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Energy Resources Alternative 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
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Energy ResourcesAlternative Sources Chapter 14
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
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
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
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
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
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 14.12 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
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
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
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
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
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
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
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