SPEEDI simulation of radioactive iodine fallout from the Fukushima Dai-ichi nuclear reactor meltdowns for 12 March 2011. The prevailing wind direction forecast shifted over time, resulting in the simulation forecasting wide dispersion of radioactive iodine inland. The simulation chart is the internal radiation exposure at the thyroid gland of a 1-year old by inhaling radioactive iodine. Japan Ministry of Education via ex-skf.blogspot.com

22 March 2012 (Mainichi) – The Fukushima Prefectural Government revealed on March 21 that it deleted five days of early radiation dispersion data almost entirely unread in the wake of the meltdowns at the Fukushima No. 1 nuclear plant.
The data from the System for Prediction of Environmental Emergency Dose Information (SPEEDI) — intended to predict the spread of radioactive contamination, information vital for issuing evacuation advisories — was emailed to the prefectural government by the Ministry of Education, Culture, Sports, Science and Technology. According to the prefecture’s disaster countermeasure office, just after the March 2011 quake and tsunami, its dedicated SPEEDI terminal was unable to receive data due to effects of the disasters. Therefore, prefectural officials asked the Nuclear Safety Technology Center, which operates SPEEDI, to send data via email on March 12, 2011 — one day into the nuclear crisis. The Nuclear Safety Technology Center then sent the data hourly starting at 11:54 p.m. that day. The Fukushima Prefectural Government, however, deleted all the data it received from March 12 to about 9 a.m. March 16. The prefectural government’s nuclear center in Okuma, one of the towns hosting the Fukushima No. 1 plant, received emailed data once at midnight on March 11, but the disaster countermeasure office in the prefectural capital was not aware of it. “We failed to share the information amid all the confusion, and the fact that we had asked for the information to be sent by email hadn’t been shared within the countermeasure office,” said Yoshihiro Koyama, head of the prefecture’s nuclear safety measures section. “We have not been able to confirm when the data was deleted and by who.” At around 10:30 a.m. on March 13, 2011, the disaster countermeasure office confirmed for the first time that it had received data from the central government’s Nuclear and Industrial Safety Agency by fax. But the disaster countermeasure office judged that “the data is useless because the predicted amount of released radiation is unrealistic.” The Fukushima Prefectural Government also failed to give the data to the people of the prefecture and local municipalities partly because the central government was supposed to release such data in the first place.

Fukushima Pref. deleted 5 days of radiation dispersion data just after meltdowns