Fukushima-Daiichi Severity Increasing

From a nuclear expert:

Spent fuel in the pools in Units 3 and 4 is now uncovered. Unlike the releases from damaged fuel in the reactor cores of Units 1, 2, and 3, which were largely filtered by scrubbing in the containment suppression pools, releases of volatile fission products (Cs, I) from these pools have direct pathways to the environment.

Efforts to deliver water to these pools have proven to be very difficult, and fuel damage is occurring. The use of the evaporation of salt water as a heat sink over periods of more than a few days is not viable because the quantities of salt deposited as the water evaporates becomes large in volume and plugs the flow paths through the fuel, degrading heat removal. Fresh water supply is difficult to come by. It may be practical to bring fresh water by helicopter (this is being attempted), but the amounts needed imply a very large number of flights and radiation levels are extremely high above the pools making overflights hazardous. If radiation levels on the ground increase further, personnel access will become more challenging. Additional spent fuel is stored in pools in Units 5 and 6 and in a large centralized storage pool. A key issue is how to continue to make up water to these pools in the longer term, particularly if site access becomes more difficult or impossible.

In short, this accident is now significantly more severe than TMI. It resulted from a unique combination of failures to plant systems caused by the tsunami, and the broad destruction of infrastructure for water and electricity supply which would normally be reestablished within a day or two following a reactor accident.

My earlier belief that this would not lead to widespread radioactivity dispersal is based on the assumption that cooling to the spent fuel pools can be maintained. This is currently uncertain. Iodine-131 poses the most significant radiological risk to the surrounding populations, and access to potassium iodide or other iodine-rich foods would be prudent.

UPDATE: Commenter Zach Clayton pointed out something that I should have made very clear in this article–there is no iodine-131 in the spent fuel. It decayed away to harmless xenon-131 a long time ago. The xenon is also completely stable, and the krypton only contains krypton-85 which poses essentially no threat. The riskiest substance in spent nuclear fuel is likely the cesium, and potassium iodide pills will do little to counteract that threat. But cesium doesn’t “bioaccumulate” in the thyroid either.



16 Replies to "Fukushima-Daiichi Severity Increasing"

  • Edward Peschko
    March 16, 2011 (9:45 pm)


    This might brighten your spirits up a bit. Its a report on the spent fuel cask setup at fukushima:

    In order for wide dispersion of radiation to be done, the rods need to catch fire, which needs 3200C, and in tests with even recently used nuclear fuel, some melting occured but this never happened. I'm still confident we'll escape from this without a Chernobyl release.

    Still, I've gotta question the wisdom of putting the nuclear fuel casks *on the roof of the facility*. No matter what happens.that is looking like a bone headed move.


  • Dan
    March 16, 2011 (10:33 pm)

    This seems to imply that there would not be a significant risk if infrastructure were intact. I don't understand why we can't deploy significant military resources to move in fresh water in at a rapid pace. Doesn't the US have bases in South Korea that could bring water in?

    It seems like preventing a nuclear disaster would be the highest priority for all nations involved.

  • mat
    March 17, 2011 (2:10 am)

    Just wanted to say thanks for all your work Kirk. Everytime I see someone post something about this on Facebook, I give them your link and tell them to go read. More times than not they thank me. You rock!

  • Rod Adams
    March 17, 2011 (2:21 am)


    I just posted this on Brave New Climate. Your readers need to see it as well.

    The spent (aka used) fuel pools are not generating hydrogen. They are not boiling away. They are not empty. UO2 CANNOT burn, it is already fully oxidized. (That is what the O2 part of the compound equation is.) Between 90-95% of the material in a used fuel pool is UO2.

    The water level in the pool at unit 4 is significantly lower than normal, which leads to higher radiation levels above the pools than normal. Here are the most recently measured levels – 410 millirem/hr at 300 feet, 8.7 REM/hr at 1000 feet. (Either the elevations or the radiation levels or a combination are off by a bit since they do not fit the usual equations exactly for dose rate attenuation with distance.)

    Those levels can be easily explained as simply a matter of a reduced amount of shielding above the still radioactive used fuel. Pools normally contain about 7M of water, the tenth thickness of water is .7 meters. You lose 70 cm of water, the dose rate above the water increases by a factor of 10.

    As swimmers know, it is never surprising to see clouds of steam rising from hot water on a cold day. However, even with an increased rate of evaporation, pools take a long time to empty out.

    The temperatures in the pool at unit 4 rose from about 24 C to 84 C during the first 4 days after the quake/tsunami. That should give you numerically inclined people the confidence to assert that boiling off of 7 meters of water could not have occurred during the 5th day. (Don't forget about the latent heat of vaporization.)

    All that said, adding even centimeters of water back to a pool is not something that a few helicopter loads can handle. They cannot carry all that much water; the stuff weighs a kilogram per liter.

    It takes a 200,000 liters to raise the level of a pool that is 10 meters wide by 20 meters long by a centimeter. A CH-46 medium lift helicopter has a capacity of about 3,180 kg. It would require 63 trips to raise the water level one centimeter if my guess on fuel pool dimensions is reasonable.

