The estimates were made on March 16th following explosions at the plant by an institute commissioned by the government using a computer system called SPEEDI. The system made its projections on the assumption that radioactive substances had been released for 24 hours from midnight on March 14th, based on the available data.
But the government was reluctant to reveal the SPEEDI projections, and did not release them until March 23rd.
The released data showed that higher levels of radioactive substances would flow over areas to the northwest and southwest of the plant.