It's not renewable, but there's a LOT of fuel around. We're just being grossly inefficient about how we use it. Breeder reactors convert thorium into uranium as they go, and the world is not in any way short of thorium. But they're expensive to run; it's cheaper, while the uranium lasts, to just burn it straight up in a less sophisticated and not quite so ruinously expensive reactor.

Uranium supplies aren't as low as it's commonly said anyway. People say there are 50-or-so years of supply. But that's only at the current price point. Once that runs out, let's say the price of uranium goes up by a factor of ten or so. That makes poorer uranium deposits economical to mine, it makes breeder reactors and reprocessing plants economical to run, and - since the cost of fuel is negligible compared to the enormous cost of running the plant itself - it doesn't much affect the price per joule of nuclear energy. Nuclear has enormous fixed costs, so it really becomes competitive when energy is expensive.

The issue with energy is not that we don't have plenty of it to use. It's that we don't have the wisdom as a species to use it well.

I'm having a hard time understanding what you're saying, Phobos.  Can you explain that a bit more for me?

There's something very important I forgot to tell you.
What?
Don't feed radioactive waste to the worms.
Why?
It would be bad.
I'm fuzzy on the whole good/bad thing. What do you mean, "bad"?
Try to imagine being swallowed whole by a giant annelid, and every molecule of your body being slowly digested over the course of several weeks.
Total food pyramid reversal.
Right. That's bad. Okay. All right. Important safety tip. Thanks.


And I second the explanation request. I'm a little hazy on how aiming into dead space is harder than aiming at the sun. I mean, granted, empty space is a lot easier to hit, but wouldn't aiming for the sun be a lot like hitting the broadside of a barn? The most effort is pretty much all in breaking out of orbit, after that it doesn't really matter much which direction you shoot for, does it?

So you've got your capsule of radioactive waste here on Earth and send it to out of Earth's gravity well.  Now, you could decide you want to send it down into the sun, but that takes some doing, because the capsule is traveling at the same huge velocity that the Earth is and if you want to actually get it into the Sun you have to cancel all the momentum of its orbit so it'll fall straight in instead of missing and falling into a new orbit that might very well hit something important some day.  Alternativly, you could speed it up in its path around the Sun so that it breaks free of the Sun's gravity and sails off into infinity. 

It turns out that doing the first actually takes about twice as much rocket propellant as doing the second.