Energy ResourcesAlternative Sources

Chapter 14

Figure 14.1

Figure 14.2

Figure 14.3

Figure 14.4

Nuclear Power - Fission• Fission – splitting apart the atom releases

energy– Currently commercially feasible– Uranium-235 fuels most fission reactors– A controlled chain reaction occurs with

continuous and moderate release of energy– The energy release heats water within the

core of a reactor– This heat is transferred through heat

exchangers to outer loops where steam generation is possible for generating power or propulsion

Figure 14.5 U-235 Nuclear fission and chain reaction

Figure 14.6 Conventional nuclear fission reactor

Geology of Uranium• 95% of uranium found in sedimentary (or

metasedimentary) rocks– Generally found in sandstones– Uranium is weathered from other rocks and

deposited by migrating ground water– Minor amounts of uranium are present in

many crustal rocks– Granitic rocks and carbonates may be rich in

uranium– Uranium oxide (U3O8): “yellowcake”

Extending the Nuclear Fuel Supply

• Uranium-235 is not the only fuel useful for fission-reactors– It is the most plentiful naturally occurring one

• Uranium-238 can absorb a neutron and converts to plutonium-239 and is fissionable– U-238 makes up 99.3% of natural uranium– Used for over 90% of reactor grade enriched uranium

• Breeder reactor can maximize the production of other radioactive fuels– Expensive and complex

Figure 14.7 the nuclear fuel cycle

Concerns Related Nuclear Reactor Safety

• Nuclear reactor safety is a serious undertaking– Controlled release of very minor amounts of radiation

occur– Major concerns are with accidents and sabotage– Loss of coolant in the core could produce a core

meltdown– This event could allow the fuel and core materials to

melt into an unmanageable mass and then migrate out of the containment structure

– Could result in a catastrophic release of radiation into the environment

– Reactors must be located away from active faults

Figure 14.8 Three Mile Island Reactors

Concerns Related to Fuel Handling• Mining and processing of uranium ore is a

radioactive hazard– Miners are exposed to higher levels of

radioactivity than the general population– Tailings piles are exposed to weather and the

uranium is mobilized into the environment

• Plutonium is both radioactive and chemically toxic– Easy to convert into nuclear weapons material– Uranium (enriched) is serious security

problem

Figure 14.9 Locations of U.S. uranium reserves

Radioactive Wastes• Energy produced by nuclear fission

produces radioactive wastes– Difficult to treat– No long-term, permanent storage or disposal

sites in operation

• Nuclear power plants are decommissioned once operations cease– Expensive to decommission these plants– Abundant radioactive contaminated material

associated with these plants that must be permanently stored somewhere and safely

Figure 14.10

Risk Assessment and Risk Projection

No energy source is risk-free with “acceptable risk”

8% of U.S. energy is supplied by nuclear power in 2002

Nuclear-plant cancellation is not without its costs

Nuclear plants have lower fueling and operating costs than coal-fired plants

Reliance on nuclear power varies widely

Different people weigh the pros and cons of nuclear fission power in different ways

Figure 14.11 U.S. nuclear power plants

Figure 14.12 Percentage of electricity generated by nuclear fission varies greatly by country

Nuclear Power - Fusion• Nuclear fusion is the opposite of nuclear fission• Sun is a gigantic fusion reactor• Fusion is a cleaner form nuclear power than

fission• Fusion – involves combining smaller nuclei to

form larger ones• Can produces abundant energy• Hydrogen is plentiful and is the raw material

required• Fusion difficult to achieve given current

technology • Theoretical – not yet economically attained

Figure 14.13 One nuclear fusion reaction

Solar Energy

• Abundant solar energy reaches the earths surface– Be dissipated in various ways– Solar energy is free, clean, and a renewable resource– Limitations are latitude and climate

• Solar Heating– Passive solar heating: no mechanical assistance– Active solar heating: mechanical circulation of solar-

heated water

• Solar Electricity– Photovoltaic cells

Figure 14.14 Distribution of solar energy

Fig. 14.15 Solar heating

Figure 14.16 A solar cell for the generation of electricity

Figures 14.17 a and b

Figures 14.18 a and b

Geothermal Power• The earth contains a great deal of heat,

most of it left over from its early history, some generated by decay of radioactive elements in the earth

• Interior of the earth is very hot– Abundant source of heat and hot water

• Magma rising into the crust bring abundant heat up into the crust as geothermal energy

• Heat escaping from the magma heats water and the water convectively circulates

Figure 14.19 Geothermal energy

Figure 14.20 Lone Star Geyser, Yellowstone

Figure 14.21 Geothermal power plants worldwide

Geothermal Power

• Applications of Geothermal Energy– Circulating geothermal water (not steam yet) through

buildings to heat them– Use the hot geothermal water to raise the

temperature of other water to reduce cost of heating that water

– Geothermal water (stream) can be used to run electric generators

• Environmental Considerations– Some locations have sulfur gases in the geothermal

fluids– Other chemical (caustic) elements may be present

that can clog geothermal circulation systems

Figure 14.22 The Geysers geothermal power complex

Figure 14.23 Mammoth Terraces, Yellowstone

Limitations on Geothermal Power

• First, most geothermal fields have limited life times and taper off

• Second, geothermal fields are stationary – not mobile

• Third, not many geothermal sites are suitable for energy production

Alternative Geothermal Sources

• Many areas away from plate boundaries have high geothermal gradients

• These areas contain hot-dry-rock type geothermal resources

• Deep drilling into such rocks may produce appreciable amounts of geothermal energy

Figure 14.24

Hydropower

• Falling or flowing water has long been used to produce energy for humans

• Hydroelectric power produces less than 5% of U.S. energy requirement

• Typically, a stream is dammed and the discharge is regulated to produce electricity– Hydropower is clean and non-polluting– Hydropower is renewable as long as streams

have water flowing in them

Figure 14.25

Figure 14.26

Figure 14.27

Limitations on Hydropower Development

• Reservoirs tend to:– Silt up– Increase surface area exposed to evaporation– Destroy habitats– Encourage earthquakes– Expensive to build

• Reservoirs are stationary power sources

Tidal Power and Ocean Thermal Energy Conversion

• Limited energy production possible– Not enough difference in high-tide versus low-tide

displacement of water (only about 1 meter difference)– Most economic potential requires about 5 meters

difference

• Ocean thermal energy conversion (OTEC) is another clean, renewable technology. It exploits the temperature difference between warm surface water and the cold water at depth

Figure 14.28 Tidal-power generation

Figure 14.29 Ocean thermal energy conversion

Wind Energy• The winds are ultimately powered by the sun,

and thus wind energy can be viewed as a variant of solar energy

• Clean and renewable energy resource• Many technological improvements have

increased the energy production from windmills• Areas of best wind generation potential tend to

be far from population centers that would benefit from them

• “Wind Farms” are large scale operations producing about 1 megawatt per windmill

• Abundant small scale windmills involve small wind turbines lifting water on a ranch or farm

Figure 14.30 The windiest places in the United States

Figure 14.31 “Art” driven by wind, Palm Springs, California

Figure 14.32 Wind power capacity

Biomass

• Biomass refers to the total mass of all the organisms living on earth

• Biomass energy uses discarded waste material that is burned as a fuel to produce energy

• Biomass fuels include wood, paper, crop waste, and other combustible waste

• Alcohol, as a fuel, is produced from grains, such as corn– Mixed with gasoline to form gasohol– Qualifies as a renewable resource