Arnie Gundersen of Fairewinds Associates has indicated a flaw in the BWR Mk I nuclear reactor containment design, pointing to a pressure test conducted at the Brunswick NPP in North Carolina 40 years ago. It involves the lid of the containment lifting up at pressures of around 100 psi (6.9 bar), allowing gasses to escape. This might have caused at least some of the hydrogen explosions that occurred at the Fukushima Daiichi NPP.
The situation at the Fukushima Daiichi nuclear power plant in Japan remains serious, regardless of the issue getting less press attention. There have been a number of earthquakes since the 11 March earthquake and tsunami, with other nuclear power plants in Japan losing off-site electrical power, at least temporarily. Off-site power availability is imperative in order to maintain nuclear reactors cool, even after shutdown. Onagawa nuclear power plant lost two out of the three power lines supplying off-site power following the 7 April earthquake. All of its reactors have been in cold shutdown since the 11 March earthquake.
The Fukushima Daiichi accident is now at a provisional level 7 on INES. This rating considers the accidents at reactors 1, 2 and 3 as a single event on INES and uses an estimated total release to the atmosphere as a justification. The only other known nuclear accident rated at this level is the Chernobyl disaster. NISA estimates that the release of radioactive material into the atmosphere amounts to approximately 10% of the Chernobyl accident. New evacuation areas beyond the 20 km radius from the Fukushima Daiichi power plant have been established on 11 April.
The IAEA maintains a daily log of the accident. Get your updates there.