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The Environmental Imperative for Renewable Energy: An Update Radiation119 |
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A. RADIOACTIVITY This section considers releases to the environment of radiation from nuclear power generation. It does not fully discuss the possibility of catastrophic accidents, although that remains a threat with low probability and potentially disastrous consequences. 120 Nor does it fully discuss decommissioning nuclear plants, although the environmental legacy of that process remains unclear. 121 Radioactive materials such as uranium naturally degrade into lighter "daughter" elements, which in turn degrade, culminating in stable elements. This process is called fission. When bombarded by neutrons, atoms of one rare type of uranium - uranium-235 - release neutrons that go on to split other uranium atoms in a chain reaction. Nuclear reactors exploit the heat given off by this process to boil water for a steam turbine. Once ingested through air, food, or water or through cuts and abrasions, living organisms may incorporate radioactive elements into their tissues. For instance, tritium mimics normal hydrogen in water; strontium-90 and radium-226 behave like calcium and collect in bones; cesium-137 resembles potassium and accumulates in the muscles; and so on. 122 Radioactive substances harm living organisms by emitting alpha particles, beta particles, and gamma radiation, which ionize the molecules they strike by knocking off a negatively charged electron. Ionization can break chemical bonds and thereby damage living cells, particularly through damage to DNA molecules, which encode genetic information. Damage to the DNA of sperm or egg cells can result in damage to future generations. 123 Current nuclear regulations assume no threshold for danger from radiation. That is, even very small amounts of radiation are assumed to have the potential to harm humans. The danger is also presumed to grow in a linear fashion, so that more radiation presents a correspondingly larger threat. Research continues on the validity of these assumptions. 124 Radiation varies in strength. For instance, while casual exposure to the gamma rays emitted by some radionuclides cause severe harm, the alpha rays emitted by uranium outside the body pose little threat to human health. When inhaled or ingested, however, uranium's emissions alter cells' reproductive processes, increasing the risk of lung and bone cancer. Animal studies indicate that radiation from uranium may affect the developing fetus, and can increase the risk of leukemia and soft tissue cancers. Research also suggests that radiation may induce "genomic instability." 125 That is, radiation in very low doses may trigger cell and chromosome damage that manifests only after cells undergo several normal divisions. Finally, some radioactive elements also prove chemically toxic. For instance, uranium at high concentrations can damage internal organs, particularly the kidneys. In general, nuclear power accounts for a very small fraction of the radiation experienced by the U. S. population - less than 1.6% of total artificial radiation, and less than 0.3% of all radiation. 126 One source estimates that New York's six nuclear power plants cause between 0.403 and 1.467 statistical cancer deaths per year, and a comparable number of survivable cancers. 127 Reckoned very roughly, this equates to between 8.3 and 30.2 annual statistical cancer deaths nationally, plus a comparable number of survivable cancers. However, individuals in contact with various segments of the nuclear fuel cycle may have much higher exposure with correspondingly higher effects: the same source notes that nuclear workers bear 99.9% of the risk of fatal cancer from normal nuclear operations. 128
B. HIGH-LEVEL RADIOACTIVE WASTE As nuclear fuel ages, it loses its capacity to sustain an efficient nuclear reaction. Each year, a nuclear facility removes about a third of its highly irradiated (" spent") fuel rods to on-site cooling pools. These assemblies contain uranium, plutonium, and fission products such as strontium and cesium. Since regulators limit the pools' capacity, the rods must eventually be placed in steel or concrete containers, known as dry casks. The assemblies remain thermally hot and highly radioactive; a person standing one yard from an unshielded spent fuel assembly could receive a lethal dose of radiation (about 500 rems) in under three minutes. A 30-second exposure (85 rems) would significantly increase the risk of cancer or genetic damage. 