A science blog with Eric Berger

Expert: Gravest threat at Japan nuclear plant is spent fuel pool


In the wake of the Japanese earthquake many questions remain, but the one I’ve been asked over and over again is what, realistically, is the greatest threat from the imperiled Fukushima nuclear plant.

For answers to some of these questions I turned to Najmedin Meshkati, a University of Southern California engineer who has spent his professional life studying major disasters, including Chernobyl and Bhopal.

As we spoke Japanese officials announced they were close to completing a temporary power line to the stricken plant, which would allow operators to restore critical cooling systems. Here’s why that’s important.

Should we be concerned most about a potential meltdown, or the spent nuclear fuel pools?

Right now I think the gravest threat is coming from the fire at the spent fuel pool of reactor number four. There are four reactors and four reactor vessels. At three of these four reactors apparently the reactor vessels are still intact, and in pretty good shape. There’s a problem with one of the reactor vessels. But in the case of all the reactors, at least there are containment domes.

This is unlike Chernobyl, which did not have a containment dome. Had the Chernobyl reactor had a containment dome we would not have been talking about it, and I would not have spent half of my life researching that accident. The Japanese reactors have a thick layer of reinforced concrete which helps contain escaped radiation. The highest priority problem, in my opinion, is the fire at spent fuel pool four. That to me is even more critical than a meltdown.


The spent fuel pools do not have any containment domes. It’s very much like a typical storage facility. And the roof over this reactor number four spent fuel pool has been blown up. It’s now on fire. Spent fuel is still heavily reactive, and it’s hot. That’s why spent fuel pools need to be under 30 or 40 feet of continuously cooled water. I think the Fukushima pool is under 31 feet of water. If the water over the pool boils away, and the fuel starts to burn, a cloud will get into the atmosphere and cause a massive fallout if they cannot control the fire. (Note: The chief of the Nuclear Regulatory Commission now says there’s no water left at the Unit 4 spent fuel pool. — eb)


The Fukushima 1 nuclear power plant in 2002.

How bad could it get?

One other thing I have heard from sources is that at least one or more of the reactors at Fukushima were using a type of fuel called mixed oxide, or MOX. Mixed oxide fuel, because it’s partly made from recycled weapons grade plutonium, is much more toxic and dangerous than the typical uranium type fuel. If this fire is in a spent fuel pond that contains that type of spent fuel we are dealing with a much more serious situation.

How wide could the fallout spread?

I really cannot answer that question. It depends on the intensity of the fire, and wind direction and I don’t think anyone can really make a sensible judgment about that now.

With that being said, is there any significant threat to the United States?

There are several thousand miles between Japan and the west coast of the United States. The dispersion of the fallout over the Pacific Ocean is subject to many, many unknown variables. It’s almost impossible to model. But realistically speaking, because of the very long distance and the weather patterns over the Pacific, I think the chance is very remote. We may get a few particles, but not a massive fallout that renders an area contaminated.

I’ll have more from Professor Meshkati tomorrow on the implications of the Japanese nuclear incident on the prospects for U.S. nuclear energy.

Categories: Natural Disasters
Eric Berger

75 Responses

  1. Festus says:

    Potential Consequences of a Spent Fuel Rod Holding Pool Fire:

  2. Bill in Houston says:

    @ Posted by: jonsey2000 at March 16, 2011 06:35 PM

    How many times are you going to post that same comment on a Chronicle blog? Check politics at the door or go back to the Puffington Host.

  3. Paul Padley says:


    As added information. The MOX fuel is in reactor 3. For those technically inclined who want a detailed explanation of what happens when a spent fuel pool looses its water, they can read a report issued by the National Academy of Sciences on this.

    This report was evaluating threats from terrorist attack, but the findings directly apply in this case.

  4. Eric Berger says:


    That’s a most helpful link, thank you.


  5. JohnD says:

    Say a fire and explosion dislodges now dry and heating spent rods and these interact to produce a chain reaction.

