Environmental Physics PHYS 1149
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This 34 page Class Notes was uploaded by Maudie Larkin on Monday October 12, 2015. The Class Notes belongs to PHYS 1149 at Georgia Southern University taught by Anand Balaraman in Fall. Since its upload, it has received 49 views. For similar materials see /class/222053/phys-1149-georgia-southern-university in Physics 2 at Georgia Southern University.
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Date Created: 10/12/15
Chapter 7 Nuclear Energy Nuclear Energy Nuclear energy accounts for about 6 of the world s primary energy and supplies about 16 of its electrical energy Nuclear energy is one of only two technologically proven nonfossil energy sources capable of making a significant contribution to the world s energy supply today the other is hydropower The term quotatomic energy is unclear and should be avoided FIGURE 702 Coovriuht W W Norton amp Comnanv 2008 Energy Environment and Climate Nucleargenerating capacity GW N 0 Jgt 01 O J m Copyright WW Norton amp Company 2008 EneI QY Environment and Climate FIGURE 701 Nucleargenerated electricity percent 0 CF 71 The Atomic Nucleus Rutherford s gold foil experiment of 1909 Chadwick s discovery of neutron The atomic nucleus consists of protons and neutrons Like charges exert repulsive electrical forces on one another so how can the nucleus stay together omic structure FIGURE 703 Energy Environment and Climate Copyright w w Nuncn a Company 2008 71 The Atomic Nucleus The strong nuclear force holds the nucleus together Short range Acts kind of like a rubber band Much stronger than the electromagnetic force 71 The Atomic Nucleus The atomic number of an atom is defined as the number of protons in the nucleus which determines the chemical element The number of protons in the nucleus determines how electrons orbit in the atom Chemical reactions involve exchanges of electrons between atoms Hydrogen1 Helium2 Carbon6 Nitrogen7 Oxygen8 ron26 Uranium92 Periodic Table of Elements Perindic Table of the Elements I hydrogen l mar metal I alkali Halt El nnnmumli quot alkalina hmuuls I nebula 9am I Intuition menu 1 mm earth metals 71 The Atomic Nucleus Different isotopes of an element have different numbers of neutrons Some isotopes are more stable than others The weak nuclear force changes neutrons into protons and vice versa towards more stable isotopes FIGURE 794 72 Energy from the Nucleus Fusion vs Fission Nuclear fusion combining lighter nuclei into heavier ones Stars get their energy from fusion Nuclear fission the process of splitting a very massive nucleus into two medium weight nuclei Used in nuclear power plants FIGURE 705 Binding energy R7 26 e h 4 2 He Fission mu 92 Fusion 3 I 2 He i 2 H 1 l l l l l 3 50 100 150 200 250 Mass number I and Climat Energy Environme Copyright WW Norton amp Company 20 e 08 72 Energy from the Nucleus Binding energy is the energy released when a nucleus forms The binding energy curve peaks at the iron nucleus which has 26 protons FIGURE 705 Binding energy 72 Energy from the Nucleus Fusion Fission 238 92 l l 100 150 Mass number l l 200 250 I nd Climate Energy Environm Copyright WW Norton amp Company 20 08 Consider adding nucleons to a nucleus one at a time For very small nuclei with few nucleons binding energy isn t very large few neighbors As nuclei get larger the binding energy grows In even larger nuclei the binding energy per nucleon levels off short range nuclear force At a certain point the size of the iron nucleus the repulsive effect of the protons begins to tip the balance FIGURE 705 Binding energy Fusion l l l l l 50 100 150 200 250 Mass number I and Climat Energy Environme Copyright WW Norton amp Company 20 e 08 72 Energy from the Nucleus It is possible to extract nuclear energy by fission of elements heavier than iron or by fusion of elements lighter than iron Nuclear reactions release some 10 million times more energy than chemical reactions do History of Nuclear Fission 1896 Henry Bacquerel discovers radioactivity 1898 Curies discover Radium 1909 Rutherford gold foil experiment 1919 Rutherford performs first artificial nuclear disintegration using alpha particles from radioactive sources 1932 Chadwick discovers neutron 1932 CockcroftWalton generator transmuted Lithium to Helium by using artificially accelerated particles 1933 Leo Szilard proposed the possibility of nuclear chain reactions History of Nuclear Fission 1938 Otto Hahn and Fritz Strassmann publish artificial transmutation of Uranium to Barium 1939 Lise Meitner and Otto Frisch discover the nuclear fission process Szilard calculated that fission of Uranium released two or more neutrons on an average Fearing its use as a weapon keeps it a secret But lreneJoliot group publishes it EinsteinSzilard letter to President Roosevelt in August Nazi Germany invades Poland in September Manhattan Project 1942 1946 History of Nuclear Fission 1942 Enrico Fermi s team performs the first self sustaining artificial nuclear chain reactions at the University of Chicago July 16 1945 First test of nuclear weapons Aug 06 1945 quotLittle Boy was dropped in Hiroshima Uranium 235 bomb Aug 09 1945 quotFatmanquot was dropped in Nagasaki Plutonium 239 bomb 73 Nuclear Fission Fissile isotopes fission when struck by Iow f energy neutrons 0 a f Fissile Isotopes J U235 Natural Pu239 Got by fertilizing U238 73 Nuclear Fission Fission releases energy and typically two or Cl three neutrons Ci o o The neutrons cause i Q Cl additional fission in 8 ll Q 39 Q l nearby atoms resulting l ClD in a chain reaction l O l FIGURE 708 Energy Envi rrrr em and Climate Copyright