SECTION 2 Nuclear Energy - Weebly

SECTION 2Nuclear EnergyObjectives왘 Describe nuclear fission.왘 Describe how a nuclear powerplant works.왘 List three advantages and threedisadvantages of nuclear energy.Key Termsnuclear energynuclear fissionnuclear fusionwww.scilinks.orgTopic: Nuclear EnergySciLinks code: HE4075Figure 13 왘 Neutrons are releasedfrom the fission, or the splitting, of auranium atom’s nucleus. Some ofthese neutrons then cause otheratoms to undergo nuclear fission in aprocess called a chain reaction.In the 1950s and 1960s, nuclear power plants were seen as thepower source of the future because the fuel they use is clean andplentiful. It was predicted that a nationwide network of nuclearpower plants would provide electricity that was “too cheap tometer.” But in the 1970s and 1980s, almost 120 planned nuclearpower plants were canceled, and about 40 partially constructednuclear plants were abandoned. What happened? In this section,you’ll learn how nuclear power works and why about 17 percentof the world’s electricity comes from nuclear power today.Fission: Splitting AtomsNuclear power plants get their power from nuclear energy, theenergy within the nucleus of an atom. The forces that holdtogether the nucleus of an atom are more than 1 million timesstronger than the chemical bonds between atoms. In nuclearpower plants, atoms of the element uranium are used as the fuel.The nuclei of uranium atoms are bombarded with atomic particles called neutrons. These collisions cause the nuclei to split ina process called nuclear fission. A fission reaction is shown inFigure 13. Nuclear fission releases a tremendous amount ofenergy and more neutrons, which in turn collide with more uranium nuclei. If a fission reaction is allowed to continue, this chainreaction will escalate quickly. One example of an uncontrolledfission reaction is the explosion of an atomic bomb. In contrast,nuclear power stations are designed so that the chain reactionproduces a controllable level of energy.444 Chapter 17 Nonrenewable EnergyCopyright by Holt, Rinehart and Winston. All rights reserved.

How Nuclear Energy WorksA nuclear reactor is surrounded by a thick pressurevessel that is filled with a cooling fluid. The pressure vessel is designed to contain the fission products in case of an accident. Thick concrete wallsalso surround reactors as shown in Figure 14.Inside a reactor, shown in Figure 15, metal fuelrods that contain solid uranium pellets are bombarded with neutrons. The chain reaction thatresults releases energy and produces more neutrons.The reactor core contains control rods, which aremade of a material such as boron or cadmium thatabsorbs the neutrons to prevent an uncontrolledchain reaction. When the control rods are loweredbetween the fuel rods, they slow the fission reactions. If the control rods are lowered completely,they prevent fission and shut down the reactor.The heat released during nuclear reactions is used to generateelectricity in the same way that power plants burn fossil fuels togenerate electricity. In a nuclear power plant, energy releasedfrom the fission reactions heats a closed loop of water that heatsanother body of water. As the water boils, it produces steam thatdrives a steam turbine, which is used to generate electricity.Figure 14 왘 Every year, the DiabloCanyon nuclear plant generatesenough energy for 2 millionCalifornian households—the energyequivalent of burning 20 millionbarrels of oil.Figure 15 왘 How a Typical Nuclear Power Plant WorksCopyright by Holt, Rinehart and Winston. All rights reserved.Section 2 Nuclear Energy 445

The Advantages of Nuclear EnergyNuclear energy has many advantages. Nuclear fuel is a very concentrated energy source, as shown in Figure 16. Furthermore,nuclear power plants do not produce air-polluting gases. Whenoperated properly, nuclear plants release less radioactivity thancoal-fired power plants do. Many countries with limited fossilfuel reserves rely heavily on nuclear plants to supply electricity.France, for example, generates about three-fourths of its electricity from nuclear power. France produces less than one-fifth of theair pollutants per person than does the United States, which relieson fossil fuels for almost 70 percent of its electricity needs.Why Aren’t We Using More Nuclear Energy?Building and maintaining a safe reactor is very expensive. As aresult, nuclear power is no longer competitive with other energysources in many countries. The last 20 nuclear reactors built inthe United States cost more than 3,000 per kilowatt of electricalcapacity. In contrast, wind power is being installed at less than 1,000 per kilowatt, and newer natural gas power plants can costless than 600 per kilowatt. However, the actual cost of newnuclear power plants is uncertain, so it is difficult to predictwhether investors will build new plants in the United States.Figure 16 왘 Uranium is a very com-pact fuel. The uranium pellets (above)can generate as much electricity asthe trainload full of coal does.GeofactRadon Uranium occurs naturallyin rock and soil. When uraniumundergoes radioactive decay, itgives off a number of products,including an invisible and odorlessradioactive gas called radon. Radoncan seep into buildings from thesurrounding rock and soil, and ifbuildings are not ventilated properly, dangerous levels of radon canbuild up. It is estimated that radoncauses 5,000 to 20,000 people inthe United States to die from lungcancer each year.Storing Waste The difficulty of finding a safe place to storenuclear wastes is one of the greatest disadvantages of nuclearpower. The fuel cycle of uranium produces fission products thatcan remain dangerously radioactive for thousands of years.Uranium mining and fuel development produce radioactive waste.In addition, the used fuel, liquids, and equipment from a reactorcore are also considered hazardous wastes. Storage sites fornuclear wastes must be located in areas that are geologically stable for tens of thousands of years. The United States has spentover two decades studying a site called Yucca Mountain in southern Nevada as a place to store nuclear waste. Scientists are alsoresearching a process called transmutation, that would recycle theradioactive elements in nuclear fuel.Safety Concerns In a poorly designed nuclear plant, the fissionprocess can potentially get out of control. This is what happenedduring the world’s worst nuclear reactor accident, which occurredat Chernobyl in the Ukraine in 1986. Engineers turned off mostof the reactor’s safety devices to conduct an unauthorized test.This test caused explosions that destroyed the reactor and blastedtons of radioactive materials into the air. Hundreds of firefighters,residents, and workers died from radiation exposure. Areas ofnorthern Europe and the Ukraine are still contaminated from thedisaster. The Chernobyl reactor was an old design that, for safetyreasons, is not used in the United States. The nuclear reactor hadno containment building. In addition, the engineers at Chernobylviolated basic safety guidelines.446 Chapter 17 Nonrenewable EnergyCopyright by Holt, Rinehart and Winston. All rights reserved.

