Thinking about the current energy crunch and the possibility of more nuclear power plants I was wondering two things.
Can’t spent fuel rods be “replenished” ? If so can you give a quick little chem equation to show? Seems to me the reason they don’t do it is because it results in weapons grade plutonium, that’s, like the nasty shit on earth.
Why can’t they put it in the space shuttle and blast it towards the sun?
Thanks for the info…
Regarding the “blast it to the sun” plan, IIRC, balsting things toward the sun is no simple task. In addition, although the failure rate of shuttles or rockets carrying the fuel rods out of the atmosphere would be very low, failure would be catastrophic.
Now I’ll yield to those who really know what their talking about.
reply to point 2). Launching things and getting them to permanently leave earth is very energy intensive. We’d have to restart the Saturn V program to build something big enough to send the shuttle out of earth orbit, and that would just get it to the moon. To actually shoot something into the sun is very difficult, and would cost billions. Also, if the rocket exploded on launch, it could scatter highly radioactive, highly poisonous plutonium into the atmosphere.
We can launch a millionaire into space… and we wouldn’t hafta slam into the sun. Just give it a little push and let inertia do the rest. We know how the planets rotate and the effects of gravity. Wonder how hard it would be to time the push?
Maybe as a secondary question, what would happen if me and another mass identical object are in orbit and moving at 0 mph relative to each other and I give it a push perpendicular to our path away from the earth. My retaining strap keeps me from falling to earth (Earth?), but what happens to the object?
I’m not a physics expert. Just curious.
We can launch tons of stuff into space. The problem is, that unless we get it out of Earth’s gravity well, it will fall back down. Just look at what happened to Skylab and Mir. And Plutonium will not burn up on re-entry! It’ll vaporize into a highly toxic dust, and absolutely sterilize whatever it lands on. And it will stay poisonous for a long, long time. Tito would have vaporized nicely, and any parts that didn’t would have been nice fertilizer.
Replenishing nuclear fuel rods:
A fuel rod contains a few percent fissile material (uranium 235) and the rest is non-fissile (uranium 238). As the fuel rod is consumed, the U235 breaks down into various other elements, many of which are radioactive. Some of the U238 is turned into plutonium 239, which is fissile.
In a normal reactor, fissile material is consumed faster than it is produced. Eventually the percentage of fissile material left is too small for the fuel rod to be viable. However, you can take your “spent” fuel rod and extract the remaining U235 and Pu239 to make new fuel rods (by adding it to natural uranium), or atomic bombs if that’s what floats your boat.
The reasons such replenishing isn’t widely practiced are:
It’s difficult. Old fuel rods are radioactive as hell. They need all sorts of careful handling, storage and transport procedures. It makes more sense to enrich natural uranium, which is far friendlier although you still wouldn’t sprinkle it on your cornflakes.
Environmentalists don’t like large quantities of spent fuel rods being shipped around, mostly on principle but also because of Murphy’s Law. While I am no fan of environmentalists, in this case they do have a point. Trying to derail nuclear freight trains in Germany is a quite a strange way to make that point (they must trust the containers rather more than they claim!), but still…
The reasons such replenishing is done AT ALL are:
It’s far easier to extract weapons-grade plutonium from spent fuel rods than it is to extract weapons-grade uranium from natural uranium. And we all need more nuclear weapons, don’t we?
There are other radioactive elements which can be extracted from the rods which are actually quite useful. One of them is in your smoke alarms, assuming you have any.
Disposing of nuclear waste in space
On the face of it, this isn’t such a bad idea. Firing it into the sun ain’t so great, and putting it in near Earth orbit is dumb, but high orbits which don’t decay for millions of years are quite feasible. Or we could put it on the Moon in a heap, it won’t hurt anything.
Right now however, we don’t have any launching technology remotely good enough to make this cost effective, or reliable enough for us to dare to do it.
An alternative which gets around the launch safety issues is to build your nuclear power stations in space with cold enriched uranium fuel, beam the power back to Earth via microwave and leave them up there when they’ve burnt out. Much cheaper than orbiting solar power stations, an idea which has been kicking around a while.
Gently nudging yourself away from Earth
I see where you’re going here. You’re thinking, if you’re in orbit already and you just give something a little push, it should keep drifting away for ever in accordance with Mr. Newton, right?
Unfortunately, being in orbit is not the same as being adrift in space. You are still being affected by Earth’s gravity, and you are moving along a curved path. Now, if you’re a few yards from the space shuttle and you want to get back to it with your rocket backpack, everything works as you expect because you don’t go too far around the curve in the time it takes you to reach the shuttle.
However, if you’re a long way from the shuttle you’re going to have problems just pointing your backpack and thrusting towards it. If you’re trying to catch it up you’ll put yourself in a higher, slower orbit and it’ll draw away from you. Or if you’re slowing down to let it catch you up, you’ll put yourself in a lower, faster orbit and pull away from it. Tricky business!
