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arcosapphire t1_j1v81m6 wrote

Reply to comment by reb390 in ELI5 what would energy from nuclear fusion mean for humanity? by odyssey92

> Also fuel for fusion contains abot 100 times the energy per pound compared to fission.

Citation? I thought energy densities were pretty similar.

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reb390 t1_j1v9y29 wrote

You can find it in this table on Wikipedia: https://en.m.wikipedia.org/wiki/Energy_density_Extended_Reference_Table Or at this site: https://epress.lib.uts.edu.au/student-journals/index.php/PAMR/article/download/1383/1464?inline=1#:~:text=Energy%20density%20of%20Deuterium%2Dtritium,reactants%20and%20products%20%5B1%5D.

The key detail is that pure uranium is only about 1/3 the energy density of Tritium-Deuterium but fission rods are only a couple percent U-235.

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arcosapphire t1_j1vbzxn wrote

The chart shows 338 vs 86 TJ/kg for fusion vs breeder reactor. That's about 4x, not 100x. The U-235 is essential for the process but not the only source of energy in a fission chain reaction, which can convert U-238 to unstable plutonium.

However, as basically every fission reactor out there is a non-breeder reactor, I can see your point. If we count all the non-fissile parts of the fuel in the density equation (which is a debatable metric), then sure, the fuel density goes way down. But ultimately that isn't too relevant for figuring out the efficiency of the process overall.

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