Nuclear Cooling Towers – an Eyesore or a Remarkable Feat of Engineering?
If you've ever travelled through a country that relies heavily on nuclear power, you may have seen cooling towers. They're hard to miss with their monstrous chimneys and clouds of steam ascending into the sky. Some people may consider cooling towers to be an eyesore, but to engineers they are a work of art. This article explains why they're needed, how they work and why we might see fewer of them in the future.
Nuclear energy accounts for about 10% of all global electricity. The United States of America is the world's largest producer of nuclear power, with nearly 100 commercial reactors. France is another large producer with 56 nuclear reactors generating about 70% of its total energy supply.
Nuclear power plants produce a lot of heat during the fission of uranium atoms. Nuclear fission is when atoms split and release energy, which raises the surrounding temperature of the atom. The heat created in this process is used to boil water and generate steam, reaching temperatures of about 500 degrees Celsius. The steam then drives a turbine to create electricity.
Because a lot of time and money goes into making sure the water in nuclear power systems is clean and pure, it is used again and again. However, the steam used to drive the turbine has to be cooled before it can be reused.
For many nuclear power stations, this cooling occurs in two places; the condenser and the cooling tower. First, the condenser converts the hot steam into warm water. Next, this warm water is piped into the cooling tower, where the temperature is further lowered.
Cooling towers on nuclear power plants are known as natural draft cooling towers. The name natural draft refers to the fact that these systems rely on warm air rising.
On the inside of cooling towers are hot water distribution systems. Hot water is sprayed onto what is called fill material, which increases the surface area of the tower and allows for the warm water to be cooled down faster. Openings at the base of the tower let cool outside air in, which lowers the temperature of the water. The excess heat escapes out the top as warm air and moisture, and the cool water can now be reused in the nuclear power system.
Natural draft cooling towers are also used on other large industrial generating facilities that require a liquid stream cooling process, such as coal burning power stations or chemical plants.
Cooling towers are remarkably strong, yet use very little material. They can be up to 200 metres high and are often less than 20 centimetres thick. That's about the width of a dinner fork. The strength comes from their hyperboloid shape, meaning the structure curves both vertically and horizontally.
Some cooling towers in Europe are over 60 years old and are just as strong as when they were built in the 1960s. They key to keeping these structures sturdy is to keep the water as pure and clean as possible. Because concrete dissolves in acid, just one little impurity in the water could cause the concrete walls to corrode.
Not all nuclear power plants use cooling towers to cool the water. Some use the ocean, lakes or rivers for cooling, as it uses less energy, and is therefore cheaper.
This is only possible when the body of water is big enough, making the ocean a popular choice for removing excess heat. The excess heat from a nuclear power station would not make a great difference when discharged into the ocean, but it could have serious impacts when released into a smaller river or lake.
Some countries have restrictions on using the natural environment for dumping water, as it can be a danger to aquatic life. Even tiny changes in the temperature or pH could affect the microorganisms living in the sea or freshwater. Although natural draft cooling towers have high building costs, they are often the only option for facilities that do not have access to large bodies of water for cooling.
Cooling towers also have a relatively low impact on the environment. Only 2% of water vapour is lost out the top of cooling towers as it evaporates and condenses, which is why we sometimes see the large clouds forming at the opening of the towers. Because this water has already run through the nuclear power station, it is clean and will not pollute the air.
When this water vapour escapes out the top, more water is needed to fill the cool water basin at the bottom of the tower. Most nuclear power stations are located near rivers or lakes and use these as a water source.
Globally, we can expect to see fewer natural draft cooling towers as the demand for nuclear and coal energy decreases. The number of safety systems required in nuclear power stations make the building costs extremely expensive compared to renewable energy like solar and wind.
Several cooling towers in Britain have already been demolished, and other coal and nuclear power stations around the world will likely follow suit. Within the next generation, all of these incredible hyperbolic structures could be gone forever.
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