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High-level radioactive waste management concerns management and disposal of highly radioactive materials created during production of nuclear power and nuclear weapons. Radioactive waste contains a mixture of short-lived and long-lived nuclides, as well as non-radioactive nuclides. There was reported some 47,000 tonnes of high-level nuclear waste stored in the USA in 2002. Nuclear waste is approximately 94% Uranium, 1.3% Plutonium, 0.14% other Actinides, and 5.2% fission products.〔(【引用サイトリンク】publisher=What is Nuclear? )〕 About 1.0% of this waste consists of long-lived isotopes 79Se, 93Zr, 99Te, 107Pd, 126Sn, 129I and 135Cs. Shorter lived isotopes including 89Sr, 90Sr, 106Ru, 125Sn, 134Cs, 137Cs, and 147Pm constitute 0.9% at one year, decreasing to 0.1% at 100 years. The remaining 3.3-4.1% consists of non-radioactive isotopes.〔(【引用サイトリンク】publisher=US Nuclear Data Program )〕〔(【引用サイトリンク】publisher=US Nuclear Data Program )〕〔(【引用サイトリンク】publisher=US Nuclear Data Program )〕 One tonne of waste, as described above, has measurable radioactivity of approximately 600 TBq equal to the natural radioactivity in one km3 of the Earth's crust, which if buried, would add only 25 parts per trillion to the total radioactivity. The difference between short-lived high-level nuclear waste and long-lived low-level waste can be illustrated by the following example. As stated above, one mole of both 131I and 129I release 3x1023 decays in a period equal to one half-life. 131I decays with the release of 970 keV whilst 129I decays with the release of 194 keV of energy. 131gm of 131I would therefore release 45 Gigajoules over eight days beginning at an initial rate of 600 EBq releasing 90 Kilowatts with the last radioactive decay occurring inside two years.〔(【引用サイトリンク】publisher=US Nuclear Data Program )〕 In contrast, 129gm of 129I would therefore release 9 Gigajoules over 15.7 million years beginning at an initial rate of 850 MBq releasing 25 microwatts with the radioactivity decreasing by less than 1% in 100,000 years.〔(【引用サイトリンク】publisher=US Nuclear Data Program )〕 〔(【引用サイトリンク】publisher=Idaho State University )〕 Radionuclides such as 129I or 131I, may be highly radioactive, or very long-lived, but they cannot be both. One mole of 129I(129 grams) undergoes the same number of decays(3x1023) in 15.7 million years, as does one mole of 131I(131 grams) in 8 days. 131I is therefore highly radioactive, but disappears very quickly, whilst 129I releases a very low level of radiation for a very long time. Two long-lived fission products, Technetium-99 (half-life 220,000 years) and Iodine-129 (half-life 15.7 million years),are of somewhat greater concern because of a greater chance of entering the biosphere.〔(【引用サイトリンク】title=Environmental Surveillance, Education and Research Program )〕 The transuranic elements in spent fuel are Neptunium-237 (half-life two million years) and Plutonium-239 (half-life 24,000 years). will also remain in the environment for long periods of time. A more complete solution to both the problem of both Actinides and to the need for low-carbon energy may be the integral fast reactor. One tonne of nuclear waste after a complete burn in an IFR reactor will have prevented 500 million tonnes of CO2 from entering the atmosphere.〔 Otherwise, waste storage usually necessitates treatment, followed by a long-term management strategy involving permanent storage, disposal or transformation of the waste into a non-toxic form. The most troublesome transuranic elements in spent fuel are neptunium-237 (half-life two million years) and plutonium-239 (half-life 24,000 years).〔 Consequently, high-level radioactive waste requires sophisticated treatment and management to successfully isolate it from the biosphere. This usually necessitates treatment, followed by a long-term management strategy involving permanent storage, disposal or transformation of the waste into a non-toxic form. Radioactive decay follows the half-life rule, which means that the rate of decay is inversely proportional to the duration of decay. In other words, the radiation from a long-lived isotope like iodine-129 will be much less intense than that of short-lived isotope like iodine-131. Governments around the world are considering a range of waste management and disposal options, usually involving deep-geologic placement, although there has been limited progress toward implementing long-term waste management solutions. This is partly because the timeframes in question when dealing with radioactive waste range from 10,000 to millions of years, according to studies based on the effect of estimated radiation doses. Thus, Alfvén identified two fundamental prerequisites for effective management of high-level radioactive waste: (1) stable geological formations, and (2) stable human institutions over hundreds of thousands of years. As Alfvén suggests, no known human civilization has ever endured for so long, and no geologic formation of adequate size for a permanent radioactive waste repository has yet been discovered that has been stable for so long a period. Nevertheless, avoiding confronting the risks associated with managing radioactive wastes may create countervailing risks of greater magnitude. Radioactive waste management is an example of policy analysis that requires special attention to ethical concerns, examined in the light of uncertainty and ''futurity'': consideration of 'the impacts of practices and technologies on future generations'.