Chapter 5 Energy Resources Section 3 Nuclear Energy Notes 5-3

Nuclear Reactions Nucleus of an atom: Convert matter into energy Central core made of protons (+) and neutrons (neutral) Convert matter into energy Einstein developed the equation E = mc2 E = energy m = mass c = speed of light (constant) It only takes a small amount of matter to create a large amount of energy

Nuclear Reactions Nuclear fission: Splitting the nucleus of atoms into smaller pieces Uranium-235 (U-235) A neutron is shot at the nucleus and it splits it into two smaller nuclei and two or more neutrons The mass is less than the original The missing is transferred to energy

Nuclear Reactions Nuclear fission: The other neutrons go off to hit other nuclei This creates a chain reaction Each time a large amount of energy is produced If the reaction is not controlled, it can cause disaster Nuclear bomb; atomic bomb Energy can be released as heat when controlled This can be used to create electricity

Nuclear Power Plants Heat from nuclear reactions is used to heat water to steam Steam turns the turbine to create electricity Reactor Vessel Where the nuclear fission occurs Fuel rods made of U-235 Control rods made of cadmium

Nuclear Power Plants Reactor Heat Exchanger: Less control rods in place makes the reaction go faster; and get hotter More control rods absorbs neutrons and slow down reaction; and get cooler Heat Exchanger: Water is used to cool the reactor; heat is transferred to other water that turns to steam Steam turns the turbine; make electricity

Risks of Nuclear Fission Chernobyl, Ukraine (1986) Nuclear reactor overheated and caused a meltdown The excessive heat increased the steam to the generator This caused explosions that blew the roof off and leaked radioactive materials into the environment Still is contaminated today

Risks of Nuclear Fission Disposal of nuclear wastes Remain radioactive for thousands of years They must be stored safely for many years Safety The safety requirements for nuclear plants are very extensive and expensive

Nuclear Fusion The source of energy for the sun Combines two atomic nuclei to make one larger nuclei Hydrogen nuclei are forced together to make a helium nuclei H-2 (deuterium) and H-3 (tritium) are the fuel H-2 has one neutron and H-3 has two neutrons Need a temperature of 10 million C°

Nuclear Fusion Helium has a smaller mass than two hydrogen The difference is converted to energy Use hydrogen from water as a source on Earth Safer, less pollution and more energy than fission

Nuclear Fusion Not able to control on Earth Too hot to make it work Needs to great a pressure Can’t find material to create the reactor Could use magnetic fields Uses more energy to make field than the reactor produces