![]() The explosions happened when the fuel rods began to melt and release gases that reacted with the surrounding steam, producing hydrogen. So far, at least three explosions have occurred in Reactors 1, 2, and 3. Pressure also began building in some of the reactors. While the nuclear technicians searched for better cooling options, the water levels continued to decrease, exposing the tops of the fuel rods. Later, technicians brought in mobile generators and also attempted to inject seawater into the nuclear reactors, which makes them permanently unusable but could help prevent a complete meltdown. The next backup measure for cooling the fuel rods was a battery system, but the batteries lasted only a few hours. But the tsunami that occurred shortly after the earthquake was larger than the plants designers had anticipated, and water flowed over the retaining wall and into the area with the generators, causing them to fail. As a backup measure, diesel generators turned on to spray the fuel rods with coolant. When the earthquake tore down the power lines, the plants main cooling system stopped working. To stop the chain reaction, control rods that absorb neutrons were inserted in between the fuel rods.īut the fuel rods are still hot, since radioactive byproducts of past fission reactions continue to produce heat. Earthquake tremors triggered the automatic shutdown of the other three reactors, Reactors 1, 2, and 3 (along with eight other nuclear reactors at other power plants). When the earthquake struck Japan, three of the six reactors (Reactors 4, 5, and 6) at the Fukushima power plant were already off for routine inspections. If they begin to melt the nuclear reactor core and the steel containment vessel, and release radiation into the environment, nuclear meltdown occurs. Without enough water, the fuel rods get so hot that they melt. ![]() Even when the reactor is turned off so nuclear reactions no longer occur, the fuel rods remain extremely radioactive and hot and need to be cooled by water for an extended period of time. Fresh water flows around the fuel rods, keeping the fuel rods from overheating and also producing steam for a turbine.īut if not enough water flows into the reactors core, the fuel rods will boil the water away faster than it can be replaced, and the water level will decrease. The neutrons can create a self-sustaining chain reaction by causing nearby uranium nuclei to split, too. When a reactor is turned on, the uranium nuclei undergo nuclear fission, splitting into lighter nuclei and producing heat and neutrons. Inside the core of a nuclear reactor are thousands of long, thin fuel rods made of zirconium alloy that contain uranium. Although employees at the plant have been risking their lives to try to keep the reactors cool, the chance of a serious meltdown seems to be increasing. Last Fridays 9.0-magnitude earthquake and 10-meter (33-foot) tsunami waves that traveled up to 10 km (6 miles) inland overpowered several of the plants safety measures. In Japan, the current nuclear crisis at the Fukushima Daiichi power plant lies somewhere in between Three Mile Island and Chernobyl, according to recent news reports. ![]() Although the accident caused public concern, no deaths or adverse health effects have been officially attributed to the meltdown. ![]() However, very little radiation was released into the environment due to the surrounding primary containment vessel. In 1979, a minor cooling system malfunction led to a series of events that caused a partial meltdown that damaged one of the reactors. Today, limited access is allowed inside a 30-km (19-mile) exclusion zone surrounding the area.īy comparison, the Three Mile Island accident in Harrisburg, Pennsylvania, was much less serious. ![]() As a result, 30 people died of acute radiation syndrome, and thousands of cases of fatal cancers and birth defects have been reported in the following years. Plagued by design flaws and operator errors, the plant experienced fires, explosions, and radiation leakage. The most serious instance happened in 1986 in Chernobyl, Ukraine. A handful of nuclear meltdowns of varying degrees of severity have occurred since the 1950s, when researchers began building and testing nuclear reactors. ![]()
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