WW Norton amp Company 2008 73 Nuclear Fission Controlled chain reaction is required for safe operation of nuclear plants Controlled Nuclear Fission Control Rods Controls the reaction rate by absorbing neutrons Control rods are made of materials that can absorb neutrons without undergoing fission SiverIridiumCadmium alloys Boron Hafnium Moderators Moderators slow down neutron enhancing their m interaction cross section In most cases it is also necessary to slow the neutrons down with a moderator so they re effective in inducing fission 74 Nuclear Reactors Nuclear power reactors come in many different designs Most common are light water reactors that use ordinary water as a moderator Whatever the reactor type nuclear reactors are used to boil water and drive a steam cycle as in fossilfueled power plants FlGUFlE 710 Steam or hot water out 0quot5339 l l l vl I l l Pressure vessel Uranium l fuel bundles l lt COId water in Energy Envi rrrr am and Climate Copyright WW Norton amp Company 2008 74 Nuclear Reactors Turbine Steam Generator 7 Condenser Q Jr k X J Water vapor and 39 waste heat out Pressure vessel Cooling tower Waste heat Energy Environment and Climate Copyright WW Norton amp Company 2008 75 Nuclear Radiation Nuclear reactions produce radiation 1000 consisting of high energy particles The halflife is the amount of time it 250 takes half the nuclei 125 in a radioactive 0 1 2 3 4 5 material to decay Timelha i39ivesl FlGUFlE7 15 500 Number of undecayed nuclei Energyv Envi rrrr ant and Climale Copyrighl WW Norton amp Company 2005 75 Nuclear Radiation Radioactivity is quantified by the number of decays per unit time and by the energy delivered and its effects on biological tissue Units of radioactivity 1 bequerel 1 decay per second 1 curie 37 billion decays per second 1 sievert unit of radiation dose adjusted for the biological impact of different types of radiation 76 Environmental and Health Impacts of Nuclear Radiation The dominant environmental impact of nuclear power is the health effects of radiation through mutations cancer or cell death The effects of high doses of radiation are well known but it s hard to quantify the effects of low doses against the background of mutations and cancers with other causes 76 Environmental and Health Impacts of Nuclear Radiation Radiation from nuclear power constitutes a tiny fraction of the radiation humans receive from natural and anthro pogenic sources Realistic estimates of nuclear energy s impact suggest that it is far lower than that of fossil fuels Consumer products Medical 3 procedures 15 Other lt1 Rocks and soils 8 FIGURE 714 Uranium Facts Uranium oxides were used to add yellow color to ceramic glasses by ancient cultures Discovered in 1789 by Heinrich Klaproth Natural Uranium U 238 99284 Fertile transmutes to Pl 239 U 235 0711 Naturally occurring fissile isotope U 234 00058 No commercial use Enriched Uranium Low enrichment Reactor grade U 235 35 High enrichment Weapons grade U 235 90 Uranium Mining Canada 23 Australia 21 Kazakhstan16 Russia 8 Niger8 Namibia7 Uzbekistan6 USA4 China2 76 Environmental and Health Impacts of Nuclear Radiation Worst commercial accident outside the US is the Chernobyl disaster in Ukraine that happened on April 26 1986 400 times more fallout than Hiroshima 56 direct death 4000 indirect deaths In the worst commercial nuclear accident to date in the United States three mile island neighbor exposure was about 10 microsieverts In contrast the average American is exposed to about 500 microsieverts each year through xrays and other radiationbased medical procedures 76 Environmental and Health Impacts of Nuclear Radiation However nuclear power has the potential for large scale accidents and is vulnerable to terrorism The technology and expertise that enable nuclear power programs can be used to produce nuclear weapons FFFFFFFF 17 Energy Environmen an Ima e Copyrighl o w w Noncn a Company 2008 77 The Nuclear Fuel Cycle and Uranium Reserves The nuclearfuel c cle ma storage y Nuclearreactor Uranium plumnium Reprocessing P39u mium Enrichment Enrichment 352 39 39 Fuel fabrication J I V quotBurningquot in a reactor E Waste storage or Mining Uglsggiguynd p n g FIGURE 715 77 The Nuclear Fuel Cycle and Uranium Reserves Nuclear waste includes isotopes with halflives as long as tens of thousands of years Isolation of these wastes from the environment is one of n U CI ea r 390 Owe r39s 7 E i 3 i zizzz ssmg thornier issues 1 10 10 s Years out of reactor Relative hazard 7 1O 1 7 Energy Environment and Climate Copyright WW Norton amp Company 2008 77 The Nuclear Fuel Cycle and Uranium Reserves Reprocessing removes fissile plutonium from spent nuclear fuel rods for use in new reactor 2 mi fuel However reprocessing g 1 is difficult and d a nge ro u s a n d it i E gg i i tiii39a makes plutonium a commercial substance Copyright WW Norton amp Company 2008 77 The Nuclear Fuel Cycle and Uranium Reserves Reprocessing especially when combined with breeder reactors which convert nonfissile 107 material into fissile could extend the life of Relative hazard Earth s uranium 1017 reserves to many ce u 10 3 Advance d reproc essmg 100 1O 102 103 104 105 106 Years out of reactor Energy Environment and Climate Copyright WW Norton amp Company 2008 78 Policy Issue Economics Politics and the Future of Nuclear Power Nuclear power has grown more slowly than anticipated because of safety and economic issues Nuclear share of world energy percent 0 Al l I l l l 1980 1990 2000 2010 2020 2030 Year FIGURE 719 E ironmem and Clin Energy nv Copyright W W Norton amp Company 2
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