March 11, 2011: Fukushima nuclear plant systems detected an earthquake. The reactors automatically shut down and emergency diesel generators were activated to keep coolant pumping around the cores, which remain extremely hot even after reactions stop due to the radioactive decay of fission products in the core, 9.0: the Richter Scale magnitude of the earthquake, the most powerful ever recorded in Japan, and the fourth most powerful in the world since the inception of modern r