Table 2.
Chronological accident description for Unit 1 of the Fukushima Daiichi NPP.
| Date | Time | Event |
|---|---|---|
| 2011/3/11 | 14:46 | Earthquake: reactor was automatically shut down. Decay heat was continuously generated |
| Loss of off-site power: diesel generators were automatically started. Therefore, AC and DC power was available in this period | ||
| 14:52–15:34 | IC cooling: reactor was cooled by Isolation Condenser (IC) with start-stop operation so that RPV cooling down rate did not exceed 55 °C/h. Unit 1 was operated to achieve a cold shutdown | |
| 15:37 | Tsunami hit: AC and DC were lost. IC was not in operation at this time | |
| After tsunami | Reactor Pressure Vessel (RPV) water inventory decreases due to no water injection | |
| After 20:00 | (PCV) pressure increased | |
| RPV bottom damage: Corium (melted fuel) slumping to PCV pedestal | ||
| 2011/3/12 | 14:30 | Regarding the containment vessel vent, the operation of AO valve of suppression chamber side was implemented at 10:17 am, and a pressure decrease was confirmed at 2:30 pm |
| 15:36 | Reactor building explosions |