Naked Science Forum
Non Life Sciences => Technology => Topic started by: Madidus_Scientia on 16/03/2011 02:49:24
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Since the problem was that the diesel generators for cooling failed, if the reactor did not automatically shutdown and therefore maintained power production, keeping the coolant water flowing, would the plants have been ok?
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You would think so, but presumably that was not an option. I would speculate that there was so much infrastructure damage that they could no longer keep producing. What I find really surprising (and very depressing) is that these reactors are anything but "fail safe". Not that anything can ever be 100% fail safe of course, but there seem to be too many weak links here.
BTW, the news is now much worse. They are pulling out the fifty workers who were trying to contain the problems because the radiation levels are too great.
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I was under the impression that they automatically shutdown from a quake, or was it a human decision?
No it isn't fail safe, but it did take a hell of a quake and a tsunami for it to happen.
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What I find really surprising (and very depressing) is that these reactors are anything but "fail safe". Not that anything can ever be 100% fail safe of course, but there seem to be too many weak links here.
If the only efficient way to extract power from nuclear energy is to have the core set-up on the brink of Neutron run-away, then how could anyone build (let alone maintain for 40 years) a power-station that could be even close to "fail-safe" under the conditions suffered in Japan?
Short of a mechanism to tip the whole intact core into the sea, I can't see a way that this amount of energy could ever be removed 'safely'.
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Short of a mechanism to tip the whole intact core into the sea, I can't see a way that this amount of energy could ever be removed 'safely'.
I seem to remember that certain types of reactors are automatically moderated in the event of a loss of power.
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This form of Nuclear power station will create a residual amount of heat for many days after it has been shut down - perhaps as much as a 5-10 MW - this boils off already hot water very quickly. It is not analogous to cooling a red hot piece of metal - the core continues to generate heat. ie they do not function with an on/off switch - which is why they have multiple levels of redundancy in backup cooling to allow the necessary gradual shutdown. Unfortunately the scale of the earth quake and tsunami removed all levels of standard backup
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The core continues to generate heat from radioactivity and normally requires about ten days of cooling after the fission process has been shut down.
No doubt it would be possible to build a nuclear power station that would withstand a force 9 earthquake and a 10 meter tsunami but I doubt that the money could be raised to do this.
The real tragedy is this will put back the construction of safe modern power stations as did the fiasco at 7 mile island.
We will have to put up with power shortages while we depend on windmills, and dangerous hydro plants and coal fired plants spewing out CO2 and uranium.
In England we are cursed with olde worlde power stations that were designed primarily to produce plutonium for our military delusions.
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I just read that Tokyo Power almost has a new power line hooked up so they can keep the pumps running and get things back under control. Here's hoping that's true, although, with their track record, I would not be surprised if it's not.
It does raise a question about how much redundancy there was in the power connection to the grid. Hopefully it was better than the system that was used to attach Newark Airport. There were redundant power feeds alright, but some genius thought it was OK to put them in the same underground conduit. The system worked great, until somebody sliced both cables with a JCB (backhoe).
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It's over.
If a technologically advanced country like Japan cannot produce safe nuclear energy under any circumstances, we humans are dreaming.
I think it is technically possible to rely on nuclear power, but I think that it is politically impossible.
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Well its safer by orders of magnitude than coal. 12,000 coal workers die per year
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Well its safer by orders of magnitude than coal. 12,000 coal workers die per year
Coal workers know the risks they take. Do the consumers of nuclear power know the risks they take?
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Reading about this, it is just a calamity of errors.
But, perhaps it just looks that way from hindsight.
Japan obviously has had lots of earthquakes... so locating a nuclear powerplant right above a fault-line on the coast with risk of tsunami inundation probably isn't the best of ideas.
The Nuclear Power Plants take a couple of days to shutdown. However, Japan was experiencing very strong foreshocks starting on March 9. So... why did they wait until March 11 to shut down the nuclear power plants.
Although, I suppose some people probably thought the March 9 quake was the main event, and the following (smaller) quakes were aftershocks. And, notes indicate that foreshocks are not always good predictors of a main quake.
