Tepco had simulation data that projected the plume would go given current weather patterns but decided not to release it to the public. The could have been protected. Does anyone believe that the crew were the only people harmed by Fukushima? What about all the locals who headed northwest when the explosion occurred (right into the plume) and then set up camp in a highly contaminated zone.
Japan just rammed through state secrecy and they had to be concealing data on illnesses even before the new law passed.
The National Atmospheric Release Advisory Center probably has plume models of the event. A FOIA request should be made. DOE/NNSA had people on the ground in Japan. What data did they collect?