The 9.0 magnitude earthquake and following tsunami on March 11 has seen a rush by officials to gain control of power plants in the north-east of the country.
The latest news is that the Fukushima Daiichi nuclear power plant has raised it's severity level from five to seven - the same level as Chernobyl in 1986. Justin McCurry writes:
"Nuclear safety officials had insisted they had no plans to raise the severity of the crisis from five – the same level as the Three Mile Island accident in 1979 – according to the international nuclear and radiological event scale.
But the government came under pressure to raise the level at the plant after Japan's nuclear safety commission estimated the amount of radioactive material released from its stricken reactors reached 10,000 terabecquerels per hour for several hours following the earthquake and tsunami that devastated the country's northeast coast on 11 March. That level of radiation constitutes a major accident, according to the INES scale."
http://www.guardian.co.uk/news/datablog/2011/mar/18/japan-nuclear-power-plant-updates