Main

# Second Presentation

## Questions from the second presentation

1. You mentioned (or maybe someone else?) that radioactive waste is stored in pools, where the water in the pool absorbs the radiation from the waste. Can these excess heat from decaying waste be used to make a little more electricity? It seemed like it wasn't being done, so I guess I not?

# First Presentation

## Questions from the first presentation

1. What is the probability of each possible reaction when a neutron is added?
2. What are the final waste products of fission reactors, what are their half lives, and is there any possible mechanism to either reuse them as nuclear fuel or degrade into less troublesome waste products?
3. Where are current uranium reserves? Who produces the most? What are there ore grades?
4. How easy is it to make a nuclear fission reactor? How likely is it that developing countries build nuclear fission reactors?
5. How do you keep reactions stable in a nuclear power plant?
6. How do you separate U235 from U238 to use in power plants; how much energy is required for that process?
7. Is there a limit on the amount of uranium that is available for use in power plants?
8. At the end of the presentation, there was some discussion of the problems that using plutonium as a nuclear fuel may pose, in terms of the risk of nuclear weapons proliferation. Since the issue of proliferation is at the forefront of the debate over nuclear energy, it would be quite interesting to learn more about that.
9. One of your slides said that a 1 GW nuclear power plant emitted 28,000 curies of radioactive emissions.  Is this a lot?  I feel like I don’t really have anything to compare it to.
10. What causes the resonance peaks in the cross section vs. neutron energy plot?
11. How has the problem of nuclear waste been addressed? It seems that one of the biggest problems for nuclear in general is negative public sentiment, is there anything being done about this?
12. The section in Muller’s ‘’Physics for Future Presidents’’ on nuclear power was decent (according to me).  It gives some interesting facts regarding dangers (or supposed dangers) of radioactivity etc.  How dangerous, exactly, are our nuclear fuels and wastes?  Can we hold them safely?

1. What is a breeder reactor, who uses them, and why don't we? What advantages do they have?
2. What are some of the fourth-generation reactor designs?
3. What is the cost of nuclear electricity in the United States, Japan, and France? What accounts for the differences in cost?
4. Can nuclear reactors be made more efficient? What limits their efficiency?
5. How do thorium reactors differ from conventional uranium reactors? What is the potential for generating significant amounts of electricity from thorium? How long would they be able to operate?
6. What are the safety implications of operating existing reactors well beyond their design lifetimes?
7. Can energy be extracted from existing wastes? Can the wastes be neutered so that we don't need to store them indefinitely? Who is working on this problem?

Take a look at http://www.nea.fr/html/ndd/reports/2003/nea4372-generation.pdf, and other reports from the NEA.

(Please coordinate with Brianna.) ~Peter Saeta 2010 March 10 at 10:30 AM PST

#### {$^{235}U$}

Overview

When the less abundant isotope U-235 is struck by a neutron it will most likely split into two fission products (elements such as zinc and above), 2 or 3 neutrons, and heat. If exactly one of these neutrons splits another U-235, then the reaction will continue at the current level. If 2 or three of these neutrons hit another U-235, then the reaction will increase (possibly to critical levels). If no neutrons hit another U-235, then the reaction will die. Balancing the average number of neutrons which hit other U-235 is what allows for nuclear power generation. U-238 will absorb a neutron but is not fissile.

• How much material is consumed by a reactor?
• A gigawatt reactor uses 162 tons of Uranium (metal not ore, but also not enriched beyond 5%) per year (2)
• How much uranium remains from terrestrial sources assuming constant burn rates?
• If you also count phosphate deposits then it climbs to ~4.5 times that amount (2)
• How much uranium can be obtained from sea water?
• 3 mg/ m3=4.5 billion tons (2)
• Is this economical/how much would this increase the cost of nuclear energy?
• No industrial scale process demonstrated. But perhaps above $200 dollars/ton. • How safe are these reactors? • Current uranium reactors cannot produce an explosion like a bomb. If the water in the core evaporates, it will no longer slow down fast neutrons. Since fast neutrons tend to leave the reactor, this will halt the chain reaction. (1) • Can a significant amount of fuel be obtained from decommissioned weapons? • The enriched uranium in 20,000 warheads is equivalent to 10.3 billion barrels of oil. • 10% of American fuel comes from Russian weapons (7) • Very dependent upon disarmament treaties. • How much waste is generated by nuclear reactors? • Over thirty years of operation the American power industry has produced 1,800 tons of fission product. These are truly waste and must be stored. But they take up a mere 93 m^3. • The plants have also generated 50,000 tons of unused uranium in spent fuel. If reprocessed and used as fuel, this could power current plants for 850 years. • The plant have generated 200,000-280,000 tons of depleted uranium that, if used as fuel could last for 3,500 to 4,800 years. (5 p. 7) • A spent fuel rod contains 0.75-1% U-235, 0.9% Pu-239, 94.5% U-238, small amounts of transuranic elements. • The U-235 in our current waste represents 250 years of complete nuclear power generation. • How safe is nuclear power generation? • Results of a 1GW generator station in 1986.  Coal Nuclear Occupation Health Deaths 0.5-5 0.1-1 Occupational Health Injuries 50 9 Total Public and Worker Fatalities 2-100 0.1-1 Air Emissions (tons) 380,000 6,200 Radioactive Emissions (curies) 1 28,000  Reproduced from R. A. Hinrichs, M. Kleinbach, Energy-Its Use and the Environment, 3rd ed. New York: Brooks/Cole, 2002, Table 14.6  #### {$ ^{239}Pu $} (breeder reactors) Overview When U-238 in a reactor absorbs a neutron it becomes U-239. It decays, with a half-life of 23.5 minutes, to Np-239. This decays, with a half-life of 2.4 days to Pu-239. When a fuel rod is removed it contains 0.9% Pu-239. (5) • What is currently done with Pu produced from U238? • This waste is currently stored along with all other spent fuel. This is either on site or at a central storage location. • What are the risks associated with plutonium (terrorist bomb, uncontrolled chain reaction)? • Plutonium bombs are significantly easier to make than U-235 bombs because of the necessary trigger. • What is the history of breeder reactors in this country? • What is their history and use in other countries? #### {$ ^{233}U \$}

Overview

If Th-232 is included in a reactor, it will absorb neutrons and become Th-233. This decays to Pa-233 (half-life 22 min). Which decays (half-life 27 days) to U-233. U-233 can be used in reactors just like U-235. (1)

• How difficult it it to produce from Th232?
• It would need to be included in the fuel rods.
• Are their safety issues with its use (by products, proliferation, etc.)
• The thorium cycle also produced U-232. This isotope emits gamma radiation which makes it difficult and dangerous to work with and far easier to detect. Otherwise the technology for bomb making with U-233 is similar to U-235 and more challenging than Pu-239.
• What is the projected time to mature the associated technologies?
• only India is pursuing Thorium reactors. Although there may be more interest in other countries.

#### General

• How energy intensive is the extraction of these metals?
• Which countries have sources of these metals?

## Sources

1. Murray, Raymond L., "Nuclear Energy", TK9146 .M87 1993
2. MacKay, David. Without the Hot Air, http://www.withouthotair.com/Contents.html