Earthquake in Japan....9.0...ouch!
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What an utter dullard of an idea.
One of the reasons the reactors go into automatic shutdown and the rods are lowered in, is for safety.
One of THE most dangerous conditions to have the reactor in should anything go wrong is having it at full power and therefore heat.
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Soldato
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good for the economy at least 
Caporegime
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You've ignored answers to all your questions many times over, I'll give it one more try. They were underground, there was this little thing that happened called a Tsunami, Diesel generators in a sealed room putting out fumes with no cooling would fail, hence the room isn't sealed, so one room, below ground level, not sealed, plus millions of tonnes of water above ground level. For about the tenth time now, the diesel generators failed because the building was flooded.
Why weren't the cooling systems powered by the reactor, because the reactor was shut off, why was the reactor shut off, because if they lost power links which is quite common in a huge earthquake, let alone a tsunami knocking power links over, or cooling had failed, things could have gone badly at full power. Remember cooling draws in water from the ocean, the Tsunami has a ridiculous amount of force, it could have damaged the cooling pipes, blocked them, thrown debrie from the ocean floor, or forced I should say, up the water pipes. Any number of things could have gone wrong so you shut the reactor down when a big "event" happens.
So I've been told 2 of the reactors were putting out close to 3000MW's of thermal energy at full capacity, the failed cooling and current cooling methods are having trouble dealing with the shutdown thermal energy which at this stage should be less than 1% of full capacity, or 30MW, it could be as low as about 0.5%, if the reactors had stayed at full capacity, and the same cooling problem had happened, almost certain reactor 2 and 3 would have had a full meltdown within a few hours.
Yes, in hindsight MAYBE keeping them on would have been better, in hindsight everythings pretty easy to get right.
The overwhelmingly safest choice in an earthquake in that situation is to shut down the reactor.
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The first thing they do is drop the control rods because if something got damaged they may not be able to later. But you are right, it seems, in this case at least, if they'd just left it running producing power everything would be fine.
Sods law.
the reactor was shut down and not producing power, had all reactors been left running we could have ended up with a worse disaster.. (however it looks like at least one is going to start reacting again anyway). I'm also sure the cooling equipment is not directly powered by the reactor anyway... if must at least go via some sub station that would ahve been trashed in teh wave..?
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These Japanese reactors were built 15 years before Chernobyl disaster happened.
Soldato
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You don't power cooling systems from the unit because if the unit trips off the power goes and so does the cooling. The grid is accepted as being a more relaible and secure source of energy than the power station. Cooling water systems are typically powered from the grid. In this case the back up to the grid was deisel generators. The problem was the tsunami damaged the electric supplies.
Soldato
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They also had battery backup as well apparently. For about 12 hours these worked in which time they did not arrange an alternative ?
Soldato
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Erm, no. There is, small as it may be, a probability that that engine failure COULD have brought that aircraft down.
*Fan blade* release has to be contained within the engine, *turbine discs* do not. For design purposes we assume infinite energy and that means anything in the discs ejection path *will* be destroyed/damaged.
Either way it doesn't matter about the failure mode. I was talking about the following:
During the *design* stage the seriousness and the probability of failure are weighed up against ways to mitigate the failure, and the cost to the aircraft as a whole in terms of performance. In theory you can mitigate every single failure scenario you can think of, but then the aircraft simply would not fly.
We design to a probability of catastrophe of a MAXIMUM of 1:20, yes 5%. [Note: In reality the probability of catastrophe is way lower than this]
Now if we talk in terms of the reactors. The designers at the time (or maybe since then if the reactor and it's systems have had updates - which I suspect is almost certainly true) found that the probability of failure of all *three* sources of power was found to be extremely low given the information they had at the time.
Now clearly they've been unlucky and that small probability of complete failure has caught them out, but now every nuclear power plant will have it's backup systems checked and double checked and now this kind of failure will be protected against.
Obviously the restrictions imposed on nuclear reactors are probably far more stringent than for the aerospace industry given they don't care about weight, but instead i'd imagine it's down to practicality and cost (as is everything...) I wouldn't be surprised at all if the reserve factors on the structure itself is in the 20+ region (aerospace work to reserve factors of 1.5 typically).
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Soldato
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armchair experts, you got to love em ain't ya.
Caporegime
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The one reacting, or listed as most in danger is reactor 4, theres no fuel in the reactor, its all in the spent fuel pool, however it was pretty much empty for a long time so heating up over time, but being spent I assume its at a lower radioactivity level than "good" fuel so heats up slower and less severely than newer fuel would. So not quite the same situation but maybe worse, because none of the reactors it would seem are directly open to the enviroment, even if some have damage and some of the buildings have damage if the fuel in a reactor got back to meltdown levels of heat and the nuclear reaction started when the melted fuel is together near the bottom of the reactor(where melted fuel would end up) theres several more layers of protection from the enviroment.
Either way its not quite the same, reactor 4 being empty, was off for inspection for a while and the fuel removed.
Actually I guess if they suspected a problem and were inspecting it, the fuel in the pond might not be all spent, but just removed until they wanted to restart the reactor?
Why do BBC compare it to three mile island and not our own nuclear accident...
http://www.lakestay.co.uk/1957.htm
http://www.lakestay.co.uk/1957.htm
I was listening to you
And I didn't ignore answers... I was drunk (it's St Patricks day for god's sake).Is it not possible to put a generator within the reactors containment itself, so that in order for the cooling system to fail the reactor itself would have to be destroyed, completely removing the liability of the power system?
Some unforeseen effect of a huge tsunami possibly compounded by earthquake damage. It's too early to speculate.
I assume you mean using the decay heat still being generated by the reactor after shutdown. The Advanced Boiling Water Reactors (ABWR) are able to operate in this manner but they came into service a quarter of a century after Fukushima was built. In fact all third generation designs incorporate various passive/self powered cooling systems in case of total power loss.
They are however meant to be stop gap measures and cannot operate indefinitely without external power.
Our government did such a good hush job almost no one has heard of Windscale
or 
or 
depending how you look at it.IIRC, no one knows how much radiation was released?
Associate
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The rods still undergo radioactive decay, the control rods simply stop the neutrons released by this decay from causing further decays. Unfortunately some of the energy from these decays is absorbed as heat, rather than taken away by the neutrons (or neutrinos for the other types of decay) .