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Reactors and Bombs
Short Version
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
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
www.ieer.org/sdafiles/ vol_5/5-1/purexch.
Breeder Reactor
TMI
Chernobyl Reactor
Contamination
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
Hanford Reactor – 239Pu
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 explosive 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
Thin metal foil
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
1st Use of Fusion
MeV) 17.6 (~ n HeHH 10
42
21
31 Energy
Fusion Boosted Fission Weapon
80206543210 2......,.........2................,.........2,2,2,2,2,2,2
Normal sequence, of fission generations.
Boom!
Boosted Weapon100654321 .2fusion.... from neutrons,........2,2,2,2,2,2
Bigger Boom!
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!
Sequence of Events1. High explosive detonates – compresses Pu and trigger2. Fission occurs3. Neutrons reflected by casing changes lithium to tritium4. X-rays focused by Styrofoam unto LD target5. Fusion occurs releasing energy AND NEUTRONS6. 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
Fusion Weapon