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CU-Boulder PHYS 3070 - PHYS 3070 Homework Assignment 8

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PHYS/ENVS 3070 Homework Assignment #8: Problem #1: I have a business proposal for growing energy with a pine forest. I plan to have 10,000 acres of land with planted pine trees. Assume the pine trees gain net biomass at the "summer day" rate (quoted in Table 5.3) throughout the year. Every year, I harvest the trees and burn them in a power plant to generate electricity. How much electricity can I generate each year in kiloWatt-hours? If I wanted to remain cost competitive (e.g. 10 cents per kiloWatt-hour), what would my yearly costs have to be? Problem #2: Estimate the number of BTU that would be generated annually in the United States of America if all the municipal waste were incinerated. Assume 1000 pounds per year per person of burnable waster at 4300 BTU/pound. What fraction of the total annual energy usage in the United States would this represent? Problem #3: Decide which of the following statements are true (T) or false (F). A. The fuel rods in a commercial thermal light water reactor such as BWR have in them (initially) UO2 pellets with the U-235 enriched to nearly 100%. B. In the textbook, the breeder reactor will have to be used (eventually) if we are to continue to have energy from fission because we will need to use the U-238 instead of U-235. C. After the control rods are inserted into a reactor and it is shut down, a great deal of energy release continues in the core. This is because of the large heat capacity of the mass of the core. D. In a typical fission of a Uranium nucleus, the number of neutrons emitted is about two to three. E. The largest amount of radiation we receive from natural sources comes from radon gas.Problem #4: In a 2000 MegaWatt (electrical output) nuclear power plant, about how many uranium nuclei are fissioning per second? Hint: Calculate the energy per second of heat energy. Then using the energy per individual fission reaction, calculate the number of fission reactions in that one second time period. Problem #5: Decide which of the following statements are true (T) or false (F). A. Critical mass refers to the maximum amount of fissionable material that will sustain a nuclear chain reaction. B. As estimated by NUREG-1150, the probability for a nuclear reactor to release a significant amount of radioactive material is greater than 1 in 500 per year per reactor. C. A pen that has a mass of 15 grams has an equivalent energy of 300,000 kiloWatt-hours. D. The main reason for going to plutonium breeder reactors is to reduce thermal pollution. E. The fission probability for U-235 generally decreases as the neutron energy increases. Problem #6: Some estimates show that at Three Mile Island there was a release of 20 Curies (a measure of radiation) of I-131, which has a half-life of 8 days. How many Curies of radiation remained after 56 days?Problem #7: It has been estimated that in the year 2010, the United States will need 1012 Watts of electrical power produced by one thousand 1000 MW(e) power plants. These would most likely (given current trends) be powered by coal, though some could be from nuclear energy. A. If the energy is provided by U-235 burning reactors only, how many tonnes of U-235 will be needed annually? Assume an efficiency of these plants of 33%. B. How many tonnes of Uranium ore must be mined annually to meet this need? C. If the energy is provided by coal, how many tonnes of coal must be mined each year, again assuming an efficiency of 33% for the power plants? D. How much less carbon dioxide is emitted into the atmosphere in scenario (B) as opposed to scenario


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CU-Boulder PHYS 3070 - PHYS 3070 Homework Assignment 8

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