Nuclear Power, Thorium, and the Role of Government

Nuclear power is an attractive candidate for meeting our future energy needs.  Nuclear plants do not release greenhouse gases.  They release significantly less radiation into the environment than coal plants, because coal contains several parts per million of radioactive thorium and uranium.  They require far less space and are far more reliable than alternative energy sources such as wind and solar.  In spite of some of the worst accidents imaginable due to human error and natural disasters, we have not lost any cities or suffered any mass casualties, and the horrific “China Syndrome” scenarios invented by the self-appointed saviors of mankind have proven to be fantasies.  That is not to say nuclear power is benign.  It is just more benign than any of the currently available alternatives.  The main problem with nuclear is not that it is unsafe, but that it is being ill-used.  In this case, government could actually be helpful.  Leadership and political will could put nuclear on a better track.

To understand why, it is necessary to know a few things about nuclear fuel, and how it “burns.”  Bear with me while I present a brief tutorial in nuclear engineering.  Nuclear energy is released by nuclear fission, or the splitting of heavy elements into two or more lighter ones.  This doesn’t usually happen spontaneously.  Before a heavy element can undergo fission, an amount of energy above a certain threshold must first be delivered to its nucleus.  How does this happen?  Imagine a deep well.  If you drop a bowling ball into the well, it will cause a large splash when it hits the water.  It does so because it has been accelerated by the force of gravity.  A heavy nucleus is something like a well, but things don’t fall into it because of gravity.  Instead, it relies on the strong force, which is very short range, but vastly more powerful than gravity.  The role of “bowling ball” can be played by a neutron.  If one happens along and gets close enough to fall into the strong force “well,” it will also cause a “splash,” releasing energy as it is bound to the heavy element’s nucleus, just as the real bowling ball is “bound” in the water well until someone fishes it out.  This “splash,” or release of energy, causes the heavy nucleus to “jiggle,” much like an unstable drop of water.  In one naturally occurring isotope – uranium with an atomic weight of 235 – this “jiggle” is so violent that it can cause the “drop of water” to split apart, or fission.

There are other isotopes of uranium.  All of them have 92 protons in their nucleus, but can have varying numbers of neutrons.  The nucleus of uranium 235, or U235, has 92 protons and 143 protons, adding up to a total of 235.  Unfortunately, U235 is only 0.7% of natural uranium.  Almost all the rest is U238, which has 92 protons and 146 neutrons.  When a neutron falls into the U238 “well,” the “splash” isn’t big enough to cause fission, or at least not unless the neutron had a lot of energy to begin with, as if the “bowling ball” had been shot from a cannon.  As a result, U238 can’t act as the fuel in a nuclear reactor.  Almost all the nuclear reactors in operation today simply burn that 0.7% of U235 and store what’s left over as radioactive waste.  Unfortunately, that’s an extremely inefficient and wasteful use of the available fuel resources.

To understand why, it’s necessary to understand something about what happens to the neutrons in a reactor that keep the nuclear chain reaction going.  First of all, where do they come from?  Well, each fission releases more neutrons.  The exact number depends on how fast the neutron that caused the fission was going, and what isotope underwent fission.  If enough are released to cause, on average, one more fission, then the resulting chain reaction will continue until the fuel is used up.  Actually, two neutrons, give or take, are released in each fission.  However, not all of them cause another fission.  Some escape the fuel region and are lost.  Others are absorbed in the fuel material.  That’s where things get interesting.

Recall that, normally, most of the fuel in a reactor isn’t U235, but the more common isotope, U238.  When U238 absorbs a neutron, it forms U239, which quickly decays to neptunium 239 and then plutonium 239.  Now it just so happens that plutonium 239, or Pu239, will also fission if a neutron “falls into its well,” just like U235.  In other words, if enough neutrons were available, the reactor could actually produce more fuel, in the form of Pu239, than it consumes, potentially burning up most of the U238 as well as the U235.  This is referred to as the “breeding” of nuclear fuel.  Instead of just lighting the U235 “match” and letting it burn out, it would be used to light and burn the entire U238 “log.”  Unfortunately, there are not enough neutrons in normal nuclear reactors to breed more fuel than is consumed.  Such reactors have, however, been built, both in the United States and other countries, and have been safely operated for periods of many years.

