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Nuclear accident follows Japanese earthqauke
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mr brightside



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PostPosted: Wed Jul 13, 2011 11:01 am    Post subject: Reply with quote

DominicJ wrote:
But the tank of water can be passivly cooled as well....


Aye, i agree, but how does the water get back up there? If it is by pumping then the pump is a failure point versus the convection of a coolant gas naturally moving around the loop.
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biffvernon



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PostPosted: Wed Jul 13, 2011 11:45 am    Post subject: Reply with quote

And what happens after something you didn't think of happens and the whole thing has exploded?

No matter how 'safe' you make it you are left with two issues: you've got a pile of stuff that produces heat, remorselessly, for a very long time, no matter what, and that pile of stuff is poisonous to even get close to and will stay that way for a very long time.

Other energy sources don't suffer from these two issues.
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DominicJ



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PostPosted: Wed Jul 13, 2011 11:56 am    Post subject: Reply with quote

Mr Brightside
If the core is passivly cooled, there would be the core, and a water store above it.
Make the water store big enough so the core can dump everything into it with just atmospheric cooling.

If I were building the next generation of nuclear power plants, I'd be colocating them with existing or new built hydro.

Biff
How many people have died because of the nuclear accident?
How many died because of the Tsunami?

Keep on banging that anti nuclear drum, an idiot might join you one day.
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PS_RalphW



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PostPosted: Wed Jul 13, 2011 1:06 pm    Post subject: Reply with quote

Does anyone here have a link to detailed plans for a passively cooled PWR? Has one ever been built? Has it been tested in operation - with a core due for refuelling, which is when the need for post-shutdown cooling is highest?

A lot of posturing on this thread and very little direct evidence.
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mr brightside



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PostPosted: Wed Jul 13, 2011 1:29 pm    Post subject: Reply with quote

DominicJ wrote:
Mr Brightside
If the core is passivly cooled, there would be the core, and a water store above it.
Make the water store big enough so the core can dump everything into it with just atmospheric cooling.


Dom, i'm not sniping or anything i was just trying to establish whether the water will be returned to the gravity fed tank after passing through the core or drained to an effluent plant. Draining to an effluent system would be the only way for the system to be failsafe, where the tank is big enough to provide sufficient feedrate to cool the core continuously until residual heat is removed.

Or, are you saying the water would be static in the lines and acting like a big radiator, with the water tank acting as an expansion/storage medium.
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kenneal - lagger
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PostPosted: Wed Jul 13, 2011 1:32 pm    Post subject: Reply with quote

DominicJ wrote:
Mr Brightside
If the core is passivly cooled, there would be the core, and a water store above it.
Make the water store big enough so the core can dump everything into it with just atmospheric cooling.

If I were building the next generation of nuclear power plants, I'd be colocating them with existing or new built hydro.

Biff
How many people have died because of the nuclear accident?
How many died because of the Tsunami?

Keep on banging that anti nuclear drum, an idiot might join you one day.


Some of the French inland stations have had to be shut down because of low water levels during periods of drought. the cooling volumes a huge, Dom. What would you do in an emergency, boil the dammed water?

The deaths will come over the next few years and will be attributed to anything else as they have been with Chernobyl. The land flooded by the tsunami will be back in production within a few years at most. The land polluted by nuclear fallout will be out of production for decades at least. If any of our Severn estuary reactors blows up there will be a huge pall of fallout blowing west towards London across some of our precious farmland as well as a few cities. What price cheap energy when we lose the use of say Bristol.
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biffvernon



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PostPosted: Wed Jul 13, 2011 1:46 pm    Post subject: Reply with quote

DominicJ wrote:

Biff
How many people have died because of the nuclear accident?
How many died because of the Tsunami?
It's comparing apples and pears, an accident with technology and a natural disaster. Something around 25000 died in the tsunami. The radiation releases could eventually be responsible for premature death numbers an order of magnitude greater, but of course the nuclear industry is reluctant to accept the 'linear no threshold' model favoured by biologists so they and Dom are likely to attempt to pour scorn on such figures. We won't know the truth for a very long time.
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PS_RalphW



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PostPosted: Wed Jul 13, 2011 2:05 pm    Post subject: Reply with quote

DominicJ wrote:
Quote:
Is the gravity feed system designed only to remove residual decay heat after an emergency shutdown? Obviously a tank of water is finite.


But the tank of water can be passivly cooled as well....


This reminds me of when I visited a remote Himalayan village, where the locals had to climb 5000 feet down the mountain, carrying their wheat on their backs, to the nearest water driven mill where it was milled into flour. They then carried the flour (that they didn't sell in the market) back up 5000 feet home to eat.

Some charity paid for a small diesel powered mill to be carted up the mountain by some poor suffering donkey so that the locals didn't need to do this. Unfortunately, the locals couldn't afford the running costs of the diesel, so it didn't get used.

My host, a charity funded school teacher, wanted to power the mill using a water chain powered by a rain water header tank a couple of hundred feet up the mountain. Unfortunately he realised that this would use their entire supply of fresh water, so he devised a plan where only part of the water from each bucket was emptied at the bottom, and the rest of the water would be carried back up the hill to the tank...
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adam2
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PostPosted: Wed Jul 13, 2011 2:47 pm    Post subject: Reply with quote

A normally functioning nuclear power station does indeed need vast volumes of cooling water.
This water is not consumed but is returned to sea or river slightly warmer.
In time of drought, the output may be limited due to low water flow or low level.

