Newsgroups: sci.physics.fusion,sci.answers,news.answers Subject: Conventional Fusion FAQ Section 2/11 (Energy) Part 2/5 (Environmental) From: rfheeter@pppl.gov Approved: news-answers-request@MIT.EDU Followup-To: sci.physics.fusion Reply-To: rfheeter@pppl.gov Summary: Fusion energy represents a promising alternative to fossil fuels and nuclear fission for world energy production. This FAQ answers Frequently Asked Questions (from the sci.physics.fusion newsgroup) about conventional areas of fusion energy research. It also provides other useful information about the subject. This FAQ does NOT discuss unconventional forms of fusion (like Cold Fusion). Expires: 1 Dec 1994 0:00:00 GMT Archive-name: fusion-faq/section2-energy/part2-enviro Last-modified: 29-Sept-1994 Posting-frequency: More-or-less-monthly Disclaimer: This is an early draft and will be revised soon. ******************************************************************** 2.2. Environmental Characteristics of Fusion as a Future Energy Source Last Revised September 29, 1994 Written by Robert F. Heeter, rfheeter@pppl.gov, unless otherwise cited. ### Please let me know if anything here is unclear. ### * A. What are fusion's major potential environmental advantages? Fusion, like fission, creates no greenhouse gases, no smog, and no acid rain. The major source of "air pollution" from fusion would be, well, helium, which is completely inert and is already a significant constituent of the earth's atmosphere. Fusion isn't chemical energy, so it doesn't create chemical byproducts that would cause air pollution. Fusion consumes less fuel mass per unit of energy produced than any other fuel-consuming energy source. There is also far more fusion fuel than for any other fuel-consuming energy source. Fusion gives you the most energy "bang for your buck" and therefore minimizes the environmental burdens of searching for and producing energy. Fusion fuel is also much more widely distributed, since all likely fuel elements are found abundantly in seawater. There would be no Persian Gulf-type wars over access to fusion fuel. Given the destructive nature of wars, this is good for the environment as well as good for people. With fusion, you don't need to rip up the ground like coal mines do, or worry about oil spills, or devote miles and miles of land to wind or solar farms. Fusion creates more energy with less resource investment than any other form of energy known to man. * B. But isn't fusion nuclear? What about radioactive waste? Fusion *is* a nuclear technology, but there are significant qualitative differences between fusion and fission. These differences add up to both safety and environmental advantages for fusion. (Safety issues are discussed in Section 2 Part 3) On the environmental side, fusion differs from fission in that one can control the waste products by controlling the fuels used and the materials exposed to neutrons produced in the fusion reaction. In fission, uranium or plutonium decays in a random way and the "daughters" of the fission process are scattered all over the periodic table, and there are lots of nasty radioactive isotopes produced. Thus fission results in large amounts of concentrated radioactive waste. In fusion, one has the opportunity to minimize or even perhaps to eliminate the radioactive waste problem. "Aneutronic" fusion fuels (discussed in Section 1) would produce little or no radioactive waste at all. Even in "neutronic" (but much easier) deuterium-tritium fusion (discussed in Section 1) most of the neutrons (which are the primary source of radioactive waste) are absorbed in a lithium blanket in order to replace the tritium fuel burned in the reactor. The only sources of radioactive waste in a D-T reactor are stray tritium atoms and the reactor structure which is exposed to neutron radiation. Tritium is a relatively benign radioactive element, because: (a) It doesn't emit strong radiation when it decays, so it's only hazardous if one breathes it in or ingests it. (b) It generally shows up in one's body as water, and your body flushes out its water fairly frequently, so tritium won't build up in a living creature. (Unlike many fission reaction products.) (c) It has a moderate half-life, only 12 years or so. This means that it won't be around forever, so it doesn't create a long-term waste problem. On the other hand, it probably won't decay in the few days that pass while it's in one's body, which is also good. Based on current tritium-handling knowledge and experience scientists believe that incidental releases of radiation from fusion reactors will be comparable to releases from either fission or coal plants. In a fusion economy, the contribution of tritium to one's radiation exposure will be orders of magnitude less than natural exposure to things like radon, cosmic rays, etc; and also much less than man-made exposure to things like medical x-rays. Radioactive waste in a fusion reactor can be minimized by choosing special structural materials which can withstand neutron bombardment without becoming highly radioactive. Two strong candidate "low-activation materials" are vanadium and silicon-carbide. Vanadium will be tested as a structural material on the TPX tokamak to be built at Princeton. If either vanadium or silicon carbide is used as a structural material, the radioactive inventory of a fusion reactor will be much less than that of a fission reactor with comparable power output. In fact, with a low-activation fusion reactor, one can wait ten or so years after shutdown, and the fusion reactor will be 1,000 to 1,000,000 times *less* radioactive than the fission reactor. The material in the fusion reactor will actually be less radioactive than some natural minerals, particularly uranium ores, and it would conceivably be safe to *recycle* the fusion reactor structure into a new fusion reactor, with little permanent waste at all. In these circumstances one must compare the problems and hazards posed by permanent *chemical* wastes from manufacturing and operating other energy sources with the problems and hazards posed by fusion energy. * C. What key technologies are needed to achieve these advantages? *Any* working fusion reactor would have minimal environmental impact relative to fossil fuels, with the exception of the radioactive waste problem. Minimizing the radioactive inventory and waste burden of a fusion reactor is the key to maximizing the environmental friendliness of fusion. Now, as can be seen from the answers to questions A and B above, the development of low-activation materials will help achieve a tremendous advantage for fusion by dramatically reducing the radioactive waste problem. This will be complemented by development of tritium-handling techniques which allow us to reduce the tritium radiation problems. More advanced fusion reactors using aneutronic fuels will eliminate the radioactive-waste problem entirely, but these fuels are much harder to burn. Aneutronic fusion is much further down the road and would probably have a harder time competing economically. Scientists believe that, from an environmental standpoint, even D-T fusion with low-activation materials would be an improvement over current energy sources. Advanced aneutronic fuels in which only charged particles (i.e., not neutrons) are released by the fusion reaction would have an additional advantage: one can directly convert charged particle energy to electrical energy with much higher efficiency than one can achieve with conventional turbine-based technologies; this would reduce the thermal pollution from a fusion plant dramatically. * D. What are the materials and fuel requirements for fusion? This question is answered in Section 2 Part 1; please look there. * E. What about renewable energy sources? Why do we need fusion at all? (After all, renewables will be ready much sooner than fusion.) Renewable energy sources depend on incident sunlight, which is a diffuse, low-density source. While renewables in many cases are great for the environment, it's not clear that they'll be able to "pull the whole load" in the future, when the population of the earth is expected to double and energy use is expected to triple even *with* aggressive conservation and population-control measures. This is especially true for the large dense cities which are developing worldwide as nations develop and continue to urbanize. Diffuse energy sources require lots of land, and dense cities don't have lots of land. So given that a major environmental constraint will be finding enough land to feed everyone, while still leaving room for wildlife and the rest of nature, it seems that it would be prudent to develop as many energy sources as possible and to make sure that at least some of those (like fusion) are not land-intensive. Renewables certainly seem to be the "energy source of tomorrow," and we should definitely develop them - but we're likely to need fusion the *day after* tomorrow, so we'd better develop it too. (Acknowledgements to W.D. Kay or Northeastern Univ. for the idea which led to this last sentence.)