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On Nuclear Energy

Posted by tigerhawkvok on November 11, 2008 23:01 in physics , politics

So, on change.gov, President-Elect Obama lets you "share your vision" via a web submission form. So, I took the time to compose a (perhaps unfocused) letter about nuclear power to him. He probably won't read it, and I probably have some damnfool mistake that makes a fool of myself, but on the off chance he does, I can always hope I made a tiny bit of difference.
President-elect Obama: I was a Republican until this election, because the (nominal) fiscal policies of the party appealed to me. However, an increasing pandering to the religious right and a strong antiscience bent made me vote for the first time this past election day for a democrat – yourself. I truly hope that the change you promise to bring to America is fulfilled, and I have high hopes that the scientific community will benefit under your administration. However, in hopes that you will truly read some of these letters, I wanted to write to urge you to consider one of John McCain’s positions, and only one. I would like you to very strongly consider the expanded use of nuclear power in the United States. One of the first things to understand about nuclear power (in this, I refer to fission power unless otherwise mentioned) is that a fission reactor is, quite literally, the third most efficient mechanism of generating energy known to exist in the universe. The only more efficient ways of generating energy known to modern physics is by fusion (1% mc^2, ten times more efficient than fissions 0.1% mc^2), throwing matter into a black hole and capturing its radiation (about 25% mc^2, though we know of no way to do this on Earth), and an antimatter reaction (100% mc^2). These numbers provided neglect reduction in efficiency due to heat transfer mechanisms. Needless to say, these numbers dwarf conventional fuels, with a cubic foot of uranium containing the same fuel-energy as several million tons of coal or several million barrels of oil [ http://en.wikipedia.org/wiki/Fuel_efficiency#Energy_content_of_fuel ]. One kilogram of gasoline will generate about 50 MJ of energy -- one kilogram of fusion fuel will generate about 630,000,000 MJ of energy, or 12 million times more efficient by mass. For comparison to a renewable such as solar power, let us calculate the total energy influx from the sun (this is the theoretical maximum amount of energy that can be taken in by photovoltaics and wind). Covering every point of the US with the most advanced photocells will give about 500 TW (trillion watts) of energy (at 50% efficiency), of which the US uses 3.5 TW. In practicality, not all of the nearly 10 million square kilometers will be used by photocells. To generate the US’s current energy demands (day and night), we would need something like Conneticut entirely covered by photocells, receiving uninterrupted maximal sunlight for 12 hours per day and storing half of it for use at night. For comparison, about 3,500 of the newest reactor designs would accomplish the same goal at a small fraction of the area requirement, which decreases when we consider the renewable energy sources already in place and simple measures like solar cells on rooftops. Furthermore, an increase in funding in fission reactor technology, particularly breeder reactors, will grant us thousands of years of clean energy (approximately 40,000 years, since a breeder reactor uses U-238) and generate more stable end isotopes [ http://matse1.mse.uiuc.edu/energy/prin.html ]. It is important to realize that the fact that something is radioactive does not make it dangerous. Both quantity and its activity on a biological time scale are important. Specifically, the half-life of the material needs to be comparable to a human life span. If it is not, only a very small fraction of the energy possible through radioactive decay is released. That is, a radioactive material that releases most of its energy over two or three years is much, much more dangerous than one that releases the same amount of energy over several million years – because any person standing around the second one receives a very small fraction of the dose, which is harmless. After all, we get small doses of radiation from a banana and even more from the sky every day, as charged particles travelling near the speed of light hit our atmosphere. So let me reiterate: long lived isotopes, like those you are more likely to get with a breeder reactor, are much, much less biologically potent than those in breeder nuclear reactors, but last much longer. It is a mystery to me why breeder reactors are so frowned upon by the government, when virtually any scientist with a knowledge of reactor design will agree that they are the best, if not the only way to proceed with fission-based nuclear power. Careful selection of pathways will allow you to tune to short or long lived isotopes, depending on goal. There are two reasons why we should proceed with fission-based power. First, and simplest, is the fact that it is incredibly “green”. It is a zero-emissions source, with manageable waste produced more cheaply in an smaller land footprint than “renewable” sources [http://www.world-nuclear.org/info/inf02.html , http://www.our-energy.com/energy_facts/nuclear_energy_facts.html ]. The second point relates to fusion, which we can all agree is a superior alternative to fission. It has no radioactive byproducts by many pathways, and it is ten times more mass-efficient with a much larger mass source than fission. However, it is important to realize that most neutron-less (aneutronic) fusion pathways are not feasible with current technology. The sun’s reaction path, the “proton-proton chain”, works only because the incredible pressures placed on the plasma by gravity allow quantum mechanical tunneling to bypass part of the coulomb barrier. In slightly more digestible terms, imagine you have the same two sides of a very powerful magnet. They are very hard to press together, because they repel. These represent two protons which are to be fused. As you press them closer and closer, the repulsive force increases, making it harder to press them a little closer together. In a star, gravity gets them so close that quantum mechanics allows for the probability that the proton will just “jump” that gap, and arrive close enough to fuse. Every single photon of light we get from the sun is due to this probabilistic jump that lets the protons