Have they located the melted fuel at Fukushima?

Kutt

Have the TEPCO workers found the precise location of the melted fuel at the affected Fukushima NPP nuclear reactors? If not, have they at least hypothesized where it might be?

Cameras have been inserted into the reactor pressure vessel, but the footage hasn't revealed very much in terms of the integrity and location of the core...

Has it been concluded whether or not the cores burned through the steel and concrete base of the reactor building and into the Earth in a "melt-through?"

zapperzero

Quote by Kutt

Cameras have been inserted into the reactor pressure vessel

No, they have not. Cameras have been inserted into the PCVs alone (and not all the PCVs at that) with less than enlightening results.
There is a gigantic dedicated thread here
http://www.physicsforums.com/showthread.php?t=480200
that you may wish to peruse

Kutt

Are you talking about this?

http://www.youtube.com/watch?v=aR--2dASoJA

The footage did not reveal the location of any of the melted fuel or core material.

Astronuc

Quote by Kutt

Are you talking about this?

http://www.youtube.com/watch?v=aR--2dASoJA

The footage did not reveal the location of any of the melted fuel or core material.

The video was uploaded on Jan 20, 2012 according to that page, so it is very old. Note the white noise in the video. This is attributed to the high radiation levels in the vicinity of the CCD in the camera.

Kutt

Quote by Astronuc

The video was uploaded on Jan 20, 2012 according to that page, so it is very old. Note the white noise in the video. This is attributed to the high radiation levels in the vicinity of the CCD in the camera.

Have they inserted a camera into the reactor pressure vessel itself yet?

Astronuc

Quote by Kutt

Have they inserted a camera into the reactor pressure vessel itself yet?

Not yet in the RPV, or underneath it (I'm assuming that if Tepco has, they would share that information). It will be a BIG story when Tepco finally looks at the damaged core and fuel.

As far as I know, they have lowered cameras to the torus of one or more units.

Tepco is busily building a structure over unit 4 that will enable them to remove the fuel from the spent fuel pool.

etudiant

It seems to be a pretty peripheral issue.
The workers on the site are tweeting that the job will take decades.
Tepco is currently working on clearing the decks, removing spent fuel, enclosing the damaged reactors and dealing with issues such as the disposal of the decontaminated water.
It is not clear what knowledge of the melted fuel's status would add. There is no way to deal with it as yet.

Astronuc

Quote by etudiant

It seems to be a pretty peripheral issue.
The workers on the site are tweeting that the job will take decades.
Tepco is currently working on clearing the decks, removing spent fuel, enclosing the damaged reactors and dealing with issues such as the disposal of the decontaminated water.
It is not clear what knowledge of the melted fuel's status would add. There is no way to deal with it as yet.

They will likely end up like TMI-2, which still has contaminated water in containment and is sealed off.

Aug. 1993 At TMI-2, the processing of accident-generated water was completed involving 2.23 million gallons. Accident was March 28, 1979. I was there during the early 90s for a project at TMI-1, and as IIRC, the water was still in containment of Unit 2.

Sept. 1993 NRC issued a possession-only license.

Dec. 1993 Monitored storage began.

Ref: http://www.nrc.gov/reading-rm/doc-co...mile-isle.html

Twenty years later, I expect it's still in monitored storage.

In 2010, the generator from TMI-2 was sold by FirstEnergy to Progress Energy for an upgrade at Shearon Harris.
http://www.world-nuclear.org/info/inf36.html

etudiant

Quote by Astronuc

They will likely end up like TMI-2, which still has contaminated water in containment and is sealed off.

Aug. 1993 At TMI-2, the processing of accident-generated water was completed involving 2.23 million gallons. Accident was March 28, 1979. I was there during the early 90s for a project at TMI-1, and as IIRC, the water was still in containment of Unit 2.

Sept. 1993 NRC issued a possession-only license.

Dec. 1993 Monitored storage began.

Ref: http://www.nrc.gov/reading-rm/doc-co...mile-isle.html

Twenty years later, I expect it's still in monitored storage.

In 2010, the generator from TMI-2 was sold by FirstEnergy to Progress Energy for an upgrade at Shearon Harris.
http://www.world-nuclear.org/info/inf36.html

Fascinating and vaguely disquieting.
I have no idea what the 'monitored storage' amounts to in practice.
Is it that a guy checks for drips once a year or is it something more substantial?
In a prior life in the aerospace industry, I did not get a good impression of government monitored storage, but maybe the nuclear industry is different.

Kutt

Quote by Astronuc

They will likely end up like TMI-2, which still has contaminated water in containment and is sealed off.

Aug. 1993 At TMI-2, the processing of accident-generated water was completed involving 2.23 million gallons. Accident was March 28, 1979. I was there during the early 90s for a project at TMI-1, and as IIRC, the water was still in containment of Unit 2.

Sept. 1993 NRC issued a possession-only license.

Dec. 1993 Monitored storage began.

Ref: http://www.nrc.gov/reading-rm/doc-co...mile-isle.html

Twenty years later, I expect it's still in monitored storage.

In 2010, the generator from TMI-2 was sold by FirstEnergy to Progress Energy for an upgrade at Shearon Harris.
http://www.world-nuclear.org/info/inf36.html

I thought that TMI reactor #2 was removed and replaced with a working reactor?

