Nuclear Fission and Fusion

Fission Fission means divided. When a heavy nucleus is bombarded by neutrons the strong nuclear force weakens, but the electric repulsion remains strong. A fast moving neutron collides with the atom and splits it into smaller fragments High levels of energy released (7 million times the energy released by one TNT molecule!)

Uranium Fission Reaction                                                                             

How it Works

Fission cont’d One neutron starts the reaction, and an average of three neutrons are released If these three neutrons hit other uranium atoms, they will split and 9 more neutrons are released and those will hit other atoms…. This sequence of reactions is known as a chain reaction

Chain Reaction

How it Works

How it Works Imagine a sample of uranium with billions of atoms of uranium, all splitting in a chain reaction.

Fusion Nuclear Fusion is the opposite of fission When two lighter nuclei must travel at high speeds to overcome repulsion and form a heavier atom The hydrogen bomb is a destructive use of power from fusion.

Fusion

Nuclear Power Plants Nuclear power plants control these reactions Parts of nuclear reactors… Control rods Fuel rods Moderator (usually water or carbon)

Control Rods Made of neutron absorbing material (cadmium or boron) Can be moved up and down and control the reaction rate

Fuel Rods Fuel made up of Uranium-238 and 3% Uranium-235 Uranium-238 dilute U-235 to prevent explosions

Moderator Moderator is kept under high pressure to prevent boiling Moderator is used to transfer heat to other parts of power plant to generate electricity

Power plant simulation http://www.ida.liu.se/~her/npp/demo.html#instructions