Tuesday, March 15, 2011

A note on Fukushima

With all of the sensationalist scare-mongering that takes place in the news, I have been remiss in providing a voice of reason (for the sake of reason, I encourage you to actually follow and read all of the included links). Of course, I do not wish to underestimate the magnitude of the disaster in Japan - the quake appears to be the largest in Japan's recorded history - and I feel it is a testament to the ingenuity and foresight of the Japanese people that more people have not lost their lives. But something must be said to cease the propagation of the "nuclear myth" in the face of the reactor accidents at Japan's Fukushima Daiichi nuclear plant. In fact, a friend and colleague pointed out yesterday that Wolf Blitzer was debating the safety of nuclear reactors with an expert in nuclear engineering*... and so I must say something.

First off, let's begin with the facts (and nothing else!). One of the reactors (a GE Mark 1 Boiling Water Reactor) at Tokyo Electric Power Company's Fukushima Daiichi plant lost its emergency cooling system because of the tsunami resulting from Saturday's anomalously strong earthquake. The reactor was shut down safely and according to protocol, but because nuclear fuel is so energy-dense (in other words, you get lots of energy out of the amount of material you have), the fuel rods were very hot. This isn't something specific to nuclear reactors, either - when you burn coal, it gets so hot that it turns red. The heating itself is not a nuclear process, but instead a byproduct of energy production. Now, this isn't usually a problem, because a constant supply of cooling water keeps the heat of the fuel under control. But in this specific instance, because of the catastrophic earthquake and tsunami, power to the cooling water was knocked out, and the backup generators were also damaged (keep in mind, before trying to point out that these kinds of things should be designed to withstand a disaster, that it wasn't just the plant - power to hundreds of thousands of people along Japan's northeast coast was lost). So because of the sheer enormity of the quake, it was exceedingly difficult for the workers at the plant to restore power to the cooling water systems. Cut them some slack, folks. This earthquake managed to shift the whole of Japan. No kidding.
So while the cooling water was off, the fuel rods - which are uranium (the nuclear part) coated in zirconium (for chemical protection) - were still hot, and unfortunately hot enough to essentially catch fire. The zirconium coating (not the uranium) burned in the presence of the oxygen in air, creating zirconium oxide (basically ash) and hydrogen gas. The hydrogen gas built up in the cooling water pumping system (which was not full of water, as it should be) and eventually reached a critical limit where it caused an explosion. Again - and I cannot stress this enough - THE EXPLOSION WAS NOT NUCLEAR, IT WAS CHEMICAL.
Japan opted to act on the safe side and evacuate a region around the plant, as they worked out innovative ways to prevent more damage by pumping seawater into the reactor to cool it. While flooding the reactor vessels with water could potentially (and it appears did) cause additional pressure buildup - more hydrogen gas, as well as steam - the mass of water would cool the reactor fuel to the point that it was no longer a potential danger. That was a judgment call, and it's difficult to tell, even with the subsequent explosions, whether it was the right move or the wrong one.

Now, for some commentary. First of all, the reactors in question are about forty years old - just old enough to have been designed before all of the lessons could be learned from Chernobyl and Three Mile Island. While that's true, however, they were built to the rigorous specifications of the day, such that
"The likelihood there will be a huge fire like at Chernobyl or a major environmental release like at Chernobyl, I think that's basically impossible," said James F. Stubbins, a nuclear energy professor at the University of Illinois.
This is really important, as it speaks directly one of the main tenets of the nuclear myth: nuclear energy is not safe. The number of nuclear reactor-related disasters worldwide can be counted on one hand, but because the word "nuclear" carries such a strangely voodoo-esque connotation, we think three disasters = unsafe. Think of all of the reactors out there which haven't failed. Think of the total number of hours they've been running in the last forty years. Statistically, nuclear energy is far safer than the more traditional oil, gas and coal plants (in fact, here are some of those stats), for many reasons (some of which may surprise you). And even radiation is not as scary or risky as you might think, as has been recently explained by a colleague of mine.
We don't need to look too far in order to see the magnitude of the imbalance: just a short distance along Japan's east coast is the Cosmo Oil refinery at Chiba, which on Saturday was consumed by flames due to the quake. Guess what? It's now Tuesday, and the fire at Chiba is still burning. But this apparently isn't as newsworthy as the word nuclear. And the fact that the news is enough to send stock markets all over the map is itself a disgusting and disappointing result.

So I'm making a stand for the future of nuclear energy. It's safe. It's reliable. It's clean. It's efficient. These things were true a week ago. And all of these things are still true.

What we need to be doing right now is not selling Japanese yen on the forex markets or buying shares in solar energy - we need to be helping the Japanese people recover.


