fission and fusion plus reactors and bombs. conservation of energy something (left) → something...
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Fission and Fusion
Plus reactors and Bombs
Conservation of Energy
• Something (left) → Something else (right)
• If Σ masses on left > Σ masses on right – Energy released and the reaction happens by itself
– (radioactive decay, fission, fusion, etc)
• If not, energy needed to cause reaction (as in a particle accelerator)
Fission and fusion can yield energy
Nuclear Fission
H:\PH 104\FISSION.mov
Liquid Drop Model
Nuclear Chain Reactions
H:\PH 104\chainreaction.mov
Neutrons From Fission
Possible Fission Fuel
Isotope Average Neutron Released
Slow Fast
233U 2.29 2.45235U 2.07 2.30238U 0 0.97
U - natural 1.34 1.02239Pu 2.08 2.45
Controlled Nuclear Fission
Spontaneous Fission
Fission Fragments
Fission Fragment Example
NOTE:|Chemical Reaction H + H + O = H2O + 3 eV
)n( 3 Sn Mo U n 110
13150
10242
235921
10 + 187 MeV
Million 4.8 eV/18 3
236/MeV 187
(Chemical) sEnergy/Mas
(Fission) sEnergy/Mas
Fission Fragment Decay
Nuclear Fusion
H:\PH 104\fusion.mov
Fusion Reactions in Sun
Energy
Energy
Energy
HHHeHeHe
HeHH
eHHH
11
11
42
32
32
32
21
11
01
21
11
11
Fusion Reactions in The Lab
MeV) 17.6 (~ n HeHH
MeV) 23 (~ HeHH10
42
21
31
42
21
21
Energy
Energy
5~ MeV/236 187
MeV/5 17.6
(Fission) sEnergy/Mas
(Fusion) sEnergy/Mas
Energy NeededEnergy Released
Need Energy to Overcome Electric Force
Magnetic Confinement
TOKAMAK
Inertial Confinement
Beam Line
NIF Target Chamber
Cold Fusion
History• 1932 - Chadwick discovers neutron
• 1934 – Fermi studies systematics of neutron capture.
• 1934 – Otto Hahn, Lise Meitner, Fritz Strassman conducted similar experiments, but didn’t publish.
• 1938 - Meitner fled to Switzerland and with her nephew, Otto Frish, conclusively demonstrated fission
• 1939 – Leo Szilard and Walter Zinn found neutrons also emitted – Chain Reaction
CCn 136
126
10
Lise Meitner 1878-1968• In 1917, she and chemist Otto Hahn discovered protactinium.
• She was given her own physics section at the Kaiser Wilhelm Institute of Chemistry
• In 1923, she discovered the cause of something known as the Auger effect
• 1933, Meitner was acting director of the Institute for Chemistry
• 1938, Meitner escaped to Holland. • She took a lab position in Stockholm, worked
w/ Niels Bohr and continued to correspond with Hahn and other German scientists.
• Hahn and Meitner met clandestinely in Copenhagen in November 1938 to plan a new round of experiments.
• The experiments which provided the evidence for nuclear fission were done at Hahn's laboratory in Berlin.
• She was the first person to realize that the nucleus of an atom could be split into smaller parts
• It was politically impossible for the exiled Meitner to publish jointly with Hahn in 1939. Hahn published the chemical findings in January 1939 and Meitner published the physical explanation two months later with her nephew, physicist Otto Robert Frisch, and named the process "nuclear fission“
• 1944, Hahn received the Nobel Prize for Chemistry for the discovery of nuclear fission.
• 1966 Hahn, Fritz Strassmann and Meitner together were awarded the Enrico Fermi Award.
Nuclear Reactors and the
Nuclear Fuel Cycle
Fission
Chain Reaction
Controlled Nuclear Fission
Neutrons From Fission
Possible Fission Fuel
Isotope Average Neutron Released
Slow Fast
233U 2.29 2.45235U 2.07 2.30238U 0 0.97
U - natural 1.34 1.02239Pu 2.08 2.45
Reactor Components• Moderator
– Small A– Small probability of absorbing neutrons;
• Water• Heavy water (deuterium)• Graphite
• Coolant• Control Rods
– Absorbers that suck up neutrons• Cadmium, indium, boron
• Delayed neutrons (0.7%)
Fuel Needed to Run a 1000 MW(e) Coal-Fired and Nuclear Power Plant
Time of Operation Fuel Used During
Operation 1 Hour 1 Day 1 Year
Coal Plant 350 Tons 8.4x103 Tons
3.0x106 Tons
Nuclear Plant 0.3 Pounds
7.2 Pounds 1.3 Tons
Uranium Isotopes
Enrichment Numbers
• Low-Enriched Uranium (LEU) or Reactor Grade Fuel = 3-5% U235
• Highly-Enriched Uranium (HEU) or Weapons Grade Fuel = 80-95% U235
World Uranium Reserves• Australia 24%• Kazakhstan 17• Canada 13• South Africa 9• Russia 6• Nambia 6• US 4• Niger 3• Uzbekistan 3
Most Uranium currently comes from Canada, followed by Australia and
Niger
Uranium Mine in Niger (Sahara Desert)
Conversion of Uranium Ore to “Yellow Cake”
Uranium Mining
Enrichment Starts with UF6
Calutron (Mass Spectrometer)
Enrichment - Centrifuge
Centrifuge Cascade
Centrifuge Cascade
Uranium Is Encased in Solid Ceramic Pellets
Fuel Pellet
Nuclear Fuel Assembly
Fuel Pellet
Reactor Core
Boiling Water Reactor
PWR
CANDU
Graphite Reactor
Plutonium Production
Characteristics of Waste from a Reactor for Each Fuel Element
Age (Years)
Heat (Watts)
Activity (Ci)
Dose at Surface
(Rem/Hr) 0 180,000 1.5x108 8x106 1 4,800 2.5x106 234,000 5 930 6x105 46,800
10 550 4x105 23,400 50 250 1x105 8,646
100 150 5x104 2,150 500 45 2.5x103 58
1000 26 1.7x103 9.6 10,000 6.4 4.5x102 1.8
Plutonium Fuel Cycle
Breeder Reactor
TMI
Smithsonian
First Entry
Summer1980
Reactor Core
Chernobyl Reactor
Aftermath
Contamination
Reactor 1
Reactor 2
Reactor 3
Reactor 4
Operational Reactors435
Permanently Shut Down140
Percent Share ofElectrical Energy
ReactorsBy Age
Under Construction
Why?