In case of an emergency shutdown, the full cooling water flow is not needed. With control rods inserted into the reactor heat output is much reduced and less water needed.
The heat produced reduces in time, as does the amount of water needed.

As a last resort the cooling water might be allowed to boil, a great deal of heat can be removed thus.

It should be possible to design a nuclear reactor that only requires active cooling whilst in use, and for perhaps a week after shutdown.
Convection circulation being sufficient after this time.
A large reservoir of water and means of replenisment would be needed, a large reserve would be needed for the first year or two after which rain might be enough. That would give a reactor that would be relatively safe even if suddenly abandoned.
I cant see it happening though. The pro nuclear lobby would say this is a needless expense, and the anti nuclear lobby would say no nukes no matter how safe they are claimed to be.
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DominicJ



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PostPosted: Wed Jul 13, 2011 2:54 pm    Post subject: Reply with quote

Mr Brightside
A woodburning boiler has to be passivly cooled, so the boiler sits on the floor, and suspended above it, is a big water tank, the boiler heats the water in contact with it, the warm water rises, and is displaced by cool water from the top, which is warmed up and displaced by the cooler water from above and the cycle continues, until either the cooler water at the top is no longer cool and the water tank explodes, or the reactor is unable to keep the entire volume of water boiled, so its safe.

Basicaly yeah, giant radiator.

Ken
Of course I would, I dont even see that as a question, boil a river dry or explode a nuclear reactor?
But as I said, I wouldnt use a river, I would use a lake.

I fully believe some people will die, or have their lives shortened because of the nuclear part of the recent tsunami. But 22,000 people died because of the none nuclear part (how many of the missing do you think are going to be found now?). Nor do I believe much land will be lost, people still live at ground zero Hiroshimi and Nagasaki.



That should be an extremely bad picture, the blue bit is water, the grey bit the dam, the green bit earth, and the black bit can be our nuclear power plant.
http://en.wikipedia.org/wiki/Kielder_Water

Lets for a moment, assume this was built in Kielder Water.
Kielder holds 200bn litres, and took two years to fill, so has annual inflow of 100bn litres.

The worlds largest reactor is currently the 1600mw EPR in Finland, which isnt actualy built yet, and has a thermal energy of 4500mw (I thought nuclear was more efficient than that, but never mind).

Water has a specific heat capacity of 4.18j, so it requires 418trn joules to raise the temperature of one years flow one degree, which the plant would pump out in 26 hours.
Wow, that is a lot quicker than I thought.


But, Kielder Water is hardly the UK's biggest river, and 1600mw is a massive reactor, and even that, ignoring any cooling through other sources, would take 195 days to boil the reservoir.
Which seems pretty safe to me.

A 400mw reactor would be capable of nearly boiling the run off.
Probably bad for the environment, but well, what isnt.

The River Thames has a flow of over 5 times the Kielder.

Well, that was interesting.
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DominicJ



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PostPosted: Wed Jul 13, 2011 3:00 pm    Post subject: Reply with quote

Biff
Let me get this straight.
A tsunami cracks a gas main, which explodes, and kills me, and thats a natural disaster.
A tsunami destroy the cooling pumps of a nuclear reactor, which explodes, and kills me, and thats a nuclear accident and so somehow different?


People died because the Tsunami defences were inadequate.
That the same reason the cooling pumps were destroyed.
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kenneal - lagger
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PostPosted: Wed Jul 13, 2011 3:36 pm    Post subject: Reply with quote

The cooling pumps were destroyed because a human made a design error. What human design error is going to be made in the UK reactors or are UK or French design engineers less human than Japanese ones?
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biffvernon



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PostPosted: Wed Jul 13, 2011 3:48 pm    Post subject: Reply with quote

DominicJ wrote:
Biff
Let me get this straight.
A tsunami cracks a gas main, which explodes, and kills me, and thats a natural disaster.
I'd call that a failure of gas main technology rather than natural disaster. Getting washed away by a mighty wave might be counted as a natural disaster. Of course natural and man-made blend into one another and I'm sure you are clever enough to think of an example which is hard to categorize. There's nothing natural about nuclear power stations.
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biffvernon



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PostPosted: Wed Jul 13, 2011 3:49 pm    Post subject: Reply with quote

kenneal wrote:
What human design error is going to be made in the UK reactors or are UK or French design engineers less human than Japanese ones?
I think the power station was designed by Americans. (Always a sound policy to blame Americans Wink )
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biffvernon



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PostPosted: Wed Jul 13, 2011 3:56 pm    Post subject: Reply with quote

adam2 wrote:

In case of an emergency shutdown, the full cooling water flow is not needed. With control rods inserted into the reactor heat output is much reduced and less water needed.
Indeed. The shut down heat output is only a couple of percent of the operating power. It was very fortunate that the earthquake was a long way off out to sea and not directly under the power station, allowing the control rods to be inserted rather than being distorted by the earthquake and getting stuck. Had that happened there would have been a very much bigger bang.
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