Keeping the fuel in the reactors cool, as well as the used fuel rods that are stored in pools of water, is crucial to preventing radiation from leaking out. Heat from the fuel rods makes water boil off of them, so it has to be constantly replaced. Helicopters were used last week to dump water into the spent fuel pools from above, while firehoses sprayed water onto the reactors. Early this week, workers were finally able to string power cables to the plant's six reactors, restoring electricity. That meant the cooling systems (at least, their non-damaged components) could be turned back on, though workers would still have to fight to clean up the radioactive material and stop the leaks.
Then radioactive iodine showed up in Tokyo's tap water. The levels weren't dangerous for adults, but the government urged parents not to let babies drink any tap water--since their thyroid glands are still developing, they're more liable to absorb the cancer-causing isotope. Radioactive iodine and cesium have also turned up in milk and vegetables (such as spinach) around Fukushima. Japan has banned the sale of these products, and the United States has stopped importing dairy and produce from the region. Luckily, the radioactive iodine has a half-life of just 8 days, so it won't stick around for very long--once it stops coming out of the nuclear plant, that is. But the radioactive cesium has a half-life of 30 years. This means its presence in farmlands could become a very long-term problem.
Differing evacuation recommendations from the Japanese and American governments have caused confusion and tension. The Japanese government ordered a total evacuation within 20 kilometers (12 miles) of the plant, and told people between 20 and 30 kilometers away to stay indoors. Meanwhile, the U.S. government urged its citizens in Japan to stay 50 miles away from the plant. The Nuclear Regulatory Commission's reasons for the 50-mile recommendation were somewhat unclear, since the radiation reaching that far from the plant is, so far, negligible. But the NRC may have been betting against Japan's ability to subdue the growing nuclear crisis.
Today, the Japanese government seemed to similarly lose confidence, widening the evacuation zone to 30 kilometers (19 miles). Those residents aren't being ordered to leave--though, after staying indoors all this time, they might be happy to. A new concern is that one building's reactor vessel may be leaking radioactive material. Two workers suffered radiation burns from water that sloshed into their boots near the reactor. An anonymous nuclear executive told the New York Times that the vessel has a "definite crack."
So where's the silver lining? Radiation levels in the Tokyo tap water dropped, making it safe for infants again. And though the Japanese government has been less than transparent about the situation at Fukushima Daiichi, people have begun gathering and distributing information on their own. Several sites are using crowd-sourced data to create maps of the radiation in Japan. This site uses Google Earth to map radiation levels, which puts the disaster into beautiful perspective even as it continues to unfold.