Published: April 8th, 2014 at 1:00 am ET
United Nation’s World Meteorological Organization, updated June 2013: The World Meteorological Organization (WMO) [received] a request from the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) to assist them with the meteorological aspects of a dose assessment from the radiological releases from the Fukushima Daiichi nuclear power plant accident. [...] Light rain was observed from the 15th to the morning of the 17th due to a weak low pressure system which moved north eastward off the east coast of Japan. In particular, rain was observed in the Fukushima prefecture during the night from 1700 JST March 15 to 0400 JST March 16 [...] corresponding with significant emissions. [...] winds were from the west [blowing any Fukushima releases over the Pacific] until the morning of 15th, but changed to a direction from north northeast [in direction of Tokyo] during the daytime of the 15th, the time when the reactor number two container burst. [...] After 1500 JST, the winds turned to a direction from east southeast, and then changed to north [blowing releases south].
Wikipedia on Fukushima Unit 2 reactor: An explosion was heard after 06:14 JST on 15 March in Unit 2 […] The radiation level was reported to exceed the legal limit and the plant’s operator started to evacuate all non-essential workers from the plant. […] Soon after, radiation equivalent dose rates had risen to 8.2 mSv/h […] Three hours after the explosion, the rates had risen to 11.9 mSv/h […] Japanese nuclear authorities emphasized that the containment had not been breached as a result of the explosion and contained no obvious holes. In a news conference on 15 March the director general of the IAEA, Yukiya Amano, said that there was a “possibility of core damage” at Unit 2 of less than 5%. [...] 27 March, TEPCO reported measurements over 1000 mSv/h in the basement of the Unit 2 turbine building, which officials reported was 10 million times higher than what would be found [TEPCO] retracted its report and stated that the figures were not credible [...] following the ensuing wave of media retractions that discredited the report worldwide, TEPCO [said it actually was] “more than 1,000 millisieverts per hour”, as originally reported, but the concentration of radioactive substances was 100,000 times higher than usual, not 10 million.
See documentary featuring the ‘burst’ here: NHK: "The unimaginable was happening" -- Workers say part of Reactor 2 containment vessel destroyed -- After alarming pressure readings, "we heard a loud bang... pressure is now zero" (VIDEO)