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Nuclear Energy: Benefits and Risks

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Only certain kinds of atoms are suitable for development of a nuclear chain reaction. ... Engineering assessments have established many plants can operate much ... – PowerPoint PPT presentation

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Title: Nuclear Energy: Benefits and Risks


1
Nuclear Energy Benefits and Risks
  • Chapter 11

2
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.

3
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).

4
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.

5
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.

6
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.

7
Nuclear Fission Chain Reaction
8
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 worlds first nuclear power plant in
    1951.

9
Dwight D. Eisenhower
  • Atoms for Peace 1953
  • Nuclear reactors will produce electricity so
    cheaply that it will not be necessary to meter
    it.
  • Todays Reality
  • Accidents have caused worldwide concern.
  • Most new projects have been stopped.
  • Many experts predict rebirth.

10
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.

11
Boiling Water Reactor
12
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.

13
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.
  • Boiling Water Reactors (BWR)

14
Plans for New Reactors Worldwide
  • Currently 439 nuclear power reactors in 31
    countries.
  • Combined capacity of 354 gigawatts.
  • Provide 16 of worlds 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.

15
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.

16
Nuclear Power Plants in North America
17
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.

18
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.

19
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.

20
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

21
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.

22
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 5050.
  • To reduce the effects of waste heat, utilities
    build cooling facilities.
  • Ponds
  • Towers

23
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.

24
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.

25
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.

26
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.

27
DOE Radioactive Transuranic Waste Sites
28
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.

29
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.

30
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.

31
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.

32
High-Level Nuclear Waste Disposal
33
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.

34
Low-Level Radioactive Waste Sites
35
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.

36
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.

37
Politics of Nuclear Power
  • Nuclear power is projected to represent a
    shrinking share of the worlds 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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