BI 105A Environmental Biology Professor Jill Nissen Montgomery College Fall 2006 Chapter 12 Nuclear Energy Chemical Energy • Chemical energy is the energy stored in the bonds of molecules • Chemical reactions involve the forming and breaking of bonds between atoms, but • atoms of one element do not change to atoms of another element, nor does any of their mass change to energy Nuclear Energy • Nuclear energy is the energy released by nuclear fission or fusion • Nuclear reactions involve changes in the nuclei of atoms, and • small amounts of mass are converted to large amounts of energy: E = mc2 Nuclear Energy • Nuclear reactions produce 100,000 times more energy per atom than do chemical reactions such as combustion Nuclear Energy Comes From Fission Split atoms Neutrons Uranium-235 Splitting Atoms Releases Neutrons, Making Heat Heat Neutrons Heat Produces Steam, Generating Electricity Steam Generator Steam produced Turbine Electricity Heat Condenser Nuclear Power Plant Turbine and Generator Steam Spinning turbine blades and generator Boiling water Uranium-235 • Uranium ore consists of 3 isotopes: U-238, U-235, and U-234 • Uranium is naturally radioactive – the emission of energetic particles or rays from unstable atomic nuclei • Only U-235 is a fissionable material that can be used for nuclear power Uranium Ore Is Mined and Refined Enrichment Concentrates the U-235 Isotope Uranium Is Encased in Solid Ceramic Pellets Fuel Rods Filled With Pellets Are Grouped Into Fuel Assemblies Controlling the Chain Reaction Fuel Assemblies Control rods Withdraw control rods, Insert control rods, reaction increases reaction decreases Pressurized Water Reactor Steam Condenser U.S. Emission-Free Electricity (2003) 80% 70% 60% 50% 40% 30% 20% 10% 0% Nuclear Hydro Geothermal Wind Solar 71% 24% 1.2% 1.0% 0.1% Source: U.S. Energy Information Administration Nuclear Energy Limits Carbon Dioxide Emissions in Power Sector 3640 (2002) 3140 3,104 2640 29% Greater Million Metric Tons 2140 2,410 1640 1140 640 140 Electric Power Estimated Electric Power Industry CO2 Industry CO2 Emissions Source: EPA Emissions Without Nuclear Power Nuclear Energy Limits Sulfur Dioxide Emissions in Power Sector (2002) 14 13.5 12 33% Greater 10.1 10 Million Short Tons 8 6 4 2 0 Electric Power Industry Without Nuclear Power Sources: EPA, EIA SO2 Emissions International Programs • Finland and China are adding reactors to meet energy demand and enhance air quality • Germany and Sweden committed to phasing out nuclear power, then – Germany later launched a pilot program that includes allowances for nuclear plants – In 2002 Sweden removed the deadline for shut down • Canada approved tax incentives for nuclear capacity • France obtains 77% of its electricity from nuclear power U.S. Programs U.S. phasing out U.S. currently ~7% of energy nuclear; no new U.S. power plants ordered since 1976 40% of 105 commercial nuclear power expected to be retired by 2015 & all by 2030; What Happened? crippled by high & uncertain costs; frequent malfunctions (Three Mile Island, Chornobyl); false assurances and cover–ups; overproduction of energy in some areas; poor management; lack of public acceptance. Three Mile Island • What happened, step by step • http://www.pbs.org/ wgbh/amex/three/sf eature/index.html History’s Worst Nuclear Accident • April 26, 1986 - During a test at the Chornobyl plant, the No. 4 reactor exploded • April 27, 1986 – The secret was out! • 203 hospitalized, 31 died • Evacuation zone 30km over a month • Thyroid cancer among children increased • Still waiting for long-term effects History’s Worst Nuclear Accident • The sum of [Chornobyl] and exposures to people all over the world," writes Bernard Cohen, "will eventually, after about fifty years, reach 60 billion millirems, enough to cause about 16,000 deaths.“ He puts Chornobyl's danger in context by pointing out that 16,000 deaths are caused every year by air pollution from coal-burning power plants in the United States alone. Pros and Cons of Nuclear Energy Impact Coal Nuclear Land use 17,000 ac 1,900 ac Daily fuel 9,000 tons/day 3 kg/day requirement Moderate to Air pollution Low severe Radioactive 1 curie 28,000 curies emissions Risk from Long-term risk Short-term over large area catastrophic local risk accidents Radioactive Wastes • Low level radioactive wastes are items contaminated by radioactivity that give off small amounts of ionizing radiation • High level radioactive wastes are produced by nuclear power plants and give off large amounts of ionizing radiation – Dangerous levels of radioactivity require special handling and secure storage – Case-in-Point: Yucca Mountain – http://msnbc.msn.com/id/3042216/ Fuel for Nuclear Weapons • The Link Between Nuclear Energy and Nuclear Weapons Can be Spent fuel from reprocessed Fuel for conventional for . . . breeder reactor nuclear plant OR Nuclear weapons The Future of Nuclear Power • The safe disposal of radioactive wastes is one of the main difficulties to be overcome if nuclear energy is to realize its potential in the 21st centure Review Objectives Introduction to Nuclear Processes • Distinguish between nuclear energy and chemical energy. • Contrast fission and fusion. • Define radioactive decay. Nuclear Fission • Describe the nuclear fuel cycle, including the process of enrichment. • Define nuclear reactor and describe a typical nuclear power reactor. Pros and Cons of Nuclear Energy • Discuss the pros and cons of electric power produced by nuclear energy versus coal. Safety Issues in Nuclear Power Plants • Describe the nuclear power plant accidents at Three Mile Island and Chornobyl. • Discuss the link between nuclear energy and nuclear weapons. Radioactive Wastes • Distinguish between low-level and high-level radioactive wastes. • Relate the pros and cons of permanent storage of high-level radioactive wastes at Yucca Mountain The Future of Nuclear Power • Briefly summarize the issues that must be addressed if nuclear power is to become a major energy source in the future.
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