Questions on Fusion

Kaldanis

I was hoping someone could help clear up a few things about fusion for me.

I've read that fission produces around 1,000,000 times more energy than any chemical recation and that fusion produces 3 to 4 times more energy than fission. I can only find 'estimated' numbers like these, but is there an actual comparison anywhere that says "A certain amount of oil gives X energy, the same mass used for fission gives Y and for fusion gives Z"?

Also, I read that when using a tokamak reactor it isn't possible to start a sustained fusion chain reaction, making it much safer than fission. Is this true?

I thought these questions would be simple enough to find the answer for but I can't find anything!

mathman

For a tokamak reactor to work, the plasma must be carefully confined. If anything goes wrong, it simply stops.

Pengwuino

No but surely you can do some googling and piece together the information on your own. I doubt many people would go beyond "gasoline vs. uranium" because it is quite staggering to think about how much mass is saved using uranium as power source instead of gasoline or coal or something of the sorts. However, I don't think you'll find too many people making such calculations because they're somewhat meaningless. Any form of nuclear power is orders of magnitude higher energy/mass than traditional methods and that's basically all there is to say.

Kaldanis

Yeah, I was beginning to think maybe people just didn't compare the data because it was pointless. Oh well! Thanks for both of the answers.

Drakkith

If you compare an individual fission reaction in Uranium to an individual Fusion reaction in, say tritium-dueterium, the fission reaction produces more energy. HOWEVER, uranium is hundreds of times heavier than hydrogen, so the energy density is much greater using Fusion. (More bang for the amount of fuel you use)

Astronuc

Browse this page - http://hyperphysics.phy-astr.gsu.edu...nucbin.html#c4

Magnetic confinement must address plasma instabilities and energy losses.

phyzguy

This page http://en.wikipedia.org/wiki/Energy_density has the comparison of nuclear and chemical energy densities that you are looking for.

Tyrannical

There are many different types of fission / fusion reactions, and the different reactions can provide different amounts of energy output. But what they all share in common is that a portion of matter is transformed into energy. Given the famous E=MC^2, a tiny amount of matter contains a LOT of energy.

phyzguy

One thing many people misunderstand (I'm not saying that you misunderstand, but your post implies it) is that they think nuclear reactions convert mass into energy via E=mc^2, but that chemical reactions don't. E=mc^2 is always satisfied, so that any reaction that generates an energy E will result in products that weight less than the initial reactants by the amount E/c^2. It is just that this mass deficit is much smaller for chemical reactions than nuclear reactions, and hence usually unmeasurable.

Tyrannical

Yeah, it is often over looked that there is a matter to energy conversion in chemical reactions too because the mass difference is so small.

Kaldanis

Thanks for all the help. Especially the wikipedia links, they seem to be exactly what I was looking for! The hyperphysics site is great too, I can't believe I forgot to check there for information on it.

I actually didn't realise it was the same conversion in chemical reactions, but it seems obvious now when I think about it. Thank you for pointing it out

Astronuc

Keep in mind that nuclear reaction energies are on the order of MeV as opposed to energies of eVs for chemical reactions. The mass defect in chemical reactions is negligible.

mheslep

With the plasma maybe so, with a 10 Tesla superconducting magnet going suddenly normal maybe not.

Drakkith

The quenching of a magnet, while not a good thing, isn't that dangerous overall. At worst you would have to replace the magnet and possibly some surrounding components. There won't be a huge explosion or anything.

capanni

The energy in the super conductive magnets in a tokamak (one which is big enough to potentially break even) is approximately 1/40 that of the first atomic bomb dropped in anger.

If that energy is releases it goes somewhere. Possibly helping to spread the lithium blanket which surrounds the plasma chamber, around the neighbourhood.

That is before you even consider the energy inside the reaction chamber.

These are not nice materials to have raining down, and as a bonus the materials that have become radioactive due to the fusion by products will be coming down too.

Drakkith

The energy is divided between the magnets. Even if all of them suddenly quenched at the same time, I don't think you would get a massive explosion. I'm guessing most of the energy would be released as Heat into the surrounding equipment. Alot of equipment damage maybe, but I don't think its nearly as destructive as you imagine it.

capanni

"energy would be released as heat into the surrounding equipment"
Yes and we are talking about a massive amount of heat, I certainly would not want to be anywhere near it.