1. Allen High School IB Physics SL Source: Chris Hamper Physics

2.  As technology has advanced, it has become easier to extract fossil fuels like coal.  This is a difficult and dangerous job; however coal produces more heat and energy than wood.  The invention of James Watt’s steam engine changed the world in 1769 and still today.  Steam engines turned a wheel and were powered by coal (twice the energy density than wood).  This invention kicked off the Industrial Revolution and the ability to transport goods around the world. Coal cities boomed.

3.  Oil technology allows us to drill and pump crude oil (thick sticky substance). Oil has a higher energy density than coal, but before 1852, it was more difficult to utilize than coal.  In 1852, Ignacy Lukasiewicz invented a method to refine crude oil to make kerosene (cleaner fuel with even higher energy density). It became possible to inject the fuel inside a piston of an engine (internal combustion), which revolutionized transport.  Easy to transport, but hard to clean up oil spills.

4.  In 1831, Michael Faraday discovered that moving a wire in a magnetic field created current. But in 1866, Werner Siemens invented the dynamo, which brought electricity generation to the big scale.  In 1884, Sir Charles Pearson invented the steam turbine, which was the final puzzle piece.  Electricity was now the easiest way to transfer energy from one place to another.

5.  Coal-fired stations burns the coal, which boils the water, then produces steam and powers the turbine, which turns a generator and produces electricity. The steam leaving the turbine is cooled, causing it to condense and is returned to the boiler.  Overall efficiency of coal-fired stations are 40%. Degraded energy is exhaust gas, waste heat, and also friction in the components of the turbine and generator.

7.  Oil-fired stations are the same as coal, but oil is cleaner and easier to transport.  Gas-fired stations are more efficient because there are two stages of energy use.  Burning gas is blasted through a turbine  Heat produced can boil water & power turbine.  Gas-fired can be 59% efficient, but if the “wasted” heat is utilized, it could be as high as 80%.

8.  What can be more efficient and cleaner??

9.  Fission: Big nucleus (U-236) splits into two smaller nuclei, resulting in a loss of mass (defect) and hence a release of energy.  236 92 U  142 56 Ba + 92 36 Kr + 1 0 n  The energy released from the ∆m is given to the fission fragments as KE.  If one mole of Uranium split, then the energy released would be 16.5 x 10 12 J, which is a lot more energy than coal.  The neutron released in the above reaction is an essential part of nuclear reactions.

10.  A neutron is added a U-235 nucleus to produce U-236, which then splits in two. As a result there are too many neutrons and some are released.  These neutrons can be captured by more U atoms and so on, leading to a chain reaction.  The chain reaction depends on slow moving neutrons. Neutrons are slowed down by introducing some other nuclei between U atoms. Colliding with the other nuclei slow down the neutrons.

12.  A minimum amount of U is needed in order for these chain reactions to take place. This is called Critical Mass.  Once U is extracted from the ground (as uranium ore) and processed, only U-235 (only 0.7%) is used as nuclear fuel. Uranium must be enriched (increasing the U-235 percentage).  The fuel is then made into fuel rods (cylinders stacked together); the rods are then bundled together and many are placed in the reactor.

13.  Is this an atomic bomb?  NO, not all nuclear energy results in a bomb.  An atomic bomb is an out-of-control reaction takes place. The total mass is above the critical mass. It depends on the initial mass. A nuclear weapon begins with 85% U-235, where normal nuclear reactions are less than 20%.  How do we prevent an out-of-control reaction?  Control the number of neutrons produced and the speed of the neutrons (we want them slowed down).

14.  A nuclear reactor produces the heat and contains the fuel rods surrounded by the moderator.  The control rods are raised/lowered to control the rate of reaction (they absorb the neutrons not needed).  There is a pressured vessel, which has a gas circulating to pick up heat from fuel rods and transfer it to the heat exchanger. The water then turns to steam and turns a turbine and generates electricity. See picture on next slide.

16.  When U-238 absorbs a neutron, it turns into U-239, which then decays to produce beta radiation and Np-239, which then decays again by beta radiation to Pu-239, Plutonium.  Plutonium also undergoes fission and can be used as a fuel or in the manufacture of nuclear weapons.  The production of Pu from U can be extracted and used for subsequent energy production (or bombs).

17.  Chernobyl; Three-Mile Island; emphasis on “nuclear” as a weapon.  As with all energy sources, there are cons/problems with nuclear.  Radioactive waste from U extraction (“short-term”) & spent fuel rods (the latter leads to long-term storage).  Nuclear meltdown: when reactions are not controlled and fuel rods melt together. Pressure vessel bursts, thus releasing radioactive material into the atmosphere. (Chernobyl, Ukraine, 1986).

18.  Fusion is the opposite of fission. Fusion involves fusing light nuclei to form a larger nuclei. Once again, the mass defect is converted to energy. Fusion happens on the Sun.  There is less known and less experience with Fusion as compared to Fission.  The difficulty with Fusion is maintaining and confining a high-temperature, high-density plasma necessary for a fusion reaction.

19.  Going back to the Energy Density chart.  Fuel Energy Density (MJ/kg)  Fusion fuel 300,000,000  Uranium-235 90,000,000  Think of the power efficiency if we were able to use Fusion more often!