Note: This rather lengthy report intends to inform and educate on the Fukushima nuclear accident. It is by no means exhaustive. I tried my best to make it understandable to the public. Kindly refer to the links provided within the report for further details.
Readings at Monitoring Post outside the 20-kilometer zone of the Fukushima Dai-Ichi nuclear power plant on 17 March between 9:20 and 15:00 showed that the radiation to peak at reading point 32. According to the Japan's Education Ministry (MEXT), this is thought to be the result of a controlled containment venting and a simultaneous fire which carried radioactive particles inland. Click here to see the MEXT data.