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#219065 - 03/14/11 10:57 AM Re: Fukushima Nuke Plant Explosion [Re: Am_Fear_Liath_Mor]
Eric Offline
Enthusiast

Registered: 09/09/06
Posts: 323
Loc: Iowa
Originally Posted By: Am_Fear_Liath_Mor
OMG, just seen the video of the No 3 reactor totally disintegrate. Looks like the pressure reactor vessel was thrown 1500 ft into the air in large pieces. All that appears to be left is the steel building framework with a missing reactor pressure vessel.


I don't know what you thought you saw but it was not the reactor vessel. Based on the latest reports on radiation levels there is no way the damage was even close to the level you are indicating. Frankly if the explosion left the steel framework it wasn't anywhere near powerful enough to lift or damage the reactor vessel.

Right now the few facts that we have are consistent with a cooling system problem in the reactors with at least some damage to the reactor cores. The explosions were all most likely vented hydrogen gas which further indicates at least some of core material is getting too hot. They aren't talking much about radiation levels but it sounds like things have dropped off quite a bit. Yesterday there were credible reports of monitors reading 1000 mSv and today they are reporting reading around 50 mSv. That is a pretty clear indication that the reactor vessels are intact and matches the statements from TEPCO and the government.

The press hypes things enough, we don't need to help them with selling fear.

-Eric


Edited by Eric (03/14/11 10:59 AM)
_________________________
You are never beaten until you admit it. - - General George S. Patton


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#219069 - 03/14/11 12:03 PM Re: Fukushima Nuke Plant Explosion [Re: Eric]
Am_Fear_Liath_Mor Offline
Carpal Tunnel

Registered: 08/03/07
Posts: 3077



http://www.youtube.com/watch?v=T_N-wNFSGyQ

The video of the No3 explosion appears to be a little difficult to find i.e. you would think that it would be the main news video link on CNN and BBC etc but yet is conspicuously absent.

No2 and No4 reactors will mostly likely go the same way.

http://e.nikkei.com/e/fr/tnks/Nni20110314D14JF802.htm

Basically the Japanese authorities are taking incredulity to new levels.

Quote:
When you say "looks like..." do you mean "It is a fact that..." or "I am speculating that..."?


In the photo about 2/3 up the column slightly to the left is a darker solid object which would approximate to the size of part of the pressure vessel.

Too put the photo into perspective and also the size of the explosion the height of the explosive column would be higher than the WTC1 tower. Nuclear reactor buildings are re-inforced concrete heavyweight structures weighing many thousands of tonnes. I have a major problem believing the hydrogen explosion hypothesis put forward by the Japanese Government, to which they were so quick to put forward.




Edited by Am_Fear_Liath_Mor (03/14/11 01:06 PM)

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#219083 - 03/14/11 02:31 PM Re: Fukushima Nuke Plant Explosion [Re: MartinFocazio]
Pete Offline
Veteran

Registered: 02/20/09
Posts: 1347
As the mass confusion goes on ...

I am now seeing reports that fuel rods are exposed, at least on one of these reactors. IF that's true, and who knows any more, it tends to shoot down the idea that we've still got containment around all of these reactors. So you've got to at least factor in the possibility that there is a serious radiation leak over there.

If we add in the fact that seawater has been pumped onto the reactors, that could imply that some radioactive material is making it into the ocean. Hopefully the Japanese navy is monitoring radiation levels near the coast in that area. Despite this - I still think that using the seawater was a very good idea.

other Pete

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#219092 - 03/14/11 03:01 PM Re: Fukushima Nuke Plant Explosion [Re: Pete]
Am_Fear_Liath_Mor Offline
Carpal Tunnel

Registered: 08/03/07
Posts: 3077

http://www.gepower.com/prod_serv/products/nuclear_energy/en/downloads/abwr_plant.pdf

20. Spent Fuel Storage Pool

I suppose the Japanese authorities would have us all believe that highly radioactive spent fuel rods in the Spent Fuel Storage Pool have also been unaffected by huge explosion which has disintegrated the reactor building (throwing it 1500 feet into the air) as well. Well there is only minor radiation problems on the site according to the Japanese authorities so the pool must still be intact.

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#219094 - 03/14/11 03:16 PM Re: Fukushima Nuke Plant Explosion [Re: Pete]
unimogbert Offline
Old Hand

Registered: 08/10/06
Posts: 854
Loc: Colorado
Originally Posted By: Pete
As the mass confusion goes on ...

