# INTRODUCTION to FUSION AND FISSION

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INTRODUCTION to FUSION AND FISSION

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?

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

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

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

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

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.

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...

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

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.

Nuclear fission

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

Nuclear FUSION DEUTERIUM NEUTRON HELIUM TRITIUM

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

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.

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

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)!

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.

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

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

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

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

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.

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

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

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)

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

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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