A significant portion of the energy of fission is converted to heat the instant that the fission reaction breaks the initial target nucleus into fission fragments. The bulk of this energy is deposited in the fuel, and a coolant is required to remove the heat in order to maintain a balanced system (and also to transfer the heat energy to the power-generating plant). The most common coolant is water, though any fluid can be used. Heavy water (deuterium oxide), air, carbon dioxide, helium, liquid sodium, sodium-potassium alloy (called NaK), molten salts, and hydrocarbons have all been used in reactors or reactor experiments.
Some research reactors are operated at very low power and have no need for a dedicated cooling system; in such units the small amount of generated heat is removed by conduction andconvection to the environment. Very high power reactors, on the other hand, must have extremely sophisticated cooling systems to remove heat quickly and reliably; otherwise, the heat will build up in the reactor fuel and melt it. Indeed, most reactors operate on the principle that their fuel cannot be allowed to melt; therefore, the systems designed to cool the fuel must operate sufficiently under both normal and abnormal conditions. Systems that enable sufficient cooling during all credible abnormal conditions in nuclear power plants are referred to as emergency core-cooling systems.
An amount of fissile material needed to produce an ongoing nuclear chain reaction.
The breakdown of a radioactive substance over time as its atoms spontaneously give off neutrons.
The process of increasing the purity of a radioactive element such as uranium to make it suitable as nuclear fuel.
The radioactive particles that fall back to Earth after being sent into the atmosphere by a nuclear event, such as the explosion of a nuclear bomb or the meltdown of a nuclear reactor.
Splitting of an atom.
The joining of atoms to produce energy.
Term used to refer to the possibility that a nuclear reactor could become so overheated that it would melt into the earth below.
A mass of radioactive material in a nuclear reactor