Study: Nuclear Fission Reactions May Have Continued After Fukushima's Alleged Shutdown

By Valerie Ross | April 4, 2011 4:50 pm

Fukushima Daiichi Reactor #3
Reactor 3 at the Fukushima Daiichi plant, on March 24

What’s the News: A non-peer-reviewed study (pdf) publicized last week by radioactivity-detection expert Ferenc Dalnoki-Veress suggests that nuclear fission reactions continued at Japan’s Fukushima nuclear power station well after the plant’s operators had allegedly shut down the reactors there. The paper says there may be what are called “localized criticalities” have occurred in the plutonium and uranium left in the reactors—little pockets of fuel that have gone critical, propagating the nuclear chain reaction and generating potentially harmful radiation. The existence of criticalities is controversial: some researchers say there are certainly none; Dalnoki-Veress himself says it’s only a possibility.

How the Heck:

  • Over three days beginning March 13—two days after the earthquake and resulting tsunami—Tokyo Electric Power Company detected a neutron beam, a stream of radioactive particles that could be evidence of continued chain-reaction fission.
  • The company observed the neutron beam 13 times, about a mile away from the reactors. The beam itself doesn’t pose a health risk, with radiation levels between 0.01 and 0.02 microsieverts per hour. (You’d get about as much radiation exposure from eating one-tenth to one-fifth of a banana.)
  • After seawater was used to cool the reactors, the water had unusually high levels of chlorine-38, a radioactive isotope of chlorine. Chlorine-38 isn’t much of a radiation risk; its half-life is 37 minutes, so it disappears quickly. What’s strange is that chlorine-38 is formed when an atom of chlorine-37 (the stable, common chlorine isotope) absorbs a neutron. High levels of chlorine-38 mean there were lots of neutrons around, raising the possibility that melted bits of fuel may have gone critical.

What’s the Context:

  • An explosion at the Fukushima nuclear plant came shortly after the earthquake and tsunami hit Japan. Workers are still pumping in seawater to keep the reactors’ fuel rods cool, with leaks and disposal of the now-radioactive water presenting a new set of problems.
  • These localized criticalities, if they’re happening, could cause surges of radiation and heat, making cooling and containment work at the reactors even more perilous for workers.

Not So Fast:

  • Other experts are divided as to whether there’s even a chance that there are accidental fission reactions occurring. The dangerous conditions at the reactor make it difficult to get a good read on what, exactly, is going on. Nuclear safety expert Edwin Lyman told Time that he’d “be wary of attributing too much significance to a single anomalous measurement.” But Denis Flory, head of the International Atomic Energy Agency‘s nuclear safety department, said in a press conference that such reactions could potentially be occurring.

Image: Wikimedia Commons / derek visser

CATEGORIZED UNDER: Environment, Physics & Math
  • http://DiscoverMagazine Templar 7

    Well well well…It seems that we have a chance to figure out something previously unobserved on this scale before. Einstien found motivation in trying to find a unifying theory of science to explain phenomenon like this, is there too much quantum mechanic application going on here??

    Also, what is the name of that light that is given off when neutrinos hit H2O in darkness?? Kreznovs? Anyways, I would suggest that someone observe the light under a spectrometer and determine it’s true composition.

    -The Templar Knight

  • Cody

    Templar, it’s called Cherenkov radiation, and I suspect that there are better methods of determining the composition, as well as the internal state of the reactor, however getting near enough may pose such significant health risks as to make it unfeasible. Also, Cherenkov radiation is created by charged particles, not neutrinos. (I believe there are some other flaws in your suggestion too but I have too little confidence in my nuclear physics to discuss any more.)

    Also, to Valerie, a minor detail concerning banana’s and radiation. According to the wikipedia article “banana equivalent dose,” eating a banana doesn’t actually change the amount of radiation your body is receiving, apparently our bodies regulate potassium very well, and eating a banana just means maybe swapping out some of the potassium currently in your body for the potassium in the banana, both of which have the same ratio of radioactive isotopes, so the net effect is zero. I know it’s being picky, I mostly just thought it was an interesting fact to share. (It still makes for a good explanation of just how little radiation we’re talking about though.)

    The detection of a neutron beam a mile away, that’s very interesting.

  • Clueless

    Ok, Templar and Cody,
    Please explain to me what all this means? Are we all going to die or what? According to a report that I saw on the news yesturday, Japan is dumping billions of gallsons of radio active water back into the ocean. Fish are coming up very radio active and now it is also getting over here to the US in the milk and drinking water. If it is in the water, then it will be in our food and if it is in our food then we eat it and then what? Cancer? Slow and agonizing death? Deformations and the end of life as we know it. Am I making too much out of this or what? Any imput is appreciated.

  • Rachael Romito

    Hope things are well back in Japan

  • Slightly Concerned

    When we are talking about the entire Pacific ocean, the radioactive pollution is so diluted by the time it gets here at the US shore that it would be extremely challenging to detect. Understandably, the seafood close to the Fukushima shore is not very appetizing in light of what happened.

  • Slightly Concerned

    A media bias obfuscates the seriousness of the incident. When it was the old communist Soviet Union, Chernobyl became an unprecedented catastrophe to mankind. But since it is a US ally and involves a GE designed reactor, it’s not that bad.

  • dave chamberlin

    I appreciate the scientific updates on the Fukushima reactors, the mainstream press has not been reliable. They report on the situation with their their idiotic one sentence scare pronouncements that are not at all informative, just ratings boosters. Thank you and keep us informed of real news.


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