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Fission and Energy Conservation

Questions on the first presentation

  1. What is the current procedure for dealing with all of the current power plant related waste? Where is it right now?
  2. How quickly could we build a sizable Pu-239 or U-233 economy?
  3. You mentioned in the presentation that some of the materials used to construct a nuclear power plant had detrimental effects on the environment. Which materials? How does the environmental harm compare to renewable energy sources?
  4. Please include visual representations, especially of decay sequences and power plant reactor mechanisms. Describing the current Yucca Mountain question was a good tie-in between science and policy, I thought. Speaking of which, are there any international bodies that regulate or inspect nuclear power plants or that determine where they can be built (i.e. not on fault lines)? I think I heard that China is building quite a few...
  5. Do you think the US should build more nuclear reactors? Is nuclear energy safe enough?
  6. You mentioned Yucca Mountain as the main option for storage of the country's nuclear waste. How viable are other options, such as dumping the waste into subduction zones in the ocean?
  7. At the current rate we are generating nuclear waste, how long until we run out of (good) space for us to put it in, and have do something else?
  8. What are the advantages and disadvantages of breeder reactors over 'normal' reactors? What are the trade-offs?
  9. Why can’t we launch the waste into space or the Sun?
  10. How much uranium is predicted to be in the world? How much energy on average can a typical nuclear power plant produce? How many nuclear power plants would be require to power the US? Is that amount feasible? How long does it take to build a power plant?
  11. What’s the estimated amount of uranium that we can mine? When is it going to run out?
  12. The US just approved $8 billion in loans for new fission plants --- what type of reactor are they going to build and what are their plans for safety and waste management?
  13. How do next generation reactors compare to current ones in waste production, and how do the properties of this waste compare to the waste generated by current reactors?
  14. Is the smaller scale of the new nuclear power plants because that is all they are capable of or is it because they are prototypes?
  15. What does the history of nuclear power and its development look like?
  16. Are there people who oppose the use of nuclear power? What are their reasons for opposition?
  17. What limits the power plant’s size?

Some additional questions

  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?

~Peter Saeta 2010 March 10 at 09:54 AM PST


Fission

Why Fission?

  • Fission is considered by many to be play an important role in energy in the coming years because it emits no CO2 or other green-house gases
    • But it does produce nuclear waste, and green-house gases are released in the building of new plants
  • 8% of the Earth's total energy related carbon is produced by fossil fuel plants in the United States 1
  • In contrast, 16% of the world’s energy is supplied by 438 commercial nuclear reactors.
    • Currently about one-fifth of U.S. electricity is generated by nuclear power plants, the only non-greenhouse emitting fuel source to produce over 10% of the total energy usage
Energy Usage Graph
Net Generation Shares by Energy Source, Year-to-Date through October, 20092
  • The installation of even a single Nuclear Power Plant can make a huge difference:

Annual Carbon Displaced by 1,000 MWe Nuclear Plant Operating at 90 Percent Capacity Factor 1

Alternative Fuel

Carbon Displaced (Metric Tons Carbon Equivalent)

Coal

2,098,580

Petroleum

1,640,995

Natural Gas

1,041,401

  • In 2001, Francois Lamoureux, the European Commission's Director-General estimated that “nuclear energy will account for savings of around 300 million tonnes in CO2 (carbon dioxide)emissions between now and 2010–equivalent to halving the number of vehicles on (European Union) roads.” 1

Types of Fission

(See also the page on fission by Daniel O'Neil) for more information

  • 235U
    • All most all nuclear power plants do fission with uranium-235. Uranium-235 is the much rarer isotope of uranium: usually uranium is 99.3% 238U and only .7% 235U. There are several different kinds of uranium-235 power plants, differentiation by the way the moderate the reaction. In the reaction, a 235U atom is struck by a neutron, releasing heat and two or three neutrons, with lighter elements left behind as by-products. One of these neutrons will most likely then go on to react with other uranium atoms. When 238U is struck by a neutron, it simply absorbs it. Another difference between the two is that 238U absorbs the most of (and only) the high-speed neutrons, so if all of the neutrons are high-speed, with the huge disparity in concentrations, no chain reaction will take place. Thus moderators are introduced to slow down the neutrons so that they are not absorbed and can create the reaction. There are different types of moderators, and this is mainly what differentiates the types of reactors.
      • Reactors which use deuterium (heavy water), like those in Canada, or graphite, like in Chernobyl, can actually use unrefined uranium. Neither deuterium nor graphite absorb many neutrons. Instead, the neutrons bounce around until they are slow enough to not be absorbed by the 238U, and thus react with the 235U.
      • Reactors which use ordinary water, like in the U.S., need partially enriched uranium, which is about 3% 235U. When the water absorbs the neutrons, it becomes deuterium. This absorption causes a decrease in the chain reaction, thus the need for the partially enriched uranium.
    • Uranium-235 reactors cannot explode like an atomic bomb - Richer Muller 4 describes the potential explosion in a reactor like Chernobyl's as like TNT, but with the added factor of radiation. This is because failure to moderate results in a halting of the chain reaction, and even run-away moderated chain reactions like in Chernobyl still can't get enough reactions in before the pressure causes an explosion.
  • 239Pu and 233U are not in widespread use. They both use by-products of 235U, and thus you can create fuel by running the reactions - hence the term "breeder reactor" is often used. However, unlike 235U reactions, plutonium-239 reactions occur with high-speed neutrons, thus the chain reactions can run away, creating a nuclear bomb-like explosion. Yet they are an attractive option, because they use what would otherwise be nuclear waste. Europe and India are looking into these types of reactors.