    Even if the fuel rods were to have a chain reaction, they wouldn’t explode like a bomb. They can’t; the physics of the situation forbids it. It is actually very difficult to make an atomic bomb, reactor fuel just won’t do it. You can refine reactor fuel for U-235 and Pu-240, but they are too diffuse in reactor fuel to explode without being refined.

    What is possible is that the rods get hot and catch fire. The smoke then carries the particulates some distance, but probably not to the lower 48 (that includes Texas {and Katy}). There would be the potential for contamination of oceanic food supplies (think salmon and tuna) but not terrestrial ones.

    What is more likely is a chain reaction in which the material heats up and melts, forming a glowing pool of radioactivity. If this gets hot enough, it could melt its way down to the water table (the so-called “China Syndrome“), where it would create a steam explosion (think water on a grill). The clean up for this would be horrendous but possible, and the contamination would be much more local. NB: This scenario cannot happen for the reactors, as they are in containment buildings designed to prevent this. It is only a remote possibility for the rods stored in containment ponds.

    And what is most likely is that the rods get very hot but do not melt. This creates a local pit of heck, filled with radioactivity and assorted poisonous ocmpounds. Eventually, water gets added to the pile and cools it off, allowing for the rods to be recovered, separated, and stored elsewhere. In this instance, the contamination is almost entirely local though some radioactivity will get spread to the littoral region near Japan (think Minimata).

  6. PDQPete says:

    The extra 30+ pounds most of us are carrying around are more likely to cause cancer, not to mention other forms of death, than what little radioactivity may or may not reach us from Japan.

    But we worry about the radioactivity because we can’t do anything about being overweight–right? Diet and exercise are just myths.

  7. R says:

    Getting back to the US: How long do the containment pools require continuous cooling? Do the spent rods ever cool down to “room temperature”?

    What do European nations do with spent rods? I heard that some nations reprocess the fuel. What does that mean and could the US do it?

    Thank you.

  8. Rick Allen says:

    It would make more sense to me to dump ice from the helicopter,s than water. Most of the water vaporizes before making contact with the reactor.

  9. Eric Berger says:

    For those who want maps of projected air trajectories of the radiation, you can find them here:


  10. xxx says:

    It sure souns like:

    1) The helicopter dumping water does appear effective. Alternatively, many ships have pumps, so all that would be needed is an above ground delivery system. Lot of ships laying around, but maybe one was enroute to Fukushima nuclear plant.

    The pump could pump water without electricity from the facility and there are portable gas driven pumps on Naval ships. Pump water directly into storage area and also as fog to trap and concentrate the radiation that does escape.

    2) If the efforts of 1 are successful in reducing radiation exposure outside the facility, prepare for rgw woerst (melt down). especially if there is an area under the structure and uranium flows like water. Put in place shielding that is required to alleviate gamma radiation exposure while dire removal processes are executed (The problem with Chernobyl appeared the gamma radiation issue was within a confined with no limited access.

  11. xxx says:

    Is there potential Profit keeping the spent fuel rods? What are the economics? Potential profit from recycling the fuel rods, when a facility, in the future, could enrich them?

    LOGIC: It probably takes tons of dirt to get an ounce of enriched uranium and a pound of spent rods to get the same result and probably 1/100th the effort.

    Platumun recycled from catalysts, a couple thousand an ounce? Can’t imagine what uranium would fetch, when it is commercially recycled.

  12. Rorschach says:

    Your expert is an idiot I’m sorry to say Eric. MOX fuel when it left the reprocessing factory might be more dangerous than virgin Uranium fuel pellets, However once the fuel has been in the reactor long enough to be pulled back out for refuelling, the plutonium/uranium ratio is not much different since the plutonium that went in will have undergone both fission and transmutation as will the Uranium in the virgin fuel pellets.

  13. xxx says:

    Salt Bond – CNN had an illustration saying there because of evaporation there is a salt deposit within those vessels which were cooled by salt water and conclusion: the deposit acted like an insulator and thus did not allow cooling.

