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Nuclear Fundamentals Part I. Unleashing the Power of the Atom. Objectives. Purpose/advantages of nuclear power Atomic structure, notation, and vocabulary Mass-to-energy conversions (how to get blood from a turnip) Basics of nuclear fission Controlling fission and nuclear reaction rates.

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nuclear fundamentals part i

Nuclear Fundamentals Part I

Unleashing the

Power of the Atom

objectives
Objectives
  • Purpose/advantages of nuclear power
  • Atomic structure, notation, and vocabulary
  • Mass-to-energy conversions (how to get blood from a turnip)
  • Basics of nuclear fission
  • Controlling fission and nuclear reaction rates
introduction
Introduction
  • Early/alternate naval boilers used oil, coal, or wood -> nuclear fission is viable option
  • Advantages:
    • Long life of nuclear core
    • Unlimited endurance/range
    • No need for outside material (air)
    • Less logistical support
    • Carrier carries more weapons, aircraft, fuel
basic atomic structure
Basic Atomic Structure
  • Nucleus: the core of an atom
    • Proton:
      • positive (+) charge
      • primary identifier of an element
      • mass: 1.00728 amu
    • Neutron:
      • no charge
      • usually about the same number as protons
      • mass: 1.00866 amu
  • Electron: orbits about the nucleus
    • Negative (-) charge
    • Mass: 0.0005485 amu (over 1000’s times smaller)
    • Help determine how element reacts chemically
atomic structure
Atomic Structure
  • Isotopes: atoms which have the same atomic number but a different atomic mass number (ie: different number of neutrons)
  • Standard Notation: AZX
  • where:
    • X = element symbol (ie: H for hydrogen)
    • A = atomic mass number (p’s and n’s)
    • Z = atomic number (p’s only)
standard notation the periodic table
Standard Notation & the Periodic Table

23892U -> U: uranium

238: p’s + n’s

92: p’s

146 n’s

mass to energy
Mass to Energy
  • Remember conservation of mass & energy
  • Mass of an element/isotope is less than individual masses of p’s, n’s, and e’s -> difference is called mass defect
  • Einstein’s Theory: E = mc2 or DE = Dmc2
  • Energy released if nucleus is formed from its components is binding energy (due to mass defect)
mass to energy1
Mass to Energy
  • Mass Defect = mass of reactants - mass of products
  • Conversion to energy
    • 1 amu = 931.48 MeV
  • Fission uses this principle -> large isotopes break into pieces releasing energy which can be harnessed
fission
Fission
  • Def’n: splitting of an atom
  • 23592U is fuel for reactor
    • Relatively stable
    • Likely to absorb a neutron (large sa)
    • 23692U fissions readily (large sf)
  • Basic Fission Equation

10n + 23592U 23692U FF1 + FF2 + 2.43 10n + Energy

basic fission equation
Basic Fission Equation

10n + 23592U 23692U FF1 + FF2 + 2.43 10n + Energy

fission fragments
Fission Fragments

10n + 23592U 23692U

FF1 + FF2 + 2.43 10n + Energy

fission1
Fission
  • Neutrons produced (2.43 avg.) will cause other fissions -> chain reaction
  • Neutrons classified by energy levels
    • Fast n’s: n’s produced by fission (>0.1 MeV)
    • Thermal/slow n’s: these cause fission (<0.1 eV)
  • So, if chain reaction is to be sustained, n’s must slow down to thermal energy levels
neutron interactions fission
Neutron Interactions & Fission
  • Interaction described in terms of probability (called microscopic cross section)
  • the larger the effective target area, the greater the probability of interaction
  • measured in barns (10-24 cm)
  • Represented by s (single neutron interacting with single nucleus)
neutron interactions fission1
Neutron Interactions & Fission
  • Scattering (ss)
    • Elastic type collision w/ nucleus (thermalized)
  • Absorption (sa)
    • Neutron absorbed by nucleus
  • Fission (sf)
    • IF absorbed, causes fission
  • Capture (sc)
    • IF absorbed, causes no fission
neutron life cycle
Neutron Life Cycle

23592U

FISSION

Capture

FAST

n’s

Thermal

Absorption

Thermal

Leakage

Fast

Leakage

THERMAL

n’s

Fast

Absorption

THERMALIZATION

condition of reaction rate
Condition of Reaction Rate
  • keff = # of neutrons in a given generation

# of neutrons in preceding generation

  • Critical: fission rate just sustained by the minimum number of thermal fissions (keff = 1)
  • Subcritical: fission rate is decreasing since not enough thermal neutrons are produced to maintain fission reactions (keff < 1)
  • Supercritical: fission rate increasing since more than necessary thermal neutrons created (keff > 1)
stability nuclear force
Stability & Nuclear Force
  • As the number of particles w/in a nucleus increases, the energy which binds nucleus together becomes weaker -> unstable isotopes -> more likely to give off particles
  • Elements undergo radioactive decay to try to achieve stability
  • All isotopes w/ atomic number > 83 are naturally radioactive
radioactivity
Radioactivity
  • Decay occurs in 3 modes:
    • Alpha (a)
    • Beta (b)
    • Gamma (g)
  • Alpha (a)
    • positively charged particle w/ 2 p’s & 2 n’s
    • usually emitted from heavy unstable nuclei
    • Virtually no threat: Easily absorbed by dead skin layer
    • Ex: 23892U 23490Th + 42a
radioactivity1
Radioactivity
  • Beta (b)
    • negatively or positively charged particle
    • emitted from nucleus when n -> p or vice versa
    • like an electron (p -> n) or positron (n -> p)
    • Minimal threat: can be absorbed by clothing
    • Ex: 23490Th 23491Pa + b-
radioactivity2
Radioactivity
  • Gamma (g)
    • electromagnetic wave of high freq/ high energy
    • Not a particle: thus no charge
    • lowers energy level of parent nuclei (no change in A or Z)
    • Potential threat to operators (must be shielded)
    • Ex: 6027Co 6028Ni + 2g + b-
radioactivity3
Radioactivity
  • Half life : time required for 1/2 of any given number of radioactive atoms to disintegrate, thus reducing radiation intensity by ½ of initial radiation
    • Some short (msec), some long (billions of years)
    • 5 t1/2’s to not be radioactive
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