Public exposure in Japan

Units 4, 5 and 6 were undergoing planned maintenance outages when disaster struck. Units 1, 2, and 3 shut down automatically in response to the earthquake. The subsequent tsunami disabled the emergency diesel generators required to cool the reactors. A loss of cooling water to the reactors and to the spent fuel cooling ponds led to hydrogen explosions, fires, leaks and core meltdown. Over the following weeks the utility TEPCO (Tokyo Electric Power Company) battled to contain the damaged reactors, a situation, which a month later, continues to pose highly complex challenges.