lowered into the fuel assembly: the byproducts of fission are radioactive and can generate energy through radioactive decay (4). If the cooling system fails, the fuel rods can overheat and melt to collect at the bottom of the reactor vessel. This situation is known as a meltdown. In a worst-case scenario, this molten fuel can pool through the reactor core’s protective casing and expose the outside world to harmful radiation (4).
What Happened at Fukushima? Immediately after the earthquake on March 11, the three reactors operating that day shut down. Authorities detected a tsunami but could not determine its magnitude or direction. A seawall protected the plant from the first wave but could not stop the second wave that followed eight minutes later (5). The wave quickly knocked out the main power supply behind the cooling pumps. Soon, it drowned the emergency diesel engines, stored in the basement, which provided the plant’s backup supply. Workers tried to power the pumps with car batteries, but their efforts could not prevent the reactor core from overheating, and fire trucks and emergency power vehicles were blocked by tsunami debris (5). As the remaining water boiled away, the Tokyo Electric Power Company, or TEPCO, operator of the Fukushima Daiichi plant, added boric acid, a neutron absorber, hoping to slow the reaction (6). All the while, the combination of steam and boric acid caused a buildup of hydrogen. The pressure inside the reactors reached dangerous levels, especially in Reactor Building No. 1, where melted fuel had begun to pool at the bottom of the containment vessel. Workers attempted to relieve this pressure by venting the excess gas, but damages to the plant prevented them from operating the gas release valve (5). Due to the hydrogen buildup, the first hydrogen explosion occurred on March 12, a day after the earthquake, in Reactor Building No. 1, and then in buildings 3 and 4. On March 15, a blast near Reactor Building No. 2 drained a suppression chamber that absorbed steam from the core, and a fire raged around a spent-fuel pool in Reactor Building No. 4 (5). A Japanese Defense Force helicopter had been used to drop seawater on the reactors, keeping them cool, but the radiation spewing upward prevented it from dousing the most damaged buildings (6). Military fire engines arrived that evening, spraying water over the plant’s remains. Several days later, a more elaborate system of fire trucks was set up to bring sea water to the reactors to cool them, steamcooling the reactors for months in an effort known as “feed and bleed” (5). Despite their efforts, workers at Fukushima could not prevent the fuel from reaching complete meltdown. Increases in the radioactive isotopes WINTER 2014
in the atmosphere above California, although harmless at their present concentrations, have provided more evidence for the catastrophic scale of the meltdown (7). In fact, the Fukushima accident still releases radiation, much of it as radioactive coolant water that finds its way into the pacific; it was estimated that up to 80 percent of the radioisotopes released by the plant have flowed into the ocean (8).
What Went Wrong? While the tsunami was the direct cause of the accident, it only revealed much larger, more fundamental problems. Since the plant’s construction, Japanese scientists overlooked evidence that suggested the Tohoku coast is susceptible to larger earthquakes and tsunamis than previously thought (1). Thus, the plant was built to withstand tsunamis of only about 19 feet—less than half the height of the wave that struck March 11 (5). TEPCO failed in other respects to ensure the safety of its nuclear plant. In 2002, TEPCO and other companies issued a report claiming that there was no need to take precautions against hydrogen explosions. TEPCO has also admitted to falsifying repair records and concealing emergencies at Fukushima and other plants (5). Much of this disregard for safety can be traced to the power of Japan’s nuclear industry. Nuclear energy had been heralded as the energy source of the future in Japan since World War II. After the country’s destruction during World War II, nuclear energy seemed to be Japan’s ticket to economic regrowth. A massive public relations campaign ensued for many years. The Japanese
Figure 2: This image illustrates the locations of explosions and the relative states of the Fukushima reactors after the tsunami.
Image courtesy of Wikimedia Commons. Available at http://upload.wikimedia.org/wikipedia/commons/thumb/3/33/Fukushima_I_nuclear_accidents_ diagram.svg/2000px-Fukushima_I_nuclear_accidents_diagram.svg.png
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