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Have they located the melted fuel at Fukushima?

  1. Feb 13, 2013 #1
    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?"
    Last edited: Feb 13, 2013
  2. jcsd
  3. Feb 14, 2013 #2
    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
    that you may wish to peruse
  4. Feb 14, 2013 #3
    Are you talking about this?

    The footage did not reveal the location of any of the melted fuel or core material.
    Last edited by a moderator: Sep 25, 2014
  5. Feb 14, 2013 #4


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    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.
    Last edited by a moderator: Sep 25, 2014
  6. Feb 14, 2013 #5
    Have they inserted a camera into the reactor pressure vessel itself yet?
  7. Feb 14, 2013 #6


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    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.
  8. Feb 14, 2013 #7


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    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.
  9. Feb 14, 2013 #8


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    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.
  10. Feb 14, 2013 #9


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    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.
  11. Feb 15, 2013 #10
    I thought that TMI reactor #2 was removed and replaced with a working reactor?
  12. Feb 15, 2013 #11


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

    Ref: http://www.nei.org/filefolder/TMI_2_Accident_Aug_2010.pdf [Broken]

    TMI-1's license has been renewed for 20 years and will expire 04/19/2034.

    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.
    Last edited by a moderator: May 6, 2017
  13. Feb 15, 2013 #12
    Why not all water was pumped out?
  14. Feb 15, 2013 #13
    Due to these "anti-economy-of-scale" effects, why do power plants opt for using one huge turbine instead of a few smaller ones?
  15. Feb 15, 2013 #14

    jim hardy

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    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/8794/bb/200773014471292994.JPG

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

    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
  16. Feb 15, 2013 #15


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


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

    I don't know. I'll have to do some investigating.
    Last edited: Feb 15, 2013
  17. Feb 16, 2013 #16
    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?
    Last edited: Feb 16, 2013
  18. Feb 16, 2013 #17
    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.
  19. Feb 16, 2013 #18
    Reactor RBMK has 2 turbines.
  20. Feb 17, 2013 #19
    You're right, having multiple smaller turbines is probably better than just one giant one for the reasons you stated.
  21. Feb 17, 2013 #20


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    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.
    (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.
    Last edited: Feb 17, 2013
  22. Feb 17, 2013 #21

    jim hardy

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    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"...
  23. Mar 3, 2013 #22
    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 [Broken]

    I went back and looked and found these associated reports.


    Last edited by a moderator: May 6, 2017
  24. Mar 3, 2013 #23
    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?
  25. Mar 4, 2013 #24
  26. Mar 4, 2013 #25
    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.

    Attached Files:

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