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8.8 Earthquake in Japan
type568
Member #8,381
March 2007
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So it's far beyond control. I suppose the reactor design shouldn't let too much of it out, but.. It's likely reactors are permanently unusable, right?

Append:
And no, I don't plan to sell Nikkei anymore :(

Crazy Photon
Member #2,588
July 2002
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gnolam said:

The reason you build plants close to the sea is so you can run the last heat exchange on seawater in an open cycle

Good point. They should upgrade the plants to have a backup passive cooling system then.

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23yrold3yrold
Member #1,134
March 2001
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I just came across this. Words fail me.

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MiquelFire
Member #3,110
January 2003
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23, you're late.

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23yrold3yrold
Member #1,134
March 2001
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Really? Sorry; I didn't see it here (still don't). Just had a friend link it on Facebook and thought the ignorance was amusing. :)

EDIT: NM, I see it now. :P Er ... post++! ::)

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ReyBrujo
Moderator
January 2001
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gnolam said:

The reason you build plants close to the sea is so you can run the last heat exchange on seawater in an open cycle, and thus don't have to build large, expensive cooling towers.

Are you sure? Because It is probably the first time in the industry's 57-year history that seawater has been used in this way, a sign of how close Japan is to facing a major nuclear disaster following the massive earthquake and tsunami on Friday, according to the scientists.[1]

There is a very nice video in the NHK showing the three cooling stages: the electrical one that is usually used, the diesel one, and the condensation one. The sea water was a last try that had never been planned. In fact analysts in the same article admit that Japan has already sacrificed those reactors, as they will likely become completely damaged by using this seawater to cool them down.

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Jonatan Hedborg
Member #4,886
July 2004
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ReyBrujo said:

Are you sure?

They (normally) use it to cool the cooling water, afaik. Instead of cooling it in cooling towers.

gnolam
Member #2,030
March 2002
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ReyBrujo said:

Are you sure? Because It is probably the first time in the industry's 57-year history that seawater has been used in this way, a sign of how close Japan is to facing a major nuclear disaster following the massive earthquake and tsunami on Friday, according to the scientists.

Yes. What they're doing now, which has apparently never been done before (because, as miran pointed out, it's tantamount to junking the reactor), is injecting the seawater directly into the reactor.

gnolam said:

The reason you build plants close to the sea is so you can run the last heat exchange on seawater in an open cycle

(Emphasis added)
The reactor coolant loop is always completely closed (both because you want the coolant to be as pure as possible, and because it will become slightly radioactive) - in a boiling water reactor, the coolant water goes through the reactor core, boils into steam, goes through a turbine to produce electricity, and then goes back in after condensing back to liquid water. The seawater never goes anywhere near the reactor. Rather, the seawater is used to cool the steam in the condenser (basically, a big heat exchanger - so the two never mix).

Oh hey, Wikipedia has a diagram:
{"name":"740px-Schema_reacteur_eau_bouillante.svg.png","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/3\/3\/3370bce98934e9d432ee725cc2875dbf.png","w":740,"h":431,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/3\/3\/3370bce98934e9d432ee725cc2875dbf"}740px-Schema_reacteur_eau_bouillante.svg.png
The condenser is #12.
If you draw the condenser's coolant from the sea (or a nearby river or lake), then you can run it on an open cycle: pump as much as you need to run it through once (the Swedish plants require 20-40 m3/s), and then just dump it back out somewhere. If you can't do that, then you have to reuse it - and that means cooling it yourself. Which in turn means huge cooling ponds or cooling towers.

This isn't unique to nuclear plants, BTW - any thermal power plant (coal, oil, gas...) has the same problem.

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ReyBrujo
Moderator
January 2001
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Aha, gotcha, thanks for the explanation.

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光子「あたしただ…奪う側に回ろうと思っただけよ」
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gnolam
Member #2,030
March 2002
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... and it looks like #2 just went up as well.

From the BBC's feed:

Quote:

2308: An explosion is heard at Fukushima's second reactor, the Kyodo news agency reports.

