Impending Global Warming Demands a New Discussion
of Nuclear Power
The Europeans have a nuclear reactor for electric power generation under construction in Belgium with the following outstanding features: 1) it cannot be used for producing the raw material for atomic bombs, 2) it cannot meltdown as happened at Chernobyl and Three Mile Island and not under any circumstances whatsoever, and 3) After 500 years its waste will be no more dangerous than the ashes from a conventional coal burning power plant. How can this be true?
This article is crash course in scientific literacy—what the general public needs to know about nuclear power for generating electricity and for high-pressure steam for industry, for that matter. The same plant for both is called cogeneration, permitting otherwise wasted heat to be utilized. Most of the public already know that atomic energy unlike burning fossil fuels (coal, petroleum, natural gas) produces no greenhouse gases, in this case carbon dioxide. Almost all of us also know about the unsolved problem of disposing of atomic waste because of its radioactivity. Radioactivity is the spontaneous transmutation of an element to another element with the release of energy as ionizing radiation. The spent fuel remains highly radioactive for tens of thousands to hundreds of thousands of years because of elements, newly formed in the reactor, with long half-lives (especially plutonium). Half-life is the time required for half of the isotope to decay to other elements by its radioactivity. Radioactivity falls to acceptable levels after 10 to 20 half-lives have passed.
Rather elementary chemistry can separate “unburned” uranium and plutonium for recycling as new fuel for reactors. This is expensive because of the cost of remote manipulation of the process occasioned by the high level of radioactivity, but it is cost-effective not only because of the value of the recovered fuel but also because the radioactivity of the remaining waste, while high initially, remains dangerously radioactive for only hundreds to a few thousand years—an order of magnitude less than the untreated waste. France and England have recycled their fuel since early in the atomic age because of these advantages—low cost new fuel and greatly reduced radioactivity of the residual waste. The United States chose to dispose of the waste without reprocessing because of concerns about diversion to make nuclear weapons by rogue states. As a result, all of our nuclear power plants are fueled by new U235, the fissionable isotope of natural uranium, so our nuclear waste contains long-lived radioactivity from “unburned” fuel.
Although uranium is a fairly prevalent element in the earth’s crust, over 99% of it is U238 and not fissionable unless transformed into plutonium239 (Pu239) in a reactor. The fact that only 0.72% of natural uranium is U235 means that nuclear power obtained from it alone, as we in the US are doing, could meet the world’s growing need for energy for only a few hundred years before running out of readily available uranium. We have purified, stockpiled, and manufactured much plutonium into bombs. Our decommissioning of nuclear weapons as part of the ongoing disarmament agreements therefore involves treating this purified plutonium as waste even though it could be used for nuclear fuel. Storing this purified plutonium, a byproduct of disarmament, as waste is not only costly, but also dangerous if only because of its long half-life. The Russians are using their plutonium for electric power production.
Separation of U235 from U238, the common isotope of uranium, cannot be done chemically because they are the same element and chemically identical. This difficult separation is accomplished by making a gaseous compound of uranium (UF6, uranium hexafluoride). The slight difference in the weight of the molecules containing the different isotopes of uranium is utilized for the separation either by diffusion through many orifices in series (with much pumping) or by fantastically powerful centrifuges to effect the separation by the enormous artificial gravity. The great complexity of these processes reduces the danger of proliferation of weapons because of the difficulty of obtaining sufficient quantities of sufficiently pure metal for a bomb. The critical mass for a bomb is only a few pounds of either U235 or Pu239. This quantity in one hunk undergoes a spontaneous chain reaction of fission into atoms of elements that are about half the atomic weight of the uranium or plutonium such as cesium137 and iodine131, all with much shorter half lives than Pu239 (24,000 years), U235 (700 million years), or U238 (4 billion years). The bomb is triggered by suddenly propelling together several pieces smaller than the critical mass of the metal but totaling more than its critical mass. The pieces have to be accurately machined to fit closely, as if they were one piece. (Don’t worry about this description getting out—all the “competent” terrorists know this part already.)
Enter thorium232 (Th232): like uranium, all of thorium’s isotopes are radioactive. Unlike uranium only one of thorium’s isotopes has a half-life long enough to be still present on earth. Th232 has a half-life of 14 billion years. Fourteen billion years is approximately the age of the universe, so thorium is toxic as a heavy metal but not because of its radioactivity—its decay is too slow for it to be dangerous. Thorium is about as prevalent on earth as lead and is less toxic. Thorium oxide (ThO2) has the highest melting point of any substance so far tested and makes dandy mantles for kerosene lanterns because of the brighter light from the higher temperature obtainable--and with no concern about its miniscule radioactivity. (Radioactivity was not discovered until decades after this use of ThO2 was invented.)