I am now seeing reports that fuel rods are exposed, at least on one of these reactors. IF that's true, and who knows any more, it tends to shoot down the idea that we've still got containment around all of these reactors. So you've got to at least factor in the possibility that there is a serious radiation leak over there.

If we add in the fact that seawater has been pumped onto the reactors, that could imply that some radioactive material is making it into the ocean. Hopefully the Japanese navy is monitoring radiation levels near the coast in that area. Despite this - I still think that using the seawater was a very good idea.

other Pete



No, and no.

"exposed fuel rods" probably means that they are not fully covered in water inside the reactor vessel. Probably does NOT mean that they are seeing the sky.
What it actually means is probably unknown to the talking heads that are reading from their scripts hastily written by people who don't understand either. (even if the translation from nuke-operator-Japanese to nuke-operator-English was perfect)

Pumping sea water IN does not imply leaking sea water out.
They are using an available source of water to continue replacing water that is being boiled off by the fuel. They have a problem that there's not a turbine they can dump the steam to because everything is broken, nor is there likely to be an approved steam dump because they don't have condenser function. So they are probably just venting steam and replenishing liquid as best they can.

Keeping the core covered is the prime directive.

As time goes on the decay heat output will diminish as the fission products finish they job of decaying.

The confusion is massive in the media and among lay people. Add to the fact that these are boiling water reactors rather than pressurized water reactors and even we ex-nukes have to work to understand the differences.

Feel free to panic because it is certainly a serious situation but I won't jump up and down with you because I think there is far too much misinformation to draw real conclusions. Besides, there's not a thing either of us can do about it.

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#219096 - 03/14/11 03:46 PM Re: Fukushima Nuke Plant Explosion [Re: unimogbert]
MartinFocazio Offline

Pooh-Bah

Registered: 01/21/03
Posts: 2148
Loc: Bucks County PA
A couple of questions about BWR systems in this crisis mode. You said:

Originally Posted By: unimogbert

Pumping sea water IN does not imply leaking sea water out.
They are using an available source of water to continue replacing water that is being boiled off by the fuel. They have a problem that there's not a turbine they can dump the steam to because everything is broken, nor is there likely to be an approved steam dump because they don't have condenser function. So they are probably just venting steam and replenishing liquid as best they can.


So, basically, what you're implying here is that the formerly closed loop of a BWR system, which is now lacking a condenser system, is operating as an open loop system (sea water in and steam out) which, while bad, is far less bad than an exposed core and the possibility of a 4,000 degree core temp that would drop through the bottom until it stalls X feet (50? 70?) below the reactor building, and likely making a big mess of things as it goes. The boric acid they are also dumping in is to deliver boron to help damp the reaction, correct?


Originally Posted By: unimogbert
As time goes on the decay heat output will diminish as the fission products finish they job of decaying.


I know that the decay heat output will diminish, but I was of the opinion that the lifetime of the fission products is quite long - but are you implying that the highly uncontrolled fission reaction is, by simple fact that it's highly uncontrolled, consuming fissile materials so that there will be less material to react, and thus less time spent reacting?

I know a core breach would be exceedingly bad, not so much for the fact that the core itself is melting, but from the influx of water into the hole that would result and the explosive reaction that would happen as cooling water, metals and so on mixed with the ultra-high temperature slag. That's the Bad Thing that I think we're talking about here, right?

And even a meltdown with a large "eruption" of steam and other particulates would eventually stabilize, right?

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#219103 - 03/14/11 04:25 PM Re: Fukushima Nuke Plant Explosion [Re: MartinFocazio]
Eric Offline
Enthusiast

Registered: 09/09/06
Posts: 323
Loc: Iowa
Since the reactors were shut down when the earthquake hit, the generation of heat through the fission of Uranium has basically stopped. Fission creates by products which continue to break down and generate heat. Nominal rule of thumb for most commercial reactors is it takes about 8-10 days for this to drop to a level where external cooling is no longer critical to maintaining core integrity.

Core integrity will basically start to fail about 45 minutes after loss of cooling water (air isn't a good enough conductor). Note this means exposing the rods to air, not loss of pumps. This initial failure will be the casing for the fuel rods which will start to melt around 2,000 degrees. If the temperature continues to climb the ceramic fuel pellets will be compromised around 3,000 degrees. As the temperatures reach these levels parts of the core will melt and may drop to the bottom of the reactor vessel, typically several inches of steel. If hot core parts hit unpressurized water on their way to the bottom they will create a lot of steam and some nuclear material can be carried along with the steam. If pressure is vented to maintain the reactor integrity, some radiation can escape with the steam. Mostly this will be very short lived particles. The makeup of the radiation is a big clue to the state of the core.

