Core meltdown (The China Syndrome)
An important nuclear accident occurred in the first nuclear plant in Fukushima Japan because of the tsunami of "Tohoku Great Kanto Earthquake" on March 11, 2011. It came for the radioactive substance to leak and to diffuse. I think that I can say core meltdown because the nuclear fuel rod melts and I damaged it.
Core meltdown are for the nuclear fuel and the reactor core to melt when the nuclear fuel of the reactor core of the nuclear plant overheats by some reasons and to break. A large amount of radioactive substances will diffuse to surroundings because the fuel rod has already been damaged when the pressure vessel and the reactor containment vessel of the nuclear reactor are damaged.
It became a situation to which the fuel rod did the overheating melt because the cooling system broke, water that cooled the fuel rod evaporated, and the fuel rod was exposed in water in case of the accident of the first nuclear plant in Fukushima.
Easy mechanism of nuclear plant
In the nuclear plant, the nuclear fuel such as uraniums of high purity is continuously made critical, and the control of the nuclear fission reaction is enabled. High-pressure steam is made from the generated thermal energy at this nuclear fission, the turbine and the dynamo are rotated by the pressure of the steam, and electricity is generated.
The steam of the high temperature generated in the nuclear reactor is returned to water and recycled. This is because the radioactive substance is included in the primary cooling water. Thus, volumes of water are necessary to cool the steam of the high temperature, and to cool a used nuclear fuel.
How to stop of nuclear reactor and cooling afterwards
When the nuclear reactor is stopped, the radiation shielding thing of control rod is inserted between nuclear fuel rods. Even if the nuclear reactor stops, the fuel rod doesn't become cold at once. It keeps making cooling water circulate at a while and the reactor core being cooled.
The cooling-off period of the spent nuclear fuel was televised in case of about three years. It fairly takes a long period.
The core meltdown
In addition, the temperature of the fuel rod rises by generation of heat of the nuclear fuel if the cooling processing of the fuel rod doesn't go well even if the nuclear reactor stops. Then, the fuel rod melts and it damages it. The fuel rod is a tube where the length of about 4m that is called a fuel coating tube made from zirconium alloys etc. is thin.
The fuel rod becomes and melted damage comes to generate hydrogen like the done temperature (The television said 2,800℃) and the accident etc. of the first nuclear plant in Fukushima and for the hydrogen detonation to happen. In the worst case, the reactor vessel, the reactor containment vessel, and the reactor building, etc. might destroy it due to the explosion and a fire. Then, a large amount of radioactive substances are discharged outside.
Cooling water might evaporate intensely when the fuel rod melts and it falls in cooling water and the steam explosion occur.
What is The China Syndrome?
It is a joke that occurs in the United States core meltdown, melts the nuclear reactor, melts even the earth's crust, and melts it in China on the other side of the planet though there is a movie of "The China Syndrome". There cannot be these kind of things. Therefore, core meltdown might be said, "The China Syndrome".