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Environmental ScienceA Study of Interrelationships

Tenth EditionTenth Edition

Enger • Smith

Chapter 11

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Nuclear Energy: Benefits and RisksChapter 11

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Outline:

• Nature of Nuclear Energy• History of Nuclear Energy Development• Nuclear Fission Reactors• Investigating Nuclear Alternatives• Nuclear Fuel Cycle• Nuclear Material and Weapons Production• Nuclear Power Concerns• Politics of Nuclear Power

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The Nature of Nuclear Energy

• Radioactive - Nuclei of certain atoms are unstable and spontaneously decompose.– Neutrons, electrons, protons, and other

larger particles are released, along with energy.

Radioactive Half-Life - Time it takes for half the radioactive material to spontaneously decompose.

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Radiation

• Types:– Alpha - Moving particles composed of

two neutrons and two protons.Stopped by layer of skin.

– Beta - Consists of electrons from nucleus.Stopped by layer of clothing.

– Gamma - Form of electromagnetic radiation.

Can pass through several centimeters of concrete.

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Radiation

• If the radiation reaches living tissue, equivalent doses of beta and gamma radiation can cause equal amounts of biological damage.– Alpha particles are more massive, thus

can cause more damage to biological tissues.

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The Nature of Nuclear Energy

• Nuclear Fission - Occurs when neutrons impact and split the nuclei of certain atoms.– Nuclear Chain Reaction - Splitting nuclei

release neutrons, which themselves strike more nuclei, in turn releasing even more neutrons.

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Nuclear Fission Chain Reaction

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The Nature of Nuclear Energy

• Only certain kinds of atoms are suitable for development of a nuclear chain reaction.– The two most common are uranium-235

and Plutonium-239.Requires certain quantity of nuclear fuel

(critical mass).

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History of Nuclear Energy Development

• First controlled fission - Germany 1938.• 1945 - U.S. dropped atomic bombs on

Hiroshima and Nagasaki.• Following WW II, people began exploring

other potential uses of nuclear energy.• U.S. built world’s first nuclear power plant in

1951.

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Dwight D. Eisenhower

• “Atoms for Peace” 1953:– “Nuclear reactors will produce electricity so

cheaply that it will not be necessary to meter it.”

• Today’s Reality:– Accidents have caused worldwide concern.– Most new projects have been stopped.

Many experts predict rebirth.

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Nuclear Fission Reactors

• Nuclear Reactor - Device that permits a controlled fission chain reaction.– Nucleus of U-235 atom struck by slowly

moving neutron from another atom.Nucleus split into smaller particles.

More neutrons released. Strike more atoms.

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Nuclear Fission Reactors

• Control Rods - Made of a non-fissionable material (boron, graphite) that are lowered into reactor to absorb neutrons.– Withdrawn to increase rate of fission.

• Moderator - A substance that absorbs energy, slowing neutrons, enabling them to split the nuclei of other atoms more efficiently.

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Workings of A Nuclear Reactor

• Nuclear reactor serves same function as fossil-fuel boiler: produces heat - converts water to steam - turns a turbine - generating electricity.– Light Water Reactors

90% of current reactors Boiling Water Reactors (BWR) Pressurized Water Reactors (PWR)

– Heavy Water Reactors– Gas Cooled Reactors

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Boiling Water Reactor

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Pressurized-Water Reactor

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Advanced Gas-Cooled Reactor

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Plans for New Reactors Worldwide

• Currently 439 nuclear power reactors in 31 countries.– Combined capacity of 354 gigawatts.– Provide 16% of world’s electricity.

• Currently 32 reactors under construction in 10 countries.– Forecasting becomes uncertain after

2005.Most planned reactors in Asia and parts

of former Soviet Union.

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Plant Life Extension

• Most nuclear power plants originally had normal design lifetime up to 40 years.– Engineering assessments have

established many plants can operate much longer.

Economic, regulatory, and political considerations have thus far led to premature closure of some plants.

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Nuclear Power Plants in North America

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Investigating Nuclear Alternatives

• Breeder Reactors - Nuclear fission reactor that forms a new supply of radioactive isotopes during operation. (i.e., U238 turns into Pu239) – Liquid Metal Fast-Breeder (LMFBR)

Because Pu is very hazardous to humans, and can be made into nuclear bombs, development has slowed significantly in most regions of the world.