Back to your thought experiment - you don’t need a retaining strap (hooked to what?) If you really don’t want to give yourself a shove as well, take two equal masses in orbit with you (say a couple of refrigerators) and shove them apart with your arms, one towards Earth, one away.
What happens? I’m not an expert, but I’ll tell you what DOESN’T happen - the refrigerator you shoved towards the Earth won’t hit it, and the one you shoved away won’t go to find its destiny among the stars.
To a first approximation, the one you shoved towards the Earth has been put in a lower orbit, which is faster and so you’ll see it pull away from you and eventually vanish over the Earth’s horizon. If you wait a really long time, it will reappear from behind the Earth on the opposite side.
The one you shoved away from the Earth has been put in a lower orbit, which is slower, and so you’ll see it fall behind your orbit and vanish over the Earth’s horizon behind you.
A couple of problems - rather than putting them into higher and lower circular orbits, you’ll likely put them into elliptical orbits and it all gets more complicated.
By this “restraining strap” I presume you mean you’re hooked up to a nice bulky spacecraft or something. Your little maneuver will change the orbit of the spacecraft slightly, but probably not by a measurable amount.
If you give a massive object a small push radially away from the earth, its orbit will become slightly less circular (more eccentric), and slightly larger. You need to give it one hell of a push to get it going fast enough to escape from the Earth, as matt said.
If you want to shoot something into the Sun, you first have to accelerate it to the Earth’s escape velocity, 11 km/s, [Tom Hanks]Faster than a bullet,[/TH]–no easy task, as many people have pointed out. Once you accompish this, instead of orbiting the Earth, the stuff will be orbiting the Sun, in an orbit that is only slightly different from the Earth’s orbit. If you do nothing else at this point, the stuff will just keep going around and around the Sun. Perturbations from the other objects in the Solar System will cause it to drift around in its orbit, perhaps toward the Earth, perhaps away.
See, it’s intertia that keeps it in orbit. It wants to keep going in a straight line and fly off at perpendcicular its orbit (not toward the Sun, but out into space), but the Sun’s gravity pulls it around into a curved path around the Sun.
If you want it to fall into the Sun, what you need to do is decrease its orbital velocity. And, unfortunately, the Earth’s orbital velocity about the Sun (and thus your nuclear waste’s velocity) is about 30 km/s, or 66,600 mph. So, while you had to increase the waste’s velocity to 11 km/s to escape the Earth, you have to decrease the velocity by much, much more to get it to fall into the Sun. Since there’s no friction in a vacuum, the only way to do that (barring exotic propulsion methods) is to fire rockets.
It defies intuition, but it’s just as hard to send a space probe to Mercury as to send it to Mars!
And, before you start investing in a business dedicated to launching tons of nuclear waste off the Earth, you should read up on how freaked out people were about 33 kg of plutonium on the Cassini space probe, bound for Saturn:
And that wasn’t even a particularly dangerous isotope of plutonium. Anything that involves radioactive materials, or even anything that people think involves radioactive materials, is a public-relations nightmare. You can do all the risk-analysis studies you want, and it won’t matter to the protestors.
Couple questions…
Objection #1 I’ve heard is the “we’re polluting the
sun” or “we’re adding mass to the sun” theory, both
of which are poppycock. Let’s say we could somehow
manage to throw the whole earth into the sun. What
percent change in mass would we cause the sun? Don’t
take my word for this, go look up the relative masses
of the earth and the sun! Folks, we could mine every
single atom of uranium out of the earth and toss it
all into the sun and the net effect would be so close
to zero that it’s comprable to a flea fart in a hurricane!
As far as “polluting” goes, don’t forget that there
are already “heavy” elements in the sun, like uranium
and plutonium. Look up the various theories on the
genesis of the solar system. The sun and the planets
formed from the same cloud/disc of interstallear dust
left by the previous supernovas of dead stars. If
we have it on earth (with the exception of stuff
we make in particle accellerators), it’s in the sun too.
Objection #2 seems even weirder to me. This is the
one where “well, we have to retro-burn the rocket
before we let it fall into the sun, or else it’s
go all the way through and shoot out the other side!”
Aside from the clever reply of “well okay then, we just
spiral it in. It gets all it’s forward momentum for free
as a result of being launched off an earth that’s
revolving around the sun already.”, there’s also
the matter of it being about a gazillion degrees
inside the sun. The rocket would vaporize to plasma
halfway down and no way would the plasma be cohesive
enough punch through the sun. It’d be like trying to
knock down a brick wall by throwing bucketfulls of
water at it.
So, besides the abovementioned massively high cost
(and risk of the rocket blowing up in mid-launch), are
there any arguments for not shooting waste into the sun?
-Ben
ModernRonin2 asks;
Well, I’ve actually pondered this a little.
Cost and danger aside, the only objection I can think of is, does the universe belong to us? What I mean is, do we have a right to go tossing such nasty stuff out there?
It could miss the sun and go wandering off to who knows where.
What if somebody gets pissed and throws it back, all at once?
Peace,
mangeorge
I know this is off topic…
It’s a dumb question too, but isn’t there a way to like break down plutonium into a less harmful element. Or would it take too much energy?