2311: The news agency said the blast was heard at 0610 local time on Tuesday (2110 GMT Monday). No other details were immediately announced.

2316: Kyodo now says that the suppression pool may have been damaged at the second reactor.

...

2333: More details on the reported blast at Fukushima's reactor 2. The explosion is feared to have damaged the reactor's pressure-suppression system, Kyodo says. It adds that "radiation tops legal limit" after the explosion.

2340: Tokyo Electric officials are now holding a news briefing. They say the blast at reactor 2 happened "near the pressure vessel". They also confirm that some staff at the nuclear power plant are being evacuated.

From Kyodo News:

Quote:

08:28: Higher radiation levels measured in Ibaraki -- south of Fukushima

08:33: Radioactive materials feared to be leaking

Quote:

09:41: Fukushima's No. 2 reactor container damaged, radiation leak feared

Quote:

11:14 Fire occurs at Fukushima plant's No. 4 reactor

... WTF? #4 wasn't even active when the quake hit.

Quote:

Hydrogen explosion occurs at Fukushima No. 4 reactor

... I think I'm going to give up updating this now. :-/

[EDIT]
Feed updates.

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miran
Member #2,407
June 2002

http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1300157986P.pdf

It looks very very very bad. Cores in reactors #1 and #3 are severely damaged (possibly melting), but that's not really much of a problem, that's still under control, but #2 is in serious trouble. It seems the reactor vessel has been damaged which means that when they vent the containment to reduce the pressure (which is necessary, otherwise the containment would be destroyed), they also let a lot of radioactive material escape into the environment. Radioactivity at the site border has increased by several thousand times since the explosion at #2.

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Mark Oates
Member #1,146
March 2001
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allegro.cc is delivering better info than the news! Not that that's really hard to do, I guess, seeing that I get American news.

type568
Member #8,381
March 2007
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I'm a bit confused about how it works.. If it is overheating, why then can't the heat be used to generate power to remove the heat.. ?(oh well, or send energy to network giving it to those need it)

Arthur Kalliokoski
Second in Command
February 2005
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type568 said:

If it is overheating, why then can't the heat be used to generate power to remove the heat..

You want to go in and install a steam turbine unit personally?

They all watch too much MSNBC... they get ideas.

miran
Member #2,407
June 2002

Latest update: http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1300168169P.pdf

There's also trouble at unit #4 which was down for maintenance at the time of the quake, but the problem occured with the spent fuel pit. Spent fuel still gives off significant amounts of heat years after it's taken out of use, so it needs to be cooled down (spent fuel is usually stored on site for decades after it has been used). With the cooling systems offline the temperature in the spent fuel pit went way up, hydrogen formed, it accumulated in the building, then there was an explosion and now there's a fire. I think the same thing could easily happen at units #5 and #6.

Radiation at the site is getting quite significant. People within 20km of the site are being evacuated and pepole within 30km are asked to stay inside. There's always some background radiation (from the earth, the sun, etc.) with the worldwide average being about 0.27μSv/h (here at our site we measure about 0.07μSv/h, I don't know what it is in Japan because it varies locally). The current rates are 38.5μSv/h at Fukushima 2 (that's about 150x background) and 8217μSv/h at Fukushima 1 (about 30.000x background).

Btw, it's interesting how only Fukushima 1 is having problems while Fukushima 2 which is located only about 10km away is relatively OK.

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type568
Member #8,381
March 2007
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You want to go in and install a steam turbine unit personally?

Guess some other time. Although the Japanese have robots :P
But anyways.. Nuclear power plant is hell of a costly project.. And cooling isn't planned to run.. "this way"?

Or was it planned, but got damaged?

miran
Member #2,407
June 2002

type568 said:

Or was it planned, but got damaged?

Gnolam posted a good diagram that shows how cooling is done.

