In part 1 of this series, I talked about Buffalo Bill Cody.
In part 2, I talked about meeting a person who wanted to talk all about naked pictures of my sister-in-law.
In part 3 I talked about Brazilian fish.
This is part 4 about cesium, and I think it's time to move on to something else, like technetium for instance, so let's cut to the chase. I am going to finish up cesium. I'll return to being amusing in future entries. If you want to see me trying to be amusing, look at the other entries. If you want to know about the constituent of so called "nuclear waste," that is cesium, I invite you to read on. Mostly the discussion is technical, but I'll throw in a little space science fiction about aliens finding us, if you need things like that to be interested.
In part 1, besides Buffalo Bill Cody, I discussed a technical issue, the Bateman equations, and the existence of radioequilbrium. By appeal to this equation I suggested, in general terms to a first approximation, how much cesium-137 - probably one of the most problematic of all constituents of spent nuclear fuel - could accumulate before it began to decay as fast as it is being formed. In this calculation I assumed that every last drop of energy now used on the planet was obtained by nuclear fission. Here is the amount I estimated: About 8,500 metric tons, a quantity that would take centuries, if not millenia, to accumulate. The first year more than 200 MT would accumulate, and each year after that, less and less and less would accumulate, until the amount of [i]new[/i] cesium-137 that accumulated, world wide, would fit in a coffee cup, and, if the world went on longer using nuclear energy, the gut of a fly.
Right now, at least until we have new types of reactors that are only the subject of pilot plants and R&D, it is only immediately possible to use nuclear energy to phase out coal, and not to drive your car or bus. This is I am arguing that this is precisely what must be done to make the world safe for future generations.
The world produced - and this is a disgrace - about 120 exajoules of primary energy by burning coal last year. If the world produced 120 exajoules of primary energy via nuclear means - displacing coal - adding the 120 exajoules to the nearly 30 exajoules produced by nuclear now (150 exajoules) the maximum amount of cesium-137 that could accumulate would be just under 3,050 MT. It would take about 200 years to approach this amount, at which point less than a ton of additional cesium-137 would be accumulating per year.
The situation with cesium-135 is very different, since cesium-135 has a long half-life compared with cesium-137, but the supply of cesium-135 could be controlled fairly easily by the power level of the reactors producing it, as I also explained in part 1. For those with a technical bent, the terms for nuclear decay in the Bateman equations do not dominate the maximum but - because of the nuclear precursor, xenon-135, the terms for neutron flux do.
When cesium is separated from a spent nuclear fuel, it will contain, a mixture of three isotopes, cesium-137, cesium-135 and cesium-133. The last is not radioactive, but it increases the (small) bulk of cesium isotopes. Over time, as the cesium stands, fraction of cesium-137 remaining will decline, eventually falling to almost zero. After a few hundred years all that will be left is cesium-133 and cesium-135.
Types of reactors that are not being built yet on a commercial scale, molten salt reactors, might potentially allow for the separation of the various cesium isotopes in some cases, by exploiting the ability to remove xenon while on line, but that's too technical and speculative right now to be seriously discussed here.
I will discuss the subject of nuclear transmutation in connection with other elements in so called "nuclear waste," but - at least purely for its own sake - nuclear transmutation of cesium-135 into a shorter lived isotope is not really, for the time being, a feasible option. It probably wouldn't work very well.
So what is the NNadir answer to the question, "what do we do with the waste?" so far as cesium is concerned?
The glib NNadir answer is "find a use for it." I have both in the main body and the comments sections of the previous three parts of this series discussed some possible uses for radiocesium. I said that the radiation from cesium-137 could be used to break-up difficult stable molecules in PCB's that contaminate Hudson River striped bass. I talked about medical therapy machines. I talked about something called "neutron transparency" I talked all about futuristic ion propulsion engines propelling Cesium-135 powered spaceships across the sky.
Blah. Blah. Blah.
OK now it's time to do the science fiction promised. When I was a young man, several nuclear powered spacecraft were launched that were designed to fly past the planets Jupiter, Saturn and beyond. One of these spacecraft visited Uranus, then Neptune. I love things like that. For me, cranky old atheist that I am, this is the true purpose of humanity, to see further and further and further, to see, just to see.
