Fission and Fusion They could be described as “Big Bang” and “Bigger Bang”.

Learning Objectives Compare the nuclear changes, fuel used and products formed in fission and fusion reactions. Identify common examples of fission and fusion reactions. Define critical mass. Describe the difference in and net results of controlled and uncontrolled fission reactions. Use Einstein’s E-mc 2 equation to relate the mass lost to the energy production in nuclear reactions.

Fission and Fusion Reactions Nuclear Fission Large unstable atom splits apart Requires minimum (critical) mass Produces a variety of toxic products Fuel-Uranium-235 or Plutonium-244 Used in power plants and ships Nuclear Fusion Small atoms fuse together Requires 100,000,000° temperature Produces Helium as product Fuel-Hydrogen-2 or Hydrogen-3 Reaction in sun and other stars Produces more energy per pound

Controlled and Uncontrolled Fission In the fission reaction, when the fuel atom splits, several neutrons are released. If enough fuel atoms (critical mass) are present the neutrons strike other fuel atoms causing them to become unstable and split, continuing the process. Uncontrolled - If the reaction is allowed to continue it speeds up out of control……Big Boom! Controlled - In nuclear reactors insulating materials (control rods) are used to absorb most of the neutrons, allowing the reaction to proceed slowly. The result is the production of useable amounts of heat energy.

E = mc 2 In both fission and fusion reactions a small amount of mass in the nucleus is changed to energy. Einstein’s equation can be used to predict the amount of energy produced by fission and fusion processes. Because the term c 2 is so large (9x10 16 ) a very very small amount of mass is converted into a very very large amount of energy. 1 gram of mass lost = 90,000,000,000,000 joules of energy

Nuclear Power Plants Worldwide

Fission Reaction

Fusion Reaction

Key Concepts Review Nuclear reactions produce tremendous amounts of usable heat energy. Fission is the breaking up of an unstable uranium atom. Fission is easier to start and control than fusion, but produces less energy and generates highly radioactive waste. In uncontrolled fission nuclear chain reactions occur resulting in a large explosion. In controlled fission water or graphite are used to absorb some of the neutrons produced by fission, controlling the rate of the fission process. Fusion is the fusing of two unstable hydrogen atoms to form helium. Fusion is harder to start and control than fission, but produces more energy per pound of fuel and produces no toxic waste products. There are 120+ nuclear power plants worldwide producing 20% of the world’s electricity