The tsunami of 11 March was the direct cause of the accident at Fukushima Daiichi NPP, not earthquake. A safe emergency shutdown was achieved within seconds of the
magnitude 9.0 earthquake, said the Fukushima Nuclear Accident
Investigation Commission composed of experts independent of plant owner
Tokyo Electric Power Company (TEPCO).
- Control rods were fully inserted within seconds
- All 13 diesel generators started as per design when tremors disconnected the grid connection
- Instrumentation was working correctly, as were cooling systems.
- The plant did cope with the shaking and maintained nuclear safety.
- Within an hour of the earthquake, however, almost the entire site was submerged to a depth of up to nine metres by a series of tsunami waves.
- >10 minutes: These flooded 6 of the diesels and ruined the supporting equipment of another 6. Only 1 diesel unit survived and this was used alternately to maintain essential systems at units 5 and 6 - using 1 of only 3 power distribution panels that had not been submerged. Some 36 other distribution panels throughout the emergency diesel generator system were made useless by water.
The 'direct cause': The
lack of emergency power and the inability to restore it eventually led
to the loss of 4 reactor units and a significant release of
radioactivity.
No comments:
Post a Comment