A coal-fired power plant is a little more efficient than a nuclear power plant (36% versus 34%). Thus, the local waste heat impacts for coal technologies should be smaller than those of nuclear technologies for a plant of equal size and similar cooling technology. In addition, the waste heat effects from coal-fired power plants are reduced because not all of the waste heat is emitted from the cooling tower. About 25% of the total waste heat of a coal-fired plant is emitted from the stack. The SPS rectenna will release waste heat with a density of 7.5 W/m^ over a 100 km^ area. This is an energy density of about 10% of the average net solar radiation at the earth’s surface. In conditions of light winds, temperature perturbations of as much as 1°C could occur in the vicinity of the rectenna.15° Changes in cloudiness near an SPS rectenna or a TPV solar collector area could occur, but an impact on precipitation distribution seems unlikely. 4.4.6 Water Pollution Insufficient information concerning the solar cell manufacturing process precludes an accurate assessment of the severity of water-polluting emissions from this activity. However, the toxicity of the raw materials and the possibility of accumulation in the environment warrants further attention. With data currently available, it is not possible to identify specific water pollution problems or effects that could occur during normal operation. However, it is possible that water pollution may result from SPS launches, SPS rectenna construction runoff, and TPV construction runoff. Acid mine drainage from underground coal mining activity is an impact of concern, and in the past such drainage has degraded many eastern waterways. Acid-contaminated waters endanger aquatic populations by altering species type, diversity, and quantity, thereby limiting commercial and recreational opportunities. Various federal and state programs have instituted water quality criteria, effluent limitations, and reclamation requirements to control the problems associated with mining activity. There is controversy over the ability of these laws to achieve the desired effect. LMFBR and fusion technologies require minimal mining activities by comparison, hence significantly smaller environmental welfare effects. LWR fuel fabrication is also an area of concern although a minor one. Existing plants have occasionally discharged ammonia, nitrates, and fluorides into low-flow streams, thereby reducing the quality of the water. 4.4.7 Water Use Changes Heavy consumption of water is treated in Sec. 4.5 as a resource issue. However, heavy use of water can decrease the amount of water available downstream for dilution and therefore can be a welfare issue as well. Mining operations can disrupt aquifers, resulting in lowering of the ground water table and alteration of water flow patterns, which could affect crop irrigation. Wet cooling towers at coal or nuclear power stations can consume large quantities of water. Technologies that do not consume water could be utilized in areas where water is scarce. During the LWR fuel cycle, the production of
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