Nuclear power plants provide power to millions of people, but many people don’t actually know how they function.

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Power Through Fission

Nuclear power plants, like most sources of power, boil water and use that to turn a turbine. The only difference is where the energy to boil this water comes from. In nuclear reactors this energy comes from fission.

The Containment Structure

The main purpose of the containment structure is to keep the reactor stable and to reduce the amount of escaping radiation. These are generally made of metal or concrete, often over a meter thick.

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The Reactor

The reactor holds another concrete dome filled with water. This water is heats up and is piped out to the turbines.

Nuclear Fuel
The Fuel is U-235 and/or Pu- 239. The fuel usually comes in small pellets. These pellets are put into metal rods to form a fuel rod. These rods are put into a fuel assembly so that they can be inserted into the nuclear reactor

The Assembly
There are about 160 fuel assemblies per nuclear reactor. They are 4-5 meters tall and about 20 cm across.
These assemblies must be made so that the fission can not go critical.

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The Control Rods
Control rods are made out of a metal that absorbs neutrons. These rods are inserted between the stacks of nuclear fuel to control the rate of fission. They are most often made out of silver, indium or cadmium.

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Types of Nuclear Reactors

There are six main types of nuclear reactors each with slightly different uses.

Most reactors use water as a coolant. There are two types of water: heavy water and light water. Heavy water has hydrogen with one neutron and light water has hydrogen with only a proton. Heavy water has an atomic mass of twenty while light water has an atomic mass of eighteen. This makes heavy water less volatile and capable of holding more energy.

Most reactors use low-enriched uranium. Natural uranium is mostly uranium 238, which can not sustain a nuclear reaction. Uranium 235, which can sustain a nuclear reaction, makes up about 0.7% of natural uranium. Low-enriched uranium contains between 0.7% and 20% uranium 235.

Reactors use moderators to slow down neutrons. Slow neutrons are more likely to cause fission. Water works well as both a coolant and a moderator so it is the one used most often.

Boiling Water Reactor

Boiling water reactors are most used in the United States, Japan, and Sweden. This reactor boils light water using low-enriched uranium. This water goes through a closed loop and pushes a turbine. The water next comes in contact with another loop to cool and condense the steam and it then re-enters the reactor.

Pressurized Water Reactor

Pressurized water reactors are by far the most common and are used in the United States, France, Japan, Russia, and China. This reactor uses two loops of light water. The first loop is highly pressurized and goes through the reactor core. This loop then comes in contact with another unpressurized loop and boils the water in that loop. That water in the second loop powers a turbine.

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Heavy Water Reactor

Heavy water reactors are really only used in Canada and India. Instead of light water this reactor uses heavy water. It functions the same as a pressurized water reactor but uses heavy water instead of light water. The properties of heavy water allows it to use natural uranium. This saves the cost of enriching the uranium but adds in the cost of finding or creating heavy water.
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Graphite Moderated Reactor

This reactor is the most dangerous type and is being fazed out. Graphite is kept in the reactor core with a mix of helium and nitrogen to cool the reactor and transfer the heat. Then either carbon, helium, or light water power a turbine. These are usually built without safety features, the Chernobyl plant was this type. This type only uses slightly-enriched uranium.

Fast Breeder Reactor
Fast breeder reactors have a different goal. They use a moderator that doesn’t slow down neutrons. This causes the uranium 238 to turn into uranium 239 and then decay into plutonium. This plutonium can be harvested for nuclear weapons. These are primarily used in the United States. Laws about the usage of radioactive material have made it hard to extract the plutonium so these reactors are not used often.

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We can’t keep using coal and oil forever, we must switch to renewable sources. There is about 4.5 billion tons of uranium in seawater alone, enough to supply all our current nuclear reactors for 6500 years.

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