536 Lesson 4

In the debate over energy, nuclear power occupies an odd position. It doesn’t pollute the air, so some people think it is an environmentally friendly alternative to fossil fuels. Yet nuclear power’s great promise has been clouded. People worry about radioactive waste disposal and nuclear power plant accidents. Concerns for public safety have limited the devel-opment of this energy source.

Of all nations, the United States generates the most electricity from nuclear power. However, only 20 percent of United States electricity comes from nuclear power. A number of other nations rely more heavily on nuclear power. France leads the list, receiving 78 percent of its energy from nuclear power.

Nuclear PowerLE

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FIGURe 19 Light Up the night The Eiffel Tower in Paris is illuminated with nuclear power.

• Relate nuclear fission to the production of energy.• Describe how a nuclear power plant generates

electricity.• Identify the advantages and disadvantages of

nuclear power.• Contrast nuclear fusion with nuclear fission, and

explain the issues related to nuclear fusion.

Reading Strategy As you read about the process of generating electricity with nuclear power, construct a flowchart to show what happens in a nuclear power plant. Use the flowchart to help answer Question 2 at the end of the lesson.

Vocabulary nuclear energy, nuclear fission, nuclear reactor, meltdown, nuclear waste, nuclear fusion

Guiding Question: What are the advantages and disadvantages of nuclear energy?

FOCUS Have students make a two-column table that lists advan-tages and disadvantages of nuclear energy. Then, have students form small groups to discuss their tables. Encourage students to add informa-tion gained from the group discus-sion to their tables.

GUIDING QUESTION

17.4 LESSON PLAN PREVIEWInquiry Students make a model of nuclear fission.Differentiated Instruction Struggling students use Figure 21 to help them learn how a power plant generates electricity.Real World Students present their opinions about a pro-posed nuclear power plant in a mock town-hall format.

17.4 RESOuRcES Lesson 17.4 Worksheets • Lesson 17.4 Assessment • Chapter 17 Overview Presentation

Energy

Uranium-235nucleus

Krypton-92nucleus

Barium-141nucleus

Neutron

Neutron

Neutron

Neutron

A neutron “bullet”strikes a U-235 nucleus.

The nucleus splits into two smaller nuclei, releasing more neutrons and a great deal of energy.

Each neutron can start a new reaction by strikinganother U-235 nucleus.

Nonrenewable Energy 537

Nuclear Energy The process of nuclear fission releases energy.

Matter is made up of tiny particles called atoms. The center of an atom is called the nucleus. The nucleus is composed of tiny particles called pro-tons and neutrons. Nuclear energy is the energy that holds these particles together in the nucleus. We use this energy by converting it to thermal energy, which can then be used to generate electricity.

The reaction that drives the release of nuclear energy in power plants is nuclear fission. Nuclear fission is the splitting of an atom’s nucleus into two smaller nuclei.

Bombardment by Neutrons To produce nuclear fission, the nuclei of large, unstable atoms, such as uranium or plutonium, are bombarded with neutrons. When a neutron smashes into the large atom’s nucleus, the large nucleus breaks apart into smaller nuclei. The breakup of the large nucleus releases energy in the form of heat and radiation. In addition, as it breaks up, the large nucleus emits neutrons. Figure 20 shows a nuclear fission reaction. An atom of one form of uranium called uranium-235 (U-235) is broken apart. The smaller nuclei produced by this reaction are nuclei of krypton and barium.

Nuclear Chain Reaction The neutrons emitted from the broken-apart nucleus can then go on to split other atomic nuclei. In Figure 20, for example, the three neutrons can go on to split other U-235 nuclei that are nearby. Each time a nucleus is split, the process releases more energy and more neutrons. If there are enough uranium atoms nearby, the repeated release of neutrons can cause a chain reaction.With each step in the chain, the amount of energy increases. If a chain reaction is not controlled, a huge explosion happens. The explosion of a nuclear bomb is the result of an uncontrolled fission chain reaction.

FIGURE 20 Nuclear Fission In the process of nuclear fission, the nucleus of a large atom splits into the nuclei of smaller atoms. The reaction releases a great deal of energy.

Coolingtower

Generator

CoolingloopCondenser

Turbine

Coolingtower

Water

Primaryloop

Secondaryloop

Reactorvessel

Controlrod

Steamgenerator

Nuclear fuel(uranium)

Containment building

2 The heat changes water into steam.

3 The steam turns a turbine that generates electricity.

4 Water from the cooling tower cools steam in the condenser, changing the steam to liquid water. The water returns to the reactor.

