Why do nuclear power plants use water or heavy water?

Nuclear power plants use water or heavy water as both a coolant and a neutron moderator.

In a nuclear power plant, the primary role of water or heavy water is to act as a coolant. The heat generated by the nuclear fission process in the reactor core is immense. This heat is used to convert water into steam, which then drives the turbines to generate electricity. Without a coolant, the reactor core would overheat, leading to a potential meltdown, which could have catastrophic consequences.

Water is an excellent coolant because of its high specific heat capacity, which is the amount of heat energy required to raise the temperature of a substance. This means that water can absorb a lot of heat before it starts to boil, making it ideal for cooling the reactor core. Moreover, water is abundant and cheap, which makes it a practical choice.

Heavy water, or deuterium oxide, is used in some types of reactors, such as the CANDU reactors. It serves a dual purpose: as a coolant and as a neutron moderator. A neutron moderator slows down the fast neutrons produced by fission to speeds at which they are more likely to cause further fissions, sustaining the chain reaction. Heavy water is an effective moderator because it does not absorb as many neutrons as regular water, allowing more neutrons to continue the chain reaction.

The use of water or heavy water in nuclear power plants is a crucial aspect of their operation. It allows the heat generated by nuclear fission to be harnessed efficiently to produce electricity, while also ensuring the reactor core remains at a safe temperature. Furthermore, in certain types of reactors, heavy water plays a vital role in sustaining the nuclear chain reaction.