Shoreham Nuclear Plant on Long Island, New York

Nuclear Share of Electrical Power

Nuclear Power in the United States

NUCLEAR ENERGY

When isotopes of uranium and plutonium undergo controlled nuclear fission, the resulting heat produces steam that spins turbines to generate electricity.The uranium oxide consists of about 97%

nonfissionable uranium-238 and 3% fissionable uranium-235.

The concentration of uranium-235 is increased through an enrichment process.

NUCLEAR ENERGY

Nuclear fusion is a nuclear change in which two isotopes are forced together.No risk of meltdown or radioactive releases.May also be used to breakdown toxic

material.Still in laboratory stages.

There is a disagreement over whether to phase out nuclear power or keep this option open in case other alternatives do not pan out.

Terms and Definitions

Fuel rods: rods full of U235 pelletsModerator: fluid (water) coolant that slows

down neutronsControl rods: moderate rate of the chain

reaction by absorbing neutrons

A Nuclear Reactor

A Nuclear Reactor Is Designed To

Sustain a continuous chain reaction.Prevent amplification into a nuclear

explosion.Consist of an array of fuel and control

rods.Make some material intensely hot.

A Nuclear Reactor

Fig. 16-16, p. 372

Small amounts of radioactive gases

Uranium fuel input (reactor core)

Control rodsContainment shell

Heat exchanger

Steam Turbine Generator

Waste heat

Electric power

Hot coolant

Useful energy 25%–30%Hot

water outputPumpPump

Coolant Pump Pump

Moderator

Cool water input

Waste heat

Shielding Pressure vessel

Coolant passage

Water CondenserPeriodic removal and storage of radioactive wastes and spent fuel assemblies

Periodic removal and storage of radioactive liquid wastes

Water source (river, lake, ocean)

Fig. 16-18, p. 373

Decommissioning of reactorFuel assemblies

ReactorEnrichment of UF6 Fuel fabrication

(conversion of enriched UF6 to UO2 and fabrication of fuel assemblies) Temporary storage of

spent fuel assemblies underwater or in dry casks

Conversion of U3O8 to UF6

Uranium-235 as UF6 Plutonium-239 as PuO2

Spent fuel reprocessing

Low-level radiation with long half-life

Geologic disposal of moderate &

high-level radioactive

wastesOpen fuel cycle today

“Closed” end fuel cycle

What Happened to Nuclear Power?

After more than 50 years of development and enormous government subsidies, nuclear power has not lived up to its promise because:Multi billion-dollar construction costs.Higher operation costs and more malfunctions

than expected.Poor management.Public concerns about safety and stricter

government safety regulations.

NUCLEAR ENERGY

In 1995, the World Bank said nuclear power is too costly and risky.

In 2006, it was found that several U.S. reactors were leaking radioactive tritium into groundwater. Figure 16-19

NUCLEAR ENERGY

When a nuclear reactor reaches the end of its useful life, its highly radioactive materials must be kept from reaching the environment for thousands of years.

At least 228 large commercial reactors worldwide (20 in the U.S.) are scheduled for retirement by 2012.Many reactors are applying to extent their 40-

year license to 60 years.Aging reactors are subject to embrittlement

and corrosion.

NUCLEAR ENERGY

Building more nuclear power plants will not lessen dependence on imported oil and will not reduce CO2 emissions as much as other alternatives.The nuclear fuel cycle contributes to CO2

emissions.Wind turbines, solar cells, geothermal energy,

and hydrogen contributes much less to CO2 emissions.

NUCLEAR ENERGYScientists disagree about the best methods

for long-term storage of high-level radioactive waste:Bury it deep underground.Shoot it into space.Bury it in the Antarctic ice sheet.Bury it in the deep-ocean floor that is geologically

stable.Change it into harmless or less harmful isotopes.

Radioactive Decay

Half life = the time for half the amount of a radioactive isotope to decay.

Half-life

Molybdenum-99 (half-life = 2.8 days)Xenon-133 (half-life = 5.3 days)Krypton-85 (half-life = 10.7 years)Cesium-137 (half-life = 30.0 years)Plutonium-239 (half-life = 24,000 years)

Half life = the time for half the amount of a radioactive isotope

to decay. This is an

exponential graph. When else have we

seen this type of graph?

Do the math, the waste will never be totally gone.

Some Uranium’s half life can be up to 700 million years.

NUCLEAR ENERGY

After three or four years in a reactor, spent fuel rods are removed and stored in a deep pool of water contained in a steel-lined concrete container.

Figure 16-17

NUCLEAR ENERGY

After spent fuel rods are cooled considerably, they are sometimes moved to dry-storage containers made of steel or concrete. Figure 16-17

Disposal of Radioactive Wastes (200 Thousand Tons)

Finding long-term containment sites Transport of highly toxic radioactive wastes

across the United States The lack of any resolution to the radioactive

waste problem Environmental protests Cost ($60 billion to 1.5 trillion)

Disposal of Radioactive Wastes

To be safe, plutonium-239 would require 240,000 years (10 half-lives) of containment!

Discuss the implications of this in terms of disposal of radioactive wastes.

Yucca mountain in southwestern Nevada = the nation’s nuclear waste repository

http://d2o6nd3dubbyr6.cloudfront.net/media/images/Radiation_Texas4_jpg_800x1000_q100.jpg

Yucca Mountain, Nevada

Nuclear Power Accidents

Three Mile Island1979Harrisburg, PALoss of coolant in reactor vesselDamage so bad, reactor shut down

permanentlyUnknown amount of radioactive waste

released into atmosphere.

Case Study: The Chernobyl Nuclear Power Plant Accident

The world’s worst nuclear power plant accident occurred in 1986 in Ukraine.

The disaster was caused by poor reactor design and human error.

By 2005, 56 people had died from radiation released.4,000 more are expected from thyroid cancer

and leukemia.

Chernobyl, Russia

Loss of water coolant perhaps triggered the accident. When the water-circulation system failed, the temperature in the reactor core increased to over 5,000 oF, causing the uranium fuel to begin melting and producing steam that reacted with the zirconium alloy cladding of the fuel rod to produce hydrogen gas.

How Chernobyl Blew Up

A second reaction between steam and graphite produced free hydrogen and carbon oxides. When this gas combined with oxygen, a blast blew off the top of the building, igniting the graphite. The burning graphite threw a dense cloud of radioactive fission products into the air.

Consequences of Radiation Exposure

Block cell division Damage biological

tissues and DNA Death Cancer Birth defects

Economic Problems with Nuclear Power

Energy demand estimates were unrealistic.

Costs increase (5X) to comply with new safety standards.

Withdrawal of government subsidies to nuclear industry.

Public protests delayed construction.Any accident financially ruins the utility.

Comparing Nuclear Power with Coal Power

NUCLEAR ENERGY

A 1,000 megawatt (MW) nuclear plant is refueled once a year, whereas a coal plant requires 80 rail cars a day.

Figure 16-20