According to published reports, backup diesel generators at the power plant failed shortly thereafter, leaving the reactors uncooled and in serious danger of overheating. In Japan the March 11 earthquake and tsunami caused blackouts that cut off the externally sourced AC power for the reactors' cooling system. If the rest of the reactor is operating normally, pumps will continue to circulate coolant (usually water) to carry away the reactor core's heat. So the reactor core continues to produce heat in the absence of fissioning. What is more, the uranium atoms that have already split in two produce radioactive by-products that themselves give off a great deal of heat. When the reactor malfunctions or when operators need to shut off the reactor for any other reason technicians can remotely plunge control rods into the reactor core to soak up neutrons and shut down the nuclear reaction.Ĭan a reactor melt down once the nuclear reaction is stopped?Įven after the control rods have done their job and arrested the fission reaction the fuel rods retain a great deal of heat. Nuclear reactors utilize control rods made from elements such as cadmium, boron or hafnium, all of which are efficient neutron absorbers. The way to cut off a fission chain reaction, then, is to intercept the neutrons. 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. 3 at the Fukushima Daiichi station runs on so-called mixed oxide (MOX) fuel, in which uranium is mixed with other fissile materials such as plutonium from spent reactor fuel or from decommissioned nuclear weapons. Enriched uranium is manufactured into fuel rods that are encased in metal cladding made of alloys such as zirconium. (Isotopes are variants of elements with different atomic masses.) Uranium 238 is much more common in nature than uranium 235 but does not fission well, so fuel manufacturers boost the uranium 235 content to a few percent, which is enough to maintain a continuous fission reaction and generate electricity. Most nuclear reactors use uranium fuel that has been "enriched" in uranium 235, an isotope of uranium that fissions readily. electricity comes from nuclear power plants, making it the third-largest source of electricity in the country after coal (45 percent) and natural gas (23 percent). produces more nuclear power overall, but nuclear constitutes a smaller share of its energy portfolio. Worldwide, nuclear energy accounts for about 15 percent of electricity generation Japan gets nearly 30 percent of its electricity from its nuclear plants. 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 1970s. and France, according to data from the International Atomic Energy Agency. With 54 nuclear reactors generating 280 billion kilowatt-hours annually, Japan is the world's third-largest producer of nuclear power, after the U.S. How much electricity does nuclear power provide in Japan and elsewhere? The chain reaction becomes self-sustaining, producing a steady supply of heat to boil water, drive steam turbines and thereby generate electricity. If another atom absorbs one of those neutrons, the atom becomes unstable and undergoes fission itself, releasing more heat and more neutrons. They rely on harnessing nuclear fission-the splitting of an atom into two smaller atoms, which also yields heat and sends neutrons flying. Most nuclear reactors, including those at Japan's Fukushima Daiichi generating station, are essentially high-tech kettles that efficiently boil water to produce electricity.
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