get closer. Without the pressures of the sun, though, for us to replicate an aneutronic chain like the sun we would need to have our reactors ten times hotter than the core of the sun. It is a strange quirk of physics that without quantum mechanics, the sun (and all stars) are literally too cold to fuse matter. So if we accept fusion-based chains that allow for neutronic reactions (reactions with neutrons as by-products, which unfortunately carry much of the reaction energy away in addition to being what most people think of as “radioactivity”), there is still an underfunding of nuclear fusion research in the US, which is in no small part due to the social stigma of fission reactors. The successful expansion of nuclear fission reactors is critical to the more rapid development of fusion reactors. It is still no small task for the scientists, but with neither funding nor social support, fusion cannot proceed. Mr. President-elect, I implore you to look past my somewhat erratic prose and strongly reconsider your position on nuclear power and help the United States enter a true nuclear age.
I followed this up with an email to some friends, in the hopes this might make it to some third level aid and have some itty bitty effect. When Peter sent me this reply: "Sorry, but I've heard that nuclear power generates nuclear waste, and even after processing it must lie underneath the ground for ~8000 years to become safe. Thus, I don't really trust nuclear power. Care to convince me otherwise?" I chose to follow up with this:
Inevitably it generates nuclear waste, but the problem is largely mitigated by breeder reactors. By using these, we can essentially tune the type of waste we would like. It is generally preferred to have short half-life products, which is primarily produced by breeder reactors (http://en.wikipedia.org/wiki/Fast_breeder_reactor ). The idea is it will lose essentially all of its radioactivity in a manageable time frame, thus having to be stored for a much reduced period of time. The standard nuclear waste has a half life on the order of 25,000 years. This isn’t particularly dangerous, if you consider the meaning of “half-life”. If you lived next to nuclear waste for say 75 years, you will absorb 1-.5^(75/25000) = 0.26 % of its total radiative output. Consider Tin-126, for example, with a half life of 2.3e5 years and a decay energy of 4.1 MeV. A LD-50 in 14 days dose for a 100 kg man (for a 126 g, or 1 mol sample) occurs after 3.7 hours, with 45 minute exposure being equivalent to 5% increase in cancer risk (1 Gray, or 1 J/kg). It is a particularly nasty by-product though, being 20-50 times worse than virtually every other byproduct with a shorter half life. A more representative isotope such as Pd-107 instead gives the same man about 9 mGy dose over an entire day – about the same as an abdominal CT scan (8 mGy). We can to some extent tailor products by choosing the reactions we use to generate energy, so we can make even these long-lived isotopes pretty safe inherently, in addition to the fact they’d be buried in a mountain. (Half life and sample products source http://en.wikipedia.org/wiki/Nuclear_waste#Physics ) Short half-life products are much worse during their toxic time, but have half lives between 5 and 90 years. The containers we have made have been theorized to have zero degredation from erosion for approximately a 10,000 year period and are furthermore tested by such means as crashing trains into them, dropping them from 10 m onto steel spikes, and underwater submersion to ensure integrity over long periods. This means the material is essentially guaranteed to stay sealed up for 100-2000 half lives, leaving less than 10^(-31) of its original mass left over. For reference, this is the equivalent of the sun reducing to a tenth of a kilogram! (HAH astro rocking the absurdly high exponents again) This may further be mitigated by new initiatives such as the LIFE project (http://www.contracostatimes.com/localnews/ci_10951822?nclick_check=1&forced=false) that recycle nuclear waste for further fission, further reducing half-lives. Whew! Hopefully this sheds some light on why I’m not particularly concerned. Besides, look at the alternatives. The only two more efficient things are throwing matter into black holes and M/AM reactions. “Renewables” such as wind and hydro are essentially secondary solar effects; to power the US, the entire state of Connecticut (at 50% efficiency for 12 hours/day, storing half of that power for night-time use, with a nominal solar radiation of 500 W/m^2 at the equator. Area: ~ 14,000 km^2 or 14e9 m^2) would be needed to produce our current 3.5 TW of power usage. It’s simply not practical. To produce the world’s current 15 TW usage, we’d need about the equivalent of West Virginia coated in photovoltaics. Multiply as appropriate to accommodate for cloud cover and room for expansion (say, quadroupling it to account for it all) and you get every last square centimeter of *Texas* covered in photovoltaics. Again, plain and simple not practical. Wind and hydro both take more area to generate the same amount of power. For other alternatives, “clean” coal isn’t, CNG is a carbon emitter and H_2 compresses so poorly that it takes as much or more fossil fuel burning to compress it as you save (simple PVNRT calcs). Finally, the P-P chain used in the sun (which is aneutronic) requires either solar compression or a temperature 10x hotter than the solar core. D-D and D-T fusion produces neutron side products, even when those neutrons are used to breed more tritium courtesy Li-6. H+B-11 can be used for aneutronic fusion, but power densities drop considerably and supersolar temperatures are still required; that is to say, the only realistic fusion will still generate radioactive byproducts. As a species and a country, we need to come to grips with the fact that to stop destroying planetary level ecology we have to accept geologically short to short-medium term storage of nuclear byproducts leading to extremely localized hot-spots. There’s simply not a good way around it. I hope this, if not outright convinces you, at least puts a little doubt into your mind that maybe makes you see why, for example, Kit and I are both extremely pro-nuclear power.
It was an interesting writing set, and a lot of research (I gained a bit of insight into isotope length choices by the end of it, though I fall lightly in favor of long-lived isotopes still), and I hope that this is an interesting read for you guys.

