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meltdown question

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ivymike

ivymike

Mechanical
Nov 9, 2000
5,653
ok, so a neighbor of mine used to work at the Japanese nuclear plant that's having the trouble currently. He's a bit of a blow-hard, and this evening he decided to bend my ear about the reactor. He said that he can't see why they're having so much trouble with it, they must just be trying to save money by not draining the water. I said that it sounds like they're having a heck of a time avoiding melting of the fuel and eventual loss of containment. He responded "all they have to do is drain the water and the fission will stop." I was like "um, no... they need the water in there to slow the reaction and help remove heat" He said "no, it's a fast neutron reactor, and the water is where the fission happens. if you drain the water, the fission will stop, but it'll get hot inside." Anyway, he started doing his "you have no business questioning me" routine, so I left. A quick look on wikipedia convinced me that I was more right about it than he was (boiling water reactor, and water helps to moderate), but it left me wondering whether there were any grains of truth in what he was saying, or things that he could have been told and misinterpreted during a safety course or similar. Are there any reactor designs where draining the water inherently results in stopping the fission?

 
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So is the issue one of keeping the spent fuel rods, which are outside of primary containment, but inside secondary containment, cool? If you're spraying water from a helicopter, does that mean that secondary containment has been breached?

Good Luck
--------------
As a circle of light increases so does the circumference of darkness around it. - Albert Einstein
 
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I'm not convinced that the picture is properly labled. What they're calling the "primary containment" looks a lot more like "secondary containment", and what they're calling "secondary containment" looks more like "a building". The explosions took place in the "building" and wrecked much of it.

That leaves the pool open to the helicopter dumps that don't look like they are accurate enough to hit the pool (but probably hit every single switchgear and electrical device in the building).

David
 
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zdas, I think they're past the point of worrying about sparks.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus
 
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Yeah, the fire suppression system (before the power went all the way out) probably already turned everything in the building into a total loss before the helicopters.

I keep thinking back to a fire we had to fight in a nuclear engine room (pressurized water reactor instead of boiling water reactor) 35 years ago--we found shorted electrical stuff months after everything was supposedly "fixed". I've been terrified of getting water on industrial electric distribution stuff ever since.

David
 
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I'm not convinced that the picture is properly labled
Click to expand...

It's right. Secondary containment is "a building". And not a particularly robust one at that.

From the level even with the top of the primary containment the building is nothing more than a steel frame with corrugated metal cladding.

Below that the siding is probably precast concrete panels.
 
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Reminds me of one of my favorite jones...
Lawyers are like fire extinguishers. You want them around if you need them, but once you use one, everything it touched is trashed.
Click to expand...
 
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The link provided by pmover states this:
Both the main containment structure and the secondary containment structure are housed in the reactor building. The reactor building is an outer shell that is supposed to keep the weather out, but nothing in. (this is the part that was damaged in the explosions, but more to that later).
Click to expand...
The picture provided by VE1BLL starts with secondary containment.

Does anyone know which is correct. Is the diagram correct, meaning that reactor building and secondary containment are the same, or does diagram simply not show the reactor building?

But perhaps more to the point, since they're apparently spraying from a helicopter, does that mean secondary containment is breached?

Good Luck
--------------
As a circle of light increases so does the circumference of darkness around it. - Albert Einstein
 
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What if we blew the melting core into a thousand pieces? If the pieces are small enough, they would not get hot enough to continue melting. If the pieces were spread over a wide enough area, they could actually be approached by humans and dealt with.

There's already fallout emanating from the core and the comntainment buildings are destroyed, so it's not a question of containment.
 
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There's enough radioactive fuel in the reactors that you could evenly spread the material across all of Japan and there would still be 4.66 mg/m^2 of radioactive fuel. An explosion big enough to do that would probably wipe out most of northern Japan.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize
 
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I'm not saying blow the core into dust. Just into pieces small enough to manage.

The temperature at the center of a piece of radioactive material is proportional to its thickness, temperature increasing with depth from surface. If the pieces are small enough, there is not enough power to heat the pieces to melting point.

Perhaps in the future we can design cores that disperse before they melt?
 
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IRstuff, I know, it was mostly tongue in cheek though with a more serious sub text.

Why are there not something like the EOD robots available for responding to this kind of situation?

Sure the radiation environment imposes serious design constraints but are they really insurmountable?

Maybe sensors and other indispensable sensors on the robots are replaceable items - you send the robot in and when they're nearly dead pull it out, or it has auto recovery or something, or a back up system that's shielded until needed...

Maybe some electronics get replaced by hydraulics/pneumatics or even mechanical systems.

Heck, maybe with fiber optics there's some way to have a limited remote viewing capability without electronics - an endoscope type device.

I'm not saying it's cheap or easy, but I just can't help but wonder.

Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​
 
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The radiation levels are, at best, only temporarily surmountable. However, rad-hard electronics are extremely expensive to develop and make, and most utilities are for-profit companies.

As for other means, people can't can't get closer than a few hundred feet, which is a long ways to get analog electronics or hydraulics to work, and again, the price comes into the picture.

Commercial CMOS cameras probably would die within a few minutes at the perimeter of the building. Unless they're rad-hard, they don't have that much robustness over a human being.

Again, cost will be the issue. We'd be talking about tens of millions of dollars per copy, probably, and a hew hundred copies.



TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize
 
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What does not being able to do repair work or damage control work near the core cost?

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
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