The document provides basic design information about BWR3 and BWR4 reactors, which are the types used at the Fukushima Daiichi nuclear power plant. It describes the Mark I containment system, typical reactor vessel configurations, and the reactor core isolation cooling system. It then summarizes the events at Fukushima Daiichi following the 2011 earthquake and tsunami, including loss of cooling, hydrogen explosions, fuel damage in reactors 1-3, and challenges with spent fuel pools.