Geology Chapter 15
What are some risks associated with fission nuclear reactors
1 Core meltdown: this occurs when the flow of cooling water to the reactor core is interrupted. The core overheats and turns into a molten mass that melts its way out of the containment building and into the environment, releasing high levels of radiation. There are also issues as to where to situate a nuclear reactor. Below are some of the considerations: 1. Reactors needs a water source for cooling purposes: this necessitates placing reactors are near rivers or large bodies of water, which makes water pollution a potential concern. New York City, for example, has 2 active nuclear reactors just 30 miles upstream that have only recently been legislated to shut down due to their longevity. 2. The further away the reactor is from a city, the higher the transmission costs: putting a plant too close to a city could place the population at risk; while putting the plant too far away means a higher cost of transmitting the generated electricity. Recall that at least 1/3 of the electrical power transmitted is lost as heat. 3. Underlying geology: reactors should perhaps not be placed along fault lines, near flood zones, or regions subject to tsunamis; but several in the US and abroad lie near such regions.
How might energy be harnessed from the oceans?
1. Harness energy from the tides: at least a 5 meter (16') difference needed between high and low tide to be effective for generating electricity, in addition to a bay / inlet with a narrow opening that could be dammed to regulate the water flow in and out. Examples where tidal-power is used to generate electricity includes St. Malo, France and the Bay of Fundy in Nova Scotia. 2. Ocean thermal energy conversion (OTEC): still in the development stages, this approach takes advantage of temperature differences between warmer surface waters and cooler deeper waters. Presently being developed in tropical island locales, where such temperature differences are at their maximum, such as Hawaii 3. Harness energy from the waves: even the bobbing of water in a wave can be harnessed to generate electricity: the bobbing can push water through a turbine (albeit slowly). Currently in use off the coast of Portugal.
What are some risks associated with spent fuel and nuclear waste handling
1. Radioactive material remains radioactive: it cannot be broken down into non-radioactive components. 2. Lack of permanent long-term storage: all of the world's radioactive waste is in temporary - as opposed to permanent - storage. Decisions have not yet been made as to how to store radioactive waste long-term. In the US, much of the high-grade nuclear waste is stored at the reactor site. 3. Decommissioning: nuclear power plants built in the US in the 1970s have been in operation for 40+ years. Reactors are aging and the cost to take one out of operation, break it down, and deliver the most radioactive elements of the plant to radioactive-waste disposal sites takes years of work and can tally nearly $1 billion per plant. 28 US reactors have been retired since 2010.
What are some of the pros and cons of nuclear energy
About 100 commercial nuclear reactors in the US are currently in operation. Those nuclear power plants account for about 9% of the nation's energy needs. Though nuclear power plants are more costly to build and pose a significant environmental risk, their operating costs are lower than that of a coal-fired plant, and the amount of energy released from the fission of 2.2 lbs of uranium is equivalent to 35,000 lbs of coal. Nuclear energy's strongest appeal, however, is that it emits no CO2 emissions. When countries sign pacts to limit their greenhouse gas emissions, their primary two options to choose from are nuclear power and hydroelectric power (i.e., building a dam).
How is wind energy generated? What are some of its benefits and limitations?
Benefits-Wind power is, like solar, renewable, but like solar it is also variable. A benefit is that as wind speed increases, power output increases to the cube. So if wind speed doubles, power output goes by a factor of 8 (23). In 2010, wind-powered electric generating facilities in the US accounted for less than 3% of actual electricity generation. However, wind-power capacity has been rising sharply in the US since 2000 and some hope that wind-power can supply 20% of our energy supply by 2030. Limitations-Again, in the US, the windiest spots in the country are unfortunately far removed from the areas that could make the best use of the wind-generated electricity. We are strongly limited by inefficiencies of long-distance electrical transmission. Another limiting factor is that strong winds do not always blow. As with solar, no effective way exists yet to store the electricity generated for later use. So despite the prevalence of wind on our planet, we have yet to find an effective way to harness it. About 1,000 wind generators (wind turbines) are required to generate as much power as an equivalent coal or nuclear-powered electric generating plant. There is also strong interest in constructing wind turbines offshore. Not only would the wind supply be plentiful, but transmission costs would be minimized for turbines that bordered coastal cities.
What is fission? What isotope of what element is used in the production of nuclear energy
Fission involves the splitting of a atom's nucleus into smaller ones. This releases energy. fission is the only commercially feasible process. In fission, the nucleus of most interest in modern nuclear power reactors is the isotope uranium-235, with 92 protons and 143 neutrons.
Is it possible to simply rely on the geothermal gradient to draw heat?
No the majority of the regions to apply this are in thinly populated regions of the United States
What is the difference between passive and active solar heating
Passive solar heating: requires no mechanical assistance: making use of an architectural design that enhances solar energy absorption (e.g. orienting a home to take advantage of winter and summer sun, using the house itself as a thermal reservoir). Active solar heating: involves pumps that circulate solar-heated water. The water is then stored in a tank to serve both as a space heater and a hot water supply.
What are some of the pros and cons (cons = limitations) of relying on solar cells as an alternative energy source?