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Formation of Pu-239 in a Breeder Reactor

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Nuclear Fusion

• Nuclear Fusion - When two lightweight atomic nuclei combine to form a heavier nucleus, a large amount of energy is released. – i.e., Sun.– Huge potential for energy, but technical

difficulties of attaining necessary conditions make this an unlikely fuel candidate for the immediate future.

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Nuclear Fusion

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Nuclear Fuel Cycle

• Mining of low-grade Uranium ore.• Naturally occurring Uranium contains about

99.3% U238, and .7% U235.– Much be enriched to 3% U235 to produce

weapons-grade material.Material is fabricated into a powder and

then into pellets. Pellets are sealed into metal rods

and lowered into the reactor (Fuel Rods).

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Nuclear Fuel Cycle

• As fission occurs, U235 concentration decreases.– After about three years of operation, fuel

rods don’t have enough radioactive material remaining to sustain a chain reaction, thus spent fuel rods are replaced by new ones.

Major source of radioactive waste as each step involves transport of radioactive materials.

High-Level Nuclear Waste

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Nuclear Fuel Cycle

• Initially, scientists proposed spent fuel rods could be reprocessed and used to manufacture new fuel rods.– Would reduce amount of nuclear waste.

Extremely dangerous and expensive. At present, India, Japan, Russia,

France and the United Kingdom operate reprocessing plants as an alternative to storing rods as waste.

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Nuclear Fuel Cycle

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Nuclear Material and Weapons Production

• Nuclear power industry is an outgrowth of weapons industry.– U.S. Department of Energy (DOE) is

responsible for nuclear research for both weapons and peaceful uses.

Research and production have typically dealt with hazardous chemicals and low-level radioactive materials in the same manner as other waste; dumping in ground or water.

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Nuclear Material and Weapons Production

• DOE (Formerly Atomic Energy Commission) has become steward of:– 3,700 contaminated sites.– One million 55-gallon drums of waste. – More than 330 underground storage tanks

with high-level radioactive waste.– 5,700 sites with wastes moving in soil.– Millions of cubic meters of low-level and

high-level radioactive wastes.

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Nuclear Material and Weapons Production

• Clean-up will take years and cost tens of billions of dollars.– Local residents and host states are not

completely trustful.– Clean-up is new mission for DOE.– Additional problem of disposing of

dismantled nuclear weapons.

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Nuclear Power Concerns

• Currently, 17% of electricity consumed worldwide comes from nuclear power.– Accidents raised questions about safety.– Contamination and disposal problems.– Plants may be terrorism targets.

Spent fuel storage facilities. More total radioactivity than the

reactor. Still not easy, or prime target.

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Reactor Safety

• Three Mile Island - Pennsylvania– March 28, 1979 - Partial Core Melt-Down.

Pump and valve malfunction. Operator error compounded problem.

Crippled reactor was de-fueled in 1990 at a cost of about $1 billion.

Placed in monitored storage until its companion reactor reaches the end of its useful life.

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Reactor Safety

• Chernobyl - Ukraine– April 26, 1986– Experiments being conducted on reactor.

Multiple serious safety violations.– Reactor Explodes.

31 deaths. 116,000 people evacuated.

24,000 evacuees received high doses of radiation.

Increased thyroid cancer in children.

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Reactor Safety

• A consequence of both of the accidents has been a deepened public concern over nuclear reactor safety.– Since 1980, 10 countries have cancelled

nuclear plant orders or mothballed plants under construction.

Increased Public Opposition: United Kingdom: 65% - 83% Germany: 46% - 83% United States: 67% - 78%

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Exposure to Radiation

• Type and degree of damage vary with radiation form, dosage and duration of exposure, and type of cells irradiated.– Because mutations are permanent,

radiation effects may build up over years and only appear later in life.

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Exposure to Radiation

• Human exposure usually expressed in rems.– Measure of biological damage to tissue.

The higher the dose, the more observable the results.

