Yomiuri: ‘Nuclear reaction’ can be triggered when removing melted fuel from Fukushima plant

Published: January 23rd, 2013 at 4:47 pm ET


Title: Astro Boy and Uran’s Encyclopedia of Current Terminology / decommissioning
Source: The Yomiuri Shimbun
Date: Jan. 24, 2013

Astro Boy and Uran’s Encyclopedia of Current Terminology / decommissioning […]

Uran [Astro Girl]: What must be done to decommission the reactors and their related facilities?

Answer: […] The decommissioning project will require the fuel in question to be carefully and slowly removed using special equipment in an effort to avoid a leak of nuclear fuel while also preventing the fuel from triggering a nuclear reaction. This will be close to an unprecedented undertaking. […]

See also: [intlink id=”watch-children-play-at-nuclear-theme-park-in-japan-characters-sing-its-very-safe-its-efficient-and-good-for-people-video” type=”post”]{{empty}}[/intlink]

Published: January 23rd, 2013 at 4:47 pm ET


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32 comments to Yomiuri: ‘Nuclear reaction’ can be triggered when removing melted fuel from Fukushima plant

  • bwoodfield bwoodfield

    M5.2 – 22km SSE of Nemuro, Japan 2013-01-23 21:34:32 UTC

    About 500-600 miles from Fuku

  • bwoodfield bwoodfield

    And another earlier 4.9 less than 50 miles

    M4.9 – 59km NE of Namie, Japan 2013-01-23 21:31:06 UTC

  • PattieB PattieB

    PattieB PattieB
    January 23, 2013 at 2:09 pm · Reply


    A fukushima preview!

    Report Comment

    January 23, 2013 at 2:42 pm · Reply

    Hi Pattie

    Some people think the melted corium will eventually cool and pool, as with the "elephant's foot" at Chernobyl

    I'm interested in why you think it will go "bang." Doesn't the geometry have to be pretty tight for that to happen?

    Just wondering…


    Report Comment

    PattieB PattieB
    January 23, 2013 at 4:33 pm · Reply

    The difference is that this corium at Fuku is Plutonium! It just needs the proper type reflector to go critical again.

    Report Comment

    PattieB PattieB
    January 23, 2013 at 4:35 pm · Reply

    It would need engulfment in water, or to hit bedrock. Both would cause enough bounce-back of neutrons to cause a chain-up to criticality.

    Report Comment

    PattieB PattieB
    January 23, 2013 at 4:39 pm · Reply

    If it was just Uranium…? The chance of re-critical bang would be negligible. As you need to work at triggering Uranium… gun/implosion. Plutonium…? Just get more than 5 kilo in one place, and BANG!

    Report Comment

    PattieB PattieB
    January 23, 2013 at 4:59 pm · Reply

    They say it's over 10 kilos.. but we have a few tons in this case anyhow! But the key is, specifically the PU-240/241.. and that's 5.2 kilo. You have to look at it from the standpoint of the…

  • PattieB PattieB

    You have to look at it from the standpoint of the highest reactive substance that's present in the mass of corium. That's going to start the chain-up.

    Report Comment

    PattieB PattieB
    January 23, 2013 at 5:03 pm · Reply

    The fact we have out-gassing, and visual radiations… that's the PU-241 that's giving us the light shows.

    Report Comment

    PattieB PattieB
    January 23, 2013 at 5:08 pm · Reply


    240 can cause fizzle… but 241? That stuffs nasty dirty rad-wise and goes "off" if you look at it wrong!

    Report Comment

    PattieB PattieB
    January 23, 2013 at 5:10 pm · Reply

    The longer that stuff is a molten mass of corium… the more P-241 you shall have created. Also, the more U-235… coincidentally… and that's not a stable mix.

    • HoTaters HoTaters

      Yes, I've been thinking a phreatic type explosion might occur.


      What you posted re: the reactivity of certain Plutonium isotopes when a mass of molten corium meets (or becomes surrounded by) water confirms my suspicions.

      That's why I'm curious about geologic strata and possible landfill around plant, and any corium outside containment.

      • HoTaters HoTaters

        Meanwhile, it's raining in Nor. California and I'm very, very itchy today. Ha ha. Who knows whether or not there is any connection. Radiation Network showing lower readings than we were getting between November and early January.

        If anyone is familiar with geologic strata around the Fukushima plants, would you please post a link here?

        • PhilipUpNorth PhilipUpNorth

          Fuku nukes were built on excavated mudrock (a sandstone), HT. The area was leveled, and the foundations were poured on a thin layer of aggregate fill used to bring the foundation back up to the desired level. The site was carved out of native rock, there is no landfill nearby. The mudrock is layered, sloping downward towards the Ocean. I'm sure you've seen this link before.
          Water is abundant. Two surface "streams" were channeled under the plants. The water table is at the basement level. The corium has abundant cooling/moderating water flowing around it and into the Harbor.
          Nice discussion, HT and Pattie.