NASA spent a lot of money recording the Rolling Stones and drawing naked pictures of a man and a woman, and digitalizing the frequency of pulsars and sending them out of the solar system. (NASA also made some plagues that were less "smutty," sending phonograph records, literally gold records, on the Voyager craft.) The idea was for space aliens to find these naked pictures and to learn about how we looked naked and how to locate the place they could learn more about Mick Jagger, and Keith Richards and those other guys who are even older and deader than NNadir.
I can't get no satisfaction. No satisfaction. No satisfaction.
What do I think about the probability of space aliens finding and being offended by Brian Jones and naked pictures of earthlings? I think it's essentially zero. On some level the whole exercise was silly, but I do understand the emotions that caused us to send the naked pictures anyway. It was our first time away from home. You can't help but to have unreasonable expectations about a thing like your first time away from home.
If I were looking for space aliens, I might not look only look for broadcasts of the ancient epidsodes of "Hoody Doody" and old commercials with sexy girls in convertibles singing about how "Lucky Strike Means Fine Tobacco." Instead, I might look for a beam of Cesium-135 contaminated by Barium-135, a cosmic ray.
A shark is shaped like a submarine not because submarine designers of submarines are fond of sharks, but because the shape shared by submarines and sharks represents the mathematically most energetically efficient way of traveling under water. Submarine designers like to minimize the energy requirements of under water travel. So do sharks. Sharks evolved as they did because of this. Submarines were designed to look like submarines, because of this.
The most energy efficient way of travelling in space is to take an atom of cesium-135 and to accelerate it to near the speed of light in an accelerator attached to a spacecraft. It doesn't get any better than that. That's the ideal solution if you live in this solar system. That's the idea solution if you live 800 zillion light years from here.
More or less, with some exceptions, if you found a lots of beams of cesium-135 mixed with barium-135, you could tell some things about the space aliens who may have created it. If you knew the laws of relativity - and who goes travelling in space without knowing that? - and all time dilation in high velocity objects you could tell when they shot off this bunch of space exhaust. You would simply measure the ratio of Cs-135 to Ba-135 and back calculate. You might also tell whence they sent it by careful examination of the direction. Of course, you wouldn't have naked pictures, but all the same, you could learn a lot, more than you could learn by listening to Bill Wyman's bass. Bill Wyman's bass, no offense, would say a lot less than a beam of cesium.
"Look," you say, "You're being ridiculous. I know something about ion propulsion engines. Nobody is even contemplating making one with cesium-135. It ain't happening. The one's that exist use xenon, not cesium, especially not radioactive cesium. Are we hearing this complete line of wishful thinking from the same beast who shits all over renewable energy because he only values what is available right now?"
In part 2 of this series, I indicated that I had a ridiculous idea about a cesium cooled reactor that was, well, ridiculous. Maybe the whole idea about ion propulsion engines is the same. Maybe not. In any case, we're not talking about grand space fleets featuring grand space admirals fighting grand space wars. If we used nuclear energy to phase out coal, in the best case we might only accumulate a hundred metric tons of cesium-135 in a year on the whole planet. This could propel one heavy spacecraft to Mars or beyond over a period of years, maybe, but not one containing Captain Kirk and all his girlfriends and the life support systems and piles of contraceptives.
In fact the vast majority of what is in so called "nuclear waste" is unchanged uranium, the same uranium that has spent more than 4 billion years on this planet, waiting to decay. Only a fraction, typically less than 5%, of what is is in spent nuclear fuel is fission products. Of those fission products, on a relatively small percent is cesium. Of that cesium, only some of it is highly radioactive, and some of it is long lived.
Our decisions about "what to do" with consituents of spent fuel will depend on how much we have. If we only have a little, our options will be esoteric. If we have a lot, we can do lots of things, different things, in fact. At least one of my ideas - which might be silly or might not be silly - an idea which I will not now discuss in any detail, requires lots of radiocesium.
But let's get real. The only "use" for radioactive cesium right now is in calibration devices and medical treatment as a few more esoteric things. In the comments section of Part 3, I indicated that all of this use could be addressed by a few kilos, which leaves metric ton quantities to sit around and do nothing. As noted in early entries, even this "use" has not been without serious setbacks, like the death of that little girl in Brazil.