In the United States, the most serious nuclear accidentoccurred in 1979 at the Three Mile Island nuclear power plantin Pennsylvania. Human error, along with blocked valves andbroken pumps, was responsible for the accident at Three MileIsland. Fortunately, only a small amount of radioactive gasescaped. Since this accident, the U.S. Nuclear RegulatoryCommission has required more than 300 safety improvementsto nuclear power plants.The Future of Nuclear PowerOne possible future energy source is nuclear fusion. Nuclear fusionoccurs when lightweight atomic nuclei combine to form a heaviernucleus and release tremendous amounts of energy. Figure 17 illustrates the process of nuclear fusion. Nuclear fusion is the processthat powers the stars, including our sun. It is potentially a saferenergy source than nuclear fission is because it creates less dangerous radioactive byproducts.Unfortunately, although the potential of fusion is great, so is thetechnical difficulty of achieving that potential. For fusion to occur,atomic nuclei must be heated to extremely high temperatures (about100,000,000ºC, or 180,000,000ºF). The nuclei also must be maintained at very high concentrations and properly confined. Achievingall three of these conditions simultaneously is extremely difficult.The technical problems are so complex that building a nuclearfusion plant may take decades or may never happen.Connection toHistoryThree Mile Island The ThreeMile Island accident was a wakeup call for the nuclear industry.Many reforms and safety measures were instituted throughoutthe industry after the accidentoccurred. In 1989, 10 years afterthe accident, the nuclear plantreceived the best INPO rating inthe world. The rating was basedon a measure of reliability, efficiency, and safety. In 1999, theplant set a world record after running continuously for 688 days.Figure 17 왘 During nuclear fusion,the nuclei of two forms of hydrogen(deuterium and tritium in this case)join to form helium, which releaseslarge amounts of energy.SECTION 2Review1. Compare a power plant that burns fossil fuels with anuclear power plant.2. Describe two advantages and two disadvantages ofnuclear power plants.3. Explain the difference between nuclear fission andnuclear fusion.Copyright by Holt, Rinehart and Winston. All rights reserved.CRITICAL THINKING4. Applying Ideas Read about the advantages ofnuclear energy. Explain why countries such as Franceand Japan rely heavily on nuclear power.READING SKILLS5. Making Decisions Which poses more of an environmental threat: transporting spent nuclear fuel ortransporting toxic chemicals? Write your opinion inthe form of a short essay. WRITING SKILLSSection 2 Nuclear Energy 447

CHAPTER171 Energy Resources andFossil Fuels2 Nuclear Energy448 Chapter 17 HighlightsHighlightsKey TermsMain Ideasfossil fuels, 435electric generator,436petroleum, 440oil reserves, 442왘 Most of the world’s energy needs are met byfossil fuels, which are nonrenewable resources.왘 Coal is abundant in North America andAsia. In the United States, coal is used primarily to produce electricity.왘 Petroleum can be refined into fuels to powervehicles and machines. Petroleum can also beused to manufacture many other products.왘 Natural gas is often found above oil deposits.In general, burning natural gas releases fewerpollutants than burning coal or oil.왘 The extraction, transportation, and use offossil fuels cause many environmental problems, including air and water pollution andhabitat destruction.왘 Calculations of fossil-fuel reserves predictthat oil production will peak and then declinein the early 21st century.nuclear energy, 444nuclear fission, 444nuclear fusion, 447Nuclear energy is energy that exists withinthe nucleus of an atom. When uranium nucleiare bombarded with neutrons, they undergofission and release large amounts of energy.왘 In a nuclear power station, the heat generated by fission is used to heat water to formsteam. The steam drives turbines that generateelectricity.왘 The main advantages of nuclear power arethat the fuel is compact and the power stationsgenerally do not pollute. The main disadvantage is that nuclear power produces radioactivewaste, which will be dangerous for centuries.왘Copyright by Holt, Rinehart and Winston. All rights reserved.