1 In the reactor vessel, uranium undergoes nuclear �ssion, producing heat.

Steam

538 Lesson 4

Generating Electricity In a nuclear power plant, nuclear fission is used to generate

electricity.

A nuclear power plant contains a nuclear reactor, which generates electricity by controlled fission reactions. Uranium-235 is used as fuel. Because the supply of U-235 is limited, nuclear power is a nonrenewable energy resource. Figure 21 shows how a nuclear reactor works.

21 3 4 65 7 8 9 Nuclear Fission Takes Place The reactor contains fuel rods, which are made of U-235. Neutrons released by U-235 begin fission reactions. The fission reactions generate heat, which is transferred to the water that surrounds the rods. The water is kept under pressure, so it cannot boil.

If the reactions produce too much heat, control rods are inserted between the fuel rods. The control rods absorb neutrons and therefore slow down the chain reaction.

21 3 4 65 7 8 9 Steam Is Produced The super-heated water passes through a pipe (primary loop) into the steam generator. In the steam generator, heat from the pipe boils the surrounding liquid water, changing it to steam. The steam flows through the secondary-loop pipe to the turbine.

21 3 4 65 7 8 9 Electricity Is Generated The steam makes the turbine rotate. The rotating turbine makes the generator move, producing electricity.

21 3 4 65 7 8 9 Water Is Cooled From the turbine, steam flows into the condenser, where it is cooled by water from the cooling tower. The cooling changes the steam to liquid water. This water is piped back into the reactor.

FIGURE 21 Nuclear Power Plant A nuclear power plant uses fission reactions to produce the energy necessary for generating electricity.

Nonrenewable Energy 539

Benefits and Costs of Nuclear Power Nuclear power does not create air pollution, but its problems

include risk of accidents and disposal of wastes.

When nuclear power was first developed and used in the 1950s, many people thought it would be a safe, nonpolluting source of energy. But today, people are concerned about the possibility of accidents in nuclear power plants. In addition, there is no really good way of disposing of leftover nuclear material.

Benefits of Nuclear Power Nuclear power plants generate electric-ity without producing air pollution. In contrast, the combustion of fossil fuels releases pollutants such as carbon dioxide, nitrous oxides, sulfur dioxide, and particulate matter. Scientists from the International Atomic Energy Agency (IAEA) estimate that nuclear power reduces carbon emis-sions worldwide each year by 600 million metric tons. That amount is equal to 8 percent of worldwide greenhouse gas emissions.

Small amounts of uranium can produce far more energy than the same amount of coal. Therefore, to produce the same amount of energy, less uranium than coal needs to be mined. Under normal conditions, nuclear power plants are safer for workers than coal-fired plants are.

ReadingCheckpoint

Identify three benefits of nuclear power.

Costs of Nuclear Power Nuclear power also has its costs. For example, nuclear power plants are very expensive to build and maintain. In addition, people fear the possibil-ity of nuclear accidents. Another problem is the disposal of the waste materials left over after nuclear energy has been produced.

▶ Accidents at Power Plants In 1986, there was an accident at the Chernobyl plant in the Ukraine, which was then a part of the Soviet Union. Human mistakes, combined with unsafe reactor design, led to the disaster.

First, workers turned off safety systems to run tests. Then the fuel rods produced so much heat that they melted, a condition known as a meltdown. Part of the power plant exploded, and clouds of dust rose into the air. The dust included material that was radioactive, meaning that it gave off radiation that could harm humans and other living things. The accident killed 31 people directly. Thousands of other people developed cancer and other illnesses caused by radia-tion. Winds carried radioactive material far from Chernobyl.

Luckily, there has not been another nuclear accident as bad as Chernobyl. Moreover, the design of most reactors in the United States is far safer than that of Chernobyl’s. However, there have been several smaller accidents since Chernobyl, and the possibility of future accidents concerns many people.

FIGURE 22 Chernobyl The explosion at the Chernobyl nuclear power plant in 1986 destroyed much of the facility and contaminated the air with radioactive material.

ANSWERS

Reading Checkpoint Nuclear power does not result in air pollution; ura-nium produces more energy than the same amount of coal; and nuclear power plants are normally safer than coal-fired plants.

What Doyou think?

What Doyou think?

Data from Office of Civilian Radioactive Waste Management, U.S. Department of Energy; and Nuclear Energy Institute, Washington, D.C.

