by Rasoul Sorkhabi Friday, January 20, 2012
The Fukushima Daiichi power plant located in the port town of Okuma in the Fukushima Prefecture, northeast Japan, has six boiling-water-type nuclear reactors supplied by General Electric (units 1, 2 and 3), Toshiba (units 3 and 5) and Hitachi (unit 4) for the Tokyo Electric Power Company (TEPCO) that runs the power station. The power plant was constructed by Kajima Corportation from 1967 to 1973, and the reactors started operating from 1971 (unit 1) to 1979 (unit 6) and had a combined power production capacity of 4.7 gigawatts — about 10 percent of Japan’s nuclear power, thus being one of the largest commercial nuclear plants in the world. What happened following the earthquakes and tsunami in March 2011 at Fukushima was not a single but a series of nuclear accidents.
TEPCO expected the power plant to withstand earthquakes with magnitudes reaching 8.2 to 8.6. The facilities apparently withstood the ground shaking from the March earthquakes, as they had done before, during a June 1978 magnitude-7.4 quake and an August 2005 magnitude-7.2 earthquake offshore northeast Honshu (both of which produced small tsunamis). TEPCO built the plant to withstand a maximum water height of 5.7 meters in the case of a tsunami. The facilities sit on bluffs 4.3 to 6.3 meters above this expected high-water mark. But in March, the 14-meter-high tsunami waves overwhelmed the protective seawall and crippled the Fukushima plant.
TEPCO officials have described the disaster as “soteigai” (roughly, "beyond expectation"). However, the organization has been criticized not only for releasing insufficient information about the Fukushima disaster but also for ignoring geologists' warnings about very large tsunamis that have hit northeast Honshu in the past, including a 1933 tsunami (28.7 meters maximum height) and an 1896 tsunami (38.2 meters high).
On the day of disaster, only units 1, 2 and 3 were operating; the other units had been shut down for a routine checkup. As soon as ground shaking started, the operating units also automatically shut down. But power had to remain on, because radioactive fuel rods — even if not in operation — generate enormous amounts of heat and must be kept cool by electric power and water. The one-two punch of the quake and tsunami, however, wrecked Fukushima’s electric grid. Then the plant’s backup power from diesel generators started and stopped abruptly and the backup batteries lasted for only eight hours. In the total station blackout, radioactive heat accumulated, the available water levels began to boil away, and within three days steam (hydrogen) explosions occurred in units 1, 2, 3 and 4 and blew up the building roofs.
Meanwhile, radiation levels in nearby areas soared, indicating partial fuel-rod melting in some units and leakage of hazardous radiation that made it even harder for workers to fix the damaged facilities.
Officials began evacuating people from the surrounding areas in the hours following the tsunami, and in the following days they increased the evacuation area from 10 kilometers to 20 kilometers, and instructed the inhabitants within 30 kilometers of the damaged power plant to stay indoors as much as possible. Interestingly, the U.S. recommended U.S. citizens in Japan stay 80 kilometers away from the plant.
In the meantime, TEPCO and government officials tried everything they could to cool down the spent fuel rods — they sent firefighters equipped with water cannons to cool down the reactors, dumped seawater and boric acid (which slows nuclear reactions) from helicopters, and tried to bring a new (1-kilometer-long) power line to the reactors. Between March 20 and 22, power was connected to all units, which was an important step. However, leakage of highly radioactive water from the reactors prevented workers from operating the new power line. And efforts to bring the Fukushima reactors completely under control and to stop any radiation leakage continue.
In the case of a nuclear reactor accident, if everything fails to remove heat sufficiently from the nuclear fuel rods, they go into either a partial meltdown — as happened at one of the units in the Three Mile Island plant in Pennsylvania in 1979 — or they go into a total meltdown, as happened at Chernobyl in the Ukraine in 1986. A complete meltdown obviously then creates an environmental and health hazard nightmare that affects even areas far from the reactor and lasts for years (with death rates difficult to measure). Radiation levels in the nearby areas increase tremendously and cancer-causing radioactive elements such as iodine-131, cesium-137, strontium-90 and plutonium-239 enter the soil, water, air, food chain, and life forms, including humans. In the case of Chernobyl, the power plant was covered with sand, cement, lead and boric acid (in bags dropped from helicopters) and was eventually buried under concrete; meanwhile the town of Chernobyl and Pripyat were abandoned and a 30-kilometer-radius exclusion zone was established.
Once the dust settles, it will be necessary to investigate the Fukushima nuclear disaster thoroughly, as this case will be instructive to prevent similar disasters in the future. Many questions need to be answered: Why, out of the four nuclear power plants located near the coast of northeast Honshu, were only the Fukushima Daiichi reactors damaged? Was it because the Fukushima Daiichi reactors are a bit older than the other power plants? Was it because this power plant was at a lower altitude or closer to the sea? Was the tsunami height at that location higher than other places? Were certain errors committed in managing this nuclear disaster once it started? Or were there actually some disruptions (as some reports suggest) in the other power plants too but they were fixed quickly or supported by their backup systems?
Hopefully these questions and more will be answered in the future (see "Nuclear plants and natural disasters: Fukushima's fallout" for more). In the meantime, Japan must now deal with the leaking radiation, which has found its way into the Pacific Ocean, as well as into drinking water, milk and some vegetables even hundreds of kilometers away.
In mid-April, the Japanese government raised the intensity of Fukushima nuclear disaster from level 5 to 7 (on par with Chernobyl) on the International Nuclear and Radiological Event Scale designed by the International Atomic Energy Agency; and TEPCO announced that it would take nine months to bring the nuclear power plant and the leaking radiation under control, further frustrating tens of thousands of families who have left their homes, farms and jobs as a result of this disaster.
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