nuclear energy released when atom split Fusion

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Transcript nuclear energy released when atom split Fusion

Chapter 11
Nuclear
Energy
Nuclear power plant in Salem,
New Jersey
There are three nuclear reactors here
Introduction to the Nuclear Process
Fission –
nuclear energy released when atom split
Fusion –
nuclear energy released when atoms fused
Nuclear reactions have the potential to release a vast amount of energy, primarily as heat
Albert Einstein first hypothesized in 1905 that mass and energy are related in his now
famous equation
E = MC2
(E) Energy is equal to Mass (M) times the speed of light (C) squared.
Also Rutherford (each atom contains a nucleus where most of it’s mass is stored.
Atoms and Radioactivity
Atomic mass = the sum of the protons and the neutrons in an
atom
Atomic number = number of protons in an atom.
Isotopes = the same (single) element that differ in their
atomic mass.
Ex. Hydrogen (1 p, 0 n), Deuterieum (1p, 1n), tritium (1p, 2n)
Unstable isostopes are called radioisotopes and are said to
be radioactive b/c they spontaneously release (emit) radiation
(see radioactive decay)
**The only radioisotope of hydrogen is tritium
Introduction to the Nuclear Process
Atoms and Radioactivity
Normally: # protons = # electrons
Neutron (0)
Atomic mass =
# protons + # neutrons
Proton (+)
Electron (-)
Atomic number =
# protons
Nucleus
Introduction to the Nuclear Process
Normally, # proton = # electrons
8P
6P
8N
6N
Oxygen
Carbon
Differing # proton =
different atom
Introduction to the Nuclear Process
6P
8N
Carbon
If actual atomic mass > normal
atomic mass  typically caused
by greater number of neutrons
Results in an isotope
Chemical behavior identical to
normal atom.
Many are radioactive
Introduction to the Nuclear Process
Common Radioactive Isotopes
Insert Table 12.1
Conventional
Nuclear
Fission
Uranium ore the, which is a mineral used in conventional nuclear power plants,
is nonrenewable resource present in limited amounts and found in
sedimentary rocks found in the earths crust.
Substantial amounts of Uranium are found in Australia (20.4% of known world
reserves), Kazakhstan (18.2%), U.S. (10.2%), Canada (9.9%), and South Africa
(8.9%)
In the U.S. uranium is found in Wyoming, Texas, Colorado, New Mexico, and
Utah.
Uranium contains three isotopes (U-238 99.28%), U-235 (0.71%), and U-234 (less
than (0.01%).
Because there is so little U-235, uranium needs to be refined after it is mined
which is called enrichment and takes a large amount of electricity.
After enrichment the uranium is produced into small pellets (fig.11.3), the
pellets are placed into fuel rods which are grouped into squares called fuel
assemblies of typically 200 rods.
The nuclear fuel cycle is the process of turning uranium into energy from
mining through disposal.
Nuclear Fission
Nuclear Fuel Cycle
Uranium mines
and mills
U-235
enrichment
Fabrication of
fuel assemblies
Nuclear power
plant
Spent fuel
reprocessing
Uranium
tailings
Depleted
uranium tails
Factory
wastes
Low-level
wastes
Spent fuel
stored on-site
Deep geological
disposal
Nuclear Fission
Starting at the
left side
Neutron
bombardment
of uranium-235
causes the
nucleus to
split into
smaller atomic
fragments and
several free
neutrons.
Those free
neutrons then
bombard
others and
cause a chain
reaction…thus
producing
nuclear energy
How electricity is produced from
nuclear energy
A typical nuclear power plant has four main parts: 1. the
reactor core 2. steam generator 3. turbine and 4.
condenser.
Fission occurs in the reactor core and the heat that is
produced is used to produce steam from liquid water in
the steam generator. The turbine then uses the steam to
generate electricity. The condenser then cools the steam
converting it back into a liquid.
Nuclear Fission
How Electricity is Produced from
Conventional Nuclear Fission
Insert Fig 12.5
Breeder Nuclear Fission
U-238 is converted to plutonium Pu-239, which is human-made and
fissionable
Breeder reactor can use U-235, Pu-239, and thorium (Th-232) as fuel
Breeder reactor have the potential to produce much larger quantities of
energy than traditional reactors.
**Use of liquid sodium as a coolant rather thena water makes them very
dangerous (sodium explodes in water)
Nuclear Fission
Breeder Nuclear Fission
Insert Fig 12.6
Pros and Cons of Nuclear Energy
Impact
Coal
Nuclear
Land use
17,000 ac
1,900 ac
Daily fuel
requirement
9,000 tons/day
3 kg/day
Air pollution
Moderate to
severe
Low
Radioactive
emissions
1 curie
28,000 curies
Short-term
local risk
Long-term
risk over
large area
Risk from
catastrophic
accidents
Pros and Cons of Nuclear Energy
Is Electricity Produced by Nuclear Energy
Cheap?
• Role of government subsidies
• 1950’s nuclear was more expensive
(help make up difference between the costs)
• The cost of building a nuclear power plant
• Fixing technical and safety problems in
existing plants
Pros and Cons of Nuclear Energy
Can Nuclear Energy Decrease Our Reliance
on Foreign Oil?
• Only 3% of electricity in US generated by
oil
• Oil primarily used for:
– heating buildings
– vehicles
Safety Issues in Nuclear Power
Plants
Probability of major accident low,
but if it occurs, consequences are widespread and long-lasting
Major accidents have included:
Three Mile Island
Chornobyl
Safety Issues in Nuclear Power
Plants
Radioactive fallout from Chornobyl:
Insert Fig 12.8
Safety Issues in Nuclear Power
Plants
The Link Between Nuclear Energy and
Nuclear Weapons
Can be
Spent fuel from reprocessed
conventional for . . .
nuclear plant
OR
Fuel for
breeder reactor
Nuclear
weapons
Radioactive Wastes
Two general types:
• Low-level radioactive wastes
• High-level radioactive wastes
Insert
Table 12.3
Radioactive Wastes
Temporary storage includes above-ground
storage casks
Insert Fig 12.10 a, b
Radioactive Wastes
Case-in-Point: Yucca
Mountain
Insert Fig 12.11 b
Radioactive Wastes
Other considerations:
• High-Level Radioactive Liquid Waste
• Radioactive Wastes with Relatively Short
Half-Lives
• Decommissioning Nuclear Power Plants
Fusion: Nuclear Energy for the
Future?
Fusion
Insert 12.12
The Future of Nuclear Power
Issues:
• Making nuclear power safer
• Standardizing power plant designs
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