In the news

At 15:36 JST (7:36 GMT) on March 12, there was an explosion at the plant and four workers were injured.[37] At 18:43 JST (9:43 GMT), officials confirmed that an explosion had occurred at the nuclear plant. Chief Cabinet Secretary Yukio Edano indicated -according to a Reuters report of 21:36 JST (7:36 ET), that the concrete outer structure had collapsed as a result of a hydrogen explosion triggered by falling water levels. At 19:37 JST (10:37 GMT) Reuters reported that Mr Ian Hore-Lacy, communications director at the World Nuclear Association, considered the same cause. Edano further indicated that the container of the reactor had remained intact and there had been no large leaks of radioactive material. An increase in radiation levels was confirmed following the explosion. ABC (Australia) reported "According to the Fukushima prefectural government, the hourly radiation from the plant reached 1.015 millisievert [0.1015 rem], an amount equivalent to that allowable for ordinary people in one year." Yaroslov Shtrombakh, a Russian nuclear expert, said he did not believe that a Chernobyl-style disaster will occur, citing the differences between the designs of the Chernobyl Nuclear Power Plant and the Fukushima I Nuclear Power Plant. He speculated that any nuclear material released during the incident would likely be confined to the grounds in and around the power plant. American nuclear expert Edwin Lyman told Reuters that although he did not have full information about what had happened, "every indication is that the type of event that has occurred there is one of the most serious things that can happen in a nuclear reactor."
At 21:00 JST (12:00 GMT) TEPCO announced that they planned to cool the leaking reactor with sea water (started at 8:30pm local time), then using boric acid to act as a neutron poison to prevent a criticality accident. The sea water would take five to ten hours to fill the reactor core, after which it would require seawater cooling for around ten days. At 23:00 JST (14:00 GMT) TEPCO announced that due to the quake at 22:15 the filling of the reactor with sea water and boric acid had been stopped.
At 01:17 JST on Sunday 13th March (16:17 GMT), the Japan Atomic Energy Agency announced that it was rating the Fukushima accident at 4 (accident with local consequences) on the 0–7 International Nuclear Event Scale (INES), below the Three Mile Island accident in seriousness.

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