Nuclear Fission
Nuclear Fission Fission = splitting of nuclei Nuclei split when hit with a neutron Nucleus breaks into: * 2 large fragments & * 2-3 neutrons Fission releases LOTS of Energy
Chain Reactions Uranium – 235 atoms will create a chain reaction When 1 U-235 atom fissions it gives off 3 neutrons Each of those neutrons will split 3 more U-235 atoms Which gives of 9 neutrons that split 9 more U-235s Which give off 27 neutrons and so on….
Nuclear power plants Use Fission to generate electricity Fission uses uranium -235 as fuel Uranium is an expensive, non-renewable fuel source (it will become scarce in ~ 60 years) Fission produces radioactive waste that is hazardous to humans (cancer, birth defects) mining the uranium also releases radioactive materials into the environment
Nuclear power plants No air pollution is created! No CO2, no smog, no acid rain, no mercury
How Fission Reactors Work Nuclear fuel (U) is formed into fuel rods (3% U-235 and 97% U-238 = can’t explode) Fuel rods are surrounded by high pressure water Neutrons are shot at the fuel rods to start chain fission reaction Neutrons from one rod travel to next rod to continue chain reaction
Control rods can be lowered over the fuel rods to keep neutrons from hitting them. This keeps the fission reaction from happening. Partially lowering control rods slows the reaction Slow chain reaction = less heat
Heat Energy from Chain reaction is absorbed by water The fuel rods, control rods and water are surrounded by a containment wall. The superheated water leaves the containment chamber and goes to a boiler (heat exchanger) Superheated water heats up water in the boiler turning it to steam
Expanding steam turns a turbine. The turbine converts mechanical energy of spinning into electrical energy Steam is cooled back into water by cool water from the cooling tower
http://www. youtube. com/watch http://www.youtube.com/watch?v=rBvUtY0PfB8 describe nuclear reactions, reactors & what happened in Japan http://www.youtube.com/watch?v=rr2PmjdpLqM comp results of japan & chyrnoble http://www.cbsnews.com/video/watch/?id=7360295n news report on contamination in area
Nucelar Fusion = fusing 2 nuclei into 1 nucleus Releases HUGE amounts of energy
Nuclei are positive and repel each other so….. it takes a LOT of energy to force them together One way to push them together is to get them moving very fast To make molecules move fast you can heat them up = Thermonuclear fusion ( >100 million °C) Which happens in the sun
Thermonuclear fusion on the sun is fine It gives us our sunlight (electromagnetic radiation) Uncontrolled thermonuclear fusion on earth is …..
Fusion nuclear reactors Thermonuclear fusion takes place when hydrogen gas is converted into a plasma ( a state of matter even hotter than a gas ) The surface of the sun is a plasma The only way to contain plasma is with magnetic fields It costs more to heat the plasma and to create the magnetic containment than is produced by the fusion
Right Now Fusion power is not economical or reliable We are working on it because Hydrogen that is used for fuel is unlimited The only waste product is Helium – no pollution and no radioactive waste
Atom bomb – fission reaction of Uranium or Plutonium Atom bombs Atom bomb – fission reaction of Uranium or Plutonium Limited by critical mass. If bomb exceeds critical mass it could explode all by itself! Chain reaction triggered by neutron production
Hydrogen bombs Use thermonuclear fusion…not limited in size by critical mass Temperatures needed a generated by a small atom bomb Thermonuclear bombs are 1000x more destructive than the atom bomb dropped on Hiroshima