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I believe the same argument was used for why we should just stick with oil. The energy density and potential output is far higher (theoretically) with fusion t

I believe the same argument was used for why we should just stick with oil. The energy density and potential output is far higher (theoretically) with fusion than with fission. You may also want to check your figures on the half a billion year fuel supply. At current rates of use, uranium fuels will last about 1000 years. Thorium is an alternative option for fission power; however, this is yet unproven in large scale deployment. There is also the fact that fusion reactors will produce far less high-level (long half-life) radioactive waste. 50 years ago, and even today, critics believed that there was no place for fission power but now it appears to be our greatest alternative to providing base load power over hydrocarbon based plants. The uses of fusion technology are not only limited to power production either. Fission power has resulted in advances in materials, medicine, the understanding of basic atomic science. There is no doubt that properly understanding fusion will lead to many advances in other fields.

DabAsteroid 18y ago
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.

DabAsteroid 18y ago

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.