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View Diary: Power of Community: Fukushima Rov #54 (225 comments)

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  •  New video of spent fuel pool at unit 4 (5+ / 0-)
    From the TEPCO website. Video taken on May 8.

    •  Lots of little bubbles coming off the fuel bundles (3+ / 0-)
      Recommended by:
      peraspera, Just Bob, rja

      in that video.

      I won't even guess, H2 or steam.

      There doesn't seem to be too many debris blocking water flow .
      The bubbles concern me.

      "People who see a contradiction between science and the bible don't really understand either." PvtJarHead

      by Tinfoil Hat on Sun May 08, 2011 at 08:05:20 AM PDT

      [ Parent ]

      •  video scary, inconclusive (1+ / 0-)
        Recommended by:
        Tinfoil Hat

        Either the fuel that is left is creating steam or gas or else the pool is leaking.  Bubbles could be drifting up from the floor of the pool where burnt and spilled fuel is burning holes in the floor, releasing gasses that were previously trapped in the concrete, or creating holes all the way to the basement, (which had five meters of highly radioactive water in it, last time they bothered to look) or else the floor of the pool could be cracked from heat, earthquake, tsunami and explosion damage, or else there is yet another unknown explanation for why this looks like a pot about to boil over.  

        What is clear is that TEPCO isn't saying.  Either they know and won't say, or else they are as clueless as I am.  Neither option is very confidence-inducing.  

        •  84 degrees (1+ / 0-)
          Recommended by:
          Just Bob

          That's my recollection of the temperature of the water in the spent fuel pool of reactor 4 from recent TEPCO reports. That means the rods are hotter than that, maybe 150 or 200 degrees and water in contact with the fuel rod casings will be making steam bubbles.

          •  how radioactive are these Steam bubbles? (0+ / 0-)

            This melted fuel is giving off more than heat, i assume.  Where does the steam go, and what drifts with it?  

            •   Nothing much (0+ / 0-)

              The risk is that more volatile radioisotopes will be vapourised and carried off in the steam or cooling water. The most likely danger is I-131, iodine which would be a vapour at those temperatures. However I-131 has a half-life of 8 days and is only created when the rods are in a reactor and fissioning. The freshest fuel rods in the spent fuel rod pool of reactor number 4 were extracted from the reactor core in November last year, six months ago so that's 24 half-lifes. A tonne of I-131 in the freshest set of fuel rods would have decayed to about 0.06 grammes by this time. My educated guess is that most of the I-131 contamination detected over the past two months has come from the steam and hydrogen explosions from the reactor cores in mid-March rather than from the spent fuel rod pools.

               The other mobile element commonly found in fuel rods is caesium which melts at 28 deg C and boils at a few hundred. Cs-137 is the most common isotope of caesium found in fuel rods and it has a much longer half-life, at about 30 years or so. There's another isotope, Cs-134 with a shorter half-life but it's less common in fuel rods. Stuff like plutonium and uranium are in oxide form in the fuel pellets. They don't melt until they reach temperatures of over 2000 deg C so they tend to stay in the fuel rods with very little being distributed into the surrounding areas by explosions or steam emissions from the reactor cores.

               I doubt there is actually much new contamination being spread inland from the spent fuel pools after the original period in mid-March when the reactors went bang. All of the measurements show continuing downward trends of contamination and general radiation and no uptick in contamination levels in areas that avoided the first load which landed mostly north-west of the Daiichi plant.

               Water and steam don't become radioactive to any great extent, at least not from exposure to radiation in themselves. Exposure to fission neutrons can cause production of tritium in small amounts and a radioactive isotope of nitrogen with a 7-second half-life but again these reactions only occur in a running reactor, not in a spent fuel pool.

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