TEACHER NOTES
Nuclear fusion and nuclear fission are two different types of energy-releasing reactions in which energy is released from high-powered atomic bonds between the particles within the nucleus. The main difference between these two processes is that fission is the splitting of an atom into two or more smaller ones while fusion is the fusing of two or more smaller atoms into a larger one.
Ask the Essential Questions before the videos (Fission; Fusion)
Come back to the questions after students complete the Venn diagram activity and take notes .
Nuclear reactions change the structure of nuclei and involve a tremendous amount of energy. The sun is fueled by nuclear reactions. Nuclear power plants are also fueled by nuclear reactions.
1. What changes occur in the nuclei of atoms involved in the reactions that fuel the sun?
2. What changes occur in the nuclei of atoms involved in the reactions that fuel nuclear power plants?
ANSWERS - Essential Questions
Nuclear reactions change the structure of nuclei and involve a tremendous amount of energy. The sun is fueled by nuclear reactions. Nuclear power plants are also fueled by nuclear reactions.
1. What changes occur in the nuclei of atoms involved in the reactions that fuel the sun?
In the sun, lighter nuclei are fused into a larger nucleus through the process of nuclear fusion.
2. What changes occur in the nuclei of atoms involved in the reactions that fuel nuclear power plants?
In nuclear power plants, large nuclei are split into smaller nuclei through the process of nuclear fission.
Comparison chart
/ Nuclear Fission / Nuclear Fusion /Definition: / Fission is the splitting of a large atom into two or more smaller (lighter) ones. / Fusion is the combining (fusing) of two or more lighter atoms into a larger (heavier) one.
Natural occurrence of the process: / Fission reaction does not normally occur in nature. / Fusion occurs in stars, such as the sun.
Byproducts of the reaction: / This reaction produces many highly radioactive particles. Disposal of nuclear waste is a great environmental problem. / Environmentally friendly – “Clean Energy”:
Few radioactive particles are produced by fusion reaction, but if a fission "trigger" is used, radioactive particles will result from that.
Conditions: / Nuclear power plants use this reaction to produce heat in nuclear reactors. The heat is used to generate steam which turns the turbines that produce electricity. Control rods are used to regulate the chain reactions.
Chain reaction: one nuclear reaction leading to more nuclear reactions. Starting material must have enough mass (critical mass) and high-speed neutrons are required.to sustain a chain.
10n à / Chain reaction is NOT involved. High density, high temperature environment is required.
Examples: / The heavy nucleus is bombarded with neutrons / Light nuclei are heated to an extremely high temperature.
Energy Requirement: / Takes little energy to split two atoms in a fission reaction. / Extremely high energy is required to bring two or more protons close enough that nuclear forces overcome their electrostatic repulsion.
Energy Released: / The energy released by fission is a million times greater than that released in chemical reactions; but lower than the energy released by nuclear fusion. / The energy released by fusion is three to four times greater than the energy released by fission.
Nuclear weapon: / One class of nuclear weapon is a fission bomb, also known as an atomic bomb. Critical mass is exceeded (supercritical mass); the chain reaction accelerates and leads to an explosion / One class of nuclear weapon is the hydrogen bomb, which uses fission reaction (atomic bomb) to "trigger" a fusion reaction to provide the high temperatures needed..
Cost: / Raw materials are NOT easily available and are costly. / Raw materials are cheap and easily available.
Summary:
Advantages of Nuclear Energy
i. The Earth has limited supplies of coal and oil. Nuclear power plants could still produce electricity after coal and oil become scarce.
ii. Nuclear power plants need less fuel than ones which burn fossil fuels. One ton of uranium produces more energy than is produced by several million tons of coal or several million barrels of oil.
iii. Coal and oil burning plants pollute the air. Well-operated nuclear power plants do not release contaminants into the environment.
Disadvantages of Nuclear Energy
iv. Nuclear explosions produce radiation. The nuclear radiation harms the cells of the body which can make people sick or even kill them (cancer). Illness can strike people years after their exposure to nuclear radiation.
v. One possible type of reactor disaster is known as a meltdown. In such an accident, the fission reaction goes out of control, leading to a nuclear explosion and the emission of great amounts of radiation.
1. In 1979, the cooling system failed at the Three Mile Island nuclear reactor near Harrisburg, Pennsylvania. Radiation leaked, forcing tens of thousands of people to flee. The problem was solved minutes before a total meltdown would have occurred. Fortunately, there were no deaths.
2. In 1986, a much worse disaster struck Russia's Chernobyl nuclear power plant (Belarus) . In this incident, a large amount of radiation escaped from the reactor. Hundreds of thousands of people were exposed to the radiation. Several dozen died within a few days. In the years to come, thousands more may die of cancers induced by the radiation.
vi. Nuclear reactors also have waste disposal problems. Reactors produce nuclear waste products which emit dangerous radiation. Because they could kill people who touch them, they cannot be thrown away like ordinary garbage. Currently, many nuclear wastes are stored in special cooling pools at the nuclear reactors.
1. The United States plans to move its nuclear waste to a remote underground dump by the year 2010.
2. In 1957, at a dump site in Russia's Ural Mountains, several hundred miles from Moscow, buried nuclear wastes mysteriously exploded, killing dozens of people.
vii. Nuclear reactors only last for about forty to fifty years.
Are you concerned about safe disposal of nuclear waste?
Radioactive waste will be isolated from the environment by several barriers:
a. Waste form – waste is mixed with insoluble glass and converted to a very durable (insoluble) solid material.
b. Engineered barriers – waste is packed into canisters to minimize contact between the waste and geologic barriers for many years.
c. Geological barriers – deep underground burial of waste in rock (isolation for millions of years).
(if time) APPLICATIONS OF RADIOACTIVE ISOTOPES
• Nuclear power plants
• Medical diagnosis and treatment e.g. PET scan monitors glucose metabolism in brain using
C-11 isotope; I-131 measures activity of thyroid
• Carbon dating (measure amount of C-14 remaining in a sample)
• Synthesis of new elements
• Irradiation of food - preserves food & destroys parasites (Food does NOT become radioactive!)
• Nuclear Weapons (Atomic bombs and H bombs)
Learning Check:
1. What subatomic particles involved in nuclear reactions? (protons, neutrons, electrons)
2. Compare and contrast nuclear fission and nuclear fusion reactions in terms of the particles involved
and the changes they undergo.
In fission, heavy nuclei break down into smaller nuclei, releasing large amounts of energy. In fusion,
two or more light nuclei join together to form a more stable nucleus and release large amount of energy.
3. Which nuclear process produces large amounts of energy?
a. Fission
b. Fusion
c. Both fission and fusion
d. Neither fission nor fusion
4. Fission is the process that ______atomic nuclei.
a. Combines
b. Burns up
c. Stores
d. Splits
5. True or false. The fission process requires heavy atomic nuclei.
6. Large nuclei splitting into smaller ones __ fission ___
7. Occurs in uranium and plutonium ___fission ___
8. Involves hydrogen nuclei joining to make helium __ fusion__
9. Name a nuclear reaction that occurs within the sun: __fusion_____
10. Releases neutrons which can trigger the next event __fission ___
11. Source of energy in a nuclear power station __ fission__
12. Always produces new nuclei which are radioactive ___fission__
13. The minimum amount of a substance that can sustain a fission reaction _critical mass __
14. Briefly describe what happens when you fire a neutron into a large amounts of U-235.
(fission à chain reaction)