Bài giảng Environmental Sciences - Chapter 13: Nuclear Power: Promise and Problems

Chapter 13: Nuclear Power: NuclearNumber of power plants today: 439 worldwideNuclear power generates about 15% of the world’s electricity (about 10% of U.S.)Pros: No CO2 emissions, no particulate emissionsCons: Radiation can lead to damaged DNA, costs, radioactive waste, thermal pollutionDefinitionsFusion- the combination of 2 atoms to form a larger atomFission- splitting an atomRadioisotope - unstable radioactive isotopeNuclear Regulatory Commission is the US governmental Agency that regulates nuclear power plants UraniumUranium 235 has 92 protons and 143 neutrons. When U235 is hit by a neutron, it is split into two smaller elements (such as Kr and Ba) plus three neutrons which sustain the chain reaction.There are three different isotopes of uranium. U234: half life = 244 thousand years, 0.0055% of all uranium.U235: half life = 704 million years, 0.72% of all uranium.U238: half life = 4.5 billion years, 99.28% of all uranium.Enrichment means to separate the U235 from U238U235 must be enriched to 4% of the total Uranium in order to be used as a fuel. (very expensive)How does it work?The fission of uranium’s nucleus gives off heat that can be used to boil water and turn a turbogenerator to create electricity.Naturally occurring Uranium is mined and enriched into a fuel. Plutonium can also be used as a fuel, but it is very dangerous.Chain ReactionU235 has the ability to create a sustaining chain reaction which results in heat. Control Rods soak up the extra neutrons to control the reactionWater moderator: slows down neutrons so they can travel @ a speed to trigger another fission reactionNeutron-absorbing material- control rodFuel Rods- approximately one-third replaced each year (results in nuclear waste)Heat transfer systemCooling systemRedundant safety systemsHow does a Power Plant Operate?Waste DisposalCurrently all fuel rods are still in cooling ponds at commercial nuclear facilitiesProposed site for disposal - Yucca Mountain in SE Nevada. Should open in 2017, pending licenseConcerns: Geological active area, Intrusion of water table, distances for wastes travel, radioactive decay and half-livesHalf Life CalculationsEvery radioactive element has a unique half life. This is the amount of time it will take for half of the radiation to decay.100μCi 50μCi 25μCi in two half lives if the half life is 10 years then it will take 20 years.How long will it take 1000μCi to decay to 125μCi if the half life is 20 years?60 years b/c 1000 500 250 125AccidentsChernobyl: 4/26/86 Ukraine, complete meltdown. Motorcycle Girl Blog Large areas of the Ukrainian, Belorussian, and Russian republics of the USSR were contaminated.Resulting in evacuation and resettlement of 200,000 people. Controversy over # of deaths (2 people died during explosion 31 died from radiation poisoning) The incidence of thyroid cancer increased among children in the areas where radiation levels were the highest. Accidents cont’dThree Mile Island: 3/28/79 Pennsylvania (Harrisburg) – partial meltdown, no one known to be hurt.Local Facilities: Diablo Canyon and San Onofre