No human is subject to zero exposure. Average person exposed to 0.2 to

0.3 rems per year from natural and medical sources.

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Thermal Pollution

• Addition of waste heat to the environment.– Especially dangerous in aquatic systems.

In a nuclear power plant, 1/3 of heat used to generate electricity while the other 2/3 is waste.

Fossil fuel plants are 50:50.To reduce the effects of waste heat,

utilities build cooling facilities. Ponds Towers

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Decommissioning Costs

• Life expectancy of most electrical generating plants is 30-40 years.– Unlike other plants, nuclear plants are

decommissioned, not demolished.Involves removing the fuel, cleaning

surfaces, and permanently barring access.

Over 70 nuclear power plants in the world are awaiting decommissioning.

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Decommissioning Costs

• By 2005, 68/104 U.S. plants will be at least 20 years old.– Nuclear Regulatory Commission may

extend authorization an additional 20 yrs.

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Decommissioning Uncertainties

• Utilities Have (3) Options:– Decontaminate and Dismantle plant ASAP.– Shut Down plant for 20-100 years, allowing

radiation to dissipate, then dismantle.– Entomb plant within concrete barrier.

Recent experience indicates decommissioning a large plant will cost between $200 and $400 million.

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Radioactive Waste Disposal

• Today, the U.S. has 380,000 cubic meters of highly radioactive military waste temporarily stored at several sites.– Waste Isolation Pilot Plant (WIPP)

Carlsbad, NM began accepting waste in March, 1999.

Transuranic wastes - High-level radioactive waste consisting primarily of various isotopes of plutonium.

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DOE Radioactive Transuranic Waste Sites

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Radioactive Waste Disposal

• In addition to high-level waste from weapons programs, 2 million cubic meters of low-level radioactive military and commercial waste are buried at various sites.– About 30,000 metric tons of highly

radioactive spent fuel rods are stored in special storage ponds at nuclear reactor sites.

Many plants are running out of storage.

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Radioactive Waste Disposal

• High Level Radioactive Waste:– At this time, no country has a permanent

storage solution for the disposal of high-level radioactive waste.

Politics of disposal are as crucial as disposal method.

Most experts feel the best solution is to bury waste in a stable geologic formation.

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High-Level Waste Storage in the United States

• In 1982, Congress called for a high-level radioactive disposal site to be selected by March 1987, and to be completed by 1998.– In 2002, the Secretary of Energy

indicated the choice of a site at Yucca Mountain in Nevada was based on scientifically sound and suitable science.

Current work is primarily exploratory and is seeking to characterize the likelihood of earthquake damage and water movement.

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High-Level Waste Storage in the United States

• If completed, the facility would hold about 70,000 metric tons of spent fuel rods and other highly radioactive material.– Not to be completed before 2015.

By that time, waste produced by nuclear power plants will exceed the storage capacity of the site.

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High-Level Nuclear Waste Disposal

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Low-Level Radioactive Waste

• Includes cooling water from nuclear reactors, material from decommissioned reactors, protective clothing, and like materials.– Prior to 1970, U.S. alone placed 90,000

barrels of low-level radioactive waste on the ocean floor.

Moratorium in 1970, banned in 1983.

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Low - Level Waste

• Currently, U.S. produces about 800,000 cubic meters of low-level radioactive waste annually.– Presently buried in various scattered

disposal sites.Political limbo.

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Low-Level Radioactive Waste Sites

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Politics of Nuclear Power

• Nuclear power is projected to represent a shrinking share of the world’s electricity consumption from 2004 through 2025.– Most nuclear additions are expected to be

in Asia. (China, India, Japan, S. Korea)Life extension and higher capacity

factors will play a major role in sustaining the U.S. nuclear industry throughout this period.

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Politics of Nuclear Power

• Nuclear power projections are subject to considerable uncertainty, both economic and political.– In large part, governmental support for

nuclear power has waxed and waned with the changing of government regimes.

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Review

• Nature of Nuclear Energy• History of Nuclear Energy Development• Nuclear Fission Reactors• Investigating Nuclear Alternatives• Nuclear Fuel Cycle• Nuclear Material and Weapons Production• Nuclear Power Concerns• Politics of Nuclear Power

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