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Lessons Learned from the Fukushima Nuclear Accident for Improving Safety of U.S. Nuclear Plants (2014) / Chapter Skim
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Appendix C: Detailed Accident Time Line
Pages 315-319

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From page 315...
... (15:37) and DC power DC lost at +60 min DC lost at +60 min DC available until (batteries)
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From page 316...
... j Estimated time of +4 h to +7 h +75 h to +85 h +36 h to +40 h core damagek First indication +8.2 to +14.1 h of offsite release of radioactive materialsl Containment +9.7 h/~+24 h +26.7 h/not +29.5 h/+42 h venting successful preparation/ successm Hydrogen +24.8 h Noneo +68.2 h explosionn Injection of +15.0/+28.8 h None/+77.2 h +42.6/+46.4 h freshwater/ seawaterp Restoration of March 20 March 20 March 22 offsite AC power NOTES: ADS = automatic depressurization system; EDGs = emergency diesel generators; HPCI = high-pressure coolant injection system; IC = isolation condenser; MSIV = main steam isolation valve; RCIC = reactor core isolation cooling system; RPV = reactor pressure vessel; SRV = safety relief valve. aTimes are from the time of the earthquake in minutes (min)
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From page 317...
... While the air-cooled Unit 2 emergency diesel generator was running at the time, the electrical switchgear located belowgrade was flooded and subsequently failed. Although there were intermittent signs of power on some indicators in Units 1 and 2, reliable DC power was only available by connecting arrays of scavenged vehicle batteries to selected systems and instrumentation in the control rooms.
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From page 318...
... As discussed in this report, the loss of all power caused by the tsunami led to automatic closing of valves which could not be reopened without AC and DC power. The entire core of Unit 1 may have penetrated the reactor pressure vessel.
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From page 319...
... Unfortunately, the open blowout panel provided direct access to the environment of radionuclides escaping from the primary containment system as a result of leakage paths. pSeawater injection was aligned earlier in each case and even started earlier especially in Unit 2, but flooding, the unavailability of fire trucks, lack of fuel for the fire trucks, RPV depressurization delays and the consequences of hydrogen explosions all contributed to much later injection times than planned and even then the injections were often interrupted.
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Key Terms

  • containment pressure
  • emergency diesel
  • pressure vessel
  • diesel generators
  • reactor building

  • reactor pressure
  • water level
  • suppression chamber
  • core debris
  • pressure boundary

  • design pressure
  • reactor water
  • fire trucks
  • blowout panel
  • hydrogen explosion

  • isolation valves
  • volatile fission
  • steam isolation
  • isolation condenser
  • reactor core

  • suppression pool
  • debris melted
  • main steam
  • manually tripped
  • scavenged vehicle

  • zirconium oxidation
  • noise heard
  • max containment
  • remained available
  • significant steam


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