Nuclear Fundamentals Part I Unleashing the Power of the Atom.
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Transcript of Nuclear Fundamentals Part I Unleashing the Power of the Atom.
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Nuclear Nuclear FundamentalFundamentals Part Is Part I
Unleashing the Unleashing the
Power of the Power of the AtomAtom
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ObjectivesObjectives
• Purpose/advantages of nuclear Purpose/advantages of nuclear powerpower
• Atomic structure, notation, and Atomic structure, notation, and vocabularyvocabulary
• Mass-to-energy conversions (how Mass-to-energy conversions (how to get blood from a turnip)to get blood from a turnip)
• Basics of nuclear fissionBasics of nuclear fission• Controlling fission and nuclear Controlling fission and nuclear
reaction ratesreaction rates
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IntroductionIntroduction
• Early/alternate naval boilers used oil, Early/alternate naval boilers used oil, coal, or wood -> nuclear fission is coal, or wood -> nuclear fission is viable optionviable option
• Advantages:Advantages:• Long life of nuclear coreLong life of nuclear core• Unlimited endurance/rangeUnlimited endurance/range• No need for outside material (air)No need for outside material (air)• Less logistical supportLess logistical support• Carrier carries more weapons, aircraft, Carrier carries more weapons, aircraft,
fuelfuel
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Basic Atomic StructureBasic Atomic Structure• Nucleus: the core of an atomNucleus: the core of an atom
• Proton: Proton: • positive (+) chargepositive (+) charge• primary identifier of an element primary identifier of an element • mass: 1.00728 amumass: 1.00728 amu
• Neutron: Neutron: • no chargeno charge• usually usually aboutabout the same number as protons the same number as protons • mass: 1.00866 amumass: 1.00866 amu
• Electron: orbits about the nucleusElectron: orbits about the nucleus• Negative (-) charge Negative (-) charge • Mass: 0.0005485 amu (over 1000’s times Mass: 0.0005485 amu (over 1000’s times
smaller)smaller)• Help determine how element reacts Help determine how element reacts
chemicallychemically
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Basic Atomic StructureBasic Atomic Structure
electron
neutron
proton
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Atomic StructureAtomic Structure
• Isotopes: atoms which have the same Isotopes: atoms which have the same atomic number but a different atomic atomic number but a different atomic massmass number (ie: different number of number (ie: different number of neutrons)neutrons)
• Standard Notation: Standard Notation: AAZZXX
• where:where:• X = element symbol (ie: H for hydrogen)X = element symbol (ie: H for hydrogen)• A = atomic mass number (p’s and n’s)A = atomic mass number (p’s and n’s)• Z = atomic number (p’s only) Z = atomic number (p’s only)
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Standard Notation & Standard Notation & the Periodic Tablethe Periodic Table
2382389292U -> U:U -> U: uraniumuranium
238: 238: p’s + n’s p’s + n’s
92:92: p’sp’s
146146 n’sn’s
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Mass to EnergyMass to Energy
• Remember conservation of mass & Remember conservation of mass & energyenergy
• Mass of an element/isotope is less Mass of an element/isotope is less than individual masses of p’s, n’s, and than individual masses of p’s, n’s, and e’s -> difference is called e’s -> difference is called mass defectmass defect
• Einstein’s Theory: Einstein’s Theory: E = mcE = mc2 2 or or E = E = mcmc22
• Energy released if nucleus is formed Energy released if nucleus is formed from its components is from its components is binding energybinding energy (due to mass defect)(due to mass defect)
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Mass to EnergyMass to Energy
• Mass Defect = mass of Mass Defect = mass of reactants - mass of productsreactants - mass of products
• Conversion to energyConversion to energy• 1 amu = 931.48 MeV1 amu = 931.48 MeV
• Fission uses this principle -> Fission uses this principle -> large isotopes break into large isotopes break into pieces releasing energy which pieces releasing energy which can be harnessedcan be harnessed
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FissionFission
• Def’n: splitting of an atomDef’n: splitting of an atom• 235235
9292U is fuel for reactorU is fuel for reactor• Relatively stableRelatively stable• Likely to absorb a neutron (large Likely to absorb a neutron (large aa))• 236236
9292U fissions readily (large U fissions readily (large ff))
• Basic Fission EquationBasic Fission Equation
1100n + n + 235235
9292U U 2362369292U FFU FF1 1 + FF+ FF2 2 + 2.43 + 2.43 11
00n + n + EnergyEnergy
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Basic Fission EquationBasic Fission Equation
1100n + n + 235235
9292U U 2362369292U FFU FF1 1 + FF+ FF2 2 + 2.43 + 2.43
1100n + Energyn + Energy
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Fission FragmentsFission Fragments
1100n + n + 235235
9292U U 236236
9292U U FFFF1 1 + FF+ FF2 2 + 2.43 + 2.43 1100n + Energyn + Energy
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FissionFission
• Neutrons produced (2.43 avg.) will Neutrons produced (2.43 avg.) will cause other fissions -> chain reactioncause other fissions -> chain reaction
