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0 pointscredit_guy7y ago0 comments

> We need 30 years of nuclear fission before we can sustain fusion.

Not sure where that comes from. I don't think we'll have competitive fusion in the next 50 years. Sure, people who talk about ITER draw (quite optimistic) plans for when we'll be able to get more from the fusion reaction than what energy we pump in, but they forget to mention that's not the end of the story. Fusion may be clean, but it's terribly inefficient. In the Sun, fusion generates about the same amount of energy per liter as a liter of warm chicken soup releases to the ambient environment [1]. The Sun is huge, so overall the amount of generated energy is huge, but on Earth a power plant that has the same power density as the Sun would need to have a volume of 4 billion m3 to be similar to a typical fission power plant (1GW). That's 4 cubes of 1 square kilometers each. And don't bet on us getting to that efficiency in the next 20-30 years. So, sorry for the bad news, but no, we won't have viable fusion power plants in the foreseeable future.

[1] https://physics.stackexchange.com/questions/370899/suns-powe...

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nbanks7y ago

The Joint European Torus had a 67% efficient reaction back in 1997. The torus wasn't designed for it, so they never tried again. It seams that ITER could achieve break-even quite realistically simply because tokamak reactors are more efficient when they're bigger. Yes, it has to be hotter than the sun and use a deuterium/tritium fuel, but it's all doable with known physics.

I'm not sure when or if a sustained reaction can be done economically.

sien7y ago

There are a number of interesting companies looking at fusion.

High Temperature Superconductors change what you can do for Tokomaks.

In the US Commonwealth Fusion Systems are exploring these paths:

https://en.wikipedia.org/wiki/Commonwealth_Fusion_Systems

In the UK Tokomak energy are exploring ideas as well:

https://www.tokamakenergy.co.uk/

This video explains why high temperature super conductors can enhance fusion's prospects:

https://www.youtube.com/watch?v=L0KuAx1COEk&t=3642s

theothermkn7y ago

> The Sun is huge, so overall the amount of generated energy is huge, but on Earth a power plant that has the same power density as the Sun would need to have a volume of 4 billion m3 to be similar to a typical fission power plant (1GW). That's 4 cubes of 1 square kilometers each.

The density, in terms of fusion events per m^3 per second, is orders of magnitude higher for a tokamak than in the Sun. Stars are very inefficient at fusion, as you point out, because the cross section oh H-H fusion is so low. Deuterium-Tritium fusion has a higher cross section, and the conditions we can reach realize a much higher rate of fusion.

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