Sea water could be used in two ways within these BWRs. Most likely is they are pumping sea water directly into the reactor vessel. As long as this is possible it is the best way to minimize the release of radioactive materials since it will keep the rods immersed in a good conductor (water). They could also be circulating seawater around the outside of the reactor vessel to help manage the temperature inside the vessel and to keep the steel from melting even if a significant portion of the core were to slag at the bottom of reactor vessel.

Even worst case - complete loss of reactor vessel cooling water would be unlikely to result in the core material escaping through the bottom of the building. The final containment structure is very very thick and designed to disperse the core material to both contain and cool it. Of course with earthquakes and tsunamis this final measure may also be compromised so the game plan seems to be keep the cores as cool as possible within the primary containment system (the reactor vessels).

Here is a reference with a lot more information: Link

- Eric



Edited by Eric (03/14/11 04:27 PM)
_________________________
You are never beaten until you admit it. - - General George S. Patton


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#219105 - 03/14/11 04:29 PM Re: Fukushima Nuke Plant Explosion [Re: Eric]
MostlyHarmless Offline
Old Hand

Registered: 06/03/09
Posts: 982
Loc: Norway
Originally Posted By: Eric
Originally Posted By: Pete

Why are they not simply telling people the truth - or at least the facts as they have them? .... Layers and layers of denial. It's just not a good way to handle information related to a public safety hazard.


I actually think this falls more to Hanlon's Razor "Never attribute to malice that which is adequately explained by stupidity."

My guess is that the guys that know what is really happening are way too busy to give good status reports that have been boiled down to a level that laymen can understand. On top of that the pressure to say/do something (brought on by our continuos live news reporting) is resulting in a lot of vague / halfway accurate information being presented by the spokespersons for the company and government.


Old fashion public statement approach seems to be based on these axioms.
1) We (the corporation/government/whatever) can control the information flow.
2) Bad news will inevitable cause massive panic.

Both axioms are wrong. No nonsense "we're not delaying or hiding bad news here" - kind of information creates confidence. You may not like how people responds (such as voluntarily evacuating outside the 10km radius), but such reaction isn't really irrational, given the circumstances.


On the flip side, hiding or delaying bad news (or make people have that impression) will make your credibility and confidence evaporate faster than water in a run away nuclear reactor.


Just as Eric, I don't think anyone is really seriously trying to hide anything. What we're seeing is just a mix of several things:
- events happening too fast
- wishful thinking and denial
- public spokesmen giving only the "best possible" version of events
- the real knowledgeable people are up to their necks trying to cope with the situation.

But I would not be surprised if there is a little component of the old fashioned "too much information will cause mass panic"-attitude in this, too.

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#219106 - 03/14/11 04:39 PM Re: Fukushima Nuke Plant Explosion [Re: MartinFocazio]
unimogbert Offline
Old Hand

Registered: 08/10/06
Posts: 854
Loc: Colorado
MartinFocazio-A couple of questions about BWR systems in this crisis mode.

M-So, basically, what you're implying here is that the formerly closed loop of a BWR system, which is now lacking a condenser system, is operating as an open loop system (sea water in and steam out) which, while bad, is far less bad than an exposed core and the possibility of a 4,000 degree core temp that would drop through the bottom until it stalls X feet (50? 70?) below the reactor building, and likely making a big mess of things as it goes. The boric acid they are also dumping in is to deliver boron to help damp the reaction, correct?

U- Right. I don't know where the "steam out" is going for sure. It may be going to atmosphere thru an overpressure relief valve. Or it's going to an overpressure relief catch tank with only gasses going to atmosphere. Hopefully that's intact. Boron is a neutron absorber they are using to ensure the reaction is really shut down. Control rods may not supply sufficient negative reactivity to be d*mn sure or the design required boron injection for shutdown maintenance activities.
BTW- since it's a boiling water reactor, boiling the water in the core isn't automatically a big problem. Better a BWR having this problem than a PWR. The temperature of the fuel pellets is the important factor. Boiling in a PWR is automatically a Bad Thing. Then again, the boiling occurring now is perhaps not removing sufficient heat to keep the fuel pellets intact because there's no circulation under pressure like for normal ops.

