1. Fission and Fusion of Atomic Nuclei
Prentice-Hall Chapter 25.3
Dr. Yager

2. What Happens in a Nuclear Chain Reaction?
When the nuclei of certain isotopes are bombarded with neutrons, they undergo fission, the splitting of a very large nucleus into two smaller, more stable nuclei.
In a chain reaction, some of the neutrons produced react with other fissionable atoms, producing more neutrons which react with still more fissionable atoms.

3. Nuclear Fission

4. Nuclear Fission
Although some isotopes undergo fission spontaneously, most fission reactions occur artificially by neutron bombardment.
235U + 1n → 93Kr Ba n
Fission of one U-235 nucleus generates three more neutrons, leading to a chain reaction.
A minimum amount of radioactive material, called critical mass, is needed to keep the reaction going.

5. Fission of Uranium-235

8. Fission as an Energy Source
Fission reactions can produce a large amount of energy.
Fission of 1 g U-235 generates as much energy as the combustion of 2,700 kg of coal.
Fission reactions are used to generate electrical energy in nuclear power plants.
Uranium-235 and plutonium-239 are the main radioisotopes used in nuclear reactors.

10. Processes Inside the Nuclear Reactor
Neutron moderation is a process that slows down neutrons so the reactor fuel (uranium-235 or plutonium-239) captures them to continue the chain reaction.
Neutron absorption is a process that decreases the number of slow-moving neutrons. Control rods, made of a material such as carbon or cadmium, are used to absorb neutrons.

11. Chain reactions that occur in reactors can be very dangerous if they are not controlled.
Water is heated by the energy released from the controlled fission of U-235 and changed into steam.
The steam drives a turbine to produce electrical energy.
The steam then passes into a condenser and is cooled by a river, lake or ocean’s water.

12. Pressurized, Light-Water Nuclear Reactor

13. Used or spent fuel rods from a nuclear reaction are stored in water because:
Water cools the spent rods, and also acts as a radiation shield to reduce the radiation levels.

14. What is the Difference Between Fission and Fusion?
Fission is the breaking apart of nuclei.
Fusion occurs when nuclei combine to produce a nucleus of greater mass.
In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei and two positrons.

15. Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split.

17. The Sun is a Fusion Reaction

19. Fusion is the process by which stars, including our sun, generate energy.
In the sun, hydrogen nuclei fuse to form a single
Very high temperatures are required to bring the nuclei together.
The temperature of the sun’s core, where some of the fusion reactions occur, is about 1.5×107 °C.
When the hydrogen nuclei are fused, some mass is converted to energy.
nucleus.

20. Fusion as an Energy Source?
One problem is that starting a fusion reaction takes a lot of energy.
So far, researchers need just as much energy to start a fusion reaction as is released by the reaction.
As a result, fusion is not yet a practical source of energy.

25. 1. One of the control mechanisms for a sustainable nuclear chain reactor involves slowing down the released neutrons so they may be captured by other nuclei. This is done using
moderators.
shielding.
absorbers.
control rods.

26. 1. One of the control mechanisms for a sustainable nuclear chain reactor involves slowing down the released neutrons so they may be captured by other nuclei. This is done using
moderators.
shielding.
absorbers.
control rods.

27. 2. Spent fuel rods are stored in
lead-lined containers.
deep pools of water.
thick concrete bunkers.
cadmium or graphite containers.

28. 2. Spent fuel rods are stored in
lead-lined containers.
deep pools of water.
thick concrete bunkers.
cadmium or graphite containers.

29. 3. Choose the correct words for the spaces
3. Choose the correct words for the spaces. In solar fusion, _______ nuclei fuse to form _______ nuclei.
helium, hydrogen
hydrogen-1, hydrogen-2
hydrogen, helium
hydrogen-1, hydrogen-3

30. 3. Choose the correct words for the spaces
3. Choose the correct words for the spaces. In solar fusion, _______ nuclei fuse to form _______ nuclei.
helium, hydrogen
hydrogen-1, hydrogen-2
hydrogen, helium
hydrogen-1, hydrogen-3

31. 4. The chain reaction of the fission of U-235 atoms in a nuclear reactor generates a large amount of energy. What is the source of the energy produced?
A. destruction of neutrons
B. lost mass that is converted to energy
C. electrical repulsion between the nuclei produced by fission
D. electrical attraction between the nuclei produced by fission

32. 4. The chain reaction of the fission of U-235 atoms in a nuclear reactor generates a large amount of energy. What is the source of the energy produced?
A. destruction of neutrons
B. lost mass that is converted to energy
C. electrical repulsion between the nuclei produced by fission
D. electrical attraction between the nuclei produced by fission

35. LMFBR

36. Cerenkov Radiation
When high velocity particles travel faster than the speed of light in a medium they create a blue flash.