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.