UNRESTRICTED | ILLIMITÉ
For an interesting and informative read on the Fukushima accidents, see the publicly-available Institute of Nuclear Power Operations (INPO) report INPO 11-005 “Special Report on the Nuclear Accident at the Fukushima Daiichi Nuclear Power Station”, Revision 0, November 2011 (2 MB pdf). The report includes well-written narratives and detailed timelines for each reactor.
Amongst other things, I learned that following the tsunamis, an air-cooled emergency diesel generator was available for units 1&2, and another for units 3&4. Unfortunately, the electrical systems from these generators to the reactors were rendered inoperable by the tsunamis. An air-cooled generator operated for units 5&6, and the electrical connections to the reactors were intact / restored. Ironically, Units 5 & 6 were not in operation at the time of the earthquake, both being in planned outages (since Jan 3 2011 for Unit 5, since Aug 14 2010 for Unit 6). Thus these two reactors had the lowest decay heat, the longest (by far) margins to fuel uncovery, and thus the lowest immediate need for backup generation and core cooling systems.
The INPO report incorporates some of the information and illustrations from the “Report of Japanese Government to IAEA Ministerial Conference on Nuclear Safety - Accident at TEPCO's Fukushima Nuclear Power Stations”, transmitted by Permanent Mission of Japan to IAEA, 7 June 2011, is available at:
Morgan Brown, P.Eng., FCNS