13 March 2011

Chernobyl as Precedent?

My thoughts and condolences are with Japan ... the Christian Science Monitor has an interesting post up as to why the unfolding events in Japan are not best compared with Chernobyl, though it is clear that the event is not over yet.
Robert Engel, former IAEA inspector and Swiss nuclear engineer told Reuters Sunday that a partial meltdown of a reactor “is not a disaster” and that he doubted a complete meltdown is possible. And the details of the current Japanese reactor crisis bear little similarity to the Soviet-era meltdown at Chernobyl, which came about through design flaws and human error before it spread a radioactive cloud across much of Europe and Asia 25 years ago.

Experts at the IAEA “aren’t planning for the next Chernobyl” says a mid-level Western diplomat familiar with how the organization works. “But nor do [they] think we are out of the woods yet. The reactors are still hot. But this situation has no relation to Chernobyl, even though I realize that in the popular lore, if you say ‘Chernobyl,’ it means 'catastrophic meltdown.' ”

Key differences

The Chernobyl Soviet RBMK-1000 reactor exploded on April 26, 1986 after inexperienced handlers took the power down and then tried to power it up too quickly in an effort to discover whether a 40-second power gap in the cooling system could be bridged.

The Chernobyl reactor was new, it was undergoing tests, and it had very little structural containment measures to ward off a meltdown.

The Japanese reactors are a completely different design known as Boiling Water Reactors, which are old and tested, and have three quite elaborate systems of containment designed to constrain radioactive leakage, points out Josef Oehmen, a research scientist at the Massachusetts Institute of Technology (MIT) in Cambridge, Mass. “The third containment is designed, built, and tested for one single purpose: To contain, indefinitely, a complete core meltdown,” he writes.

Robin Grimes, director of the Centre for Nuclear Engineering at Imperial College London, told Reuters that the core of the Japanese reactors may be still intact.

"After it's all cooled down, it may well still be possible to simply remove the fuel and dispose of it in a relatively normal procedure," said Mr. Grimes. "What's clear, because of the incidental radiation being released at the moment, which is significant but not overwhelming, is that the structure of the core is probably still intact. So it's not as bad as Three Mile Island."

9 comments:

  1. This one has more detail: http://theenergycollective.com/barrybrook/53461/fukushima-nuclear-accident-simple-and-accurate-explanation

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  2. It's worse than Three Mile Island. Given the amount of hydrogen that appears to have been released, it is almost certain that a significant amount of core damage has occurred as a result of self-sustaining, exothermic CHEMICAL reaction that occurs at high temperatures when a reactor cool is not cooled.

    The GE designed plants do not have a massive containment structure. There were concerns prior to this that about the pressure containment ability of the early boiling water reactor containment structure designs, which almost certainly were not designed to contain a hydrogen explosion.

    The hydrogen explosion at TMI was completely contained within the the containment building with no damage to that building. As we've seen, this has not been the case at two of the plants in Japan.

    The hydrogen that exploded at the Japanese reactors was almost certainly produced by a self-sustaining, exothermic zirc-water reaction that occurs when the core is heated above 2200°F. Parts of the cores almost certainly melted. A large part of the rest of the core probably shattered when relatively cold seawater was finally injected.

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  3. Roger

    there are interesting differences in media coverage across countries. While the BBC keeps it cool, the German ARD (public television) talks about meltdown and worst case scenario, or GAU ("grösster anzunehmender Unfall" - literally meaning "largest imaginable accident").

    The main concern seems to be how nuclear energy can be promoted in a situation where no progress on climate policy targets without nuclear seems possible BUT where we also have a new, heightened sense of risk (the reactors' cooling systems might fail in other circumstances than tsunamis).

    Apparently the German reactors are similar in design to the Japanese and therefore the easy line of reassurance a la Chernobyl does not work in this case. After the Chernobyl explosion the German nuclear lobby did not tire to point out that their reactors had a safe design but the Russians did not.

    Chancellor Merkel allegedly reconsiders her reconsideration of nuclear. The political price might be too high. Previous campaigns around anti-nuclear, especially using GAU, are still fresh in the collective memory. And the exit strategy from nuclear was something agreed by Merkel's political opponents (previous red-green government). So the framing of Japan's nuclear problems is closely linked to the German domestic policy game around climate policy.

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  4. The overconfidence expressed by the experts in that post is stunning. This can backfire badly.

    Contrast the judgments in this story with the NY Times's quote from an anonymous source:

    “They’re basically in a full-scale panic” among Japanese power industry managers, said a senior nuclear industry executive late Monday night. The executive is not involved in managing the response to the reactors’ difficulties but has many contacts in Japan. “They’re in total disarray, they don’t know what to do.”

    If we look ahead to future public opinion about the safety of nuclear power, the failure of overconfident assurances given in the CSM may well push the public to the opposite extreme of embracing the attitude quoted in the Times.

    Sheila Jasanoff documented this phenomenon in her "Civilization and Madness: The Great BSE Scare of 1996," Public Understanding of Science 6, 221 (1997): The British Ministry of Agriculture, Fisheries, and Foods assured the public that British beef was completely safe and carried zero risk of mad cow disease. When the public realized there was no scientific basis for this assurance, the Ministry lost all credibility and the public swung to the opposite extreme, embracing wild estimates that millions would die.

    If experts want to prevent panic and retain the public trust, the best thing is to acknowledge ignorance and uncertainty and honestly say, "I don't know." In this regard, I commend William Broad's story in the Times, "Danger Posed by Radioactivity in Japan Hard to Assess"

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  5. Jonathan Gilligan said... (#4)

    "If experts want to prevent panic and retain the public trust, the best thing is to acknowledge ignorance and uncertainty and honestly say, "I don't know.""

    That's good advice even outside the nuclear energy field...like...maybe even...climate science.

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  6. Jonathan Gilligan said... 4

    The overconfidence expressed by the experts in that post is stunning

    If I understand the nuclear engineers that are floating around the blogging world.

    A 650MWe reactor produces 2,000MWt(thermal) with the control rods out. With control rods in that drops to 200MWt immediately then 50 MWt within an hour.

    3 of the 4 Units at Daini have reached 'cold shutdown'.

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  7. Hi,

    I was very surprised, but the Union of Concerned Scientists blog coverage of the Fukushimi Dai-ichi reactors situation is excellent:

    http://allthingsnuclear.org/

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  8. Even at cold shutdown, the residual heat from the decay of fission products must be removed. Cold shutdown doesn't necessarily mean safe, especially in the catastrophically terrible condition of the Japanese infrastructure and everything else that has to be dealt with.

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  9. Since we are techies (for the most part), perhaps we could have some focused thoughts/prayers on those who are working to resolve this crisis.

    That they may have courage and strength,
    That they may be creative,
    That they may be inspired,
    That they might find everything they need.

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