One of the most important nuclear reactions for the nuclear power industry occurs when a neutron is absorbed by a heavy nucleus, causing it to become excited and subsequently split into two fragments. During this reaction, typically two or three neutrons are released together with about 200 MeV of energy. This energy is ultimately converted into heat that can be used to generate electricity. If the released neutrons cause further fissions in other heavy nuclei, the process is known as a fission chain reaction. The course of a fission chain reaction depends on many factors, such as the presence and properties of a moderator that slows down fast neutrons, the placement and concentration of neutron absorbers used to control the reaction, and the amount and configuration of fissile material in the reactor core. The heat released by nuclear fission must be removed safely using a suitable gaseous or liquid coolant.