      • HoTaters HoTaters

        Pattie B., am thinking if you add water to the mix of a Pu type explosion or corium/fuel goes critical again, it could get really messy with a phreatic type exlosion. That's assuming any of the fuel is melted into lava-like blobs in the pools.

          • HoTaters HoTaters

            Beautiful! You're amazing. Thanks.

            Am having a bit of difficulty in viewing it. Do I need to join in order to download?

            Is that a .jpeg file, or is in done in GIS? What type of rendering is it?

            Folks, THIS is the type of thing IMHO we need to collectively put our brainpower to work on analyzing. Risk/threat analysis, that is. This could make the potential terrorist threat pale in comparison. Well, maybe not, if one considers the potential sabotage of spent fuel pools (compromised power/cooling, fires).

            I'm not certified/credentialed scientist, but I have technical background & tech writing/editing skills, professional exposure to GIS, seismology, and civil engineering.

            If there is truly danger of PU criticalities, even phreatic type explosions, then IMHO there needs to be study done to assess the risk.

            Are governments, Japan's and US's nuclear agencies, the DOE, nuclear laboratories, and Universities looking at this? If not, they should be.

            Were a phreatic explosion to occur and launch the corium into the atmosphere, it could be absolutely devastating. I hope this is not just my overactive mind and imagination visualizing something that couldn't or wouldn't occur.

            • HoTaters HoTaters

              Or maybe we can collectively make a convincing argument to have SOMEONE throw some $$ at a serious threat analysis.

            • PhilipUpNorth PhilipUpNorth

              TEPCO and JNES seem to be arguing over how far the melted fuel ate into the concrete at the bottom of Containment1,2,&3. The discussion is whether TEPCO's "conservative" view or the "less conservative" JNES view of the situation is correct.
              The US NRC and DOE are defering to Japanese leadership, and are being kept at arm's length by the Japanese. The Japanese do not consider that a melt-out of corium into the mudrock has occurred in any of the three reactors. If anyone in the world is looking into what is actually happening with the corium, it is definitely not NRC/DOE/TEPCO/JNES. I have found no better discussion of the future of the corium than at ENEnews.

              My current view, as a non-nuke-professional is this:
              Corium1,2,&3 are located in mudrock under Units1,2,&3.
              The corium is being cooled by the continuous flow of abundant ground water.
              The flow of highly contaminated ground water into the Pacific Ocean is IMO the most serious aspect of the ongoing Fuku Calamity.
              Ground water moderation of neutrons creates criticalities in the corium from time to time.
              Some venting of steam or smoke from the ground between the reactors has occurred.
              Continuous outgassing as the corium spits and sputters is evident in radiation readings (I saw 425 cpm near the plant on a radiation map recently).
              There have been no further explosions at Fuku, after Units1,3,&4 were demolished.

          • HoTaters HoTaters

            I'm assuming the strata is more dense, as one goes downward. Wish I could read and interpret what I'm seeing.

            Can you tell us where the original data was found?

            • HoTaters HoTaters

              Whatever the several hundred feet in the first layers is composed of, it doesn't look too dense. That's not reassuring.

              So — if there is a lot of silica content, and that's present in the top layers, would that tend to form a glasslike substance, when exposed to corium?

              Also — water passes fairly easily through sandstone and any substrate (stratum) containing sandy particles (as opposed to clay-like stratum). So it might not be too dim a scenario until the corium begins to meet the denser layers (getting into the red/orange or green areas).

              Am picturing the water table being somewhere in the green layers. Or the red layer? If the corium reaches that level, the potential for a phreatic type explosion might greatly increase.

              I guess we're all novices when it comes to assessing the behavior of corium underground — except for the people who have analyzed what happened at Chernobyl.

              • HoTaters HoTaters

                And if there's a glasslike substance forming around the corium, how does that influence the behavior or "flow" of the corium? The viscosity?

                • PhilipUpNorth PhilipUpNorth

                  My take is that the corium has exhausted itself, and is no longer moving. The exterior is a crust, cooled by ground water. But ground water is able to cool only the exterior crust, while the interior remains quite hot. The corium is now incapable of sustained criticalities. When disturbed, as from an earthquake, the outer crust breaks to expose hot corium underneath to water, allowing new criticalities to occur for a time. The decay heat within the corium might keep the temperature in the middle of the 3 blobs at about 500 to 1,500 F at present. Spreading out of the blobs, as they flowed in the mudrock, would help to reduce the interior temperature of the corium over time.

