Fission
The break-up of the nucleus of an atom into two major fragments, plus smaller fragments and free neutrons, when the nucleus is struck by a fast-moving free neutron.
Source: AECL
Fuel Bundle
The package of natural uranium fuel elements for insertion into a CANDU reactor. The uranium is contained in zirconium alloy tubes or elements and the elements are held together by welding them to zirconium alloy plates. Each bundle is a half a metre long and weighs about 20 kg.