    That did not make sense for two reasons: one, I know the heat within these facilities break the water bond. If it is that hot, would it not break the salt into sodium and chlorine and the chlorine gas evaporate and the sodium stay behind? And, if true could the periodic black plumes that occur be burn off of this sodium residue (Class A fire)?

    Second, I blogged here, without a response:


    If the “radiation” is alpha and beta particles, it appears that if they fog the plume, they could redirect the water stream into several collection vats/barges (collection Vessel) for two week storage and after the half life reuse the water in barges. I understand that the salt water has high levels of “radiation.

    Second, if it is Iodine (**1) radiation with a 10,000-year half life, there is an acceptable/safe level 1 part per trillion (Acceptable Level), whatever. Time release the radiation plume. The Navy has an NBC protocol for decontamination (spray fog). The objective here is to keep radiation from coming in contact with the ship and wash it away. In this instance, the fog would be used to knock the radiation from the air and capture it (before it blows to Tokyo).

    Test the process/protocol proposed above for the Alpha and Beta particles above. With one addition, execute the process for gamma radiation.


    Time release the iodine by freezing the water in the Collection Vessel (Vessel). Partition the Vessel into segments and have a series of disposable eyelets that the ice would freeze around. Add more water as needed. Lift the ice out by helicopter and transport. The ice may melt in transit to whatever permanent destiny and release the iodine at a rate that as dispersed would be at the acceptable level.

    **1 (Iodine means all radioactive particles with half life greater than one year)

  14. Betty says:


    Would you do an article on how reactors are built, what sort of stuff they use, how they work, what they do with the spent fuel, how long they need to store it. Maybe in sections or just links somewhere non-science folk?

  15. xxx says:

    Shocker “TOKYO — A suspected breach in the core of a reactor at the stricken Fukushima nuclear plant could mean more serious radioactive contamination ”


    Consider hot the plume will be if there is a meltdown. The thermal differential will be so significant that the heat will carry the radioactivity into the Jet Stream and mail this dirty bomb anywhere in the world.

    Special delivery for Wen Jiabao and Steven Spielberg.

    Execute the worst case scenario guys. Build around the infrastructure for as though meltdown is inevitable. Control the uranium and the plume. (Chernobyl paper)

    Horizon leadership all over again.

  16. xxx says:

    Water distillery – Pursuant to my post

    March 24, 2011 02:10 PM


    1) The Salt bond broke the chemical bond between Chlorine and Sodium

    2) The half lives of the radioactive isotopes are weeks (Iodine)

    Technically all that is missing is something to capture the steam and stored the distilled steam until such time the water not radioactive and is potable or drinkable. If, in fact, the steam energy would be sufficient enough, carry the steam into a water tower and chill the water here (Enron Suggestion to Ken: Compressor Station & Power Plant Suggestion Gaza/Palestine Project [*]) Gravity feed water, rather than pump.

    Use process off coast of California and the Sahara Dessert

    [*] Ammonia Generator for water chilling/cooling, proposed by Enron engineer on a bus discussion and in office

  17. xxx says:

    Does anyone know what the problem(s) with this/These issue(s)??:

    “The water must be removed and safely stored before work can continue to power up the plant’s regular cooling system, nuclear safety officials said.

    “Contaminated water inside Unit 2 has tested at radiation levels some 100,000 times normal amounts, plant operator Tokyo Electric Power Co. said.”

  18. xxx says:

    YellowRose this may be an answer…

    Massachusetts drinking water

    At least we know the target, minimum range, of the nasty radiation

    “Massachusetts officials are testing drinking water supplies after a routine sample of rainwater collected in the state showed low levels of radiation that likely originated from Japan’s crippled nuclear plant.

    The sample’s concentration of I-131 was 79 pCi/L (picocuries per liter), The Boston Globe said. Even if people did drink the rainwater, it is “still 25 times less risky than it would need to be in order to cause any kind of health concerns” Auerbach said, according to the Globe.”

