This was originally posted on Saturday, March 12 at 2:01 PM EST and is being updated regularly. Some of the information at the top is very basic; if you're familiar with the outlines of the problem, you can jump straight to the latest updates.
Fears of a potential nuclear catastrophe are high in northern Japan, where multiple explosions have occurred at the Fukushima Daiichi Nuclear Power Station and the cooling systems at four separate reactors are suffering problems. Officials have reported that a partial meltdown has likely occured at three reactors, though the extent of the damage to their cores is not yet clear. Spent fuel rods at a fourth reactor also threaten to melt down. The emergency at the plant comes on top of the devastation caused by an 9.0-magnitude earthquake and a 33-foot tsunami.
What is wrong with the plant? There are six boiling-water reactors on the site, though only three were in operation at the time of the earthquake. These systems, designed by General Electric, rely on an influx of water to cool the reactor core. But the water systems require electricity that was cut off by the earthquake. It also appears that something—the initial quake, the tsunami, or aftershocks—knocked the site's back-up generators offline. Without the cooling system bringing in water, the core of a reactor will start to overheat—which in turn heats up the water already in the system and causes more of it to turn to steam. Emergency responders have been forced to vent some of the steam, releasing radiation, in order to prevent the containment domes from exploding. They are in a race against the clock to bring in new water supplies before the reacting nuclear fuel heats up beyond control.
It is believed that all of units have already suffered a partial meltdowns of their reactor cores—the uranium fuel rods where the nuclear chain reaction happens—and four of the plants have been damaged by explosions or fires. There was a blast on Saturday March 12th at Unit 1, followed by explosions at Unit 3 the following Monday and Unit 2 on Tuesday along with a fire at Unit 4, where spent fuel rods may have boiled off all of the water in their cooling pond.
Tokyo Electric Power Company, the owner of the plant, has been flooding the reactors with a mix of sea water and boric acid, which is used to slow down the chain reaction. They have encountered multiple problems, however, with keeping water levels up. Leaving the rods exposed causes them to heat up faster and increases the risk of a meltdown.
How large is the area affected by radiation? Trace levels of radiation from the plant are expected to travel thousands of miles. Of course, radiation powerful enough to pose a health threat will cover a much smaller area. The Fukushima plant is about 160 miles north of Tokyo, and residents within a 12.6-mile radius have been evacuated. However, US officials have advised Americans in Japan to evacuate to at least 50 miles from the plant. British authorities are recommending that their citizens leave Tokyo and the whole of northern Japan. It's still unknown how large an area will be seriously affected.
On March 13th, the aircraft carrier USS George Washington, which is docked at the US naval base in Yokosuka 200 miles south of the reactors, detected "low levels of radioactivity" on its decks. The ship's commander recommended the military personnel limit outdoor activities. A 17-man Naval helicopter crew flying a relief mission about 60 miles from the reactor passed through a radiation plume that exposed them to a month's worth of radiation within one hour. A US Navy spokesman told Bloomberg that low-level radiation exposure will probably become "a fact of life" for military personnel flying relief missions in the area.
Levels of radiation more than four times the legal limit have been found in milk more than 40 miles from the plant. Radiation has also contaminated local crops and tap water.
The IAEA reports that officials are working in the most affected areas to distribute iodine tablets, which are used to block the absorption of radiation.
Will the radiation reach the West Coast of United States? Yes, but experts don't think the levels will pose any danger. MoJo's Julia Whitty has a rundown of the latest modeling and key uncertainties.
How many people have been killed or injured as a result of the disaster? As of Sunday, 8,277 people are dead and more than 12,000 are missing in the aftermath of the earthquake. The precise impact of the nuclear accident is unknown, and its worst-case impacts could ultimately be longer-term health problems such as cancer. According to the New York Times, five Tokyo Electric workers "have died since the quake and 22 more have been injured for various reasons, while two are missing. One worker was hospitalized after suddenly grasping his chest and finding himself unable to stand, and another needed treatment after receiving a blast of radiation near a damaged reactor. Eleven workers were injured in a hydrogen explosion at reactor No. 3."
Hundreds of Japanese soliders and firemen have been working to cool the reactor units. On Thursday, Gregory Jaczko, the chairman of the US Nuclear Regulatory Commission, expressed fears that many of them will suffer lethal radiation doses, despite their protective gear. On March 19th, Tokyo Electric (TEPCO) raised the radiation threshold for workers responding to the crisis from 100 to 150 millisieverts. Earlier in the week, the Japanese government had raised the legal limit to 250 millisieverts. The typical person is exposed to about 3 millisieverts of radiation a year. The International Commission of Radiological Protection recommends no more than 50 millisieverts of radiation a year for nuclear recovery workers. However, it offers no restriction in a crisis when "the benefit to others clearly outweighs the rescuer's risk."
Where can I learn more about the science and health effects of radiation exposure? Here and here.
We'll be providing updates on this developing story below:
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