How The Chernobyl Nuclear Plant Meltdown Formed World’s Most Dangerous Lava Flow

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On the morning of Saturday, 26 April 1986, Reactor 4 of the Wladimir Iljitsch Lenin Atomic Power Station near the town of Chernobyl in modern Ukraine experienced a “minor accident.” As the cooling system was shut down, part of a scheduled safety test, the reactor experienced a catastrophic core meltdown, exploded and parts of the nuclear fuel were released into the atmosphere. Fire-fighters, doctors and nurses rushed to the plant not aware of the danger. As authorities realized the extent of the catastrophe, more than 16,000 policemen and military personnel where sent to the power plant to extinguish the fire, remove the radioactive debris and enclose the ruin in a protective shell made of steel and concrete. Confirmed 31 people died from radiation sickness in the first days after the accident. The long term effects on the evacuated 100,000 people from the towns of Chernobyl and Pripyat are still poorly understood, however, an increase of various cancer types was blamed on the released radioactivity. The effects on the fauna and flora inside the evacuated region became an investigation field for geneticists, ecologists, botanists and zoologists. Even areas thousands of kilometers away from Chernobyl are still today contaminated with radioactive particles, transported by the wind in a gigantic plume over Europe.

As the cooling system of the reactor was shut down and the insertion of control rods into the reactor core failed, the nuclear fission went out of control, releasing enough heat to melt the fuel rods, cases, core containment vessel and anything else nearby, including the concrete floor of the reactor building. The fuel pellets inside the fuel rods are almost entirely made of Uranium-oxide while the encasing in which the pellets are placed is made of Zirconium alloys. Melting at over 1,200°C the Uranium and Zirconium, together with melted metal, formed radioactive lava burning through the steel hull of the reactor and concrete foundations. Concrete doesn’t melt, but decomposed and becomes brittle at high temperatures. Parts of the concrete was incorporated in the lava flow, explaining its high content of silicate (complex Silicon-Magnesium-Aluminium-oxides) minerals. The lava-like material resulting from a nuclear meltdown is also named Corium, after the core of the reactor.

Solidified Corium lava that melted through the basement of the Chernobyl nuclear reactor in 1986. The poor quality of the image is a result of high radiation levels, damaging electronic devices and film. Photo credit Wikipedia/Manzoliu17.

Wikipedia/Manzoliu17

About eight months after the incident, the solidified lava mass was discovered in the basements of the reactor building. Externally resembling tree bark and grey in color, the mass was nicknamed the Elephant’s Foot. At the time of its discovery, radioactivity near the Elephant’s Foot was high enough to be lethal in less than three minutes. In 1996, radioactivity levels were low enough to visit the basement and took some photographs.

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