*Wolf, you are yet another example of the reason so many people in the US distrust science and scientists, and you're contributing to the scientific illiteracy of the public. What right do you have as a reporter to debate an expert in a specific field? The reason you've brought them on the show to begin with is to provide expert opinion - and an expert, by definition, is someone who knows more about a given subject than probably anyone else. That includes you. This expert has spent his or her entire life studying the topic in question, and yet you, who has known nothing but the basic generalities of the topic for a mere seventeen minutes, think you're qualified to argue over the details? Shame on you. Of course an expert's opinion shouldn't be taken as gospel, so to speak, but it should be given the credence it rightly deserves. You, on the other hand, are a news reporter. Your job (strange as it may seem) is to report the news. Not debate it.
As someone rather eloquently stated the other day, "we call them 'news anchors' because they're slowly drowning us all."

19 comments:

  1. Hi, Kelly-

    I am sure you are right, though you don't really detail what faux pas Wolf was guilty of. But the oil refinery fires don't offer the prospect of a perpetual dead zone in northern Japan, as Chernobyl has created. So while you are right that people are getting a bit off their meds here, the scope of possible disaster is more dramatically volatile for the nuclear plants, thus worthy of (educated) news coverage. You might like Bob Cringely.

    Tens of thousands killed- that is the real story, however. It is unimaginable.

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  2. Burk, of course there is reason for concern - we should not ignore the issue any more than we obsess over it. But if all we can point to is Chernobyl and TMI, shouldn't that say something? As opposed to oil or coal where we can point to instance after instance of tragedy? You're right that the "real story" is the disaster itself, the root cause of all of this, the quake and subsequent tsunami (mostly, in fact, the tsunami) which has devastated Japan and killed thousands of people.

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  3. Yes- it has to do with human nature. The grinding day-in, day-out death toll of, say driving cars, breathing coal plant effluents/exhausts, smoking, etc.. are discounted as being familiar tradeoffs. In sight, out of mind, I guess!

    But dying in an airplane crash, or a nuclear accident.. now there's some drama! Perhaps if we had more nuclear accidents then people would take them in stride better. HA!

    In that connection, Cringely mentions the idea of lots of little, ultra-safe(?) nuclear plants all over the country. What do you think of that? I hear the technology has advanced pretty significantly.

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  4. Thanks for the great information!

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  5. Didn't they scram the reactors - put the control rods fully in ? But the reactors, even with the control rods fully in, still required active cooling ? Is that right, or am I missing something ?

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  6. John, you're correct - after a reactor is "shut down" (ie, the control rods are thrown in), there is still a lot of residual heat in the reactor fuel which requires cooling (this is mainly due to the fact that the nuclear fuel is so energy dense). The issue with the reactors at the Daiichi plant is that the emergency power to the cooling water, which is run using diesel backup generators, failed (the diesel generators were essentially under water, thanks to the tsunami).

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  7. Miss Atomic Bomb (I can call you something else if you prefer),

    What do you mean by "residual heat" ? Do you mean the heat inside the nuclear reactor just by it being at a high temperature when the control rods are put in ? Specific heat, so to speak ? If that was all the heat, you'd think it could conduct via water to the wall and then to the building etc. etc.
    Or is heat still generated after the control rods are put in ? Would that be a nuclear reaction still happening in spite of the control rods being in (that is, the control rods don't totally stop the reaction ), or because the fission products still produce heat naturally - without the need to be struck by neutrons (like the spent fuel rods in the pond, only they're in the nuclear reactor ) ?
    Saying the fuel is "energy dense" is not that detailed an explanation - but it's cool if you don't know ...

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  8. Hi, John-

    If I could help out here, there is a great deal of heat left in the fuel rods. But in addition, there are residual nuclear reactions going on, like the notorious radioactive iodine, which is a product of other fission chains and was supposed to remain inside the fuel rods. It has a half-life of about a week, during which its decay emits more heat, which needs to be carried off. There are a bunch of short-lived isotopes of this sort that require active cooling for at least a week after the control rod shutdown of the main chain reaction, from what I understand.

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  9. John, there's a little bit of both - there is just residual high temperature, which the cooling water can take care of (assuming there is cooling water), and there are also (as Burk says) residual nuclear decays taking place. The fission of uranium is what provides the energy for a (typical) reactor, and it's something uranium will do naturally. Whenever a uranium nucleus fissions (splits into pieces), it throws off two larger chunks as well as a few neutrons. Here's the catch - those neutrons can fly off, strike another uranium nucleus, and cause it to fission. That's how we get the power from a reactor: not by waiting around for the uranium to spontaneously fission, but by putting enough of it together that there are enough neutrons to keep the reaction (the fissioning) going constantly. That's "criticality" - when a reactor can sustain itself on these fissions. When the control rods are in, they absorb lots of extra neutrons and bring the reactor below criticality (so it's no longer sustaining the fission reactions), but the control rods can't actually stop the uranium from still being naturally radioactive (ie, a boron control rod doesn't change a uranium fuel's intrinsic likelihood to decay via fission; it removes the extra neutrons that might cause the uranium to fission faster or more often). Because of the half life of some of the stuff in nuclear fuel, there may be residual radioactive heat for weeks. This isn't unnatural, and it's generally not a problem - only when you're hit by a 35-foot tsunami, it seems.

