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Electricity : Operation : Cooling Towers
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Because heated water could have an adverse effect on the environment, most states have laws that prohibit power plants returning water that is too hot directly to the river, ocean, or lake. For this reason, cooling water in the third loop has to be pumped to the cooling tower to have some of its heat removed. The cooling tower is a giant hollow cylinder, pinched in near the top. It is supported on legs that allow air to flow under the tower. Like many other power plant structures, the tower is made of concrete and thick steel reinforcement bars.
About 50 feet up inside the cooling tower there are several layers of special tiles called baffles. The baffles in the cooling tower provide 390 acres of surface area for cooling water. Heated water in the third loop is sprayed on these tiles. This water trickles down through many stair-stepped layers of baffles, losing heat as it goes. Heat from the third loop is transferred into the air. Hot air rises and moves up through the cooling tower. This causes more air to flow under the tower to replace the heated air. As this process continues, a natural breeze begins to blow up through the baffles and out of the cooling tower. This process evaporates about 11,000 gallons of water each minute.
However, most of the cooling water does not evaporate. It is cooled to about 24 Celsius (75 Fahrenheit) and collected at the bottom of the cooling tower. Some of this water is returned to the source, but most is used again in the third loop.
Evaporated water leaves the tower at about 10 miles per hour and spreads out into the atmosphere. Because there are separate loops used in the power plant, this vapor has never come in contact with the reactor core. The vapor coming out of the top of a cooling tower is not radioactive.
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