The Future of Fission

The Gen IV Reactors are theoretical nuclear reactor designs that are currently being researched. They aren't expected to be available for widespread commercial use until 2020-2030. There are two main types: Fast Reactors and Thermal Reactors.

  • Thermal Reactors:
    • Very-High-Temperature Reactors such as pebble bed reactors. Pebble bed reactors contain 2 1/2 -inch deep beds of pyrolytic graphic pebbles. Pyrolytic graphite is extremely resistant to heat (in contrast the the graphite used in Chernobyl). PBR's are very safe because the reaction will self-regulate in the case of accidents and slow down at temperatures that are below those than cause damage to the pebbles, without human or mechanical interference. They are also more efficient: 40-50% of the uranium goes into electricity, rather than 32-35% from normal reactors4. However, generally speaking these reactors operate on a significantly smaller scale: 130 MWe as opposed to the more common 1000MWe reactors.1 There are several prototypes, and research is being done in the U.S., China, and South Africa, but the only one currently operating is in China.
    • Supercritical-water-cooled reactors use supercritical water as the moderation and coolant fluid.
    • Molten-Salt reactors use molten salt as a coolant, and a graphite core as the moderator
  • Fast Reactors
    • Fast Reactors are like breeder reactors - the use the neutrons at high-speeds to create the reactions.

There are Gas-cooled, Sodium-cooled, and Lead-cooled fast reactors being researched.

  • If fusion is to be an energy source in the future, how can we assure safety, and restore positive public opinion about nuclear energy?

Disposal of Waste

  • The radioactive waste isn't just the spent fuel rods. It is also the tailings from mining the uranium, the water used to cool down the reactors, and the by-products of refinement.
  • Since 1957, when nuclear power first began in the U.S., 38,000 tons of high-level nuclear waste have been generated from nuclear power alone1, and 27,000 tons of low-level nuclear waste3. This is saying nothing about the thousands of tons of waste from production nuclear weapons that also have to be safely disposed of. The Department of Energy has a long history of poor disposal techniques of nuclear waste, dumping it in rivers, oceans, and shallow landfills. The water used to cool reactors, for example, typically become radioactive, but is usually dumped right back into the source.3
  • Currently, the only major proposal for the disposal of the waste is to bury it deep in Yucca Mountain. As it is, all the waste we have is simply kept in storage, and in the past, much of it was disposed of inappropriately due to the large amounts generated by the production of nuclear weapons. There are strong proponents and opponents to this proposal.
  • Opposed:
    • The original notions about Yucca Mountain was that it was geologically stable, very dry, and had a very thick unsaturated zone (the area between groundwater and the surface). Additionally, it was thought that the zeolite minerals found in the area made it even better - Zeolites absorb uranium and other radioactive materials. But it has since been discovered that water moves through the area much faster than previously thought, there are major fault zones, and previously unknown ways for radiation to leak. The zeolites producing small "colloid" particles that then can travel into the groundwater and leave the containment zone. Since there is more water than originally thought, the 'anti-leak' canisters are officially estimated to fail completely around 5,000 years. The conditions in the area are conducive to the oxidation of the radionuclides, releasing them relatively quickly. 3
  • In favor:
    • Muller argues that "calling storage unacceptable is itself and unacceptable answer. We have the waste, and we have to do something with it."4 He says that aside from the plutonium, we don't have to worry about the radioactive waste beyond 10,000 years. This may seem like a long time, but it doesn't have to be 100% secure for all 10,000 years. Since the radioactivity is about 1000 times the radioactivity of the uranium naturally present, if we have a leakage change of .1%, the "net risk" is 1000 x .001 = 1, so no worse than if we hadn't mined it at all. Additionally, this level of security isn't necessary for all 10,000 years. after 300 years, the radioactivity will have gone down by a factor of 10, making it only 100 times worse than natural uranium, so security only need to be at the 1% risk of leakage level, and it will continue to go down. Moreover, this is assuming 100% leakage. If there is 100% chance of a 1% leak after 300 years, then we have again the same risk level as if we hadn't mined it at all. Thus we don't have to worry about the security nearly as much as most people think, and since we have to put it somewhere, this is a good enough solution.
  • Some other suggestions include sending it in a rocket into the sun and burying it deep in the ocean.

Sources

  1. http://tonto.eia.doe.gov/FTPROOT/nuclear/ghg.pdf
  2. http://www.eia.doe.gov/cneaf/electricity/epm/epm_sum.html
  3. The American West at Risk
  4. Physics for Future Presidents