SPEEDI, a computer simulation system used to determine or predict dispersions of radioactive substances, is supposed to be utilized during a nuclear disaster to help people evacuate to safe areas.

But in the early stage of the crisis at Tokyo Electric Power Co.’s Fukushima No. 1 nuclear power plant, the government did not make public the predictions made by SPEEDI. In the absence of relevant information, some people fled to places where radiation levels were actually higher.

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