Nuclear FissionNuclear FissionNuclear FissionNuclear Fission is when a large nucleus splits into two smaller nuclei, releasing is when a large nucleus splits into two smaller nuclei, releasing

neutrons and energyneutrons and energy– Heavier nuclei tend to be more unstableHeavier nuclei tend to be more unstable

Energya small amount of mass changes to energya small amount of mass changes to energy

E = mcE = mc22

Matter and energy are interchanged in a Matter and energy are interchanged in a nuclear reaction nuclear reaction (the mass of the products is (the mass of the products is slightly less than the mass of the reactant)slightly less than the mass of the reactant)

All nuclear power generation is accomplished All nuclear power generation is accomplished through nuclear fission.through nuclear fission.

n10

Nuclear reactionsNuclear reactions vs vs Chemical reactionsChemical reactionsChemical reactionsChemical reactions::– mass is conservedmass is conserved, and energy changes are relatively small., and energy changes are relatively small.– There are There are no changes to the nucleino changes to the nuclei in chemical reactions. in chemical reactions.

Nuclear reactionsNuclear reactions::– the actual the actual nucleus of atoms changesnucleus of atoms changes..– Protons, neutrons, electrons, and/or gamma rays can be lost or gained.Protons, neutrons, electrons, and/or gamma rays can be lost or gained.– Small changes of mass = huge changes in energySmall changes of mass = huge changes in energy

– The nuclear fission of The nuclear fission of 1 g of uranium-2351 g of uranium-235 produces the produces the same same amount of energyamount of energy as burning as burning 2 tonnes of coal!2 tonnes of coal!

Induced Nuclear ReactionsInduced Nuclear ReactionsIn addition to natural radioactive decay, scientists can also In addition to natural radioactive decay, scientists can also create nuclear reactionscreate nuclear reactions

by by smashing nuclei with alpha, beta and gamma radiation or other subatomic smashing nuclei with alpha, beta and gamma radiation or other subatomic particles.particles.

24 + 7

14 N 817 O + 1

1p

or

24 He + 7

14 N 817 O + 1

1H

Nuclear Fission of U-235Nuclear Fission of U-235It is much It is much easier to crash a neutral neutroneasier to crash a neutral neutron than a positive proton than a positive proton into a nucleusinto a nucleus to release energy. to release energy.– Most nuclear fission Most nuclear fission reactors and weaponsreactors and weapons use this principle. use this principle.– A A neutronneutron crashes into an atom of crashes into an atom of stable U-235stable U-235 to create to create unstable U-236unstable U-236, which then undergoes , which then undergoes radioactive decayradioactive decay..– After several steps, atoms of After several steps, atoms of krypton and barium are formedkrypton and barium are formed, along with the release of , along with the release of three neutronsthree neutrons and and huge quantities of energyhuge quantities of energy..

Chain ReactionsChain ReactionsOnce the nuclear fission reaction has started, it can Once the nuclear fission reaction has started, it can keep going.keep going.

– The The neutrons released trigger more reactionsneutrons released trigger more reactions on other U-235 atoms. on other U-235 atoms.– This This chain reactionchain reaction can quickly get can quickly get out of controlout of control..– materials that absorb neutrons help to control the chain reactionmaterials that absorb neutrons help to control the chain reaction ..

eg: Cadmium Rodseg: Cadmium Rods

– Nuclear bombs are Nuclear bombs are uncontrolled reactionsuncontrolled reactions

CANDU ReactorsCANDU ReactorsCANCANadian adian DDeuterium euterium UUranium reactorranium reactor

– safe and easy to shut down in an emergency.safe and easy to shut down in an emergency.– produces a lot of heat to generate steam to drive a turbine that produces a lot of heat to generate steam to drive a turbine that

produces electricity.produces electricity.

Hazardous wastes– Some waste products, like fuel rods,

can be re-used.

– Some products are very radioactive, however, and must be stored away from living things.

– Most of this waste is buried underground or stored in concrete.– It will take 20 half-lives (thousands of years) before the material

is safe.

Nuclear FusionNuclear FusionNuclear FusionNuclear Fusion is when two small nuclei join together into is when two small nuclei join together into

one larger nucleus, releasing large amounts of energyone larger nucleus, releasing large amounts of energy

Energy

Nuclear FusionNuclear Fusion produces produces much more energymuch more energy for a for a given mass of fuel thangiven mass of fuel than Nuclear Fission Nuclear Fission..

e.g.:e.g.: The Sun and other starsThe Sun and other stars Hydrogen BombHydrogen Bomb the basic source of energy in the universe the basic source of energy in the universe

(how all elements are formed)(how all elements are formed)

Nuclear Fusion continuedNuclear Fusion continued

As an energy source it is clean and plentiful, As an energy source it is clean and plentiful, however it is very hard to control as it needs however it is very hard to control as it needs very high temperaturesvery high temperatures (100,000,000 (100,000,000°C)°C)

Scientists cannot yet find a safe, manageable method to harness the energy of nuclear fusion.– So-called “cold fusion” would occur at temperatures and

pressures that could be controlled.

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