Union of Concerned Scientists on Japan

A good source of information is the Union of Concerned Scientists at http://www.ucsusa.org/ :

 

Nuclear Reactor Crisis in Japan Worsens
The massive earthquake and tsunami off the northeast coast of Japan has caused a potentially catastrophic situation at multiple nuclear power facilities there. The situation is still evolving, but we have linked to an assessment based on the facts as experts at the Union of Concerned Scientists currently understand them.