〔Genevieve Fuji Johnson, (''Deliberative Democracy for the Future: The Case of Nuclear Waste Management in Canada'' ), University of Toronto Press, 2008, p.9 ISBN 0-8020-9607-7〕 There is a debate over what should constitute an acceptable scientific and engineering foundation for proceeding with radioactive waste disposal strategies. There are those who have argued, on the basis of complex geochemical simulation models, that relinquishing control over radioactive materials to geohydrologic processes at repository closure is an acceptable risk. They maintain that so-called “natural analogues” inhibit subterranean movement of radionuclides, making disposal of radioactive wastes in stable geologic formations unnecessary.〔Bruno, Jordi, Lara Duro, and Mireia Grivé. 2001. ''The applicability and limitations of the geochemical models and tools used in simulating radionuclide behavior in natural waters: Lessons learned from the blind predictive modelling exercises performed in conjunction with natural analogue studies''. QuantiSci S. L. Parc Tecnològic del Vallès, Spain, for Swedish Nuclear Fuel and Waste Management Co.〕 However, existing models of these processes are empirically underdetermined:〔Shrader-Frechette, Kristin S. 1988. (“Values and hydrogeological method: How not to site the world’s largest nuclear dump” ) In ''Planning for Changing Energy conditions'', John Byrne and Daniel Rich, eds. New Brunswick, NJ: Transaction Books, p. 101 ISBN 0-88738-713-6〕 due to the subterranean nature of such processes in solid geologic formations, the accuracy of computer simulation models has not been verified by empirical observation, certainly not over periods of time equivalent to the lethal half-lives of high-level radioactive waste.〔Shrader-Frechette, Kristin S. (''Burying uncertainty: Risk and the case against geological disposal of nuclear waste'' ) Berkeley: University of California Press (1993) p. 2 ISBN 0-520-08244-3〕〔Shrader-Frechette, Kristin S. ''Expert judgment in assessing radwaste risks: What Nevadans should know about Yucca Mountain''. Carson City: Nevada Agency for Nuclear Projects, Nuclear Waste Project, 1992 ISBN 0-7881-0683-X〕 On the other hand, some insist deep geologic repositories in stable geologic formations are necessary. National management plans of various countries display a variety of approaches to resolving this debate. Researchers suggest that forecasts of health detriment for such long periods ''should be examined critically''. Practical studies only consider up to 100 years as far as effective planning and cost evaluations are concerned. Long term behaviour of radioactive wastes remains a subject for ongoing research. Management strategies and implementation plans of several representative national governments are described below. ==Geologic disposal== The International Panel on Fissile Materials has said:
The process of selecting appropriate permanent repositories for high level waste and spent fuel is now under way in several countries with the first expected to be commissioned some time after 2017. The basic concept is to locate a large, stable geologic formation and use mining technology to excavate a tunnel, or large-bore tunnel boring machines (similar to those used to drill the Chunnel from England to France) to drill a shaft 500–1,000 meters below the surface where rooms or vaults can be excavated for disposal of high-level radioactive waste. The goal is to permanently isolate nuclear waste from the human environment. However, many people remain uncomfortable with the immediate stewardship cessation of this disposal system, suggesting perpetual management and monitoring would be more prudent. Because some radioactive species have half-lives longer than one million years, even very low container leakage and radionuclide migration rates must be taken into account. Moreover, it may require more than one half-life until some nuclear materials lose enough radioactivity to no longer be lethal to living organisms. A 1983 review of the Swedish radioactive waste disposal program by the National Academy of Sciences found that country’s estimate of several hundred thousand years—perhaps up to one million years—being necessary for waste isolation “fully justified.” The proposed land-based subductive waste disposal method would dispose of nuclear waste in a subduction zone accessed from land, and therefore is not prohibited by international agreement. This method has been described as a viable means of disposing of radioactive waste, and as a state-of-the-art nuclear waste disposal technology. In nature, sixteen repositories were discovered at the Oklo mine in Gabon where natural nuclear fission reactions took place 1.7 billion years ago. The fission products in these natural formations were found to have moved less than 10 ft (3 m) over this period, though the lack of movement may be due more to retention in the uraninite structure than to insolubility and sorption from moving ground water; uraninite crystals are better preserved here than those in spent fuel rods because of a less complete nuclear reaction, so that reaction products would be less accessible to groundwater attack.〔Krauskopf, Konrad B. 1988. ''Radioactive waste and geology''. New York: Chapman and Hall, 101–102. ISBN 0-412-28630-0〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「High-level radioactive waste management」の詳細全文を読む スポンサード リンク
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