The diesel generators and the switchgear operated for two hours following the tsunami. That means the diesels probably shutdown after the linited fuel in the day tanks was exhausted. The question is why weren’t the day tanks refilled from the main storage tanks.
That's where things are sketchy for me. I heard that they ran for an hour, and I also heard that they ran until the tsunami caused them to trip.
The "day tank" idea is plausable. Perhaps they didn't expect such a huge tsunami, having never experienced one before, so they never bothered to top off the day tanks. Once the main tanks got wiped, they were finished. Alternatively, maybe they were in the process of transferring fuel to the day tanks, but started on unit 6 (which either kept a single diesel on line, or regained it very quickly) at the other end of the plant property.
Frankly, I think that they were caught with their pants down just a bit, since this was an unprecidented event. I'm also certain that they had their hands full already when 1-3 scrammed because of the earthquake. The tsunami was the icing on the cake.
A DAY Tank, by definition is good for that long. The twinned 3 MW gensets I am responsible for will run for 26 hours on the "DAY" tanks assigned them. What happened in Japan is: the "day" tanks, the gensets, and the related switchgear itself were all WASHED AWAY in a wholly unprecedented and unanticipated by ANYONE, even in a worst-case-scenario, event.
To further refute your alleged "information" regarding the reactor incident in Japan, even though the PRIMARY backup system failed after one hour (when the tsunami hit), the secondary (battery) system kicked in right on schedule, powering the pumps for another EIGHT hours, until the battery system too failed, due to lack of recharge. NINE HOURS of backup power was there, but no-one ever thought that another power source COULDN'T avail itself before the auxiliaries were exhausted.
That the reactors, spent fuel pools and secondary containment structures have done so well in spite of the several orders of magnitude worse than expected events of last month is a TESTAMENT to the SAFETY of nuclear power!
The reactors in question were of 40+ year old design and were about to be phased out and replaced with newer, more modern and safer designed reactors. Your posts show how full of fear and misinformation the public is regarding nuclear power, which is the ULTIMATE in carbon-free electricity.
OH, BTW, where I work, the “Day” tanks are AUTOMATICALLY refilled from the main tanks when they reach the 40% full/60%empty mark. The valves open, the pumps start, and the day tanks are refilled to 85%, then the pumps shut down, even if the gensets are running. If there is insufficient fuel in the main tank, *I* get an alarm and , well, there better be a GOOD reason why I didn’t have fuel there.
Any operator in the control room can override this parameter, but there has never in my experience been any reason to override the level controller during non-emergent conditions.