How nuclear energy works

Nuclear Power Plant Reactor Types-

There are two main types of Nuclear Fission reactors – the Pressurized Water Reactor and the Boiling Water Reactor. Each type also has two variants – one with normal water and one with heavy water.

Pressurized Water Reactor

The radioactive water in the reactor core is kept under extreme pressure so that it does not boil when it hits 100 degrees celsius but continues to absorb heat. This super hot water goes through a heat exchanger which transfers the heat to non-radioactive water. This water forms super-heated steam which is used to power the turbines of the power station.

A Pressurized Water Reactor in a Nuclear Power Plant

Boiling Water Reactor

In this reactor the water in the core is not pressurized and so it boils into steam in the core. This water is then piped out to the turbines where it is used to generate electricity. Upon cooling, the water is returned to the core. While this reactor type saves somewhat on the cost of pressurizing the core, it does mean that the radioactive water from the core is passed through the turbines which then also become contaminated with radiation. This reactor model carries a far greater clean up cost when it is dismantled as there are far more heavily radiated components.

Boiling water reactor in a nuclear power plant

Use of Heavy Water in a Nuclear Power Plant-

Both the reactor types described above can also incorporate heavy water. Heavy water is water that is made of oxygen and an isotope of the element Hydrogen called Deuterium, which is the same as Hydrogen except it has an extra neutron in the nucleus and is radioactive. This is used because heavy water is better at slowing down the released neutrons than regular water is.

Heat Loss and Water Return in a Nuclear Power Plant-

The steam generates electricity by pushing the turbines as it passes through them. This means that only some of the energy in the steam is converted into power. Once the steam has passed out of the turbine, it needs to be returned to water form to be passed back into the heat exchanger or the core, depending on the model of reactor in use. In order to cool the steam enough for it to return to liquid form it is passed through cooling towers. In these, some of the steam is sacrificed to remove sufficient energy to condense the rest. This is the source of the great white plumes coming from the classic curved towers we all associate with nuclear power plants.

This is done to minimize wasted heat. While at first it seems a little ridiculous to release steam to save heat, it is the only effective large scale way power stations can retain the maximum amount of hot water after it has turned into gaseous form.

Obviously, the steam coming out of the towers represents water loss, so the water in the reactor needs to be continually topped up from a local water source such as a lake or river.