•http://www.oncorgroup.com/community/education/
knowledgecollege/energy_library/elec_nuc.asp
•Efficient!
•No Atmospheric Pollution
Cons
• Potential for serious disaster. i.e. Chernobyl, Three Mile Island, etc.
• Fuel is expensive to mine, enrich, and transport
• Once fuel is spent no easy way to get rid of it!
• Nuclear Waste
Nuclear Weapons
Classified
History Part 2• 1939 – Neils Bohr and John Wheeler proposed
detailed theory (Liquid Drop Model)
• 1939 – Fermi unsuccessfully tried to alert US Navy of importance of research
• 1939 – Einstein’s famous letter to Roosevelt (Szilard, and Wigner)
• 1941 – Britain joins US effort
• 1942 – Fermi, first reactor in Chicago, Oppenheimer in charge.
Neutrons From Fission
Possible Fission Fuel
Isotope Average Neutron Released
Slow Fast
233U 2.29 2.45235U 2.07 2.30238U 0 0.97
U - natural 1.34 1.02239Pu 2.08 2.45
Manhattan Project
Gen Groves Oppenheimer
Oak Ridge - K-25 Enrichment Plant - 235U
K-25 Enrichment Plant
1st ReactorFermi’s First Reactor
Fermi’s First Reactor
Hanford Reactor – 239Pu
Hanford Reactor
Los Alamos – Science, Assembly
Critical “Mass”
• How much material needed to sustain a chain reaction and build a weapon.
• Depends on– Mass– Shape– Density– Configuration
Critical Masses
Fuel Critical Mass W/O
With Tamper
(U)
With Tamper
(Be)
Natural Uranium
No!
20 % 235U 160 kg 65 kg
50 % 235U 68 kg 25 kg
100 % 235U 47 kg 16 kg 14 kg
80 % 239Pu 5.4 kg
100 % 239Pu 10 kg 4.5 kg 4 kg
Ben2Ben 84
10
94
10
Explosion Sequence
80206543210 2......,.........2................,.........2,2,2,2,2,2,2
Numbers of Fissions
Boom!
The whole process takes about 1 µs and the last five generations release about 98% of the energy in 10-8s.
Yield
• Yield of Nuclear Weapons in equivalent exposive power of tonnes of TNT – (1 tonne = 1000 kg)
• 1 kT = 1000 tonnes is equivalent to 4.2x1012 J of energy – (from 0.056 kg of 235U)
• 1 MT = 1 million tonnes of TNT
Gun-Barrel Device
Little Boy: A Gun-Type Bomb
28” in diameter, 10” long, 9,000 lbs50 kg of Uranium, 70% 235UCritical mass = 17” in diameterY = 12.5 kT
Neutron Trigger
n C He Be 10
126
42
94
Po Be
Plutonium Bomb
• In a Reactor three isotopes of Plutonium produced
• 239Pu, 240Pu, 241Pu
• 240Pu and 241Pu undergo spontaneous fission
• A gun barrel design too slow to prevent a “fizzle”
Spontaneous Fission 240Pu and 241Pu
Plutonium Bomb
• In a Reactor three isotopes of Plutonium produced
• 239Pu, 240Pu, 241Pu
• 240Pu and 241Pu undergo spontaneous fission
• A gun barrel design too slow to prevent a “fizzle”
Fat Man: Implosion-type bomb
Fat Man: Implosion-Type Bomb
60” in diameter, 10”8” long5 kg of PuY = 20 kT
Nuclear Fusion
Second Use of Fusion
• Actual Fusion Explosion
• Used Liquid tritium and deuterium
• Size of a building
• 10 MT 1952
Important Elements of Fusion Bomb
H He n Li 31
42
10
63
Lithium Hydride (LH) but made with deuteriumLithium deuteride LD
Just need a source of neutrons and lots of energy and high temperatures
Fission Bomb!
Fusion Weapon
Sequence of Events1. High explosive detonates – compresses Pu and
trigger
2. Fission occurs
3. Neutrons reflected by casing changes lithium to tritium
4. X-rays focused by Styrofoam unto LD target
5. Fusion occurs releasing energy AND NEUTRONS
6. If outer casing made of 238U, a second large fission explosion occurs! (If made of 235U, an even bigger fission explosion (x2))
Possible Fission Fuel
Isotope Average Neutron Released
Slow Fast
233U 2.29 2.45235U 2.07 2.30238U 0 0.97
U - natural 1.34 1.02239Pu 2.08 2.45
Bravo Test 1954
• 1st deliverable weapon
• 15 MT
• Didn’t realize extra yield from outer casing.