Plutonium breeders aren’t the only feasible type.  In addition to U235 and Pu239, another isotope will also fission if a neutron falls into its “well” – uranium 233.  Like Pu239, U233 doesn’t occur in nature.  However, it can be “bred,” just like Pu239, from another element that does occur in nature, and is actually more common than uranium – thorium.  I’ve had a few critical things to say about some of the popular science articles I’ve seen on thorium lately, but my criticisms were directed at inaccuracies in the articles, not at thorium technology itself.  Thorium breeders actually have some important advantages over plutonium.  When U233 fissions, it produces more neutrons than Pu239, and it does so in a “cooler” neutron spectrum, where the average neutron energy is much lower, making the reactor significantly easier to control.  These extra neutrons could not only breed more fuel.  They could also be used to burn up the transuranic elements – those beyond uranium on the table of the elements – that are produced in conventional nuclear reactors, and account for the lion’s share of the long-lived radioactive waste.  This would be a huge advantage.  Destroy the transuranics, and the residual radioactivity from a reactor would be less than that of the original ore, potentially in a few hundred years, rather than many thousands.

Thorium breeders have other potentially important advantages.  The fuel material could be circulated through the core in the form of a liquid, suspended in a special “salt” material.  Of course, this would eliminate the danger of a fuel meltdown.  In the event of an accident like the one at Fukushima, the fuel would simply be allowed to run into a holding basin, where it would be sub-critical and cool quickly.  Perhaps more importantly, the United States has the biggest proven reserves of thorium on the planet.

Breeders aren’t the only reactor types that hold great promise for meeting our future energy needs.  High temperature gas cooled reactors would produce gas heated to high temperature in addition to electricity.  This could be used to produce hydrogen gas via electrolysis, which is much more efficient at such high temperatures.  When hydrogen burns, it produces only water.  Such reactors could also be built over the massive oil shale deposits in the western United States.  The hot gas could then be used to efficiently extract oil from the shale “in situ” without the need to mine it.  It is estimated that the amount of oil that could be economically recovered in this way from the Green River Basin deposits in Utah, Wyoming and Colorado alone is three times greater than the oil reserves of Saudi Arabia.

Will any of this happen without government support and leadership?  Not any time soon.  The people who build nuclear reactors expect to make a profit, and the easiest way to make a profit is to build more conventional reactors of the type we already have.  Raise the points I’ve mentioned above, and they’ll simply tell you that there’s plenty of cheap uranium around and therefore no need to breed more fuel, the radioactive danger of transuranics has been much exaggerated, etc., etc.  All these meretricious arguments make sense if your goal is to make a profit in the short run.  They make no sense at all if you have any concern for the energy security and welfare of future generations.

Unless the proponents of controlled fusion or solar and other forms of alternative energy manage to pull a rabbit out of their collective hats, I suspect we will eventually adopt breeder technology.  The question is when.  After we have finally burnt our last reserves of fossil fuel?  After we have used up all our precious reserves of U238 by scattering it hither and yon in the form of “depleted uranium” munitions?  The longer we wait, the harder and more expensive it will become to develop a breeder economy.  It would be well if, in this unusual case, government stepped in and did what it is theoretically supposed to do; lead.

Author: Helian

I am Doug Drake, and I live in Maryland, not far from Washington, DC. I am a graduate of West Point, and I hold a Ph.D. in nuclear engineering from the University of Wisconsin. My blog reflects my enduring fascination with human nature and human morality.

9 thoughts on “Nuclear Power, Thorium, and the Role of Government”

  1. Excellent, informative post. By the way, I ordered the article you recommended the other day and will read it soon. Thanks very much.

