Wastes, nuclear fission problem

See also Electric Power, Generation of Environmental Problems and Energy Use Explosives and Propellants Meitner, Lise Military Energy Use, Historical Aspects of Molecular Energy Nuclear Energy Nuclear Energy, Historical Evolution of the Use of Nuclear Fission Fuel Nuclear Fusion Nuclear Waste. 

Half-lives may be very short, 4.2 x 10-6 seconds for Po-213, or very long, 4.5 x 109 years for U-238. The long half-lives of some waste products is a major problem with nuclear fission reactors. Remember, it takes 10 half-lives for the sample to be safe. 

The production of electricity fiom nuclear fission energy is accompanied by formation of radioactive waste, of which the larger hazard is the presence of long-lived transuranium isotopes. The problems associated with this waste are still debated, but if the transuranium isotopes could be removed by exhaustive reprocessing and transmuted in special nuclear devices, the hazard of the waste would be drastically reduced (Chapter 12). This may require new selective extractants and diluents as well as new process schemes. Research in this field is very active. 

Unenriched uranium—which contains more than 99 percent of the nonfissionable isotope U-238—undergoes a chain reaction only if it is mixed with a moderator to slow down the neutrons. Uranium in ore is mixed with other substances that impede the reaction and has no moderator to slow down the neutrons, so no chain reaction occurs. 75- Nuclear fission is a poor prospect for powering automobiles primarily because of the massive shielding that would be required to protect the occupants and others from the radioactivity and the problem of radioactive waste disposal. 

This chapter first introduces the fundamentals of radioactivity and its environmental significance. The following sections focus on the geochemistry of uranium and uranium ore deposits as the basis of the nuclear fuel cycle. Later sections consider nuclear power and the geochemistry of important radionuclides in nuclear wastes, with emphasis on the actinide elements and some of their fission products which make nuclear wastes a potential problem for future generations because of their very long half-lives. 

Nuclear fission energy of the type currently in use has the potential to provide enough energy for the operation of civilization, but it presents much the same supply lifetime problem as fossil fuels. The waste products present a severe environmental problem. The problem is very different from that presented by fossil fuels but possibly more dangerous. Despite much criticism of the use of fission nuclear power, its use may be preferred to fossil fuels because of the lack of other peaceful use for uranium and the fact that the waste products can be confined. Remember, fossil fuels wastes are not confined. They are dispersed through the ecosphere as acid rain and carbon dioxide. 

Nuclear energy, which is obtained when nucleons (protons and neutrons) are allowed to adopt lower energy arrangements and to release the excess energy as heat, does not contribute to the carbon dioxide load of the atmosphere, but it does present pollution problems of a different land radioactive waste. Optimists presume that this waste can be contained, in contrast to the burden of carbon dioxide, which spreads globally. Pessimists doubt that the waste can be contained—for thousands of years. Nuclear power depends directly on the discipline of chemistry in so far as chemical processes are used to extract and prepare the uranium fuel, to process spent fuel, and to encapsulate waste material in stable glass blocks prior to burial. Nuclear fusion, in contrast to nuclear fission, does not present such serious disposal-related problems, but it has not yet been carried out in an economic, controlled manner. 

In contrast to the nuclear fission, nuclear fusion seems very promising as an energy source, at least on paper. Although thermal pollution would be a problem, fusion fuels are cheap and almost inexhaustible and the fusion process produces little radioactive waste. If a fusion generator were turned off, it would shut down completely and instantly, without any danger of a meltdown. 

Mr. Kazakov discussed problems associated with contamination from the Chernobyl nuclear accident. The first problem is in characterising what portion of the contaminated material in the exclusion zone should be considered radioactive waste and how to deal with it remove it or possibly use materials for construction. Consideration of the extent to which contaminated materials should be removed, as radioactive waste, presents a problem as well. This is related to the second problem in properly characterising the total inventory of the radioactive waste. The waste is characterised at temporary locations of radioactive waste (TLPRW) and radioactive waste burial sites (RWBS). Although there is a great deal of documented information on the locations, volumes and activities, it is unclear whether to categorise the radioactive waste by specific activity, volume or presence of transuranic and fissionable elements in the radioactive waste. 

The essential components of a fission-powered generating plant are shown in > Figure 10.13. The use of nuclear power plants has created much controversy. The plants release large amounts of waste heat and thus cause thermal pollution of natural waters. In addition, radioactive wastes create disposal problems—where do you dump radioactive... 

In contrast to the nuclear fission process, nuclear fusion, the combining of small nuclei into larger ones, is largely exempt from the waste disposal problem. 

Nuclear fission is used to generate electricity without the harmful side effects associated with fossil fuel combustion. Yet nuclear power has its own problems, namely the potential for accidents and waste disposal (8.7). Will the United States build a permanent site for nuclear waste disposal Will we turn to nuclear power as the fossil fuel supply dwindles away How many resources will we put into the development of fusion as a future energy source These are all questions that our society faces as we begin this new millennium. 

The advantages of fusion over fission could be enormous. Since deuterium constitutes about one in every 65(X) H atoms, the oceans of the world can supply an almost limitless amoimt of nuclear fuel. It is estimated that there is sufficient lithium on Earth to provide a source of tritium for about 1 million years. Also, nuclear fusion would not pose the vexing problems of radioactive waste storage and disposal associated with nuclear fission. 

The fear of accidents like Chernobyl, and the high cost of nuclear waste disposal, halted nuclear power plant construction in the United States m the 1980s, and in most ol the rest ol the world by the 1990s. Because nuclear fusion does not present the waste disposal problem of fission reactors, there is hope that fusion will be the primary energy source late in the twenty-first centuiy as the supplies of natural gas and petroleum dwindle. 

What are the opportunities for using forms of energy that do not lead to CO2 formation Nuclear power from fission reactors presents problems with the handling and deposition of nuclear waste. Fusion reactors are more appealing, but may need several decades of further development. However, solar and wind energy offer realistic alternatives. 

Fuel reprocessing has three objectives (a) to recover U or Pu from the spent fuel for reuse as a nuclear reactor fuel or to render the waste less hazardous, (b) to remove fission products from the actinides to lessen short-term radioactivity problems and in the case of recycle of the actinides, to remove reactor poisons, and (c) to convert the radioactive waste into a safe form for storage. Fuel reprocessing was/is important in the production of plutonium for weapons use. 

The fissioning of U and Pu in a nuclear reactor produces a large number of radioactive fission products. Most of these decay to stable isotopes within a few minutes to a few years after the fuel has been discharged from the reactor and therefore pose no problem in the management of nuclear fuel wastes. There are, however, a number of longer lived radionuclides that must be considered in assessing the environmental impact of any nuclear fuel waste disposal vault in the geosphere. 

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