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0 pointsnobody99994y ago0 comments

>What does fusion give us that existing nuclear power plant tech doesn't?

The energy generated per unit mass in a fusion reaction is ~9 times that generated in a fission reaction[0]:

   Considering the mass of the four protons/hydrogen
   nuclei (4.029106u) and the mass of the Helium 
   produced (4.002603u) we get a mass difference of 
   0.026503u or 24.69MeV. So it is easy to see that 
   fusion reactions give out more energy per 
   reaction. However, the energy per unit mass is 
   more relevant. This is 0.7MeV for fission and 
   6.2MeV for fusion so it is obvious that fusion is 
   the more effective nuclear reaction.

Which leads to a great deal of confusion on my part as to why we're not spending enormous amounts of money on Fusion R&D. Given the potential of the technology, you'd think we'd have long ago decided to spend whatever was necessary to commercialize hydrogen fusion as a power generation mechanism.

The phrase "electricity too cheap to meter" is likely somewhat hyperbolic, but in comparison to pretty much any other mechanism fusion is enormously more productive and efficient.

[0] https://www.physlink.com/education/askexperts/ae534.cfm

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Firadeoclus4y ago

Would you be willing to elaborate why "energy per unit mass" matters when the mass in question is a completely different substance with different cost and availability profile?

If we found a way to extract 10x as much energy from coal as we currently do, electricity from coal wouldn't become 10x cheaper, nor would we build power plants 10x as big.

nobody9999OP4y ago

>Would you be willing to elaborate why "energy per unit mass" matters when the mass in question is a completely different substance with different cost and availability profile?

Sure. Specific energy (or energy per unit mass) between different types of materials makes a huge difference. For example (Source here[0]):

   Material   Type of generation   Specific energy (MJ/Kg)
   Hydrogen   Fusion               639,780,320
   
   Coal       Oxidation            24.0-35.0

Note the specific energy of a Kg of burned coal compared with a Kg of fused hydrogen. Fused hydrogen generates roughly 200,000 times the energy per unit mass than burning coal.

You're right. Cost and availability play into this as well. There are estimated to be ~1.06 trillion tons of coal on earth[1], hydrogen is the most abundant element in the universe and even makes up a significant amount of the mass of coal.

Burning hydrogen/hydrocarbons is, compared to fusing hydrogen, an incredibly inefficient process.

I'd say that being able to generate 200,000 times the energy per unit mass is an important consideration.

As for availability, hydrogen is more abundant and cheaper to produce (unless you have petatons of plant matter, the right conditions and a few tens of millions of years at no cost to you) than any fossil fuels. Or just about anything else.

[0] https://en.wikipedia.org/wiki/Energy_density#List_of_materia...

[1] https://www.worldcoal.org/coal-facts/what-is-coal-where-is-i...

Edit: Clarified availability.

pfdietz4y ago

It's not that cost plays into it, it's that cost (broadly defined) matters, and the metric you have chosen doesn't matter. As a consumer I don't care how energy dense a fuel is; I care only about what it costs me to get that energy.

You might try to argue high fuel energy density implies low cost, but this is clearly not the case in general.

Firadeoclus4y ago

Exactly, and fuel is only a part of the consideration.

Though it's also true that the infrastructure to process, deliver and store large amounts of fossil fuel comes at a higher cost than is usually considered (as some of it is subsidised and socialised), plus there's the pollution.

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Firadeoclus4y ago

Would you be willing to elaborate why "energy per unit mass" matters when the mass in question is a completely different substance with different cost and availability profile?

If we found a way to extract 10x as much energy from coal as we currently do, electricity from coal wouldn't become 10x cheaper, nor would we build power plants 10x as big.

nobody9999OP4y ago

>Would you be willing to elaborate why "energy per unit mass" matters when the mass in question is a completely different substance with different cost and availability profile?

Sure. Specific energy (or energy per unit mass) between different types of materials makes a huge difference. For example (Source here[0]):

   Material   Type of generation   Specific energy (MJ/Kg)
   Hydrogen   Fusion               639,780,320
   
   Coal       Oxidation            24.0-35.0

Note the specific energy of a Kg of burned coal compared with a Kg of fused hydrogen. Fused hydrogen generates roughly 200,000 times the energy per unit mass than burning coal.

Burning hydrogen/hydrocarbons is, compared to fusing hydrogen, an incredibly inefficient process.

I'd say that being able to generate 200,000 times the energy per unit mass is an important consideration.

[0] https://en.wikipedia.org/wiki/Energy_density#List_of_materia...

[1] https://www.worldcoal.org/coal-facts/what-is-coal-where-is-i...

Edit: Clarified availability.

pfdietz4y ago

You might try to argue high fuel energy density implies low cost, but this is clearly not the case in general.

Firadeoclus4y ago

Exactly, and fuel is only a part of the consideration.

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