2. Every second, the sun converts 500
million metric tons of hydrogen to
helium. Due to the process of fusion,
5 million metric tons of excess
material is converted into energy in
each second. This means that every
year, 157,680,000,000,000 metric
tons are converted into energy.
3. Nuclear Fusion
• Nuclear fusion is the process by which
multiple nuclei join together to form a
• It is accompanied by the release or
absorption of energy depending on the
masses of the nuclei involved.
4. Nuclear Fusion
• Iron and nickel nuclei have the largest binding
energies per nucleon of all nuclei and
therefore are the most stable.
5. Nuclear Fusion
• The fusion of two nuclei lighter than iron or
nickel generally releases energy.
• The fusion of nuclei heavier than them
7. Learning Check
What process creates energy in the Sun?
Fusion of hydrogen into helium in the Sun’s core generates
the Sun’s energy.
How long ago did fusion generate the energy we
now receive as sunlight?
Fusion created the energy we receive today about a million
years ago. This is the time it takes for photons and then
convection to transport energy through the solar interior
to the photosphere. Once sunlight emerges from the
photosphere, it takes only about 8 minutes to reach Earth.
8. NUCLEAR FISSION
A reaction in which an atomic
nucleus of a radioactive element
splits by bombardment from an
external source, with
simultaneous release of large
amounts of energy, used for
electric power generation
9. Nuclear Fission
Neutron induced in U235
Fission is Exothermic
The sum of the masses of
the resulting nuclei is less
than the original mass (about 0.1%
The “missing mass” is converted to
energy according to E=mc2
10. Neutrons may:
1 - Cause another fission by colliding with a U235
2 - Be absorbed in other material
3 - Lost in the system
If sufficient neutrons are present,
we may achieve a chain reaction
Each split (fission) is
accompanied by a large
quantity of E-N-E-R-G-Y
• Creates two smaller nuclides and free neutrons
• The free neutrons potentially collide with nearby U235
• May cause the nuclide to split as well
11. Fission can be controlled…
So energy is released more slowly.
Neutron moderation is a process that sows
down neutrons so the reactor fuel (uranium or
plutonium) captures them to continue the
Neutron absorption decreases the number of
slow moving neutrons
12. Fission can be controlled…
Why must neutrons in a reactor be slowed
So the reactor fuel can capture them to
continue the chain reaction… thus more
energy is produced
15. Nuclear Fuel Costs
• Nuclear Fuel Costs Include
– Waste Disposal
• Total Nuclear Fuel Cost is Only About 0.5 cents per
– Uranium accounts for only about 20% of this cost or 0.1
cents per kilowatt-hour
– Increasing Uranium Cost has Minimal Impact
A large nucleus splits into several
small nuclei when impacted by a
neutron, and energy is released in
Several small nuclei fuse
together and release
18. Fuel rods are a hugh source of
• The rods are made from uranium-235 or
plutonium-239, which are both fissionable
• Once the rods are “spent” they are still
considered high-level nuclear waste because
they continue to emit radiation
• They are placed in holding tanks or storage
20. the growing concerns…
• The rods spend years in the storage tanks
• Its cheaper to mine new sources of isotope
than it is to recycle the isotope remaining in
• The rods are moved to an off-site storage
facility and are taking up LOTS of room
• The DOE is responsible for cleaning up nuclear
sites and managing their waste
Notas del editor
The United States has 103 nuclear power reactors in 31 states.
Nuclear energy provides electricity for one of every five homes and business … the second-largest source of electricity after coal.
Some states are clearly are more dependent on nuclear energy than others. Vermont gets 76 percent of its electricity from nuclear reactors … New Hampshire, 58 percent … and South Carolina, 55 percent.
In Virginia, nuclear power provides more than 40 percent of the electricity used.