The “elephant’s foot” formation at the Chernobyl nuclear power plant. The mass formed during the … [+]
Wikipedia / Manzoliu17
On the morning of April 26, 1986, Reactor 4 of the Vladimir Ilyich Lenin nuclear power plant near the city of Chernobyl in modern Ukraine suffered a “minor accident”. When the cooling system was shut down for a scheduled safety test, the reactor went critical and experienced a catastrophic core meltdown.
The fission released enough heat to melt the fuel rods, casings, core canister, and everything else in the vicinity, including the concrete floor of the reactor building.
The fuel pellets in the fuel rods consist almost exclusively of uranium oxide, while the shell into which the pellets are inserted consists of zirconium alloys. When melted above 2,000 ° C (3,600 ° F), uranium and zirconium, along with molten metal, formed radioactive lava that burned through the reactor’s steel hull and concrete foundations at a rate of 30 cm per hour. Concrete does not melt, but chunks of concrete have been worked into the lava flow.
Due to its chemical composition and high temperature, the lava had a very low viscosity. When lava has a low viscosity, it can flow very easily, as shown by solidified stalactites hanging from valves and pipes in the destroyed reactor building.
Corium Lava flows out of a safety valve at the Chernobyl plant.
INSP
About eight months after the incident, the lava was discovered with the help of a remote-controlled camera in the ruins of the reactor building. With a diameter of 3 m, which externally resembles the bark of a tree and is gray, the solidified lava flow was called “elephant foot”.
The elephant foot is made up of 11 tons of a very unique type of lava called Corium, which comes from molten nuclear waste. Corium behaves similarly to lava, but is about twice as hot as naturally occurring lava. The solidified rock has a very high content of silicates, minerals that mainly consist of silicon, aluminum and magnesium and come from the concrete absorbed by the lava flow. A previously unknown uranium-zirconium silicate found in the Chernobyl corium was later referred to as Chernobylite. Chernobylite is highly radioactive due to its high uranium content and contamination by fission products.
At the time of its discovery, the radioactivity near the Corium Lava was approximately 10,000 roentgen. Three minutes of exposure to such a high level would prove fatal to any human being. In 1996 the radioactivity was low enough to visit the basement of the reactor for the first time and take some pictures. The photos are still blurry due to radiation damage.
In February 2020, scientists restored Corium in a laboratory by heating a mixture of depleted uranium, zirconium, and various metals in an oxygen-free atmosphere to 1,500 ° C for four hours and then to 720 ° C) for another three days, around the To simulate heat generated by radioactive decay in a stream of corium. This and similar experiments are being carried out to better understand how accidents can be reduced in the future. For example, research has found that draining water onto lava-like fuel-containing material after it has formed actually prevents some fission products from breaking down and producing more heat and dangerous isotopes.
Corium was made outside the laboratory at least five times: once in the Three Mile Island reactor in Pennsylvania in 1979, once in Chernobyl, and three times during the 2011 Fukushima Daiichi power plant collapse in Japan. Only Chernobyl’s Corium escaped containment. It will likely remain radioactive for the next decades to centuries.
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