Core On The Floor

We have news from a newspaper. In this case The Guardian – UK, which has some bad news about the Fukushima reactor accidents.

Richard Lahey, who was head of safety research for boiling-water reactors at General Electric when the company installed the units at Fukushima, told the Guardian workers at the site appeared to have “lost the race” to save the reactor, but said there was no danger of a Chernobyl-style catastrophe.
Workers have been pumping water into three reactors at the stricken plant in a desperate bid to keep the fuel rods from melting down, but the fuel is at least partially exposed in all the reactors.
At least part of the molten core, which includes melted fuel rods and zirconium alloy cladding, seemed to have sunk through the steel “lower head” of the pressure vessel around reactor two, Lahey said.
“The indications we have, from the reactor to radiation readings and the materials they are seeing, suggest that the core has melted through the bottom of the pressure vessel in unit two, and at least some of it is down on the floor of the drywell,” Lahey said. “I hope I am wrong, but that is certainly what the evidence is pointing towards.”

And if we should get unlucky and that mass of junk that was formerly a reactor core has a Criticality Accident? Well all kinds of bad things could happen. Will it be an all out nuclear explosion? No. But it could be a very small one. Which will spread the radioactive fission fragments around. Or the crud might hit a pool of water causing a steam explosion. Spreading the junk around. Or it might melt into the ground and the radioactivity will get spread into the ground water by natural flows. Or we could get lucky and nothing much worse than is already happening will continue to happen. At the current time I’m not voting for Lucky. I’m voting for Murphy.
For your amusement we have a map of the aquifers of the world in pdf so you can keep enlarging it until Japan gets to a reasonable size. Now compare it to this earthquake map of Japan. From my crude measurements it appears that Fukushima is just outside the Tokyo aquifer. Or it might be close enough that it will be a problem if the radioactive sludge reaches the aquifer. I look forward to seeing better maps in the next few days as the SHTF (or if you prefer – the news gets out).
So how about a recap? We have three reactors and four spent fuel rod pools in trouble, but everything is fine so far.
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You know, I just had a funny thought. Of course we couldn’t have a Chernobyl “style” event. There is no mass quantity of carbon to burn. But could we have a Chernobyl “quality” of event (radiation spread) if things go bad wrong? I think so.
Cross Posted at Power and Control


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6 responses to “Core On The Floor”

  1. Joseph Somsel Avatar
    Joseph Somsel

    Sorry, for a light water reactor like Fukushima, a criticality event AFTER a melt-down is not plausible. One needs the fuel and water in exact proportions and precise geometry plus the control rods are part of the melted mess, called “corium.”
    For a few types of reactors this might be possible, like fast breeder reactors, but not for the commercial reactors of Japan, the US, France or most of Europe.

  2. Joseph Somsel Avatar
    Joseph Somsel

    Sorry, for a light water reactor like Fukushima, a criticality event AFTER a melt-down is not plausible. One needs the fuel and water in exact proportions and precise geometry plus the control rods are part of the melted mess, called “corium.”
    For a few types of reactors this might be possible, like fast breeder reactors, but not for the commercial reactors of Japan, the US, France or most of Europe.

  3. M. Simon Avatar

    ftp://ftp.cordis.europa.eu/pub/fp5-euratom/docs/09-sara.pdf
    Severe Accident Recriticality Analyses
    “Recriticality is possible during reflooding with unborated water of a partly degraded
    core”

  4. M. Simon Avatar

    ftp://ftp.cordis.europa.eu/pub/fp5-euratom/docs/09-sara.pdf
    I guess you have to type an ftp into your browser. I tried it and it works.

  5. Joseph Somsel Avatar
    Joseph Somsel

    Please note that I said “not plausible.”
    There MAY exist certain exceptions and rare cases but we don’t really have much real world experience.