I believe this situation will change, especially as we get more of radiocesium with which to play, but I cannot prove it. Let me tell you right here. Cesium is the most problematic fission product there is in my view. It's difficult stuff to handle.
A young future nuclear engineer wrote in here to tell me something I already knew, that the main use of radiocesium today is to keep people - some of whom may have bad intentions - away from spent nuclear fuel. This is a good thing, such as it is, but it is not what I would intend for the long term. I think people do in fact, need to get at the other stuff in that spent nuclear fuel.
So again, what is the NNadir plan for cesium in spent nuclear fuel? I believe the best course of action would be to isolate the cesium, remove all of the elements in it about which I will talk in future entries. Then what?
Well how about being patient? How about adopting a "hold on it to it, catalog it, watch it, keep it where it is readily accessible until we have thought long, hard, and deeply about it." Suppose we want energy efficient ion propulsion engines powered by cesium-135? What then? Suppose that any of other ideas that people like me (and I have lots more) pan out? What then?
Cesium capsules from the 1970s and earlier exist and are well characterized. Linked below is a report from the National Academy of Sciences that talks about the status of cesium capsules. NNadir ideas about the use of cesium do not have pan out for cesium to prove useful in the near or long term future. There are many tens of thousands of nuclear professionals working all over the world, many who are much, much, much smarter than I am.
There are 2,000 stainless steel cesium capsules at Hanford, Washington, containing, all together, 67 million curies of radioactive cesium, about 35,000 curies each. One canister leaked, the other 1999 didn't. Each puts out about 190 watts, something considerably less than a floodlight at an "No Nukes" Sting concert. The idea that some people have is to dispose of them. How about we don't? These capsules are more than 30 years old. They are information about time and radiation and it's long term effect on stainless steel. I suggest we hold on to them. They are important. The are valuable. They have been irradiated for more than a half-life of cesium-137. There is so much to learn from them, I cannot begin to guess.
Here is the number of deaths associated with the 2,000 stainless steel cannisters at Hanford: Zero. (Still, in spite of killing zero people, they are yet described by some, as the "most lethal" single source of radiation in the earth. That description is most curious, since generally the condition of being lethal is associated with dead bodies.)
Suppose I am wrong, suppose there is no way to effectively to use radiocesium?
The equilibrium cesium concentration at 150 exajoules per year of nuclear energy (the coal phase out number) represents about 260 billion curies of radioactivity. This is about 50% of the potassium-40 now found in the ocean, and is roughly equivalent to the radioactivity found in the ocean about 1.2 billion years ago, if one only restricts oneself to the radioactivity of potassium, assumes constant salinity, and ignores all of the other radioactive substances there, like those in U-235's decay chain, and that associated with rubidium. (The latter factors, in fact, make the radioactivity even higher, not lower.)
(Someone asked me to provide links for the radioactivity of the ocean. Here are some from which the calculation may be accomplished:
The Volume of the Ocean. Chemical Composition of Seawater, Including Potassium. The other relevant data, decay constant, isotopic composition, etc, can be found in the Table of Nuclides. If need be, I can walk us through the calculations involved, but only if requested. An interesting discussion of potassium in seawater was conducted by readers in the comments section of part 3.)
It is, however, not likely that radiocesium need ever find itself into the ocean at all. I have alluded in a few places in this series to the oldest rocks on earth, the rocks of the Canadian Shield (also of Greenland) that are many billions of years old. These pegamatites contain the mineral pollucite, which is a cesium mineral. These rocks have taken everything the earth can dish out and have remained unchanged for billions of years. People like to pretend, when making anti-nuclear arguments, that if any single incidence of failure implies the failure of all the systems. This is nonsense.
What if in two hundred, three hundred, one thousand years, someone for some reason wants to dump cesium?
It has been shown in many places in the scientific literature that the migration of cesium in geochemical systems is not straight-forward. For instance, even though cesium-137 from chernobyl has a half-life of 30 years, the half-life for bioavailability is much lower, about 2 years. This is because the cesium forms complexes certain constituents of soils that are very stable, making it unavailable for uptake by plants as a potassium mimetic.
"But, but, but, but...NNadir!" you say, the cesium in the Canadian shield is not radioactive!"
