Radioactive waste disposal nuclear fission

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. 

Haug, H. 0., "Production, Disposal, and Relative Toxicity of Long-Lived Fission Products and Actinides in the Radioactive Wastes from Nuclear Fuel Cycles," (in German), KFK-2022, translated as 0RNL-tr-it302, Oak Ridge National Laboratory,... 

Nuclear energy Nuclear facilities Nuclear fission Nuclear fuel Nuclear fuel elements Nuclear fuels Nuclear industry Nuclear power plants Nuclear reactors Radioactive decontamination Radioactive waste disposal Radioactive wastes Spent nuclear fuels... 

Strontium ( Sr) is a fission product that is common in spent fuel. Nuclear fuel processing, above ground nuclear weapons testing, and nuclear accidents are primary environmental sources of Sr. Strontium-90 also is released by nuclear power plants, submarine propulsion reactors, and radioactive waste disposal in the oceans. Sr has a half-life of roughly 29 yr. The decay products are Yt (ri/2 = 64 h, with the emission of a 546 keV maximum energy P particle) and then the stable Zr with the emission of a 2284 keV maximum energy p particle from Infre-... 

Usually atoms resulting from nuclear fission arc radioactive. There are also radioactive atoms produced from neutron capture by both U and U. Both types of radioactive atoms remain in the nuclear fuel. It is these radioactive atoms that comprise the nuclear wastes that require disposal in an environmentally acceptable manner. 

The main drawback to nuclear power is the production of radioactive waste. Spent fuel from a nuclear reactor is considered a high-level radioactive waste, and remains radioactive for a veiy long time. Spent fuel consists of fission products from the U-235 and Pu-239 fission process, and also from unspent U-238, Pu-240, and other heavy metals produced during the fuel cycle. That is why special programs exist for the handling and disposal of nuclear waste. 

The fact that spent fuel reprocessing and recycle are essential components ofgood nuclear non-proliferation and radioactive waste management practices. These actions are needed so that more efficient use can be made offissionablc materials, and unwanted radioactive fission products can be disposed of without need for permanent safeguards. In addition, potential weapons usable materials are destroyed through beneficial use. 

The radioactive wastes associated with nuclear reactors fall into two categories (1) commercial wastes — the result of operating nuclear-powered electric generating facilities and (2) military wastes—the result of reactor operations associated with weapons manufacture, Because the fuel in plutonium production reactors, as required by weapons, is irradiated less than the fuel in commercial power reactors, the military wastes contain fewer fission products and thus are not as active radiologically or thermally. They are nevertheless hazardous and require careful disposal. 

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. 

Fission products of uranium and other actinides are released to the environment during weapons production and testing, and by nuclear accidents. Because of their relatively short half-lives, they commonly account for a large fraction of the activity in radioactive waste for the first several hundred years. Important fission products are shown in Table 3. Many of these have very short half-lives and do not represent a long-term hazard in the environment, but they do constitute a significant fraction of the total released in a nuclear accident. Only radionuclides with half-lives of several years or longer represent a persistent environmental or disposal problem. Of primary interest are °Sr, Tc, and... 

Bebbington, William P., "The Reprocessing of Nuclear Fuel", Scientific American, Vol. 235, No. 6, December 1976, Page 30 Cohen, Bernard L., "The Disposal of Radioactive Waste from Fission Reactors", Scientific American, Vol. 236, No. 6, June 1977, Page 21... 

Unlike burning fossil fuels, nuclear reactions do not produce pollutants such as carbon dioxide and acidic sulfur and nitrogen compounds. However, the nuclear reactions do form highly radioactive waste that is hard to dispose of safely. Other serious problems include the potential release of radioactive materials into the environment when fires or explosions take place, and also the limited supply of fissionable fuel and the higher cost of producing electricity using nuclear fuels rather than fossil fuels. Nuclear reactors that have experienced serious accidents are shown in Figure 21.13. 

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. 

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