M-I know that the decay heat output will diminish, but I was of the opinion that the lifetime of the fission products is quite long - but are you implying that the highly uncontrolled fission reaction is, by simple fact that it's highly uncontrolled, consuming fissile materials so that there will be less material to react, and thus less time spent reacting?

U- There are the prompt decay products which have half-lives of minutes to hours and the long term decay products which make spent fuel rods radioactive for years to millenia. The initial decay products decay to other radioactive elements which themselves decay further some of which are radioactive and they decay further and so on. At reactor scram the prompt decay products are numerous and produce nearly 10% of the reactor power that was steady-state just before the scram. This 10% drops off quickly (exponential decay) to something like 1% after a week (I probably have this figure wrong) Handling this overshoot reaction heating is what has to be done to prevent melting. It's a significant factor in a normal shutdown plan because it takes time and attention to deal with it.

M-I know a core breach would be exceedingly bad, not so much for the fact that the core itself is melting, but from the influx of water into the hole that would result and the explosive reaction that would happen as cooling water, metals and so on mixed with the ultra-high temperature slag. That's the Bad Thing that I think we're talking about here, right?

M-And even a meltdown with a large "eruption" of steam and other particulates would eventually stabilize, right?

U- "core breach" might mean different things to different people. Influx of water into the hole.... doesn't exactly match here.
The potential problem here is- loss of coolant sufficient to allow rods to uncover, rods uncover then the zirc fuel cladding "corrodes" (at a high rate btw creating H2 gas as the zirc oxidizes), exposing uranium pellets. This alone will release radioactive gasses to the area above the reactor which I think is venting to atmosphere. Erosion/corrosion of the pellets will release stuff into the liquid/steam AND if the fuel pellets melt, then their geometry wants to change. If the zirc cladding ruptures from the heat (probably will) the u-slag can escape the cladding and drain downwards.

U-At this point it's still only airborne gas (albeit radioactive) release from pellet, thru breached cladding, to relief valve venting.

U- But once the u-slag collects in a pool, there is the chance that the new geometry (of a puddle of hot fissionable slag) can go to criticality then supercriticality creating uncontrolled heat and radiation and fission products. Of course eventually the active badness has to stop as fuel is consumed or splattered about to where it no longer has the geometry to remain critical. Even Chernobyl stopped thrashing about.



I may not have these things quite right. Just thinking thru what I know to a new situation.

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#219110 - 03/14/11 04:49 PM Re: Fukushima Nuke Plant Explosion [Re: MartinFocazio]
Pete Offline
Veteran

Registered: 02/20/09
Posts: 1347
unimogbert ... thanks. That's an important distinction. Does "exposed fuel rods" mean that the rods are simply not covered by coolant, or that they are seeing the sky.

You can see how the language in these statements could be misinterpreted by people - especially those on the outside. Most of us do not have a clear understanding of the construction of the reactor - or any understanding at all. So it is not easy for us to interpret correctly what the plant managers are saying. I would argue that it's not OUR responsibility to try to make these educated guesses about the situation. Surely the agency running the nuclear power plant can do a much better job of providing essential information. What is to stop them taking one of their senior engineers and staging a daily press conference for one hour - so everybody gets a clear set of facts about the current situation?

I did notice that there are somewhat clearer remarks now coming from the Govt over there - including statements that they cannot verify the exact condition of the reactors and possibly some melting may have taken place. I also noticed the following statement ...

"Japan's meteorological agency did report one good sign. It said the prevailing wind in the area of the stricken plant was heading east into the Pacific, which experts said would help carry away any radiation. "

This may be helpful to Japan, but those of us on the west coast of the USA will be wondering a little bit. I am not really all that bothered, because the Pacific Ocean is a big place (!). Radiation can disperse over a wide area. But I have noticed that we are NOT getting a lot of info from our own government on possible radiation levels. Surely by this time the President has authorized airborne and shipborne sensors to check radiation levels - even if it's just a routine precaution. But no apparent statements from our Gov't either.

Even if the seawater on the reactors has caused some problems, I'm not sure that cooling them down wasn't the best idea. I don't necessarily think that was a mistake. However, the explosions are posing a serious risk to workers at the power plant.

other Pete



Edited by Pete (03/14/11 04:54 PM)

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