129 Spent fuel accounts for the majority of U. S. highlevel nuclear waste. (Nuclear weapons facilities also contribute to the total.) As of 1997, about 70 power plants across the nation stored 35,000 metric tons of spent fuel. Increasing by about 2,000 metric tons per year, total highlevel waste will reach at least 60,000 metric tons by 2010, and 80,000 metric tons by 2020. 130 In theory, onsite storage waste represents only a temporary solution to high-level radioactive waste. The Nuclear Waste Policy Act of 1982 orders the U. S. Department of Energy (DOE) to select a geologic repository for high-level waste. Amendments in 1987 limited possible sites to Nevada's Yucca Mountain. DOE plans to begin storing waste in 2010. Under current law, the repository could host up to 70,000 metric tons of waste, including 63,000 metric tons from civilian reactors. 131 In addition to fears that uninformed future generations might stumble on the repository, opponents of the Yucca Mountain plan note three environmental problems. First, experts disagree on the potential of leaks from the repository into the local water supply. Second, seismologists note that the area has experienced more than 600 seismic events above 2.5 on the Richter scale since 1976, raising the possibility of earthquake damage to containers. 132 Third, many communities worry about how the waste will reach Yucca Mountain. The State of Nevada, which opposes the proposal, calculates that transporting waste from its current locations during the repository's 25-year emplacement phase would require between 35,000 and 100,000 shipments crossing 43 states, affecting 109 cities. 133 The Congressional Research Service estimates a possible 154 truck and 18 rail accidents over 30 years, although the vast majority of those accidents would not release radiation. 134
C. "LOW-LEVEL" WASTE While high-level waste and spent fuel are Federal responsibilities, states are required to develop disposal sites for so-called low-level waste; such sites received perhaps 325,000 cubic feet of material in 1997. Utilities produced about two-thirds of the total by volume, but 85% of the total radioactivity in question. 135 (Other sources include defense facilities, hospitals, and labs.) This material includes radioactive corrosion products that adhere to the interior of the reactor vessel, ion-exchange resins, irradiated parts and equipment, and matter trapped by filters. As electric companies decommission retired nuclear plants, the volume of low-level waste may grow substantially. 136 State and federal documents indicate that every low-level nuclear waste dump ever used - a total of six - has leaked, as indicated by the presence of tritium or other radionuclides in groundwater, vegetation, and elsewhere. 137 The term "low-level" may mislead. Although this material in general contains less radioactivity and decays more rapidly than high-level waste, the two classes can contain the same radionuclides. In fact, some types of low-level waste can be more radioactive than some types of high-level waste. 138 Unshielded low-level waste can deliver a lethal dose of radioactivity in as little as 30 seconds. 139
D. ROUTINE RELEASES FROM NORMAL OPERATIONS Nuclear reactors release low levels of radioactivity as part of normal operations. Volatile fission products including tritium and noble gases may escape through the fuel rods' metal cladding; operators may also vent gas to control temperature, humidity, and radioactivity inside the plant. Plants monitor these radioactive emissions and store them in decay tanks before releasing them. Water released to the environment may contain tritium, cobalt, cesium, or other radionuclides. Radiation from these sources are a small fraction of background radiation, but the isotopes can be detected. 140
E. RADIATION AND COAL PLANTS Some analysts suggest that coal-fired power plants expose nearby residents to higher radiation doses than nuclear plants meeting U. S. government regulations. 141 Among the other trace elements listed in Table 3, coal contains between <1 and 10 parts per million (ppm) of uranium, and between <2.5 and 25 ppm of thorium, as well as radioactive potassium-40. Only 1% of the original radioactive material escapes as airborne matter. Rather, these heavy, radioactive metals concentrate in the bottom ash, which is generally stored onsite by utilities, buried in landfills, or sold for purposes such as cement making. One source estimates that in 1982, U. S. coal-fired plants released 801 tons of uranium (including 11,371 pounds of fissionable uranium-235) and 1,971 tons of thorium. 142 Although the risk to human health from a given coal plant's radioactive emissions may be small, this unnoticed source of radioactivity may over time represent a significant source of background radiation.
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The Environmental Imperative for |
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