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Comments

That's too bad. . .

Chibibluepenguin | 02/06/2009, 16:55

Ha, ha, it seems like quite a few people from the Berkeley College Republican club voted the way you did. Though I guess that's to be expected from a Republican club in Berkeley. I mean I see you have your reasons, which I disagree with, but its funny. I would have never guessed several years back that you would have voted Democrat. Well I guess you were never a true Conservative then. Though to be fair, John McCain wasn't really a Republican. . . he was a moderate; Sarah Palin was a Republican. Obama, well he's more so a socialist, then a democrat, which he is proving at the moment. Anyway, it seems like Conservatism is becoming an underground movement. I'm rooting for Bobby Jindal for the next election. I agree with you on the whole nuclear power thing though. Sorry if my words seem offensive, I was just sad that you converted, along with a few other people in the Berkeley College Republican Club.

Ooh, shiny, a comment

tigerhawkvok | 02/07/2009, 17:13

tigerhawkvok

I'm not quite sure who you are, but, well, I think Republicans have moved *too* far to the idealogical right overall. Add in bible-thumping and all this 'faith-based' nonsense, and trying to impose personal morals (certainly not in government purview), and I have a problem with the current Republican social standpoint. Economically, the Repubs. have been in favor of cutting taxes and higher spending with lower accountability. Really, low accountability should be right out and you have to pick one of lower taxes or higher spending.

I freely admit to having environmentalism influence me more than before, but if nothing else, system complexity should convince you of that. Remember -- removing wolves from Yellowstone increases flooding. Whether or not you think it's natural is moot — what is important is that it would suck for humans.