Nuclear Fusion

[VicTree]

Before you continue reading, I'd like to say that I have minimal education in physics, and that this is a topic I'm interested in. If you don't have time to waste, please move on, and have a nice day =)

 

I was reading up on the Chernobyl disaster, and how Fission is so far the only attainable method of Nuclear energy, and how Fusion gives 3-4 times the power of Fission, and doesn't have near the same quantities of harmful byproducts.

 

So, my question is, what is preventing us from being able to use Fusion? And why are high density and temperature necessary to create it?

 

Again, bear in mind that I'm a novice with minimal education in physics. Thank you =)

[insane_alien]

plasma confinement is hard. not to mention the extreme heat and neutron fluxes make material choice very limited. its also really hard to build small test-scale fusion reactors, the bigger the easier, but also the more investment you need.

 

the high pressures and temperatures are necessary because you need the nuclei to get really really close when they collide. this means they need to be moving FAST. and fast moving atoms is the definition of high temperature.

[swansont]

In addition to what insane_alien said, also note that nuclei repel each other electrostatically. There's a large potential barrier to overcome, which is why you need the high speeds.

[rogerxd45]

yea i think a lot of it has to deal with being able to controle the heat. it would pretty much just melt everything close to it.

 

but if some day we can harness fusion power our energy trouble will be a thing of the past, and i have faith that someday it will happen but not for a while and probably not in my lifetime

[Mr Skeptic]

To get fusion to happen, we need to heat the plasma to temperatures at which all materials evaporate. So, we can't just stick it in a box, and have to confine it by other means. Magnetic and inertial confinement are two options, each with their own problems. Magnetic confinement uses tons of energy and also is not perfect. Inertial confinement means you are making small explosions and using the fuel itself to hold the material in place for a tiny fraction of a second.

 

The reason for all this is that the nuclei are positively charged and so repel each other quite strongly. To get fusion to happen, two nuclei need to get close enough together. The heat is needed for the collisions to have enough energy to pass that barrier. The density is needed so collisions are frequent enough.

[Moontanman]

I don't think standard fusion is the panacea everyone seems to think it is. Fusion releases energy in the form of neutrons. These neutrons make surrounding materials radioactive. Stopping these neutrons is difficult and makes the material that stops them radioactive. there is a possibility of aneutronic fusion which could be used to turn electromagnetic radiation directly into electricity with no neutrons and the accompanying radioactivity but we will have to master regular fusion first. The fuel for aneutronic fusion is very rare on the earth as well, further compounding the problem.

[swansont]

Neutron activation of containment vessels is a very small component of the current nuclear waste problem, AFAIK.

[dalemiller]

the high pressures and temperatures are necessary because you need the nuclei to get really really close when they collide.

 

How far apart can nuclei otherwise be during collisions?

Edited January 29, 2010 by swansont
fix quote tag

[insane_alien]

under normal circumstances, you can probably get it down to 0.1 angstrom or so, for fusion you need something like 0.0001 angstrom. i don't know the actual numbers but its going to be on that sort of scale.

[Electric]

 

So, my question is, what is preventing us from being able to use Fusion? And why are high density and temperature necessary to create it?

 

If fusion reactors are used, then

disasters will not be similar to Chernobol.

Why?

Fission reactors in large reserves of fuel (uranium 235 or plutonium 239 is ~ 500-700tonn).

In Chernobol explosion threw portion of fuel(uranium ~ 40 tonn) into the atmosphere.

Fuel(deuterium and tritium) in fusion reactors is very small (a few killogram).

 

For fusion reactions require extremely high temperatures or pressures.

No such materials capable of withstanding even the minimum temperature fusion reactions. Therefore it is necessary to raise it (temperature).

(Very high temperature (~ 103 * 10 ^ 6 degrees Kelvin) is needed to accelerate the reaction in fusion reactors.)

Edited January 28, 2010 by Electric

[insane_alien]

electric, in a fusion reactor you only have a few GRAMS of fuel in the chamber. not kilograms.

 

and while it is very hot, there isn't much heat(dues to the low mass of burning plasma) so it twill be covered by evapouration of the reactor walls when containment is lost.

[Astroreeper]

Of course this is one of the most challenging problems facing science. Yet the investment is happening at a relitavly low level.

 

But it will happen so long as the theories are correct. All that is required is the third stage fuel of Helium 3 for the most difficult yet efficient reactions to occur.

 

http://revver.com/video/458826/nuclear-fusion-helium-3/

 

There are manned missions to the moon by of course NASA, ESA, China and Russia. With Japan and even India said to have an interest.

 

Why? Because Helium 3 in abundance is worth about £3bn per ton, if we can make a Helium 3-Helium 3 reaction.

 

Currently we have been floundering with Trtium-Deuterium reactions which do indeed expell neutrons that would damage any reactor.

But helium 3 is said to be a true fusion without cast off, and condensates to plain old water.

 

It will happen guys, we just have to find the investment which will require a higher profile of the technology.