Pros-Like solar heating, they do no emit pollutants, and solar cells have no moving parts. Cons- 1. Cost: though the prices have dropped considerably to have solar cells installed in one's home, the cost is still high, and solar cell companies are still working on producing viable business models to stay in business. 2. Efficiency: current solar cells are designed to only make use of a small fraction of sun's rays, preventing some industrial operations from using solar for energy-intensive applications 3.Scale: to keep a 100-watt lightbulb burning would require at least 2 square meters of collectors with the sun always shining. A 100-mega-watt power plant would require 2 square km of collectors. Using solar cells at that scale represents a large commitment of both land and the mineral resources from which the collectors are made (some of which are toxic, others of which the US would need to import). 4. Storage: the ability to store solar electricity is not practical beyond the homeowner stage.
What is geothermal energy? How do we make use of it? For large-scale use, where do we find an appropriate heat source? What are some drawbacks to geothermal energy
Rocks are a poor conductor of heat (their temperatures do not fluctuate quickly, especially at depth): the average temperatures at depth fluctuate only a few degrees, averaging 50-60°F. Geothermal heat pumps take advantage of this and are suitable for individual homes or for single building office dwellings. Pipes are drilled deep into the soil and circulate water down into the Earth and then back up: on a cool day, the cold water is warmed by the Earth, and that warm water can be used to heat a home. On a warm day, the warm water is cooled by the Earth, and that cooled water can be used to cool a home. No CO2 emissions are generated. Homeowners stand to save 30-70% on heating and 20-50% on cooling costs. The downside is the installation cost. traditional source draw their heat from existing underground magma chambers, most often associated at or near plate boundaries.The largest US geothermal facility is called The Geysers, in California, and has been operational since 1960. drawbacks with this method: 1. the warmed geothermal waters may contain contaminants that can damage ground or surface waters. 2. the heat source cools off with time, limiting the life of the facility to a few decades. 3. the power plants are not efficient for transmitting the power elsewhere; it is best used for sites nearby. Most large cities are not near geothermal resources.
In general, how to photovoltaic cells work
Solar cells, aka photovoltaic cells are a way to produce electricity using sunlight. The cells consist of two layers of semiconductor material oriented to produce an electric current when struck by the sun's rays.
What is enriched uranium?
U-235: 0.7% the only naturally occurring fissionable isotope of uranium, this isotope is essential to the production of nuclear energy U-235 is processed from 0.7% to 3.0% before it is used in a reactor: processed fuel is called enriched uranium.
In general, what happens in a nuclear fission chain reaction
Uranium-235 is induced to undergo fission by firing a free neutron into the nucleus of one U-235 atom. When the neutron strikes the U-235 nucleus, the uranium nucleus splits into two smaller nuclei and produces subatomic particles, free neutrons, and heat. Each released neutron then strikes another U-235 atom, releasing more neutrons, beginning a nuclear chain reaction. Fission-powered nuclear reactors rely on controlled chain reactions for their energy supply. The energy released heats cooling water that circulates through the reactor's core. That heat is converted into steam, which runs turbines to produce electricity.
Why are biofuels called unfossil fuels? What is the difference between waste-derived and alcohol-derived fuels? What crop is used to create ethanol? What are some benefits and drawbacks to relying on ethanol as an alternative fuel source
biofuels uses the remains (or biomass) of dead organisms to produce energy. Indirectly, since these organisms need sunlight to grow, biofuels can be considered a type of solar energy. They are also considered "unfossil fuels" because they are created from recently dead organisms, as opposed to long-fossilized ones. Waste-Derived Fuels There is increasing interest in burning waste plant materials - either crop waste or urban refuse to provide heat for electric generating plants. Some waste-derived fuels are liquids, or research is ongoing to derive liquid fuels from animal waste, such as manure, which is rich in organic matter. Fuels can be derived from vegetable oil or animal fats to run diesel- powered engines. Another waste-derived biomass fuel growing in use is "gas from garbage," or biogas. Landfills and manure piles can contain large amounts of trapped methane gas (CH4) that develop when organic waste breaks down. Alcohol Fuels Most gasoline contains about 10% ethanol, an alcohol produced from domestically-grown corn. The reason for the mix is that the more alcohol can be used, the further the gas supply can be stretched, lessening our reliance on imported fuels. This method became popular in the 1970s as gasoline prices began to increase. The concern about ethanol as a fuel source is that it can take more energy to grow and harvest the corn than is released from burning the ethanol. A further concern is that food is being grown for use other than to feed those who might otherwise need it, and has led to pressure to grow crops on land that might be normally unsuitable or unsustainable for short or long-term use. These reasons, among other, are in part why researchers are trying to produce ethanol from waste organic matter instead of from living crops.
How is hydroelectric power generated? What are some of its benefits and limitations
the power is generated from the energy of the flowing or falling water. Usually, this is generated by damming up a river and releasing the water slowly so that the energy generated is constant as opposed to seasonal. Hydropower is a clean energy source, and a further benefit is that the water used is not consumed - it is just "passing through" and then returns to its source. Limitations on Hydropower Development 1. Loss of ecological habitats, both upstream (which gets flooded by the dam) and downstream (which loses its water source, sediment supply and reduction in periodic floods). 2. Silting up of reservoirs: because only water passes through the dam, the regions downstream lose their sediment supply, which leads to erosion of the downstream sedimentary structures (deltas, beaches, etc.); while the region above the dam accumulates an excess sediment supply, which can choke up the streambed. 3. Dam failure: there are over 1,000 dams in the US (not all for hydropower) and invariably some fail, either due to poor construction or underlying geology
