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FUSION AND FISSION

Jefferson Lab

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THE SUN

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.

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Nuclear Fusion

  • Nuclear fusion is the process by which multiple nuclei join together to form a heavier nucleus.
  • It is accompanied by the release or absorption of energy depending on the masses of the nuclei involved..

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FUSION

DEUTERIUM

TRITIUM

HELIUM

NEUTRON

http://fusioned.gat.com

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Nuclear Fusion

  • Iron and nickel nuclei have the largest binding energies per nucleon of all nuclei and therefore are the most stable.

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Nuclear Fusion

  • The fusion of two nuclei lighter than iron or nickel generally releases energy.
  • The fusion of nuclei heavier than them absorbs energy.

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Complete the Reaction

1H

4Be

1H

8O

4Be

2He

2He

1H

2He

2He

2He

6C

1H element

atomic number (protons)

6C

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Energy needed for Fusion

The thermal activity of a gas is described by its temperature measurement which is really an indication of its velocity/energy.

Thermal energy is represented by the height that the upper magnet.

The upper ring has a potential energy given by PE = mgh at its drop point which is converted into kinetic energy (KE = 1/2 mv2)

As the magnet falls towards the lower magnet. The two magnets click lightly when the kinetic energy is just greater than the magnetic energy that holds them apart.

Since Kinetic Energy = Potential Energy (ignoring frictional components), the gravitational pull and mass of the upper magnet are constant, then the height needed to overcome the magnetic repelling force is proportional to that magnetic repelling force.

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Energy needed for Fusion

PE =mg x h2-h1

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PE = KE = Fxh1

F=force of repulsion

F=PE/h1

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Upper Drop

Position

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Ring

Magnets

Float Position

Lower

Magnet

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Wood Block

h2

h1

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Fusion Changes Mass to Energy�E=mc2

H

He

1kg Hydrogen

.993 kg Helium

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Cookie Fusion

  • Procedure
  • Cut 2 squares of wax paper 10 cm on a side
  • Cut 5 cm wide slice of cookie dough (atom)
  • Find the mass of the atom and record on the table
  • Place the atom one cm away from the edge of a wax paper square
  • Repeat step 2 thru 4 for a second atom
  • Place the atoms about 2 cm from each other
  • Place both atoms on a plate and microwave for 1 minute
  • Remove the “new element” and let cool for 2 minutes
  • Find the mass of the “new element”
  • Complete the table

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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.

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Learning Check

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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

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Nuclear Fission

Neutron induced in U235

Fission is Exothermic

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The sum of the masses of

the resulting nuclei is less

than the original mass (about 0.1% less)

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The “missing mass” is converted to energy according to E=mc2

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Neutrons may:

1 - Cause another fission by colliding with a U235 nucleus

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2 - Be absorbed in other material

3 - Lost in the system

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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 nuclei
  • May cause the nuclide to split as well

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U.S. Electrical Power Production by Source

Source: EIA

(2004)

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Nuclear Fuel Costs

  • Nuclear Fuel Costs Include
    • Uranium
    • Enrichment
    • Manufacturing
    • Waste Disposal
  • Total Nuclear Fuel Cost is Only About 0.5 cents per kilowatt-hour
    • Uranium accounts for only about 20% of this cost or 0.1 cents per kilowatt-hour
    • Increasing Uranium Cost has Minimal Impact

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Review

Nuclear fission:

A large nucleus splits into several small nuclei when impacted by a neutron, and energy is released in this process

Nuclear fusion:

Several small nuclei fuse together and release energy.

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Draw a Double Bubble Map of Fusion and Fission

fusion

fission

Differences Similarities Differences