According to Japanese law, nuclear plant workers can be exposed to no more than 50 millisieverts of radiation per year and 100 millisieverts over the span of 5 years.

The labor ministry says that as of March 2012, just one year since the onset of the Fukushima nuclear disaster, 167 workers had left the plant with cumulative exposure levels of over 100 millisieverts.

During the spring months of April, May, and June, 79 workers were exposed to more than 20 millisieverts, and 215 others from 10 to 20 millisieverts.

University of Tokyo Professor Kazumitsu Nawata warns of the consequences of losing nuclear plant workers with necessary expertise. He says young workers must be trained due to the need for massive manpower to fully bring the Daiichi plant under control...