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  10. OK, thanks for that. It is interesting that there's so much heat generated even with the control rods in that there's still a need for active cooling.
    What about the rods in the ponds ? How hot can they get ? Hot enough to burn ? Hot enough to decompose ? Or just hot enough to melt into a noxious mess that stays where it is ?

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  11. John, there is a need for cooling, but not indefinitely. Think of your car's engine - it gets hot as it's working, but eventually it cools to a safe temperature. Same goes.

    As for the spent fuel containment ponds, what happened at the Daiichi plant (so far as we can tell, with the information available) is this: the cooling water in the containment ponds disappeared (again, tsunami is to blame). This allowed the coating on the fuel rods to get hot enough to react with air (this temperature being a few thousand degrees Fahrenheit), creating hydrogen gas (keep in mind that the uranium of the fuel rods didn't react). So if the cooling water had been present, the rods would not have been so hot, and the chemical reaction wouldn't have taken place. Does that help?

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  12. OK, interesting. Question is, does the reaction of the fuel rod material with air generate free atoms and molecules of radioactive material, or actual dust-sized particles ? As I understand it, the two are in very different categories. You're saying the uranium did not react, presumably you're talking about a surrounding material which is of a relatively more reactive metal.

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  13. Hi, John- Firstly, the nuclear fuel remains not just hot like a car engine, but continues to generate heat due to residual nuclear breakdowns (though not the chain reaction). That is why you can't just let it sit to get cool, as you can a car or a laptop that you turn off. Spent fuel rods take several years of constant cooling before they are stable enough so that someone can think of putting them into dry storage, like was going to happen in Yucca mountain.

    Secondly, without continued cooling, the heat generated is enough to destroy the fuel assemblies (4,000 degrees F and beyond). The cladding burns up, and everything inside-the uranium and its radioactive products- are freed in very hot- i.e. volatile- conditions. The iodine and xenon escape as gasses, the uranium, strontium, plutonium, etc. tend to melt into a viscous mess, (termed corium, from the meltdown), but some is also volatilized, as you heard.. small amounts of plutonium were found outside the plant.

    It beats me why the zirconium cladding burns up, and why it is chosen as the cladding. It is probably very tight vs radioactive xenon escape, has low neutron capture, and resists corrosion/deformation at high heat.

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  14. John, Burk is correct - there are different things which can be released. Some (such as xenon) would be released as gas and thus be molecular, though radon (also a gas) tends to stick to dust particles in the air. Other materials remain "intact" but as a melted mass.
    Burk, as far as I can tell, zirconium is one of the least reactive metals (with dangerous, acidic, caustic, etc, materials). I'm sure newer reactors have different designs.

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  15. Thanks all. I've found a very interesting blog at http://reindeerflotilla.wordpress.com/2011/03/13/all-right-its-time-to-stop-the-fukushima-hysteria/

    Regards,

    John.

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  16. Try that again ...
    http://reindeerflotilla.wordpress.com/2011/03/13/
    all-right-its-time-to-stop-the-fukushima-hysteria/

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  17. Thanks, John - there's a lot of good information there!

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  18. .. and some bad information too:

    "The absolute worst case scenario that we could potentially be looking at here is partial melting damage to the nuclear fuel – similar to the Three Mile Island accident. This will not harm any people or harm the environment,"

    While health effects are minor so far, there has been harm, especially to the workers. And there has been substantial release of radioactive material... 10% that of Chernobyl, from what I hear. The exclusion zone looks increasingly long-term, while the ocean has been the dumping ground for prodigious amounts of radioactive water.

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  19. Burk, sure... first responders are often the worst effected, because of a lack of information regarding the nature or severity of the incident. This is true of many, many things (too numerous to mention), and emergency workers know this. They heroically choose to save the rest of us at the cost of their own health.

    As for the exclusion zone, again, radioactivity is not the end-of-the-world scenario it's made out to be. Much of the what's released from a nuclear accident is very short-lived, and secondarily, radiation has existed to various degrees in the environment since the dawn of life on this planet. The amount we humans have contributed is still pretty negligible. As for the oceans, medical isotopes (from treated wastewater) and leaching from fly ash account for orders of magnitude more radioactive contamination in the oceans than individual events (like Fukushima) do. I'm not trying to argue that it isn't bad, I'm simply trying to put its badness in perspective.

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