Part of the problem is that shutting down half the countries reactors as a preventative measure would have been crippling, especially if the series of quakes continued to get weaker, rather than getting worse.
But... if I thought there were active nuclear reactors in a zone experiencing 7+ earthquakes, I'd expect them to shut down the reactors until the quakes had settled down. How long does it take to power the plants back up after a shutdown?
The plants were supposed to have had steam driven pumps that could technically run without power, but became ineffective under the low pressures during shutdown. But, they are still generating a lot of heat... can't there be a system designed to capture and utilize that excess heat, even during shutdown?
Madidus makes a good point that if the plants had continued to generate power, they might have been ok, provided that there wasn't extensive earthquake damage to the reactors and their piping.
While a fixed blade windmill can't function under no load, a steam turbine should have a bypass mode to vent off excess pressure.
Why weren't the backup generators better protected from a tsunami? That had to be considered in the plans. Heck the Nuke Plants must be over 30 feet tall, couldn't they put a generator in an upper level?
How could they possibly run out of seawater when filling the reactor cores?
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Yeah why did the seawater thing fail? Did their pumps break? Or weren't fast enough or something?
Also, you'd think that they'd have a pipe that runs from inside the plant to well outside it incase of a situation like this, so that instead of trying to drop water from choppers and water cannons they can just pump it in. An onsite reservoir of fresh water to buy them some time might help too, although i'm not sure if they did have one and they already used it or what.
But on the matter of dropping and spraying water in, would this have been possible if the hydrogen explosion didn't blow the roof off? And does anyone know what kind of flow rate of water they would typically need?
Some might say it's easy for us to come up with this kind of stuff in hindsight, but alot of people get paid alot of money to run simulations of disasters and think about all this kind of stuff. So surely this stuff has been thought of, but just not implemented?
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I'm not sure of the actual flow rate.
Wikipedia had some good notes on the disaster, and nuclear plants.
http://en.wikipedia.org/wiki/2011_T%C5%8Dhoku_earthquake_and_tsunami
http://en.wikipedia.org/wiki/Fukushima_I_nuclear_accidents
http://en.wikipedia.org/wiki/Timeline_of_the_Fukushima_nuclear_accidents
The volume of water to fill the secondary containment building sounds like it is greater than what would be in an ordinary water reservoir. The Japanese did also loose one dam, and sustained damage to several dams. They should have had access to plenty of seawater. And, while the salt water may damage components of the nuclear plant, at least plants 1,2,& 3 will likely have to be completely rebuilt.
I didn't see any notes on the flow of water required for cooling the reactors. It has to be high. A pressure differential can be problematic, but they should be able to lower the pressure to allow for secondary water injection.
I don't see any notes on Diesel pumps.
While electricity and water don't go well together... technically a well designed diesel engine/pump should be able to function just fine 30 feet underwater.
In a sense, this is a major design flaw in a lot of commercial construction the power distribution of buildings going through the basement, without any secondary systems that don't go through the basement.
We saw it with Hurricane Katrina. Many of the hospitals in the affected area would have otherwise been fine, they just lost power because the backup generators were flooded in the basement. Of course, water and sewage would eventually have been a problem, but they should have been able to maintain their systems for at least a week or so.
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At one point, I heard that the diesel generators simply ran out of fuel. For what reason I do not know. Hopefully it was not just because of a communication foul up, but I would not be in the least surprised to learn that some poor guy was screaming for the army to deliver an emergency supply of fuel, but his request had to be "processed" through the appropriate channels before the guys at the top even knew they had to make a decision.
If this sounds like an observation on culture, it is.
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I would not be in the least surprised to learn that some poor guy was screaming for the army to deliver an emergency supply of fuel,
There was probably an American Marine there... who thought the request was for an order of Sushi!!!
I suppose one should keep in mind that there are some pretty extraordinary conditions. Debris everywhere. Damaged roads. And continuing aftershocks.
I've always thought that our military ships, especially the big nuclear carriers and nuclear subs should have the ability to supply emergency civilian power.
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Since the problem was that the diesel generators for cooling failed, if the reactor did not automatically shutdown and therefore maintained power production, keeping the coolant water flowing, would the plants have been ok?