                  PattieB, if Units3&4 were using an exotic plutonium fuel (not MOX), what is your opinion of the present location and state of the corium?

  • PhilipUpNorth PhilipUpNorth

    Removing spent fuel assemblies presents tremendous hazzards at Fukushima:
    Fuel handling cranes were destroyed when Buildings1,3,&4 were blew up.
    A new crane support structure, being constructed at Unit4, to allow fuel removal, will take a year to complete.
    Buildings1,2,&3 are too radioactive for workers to enter or get near the spent fuel pools.
    Building3 used MOX fuel, with a large plutonium component, making this building exceedingly toxic to humans.
    Sea water, used as emergency cooling water, corroded spent fuel assemblies, which may begin to fail within the next 3 years or so.
    Fuel assemblies at Unit4 burst into flames not once, but twice, and the fires may have destroyed the handles used to pick up the fuel assemblies.
    The zirconium cladding of damaged fuel assemblies may fail completely, dumping half a ton of hot fuel pellets onto the floor of a spent fuel pool, causing criticalities.
    And there is more.

    • HoTaters HoTaters

      And wasn't there MOX fuel in the SFP for #4, or was that in the Common SFP? Can anyone remark on this? Can't recall where they were storing the second load of MOX which was to be loaded into the #3 reactor. The first load was supposed to have gone in, in Oct. 2010, and they were (as I recall) going to load up #3 with the second load of MOX in April, 2011. Which didn't happen for obvious reasons.

      Maybe part of the concern over the precarious position of the #4 SFP is because there's a bunch of MOX sitting up there?

      Can anyone comment on how hazardous that might be, if it's MOX but not spent fuel?

      More plutonium. And?

    • PhilipUpNorth PhilipUpNorth

      The zirconium cladding of a damaged fuel assembly may fail completely, dumping half a ton of hot fuel pellets onto the floor of the spent fuel pool.
      What will spent fuel pellets do when they are spilled into a pile in a pool of water?
      Here is my guess:
      The pellets are touching other pellets.
      Neutrons are partily moderated by the water between pellets.
      The pellets will begin to fission immediately, and heat up.
      Prompt moderated criticalities will occur.
      Water temperature will rapidly increase.
      Radiation will rapidly increase.
      Pellets will melt into pools of molten "corium" on the floor of the pool.
      Spent fuel pellets probably cannot be vacuumed up, or scopped up, or handled using current technology.
      Remote controlled cranes will drop boron, lead, and other materials on the fuel pellets to stop fission.
      Hopefully, work will be able to proceed to remove other fuel assemblies.
      But many spent fuel assemblies are likely to fail as fuel removal proceeds in SFP1,2,3,&4.
      Eventually, borated sand will be dumped into the pool to replace the water.
      Hopefully, fuel removal will not cause an explosion, like the one that many believe originated in SFP3.
      Eventually, the empty spent fuel pools will be covered by a concrete Sarcophagus.

  • PattieB PattieB

    It's not the MOX that's problematical… it's the PU-Breeder types that are what goes BANG! Pool of 4 has 40. Pool of 3 had over 50, but they were over 10 years old. The core had new ones!

  • Jay

    If you break down the actual physical process of removing anything from around/inside the reactor and SF rods it becames obvious that the video cameras employed will have their CCD ( CMOS/MOS ) burned in Seconds .
    I have seen 'broken' pixels on a HD video professional camera caused by just X-rays at the airport …

    How many hundred of thousands of cameras would they calculate to be needed ?

    How else will they see what to handle in that mangled structure ?

    But very soon more worries are coming , by mid February to mid March , the bi-anual passage and pressure by the Centrifugal Bulge created by the orbiting Earth around the sun , will pass over the Japan latitude and act as a butterfly-effect on the tectonic situation …

    Take that a few notches higher and start considering the effect on tectonics by the approaching ( a few thousand years ) of Orion Arm as part of our galaxy , and that it is a much higher concentration of stars hence gravitational 'knots' or Vortexes that the Earth will go through , enough to stir the magma and tectonic plates to release heat so bananas can grow AGAIN at the Poles ( ya , passing through the dense Orion Arm is periodic ) .

    But will the bananas , this time , be radioactive ?

    • richard richard

      thanks Jay, good point on the Centrifugal Bulge, I can understand how that may affect things.

      What I'm not so sure of is the gravitational effects of another far away galaxy. I would expect that the Sun would have a far higher order of gravity on us then anything that far away. Sure, our solar system will be influenced, but in relative terms, the Sun is the controller.

      I'd be glad to read any material you may have on galatic gravity.