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reb390 t1_j1v78un wrote

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

This isn't really that accurate. Yes, both fission and fusion have zero carbon footprint and in the end will (at least in most cases) just boil water. Fusion however, if fully realized in its most ideal form, would allow us essentially turn seawater into fuel (so the source is basically limitless). Also fuel for fusion contains abot 100 times the energy per pound compared to fission. Finally, fusion has much less risk (but not zero risk) of danger from radioactive byproducts.

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arcosapphire t1_j1v81m6 wrote

> 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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CFDietCoke t1_j1v83xb wrote

> . Fusion however, if fully realized in its most ideal form, would allow us essentially turn seawater into fuel

Incorrect. Seawater is not H3 and cannot be fused.

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reb390 t1_j1vajxr wrote

Seawater contains Deuterium (D) which can be used in a full cycle fusion reactor. Basically D+D creates either Tritium (T) + H or He3+ a neutron. Those products can then react with one another. The easiest reaction to do is D+T since it requires the lowest temperautures but Tritium needs to be manufactured which can be difficult.

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