Fission and Fusion Plus reactors and Bombs. Conservation of Energy Something (left) → Something...

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

www.ieer.org/sdafiles/ vol_5/5-1/purexch.

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.

Federation of American Scientists