# Thread: Help with fusion number crunching

1. ## Help with fusion number crunching

So I'm an ME student with a basic knowledge of the physics and chemistry in my field.

I read for a paper a couple years ago that the EU is looking to break ground on a fusion reactor in 2025.

My understanding of fusion is the difficulty is maintaining the enormous heat and pressure to have a stable reaction. The solution to that is a magnetic bottle a la Spider-Man 2.

The numbers part I'm curious about is how much energy is released in a fusion reaction? I know it's at least an order of magnitude larger than fission, but some numbers would be nice. I've heard crazy things, like one or two stable fusion reactors could supply enough power for the planet.

Secondary question, how would the released energy be harnessed. You can't exactly do a water turbine if we are looking at tungsten melting temperatures.

2. ## Re: Help with fusion number crunching

For the turbine, you'd probably use a steam turbine, like you do in a fission plant:
Spoiler: Picture

How much energy is put out depends on how much fuel you put in, for instance the ITER fusion reactor aims to put out 500 MW.

On more general principles the energy released in any fusion reaction depends on the difference in mass between the reactants and the products in the reaction, E = Δmc2.

3. ## Re: Help with fusion number crunching

I'm familiar with Einstein's theory of (General?) Relativity. However the mass term was tripping me up. I wasn't sure how much mass was "lost".

I've zero experience with quantum mechanics so the subtleties were escaping me.

But 500MW? That gives me a soft number. Now to compare output to a fission reactor out coal plant for some prospective. I'm off!

4. ## Re: Help with fusion number crunching

Originally Posted by Sivarias
I'm familiar with Einstein's theory of (General?) Relativity. However the mass term was tripping me up. I wasn't sure how much mass was "lost".
That part is actually really easy - just look at the molecular weights of deuterium and helium to a whole lot of significant figures. Alternately there are plenty of charts that graph per-nucleon energy levels that can be easily used instead.

5. ## Re: Help with fusion number crunching

What are the names of these charts for Google purposes?

6. ## Re: Help with fusion number crunching

"Nuclear binding energy per nucleon" will do the trick, although a lot of them have weird sign conventions such that going higher on the graph corresponds to a lower energy state, such as this example. Also that's energy and not mass, so it cuts out a lot of the middle steps.

*Which isn't exactly new when dealing with energy.

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