Astronuc

Quote by Kutt

I thought that TMI reactor #2 was removed and replaced with a working reactor?

No. TMI-2 still exists in a condition known as 'post-defueled, monitored storage (PDMS). The older sibling unit continues to operate.

TMI 2 Placed in Monitored Storage

After cleaning up the damaged TMI 2 reactor, GPU Nuclear placed the plant in monitored storage in December 1993. In December 1999, GPU sold TMI 1 to AmerGen Energy Co., a joint venture of Exelon and British Energy Co. British Energy subsequently sold its interest in TMI 1 to Exelon. In 2008, AmerGen Energy Co. was integrated into Exelon Generation, and the AmerGen legal entity was dissolved.

Under the terms of the sale, GPU retained ownership of TMI 2. GPU subsequently merged with FirstEnergy, making First Energy financially responsible for the decommissioning of TMI 2. In-plant and off-site monitoring of TMI 2 will continue until it is fully decommissioned, with regular reports made to the U.S. Nuclear Regulatory Commission, the commonwealth of Pennsylvania and the public.

The two reactors will be decommissioned jointly when TMI 1 is taken out of service.

Ref: http://www.nei.org/filefolder/TMI_2_...t_Aug_2010.pdf

TMI-1's license has been renewed for 20 years and will expire 04/19/2034.
http://www.nrc.gov/info-finder/reactor/tmi1.html

If TEPCO has keeped the generators and turbines in good condition, they could in theory be sold for other generation and the utility could recover some cost. However, maintaining a large turbine means that they have to keep the shaft rotating otherwise it will deform under its own weight. A warped shaft is scrap.

nikkkom

Quote by Astronuc

They will likely end up like TMI-2, which still has contaminated water in containment and is sealed off.

Aug. 1993 At TMI-2, the processing of accident-generated water was completed involving 2.23 million gallons. Accident was March 28, 1979. I was there during the early 90s for a project at TMI-1, and as IIRC, the water was still in containment of Unit 2.

Why not all water was pumped out?

nikkkom

Quote by Astronuc

However, maintaining a large turbine means that they have to keep the shaft rotating otherwise it will deform under its own weight. A warped shaft is scrap.

Due to these "anti-economy-of-scale" effects, why do power plants opt for using one huge turbine instead of a few smaller ones?

jim hardy

As Astronuc said the turbine must be rotated else the shaft will warp. That's because of uneven temperature in the casing as it cools down.
To that end there's a "turning gear" motor that rotates it very slowly. We had a backup DC turning gear motor in case of station blackout, and a place for a handcrank.

Once it's reached ambient temperature you can stop it.
Here's a photo of a small one apart for maintenance.

picture courtesy these folks.. http://www.biztrademarket.com/User/8...4471292994.JPG

and a bigger one from wikipedia http://en.wikipedia.org/wiki/Steam_turbine.

Quote by nikkkom

Due to these "anti-economy-of-scale" effects, why do power plants opt for using one huge turbine instead of a few smaller ones?

It takes no more people to operate a large one than a small one.
And as Lindbergh observed when choosing a single engine airplane to cross the Atlanic,
with just one there's fewer things to go wrong.

old jim

Astronuc

Quote by nikkkom

Due to these "anti-economy-of-scale" effects, why do power plants opt for using one huge turbine instead of a few smaller ones?

I only know of one PWR that has twin turbine trains, Sizewell B in the UK.

So that orders could be given to UK manufacturers, and to avoid project risk in dealing with what were at the time newly designed very large turbo-alternator sets, Sizewell B uses two full-speed, 3,000 RPM (50 Hz), nominal 660 MW turbo-alternator sets . . .

http://en.wikipedia.org/wiki/Sizewel...tions#Design_2

Sizewell B is similar in design to Wolfcreek and Callaway units in the US, except, like US plants, they have one turbine set.

Quote by nikkkom

Why not all water was pumped out?

I don't know. I'll have to do some investigating.

Kutt

So TMI has two reactors but only one of them works?

I thought that the damaged reactor #2 had been completely removed and replaced with a working one.

Umm.. I assume that the energy production of the plant is halved?

nikkkom

Quote by jim hardy

It takes no more people to operate a large one than a small one.

Sure, I understand the basic idea of economies of scale.

However, scaling up things tends to bump into various obstacles at some point.

If you go from 1 ton to 2 ton piece of machinery, it's usually not a big deal, but when you go from 20 tons to 40 tons it sometimes is.

Just off the top of my head:

* larger objects are not road-transportable
* very heavy objects need specialized cranes
* disassembly and repair work becomes harder, because even individual parts need lifting equipment, they can't be handled just by hands.

So, why bother and torture yourself with one humongous turbine instead of having two smaller, but still quite large ones?

Also, this gives redundancy.

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Kutt	Are you talking about this? http://www.youtube.com/watch?v=aR--2dASoJA The footage did not reveal the location of any of the melted fuel or core material.

etudiant Recognitions: Gold Member	It seems to be a pretty peripheral issue. The workers on the site are tweeting that the job will take decades. Tepco is currently working on clearing the decks, removing spent fuel, enclosing the damaged reactors and dealing with issues such as the disposal of the decontaminated water. It is not clear what knowledge of the melted fuel's status would add. There is no way to deal with it as yet.