When the reactor shuts down, the residual heat is initially only about 2 or 3% of total reactor power and quickly goes down. This isn't nearly enough power to make sense to design the plant in a way to use this residual heat to generate electricity after the core is shut down. It's still a significant amount of heat though and needs to be removed somehow otherwise pressure would build up until the reactor vessel exploded. In normal operation when the reactor is shut down for refueling, residual heat in BWR type reactors is removed by pumping primary coolant through the primary loop and cooling that in the secondary loop with whatever cooling system is installed (cooling towers, river, lake, sea). The primary loop is completely sealed and the heat is transfered to the secondary loop with a heat exchanger and then that is transfered to the secondary coolant in a large condenser. All this normally takes a few days to complete. The pumps that pump the water in both loops are powered by an external power source (i.e. the national power grid or a dedicated backup power plant). In case the power grid is obliterated in some sort of freak natural disaster (e.g. a tsunami), on-site diesel generators are used to provide power (every plant stores enough diesel fuel to cool down the reactor just with the diesels). In case the diesels too are destroyed (tsunami), there are also backup accus to provide power for the most essential systems, but they last just about 8 hours, which by design should be enough time to bring external power or diesels online. In the case of Fukishima it took them longer than that, so for several hours the reactors were left without cooling. This resulted in increased pressure in the reactor vessel where steam formed and that had to be vented out quickly before the fuel melted. This meant that a lot of primary coolant was lost and the only way to replace it quickly was to inject sea water into the reactor as soon as power was available.

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type568
Member #8,381
March 2007
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miran said:

This isn't nearly enough power to make sense to design the plant in a way to use this residual heat to generate electricity after the core is shut down. It's still a significant amount of heat though and needs to be removed somehow otherwise pressure would build up until the reactor vessel exploded.

When there's pressure you can use it to generate power.

Append:

Quote:

The primary loop is completely sealed and the heat is transfered to the secondary loop with a heat exchanger and then that is transfered to the secondary coolant in a large condenser. All this normally takes a few days to complete.

What "all this"?

Append1:
Erm. Okay. But I still don't understand why not power the pumps with the actual heat.. Furthermore, the inner cycle isn't pumped, as I understand all the idea of a power station is to use the pressure of the inner cycle to generate power...

miran
Member #2,407
June 2002

type568 said:

When there's pressure you can use it to generate power.

Not nearly enough to make sense.

But actually 2nd generation BWRs are designed in such a way that they can use steam from residual heat to power a small turbine to power a pump that provides at least a little bit of cooling in case everything else fails. Unit #1 is 1st generation and doesn't have that system, that's why it was the first to go.

Quote:

What "all this"?

Cooling down of the core to a manageable temperature and pressure.

Quote:

Furthermore, the inner cycle isn't pumped, as I understand all the idea of a power station is to use the pressure of the inner cycle to generate power...

No, the primary coolant has to be forcefully pumped through the reactor core. Well, the primary loop is actually designed so that there is some natural recirculation (same effect as a chimney) but for the cooling to be really efficient, the coolant (water) has to be pumped through.

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type568
Member #8,381
March 2007
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Hopefully I've gotten some basic understanding of the state of things. Thank you.

Matthew Leverton
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January 1999
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Arthur Kalliokoski
Second in Command
February 2005
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You left out Pepsi(TM) expert! >:(

They all watch too much MSNBC... they get ideas.

miran
Member #2,407
June 2002

@Matthew: Is there anything wrong about being an expert in something? ???

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GullRaDriel
Member #3,861
September 2003
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That's was self pleasure. ;D

Ninja edit:

The crisis is going mad, number 3 and 4 are hit

And now (10h38) two breach of 8 meters are appearing on the number 4 !!

Now what are your estimations of the risk of melting ?

They're at level 6 of 7. Tcherno was the level 7... It's going bad my friends :-/

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gnolam
Member #2,030
March 2002
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And naturally, the knee-jerk mouth breathers are out in full force.

Quote:

EU energy chief Günther Oettinger has said Europe should consider whether it can meet its energy needs without nuclear power, Reuters reports.

Let me think about that for a minute... hmm...

NO

No no no no, big fat NO.


Building 100 coal plants is not an option. :P
Let's hope that guy doesn't get put in charge of transport. Then we'll have to stop flying after the first plane crashes. :P

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