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Nuclear EnergyChapter 16

Atoms and Radioactivity

• All common forms of matter are composed of atoms.

• All atoms are composed of:

1) Protons (found in the nucleus)

2) Neutrons (found in the nucleus)

3) Electrons (found orbiting the nucleus)

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Isotopes

Elements that have the same number of

protons and electrons but

Different numbers of neutrons

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1 proton and 1 electron

1 proton and 1 electron and 1 neutron

1 proton and 1 electron and 2 neutrons

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16.1 Atoms and Radioactivity

• Radioactive - Nuclei of certain atoms are unstable and spontaneously decompose and release particles and energy.

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

What is released by radiation?

3 Things:

• Alpha Particles • Beta Particles• Gamma Rays

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16.2 Reactions and Reactors

• Nuclear Fission – A reactions in which the nucleus of a large atom is split into smaller nuclei

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– Nuclear Chain Reaction - Splitting nuclei release neutrons, which themselves strike more nuclei, in turn releasing even more neutrons.

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Control Rods - Made of a non-fissionable material (boron, graphite) that are lowered into reactor to absorb neutrons.– Withdrawn to increase rate of fission.

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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.

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

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Boiling Water Reactor

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Nuclear Power Plants in North America

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16.3 Radioactive Waste

• 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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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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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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