a-charles writes "Just as power companies are considering the first expansion of nuclear power usage in the US since the 70s, Reuters reports on a disturbing anouncement from the nation of Japan. On Thursday the Japanese power company Hokuriku Electric Power admitted it had covered up a 1999 incident in which mishandling of nuclear fuel rods led to an unintended self-sustaining nuclear fission chain reaction. The mishap caused the plant, located in central Japan, to enter a 'critical state' for much of those 15 minutes. Apparently, this was in the same year that two workers were killed in a separate incident in Tokaimura, northeast of Tokyo. A pair of workers were killed after using buckets to mix nuclear fuel in a lab, a test that also created an uncontrolled chain reaction for a short time. The nuclear power industry already has a bad name for safety violations in Japan, and these revelations are unlikely to help with that public image."