Fusion. Bout Time..

Finally, it's here. This will change everything.

Here's a question.

I assume that fission isn't necessarily dangerous as a process, but the danger comes from what must be used as fuel. All fission reactors use crazy radioactive stuff that's just dying to explode, and if/when it does, it sprays its poisonous self everywhere. And, even if it goes swimmingly, you still have crazy poisonous refuse, which is nearly impossible to discard of properly.

With fusion, you can use good ol wholesome H2 and poop out some entertaining He. I get that makes it "safe". But fusion is what our sun does, and that cranky ol git causes a thousand cancers from 93mm miles away.

What gives?

Quote: Face

I assume that fission isn't necessarily dangerous as a process, but the danger comes from what must be used as fuel.

Not exactly. Although Plutonium is about the most dangerous heavy metal there is.

Quote:

All fission reactors use crazy radioactive stuff that's just dying to explode,

Hell, no!

It's hard to get a chain reaction. It's very hard to get an explosion. To wit:

1) You need to separate the Uranium 235 out of the mix which contains the far more abundant Uranium 238. U-238 cannot, I repeat CANNOT, be made to blow up, no matter what you do to it.

2) For a reactor, you need to remix it with U-238 so it won't get too "hot."

3) For a bomb, you need your U-235 as pure as possible and then some. To detonate it, you must reduce its volume to a tiny fraction of what it was, and you need to do it to a large enough piece, say 10 kilos (abt 22 lbs). And it all must happen at once.

But 3) is the easy part. Separating U-235 from U-238 is hard work. Chemically they are identical, so that's out. Physically the U-235 is less massive, by the weight of three (3) Neutrons. Separating them is a difficult process which begins by making Uranium Hexafluoride gas (nasty stuff).

The thing is that fission requires a lot of slow neutrons to race all over the place to strike atoms so they'll split, thereby releasing energy and two more neutrons, which will hit two more atoms (eventually) which will split generating energy and two more neutrons, etc. (chain reaction, see?) I recommend looking up Disney's cartoon on nuclear power. It must be on YouTube by now.

But neutrons won't split only Uranium atoms. they'll split other things, too. Not cadmium, though. Cadmium can absorb neutrons all day long, ergo the cadmium control rods to regulate the reaction. But I digress. The reactor walls, which get a neutron bombardment daily, slowly become radioactive. The split Uranium atoms become other things, many of them more radioactive than the original uranium. these are the fission by-products, or nuclear waste, which are deadly dangerous. Not because they can blow up, but because they emit a lot of radiation, well above natural levels. And they stay radioactive for many years (millennia for some).

Quote:

With fusion, you can use good ol wholesome H2 and poop out some entertaining He. I get that makes it "safe". But fusion is what our sun does, and that cranky ol git causes a thousand cancers from 93mm miles away.

The direct by-product is Helium, yes. But Fusion produces positrons (positive electrons) and fast neutrons. fast neutrons aren't as apt to split atoms as slow neutrons, but they will, just at a slower rate. In time, the reactor walls also become radioactive. This can be calculated theoretically but not measured in practice. not yet anyway, because no fusion reactor has worked steadily for more than a tiny fraction of a second as yet.

Oh, the fusion reaction takes place at millions of degrees at very, very, very high pressures. If your containment fails, it will blow out explosively, much as a shaken champagne bottle will spew its contents. So there's that danger. The containment consists of a strong magnetic field.

Heinlein said it best: There Ain't No Such Thing As A Free Lunch.

Of course, as yet no more than a few grams of fuel have ever been used. And fusion is MUCH more energetic than fission. meaning fusion reactors will handle smaller masses of fuel. to give you an idea, a medium-sized atomic bomb requires about ten kilograms of Uranium or Plutonium to yield a few tens of kilotons. A hydrogen (fusion) bomb requires only a few grams of tritium to yield a few hundred kilotons. But to detonate the tritium, you need a regular A-bomb as the trigger. What Heinlein said.

Any thoughts on Thorium Reactors? From what I have read the waste is many times smaller and safer than current spent fuel.

Also the reason for using the radioactive U what ever it is, is because that's how we get the ingredients for nuclear bombs otherwise we wouldn't make nuclear power the way we do?

http://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reactor

Quote: Face

With fusion, you can use good ol wholesome H2 and poop out some entertaining He

In Back to the Future, at the end when
the prof comes back from the future,
he puts a banana peel in the fusion
engine for fuel. Is that possible?

Quote: Face

Here's a question.

I assume that fission isn't necessarily dangerous as a process, but the danger comes from what must be used as fuel. All fission reactors use crazy radioactive stuff that's just dying to explode, and if/when it does, it sprays its poisonous self everywhere. And, even if it goes swimmingly, you still have crazy poisonous refuse, which is nearly impossible to discard of properly.

With fusion, you can use good ol wholesome H2 and poop out some entertaining He. I get that makes it "safe". But fusion is what our sun does, and that cranky ol git causes a thousand cancers from 93mm miles away.

What gives?

I am not a scientist but IIRC the cancers the sun cause are because of the UV in the light it gives off. If you do fusion locally then the reaction will be much smaller and no light getting out. The way I read it anyways.

See Slashdot for roundup on Cold Fusion.

https://medium.com/starts-with-a-bang/the-e-cat-cold-fusion-or-scientific-fraud-624f15676f96

Quote: Evenbob

Is that possible?

In theory given enough pressure and temperature any atom could be fused. But their is no attempts to fuse anything other than hydrogen to make a power plant.

Quote: Pacomartin

In theory given enough pressure and temperature any atom could be fused..

This has been proved empirically from observations of stars and supernovae. All elements(*), save hydrogen and some helium, are the result of fusion either in the cores of main sequence stars, or the death-throes of a supernova.


(*) While Earth has gravity enough to hold on to an atmosphere, it cannot hold on to all gases. Any helium present at the Earth's formation is long gone, swept up by the solar wind. The helium currently found on Earth comes from the natural breakdown of heavy nuclei, such as Uranium and Thorium, which produce alpha particles when they decay. Alpha particles are made of two protons and two neutrons, or are Helium nuclei in other words.

All of Earth's hydrogen is bound in compounds, mostly in water.

Quote: Evenbob

In Back to the Future, at the end when
the prof comes back from the future,
he puts a banana peel in the fusion
engine for fuel. Is that possible?

The prof? I think you mean Doc.