• Neutrons classified by energy levelsNeutrons classified by energy levels• Fast n’s: n’s produced by fission (>0.1 Fast n’s: n’s produced by fission (>0.1
MeV)MeV)• Thermal/slow n’s: these cause fission Thermal/slow n’s: these cause fission
(<0.1 eV)(<0.1 eV)• So, if chain reaction is to be So, if chain reaction is to be
sustained, n’s must slow down to sustained, n’s must slow down to thermal energy levelsthermal energy levels
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Neutron Interactions & Neutron Interactions & FissionFission
• Interaction described in terms of Interaction described in terms of probability (called probability (called microscopic microscopic cross sectioncross section))
• the larger the effective target the larger the effective target area, the greater the probability area, the greater the probability of interactionof interaction
• measured in barns (10measured in barns (10-24 -24 cm)cm)• Represented by Represented by (single neutron (single neutron
interacting with single nucleus)interacting with single nucleus)
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Neutron Interactions & Neutron Interactions & FissionFission
• Scattering (Scattering (ss))• Elastic type collision w/ nucleus Elastic type collision w/ nucleus
(thermalized)(thermalized)
• Absorption (Absorption (aa))• Neutron absorbed by nucleusNeutron absorbed by nucleus
• Fission (Fission (ff))• IF absorbed, causes fissionIF absorbed, causes fission
• Capture (Capture (cc))• IF absorbed, causes no fissionIF absorbed, causes no fission
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Neutron Life CycleNeutron Life Cycle
THERMALIZATION
23592U FISSION
FASTn’s
THERMALn’s
ThermalAbsorption
FastAbsorption
Capture
FastLeakage
ThermalLeakage
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Condition of Reaction Condition of Reaction RateRate
• kkeffeff = = # of neutrons in a given generation# of neutrons in a given generation
## of neutrons in preceding generation of neutrons in preceding generation• CriticalCritical: fission rate just sustained by the : fission rate just sustained by the
minimum number of thermal fissions (kminimum number of thermal fissions (keffeff = 1) = 1) • SubcriticalSubcritical: fission rate is decreasing since : fission rate is decreasing since
not enough thermal neutrons are produced to not enough thermal neutrons are produced to maintain fission reactions (kmaintain fission reactions (keff eff < 1)< 1)
• SupercriticalSupercritical: fission rate increasing since : fission rate increasing since more than necessary thermal neutrons more than necessary thermal neutrons created (kcreated (keffeff > 1) > 1)
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Stability & Nuclear Stability & Nuclear ForceForce
• As the number of particles w/in a As the number of particles w/in a nucleus increases, the energy which nucleus increases, the energy which binds nucleus together becomes binds nucleus together becomes weaker -> unstable isotopes -> weaker -> unstable isotopes -> more likely to give off particlesmore likely to give off particles
• Elements undergo radioactive Elements undergo radioactive decay to try to achieve stabilitydecay to try to achieve stability
• All isotopes w/ atomic number > 83 All isotopes w/ atomic number > 83 are naturally radioactive are naturally radioactive
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RadioactivityRadioactivity• Decay occurs in 3 modes:Decay occurs in 3 modes:
• Alpha (Alpha ())• Beta (Beta ())• Gamma (Gamma ())
• Alpha (Alpha (• positively charged particle w/ 2 p’s & 2 n’spositively charged particle w/ 2 p’s & 2 n’s• usually emitted from heavy unstable usually emitted from heavy unstable
nucleinuclei• Virtually no threat: Easily absorbed by Virtually no threat: Easily absorbed by
dead skin layerdead skin layer• Ex: Ex: 238 238
9292U U 2342349090Th + Th + 44
22
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RadioactivityRadioactivity
• BetaBeta• negatively or positively charged negatively or positively charged
particleparticle• emitted from nucleus when n -> p or emitted from nucleus when n -> p or
vice versavice versa• like an electron (p -> n) or positron (n -like an electron (p -> n) or positron (n -
> p)> p)• Minimal threat: can be absorbed by Minimal threat: can be absorbed by
clothingclothing• Ex: Ex: 234234
9090Th Th 2342349191Pa + Pa + --
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RadioactivityRadioactivity
• Gamma (Gamma (• electromagnetic wave of high electromagnetic wave of high
freq/ high energyfreq/ high energy• Not a particle: thus no chargeNot a particle: thus no charge• lowers energy level of parent lowers energy level of parent
nuclei (no change in A or Z)nuclei (no change in A or Z)• Potential threat to operators Potential threat to operators
(must be shielded)(must be shielded)• Ex: Ex: 6060
2727Co Co 60602828Ni + 2Ni + 2 + + - -
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RadioactivityRadioactivity
• Half life : time required for 1/2 of Half life : time required for 1/2 of any given number of radioactive any given number of radioactive atoms to disintegrate, thus atoms to disintegrate, thus reducing radiation intensity by ½ reducing radiation intensity by ½ of initial radiationof initial radiation• Some short (Some short (sec), some long sec), some long
(billions of years)(billions of years)• 5 t5 t1/21/2’s to not be radioactive’s to not be radioactive
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QuestioQuestions?ns?