Former science minister Yoshiaki Takaki and other top ministry officials decided to withhold radiation forecast data from the public four days after the March 11 disasters triggered the nuclear crisis, an internal document shows.
Takaki, lawmakers serving as top ministry officials and senior bureaucrats decided March 15 to withhold data about the predicted spread of radioactivity, including an assumption that all radioactive material would be discharged from the crippled reactors' cores at the Fukushima No. 1 nuclear plant.
The prediction of the spread of radioactive substances, compiled through the System for Prediction of Environmental Emergency Dose Information (SPEEDI), "could by no means be released to the public," the document, dated March 19, shows.
Asked about the matter, a ministry official denied that senior officials had made a decision on releasing the data and said the contents of the document, an internal memorandum prepared by ministry officials, were inaccurate.
The document states that radioactive clouds could spread from the wrecked nuclear power plant to the Kanto and Tohoku regions, indicating that the ministry had made various estimates about the spread of radioactive substances, including the worst-case scenario.
Takaki and the other officials concluded that estimated data from SPEEDI should not be released and that more general data should be prepared for the public, it says.
Kan Suzuki, then vice science minister, said there had been no assumption that all radioactive substances would escape, adding that releasing such an estimate could have panicked the public.