One of the most famous picture of the chernobyl disaster pictures Artur Korneyev, Deputy Director of Shelter Object, viewing the deadly “elephants foot” corium lava flow of the ractor 4 in Chernobyl , 1996.
Corium is a metallic and mineral man made magma made up of melted elements of core of a nuclear reactor , then minerals it can absorb during its journey oozing through pipes, eating through the basement concrete, and eventually cooled enough to solidfy. It is formed at a very high temperature (about 3000 ° C, melting temperature of uranium oxide) .
Nuclear central core meltdown ‘s Coriumwas formed 5 times in history, once at the Three Mile Island reactor incident in Pennsylvania in 1979, once in Chernobyl in 1986 , and at three separate moments during the Fukushima Daiichi incident in Japan in 2011.
In Japan, Tepco conducted an investigation inside the Fukushima Daiichi reactor 2 containment enclosure using a robotic 13 meter probe with a camera and a dosimeter. On the video you can clearly see the corium stalactites that solidified on metal structures under the one of the reactor vessel., the radiocativity level is around the deadly level 530 Sv/h.
Some Modern nuclear reactors are now designed with “core catcher” , sand boxe like device , in order to catch the molten core in case of a nuclear meltdown and prevent it from escaping the containment building.