According to the Washington Post, Japanese nuclear officials had enough monitoring data as early as March 16 regarding the March 11 nuclear disaster to make the determination that the radiation releases were on par with a Level 7 accident, a "major nuclear accident" by the International Atomic Energy Agency scale. The Level 7 rating is based on the 1986 Chernobyl nuclear catastrophe in Ukraine indictating that serious public health and safety conditions existed not only in Japan but potentially spreading internationally. At the time however, those same Japanese officials were publicly stating that there was no "immediate health concerns" from the ongoing and mounting radiation releases.
"Their response has been extremely regrettable. The government is being very careful not to cause unnecessary panic, but they are being too cautious," said Professor Hironobu Unesaki at Kyoto University Research Reactor Institutte.
In fact, the same such "cautious" release of information during severe nuclear accidents releasing dangerous levels of radioactivity has been the historical standard for the entire global nuclear industry. It was three days following the March 28, 1979 Three Mile Island accident before Governor Thornberg got enough conflicted information together from the NRC and Metropolitan Edison Company to "advise" pregnant women and young children to evacuate a 5 mile radius around the melting Unit 2 reactor. And it was a nuclear engineer in Sweden that first reported a radioactive plume days after Chernobyl Unit 4 reactor had exploded more than a thousand miles away in Ukraine.