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