Unit 1.3Nuclear Chemistry1.3-2 Nuclear Reactions and Energy

Nuclear Fission Chain Reaction Nuclear Reactor Nuclear Fusion

Important Terms

Nuclear reactions involve enormous changes in energy.

E=mc2

◦ E – energy◦ m – mass◦ c – speed of light (3.00 x 108 m/s)

During a nuclear reaction a small amount of mass can be converted into a large amount of energy.

The Power of the Nucleus

Nuclear fission is the process of splitting a nucleus into two or more smaller fragments.◦This is accompanied by a large release of

energy.

Nuclear Fission

◦Note that the sums of the mass numbers on the left and right are equal.

Nuclear Fission Using Uranium-235

As WWII started scientists were trying to find a way to sustain nuclear fission in a chain reaction.◦ A chain reaction is a continuing series of reactions in

which each produces a product that can react again.

Nuclear Fission

In the fission of uranium, each neutron produced has the potential to cause the fission of another atom of uranium-235.

In order for a chain reaction to occur there must be enough of a sample of the material for the neutrons to collide with other atoms.

Nuclear Fission

Critical Mass: the point where the chain reaction can become self-sustaining is referred to as critical mass

Supercritical mass◦If the amount of fissionable material is much greater than the critical mass the chain reaction escalates out of control and an explosion results.

Nuclear Fission

Nuclear Fission – SupercriticalAll of the energy is released at once. This is what happens when an atomic bomb explodes.

In order for nuclear energy to be useful the reaction must be controlled so that the energy can be released slowly.

Nuclear Fission and Nuclear Energy

Nuclear power plants generate electrical energy through the controlled fission of uranium.

◦This is done in a nuclear reactor A nuclear reactor is a device that is used to extract energy from radioactive fuel.

Nuclear Fission

Nuclear Fission - Reactors

◦Nuclear reactors do not produce CO2 and other pollutants.

◦They do produce radioactive waste that is difficult to safely dispose of. New technologies allow much of the waste to be decayed, reducing the amount of hazardous waste produced.

There is some risk of the release of this nuclear waste into the environment.

Nuclear Reactors and Pollution

◦Nuclear energy costs more to produce than energy produced through the burning of fossil fuels.

◦It is more expensive than using fossil fuels

Nuclear Fission: Problems with Nuclear Reactors

Nuclear fusion is the process of combining two or more nuclei to form a larger nucleus.

◦Nuclear fusion is the process that occurs in the sun and other stars to produce energy.

Nuclear Fusion…Hydrogen to Helium

Nuclear Fusion

Nuclear Fusion on the Sun

The fusion of hydrogen to produce helium produces 20x more energy than the fission of the same amount of uranium.◦It does not produce any radioactive waste.

◦Fusion reactions are easier to control than fission reaction.

Nuclear Fusion

◦ Difficulty initiating and containing a fusion reaction has prevented its use as a practical energy source. Nuclear fusion reactions require a large amount of

energy to start the fusion reaction. In order to initiate a fusion reaction on earth a

temperature greater than 100million Kelvins would be required.

◦No material exists on earth that could contain the reaction.

◦A great goal for the future!!!

Problems with Nuclear Fusion

Fission Fusion•Splitting of an atomic Nuclei caused by a neutron

•Combining of two or more nuclei

•Chain reaction •Multi-step process•Produces radioactive waste •Does not produce radioactive

waste•Used in nuclear power plants and bombs

•Not able to be initiated and contained because requires a great deal of energy to start

•Can generate a great deal of energy!

• Occurs on the sun tremendous of energy released!

Fission vs Fusion