|Fig. 1: Arkansas Nuclear One Cooling Tower seen from a distance. (Source: Wikimedia Commons)|
Nuclear power plants carry many stigmas. Some of these connotations are legitimate, while many are fictitious. One of the biggest images and representations of these power plants are the massive cooling towers. People see the massive, sometimes 600 feet high, hyperboloid structures from miles away and immediately associate them with nuclear power plants. Fig. 1 shows a great example of how a cooling tower can can be seen from a great distance away. Interestingly, nuclear plants are not the only energy plants that use cooling tower; coal and other fossil fuel stations utilize the towers. Most people have seen pictures or illustrations of these massive structures in contexts related to nuclear plants because media chooses to use the image as the face of nuclear energy. As the iconic image for nuclear power, why do some nuclear power plants utilize these towers while others do not?
The process begins with a reactor pressure vessel which houses fuel assemblies. These fuel assemblies cause fission chain reactions, which release great amounts of heat. This process heats up water, which is transported to the heat exchanger. After different water is transformed into steam in a heat exchanger, it flows through a set of turbines that are attached to a steam generator, which creates energy. It then travels through a condenser, which converts it back to liquid form. The condenser acts as a reverse heat exchanger and cools the steam into water. The condenser takes in cold water and generates hot water. The cooling tower transforms the hot water back to cold water. Because there are three contained water cycles, (the primary which reacts directly with the fuel assemblies, secondary, which cools the primary, and tertiary, which cools the secondary) the water used in the condenser is not radioactive and can be released into the environment through cooling towers. This entire process is shown in Fig. 2.
The tower has fans that pump air into the bottom of the hyperboloid shaped structure and pumps air out of the top as well. This creates a fairly strong upward airflow. The heated water is then released at roughly 10% of the total height. As this water falls it is cooled by the upward airflow. About 2% of the water is transferred into steam and released out of the top. The rest cools and falls into a water basin at the bottom of the tower. This basin then feeds the condenser with cold water. 
|Fig. 2: This is the process of how the Cooling Tower interacts with the other systems in nuclear power plant. (Source: Wikimedia Commons)|
There are many factors that go into the decision of whether or not to use a cooling tower. Cooling towers require a great deal of water, which can be a very expensive resource in certain parts of the country. If a plant is not near a river or lake, it can be difficult to obtain enough water for the plant. There are also other concerns with the system including: impact on aquatic organisms and discharge streams.  All of these factors can cause a government to ban the use of cooling towers, forcing engineers and scientists to use other methods. For that reason, every nuclear power plant needs to be analyzed individually. Furthermore, having a massive cooling tower close to a town can cause residents to be uneasy. Even though the tower is completely harmless, the structure acts as a constant reminder of the nuclear plant.
Nuclear power plants are more than just a source of energy. They symbol for disaster, but also man's ability to harness extreme amounts of energy. In all cases, engineers want to maximize the efficiency of the plant. However, this cannot always happen due to the potential risks that nuclear plants have. In most areas, nuclear plants are very regulated, which inhibit an engineer's ability to maximize the plant's efficiency. If there were no regulations, nearly all plants would utilize cooling towers. Even though cooling towers are very efficient and important step in the process, other factors, like climate change, will decrease their use in the near future. 
© Kevin Anderson. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 J. C. Hensley, Ed., Cooling Tower Fundamentals, 2nd Edition (Marley Cooling Tower Co., 1985).
 J. Maulbetch and J. Stallings, "Evaluating the Economics of Alternative Cooling Technologies," Power Engineering, 1 Nov 12.
 "Cooling Towers: Understanding Key Components of Cooling Towers and How to Improve Water Efficiency," U.S. Office of Energy Efficiency and Reneweable Energy, February 2011.