A nuclear power plant generates electricity based on the steam power process and therefore consists of the following four components: Combustion chamber, turbine, condenser and pump.

kraftwerk gersteinwerk luftbild - rwe pressebilder
© rwe pressebilder

Nuclear power plants

In contrast to power plants based on the combustion of fossil fuels, the heat generated in a nuclear power plants originated from a reactor. In the reactor, the nuclear fuel releases energy during a process called nuclear fission.

A light water reactor is fitted with up-right fuel rods (several meters in length and circa 1 cm in diameter), which are filled with enriched uranium. Germany’s nuclear power plant types all use water to enclose the fuel rods. Water serves as both a moderator and as cooling. In a controlled chain reaction, nuclear fission releases high velocity neutrons.

While penetrating the water, the neutrons are slowed down (“moderated”), as they collide with water particles. Thereby, the kinetic energy of the neutrons is transferred to the water and heats it up.

The controlled chain reaction

When the neutrons have been decelerating they are able to induce further nuclear fission. For that to happen the neutrons have to collide with a uranium atom. This atom splits into smaller atomic nuclei and releases several high-energy neutrons.

In the statistical mean one nuclear fission is only allowed to effectuate one further nuclear fission. If more than one further nuclear fission is triggered, a so-called uncontrolled chain reaction is initiated. In such a runaway reaction the number of nuclear fissions would grow exponentially, and along with it the energy released. This principle is used for nuclear bombs.

If on average one fission triggers less than one further fission, the reaction comes to a standstill.

In order to control the number of new fissions, triggered by one fission, the inside of the reactor is also equipped with control rods. Those can be either driven between the fuel rods or pulled out according to the desired effect.

The control rods are made of a material that readily absorbs released neutrons and thus can control the chain reaction. Compounds consisting of cadmium or boron are common.