Fission and Fusion

Chapter 9 Key terms

Atomic Mass Constant

The standard unit of mass used with nuclear particles. It has the symbol u and is equal to one-twelfth the mass of a carbon-12 nucleus in the ground state and unbound. The unit of the atomic mass constant is the Dalton (Da). One Dalton is equal to 1.66 × 10−27kg.

Binding Energy

Energy required to split a nucleus into its separate nucleons.

Chain Reaction

A series of nuclear fissions that may be controlled or uncontrolled.

Control Rod

Material, commonly boron, steel or cadmium, that absorbs neutrons in a nuclear reactor.

Coolant

A substance, commonly water, carbon dioxide or liquid sodium, used to transfer thermal energy from the core of a nuclear reactor.

Core

Part of a nuclear reactor where nuclear fssion occurs, and thermal energy is produced.

Critical Mass

The minimum amount of enriched fssile material in the shape of a sphere that leads to a sustained fssion reaction.

Daughter Nucleus

A nucleus on the product side of a nuclear equation; it results when a nucleus undergoes fission or radioactive decay.

Fast Breeder Reactor

A nuclear fssion reactor in which some neutrons from the fssion of uranium-235 are absorbed by non-fssile uranium-238. After absorbing a neutron the U-238 undergoes two beta-minus decays to transmutate into the fssile plutonium-239 isotope. The term ‘fast’ refers to the fact that fast neutrons are more effectively absorbed by U-238 than slow neutrons, and so a moderator is not required.

Fissile

Capable of undergoing nuclear fssion after capturing low-energy neutrons.

Fission Fragments

Nuclides formed during nuclear fssion; these are usually radioactive.

Fuel Rod

Long, thin rod of enriched uranium used in a nuclear reactor.

Fusion

A process taking place inside stars in which small nuclei are forced together to make larger nuclei. Energy is released.

Heat Exchanger

Part of a nuclear reactor where heat drawn from the reactor core is used to turn water into steam.

Heavy Water

Water that has a higher than normal proportion of water molecules that contain deuterium.

Mass Defect

The change in mass of the reactants to the products of a nuclear reaction. The mass defect is converted to energy.

Moderator

A material, usually graphite or water, that slows neutrons in a nuclear reactor.

Radiation Shield

A thick concrete wall that prevents neutrons escaping from a nuclear reactor.

Subcritical Mass

A quantity of fssile material that is too small to sustain a chain reaction.

Supercritical mass

A quantity of fissile material that is large enough to sustain a chain reaction.

Transuranic

Elements with atomic numbers greater than uranium (Z = 92). All of these elements are unstable and radioactively decay into lighter elements.