made from a special concrete ceramic to prevent material from trickling through; it is also a cooling mechanism to cool down the core material. The core catcher of the European Pressurized Reactor (EPR) has 170 m² expansion area and a mass of 500 t.