Some of what I say here may strike you as original, but I assure you it is not. Very few of my ideas are new. Mostly they are derivative. The properties of cesium based pollucites have already garnered the attention of researchers and synthetic cesium-137 based pollucite synthesized. Frankly the researchers expected problems, but found none.
Note that the idea here - and I'm fairly sure it will never become necessary, is not the same idea as Yucca Mountain or similar places proposed around the world. In those places the foolish idea is being proposed of disposing of everything in spent fuel, and not just the small fraction represented by cesium. This is not a good idea and I oppose Yucca Mountain. In my view something like Yucca Mountain may be worth considering a few hundred years from now if better options don't present themselves. But I'm fairly certain that better ideas will present themselves, since even a fool like me can imagine a large number of them. In any case, in the worst case, cesium might be the only thing we need to contain, and that's not a big problem.
This Study from the National Academy of Engineering suggests something of this idea and indicates that the volume requirements for geologicial disposal - if ever needed - would be vastly smaller than currently evisioned.
Suppose one made a synthetic pollucite containing Cs-137 that failed after sixty years? What then? Would it all end up the ocean? In your breakfast cereal? In your flesh right next to the coal wastes you already contain? No, not at all. The cesium would need to be transported somehow from the area outside of the failed pollucite. Effectively there is only one way for this to happen, which is to be transported, at least until it can form a blowable dust, through the intermediate of a water solution, water that percolates through the pollucite. If cesium by magic made it out of pollucite, it would still need to migrate, probably across tens, maybe hundreds, of kilometers. As it did so, it would become more diffuse and most importantly, it would, unlike coal wastes, continue to decay. The most likely state of affairs is that by the time it got to a place where it might make trouble, it would have mostly disappeared.
Thus, after a few centuries, we find that we don't want cesium, we could take some of the old, cooler mixtures (essentially decayed only to Cs-133/Cs-135 mixes) and make pollucite. The risks of doing this are almost vanishiningly small.
The fact is that cesium can be managed, even in the less than certain case that it doesn't prove to be an important resource.
Of course, when people oppose nuclear power, they want you to think very differently than I do. They want you to imagine that all of any released radionuclides are going to make a beeline right for your flesh and magically be concentrated there. They want you to run with your imagination.
Well, if you must imagine things, how about climate change?
In fact though, at least in the case of cesium, there are few, if any, concentration mechanisms, at least not like the concentration mechanism that exists for just one of the coal wastes, mercury. I am speaking of course, of the horrible situation in fish throughout the world.
By comparison, unless rendered into an aerosol form (such as at Chernobyl) cesium tends to move relatively slowly in the environment, much slower in fact than people expected.
The situation quickly degenerates to absurdity, as follows: First the pollucite has to leak, then it has to be leached then it has to travel long distances, and then you has to find itself into living systems, and then you have to eat it or drink it, and then you have to wait around to get some kind of cancer. Somehow, nevertheless, you manage to convince yourself that all of these improbable events somehow are the same as a certainty.
It the meantime, let me assure you, without any appeal to probabilistic events, you are breathing coal waste - some of it quite carcinogenic - right now.
I invite those with access to the scientific literature to access a recent article in the literature on the subject of cesium, Environ. Sci. Technol. 2006, 40, 4500-4505. This is about cesium at the Savannah River Site, a nuclear weapons site. (Note that I oppose all nuclear weapons.) The site is considered contaminated. Refer to figure 3 and the units. If you are really, really diligent, I invite you to consider if a kilogram of a contaminated plant is experiencing more decays than you are as a result of the natural potassium in your body.
I am sounding very cavalier, and actually I don't mean to be so. Radiocesium has risks, real risks. However these risks can only be viewed as extreme in isolation. To be make wise choices we have to compare these risks to the risks of not making radiocesium, which is precisely coterminous with the risk of burning coal. I submit that the risk of burning coal is much larger, by many orders of magnitude.
When I planned this series, I had collected a load of scientific papers. I wanted to talk about biological half-life, behavior in illitic clays and many other things. But there is not time. I am going to move on and talk about other elements, strontium, technetium, neptunium, plutonium, etc, etc. Keep in the back of your mind should you bother to read another article by me, however, that I regard cesium as the most problematic of all so called "nuclear wastes," and I actually don't think it's all that bad.