“Very serious” possibility that pools of molten fuel in reactors could restart nuclear reactions

Published: June 7th, 2011 at 6:30 am ET


Plutonium found near Fukushima shows nuclear “crisis is far from over”, Yahoo by Laura Rozen, June 6, 2011:

[…] There are several other ongoing concerns at Fukushima some three months after the natural disasters hit, according to arms control expert Joe Cirincione of the Ploughshares Fund. Among them, he said: […] the very serious possibility that the molten fuel now pooled at the bottom of the reactors could start nuclear reactions again.

“This crisis is far from over,” said Cirincione. “Recent readings show that the radiation levels are the highest they have ever been (and) the plutonium detected in the soil show radioactive particulates continue to spew from the reactors.”

Published: June 7th, 2011 at 6:30 am ET


Related Posts

  1. More serious than a meltdown — Japan Gov’t now raising possibility that fuel had a “melt through” at all 3 reactors June 7, 2011
  2. “It’s certain that fission is occurring” says TEPCO — Chain reactions may also be underway at Reactors No. 1, 3 — Trying to determine if reactions continue November 2, 2011
  3. Experts: Nuclear chain reactions may have lasted over 7 months at Fukushima — Neutron leakage from ‘active’ molten fuel — “Core producing radioactive sulfur” — Top Gov’t Official: MOX fuel could be neutron source April 10, 2014
  4. Kyodo: “If we find where the molten nuclear fuel is located, it will give us a clue” says researcher — Detectors to locate corium already placed near Reactors 1 and 2 in May by Los Alamos Lab October 18, 2012
  5. MIT: Nuclear chain reactions must have been burning at damaged reactors long after disaster unfolded May 11, 2011

33 comments to “Very serious” possibility that pools of molten fuel in reactors could restart nuclear reactions

  • rainyation

    did anybody else notice ?

    veracruz mexico earthquake
    4.6 on 6-3-11

    popocatepetl volcano eruption
    6-3-11 south east of mexico city

    laguna verde nuclear power plant
    alto lucero veracruz mexico
    2 ge bwr’s

  • itstomd

    not a big deal

    • BreadAndButter BreadAndButter

      I think it’s interesting, though.
      I saw a post here from a guy who seems to be quite educated in terms of earthquakes (he has an Indian name, I think). He posted that at the moment there was a “time window” for new bigger earthquakes along the pacific “ring of fore” from June 12th to middle of August.
      From time to time I check the Japan Meteorological Agency site; there’s at least one magn. 4 earthquake each day in the region of Fuku.
      I hope they will get “el diablo” plant in California off the grid in time.

  • mjmcato

    Arnie Gunderson has previously said that he does not believe that fuel which has melted to the bottom of the reactors (now through it of course) will go critical as the fuel is not concentrated enough and will be spread out at the bottom. His view had been that some of the core was likely still intact (albeit brittle) inside reactor three, and that intact fuel was likely starting up on its own and releasing fresh iodine. His view was you actually needed some of the core to be still intact if there was to be ongoing fission. The other possibility presumably for that is rods that are still intact in the fuel pools.

    To get fission you need a great enough quantity of uranium or plutonium in enough concentration in one spot. If its melted and has other stuff mixed with it, then it is diluted, also, if it is spreading out over a flat surface, once again it is less likely to start fissioning again.

    • fjn

      There are several assumptions that Arnie is making that may not be warranted. First that the containment chamber is fully intact. We all ready know that there are numerous cracks in all the containment chambers. Second that the bottoms of the containment chambers are plumb. We can see building four leaning. If all the other buildings are slightly out of plumb the corium will pool in a corner. It there are cracks in the bottom it will pool in those cracks. There have already been way to many assumptions made about how things should work that we have found to be outright misinformation. Even Arnie is not free of making assumptions based on knowledge that is presumed and not observed. Even if one hot spot forms it will burn a depression that the rest of the corium will flow to. To presume that the corium is not molten is rather a large presumption. If it was the case then this situation would already be half way under control and as far as I can see it is just continuing to get worse.

  • Earthquakes are linked to solar activity. I bet if you go back 24-48 hours from the earthquake… There was a class c “CME” (coronal mass ejection). my guess a c-7 near earth bound, with high solar winds…

    Just a hint.

    Were approaching the biggest solar storm in history…
    2011 – 2012…


  • This is going to get Ugly !

  • nomade

    Arnie seemed to think the main problem was the spent fuel pool at #4 going critical.

    I see that the water temp in the pool at #4 is now 89 degrees Celsius.

    Is this a cause for concern?


    • That would be 11 below boiling temperature, hope it doesn’t raise any more !

    • from the top its 89.. so I am guessing that the fuel is critical. Otherwise the water would be 45f (like the ocean).

      Basically this is a lying game…

      Heres where the reality is….

      Ocean water is friggin cold. when its warming up… WEll you guessed it. The fuel is critical… So in this respect the fuel is a molten fizzle, rubbing against the bottom of the reactor…
      So if it slipps through the bottom of the containment, then the fuel will kill anyone on site. (as it will be exposed).