Thorium by itself cannot be used as nuclear fuel because it, like U238, is not fissionable, but mixed with U235 or Pu239, their neutrons convert some of it to U233, more fissionable than U235. This technology is fairly well along toward practical application and can be used to dispose of excess plutonium from weapons. Two additional advantages: such reactors are less subject to meltdown as occurred at Chernobyl* and the final waste products are only dangerous for about 500 years—even extra plutonium added to these reactors at the time of fueling is consumed before refueling is needed. Research into this technology is occurring especially in Russia to get rid of their plutonium and in India because they have very high grade thorium deposits and would have to import uranium. There is a second type of thorium-fueled reactor that cannot produce enough neutrons for continuous fission so that it must be kept fissile with an external proton beam from a small linear accelerator integrated with the reactor. The proton beam emits neutrons from a lead target. Physicists call the process spallation. Again the neutrons create U233 from Thorium232. The U233 fissions promptly with no further neutron production, therefore no possibility of a chain reaction—shut off the linear accelerator and the action stops immediately. This makes it totally immune to meltdown and, also important, it cannot produce material for bombs. No full sized facility has yet been constructed, but the nuclear reactions are well known and any new engineering required will be quite standard. This reactor is called an Accelerator Driven System, ADS for short. A prototype is currently under construction in Belgium and scheduled for full power production in 2003.
* The accident at Chernobyl was not, strictly speaking, meltdown as occurred at Three Mile Island, Pennsylvania. High pressure steam ruptured the cooling water pipes and reacted with the hot graphite control rods producing hydrogen and carbon monoxide which produced a chemical explosion that distributed radioactivity much more widely than meltdown would have. The chemical explosion and fire would not have occurred with a modern gas cooled reactor or even with a liquid sodium cooled reactor (personal communication from Kelly Clifton, radiation biologist at the University of Wisconsin).
Certainly more research on ADS reactors can wait until inexpensive uranium sources are exhausted and plutonium from scrapped atomic weapons has all been converted to electricity. Meanwhile, using some thorium232 in reactors permits heat and electric power production without creating high level radioactive waste. Europe is pursuing a new integrated approach to fast breeder reactors called Generation IV. The integrated fuel reprocessing process creates only new fuel, none of it as metallic plutonium (refined bomb material), and the same low level waste of ADS reactors with the additional benefit of being a source of technetium and stable isotopes of ruthenium, rhodium, palladium for other industrial uses. Roland Schenkel, European Commission, Joint Research Center, Brussels, Belgium, stated, “Generation IV reactors are resistant to atomic weapons proliferation because there is no purified plutonium anywhere in their fuel cycle and the plutonium remains mixed with americium, curium and neptunium, long half life elements that would help to identify the source of any diverted plutonium.” This is from a symposium entitled Nuclear Reactor Systems of the Future organized by Aidan Gilligan of the EU Commission at the American Association for the Advancement of Science annual meeting in Boston on February 16, 2008. The speakers at this symposium agreed with Roland Schenkel that the existing nonproliferation treaty needs only a little tweaking (already well on the way to successful negotiation)—specifically that the current treaty is too permissive about concentrating U235 for fuel for power plants and that in the long run the countries possessing atomic weapons must more actively pursue disarmament.
So the solutions are political and are needed for many reasons besides nuclear proliferation. Start with educating the public and reforming the UN’s efficiency—some world government will be needed for disarmament and inspection at least. Put your money on a vastly expanded European Union if you think the UN is doomed. (Canada, South Africa, Argentina and Chile are already more “European” than Turkey, a current candidate for membership.) It seems obvious that there will be no world government beside the UN any time soon—so hats off to innovative thinking like Ted Turner’s in paying the United States’ back dues to the UN ($800 million). This paragraph is intended to get our thinking off dead center, not to make political suggestions. I hope I have provided some facts for the thinking process. We should increase research in ADS technology so we are less likely to feel compelled to build more conventional nuclear power plants--they are susceptible to meltdown, produce more long-lived waste, and can be used to produce pure Pu239, a raw material for bombs. Thorium fueled nuclear power does look very promising in the long term.
After thorough demonstration of no danger of meltdown, it could even be incorporated in cogeneration projects—it would become safe enough for densely populated areas where the incidentally produced high pressure steam could be readily utilized. Watch the progress of the “MYRRHA” ADS reactor in Belgium already mentioned.
Meanwhile, nuclear power can be justified except that the costs are much higher than the alternatives—renewable sources of energy and, above all, avoiding waste.
I close with a quotation from John Maynard Keynes: “The difficulty lies not in the new ideas but in escaping the old ones, which ramify, for those of us brought up as most of us have been, into every corner of our minds.”
John A. Frantz, MD
August 14, 2006, revised January 25, 2007
Addendum, April 27, 2011
The major obstacle to deploying nuclear power is cost both of construction and guaranteeing funds available for cleaning up after accidents such as Chernobyl in1986 and the ongoing crisis in Japan (Three Mile Island in Pennsylvania was very minor by comparison). However, the tremendous costs of such accidents must be compared to the avoided costs of other methods of power production, our next topic.
