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]

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
https://www.physicsforums.com/showthread.php?t=480200
that you may wish to peruse

 

[Kutt]

Are you talking about this?



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

 

[Astronuc]

Are you talking about this?



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]

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]

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]

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-collections/fact-sheets/3mile-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]

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-collections/fact-sheets/3mile-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]

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-collections/fact-sheets/3mile-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]

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_Accident_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]

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]

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.
http://www.biztrademarket.com/User/8794/bb/200773014471292994.JPG
picture courtesy these folks.. http://www.biztrademarket.com/User/8794/bb/200773014471292994.JPG

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

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]

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/Sizewell_nuclear_power_stations#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.

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]

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.

 

[a.ua.]

Reactor RBMK has 2 turbines.

 

[Kutt]

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.

You're right, having multiple smaller turbines is probably better than just one giant one for the reasons you stated.

 

[Astronuc]

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.

Large equipment is transportable by road. That's usually how it gets to (of from) the plant. Each steam generator at San Onofre was about ~400 tons, ~65 feet in height and about 17 feet at maximum width.
http://www.ocregister.com/articles/san-376670-onofre-generators.html
http://www.huffingtonpost.com/2012/11/05/san-onofre-nuclear-generator_n_2077732.html
(turn down the volume and ignore that advertisements)

Two 600 MWe turbines still need specialized cranes/equipment, and each turbine rotor and the casings cannot be lifted by hand. Most people cannot lift and carry an object of their body weight very well. There are usually limits on what people lift, <25 kg.

 

[jim hardy]

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.


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

Also, this gives redundancy.

Well,, our generator stator weighed about 392 tons.
It arrived in town by rail the first time, and a special hundred wheeled trailer was supposed to haul it the last ten miles.
But on that road out to the plant the Earth beneath the pavement squished away and the generator tumbled into the swamp. So next time they barged it right to the plant.
Would a 200 ton generator on fifty wheels have squished the road? Anybody's guess...

It's really no more trouble to lift a 400 ton piece than a 200 ton piece just the crane is slightly bigger.

I think economy of scale applies - it's twice the complexity and twice the labor cost to build and maintain two half size machines instead of one full size one.
Dont forget the auxilliaries - a steam turbine needs a condenser, lubrication system, feedwater heaters, pipes, pumps , valves, etc.

Heed Thoreau - 'Simplify, Simplify"...

 

[LabratSR]

To the original question,

According to this report, TEPCO stuck a camera into the PCV "near" the pedestal room of Unit one but did not see anything that appeared to be corium.

From the summary of the report.

"Recently, within the October 2012 timeframe, TEPCO was able to insert a camera along with instrumentation through a penetration into the Unit 1 PCV [83]. Video within containment was obtained; however, the information has not been fully scrutinized and interpreted as of this report. The camera was able to view a small portion of the drywell floor [84] in a drywell location approximately 180 degrees opposite from the pedestal doorway. Core melt did not appear to be present in this view. Future analysis and data collection as to the debris location will provide insight into the accident progression."

I posted this in the big thread but it seems to fit here.

Enhanced Ex-Vessel Analysis for Fukushima Daiichi Unit 1:
Melt Spreading and Core-Concrete Interaction Analyses with MELTSPREAD and CORQUENCH

https://fukushima.inl.gov/PDF/MELTSPREAD%20CORQUENCH%20Analysis%201F1%20ORNL_ANL%20Feb2013.pdf

I went back and looked and found these associated reports.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_121015_05-e.pdf

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_121015_04-e.pdf

 

[Kutt]

Have they concluded whether or not the cores have burned their way through the concrete base of the reactor building and into the Earth beneath it?

 

[zapperzero]

Have they concluded whether or not the cores have burned their way through the concrete base of the reactor building and into the Earth beneath it?

There is no conclusion and there won't be for a long time. The modeling runs so far point to the fuel having eaten just a little into the basemat and stabilized there. Muon radiography is being considered

https://www.lanl.gov/newsroom/news-releases/2012/October/10.17-fukushimas-nuclear-scar.php

 

[nikkkom]

Have they concluded whether or not the cores have burned their way through the concrete base of the reactor building and into the Earth beneath it?

Thankfully, concrete base is about 10 meters thick.

Models so far say that corium almost reached the containment bottom (the light-bulb shaped thing), and if they are wrong, it may indeed reached it, but there are 7.5 more meters of concrete below it.

 

[Kutt]

How come giant containers at a steel mill which contain hundreds of tons worth of superheated white-hot molten steel do not have that molten mass burn through it's base? While a nuclear reactor pressure vessel cannot physically contain it's core if it melts?

 

[russ_watters]

How come giant containers at a steel mill which contain hundreds of tons worth of superheated white-hot molten steel do not have that molten mass burn through it's base? While a nuclear reactor pressure vessel cannot physically contain it's core if it melts?

Perhaps look up the melting temperature of steel vs the melting temperature of the container holding it?

 

[Kutt]

Perhaps look up the melting temperature of steel vs the melting temperature of the container holding it?

Why can't reactor vessels be made of a material that has a melting temperature greater than the temperature of molten corium?

 

[nikkkom]

Why can't reactor vessels be made of a material that has a melting temperature greater than the temperature of molten corium?

Corium has no defined temperature. It heats up due to decay heat, and without sufficient cooling will become hotter and hotter until it melts the vessel.

Tougher vessels theoretically can be built (say, using vanadium, molybdenum alloys and such), but they will cost astronomical sums and still won't be 100% safe wrt meltdown.

Safety versus meltdown can be achieved only by designing in very robust emergency cooling systems. In my "armchair engineer" view, something like "reactor sitting in a stainless steel lined pit with no drains, and with a set of large tanks beside it which can be manually drained into the pit, no electricity needed" should work.

 

[zapperzero]

with a set of large tanks beside it which can be manually drained into the pit, no electricity needed" should work.

Large tanks of what, please?