      This will eventually happen btw…
      Because nothing can stop it from doing so… unless they put thousands of tons of cement under it, which they cant…
      on the bright side, this will mostly just effect people in japan. However once it happened, tepco would be forced to abandon the site… And then the rest will effect you…

      • These will not drop directly into ocean water but I will agree that water in the ground can be quite cold indeed but also may become heated in the ground prior to the core reaching it water warming it a bit if not a lot prior to contact. (It may more likely be a Mix of mud and not water in itself) Now if there is and underground stream this core drops down to, no dought there will be a sudden reaction were even a drop of water will turn 1700 times its size instantly !

      • Prof. Neutron

        Hey tacomagroove, you are clearly well-read and have a scientific mind about these matters. But through all your comments I think that you may have a misconception about how fission reactions work.

        You say “the fuel is critical”. But let’s be precise about the term “critical”. What it means is that the neutron flux from ongoing fission is *exactly* equal to the flux required to keep the fission going. If the neutron flux is even a tiny bit greater than the critical flux, then each fission (which releases about 2.5 neutrons) will cause more than one additional fission, and very quickly the fission rate, and the energy released, will increase very rapidly. If the neutron flux is a tiny bit less than the critical level, the fission rate will die off rapidly. Maintaining exact criticality is a real trick – there needs to be some feedback mechanism to keep a nuclear reactor right at criticality. That’s what the control rods do.

        Also, the neutrons from fission need to be slowed down in order to be able to cause more fissions. That is, the reactor must be moderated. Light elements like the hydrogen and oxygen in water, or carbon (in eastern bloc reactors like Chernobyl) are typically used. If these elements are not present, the neutrons tend to leave the fission region without causing more fission.

        So if we have corium blobs that have escaped the steel pressure vessels, and pooled on the concrete floor of the containment, we lack the conditions for criticality.

        Early on in the accident when the damaged fuel was falling to the bottom of the RPVs, it is entirely possible that fission occurred in whatever water remained at the bottom of the RPVs. This may have played a big role in the dramatic explosion in Unit 3, for example, as Arnie has pointed out.

        Again the key point here is that there is no possibility of stable fission energy release. It either skyrockets, and that part of the fuel/corium/whatever blows itself apart, stopping…

      • Prof. Neutron

        …the fission reaction.

        This having been said, the decay heat in the corium is quite sufficient to drill down through meters of concrete on a time scale of weeks to months. See this study:


        What happen next is a really interesting question, but a gian fission reaction and explosion is not really plausible.

        • Dory

          Very interesting, thank you.

        • Steven Steven


          “If the neutron flux is even a tiny bit greater than the critical flux, then each fission (which releases about 2.5 neutrons) will cause more than one additional fission, and very quickly the fission rate, and the energy released, will increase very rapidly.”

          Are these not the conditions for a prompt criticality? You state further on in your piece,

          “the neutrons from fission need to be slowed down in order to be able to cause more fissions”.

          Which causes me to wonder, how can a prompt criticality occur? How could an atom bomb function without such a moderator? I was under the impression they just explosively introduced a critical mass together, no mention of moderators?

      • Prof. Neutron

        One more technical report from SAR (the European Severe Accident Research organization):


        Nice photos of simulated corium drilling down through concrete. Yeesh.

        It’s really hard to imagine anything other than that the corium in Units 1-3 has drilled many meters down by now, possibly to the rock below, and soon (if not already) the water table.

  • nomade

    Watch the video, steam is billowing out big time and the outside temperature is not cold. (Mind you I don’t know when they made that video)

  • nomade

    I thought #4 held spent fuel rods and core wasn’t in use and that these were located near the roof.

    Why are you talking about the core hitting the water below xdrfox?

    Won’t it all just blow up in the air if it goes critical? Before it hits the ground?

  • nomade

    The 89C I mentioned earlier was the temperature of #4 cooling pool.

    Sorry I thought you two were replying to my post.

  • Anthony Anthony

    **….samples taken some 1.7 kilometers from the power station’s front gate on April 21 “found minute amounts of three kinds of plutonium,” NHK reported. The Japanese researchers said the quantities of plutonium found in the soil are roughly similar to that which has been found at past nuclear bomb test sites.

    Plutonium is highly toxic–whether ingested or inhaled–because it emits alpha radiation “that can easily penetrate membranes inside the body,” Daryl Kimball, executive director of the Washington, D.C.-based Arms Control Association, told The Envoy.

    The reports of this elevated health threat come as Japanese citizens and activists are urging the Japanese government to take over the complex cleanup operation of Fukushima from the Tokyo Electric Power Company (TEPCO). TEPCO has been accused of downplaying the risk to plant workers and the public from the station’s nuclear reactors meltdown. …***

  • nomade

    Is arms control expert Joe Cirincione of the Ploughshares Fund a nuclear physicist?

