Fears are growing of a nuclear meltdown in Japan amidst widespread speculation that efforts to cool a tsunami-hit nuclear power plant are failing to have an impact. Japan has begun using military helicopters and water cannons to dump water on the crippled Fukushima Daiichi nuclear power station to help cool the plant’s reactors and spent fuel rods. But water dropped from the helicopters has been blowing off course. The U.S. Nuclear Regulatory Commission has warned that water in the spent fuel pool at one of the plant’s six nuclear reactors had boiled away entirely, leaving “extremely high” radiation levels. Japan has disputed this account. Meanwhile, the United States government has urged all Americans living within 50 miles of the plant to evacuate. So far, Japan has only issued evacuation orders for residents living within 12 miles of the plant.