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The energy density ... is far higher (theoretically) with fusion than with fission. Is that true by volume of fuel? By weight, the energy density is only 4 tim

The energy density ... is far higher (theoretically) with fusion than with fission. Is that true by volume of fuel? By weight, the energy density is only 4 times as high (D-T) (http://en.wikipedia.org/wiki/Energy_density#Energy_density_in_energy_storage_and_in_fuel http://en.wikipedia.org/wiki/Energy_density#Energy_density_i...). By volume, the density of uranium/thorium might very well be typically higher, since uranium/thorium is a heavy-metal, and therefore notably dense. For convenient fuel storage, the deuterium and tritium might be temporarily be converted to water. I'm not going to do the math right now, but I think it would be interesting to see how that compares volumetrically to uranium/thorium energy density. . The ... potential output is far higher Please clarify. . At current rates of use, uranium fuels will last about 1000 years. There are more than 40 trillion tons of uranium in the earth's crust (mostly in the continents, and mostly near the surface of those continents): http://nuclearinfo.net/Nuclearpower/UraniuamDistribution http://nuclearinfo.net/Nuclearpower/UraniuamDistribution The world currently uses ~60,000 tons per year of uranium. http://www.world-nuclear.org/info/reactors.html http://www.world-nuclear.org/info/reactors.html ~60,000 tons/year / 60x breeder-factor / 2.5x thermal-efficiency improvement = 400 tons/year fuel use. 40 trillion tons of uranium / 400 tons used/year = .1 trillion years of uranium. Thorium is available in the crust at some 4 times the ubiquity of uranium = .4 trillion years of thorium. Adding the uranium and thorium together gives us .5 trillion years of fission fuel. . How did you come up with 1000 years? Even limiting ourselves to the mere 9 billion tons of uranium/thorium present in seawater would provide 20 million years worth of fuel. ...And that supply is constantly being replenished by rivers, and by the seabed (the uranium/thorium suspended in the oceans is in equilibrium with that on the seabed -- if some is taken out, it is creates disequilibrium that can be relieved by the seabed uranium/thorium dissolving into the seawater).

jmackinn 18y ago
Here are the energy densities in MJ/kg: Deuterium-Tritium fusion - 337,000,000 MJ/kg Nuclear fission (of U-235) - 88,250,000 MJ/kg Natural uranium (99.3% U238, 0.7% U235) in fast breeder reactor - 24,000,000 MJ/kg Enriched uranium (3.5% U235) in light water reactor - 3,456,000 MJ/kg Natural uranium (0.7% U235) in light water reactor - 443,000 MJ/kg The higher output is a function of the higher energy density. Your numbers may be correct about how much uranium there is in the earth's crust but you are missing two very important points. Only a tiny fraction of the uranium is in concentrated enough deposits to allow for economic recovery of the mineral. This and the fact that U-235, the fissile isotope of natural uranium, occurs in only 0.711% of uranium containing minerals leaves only enough uranium with reprocessing for the next 1000 years. http://www.world-nuclear-news.org/ENF_Exploration_drives_uranium_resources_up_17_0206082.html http://www.world-nuclear-news.org/ENF_Exploration_drives_ura... Thorium required a breeder reactor in order to produce the U-233 necessary for fission, and as stated in another comment, these reactors are still in experimental stages and have a much lower level of operational safety record.
- DabAsteroid 18y ago
  The higher output is a function of the higher energy density. That might have cleared everything up for me, except that I do not know what you mean by "higher output". Are you referring to power output? You are saying that, generally, in a given case of equal-sized reactors, a fusion reactor would be able to produce higher power than a fission reactor?
- DabAsteroid 18y ago
  Only a tiny fraction of the uranium is in concentrated enough deposits to allow for economic recovery of the mineral. Given that that very point was addressed at the link I provided, one might suspect that you did not visit it before answering. It is not merely 40 trillion tons of uranium that are in the crust. It is 40 trillion of uranium that is also economically-recoverable. Why is nearly all of the uranium in the crust is economically-recoverable? It is because the energy density of uranium is so high. The same goes for thorium.
  - jmackinn 18y ago
    On the contrary the article you provided did not once mention the words 'economically recoverable'. What you are looking for is the reserves of Uranium in the world. Reserves, in mining means the amount of ore that can be economically removed from the earth. For those numbers please refer to the link that I listed previously. If the percent of uranium oxide in an ore is less than 0.1% (by weight) then it is not economical to mine.
    - DabAsteroid 18y ago
      Reserves, in mining means the amount of ore that can be economically removed from the earth. No, it doesn't. http://www.google.com/search?q=site%3Ajuliansimon.com%2Fwritings%2FUltimate_Resource+reserves http://www.google.com/search?q=site%3Ajuliansimon.com%2Fwrit...
      - jmackinn 18y ago
        Julian Simon was a professor business administration, not a mining engineer. Those articles refer to scare tactics presented in terms of resource scarcity by environmental fanatics. He says nothing about the definition of a mineral reserve. But I can help us with that. Reserve definition Reserve definition is undertaken to convert a mineral resource into an ore reserve, which is an economic asset. The process is similar to resource evaluation, except more intensive and technical, aimed at statistically quantifying the grade continuity and mass of ore. Reserve definition also takes into account the milling and extractability characteristics of the ore, and generates bulk samples for metallurgical testwork, involving crushability, floatability and other ore recovery parameters. Reserve definition includes geotechnical assessment and engineering studies of the rocks within and surrounding the deposit to determine the potential instabilities of proposed open pit or underground mining methods. This process may involve drilling diamond core samples to derive structural information on weaknesses within the rock mass such as faults, foliations, joints and shearing. At the end of this process, a feasibility study is published, and the ore deposit may be either deemed uneconomic or economic. from http://en.wikipedia.org/wiki/Mineral_exploration http://en.wikipedia.org/wiki/Mineral_exploration

