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