This set of modeling images were taken from an NHK documentary. A group of researchers modeled the releases of iodine 131 over the early days of the disaster. Their modeling shows iodine 131 contamination as far away as Tokyo and Yokohama. Considerable amounts of Iodine 131 blew over Chiba. A concentrated wave also went over the Fukushima City area. Iodine 131 repeatedly blew over Miyagi prefecture north of the disaster site. The model estimates a 5-year-old child would receive a 200 mSv thyroid dose if exposed continually with no protection at the highest range in the model. This does not assume this was an actual exposure but is intended to be a “maximum possible exposure” example.
The chart on the images is in becquerels per square meter. The ranges are: (blue) 10, 100, 1000, 10 thousand, 100 thousand, and one million (red)
The significant iodine 131 plume around March 23rd represents an event at Fukushima Daiichi that was later found to be a major release of radioactive materials. TEPCO reduced the amount of water injected into units 2 and 3 around March 17th. Over a period of days, this caused the reactors to heat up and release significant amounts of radiation into the environment. TEPCO’s on-site monitors at ground level did not pick up this increase in radioactive releases.