Continued business as usual threatens rising sea level that could amount to tens of meters in a few hundred years by way of increased carbon dioxide in our atmosphere, its ensuing global warming, and consequent melting of Greenland’s and Antarctic ice caps. Greenland’s ice alone could raise sea level about 6 meters (20 feet) and Antarctica’s several times that. Such changes in sea level are documented in the geological record. During the continental glaciations sea level was about 100 meters lower than current levels. The most recent continental glaciation ended about 15,000 years ago. Shortly before the end of that ice age, there was dry land clear across the Berring Strait between Alaska and Asia permitting stone-age man to colonize the Americas without any major water barrier.
Continued business as usual also involves accumulating universal contamination of our air and land from burning fossil fuels especially coal. For example, heavy metals from fossil fuels, predominantly mercury, account for a diffuse persistent human morbidity which sums to greater damage than produced by relatively rare nuclear contamination. Low sulfur coal (in our case from Wyoming) mitigates acid rain by greatly reducing the contribution of sulfur dioxide, but does nothing to help the acid rain from carbon dioxide—it is still worth the extra cost of transporting it from Wyoming (instead of Illinois’ high sulfur coal).
Assuming that we continue to accumulate atomic waste at the present rate (in order to avoid reprocessing it), current known supplies of uranium will last only a few hundred years. The isotope of uranium we currently use for power plants in America, U235, is only 0.7% of uranium as mined. Known supplies of U238 and Th232 are sufficient for electric power production at the present rate for thousands of years. To avoid atomic warfare requires improved social and political organization and cannot be assured by failure to reprocess the waste. Furthermore reprocessed waste requires only a few hundred years of radioactive decay to become relatively harmless (like ThO2 for gas lantern mantles), whereas the plutonium in our present stored waste requires many tens of thousands of years (¼ to ½ million) to become similarly harmless. How can we reliably keep it out of our aquifers for more than a few hundred years? Reprocessing the waste and using it for energy becomes the cheapest and only reliable method of dealing with it.
Finally, the elephant in the living room that the guests all fail to mention is not the dangers of nuclear power. Overpopulation will devastate the environment much more surely and is incompatible with appropriate social and political stability. Education especially of women is the ultimate answer. Throughout the animal world females seek quality in their offspring more than males do. Parenthetically, it is intriguing that Bangladesh has more than 100 girls per 100 boys in primary and secondary education. Children per woman has dropped from 6.6 in 1977 to 2.4 in 2010. Meanwhile, China did not wake up in time for the Bangladesh solution and did the best they could with too little too late. Incidentally, successfully feeding too many people does not sufficiently mitigate the population problem.
Bottom line: we will probably soft pedal nuclear power until dramatic accidents become rare indeed. ADS reactors using Th232 look very good for cogeneration of electricity and heat in the megacities of the future.
Note added May 24, 2011:
I have just heard from http://www.telegraph.co.uk/finance/comment/ambroseevans_pritchard/ that china is proposing to build thorium reactors as described above. The Chinese design is fairly well along and involves the thorium fuel to be dissolved in molten salts. An intriguing safety feature: a fusible plug in the bottom of the reactor chamber will melt on overheating (failure to modulate the linear accelerator and its activating neutrons comes to mind) and all the fuel in its melted salts drains out below—no need for alert operators or even pumps to avert disaster and there would be “orders of magnitude” less residual heat than in a uranium reactor.
Ironically, the United States shelved the idea of thorium reactors in the 1940s because they do not produce plutonium—raw material for bombs.
Note added September 2, 2010:
Uranium 233 can be produced by bombarding thorium 232 with neutrons---similar to producing plutonium by bombarding uranium 238 with neutrons. U233 is fissionable similarly to uranium 235, which is 0.7% of uranium as mined. U233 is created as needed in all thorium fueled reactors and consumed promptly, and not as conveniently made into bombs as uranium 235 or plutonium 239. Also the critical mass (the minimum mass needed for a bomb) is several times that of uranium 235 or plutonium 239; so a given effort would make far fewer but more powerful bombs.
We have been talking about thorium reactors not producing atomic bomb material. It has occurred to me, "Why isn't U233 bomb material?" so I googled U233 and found that the US had considered using it and has about 3100 tons of it in stock with a plan to dispose of it (at great expense) by diluting it with depleted uranium (the non-fisionable 99.3% of uranium). This would make it as useless for bombs as ordinary uranium. What a waste of resources---one pound of U233 would produce as much electricity as 1500 tons of coal. We (the US) did one successful test with one bomb containing only some U233 many years ago.
If we wise up and ask the Europeans to teach us how to securely recycle plutonium from spent nuclear fuel, we could use a similar process on our excess U233 and save big money. It makes me surprised that I have not become a Quaker long ago.