1. INTRODUCTION to FUSION AND FISSION

2. Warm-up There are 1200 students in a hall. A student starts talking.
If each talking student starts 3 others to talk each second, ...
… what is the minimum time required for all students to be talking?

3. Warm-up The time required = 6 s
How to stop it from being out of control?
Sec. No. of talking students
0 1
 3 = 4
2 4 + ____  3 = ____
3 ____ + ____  3 = ____
4 ____ + ____  3 = ____
5 ____ + ____  3 = ____
6 ____ + ____  3 = ____ 4 16 16 16 64 64
256
Ask teachers responsible for discipline to patrol around the hall.
256
1024
1024
4096

5. Nuclear Reactions When a heavy nucleus splits up,
 huge amount of energy is released.
E.g. atomic bomb
When 2 light nuclei join together to form a heavy nucleus,
 huge amount of energy is released.
E.g. the Sun

6. Nuclear Fission
Fission is the process of splitting a nucleus into two nuclei with smaller masses.
Large amount of energy is releases
A chain reaction is an on-going series of fission reactions.
Critical mass is the amount of fissionable material required to continue a reaction at a constant rate
Exothermic Reaction

7. Nuclear fission U 235 92 + n 1 144 56 Ba + Kr 90 36 + n 1 + n 1 +
uncharged
 not repelled on
approaching
nuclei
Ba-144 nucleus
neutron
neutron
neutron
U-235 nucleus
Kr-90 nucleus U
235 92 + n 1
144 56 Ba + Kr 90 36 + n 1 + n 1 +
energy

8. Nuclear fission U 235 92 + n 1 144 56 Ba + Kr 90 36 + n 1 + n 1 +
144 56 Ba + Kr 90 36 + n 1 + n 1 +
energy
The total mass of the fission products is found less than the total mass before fission takes place.
Naturally-occurring uranium consists of 2 isotopes, U-238 (99.3%) & U-235 (0.7 %).
 It is the rare isotope (U-235) which undergoes fission.

9. Chain reaction
When a uranium nucleus splits, 2 or 3 neutrons are emitted.
neutron
U-235 nucleus splits
If these neutrons carry on splitting other uranium nucleus...

10. Chain reaction self-sustaining  chain reaction neutron
escapes
neutron
U-235 nucleus splits

11. Chain reaction If a small piece of uranium is used,
 the fraction of neutrons escaping .
If the mass of uranium is below a critical mass,
 the chain will break very quickly.

12. Nuclear fission

13. Neutrons may:
1 - Cause another fission by colliding with a U235 nucleus
2 - Be absorbed in other material
3 - Lost in the system
If sufficient neutrons are present, we may achieve a chain reaction
Creates two smaller nuclides and free neutrons
The free neutrons potentially collide with nearby U235 nuclei
May cause the nuclide to split as well
Each split (fission) is accompanied by a large quantity of E-N-E-R-G-Y

14. Nuclear FUSION DEUTERIUM NEUTRON HELIUM TRITIUM

15. Nuclear Fusion
Fusion occurs when two nuclei with low masses are combined to form one nucleus of larger mass.
Can only happen when the nuclei are moving fast enough to get “close” to each other
Temperature in stars are high enough for fusion to occur (millions of degrees Celsius)
FUSION video clip

16. Nuclear fusion This process is called nuclear fusion.
A HUGE AMOUNT of energy is also released when two light nuclei join together to form a heavy nucleus.
This process is called nuclear fusion.

17. Nuclear fusion H 2 1 + H 3 1 He 4 2 + n 1 + energy fusion
hydrogen-2 nucleus
hydrogen-3 nucleus
fusion
neutron
helium-4 H 2 1 + H 3 1 He 4 2 + n 1 +
energy

18. Nuclear fusion H 2 1 + H 3 1 He 4 2 + n 1 + energy+
energy
Since nuclei carry “+” charges, they repel each other.
For fusion to occur, the 2 hydrogen nuclei must approach each other with very high speed.
 hydrogen gas of high temperature
(108 C)!

19. Nuclear fusion
Nuclear fusion occurs in the core of the Sun, giving out heat and light. The reaction takes place continuously for billions of years.

20. Q1 Which of the following…
Which of the following elements is used in nuclear fission?
A U-235
B U-238
C Hydrogen
D Helium

21. Q2 According to Einstein’s…
According to Einstein’s mass-energy equation E = mc2, what is the amount of energy produced if 1 kg of a certain element completely changes into energy?
A 3  108 J
B 3  1016 J
C 6  1016 J
D 9  1016 J

22. Q3 In nuclear… (U) fission In nuclear ___________, nuclei of uranium
are split into smaller pieces and large amount
of energy will be released. In order to
maintain the ___________ reaction, mass of
uranium used should exceed the __________
mass.
fission
chain
critical

23. Q4 In nuclear… (H) fusion In nuclear __________, nuclei of
hydrogen are joined together and
____________ nucleus is formed.
helium

24. 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.

25. Complete the Reaction 4Be 1H element 4Be 2He 6C 2He 2He 6C 8O 2He
atomic number (protons)
4Be 1H
2He 6C
2He 1H 1H 6C
2He
4Be 8O
2He
2He

26. 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% less)
The “missing mass” is converted to energy according to E=mc2

27. U.S. Electrical Power Production by Source
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.
Source: EIA
(2004)

28. 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

29. 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.