Intro. Into Nuclear Energy And you

What are the fundamental forces of the Universe??? Gravitational Force (interaction of massive bodies) Electromagnetic Force (interaction of charged particles) Weak Nuclear Force (short distance – responsible for radioactive decay of subatomic particles) Strong Nuclear Force (binds nucleons together despite electrostatic repulsion of protons – very strong force – only acts at very small distances)

How it relates to nuclear Energy Let’s discuss really big atoms – like Uranium -235 92 protons, 143 neutrons 235 92 U The large number of neutrons help the nucleus to stay together (keeps P+s apart) Stays together due to strong nuclear force

Fission reactions Breaking apart of nuclei 14156Ba 23592U 10 n  23592U Δ 23692 U 3 10 n 23592U 9236 Kr 23592U Release of large amounts of energy Process takes about 10-12 s Starts a chain reaction!!!!!

E = mc2

Historical highlight E = mc2 small amounts of mass converted to E Started ~ 1940 in U.S. Manhattan project Did not take place in Manhattan Very fast pace A great deal of knowledge of atomic physics was learned in this time period

Not just used for bombs!!! Fission used in nuclear reactions as well

Where does the U-235 come from? Mined Uranium is a combination of Uranium isotopes. Most is U-238, some U-237, and less than 1% is U-235 Enrichment = separation of isotopes to isolate U-235 to use in nuclear reactors

What happens when you have large amounts of U-235? When you have enough U-235, and therefore, enough slow moving neutrons to have a self sustaining nuclear reaction going in a reaction = critical mass. Is that all you need? No, you need something else to slow down the neutrons

How you say?? The use of a moderator (graphite or heavy water) to slow down the neutrons that bombard the U-235 (too fast = bounce off)

So why don’t the nuclear reactors just blow up like a bomb? The use of control rods (Cd or B) help to slow down the reaction if it gets going too fast – they absorb neutrons (so they are not hitting the U-235) The control rods are adjustable – so they can be changed in their orientation – to control the rate of the nuclear reaction What if the reaction goes too fast? Meltdown (like 3 mile island or Chernobyl)

How does the reactor work? Shield molten Na steam to turbine (generates electricity) Core reactor heat exchanger Fuel rods water

What do we do with the waste? Left over 238U undergoes radioactive decay Fission daughter products also undergo decay β decay 238U ½ life = 4.5 x 109 year What is to be done with it???????

Fusion reactions Put together small nuclei to make a larger nuclei P+ + P+  22He (fusion on the Sun) Enormous E released (high TO, P plasma gas) Very hard to start fusion reaction Net E gain is so large – that it melts everything!

Example (Deuterium) 21H 42He + 10n smash together 31H (Tritium) Non radioactive products 100 mill oC fusion plasma Contain in a magnetic chamber ~ 2035 (hopefully)