With events shifting quickly, and a sometimes confusing succession of announcements coming from authorities, it can be hard to get a clear sense of exactly what's happening, and of what to expect going forward. So here's a rundown, based on several recent news reports, on where things stand five days in…
What's at the root of the problem?
Friday's earthquake and tsunami caused power outages across northern Japan -- including at the Daiichi plant, which comprises six separate reactors. That in turn caused a failure of the reactors' cooling systems, which are needed to keep the nuclear fuel from overheating and melting down and/or triggering an explosion, releasing poisonous radiation into the atmosphere.
What's the current situation at the plant?
Yesterday, an explosion caused the containment vessel covering the Number 2 reactor to crack, releasing into the air a surge of radiation 800 times more intense than the recommended hourly exposure limit in Japan. One third of the fuel rods at the reactor were reportedly damaged. In addition, another powerful explosion blew a 26-foot wide hole in the side of Number 4 reactor, causing fires to break out and a pool containing spent fuel rods to begin dangerously overheating.
The Japanese military tried to use helicopters to dump water from the air to cool the Number 4 reactor, but that plan was abandoned after a third explosion -- this one damaging the roof and cooling system of the Number 3 reactor -- because it would have meant flying a helicopter into radioactive steam. Gregory Jaczko, the top U.S. nuclear official, said today that all the water was gone from the pool containing the fuel rods at the Number 4 reactor -- an assertion denied by a spokesman for the Japanese power company that runs the plant. If Jaczko is correct, it would mean there is nothing to stop the fuel from melting down, spewing radiation.
Water was also poured into the Numbers 5 and 6 reactors, suggesting that essentially the entire plant could be at risk of overheating.
In what appears to have been an understatement, the plant operator described the situation at the Number 4 reactor as "not so good." But in some ways the rupture at the Number 3 reactor is especially troubling, because it's the only reactor that uses plutonium as part of its fuel mix. If absorbed into the bloodstream, plutonium can stay in the liver or bone marrow and cause cancer.
Japanese officials said early Thursday they're close to completing a new power line which would restore the cooling systems for the reactors, but it's unclear when the line will be up and running.
How much of the surrounding area is likely to be affected by the radiation?
The government has told the roughly 140,000 people who live within 18 miles of the plant to stay indoors, but has said that people outside that zone can safely go outside. However, some experts have accused the Japanese authorities of underplaying the severity of the crisis. The U.S. embassy has recommended that Americans within 50 miles of the plant evacuate the area or stay indoors.
Tokyo, 180 miles south of the plant, has recorded radiation levels only slightly above normal. Still, both France and Australia have urged their nationals throughout the country to leave, and many Tokyo residents have been staying indoors. One American couple living in Tokyo told family they don't yet see a need to leave, but are monitoring the situation closely.
What other ideas are being considered?
In what experts describe as a last-ditch effort, police are hoping to use a water cannon -- usually used to quell riots -- to cool the nuclear fuel. Officials have also proposed using boric acid, which can help slow nuclear reactions by absorbing neutrons.
On Monday, 750 workers were withdrawn from the facility, leaving a core of 50 to battle the crisis alone while exposing themselves to potentially deadly levels of radiation. But even those workers appeared to have been withdrawn today after a surge in radiation caused by new explosions made the area too dangerous.
What are the best- and worst-case scenarios?
The best case scenario is that efforts to cool the fuel rods succeed, and damage to the surrounding environment is limited to an area within about 15 miles of the plant. The worst is a full-scale meltdown of the reactors caused by overheating, which would release much larger amounts of radiation into the air than has yet occurred. In that case, the damage could potentially approach the level of the Soviet Union's 1986 Chernobyl disaster, for which estimates of deaths vary from 4000 to close to one million.
How does the crisis rank, in terms of nuclear plant accidents?
On Saturday, Japanese authorities ranked the incident a Level Four on a one-to-seven scale used to rank nuclear accidents. but things have worsened since then, and yesterday France's nuclear authority said it should be classified as a Level Six. Chernobyl is the only Level 7 accident ever to have occurred.
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