A report by the Japan Atomic Energy Agency said that untimely heavy rainfall and shifting winds caused huge amounts of airborne radioactive fallout from the plant to pour down on an unwarned population.

The bulk of the radiation had been predicted to drift offshore over the Pacific, leaving Fukushima residents relatively safe.

“Local residents would have stayed indoors and avoided radiation if they had been told about the dangers of the rainfall,” Tetsuo Sawada, assistant professor of reactor engineering at the Tokyo Institute of Technology, told The Wall Street Journal.

The agency report said the downpours came at the worst possible time on March 15 -- a day after an explosion punched a large hole in the plant’s No. 2 reactor containment vessel.

Photo: Tokyo Electric Power Co.