Leaving aside the risks of trying to keep the reactor running when there's a risk of damage to the mechanics and the electrical control systems...
Remember that the electrical connection to the outside world was severed in the earthquake... you have to dump the energy somewhere if you can't send it anywhere useful. They might have some heaters in the sea - but I very much doubt they could dump the full electrical power of the the three operating reactors for any length of time. The total output of those three stations was somewhere in the ballpark of 2000MW (MEe = electrical).
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http://www.iaea.org/newscenter/news/tsunamiupdate01.html
http://mitnse.com/
Reactors 1,2, and 3 have electrical outputs of 460/784/784 MW electrical, and 1380,2381,2381 MW thermal (i.e. heat output of the core).
To put that into some kind of perspective, each nuclear core, when operating normally, would have been generating as much heat as around 6-700000 electric kettle (or 3kW domestic immersion heater) elements. That's something of the order of 100 builder's refuse-skips full of immersion-heater elements!
After shutdown (when the nuclear chain reaction is stopped) you still get a residual "decay heat", which by now should be about 0.4% of full power, or around 10MWth. That's still half a skip-full of immersion-heater elements... and the nuclear core will continue to generate this much heat (falling only very slowly) for weeks and weeks. So the task now is keeping that cool. We know what happens if you boil a kettle dry - the element gets red hot quite quickly, and red-hot means 1000-2000Celcius).
Hence the need to pump a LOT of water into there.
Apparently Unit 1 was due to be permanently shut down in just 2 weeks time, after about 40 years of service. So destroying that reactor by pumping in seawater is no great loss. I understand Units 2 and 3 also only had a couple more years of life ahead of them.
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Since the problem was that the diesel generators for cooling failed, if the reactor did not automatically shutdown and therefore maintained power production, keeping the coolant water flowing, would the plants have been ok?
No the diesel generators were back up, the actual plant worked off of the grid. The generators come on simply to keep the reactors cool.
And no they wouldnt have been ok if they carried on because the grid connection to the plant got broken, plus if they had not shut down they would have over heated even more.
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At one point, I heard that the diesel generators simply ran out of fuel. For what reason I do not know. Hopefully it was not just because of a communication foul up, but I would not be in the least surprised to learn that some poor guy was screaming for the army to deliver an emergency supply of fuel, but his request had to be "processed" through the appropriate channels before the guys at the top even knew they had to make a decision.
If this sounds like an observation on culture, it is.
No, the back up generator were taken out by the sunami, but I think they only had fuel for a few hours, enought fuel or not the sunami took them out, according to news bulletins at the time.
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Yeah why did the seawater thing fail?
Pumping in dirty sea water was not a good idea, they pumped in fish and crabs and mud with it. it was a last ditch attempt to keep them cool. although they must have had some form of power to pump in the sea water.
Did their pumps break?
It's hard to say what is working and what is not, apparently after they hooked up the mains power over this weekend they flicked the switch and nothing happened. Electrics are down, pipes are busted, pumps broken, either from the earth quake, the tsunami or the pressure explosions that happened a few days later and the fires.
Or weren't fast enough or something?
that's an understatement, where they have not been slow they have been limited. Gotta say a huge thankyou to the workers but they should have been assisted more.
Also, you'd think that they'd have a pipe that runs from inside the plant to well outside it in case of a situation like this, so that instead of trying to drop water from choppers and water cannons they can just pump it in. An on site reservoir of fresh water to buy them some time might help too, although i'm not sure if they did have one and they already used it or what.
But on the matter of dropping and spraying water in, would this have been possible if the hydrogen explosion didn't blow the roof off?
maybe not, so in some ways the roof going did allow water to be pumped in.
And does anyone know what kind of flow rate of water they would typically need?
The water circulates inside the reactor, it goes in cool comes out hot gets cooled and goes back in again. The speed might be relative to the temp and so vary.
Some might say it's easy for us to come up with this kind of stuff in hindsight, but alot of people get paid alot of money to run simulations of disasters and think about all this kind of stuff. So surely this stuff has been thought of, but just not implemented?
Yeah the industry love to save money, these plants should never have built in the first place.