Physics 362 – week 9
Modern Physics Seminars
The energy challenge
The energy challenge
HDI: longevity (life expectancy), educational attainment, and standard of living (gross domestic product per capita)
How to produce electricity?
• Conversion of mechanical energy into electricity (dynamo)
• Conversion of chemical energy into electricity
• Conversion of nuclear energy into electricity
• Conversion of photon energy into electricity
Energy sources• Oil, Natural Gas, and Coal
• Nuclear
• Renewable energy source
•Solar Cells
•Water Power plants
•Windmills
•Biomass
• Hydrogen
Energy sources
Cost of energy production
Photovoltaic cells: $0.2-0.3 per kW h
Wind turbines: $0.04-0.05 per kW h
Gas: ~ $0.02 per kW h
Carbon reduction
Carbon Reduction
World and U.S. reserves
Nuclear Energy Production
E = m c2
?
Chronology
1905 E=mc2 – Einstein
1939 First nuclear fission – Hahn and Strassmann
1942 First nuclear reactor – Fermi
1951 First reactor to generate electricity
Nuclear Forces
The nucleus is stable if the nuclear attraction dominates over the EM
repulsion
• EM repulsion between protons
• Nuclear attraction
Binding Energy2
np22
i c)MNmZm(MccmBE
• BE > 0
• Higher Binding energy means more stable nuclei
• <BE/A> ~ 8 MeV/nucleon
• BE/A ~ constant for A>20
Energy production
If BE/A initial < BE/A final
Einitial = Mjc2 = (Zjmp+Njmn)c2-BEj/Aj·Aj]
Efinal = Mic2 = (Zimp+Nimn)c2-BEi/Ai·Ai]
Efinal - Einitial = BEi/Ai·Ai - BEj/Aj·Aj > 0
Energy productionfissionfusion
Uranium Isotopes
Isotope Percent Half-life (years)238U 99.284 4.46 billions
235U 0.711 704 millions
234U 0.0055 245,000
239Pu 93/57 24,110
Nuclear FissionHeavy nucleus is bombarded with neutrons It decays into two smaller nuclei + neutrons
n3KrBaUn 9236
14156
23592
Uranium Fission
n3KrBa*UUn 9236
14156
23692
23592
Uranium Fission
n3KrBa*UUn 9236
14156
23692
23592
Chain reaction
Self sustained chain reactionK = Reproduction Constant
K < 1 The reactor is sub-critical it dies out
K = 1 The reactor is critical self sustained chain
K>>1 The reactor becomes unstable
Energy Production
K ~ 1
• Neutron leakage area/volume ratio
• Neutron Energy
• Neutron capture by non-fission elements
• Control of power level
• Safety
Nuclear Reactor
Nuclear Power Plants
Generation I reactors
Fuel:
235U238U/239Pu232Th/233U
OxidesCarbides
Metal alloys
n3KrBa*UUn 9236
14156
23692
23592
Generation I reactors
Fuel:
235U238U/239Pu232Th/233U
OxidesCarbides
Metal alloys
Coolants:
Light waterGases
Heavy waterOrganic liquidLiquid metalMolten salts
System configuration:
Pressurized waterBoiling water
Pressurized Water Reactor
Next Generation
Solar cells
Solar cells
Satellites
Solar Cells
Water Power plants
Windmills
Up to 72 m in rotor diameter
Estimated 3-22 Q of energy
BiomassWood burningFermentation and distillation to produce ethanolSteam-powered generators
Hydrogen fuel cells
Gemini and Apollo spacecrafts
2H2+O22H2O+electricity+heat