  19. xxx says:

    This is not rocket science:

    “”The removal of the contaminated water is the most urgent task now, and hopefully we can adjust the amount of cooling water going in,”"

    And seeing the brief photos on the news they have not begun to address the most pervasive issue with any respect to accomplish the task(s).

    Just because you have a Doctorate in physics, does not mean you have the skill and ability to dewater and clean up your mess.

  20. xxx says:

    I believe I can accomplish this:



    For the suggestion: I would need the layout of the facility, land and sea, and review of the damage around the source of water. If the source of water from the venting/plume I believe the solution will be relatively primative and will involve loading barges probably without pumps (two miles away)

  21. xxx says:

    If they cannot get reading correct presume every said is corrupted?

    Maybe, “…since groundwater would flow toward the ocean, and the plant is right on the coast…” Percolator effect and flows downhill (probably igneous non-porous rock) are exceptions.

    “Contamination has also affected work at the plant itself, where radioactive water has been pooling, often thwarting the vital work of powering up the complex’s cooling systems.”


    PROPOSALS: First, turn pools of water into cement until it the foundation of cement is so high the pool is outside “the work area”. Second, get the Sea Bea (Navy?) to erect floating bridges, and if the water is low enough fill pontoons with cement for added strength. Form matrix of bridge material and line the boxes such that the water can be pumped into and out of the lined boxes, these will become the water containers (Collection Pond). Direct the water to awaiting barges (store to half life). Create a platform for pumps. Third, if the source of pooling water, shroud the exhaust plume and make a distillery. The cement will be the foundation for the structures add scap iron created by tsunami for reinforcement.


    Another tsunami will shove any structure created in PORPOSAL into the facility and destroy the facility.

  22. xxx says:

    At the risk of living up to the namesake of my birthday, I am going to venture a thought.

    First, I know everything radioactive at the facility got there some how? Then, I know professionals have a tendency of thinking and placing themselves in a really small box. This box, however, is worth about $300 Billion, not to mention a few lives and disruption to the world.

    At the risk of overlooking or ignoring the obvious:

    1) Build a temporary storage facility (*) for all things radioactive

    2)Move the radioactive materials from damaged buildings

    3)Fix the damaged buildings

    4)Move everything radioactive back into the repaired buildings.

    (*) Circulate the water in a fancy pool, maybe even outdoors. It does not seem like you could do much worse than that which you have already created, when the lower limit is $300 Billion. Don’t increase the amount of contaminated water, see below:


    Restate preivious blog

    Aerate water, in the pool described above (Bridge Box), with liquid nitrogen to cool the water; and then re-circulate this contaminated water into the cool down process.

    Happy Birthday.

  23. xxx says:

    This approach, like managing the Horizon Incident, is misplaced, “It is clear that more needs to be done to strengthen the safety of nuclear power plants so that the risk of a future accident is significantly reduced,” he said.” (*)

    Assume there will be a failure. This comment is a joke against nature, “”I am confident that valuable lessons will be learned from the Fukushima Dai-ichi accident, which will result in substantial improvements in nuclear operating safety, regulation and the overall safety culture,” he said.” (*)

    This second level approach presumes failure and the industry should design a policy and procedure addressing the question, “What do we do ”’when”’ failure occurs?” In this approach, you presume that the inevitable will occur and design the policy from scratch:

    1) The rods mechanical:

    a. Remove without electricity

    b. Cool without pumps

    2) Capture escaping radiation during procedure 1

    3) Retrieve melted rods during melt down (gravity)

    4) Protect personnel during the “extended” execution of procedures


  24. xxx says:

    1) Try 1000 gallons of tracer die (red, blue and black)at discharge

    2) There was an article on a nano-submarine going into the eye (PM last year?) send out radio impulses? Use a thousand coded and track at discharge?

    3) E-Z Tag and track flow or at discharge

    4) Blood trackers at discharge


  25. xxx says:

    Satelite spectometer can detect “changes” in water color upshore and downshore from reactors, for item 1 April4, 2011 4:01 PM?