Following the "highly likely" meltdown of the uranium rods at the Fukushima Daiichi nuclear power plant - after a drop in liquid levels caused by a lack of fuel in the water pumping machines - the Japanese government has raised the nuclear alert level to 5: "Accident with wider consequences."
According to the International Nuclear and Radiological Event Scale, this means:
Impact on People and Environment • Limited release of radioactive material likely to require implementation of some planned countermeasures. • Several deaths from radiation.
Impact on Radiological Barriers and Control • Severe damage to reactor core. • Release of large quantities of radioactive material within an installation with a high probability of significant public exposure. This could arise from a major criticality accident or fire.
An example of this accident was the March 28, 1979 Three Mile Island in Harriburg, Philadelphia, where design and operation errors lead to partial exposure of nuclear fuel rods and partial meltdown. As a result, radioactive gases were released to the atmosphere.
The Japanese government is now asking for help to the IAEA (International Atomic Energy Agency), according to Yukiya Amano, director of the United Nations atomic organisation. As of March 13, 185,000 residents had been evacuated from towns around the Fukushima Daiichi and Fukushima Daini nuclear plants. [IAEA]