jmackinn 18y ago

Here are the energy densities in MJ/kg: Deuterium-Tritium fusion - 337,000,000 MJ/kg Nuclear fission (of U-235) - 88,250,000 MJ/kg Natural uranium (99.3% U238, 0.7% U235) in fast breeder reactor - 24,000,000 MJ/kg Enriched uranium (3.5% U235) in light water reactor - 3,456,000 MJ/kg Natural uranium (0.7% U235) in light water reactor - 443,000 MJ/kg The higher output is a function of the higher energy density. Your numbers may be correct about how much uranium there is in the earth's crust but you are missing two very important points. Only a tiny fraction of the uranium is in concentrated enough deposits to allow for economic recovery of the mineral. This and the fact that U-235, the fissile isotope of natural uranium, occurs in only 0.711% of uranium containing minerals leaves only enough uranium with reprocessing for the next 1000 years. http://www.world-nuclear-news.org/ENF_Exploration_drives_uranium_resources_up_17_0206082.html http://www.world-nuclear-news.org/ENF_Exploration_drives_ura... Thorium required a breeder reactor in order to produce the U-233 necessary for fission, and as stated in another comment, these reactors are still in experimental stages and have a much lower level of operational safety record.

DabAsteroid 18y ago
The higher output is a function of the higher energy density. That might have cleared everything up for me, except that I do not know what you mean by "higher output". Are you referring to power output? You are saying that, generally, in a given case of equal-sized reactors, a fusion reactor would be able to produce higher power than a fission reactor?
DabAsteroid 18y ago
Only a tiny fraction of the uranium is in concentrated enough deposits to allow for economic recovery of the mineral. Given that that very point was addressed at the link I provided, one might suspect that you did not visit it before answering. It is not merely 40 trillion tons of uranium that are in the crust. It is 40 trillion of uranium that is also economically-recoverable. Why is nearly all of the uranium in the crust is economically-recoverable? It is because the energy density of uranium is so high. The same goes for thorium.
- jmackinn 18y ago
  On the contrary the article you provided did not once mention the words 'economically recoverable'. What you are looking for is the reserves of Uranium in the world. Reserves, in mining means the amount of ore that can be economically removed from the earth. For those numbers please refer to the link that I listed previously. If the percent of uranium oxide in an ore is less than 0.1% (by weight) then it is not economical to mine.
  - DabAsteroid 18y ago
    Reserves, in mining means the amount of ore that can be economically removed from the earth. No, it doesn't. http://www.google.com/search?q=site%3Ajuliansimon.com%2Fwritings%2FUltimate_Resource+reserves http://www.google.com/search?q=site%3Ajuliansimon.com%2Fwrit...
    - jmackinn 18y ago
      Julian Simon was a professor business administration, not a mining engineer. Those articles refer to scare tactics presented in terms of resource scarcity by environmental fanatics. He says nothing about the definition of a mineral reserve. But I can help us with that. Reserve definition Reserve definition is undertaken to convert a mineral resource into an ore reserve, which is an economic asset. The process is similar to resource evaluation, except more intensive and technical, aimed at statistically quantifying the grade continuity and mass of ore. Reserve definition also takes into account the milling and extractability characteristics of the ore, and generates bulk samples for metallurgical testwork, involving crushability, floatability and other ore recovery parameters. Reserve definition includes geotechnical assessment and engineering studies of the rocks within and surrounding the deposit to determine the potential instabilities of proposed open pit or underground mining methods. This process may involve drilling diamond core samples to derive structural information on weaknesses within the rock mass such as faults, foliations, joints and shearing. At the end of this process, a feasibility study is published, and the ore deposit may be either deemed uneconomic or economic. from http://en.wikipedia.org/wiki/Mineral_exploration http://en.wikipedia.org/wiki/Mineral_exploration