If the fuel gets hot enough, the uranium can melt, eventually falling to the bottom of the reactor and even burning through it. This is a meltdown. If it is bad enough, the molten, radioactive uranium could burn through all the protective layers surrounding the reactor and get released into the surrounding environs.
The most famous nuclear accident here in the United States, Three Mile Island in , is called a partial meltdown because the fuel rods were only partially exposed, though melting did occur. Washington Post : How the nuclear emergency unfolded. Four hundred miners were brought to Chernobyl to dig a tunnel underneath. It was feared that the radioactive lava would burn through the containment structure and contaminate the groundwater. Only later it was discovered that the lava flow stopped after 3 meters 9 feet.
About eight months after the incident and with the help of a remotely operated camera, the solidified lava was discovered in the ruins of the reactor building. In , radioactivity levels were low enough to visit the reactor's basement and took some photographs.
The photos are blurry due to radiation damage. The lava-like material resulting from a nuclear meltdown is also named corium , after the core of the reactor. An unknown uranium-zirconium-silicate found in the corium of Chernobyl was named later chernobylite. Your opinion can help us make it better.
We use cookies to improve our service for you. You can find more information in our data protection declaration. After the disasters of an earthquake and tsunami, Japan also suffered under the threat of a meltdown in a nuclear reactor. Here's how a meltdown happens. In a nuclear meltdown, it all comes down to a power plant's reactor. Japan's Fukushima Daiichi plant, which was damaged by Friday's earthquake, employs six boiling water reactors.
When functioning normally, energy production in a boiling water reactor starts with a process known as nuclear fission. That heats up fuel rods in the reactor, which in turn bring water in the reactor to a boil and convert it to steam. Electricity is produced when the steam passes through a turbine. Then, the water is cooled and pumped back into the reactor and the process can begin again. It's the nuclear fission - how fuel rods are heated up - that is important. During the process, the rods, which are made of enriched uranium, undergo radioactive decay and release large amounts of energy.
That's how water in the reactor is brought to a boil. The process is regulated with so-called control rods located between the fuel rods. How much electricity does nuclear power provide in Japan and elsewhere? With 54 nuclear reactors generating billion kilowatt-hours annually, Japan is the world's third-largest producer of nuclear power, after the U. The Fukushima Daiichi station, which has been hit hard by the March 11 earthquake, houses six of those reactors, all of which came online in the s.
Worldwide, nuclear energy accounts for about 15 percent of electricity generation; Japan gets nearly 30 percent of its electricity from its nuclear plants. The U. About 20 percent of U. What fuels a nuclear reactor?
Most nuclear reactors use uranium fuel that has been "enriched" in uranium , an isotope of uranium that fissions readily. Isotopes are variants of elements with different atomic masses. Uranium is much more common in nature than uranium but does not fission well, so fuel manufacturers boost the uranium content to a few percent, which is enough to maintain a continuous fission reaction and generate electricity.
Enriched uranium is manufactured into fuel rods that are encased in metal cladding made of alloys such as zirconium. Reactor No. How do you turn off a nuclear reaction? Sustained nuclear fission reactions rely on the passing of neutrons from one atom to another—the neutrons released in one atom's fissioning trigger the fissioning of the next atom.
The way to cut off a fission chain reaction, then, is to intercept the neutrons. Nuclear reactors utilize control rods made from elements such as cadmium, boron or hafnium, all of which are efficient neutron absorbers.
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