Can we “pollute” the sun?
ModernRonin2’s arguments are quite compelling - the Sun is truly massive and tremendously energetic, and anything we did to it would be the flapping of a mosquito’s wing in a hurricane in such absolute terms.
However, the Sun isn’t just a big homogeneous ball of gas. It has structure. It has weather. It has storms and flares. It has a magnetic field, and periodic variations in activity and output. It’s surface temperature is only around 6000K, while its core temperature is in the tens of millions. And since it’s rather hard to get close, or do experiments on it, or look below the surface, we really don’t know very much about it.
So while I doubt dropping nuclear waste into the Sun would harm it, I’d rather we tried it in someone else’s solar system first.
ModernRonin2 also said: “Objection #2 seems even weirder to me. This is the one where “well, we have to retro-burn the rocket before we let it fall into the sun, or else it’s go all the way through and shoot out the other side!” Aside from the clever reply of “well okay then, we just spiral it in. It gets all it’s forward momentum for free as a result of being launched off an earth that’s revolving around the sun already.””
Haven’t heard this one. The problem is getting the waste into the Sun in the first place. The “forward momentum” from being launched off the Earth isn’t towards the sun, it’s tangential. So you are going at 65000 mph in the wrong direction. You have to kill all that sideways speed to get to the Sun, and that takes a lot of energy.
For much less effort we could put waste in a long-lasting high Earth orbit (I know Mir and Skylab came down, but the Moon’s stayed up there a while), or put it on the Moon itself. But space waste disposal is a red herring - if we had that sort of cheap reliable launch capability, we would build space solar power stations and not create the waste in the first place.
Amedeus Plutonium as a waste product isn’t that big a problem. It isn’t terribly radioactive, and it isn’t particularly poisonous when compared to other heavy metals. (Yeah, yeah, it’s “the most toxic substance known to man.” Not true. Check out http://www.fortfreedom.org/p22.htm)It is however a relatively easily extracted fissile element, and that means the truly dedicated could use it to make atomic bombs.
It can be broken down into more harmful elements by using it as a nuclear fuel in a reactor. I say more harmful as in much more radioactive - the fission products cannot be used to make bombs, which is one problem out of the way. You’re substituting the problem of weapons-viable nuclear material with the problem of nuclear waste, although you’re generating some energy in the process.
ModernRonin2, whoever raised those objections has no freakin’ clue how big the Sun is.
I think it was on a “Frontline” program, or some other PBS show, where they showed what was called an IFR reactor. Don’t remember all the details, but it basically operated by having nuclear waste shoved into it, it then converted the waste into electricity and non or low radioactive materials. Naturally, the program researching this got cancelled. One of the more dramatic moments showed them walking around the core of the reactor with it operating and carrying a geiger counter. The counter was barely clicking and the project director pointed out that you couldn’t even get this close to the core of an ordinary reactor without absorbing a lethal dose of radiation.
As for the space based solar panels beaming power back to Earth, great idea, and similar ones have been kicked around since the 1950s (Heinlein wrote about space based nuclear power plants that beamed electricity back to Earth), but there’s one small problem: anything in the path of those beams (birds, planes off-course, etc.) would be cooked by the microwaves! Not cool.
You can read about the IFR at this site http://www.nuc.berkeley.edu/designs/ifr/
Thanks Manny. I’ve been looking for a site on that for a while now. Anybody want to take bets that the Bush Administration will try and revive this idea in its push for more nuclear power? I’m betting they won’t. Too damn smart for those guys.
Why would you want to deprive our descendents of a potentially good rocket fuel?
I’m missing something here about shooting stuff into the sun. If accelerating something to 11 km/s will get it off the earth, and the earth is rotating the sun at a linear speed of 30km/s, couldn’t we just make sure that we accelerate it 11km/s in the correct direction (i.e. exactly opposite the direction of travel of the earth around the sun)? Then the stuff would start out in the same trajectory around the sun as the earth currently is, but it would only be going 19 km/s, which isn’t fast enough to sustain an orbit at this radius.
I suppose there’s the possibility that it will swing around the other side of the sun and slingshot back out, ending up in a highly eccentric orbit which crosses ours occasionally, with the exciting possibility of colliding with us. It could make Halley’s Comet sightings look pretty dull in comparison. 
No, but so far those reasons have kept it from happening.
Probably not a technical reason not to do it, but it’s an interesting question of philosophy. Do we, as a species, just fall back to brute force methods like dumping for all of our wastes or is there some more elegant solution? Sure, it works, but it’s a short-term mindset which falls short of human potential, IMHO.
The problem is that the 11 km/s gets “used up.” Imagine that you’re throwing a baseball straight up. When the ball leaves your hand, say it’s going a certain speed–a few meters a second. The ball goes up, its speed decreasing until it reaches the top of its arc, when its velocity goes to zero, and then it falls down. The escape velocity is the starting velocity; by the time a rocket leaves the Earth, it has lost much of that initial velocity.