WA

OR

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CO

NM

TX

OK

KS

AZ

CA

HIAK

IDWY

MT NDMN

WI

IA

MO

AR

LA

MS AL GASC

NC

VAWV

OH

PA

MDDE

MANY

VTNH

ME

INKY

TN

IL

FL

MISDSD

NE NJ

RICT

More than 1000

Metric tons of spent fuel

101–1000

1–100

0

540 Lesson 4

▶ Temporary Storage of Nuclear Waste Nuclear power plants produce nuclear waste, which is radioactive material left over from the produc-tion of energy and other processes. This material will continue to release radiation for thousands of years. Currently, nuclear waste from power generation is being held at nuclear power plants all over the world. Used fuel rods are sunk in deep pools of cooling water to prevent radiation from leaking out. This storage, however, is only a temporary solution.

▶ Long-Term Disposal The United States government is trying to solve the problem of nuclear waste. When wastes are stored at many loca-tions throughout the nation, each of those places is a potential nuclear hazard. Therefore, it would be better to keep all the waste in one safe site. After extensive study by scientists and policy makers, in the 1980s Congress chose a possible location for disposing the nuclear waste—Yucca Mountain, a remote place in the Nevada desert. Yucca Mountain was chosen for many reasons—its location is far from where people live, and it can be protected from sabotage. Also, there is little rainfall or risk of earthquakes. Because the water table is very deep, water is unlikely to become contaminated with radioactivity.

However, some scientists and people who live in Nevada protested that Yucca Mountain isn’t a good place to store hazardous waste. They argued that the site isn’t as geologically stable as has been claimed. They were concerned that earthquakes and volcanoes could open underground cracks, and that waste could leak from the cracks. In 2010, the federal government ended its support for the Yucca Mountain project. Without Yucca Mountain, the United States has no central place for disposing of radioactive waste from nuclear power plants. Therefore, for now, the nuclear waste will remain stored at numerous locations across the nation.

You are on a committee to find a location for a new school. One site is located next to a nuclear power plant. The other is located next to a coal-fired power plant. Which location would you choose? What would concern you most about each choice?

FIGURE 23 Nuclear Waste Sites The dots on the map show where radioactive wastes are stored in the United States. (Note that some of the sites store radioactive wastes that are not spent nuclear fuel.)

Can we depend on nonrenewable energy resources for our energy needs?Application Ask students to state whether or not the information they have learned about nuclear energy has changed their opinion of whether or not we can depend on nonrenewable energy resources for our energy needs. Have students write several sentences summarizing why their opinion has changed, or why it has not changed.

BIG QUESTION

ANSWERS

What Do You Think? Answers will vary but should show knowledge of the relative safety of coal-fired and nuclear power plants.

Hydrogen-3nucleus

Tremendous heat and pressure force two kinds of hydrogen nuclei together.

The reaction creates a huge amount of energy.

Hydrogen-2nucleus

Heliumnucleus

Neutronplus energy

Nonrenewable Energy 541

1. Apply Concepts What is a nuclear chain reaction?2. Sequence List the steps involved in using nuclear

fission to generate electricity. Begin with the role of the fuel rods.

3. Infer Why is the disposal of nuclear waste a greater problem than the disposal of the trash that you and your family need to get rid of?

4. Compare and Contrast Compare and contrast nuclear fusion and nuclear fission. How are they similar? How are they different?

5. Explore the BIGQUESTION Which do you think has more advantages: electricity generated by nuclear power or electricity generated by coal? Support your opinion with specific details.

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Nuclear Fusion: The Future? Nuclear fusion has advantages over fission, but the technology

does not yet exist to use fusion to generate power.

Nuclear fusion reactions generate the energy released by the sun. In nuclear fission, an atomic nucleus is split apart. The opposite happens in nuclear fusion—small nuclei of lightweight elements are forced together to form a heavier nucleus. Figure 24 shows a fusion reaction in which two hydrogen atoms with different numbers of neutrons are fused together to form helium. This fusion reaction releases a neutron and huge amounts of energy.

Nuclear fusion could produce much more energy per amount of fuel than nuclear fission can. However, fusion reactions require a temperature of many millions of degrees Celsius. This extremely high temperature and other requirements have made it impossible to use fusion to gener-ate electric power. Despite much research, fusion reactions in the lab still require more energy than they produce.

Fusion’s possible payoffs, however, make scientists keep trying. Theoretically, in a controlled fusion reactor, water could serve as a fuel to produce vast amounts of energy. The process would create only small amounts of radioactive waste. It would not pollute the air. However, power from nuclear fusion is probably a long way off.

FIGURE 24 Nuclear Fusion In nuclear fusion, two hydrogen nuclei are forced together. This reaction, which releases energy and a neutron, forms a nucleus of helium.

ANSWERS

Lesson 4 Assessment For answers to the Lesson 4 Assessment, see page A–28 at the back of the book.