tungtvandsreaktorer

Tungtvandsreaktorer are a type of nuclear reactor that uses heavy water as both a moderator and a coolant. Heavy water, also known as deuterium oxide (D2O), is water in which the hydrogen atoms are replaced by deuterium, an isotope of hydrogen with an extra neutron. This difference in atomic structure gives heavy water unique properties that are advantageous for nuclear reactors.

The primary role of a moderator in a nuclear reactor is to slow down fast neutrons released during nuclear fission to thermal speeds. Thermal neutrons are more likely to cause further fission reactions in uranium-235, sustaining the chain reaction. Heavy water is an excellent moderator because it absorbs very few neutrons compared to light water, allowing for a more efficient chain reaction. This efficiency means that heavy water reactors can often use natural uranium as fuel, which is not enriched in the fissile isotope U-235. This contrasts with most other reactor types, which require enriched uranium.

As a coolant, heavy water circulates through the reactor core, absorbing the heat generated by fission and transferring it to produce steam, which then drives turbines to generate electricity. The use of heavy water as both moderator and coolant simplifies the reactor design and can contribute to its overall safety and efficiency.

The CANDU (CANada Deuterium Uranium) reactor design is the most well-known example of a heavy water reactor. These reactors are known for their ability to operate with on-power refueling, meaning spent fuel can be removed and fresh fuel inserted while the reactor is running, leading to high capacity factors and operational flexibility. Heavy water reactors are used in several countries, including Canada, India, South Korea, and Romania.