    See why they want to bring in fire cannons to top off the pool? This is not desperation, it is simple math and logistics.

  • Rod Adams
    March 17, 2011 (2:31 am)

    @Ed – there are good, practical reasons for putting a used fuel pool at the elevation chosen. If you read the link that you provided, you will see how small the risk is.

    This whole notion of spent fuel pool fires is a fantasy. Can't happen in the real world of chemistry, thermodynamics and physics.

  • Edward Peschko
    March 17, 2011 (2:48 am)


    The one thing that bugged me about it was this:

    :The only way to rapidly drain down the pool is if there is structural damage to the walls or the floor."

    which implies that a leak *can* occur. put it at ground level, and no large scale leak can (easily) happen. Worst case, small ones. And – most important of all, no likelihood of not being able to deal with reactor issues in the case that the shielding DOES go away (which is plaguing fukushima right now)

    If the rationale was to keep it there for easy loading and unloading of the fuel, I'd say that was misplaced. Better to have a automated system that lowers the fuel in.

  • Rod Adams
    March 17, 2011 (2:59 am)

    Correction to math above – it takes 63 fully loaded trips of a CH-46 to raise the water level in a 10 m x 20 m pool by 1 m (vice previous word of 1 cm).

    Sorry. It is kind of early this morning.

  • Chris Crowe
    March 17, 2011 (2:59 am)

    Thermodynamics is my thing, nuclear isn't. Spent fuel pools may not be able to catch fire, but spent fuel pools can get hot, and they can melt. UO2 is v refractory, so melting point is very high, so I doubt that the problem is that they can melt, but they might be able to melt the vessel walls that they are contained in.

    In my fleid of metallurgy, there are histories of accidents where very hot material accidentally falls intio a pool of water. This results in an explosion, and its nothing to do with H2 and O2 recombining, but rather 18 g of water (3 teaspoons) expanding within miliseconds to a few 100 litres of steam. You would not believe the violence of these explosions.

    I wonder if anyone has considered anything other than water, like eg lead (melts at a few hundred degrees, only boils at 1600, no water explosions) or calcium carbonate (takes a lot of heat to calcine to lime and CO2)

  • Rod Adams
    March 17, 2011 (3:01 am)

    Oops, did not correct all of the numbers. It takes 200,000 liters to raise the level of the 10 m x 20 m pool by a meter (vice centimeter).

  • Kirk Sorensen
    March 17, 2011 (5:09 am)

    Thanks Rod and Chris, I appreciate your insights and inputs, and especially your calculations.

  • David L.
    March 17, 2011 (9:16 am)

    I've asked this on BraveNewClimate as well,

    What volatile fission products are of concern in the spent fuel bays (that have fuel at least several months old)? In the BraveNewClimate article there is this comment

    releases of volatile fission products (e.g., cesium and iodine) from these spent fuel pools have direct pathways to the environment, if they remain dry for an extended period.

    But would there actually be any iodine to worry about any more (8 day half life)? Is there secondary production from another decay chain? I know there will be some Iodine 131 but that has a million year half life so virtually harmless.

    How much cesium might be release from these spent fuel bays and how much of a concern would they be? Is cesium only mobile by its precursor Xenon which would also be stable by now in the spent fuel bays.

    Am I missing something or is there very little volatile fission product danger here and with the low heat rate also very little chance of zirconium producing hydrogen?

    David L.

  • Zack Clayton
    March 17, 2011 (9:23 am)

    I am looking at the I-131 comment at the end of the article. If these are spent fuel elements then Iodine of any nuclide is not being produced by direct fission. The direct precursor of I-131 is Tc-131 which has a 1/2 life of 1.35 days. So I-131 has a half life of 8.04 days. That means in a little over 80 days the I-131 will have gone through 10 half lives. A negligible amount will be left. Unless reactors 4 5 and 6 were just unloaded there is not a full core's worth of Iodine-131 left in there to release.

  • konst
    March 17, 2011 (12:42 pm)

    Interesting article by Leo Dirac on using reactor decay heat after shutdown to power electric generators for continued cooling when electric grid is not available.

    He says this is what Chernobyl operators were trying to accomplish but it failed catastrophically in the third and final attempt.

  • Paul Hardy
    March 18, 2011 (11:58 am)

    What happens to the Strontium?

  • 34mind
    March 19, 2011 (8:16 am)

    Spinach and milk tested in farms near troubled Fukushima plant are contaminated with iodine-131 and cesium-137. Five times higher than safe levels in milk, seven times higher in spinach (iodine-131). Spinach also has higher levels of cesium-137.

  • Brian H Campbell
    April 1, 2011 (8:48 pm)

    We need to get the word out about thorium energy. I've called 3 or 4 popular live radio talk shows and none of the hosts knew anything about thorium energy.

    One of the radio hosts said he might get an expert on his show to talk to his audience about it. Kirk, please email me. I truly believe the live talk shows will generate the buzz thorium energy and LFTR specifically needs.

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