Could the Sun be used to dispose nuclear fission waste??

[Lord of the Abyss]

Given that the Sun isn't solid and that they are made of much heavier elements than the hydrogen and helium that make up most of the Sun I expect that their vaporized remnants would sink, eventually. How long that would take though, I've no idea.

[Lord Baal]

I quite like this thread, it has reading value

[Imperial528]

Given that the Sun isn't solid and that they are made of much heavier elements than the hydrogen and helium that make up most of the Sun I expect that their vaporized remnants would sink, eventually. How long that would take though, I've no idea.

IIRC, a long time. While the sun is by no means a solid mass, it isn't necessarily easy to go through, either. At the surface layers it isn't quite dense, but in the layers above the core (and of course the core itself) are quite dense, to the point where energy coming from the core can take many thousands or even hundreds of thousands of years to reach the surface, and that is with all the energy pushing in the same direction. With anything trying to sink in, it has to push past all of the energy trying to get out.

[Lord Baal]

But gravity don't pull the thing the other way than the energy (photons)?

I once took a beginners class to astronomy, as a matter of fact I belong ALDA (Asociación Larense de Astronomia, or Larense Association of Astronomers), but that's an amateur mostly community, I did learn to recognize stars, constellations and even trace planetary orbits on the sky with some charts, mostly practical stuff, but we never discussed this kind of stuff in deep, beyond some basic courses.

[Eternal_Freedom]

You wouldn't have in an astronomy club, this is astrophysics.

AS for gravity pulling it down to the core, yes it would be. But gravity is the weakest force, and I think the vaporised transuranics would probably get caught in one of the convection currents and stay there as a useless oddity.

[Lord Baal]

Yeap, that's why I'm making lots of questions.

This bring in another question, does the Sun naturally have any transuranic (or any other kind of) trace elements?

[Eternal_Freedom]

It'll have Uranium. Trace amounts. It's a logical conlusion:

1. All matter in the solar system came from the same molecular cloud.
2. Uranium is present on Earth.
3. Therefore Uranium was present in the molecular cloud.
4. Therefore there is some present in the sun.

If it has transuranics or not I don't know. On Earth they occur in nuclear reactors but not naturally, so they might not exist in the sun.

[Darth Yoshi]

As I understand it, the really heavy elements are all made in supernovae, since that's when the neutron concentration is the greatest. So the sun itself won't produce any transuranic elements on its own. The problem is that transuranics all have pretty short lifespans, so any that's produced by supernovae will have all decayed into lighter elements long before the debris can form new stars.

[Lord Baal]

Oh! Great knowledge! Also, I'm not a red shirt any more! Yay, now I'm a Youngling, I hope that's a good thing.

[Eternal_Freedom]

As I understand it, the really heavy elements are all made in supernovae, since that's when the neutron concentration is the greatest. So the sun itself won't produce any transuranic elements on its own. The problem is that transuranics all have pretty short lifespans, so any that's produced by supernovae will have all decayed into lighter elements long before the debris can form new stars.

Not quite.

The heavy elements (Iron-56 up to Uranium-238) are indeed produced in supernovae. I don't know whether transuranics aer made in supernovae, but if they are, you rightly say that they woudl have decayed by now.

However, slightly lighter (and still radioactive) elements would not have decayed as quickly. Let's use Uranium as an example. U-235 (the stuff in nukes) has a half-life of ~450 million years, so that will be pretty much gone over the timescales we are talking about (although it's still present on Earth, so it might exist in the Sun).

But U-238 (Uranium's most stable isotope) has a half-life of ~4.5 billion years, so the Sun will still have some in it. Indeed, logically is must do. There is still Uranium on Earth, and Earth came from the same stellar debris cloud, then the Sun will have some Uranium and similar (but lighter) elements.

A quick rough-and-ready bit of maths shows that if the Supernova that formed the Sun occurred 10 billion years (please note: I don't know the actual number, this is just for illustration) ago, the Sun will still have between 1/16 and 1/4 the amount of U-238 that was produced in the supernova. If we assume that heavy metal elements like Uranium were ~0.01% of the Sun's mass at formation, then anywhere between 0.000625% and 0.0025% of the Sun's mass is Uranium and similar.

Going with the 0.000625% figure, and a solar mass of 2e30 kg, that means the Sun contains 1.25e25 kg of Uranium and similar. Which is an order of magnitude GREATER than the mass of the Earth.

Sorry for the info-dump there, but I think those last numbers nicely illustrate that any elemetns we introduce are a fart in a hurricane.

[Zixinus]

Another thought on the thing: the Sun itself is moving and so are a good deal of stuff out that that is moving too. It's not impossible for the Sun (and thus, it's kids, the planets) to pick up debris from a supernova.

The distances involved are massive of course, but a supernova is energetic enough to fuse iron into transuranic elements, then it probably can speed things up enough for some of that matter to find itself in our solar system before it has decayed.

[Eternal_Freedom]

I think some people have trouble grasping just how big the masses involved are. Yes, transuranics may have short lifespans. But if you have massive amounts to start with, you'll still have massive amounts afterwards.

