Nuclear FissionNuclear Fission

The basis for The basis for

old bombs and old bombs and

new energynew energy

History of Nuclear FissionHistory of Nuclear Fission

In 1939, German scientists Lise Meitner and In 1939, German scientists Lise Meitner and Otto Hahn discovered that the uranium Otto Hahn discovered that the uranium nucleus could be split nucleus could be split (review atomic structure on board)(review atomic structure on board)

FissionFission is the fancy word for splitting is the fancy word for splitting The fission reaction produced The fission reaction produced a lot a lot of energyof energy

• MUCH more energy than burning fossil fuelsMUCH more energy than burning fossil fuels

Fission could result in a Fission could result in a chain reactionchain reaction that that could grow faster and more energetic quicklycould grow faster and more energetic quickly

The energy comes from E = mcThe energy comes from E = mc22

History of Nuclear FissionHistory of Nuclear Fission

Meitner sent the information to her nephew, Otto Meitner sent the information to her nephew, Otto Frisch, in the U.S.Frisch, in the U.S. Germans had the infoGermans had the info the info could be used to make a bombthe info could be used to make a bomb

Meitner’s colleague, Leo Szilard, wrote the famous Meitner’s colleague, Leo Szilard, wrote the famous letter to FDR letter to FDR the letter argued for an intense effort to create a nuclear the letter argued for an intense effort to create a nuclear

weapon before the Germansweapon before the Germans the letter was signed by Einsteinthe letter was signed by Einstein FDR initiated the FDR initiated the Manhattan ProjectManhattan Project as a result as a result

History of Nuclear FissionHistory of Nuclear Fission

Hahn received a Nobel prize, Meitner didn’t. Hahn received a Nobel prize, Meitner didn’t.

Meitner emigrated to the USMeitner emigrated to the US but she refused to work on the Manhattan Projectbut she refused to work on the Manhattan Project

The Fission ReactionThe Fission Reaction

U-235 + neutron U-235 + neutron U-236* U-236* U-236* is very unstable and undergoes U-236* is very unstable and undergoes

spontaneous fissionspontaneous fission

U-236* U-236* 2 fission products + 3 neutrons + 2 fission products + 3 neutrons + ENERGYENERGY

The 3 neutrons can go on to cause 3 more fissions, The 3 neutrons can go on to cause 3 more fissions, creating 9 neutronscreating 9 neutrons

The 9 neutrons can go on to cause 27 more fissionsThe 9 neutrons can go on to cause 27 more fissions etc…etc…

The Nuclear Fission ReactionThe Nuclear Fission Reaction

Notice that no GREENHOUSE GASES are produced

Fission WeaponsFission Weapons

Making the Making the Atom BombAtom Bomb is easy in theory is easy in theory the fission reaction does NOT need to be the fission reaction does NOT need to be

controlledcontrolled

The key is to rapidly create a The key is to rapidly create a supercritical supercritical massmass of fissionable material of fissionable material A A critical masscritical mass is the smallest amount of fissile is the smallest amount of fissile

material needed for a sustained nuclear chain material needed for a sustained nuclear chain reaction. reaction.

must bring together two must bring together two subcritical massessubcritical masses

The Hiroshima BombThe Hiroshima Bomb Gun barrel design called Gun barrel design called Little BoyLittle Boy

Uses enriched Uranium fuelUses enriched Uranium fuel Uranium is naturally occurringUranium is naturally occurring Uranium is a less efficient fuelUranium is a less efficient fuel Bomb was approx. 33 lbs fuel = 16 kilotons TNTBomb was approx. 33 lbs fuel = 16 kilotons TNT

= 32,000,000 lbs TNT = 32,000,000 lbs TNT = 800 semi-trucks = 800 semi-trucks

fully loadedfully loaded One subcritical mass is fired down a tube at the other subcritical One subcritical mass is fired down a tube at the other subcritical

massmass

Bomb resulted in approx 140,000 deathsBomb resulted in approx 140,000 deaths

The Little Boy designThe Little Boy design

The Trinity and Nagasaki BombsThe Trinity and Nagasaki Bombs Spherical implosion design called Spherical implosion design called Fat Man (or “The Gadget”)Fat Man (or “The Gadget”)

Very complicated, which is why they tested itVery complicated, which is why they tested it

Uses Plutonium fuelUses Plutonium fuel Plutonium is not naturally occurringPlutonium is not naturally occurring

• Must be Must be bredbred from from fertilefertile fuel, usually U-238 fuel, usually U-238 Plutonium is a more efficient fuelPlutonium is a more efficient fuel Bomb was approx. 11 lbs fuel = 20 kilotons TNT Bomb was approx. 11 lbs fuel = 20 kilotons TNT

= 40,000,000 lbs TNT = 40,000,000 lbs TNT = 1000 semi trucks fully loaded= 1000 semi trucks fully loaded

Two hemispheres of fuel are imploded inward toward each otherTwo hemispheres of fuel are imploded inward toward each other

The Nagasaki bomb resulted in approx. 80,000 deathsThe Nagasaki bomb resulted in approx. 80,000 deaths

The Fat Man designThe Fat Man design

Obtaining Weapons Grade FuelObtaining Weapons Grade Fuel The fuel in a nuclear bomb must be 80-100% pureThe fuel in a nuclear bomb must be 80-100% pure

Natural uranium is only 0.7% U-235 (99.3% U-238)Natural uranium is only 0.7% U-235 (99.3% U-238) Power plant fuel only about 3%Power plant fuel only about 3%

Uranium is naturally occurring Uranium is naturally occurring but it must be concentrated, or but it must be concentrated, or enrichedenriched Enrichment is VERY difficult, requires huge centrifugesEnrichment is VERY difficult, requires huge centrifuges

Plutonium does not occur naturallyPlutonium does not occur naturally but it can be made from waste nuclear fuelbut it can be made from waste nuclear fuel process is EASY, but requires a breeder reactorprocess is EASY, but requires a breeder reactor

Good news, Bad newsGood news, Bad news The bad news is that nuclear weapons are easy to The bad news is that nuclear weapons are easy to

make if you have make if you have weapons grade fuelweapons grade fuel

The good news is that The good news is that weapons grade fuelweapons grade fuel is VERY is VERY difficult to come bydifficult to come by

We are reluctant to let rogue nations build any kind of We are reluctant to let rogue nations build any kind of nuclear facility nuclear facility we’re afraid the plant might be a centrifuge for we’re afraid the plant might be a centrifuge for enrichingenriching

UraniumUranium or a reactor for or a reactor for breedingbreeding Plutonium Plutonium