    What are his credentials? Just wondering why this was posted as a news item.

    The plutonium outside the plant was known about back in March (even ABC reported it) and govt admitted the radiation readings were in line with a nuclear bomb test explosion last week if I remember right.

    Old news.

    Old Arnie said the molten fuel wouldn’t go critical (though it may cause an explosion when it hits cold water)

    Anyway, repeat, what are Joe Cirincione of the Ploughshares Fund’s academic credentials.

    • a simple google can get you an answer:

      Joseph Cirincione joined Ploughshares Fund as president in March 2008. He is author of Bomb Scare: The History and Future of Nuclear Weapons and served previously as senior vice president for national security and international policy at the Center for American Progress and as director for nonproliferation at the Carnegie Endowment for International Peace for eight years. He worked for nine years in the U.S. House of Representatives as a professional staff member of the Committee on Armed Services and the Committee on Government Operations, and served as staff director of the bipartisan Military Reform Caucus. He teaches at the Georgetown University Graduate School of Foreign Service and is a member of the Council on Foreign Relations.

      His previous books include two editions of Deadly Arsenals: Nuclear, Biological and Chemical Threats, (2005 and 2002), and previous reports include Universal Compliance: A Strategy for Nuclear Security (co-author, March 2005) and WMD in Iraq (co-author, January 2004). He is the author of over 200 articles on defense issues, the producer of two DVDs on proliferation, the former publisher of the comprehensive proliferation website, Proliferation News, and is a frequent commentator in the media. In the past two years has delivered over 150 speeches around the world and appeared in the 2006 award-winning documentary, Why We Fight.

      Cirincione is an expert advisor to the Congressional Commission on the Strategic Posture of the United States, chaired by former Secretary of Defense William J. Perry and former Secretary of Energy and Secretary of Defense James R. Schlesinger. He also serves as a member of the Advisory Committee to the Commission on the Prevention of WMD Proliferation and Terrorism, headed by former Senator Bob Graham (D-FL) and former Senator Jim Talent (R-MO).

      Cirincione is an honors graduate of Boston College and holds a Masters of Science from the Georgetown School of…

  • Cirincione is an honors graduate of Boston College and holds a Masters of Science from the Georgetown School of Foreign Service.
    Geographic Expertise:
    Europe, India, Pakistan & Afghanistan, Korean Peninsula, Middle East & Persian Gulf, Iran, Russia & Former Soviet Union, United States
    Principal Areas of Expertise:
    Nuclear Weapons(Cooperative Threat Reduction, Nuclear Terrorism, Proliferation, U.S. Nuclear Policy)
    Nuclear Materials(Nuclear Fuel Cycle, Radiological weapons)
    Missiles & Space(Missile Defense, Missile Proliferation)
    Other( U.S. Foreign Policy, Defense Budget, Military Strategy)
    More information

  • nomade

    So he’s not actually a nuclear physicist.

  • Elenin Velikovsky Elenin Velikovsky

    So, Cirincione’s extensive Credentials indicate a man
    who clearly knows Which Side his Bread is Buttered on.
    Georgetown and CFR and all that….his mama should be

  • BlueMirror

    Criticality question

    I don’t understand…

    When a reactor scrams, the remaining fissions are no longer self-sustaining, and gradually dwindle. The fuel continues to generate heat, but initially only 2% of what it produced pre-scram, and thereafter less and less. Natural post-scram cooling was the reason many believed fears for Fukushima were overblown.

    Except… post-scram cooling doesn’t work on its own. The residual heat and residual fissions are enough to cause the fuel to melt unless it is also cooled with water, and now it *is* melted.

    So why is recriticality merely a “danger.” Now that the fuel is melted, it’s no longer scrammed. It’s completely without the protection control rods, zirconium cladding, and space between the rods; it’s a 5000 degree blob that’s melting downward, cooled only at the top by toxifying a constant stream of water.

    But if the fuel is hot enough to melt into a blob, doesn’t that also mean it *is* critical? I understand that the physical configuration matters — a ball of fissable material is more likely to be self-sustaining than the same mass spread around the floor. And perhaps the fuel is now diluted with boron, zirconium, melted steel from the containment vessel.

    But to my (non-physicist) way of thinking, there is a lot more than the “chance” of criticality. If the blob is short of criticality,the remaining drips of what’s left in the steel containment might be enough to when added to the blob below to set it off.

    I’m not talking about “prompt” criticality — just enough mass of fissable material to continue a self-sustaining reaction, making tons of fuel 5000 degrees melt relentlessly downward.


    1. Why is my analysis wrong — and the reports only speak of the “possibility” of recriticality?

    2. Is the fact the Fukushima plant was built on granite helpful (no soggy earth and groundwater table below?

    3. Why doesn’t Japan do what the CCCP did? Did a tunnel underneath to flood with liquid nitrogen, or sand to dilute the molten fuel to make it no longer critical (dilution by and is what happened at Chernobyl by luck).