Suppose you have an isotope with a half-life of 500 million years, and it was last formed naturally 8 billion years ago in a supernova over Rigel way. In that 8 billion years it's gone through 16 half-lives, so the amount of that isotope remaining is 1/(2^16), or 1/65536. That's a small amount. But if you start out with 10^16 kg (a not unreasonable amount for supernova leftovers), you'll still have 152,587,890 tonnes of that isotope. (I know I'm mixing units).

152 million tonnes. Of an ultra-rare and relatively short-lived element. (this example has lots of assumptions built-in, you obviously won't get that much all in one block).

For reference, the amount of an isotope remaining after a given length of time is equal to 1/(2^ Elapsed half-lives). That fraction get's very small very fast, and anything with a half life of less than about a hundred million years will be almost completely gone by now (and I mean there might be a few grams left in the solar system).

[Darth Yoshi]

Another thought on the thing: the Sun itself is moving and so are a good deal of stuff out that that is moving too. It's not impossible for the Sun (and thus, it's kids, the planets) to pick up debris from a supernova.

The distances involved are massive of course, but a supernova is energetic enough to fuse iron into transuranic elements, then it probably can speed things up enough for some of that matter to find itself in our solar system before it has decayed.

I dunno about that. Molecular clouds and nebulae are pretty massive, but that's because they span lightyears across. The actually density is something along the lines of 1 particle per AU^3.

[Darth Wong]

Better and more realistic idea: dump the spent fuel rods inside a fusion reactor. That will also provide an energy boost.

Totally ridiculous idea. Steady-state nuclear fusion is an extremely delicate state to achieve: so much so that it is currently beyond our technology, although hopefully not for too much longer. The mass of the entire plasmoid is miniscule: measured in grams, not kilograms. The density is just a hair above hard vacuum. Dumping fuel rods into it, or even powdered metal, would instantly kill the reaction.

[18-Till-I-Die]

Perhaps this is a stupid question, but if you have, hypothetically, perfect interplanetary travel technology that means there will be no accidents on the ground...

Why not drop the shit on the moon instead. It's much closer, you could probably hit it with a relatively small railgun or something similar NOW if you could afford building it, and more importantly there is nothing really there worth a damn (that we couldn't get more off on, say, Mars or the Asteroid Belt or whatever) and no air, and no people, so no possible risk of contaminating anything. Certainly it'd make the moon uninhabitable if done long enough but we're suggesting a world where space travel is apparently cheap and efficient enough that "throw garbage into space" is more economical than "burry it" soooo...I figure by this point in the future we've already colonized another planet or two and interplanetary travel is common enough that going to the moon will be beyond pointless.

Like, I'm imagining the cartoon Exosquad (go from Earth to Jupiter in a few weeks on a civilian "tramp freighter") where relativistic travel is pretty much available to the masses. Because really, that's the only level of technology where "throw your garbage into space, it's fun!" will ever be a realistic solution.

[Eternal_Freedom]

Burying nuclear waste on the Moon was the central point behind Space: 1999. It didn't work out so well for them, but that was bad sci-fi.

It sounds like a good idea: the moon is big, empty and geologically stable. Better yet, if there is a leak, there's no atmosphere to carry fallout or whatever to distant areas.

[Zixinus]

I don't know, it seems to me that if you're going to put it up into space, you might was well just leave it freely in an orbit somewhere. No need to land it anywhere.

Aside it being a navigation hazard and contribution to orbit trash: don't orbits themselves degrade?

[Eternal_Freedom]

Leaving it in space seems wasteful to me. If we have it buried on the Moon, we know where it all is and (if it becomes possible) can remove it for use in other processes. That's much harder to do if it's floating aroudn the solar system.

[Darth Wong]

It's really none of the above. Let's work backward.

Do orbits degrade? No: the Earth has been in orbit around the sun for... what, 2,000 years now? And it hasn't degraded.

Uhh .... where do you figure the Earth was before 2000 years ago?

I'm still not sure why people are even exploring this option; it seems completely absurd when one could simply bury the stuff.

[Hamstray]

It's really none of the above. Let's work backward.

Do orbits degrade? No: the Earth has been in orbit around the sun for... what, 2,000 years now? And it hasn't degraded.

Uhh .... where do you figure the Earth was before 2000 years ago?

first thing that sprung to my mind upon having read that:
one of them tricky statements with protruding duplicity if challenged weasels it's way out through ambiguity. makes it in essence superfluous though.
took me a while to figure out how it would. Spoiler

he must not have meant terrestrial years

[Lord Baal]

I was going to point out the fact that apparently earth was not present in reality unlit "Jesus was eleven"... the I assumed it was a typo, because it was right???

[AniThyng]

I was going to point out the fact that apparently earth was not present in reality unlit "Jesus was eleven"... the I assumed it was a typo, because it was right???

It was obviously hyperbole, he could have just as easily said 'a zillion years ago' and not change the meaning of his sentence.

[Lord Baal]

Sorry.

[Batman]

I'm still not sure why people are even exploring this option; it seems completely absurd when one could simply bury the stuff.

You're speaking as someone who actually knows the dangers of fission leftovers (i.e. none really if we actually dealt with them properly) vs a populace that wants them as far away as possible, while at the same time thinking that dumping a minuscule amount of spent rods into the sun might upset it while not wasting a single thought on the problems arising from a bumbled launch.