  2. Thanks. You can usually rent articles like that on DeepDyve a lot cheaper than you can buy them.

  3. Makhijani and Boyd are well known long-time anti-nukes, and their reflexive opposition to anything nuclear can be taken for granted. Their arguments are contrived and contradictory. For example, in one part of their “factsheet,” they claim that U232 would make it excessively difficult to handle spent fuel from thorium breeders, but in another they say that it would pose no problem for bomb proliferators. Let’s go down the list.

    They claim that very little additional work is needed to get from 20% enriched uranium to 90%. This is nonsense. In the first place, enriching from 20% to 90% is anything but easy. In the second, any nation or group that can enrich from 20% to 90% can also enrich from 0.7% to 20%. It’s merely a matter of time.

    They claim that “While the mix of fission products is somewhat different than with uranium fuel, the same range of fission products is created.” This displays a fundamental ignorance of what goes on in thorium breeders. Because of the extra neutrons available, it is possible to destroy the actinides beyond uranium in the table of the elements that are the primary reason that spent fuel from conventional reactors remains highly radioactive for such long periods of time. Fission products are not the main culprit in long-lived radioactive wastes. Actinides are. In fact, assuming efficient separation of actinides, which is demonstrably entirely feasible, the spent fuel from thorium breeders will potentially be less radioactive than the original thorium and uranium ore after around 500 years. This is not just a speculation. It has been demonstrated by experiment. The fact that these two simply ignore actinides demonstrates better than anything else in their paper that they don’t have a clue what they are talking about.

    The claim that the radioactive danger of thorium is much higher than that of uranium is poppycock. Both emit alpha particles. Both decay chains terminate with stable lead. The author’s claim is based on the unstated assumption that radionuclides will actually be ingested into the body, where thorium, with an affinity for bone tissue, is retained much longer than uranium. There are demonstrably effective measures for preventing ingestion of either element in both mining and refining operations. If the authors were really worried about this problem, they would be promoting the rapid building of nuclear plants, because there is a very real danger of ingestion of both uranium and thorium into the body from the coal plants that are currently being built in large numbers, for example, in Germany, to replace the nuclear plants that country is in the process of decommissioning. Coal contains several parts per million of both elements.

    As for the danger of proliferation, the authors pretend that it would be a mere bagatelle for highly motivated terrorists to separate U233 from fuel elements that have been denatured with U238. They would be stupid to even attempt it. Such material would be highly radioactive due to the presence of, among other things, U232, which cannot be easily separated from U233. It would not only be extremely deadly to work with, but easy to track. Any nation or group with the technological savvy to separate U233 from U238 under such conditions would find it much easier and technically less demanding to simply build a natural uranium reactor and extract the plutonium.

  4. If it is so easy to make U-233 without U-232, why aren’t the rogue states doing it right now- Thorium is much more common than gold and much more common that U-235 and so it would much harder to stop them- they wouldn’t need specialised centrifuges. They wouldn’t care what that US isn’t doing it now- it did it once to make one U-233 nuclear bomb with lots of difficulty. Its because they know its hideously difficult.

  5. To whom it may concern,

    I recently was exposed to the thorium possibilities and I am hopeful. My question is about one aspect of the Thorium process. I have read about thoriums ability to help neutralize the radioactive waste from our current nuclear reactors. My question is the idea being entertained, if possible, that a similar process could be used to help with the radiation in areas like Fukushima and Chernobyl. I would appreciate your time to touch on this, no matter how brief.

    Thank you.

  6. Neutrons can transmute long-lived transuranic actinides as well as the more dangerous long-lived fission products by transmutation. Thorium breeders could potentially provide the necessary neutrons. To the extent that these dangerous isotopes could be separated from the Fukushima waste and stored, they could eventually be dealt with in the same way as any other radioactive waste. The problem is that a significant amount of soluble radioactive material escaped into the ground water around the damaged plants. This is now so widely dispersed that it would probably be impractical to concentrate it and deal with it in the same way.

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