Sending Plutonium into space

Factual Questions
21

Why the heck does everybody want to dispose of things by putting them in the sun?

It’s incredibly hard to get things to the sun – you have to put things into a highly elliptical orbit to get near the sun (far more effective and “cheaper” in energy than trying to kill ALL of the object’s velocity and letting it fall into the sun). To do this you need both a lot of reaction mass and a lot of energy to accelerate the reaction mass and toss it out the back. You could, I suppose, use less reaction mass and accelerate it to relativistic speeds, but then you need a hell of a lot more energy.

In any case, you’ll need a LOT of energy. Where are you going to get it?

Nuclear reactors, maybe?

22

What Podkayne said.

The only scientifically reasons against shooting waste into the Sun are the two that have already been mentioned: cost and launch safety.

If we put reactors at geo-sync orbits and beamed the energy back to earth, that would take care of most of the saftey issues (although the general public would still be pretty damn nervious about launching fresh fuel rods).

Getting the spent fuel into the Sun wouldn’t be quite as difficult as it may seem. You seem to be forgetting about using planets to change orbits.

We usually think of the “sling shot” effect of using a planet to shoot probes into the far reaches of the solar system. But it is just as easy to use a planet to slow down a probe and send it into a lower orbit. Sure, we would need to use rockets to steer the fly-bys, but the energy required would be about the same as what is required to send a probe to Jupiter. In fact, using an ion drive (like DS1) would be a relatively cheap way to get a craft into the sun.

The key word there is “relatively”. These space probes still cost big bux. And it’s not just the initial cost of the spacecreft. These spacecraft need a staff that keeps the craft in course and monitors the craft’s health, downloading fixes when necessary, and in general using up gobs of time on our deep-space network (much to the scientific community’s woe). It would take well over a year, probably more than two, to get a craft into the Sun. Paying those astro-physicists ain’t cheap, and neither would beefing up our deep-space network.

Technologically, we could do it today. It’s just not cost effective, and I doubt it will ever become cost effective.

P.S. - about something passing all the way through the sun, you’re forgetting friction. The Earth’s atmosphere is thin and not very dense, and yet very few object manage to make it to the ground. Most meteors become just so much vapor and dust that floats around in the atmosphere and slowly rains down.

Comets that are MUCH bigger than any spacecraft routinely fall into the Sun without causing so much as a twitch. They don’t even make it anywhere near the core. A spacecraft would become vapor and soot before it even reached the photosphere, and solar wind would probably carry most of that away. The heavier particles would simply get caught in the convection currents and continue to cycle until the Sun burps off it’s outer layers as it becomes a white dwarf, a few billion years from now.

23

The IFR looks interesting, but I’m curious that it states it will neither require new fuel nor have waste to dispose of during its production run. If this is the case, then it seems to me that it would not be an especially good method of reducing the wastes/byproductes of current nuclear facilities.

My question, as one almost totally uneducated in nuclear processing, is: why can we not develop a reactor that runs off the radioactive wastes produced by the current systems? Admitting my lack of education on this, I’m wondering why the radioactive wastes produced could not be further used to produce energy?

24

Put me down for a big “DUH”.

Ok, ignoring the idea of conserving the energy used in accelerating the thing to 11 km/s, how much slower than the earth would something have to be traveling in order for its orbit to decay into the sun?

25

Nuclear reprocessing hijack:

thinksnow asked: “why can we not develop a reactor that runs off the radioactive wastes produced by the current systems?”

The short answer: only some radioactive components of nuclear waste can consumed in a reactor.

The short(ish) answer: Nuclear waste is radioactive. This means it contains atoms which are unstable, and which try to become more stable atoms by spitting out particles.
However, to run a nuclear reactor you need atoms which are fissile. These are atoms which are unstable, and which try to become more stable by splitting into smaller atoms and neutrons. These neutrons hit other fissile atoms and make them split too, giving you a chain reaction.

Most of the elements in nuclear waste are radioactive but not fissile, so they can’t be used as a nuclear fuel. Those which are fissile usually have to be extracted and concentrated from the nuclear waste which is a pain, see my previous answer this thread.

The long answer: There are no hard-and-fast rules as to how a fissile atom splits - it may break into two, roughly equal sized atoms, or one big and one small, or it may break into three atoms, or four. Nuclear waste therefore consists of a mixture of just about all the elements in the book, including those we know and trust such as hydrogen, gold and iodine.

However, unlike the stable forms of these elements, they are frequently unstable because they have the wrong balance of protons to neutrons in their nucleus. They try to redress this balance by spitting out beta particles, which allows a neutron to change into a proton, or alpha particles, which kicks two protons and two neutrons clean out of the nucleus. This is called radioactive decay. Eventually, all the elements will reach stable forms and not be radioactive anymore.

For a given sample of radioactive material, the time it takes to decay to stable elements (become “safe”) depends how fast it is spitting out particles (radiation.) If it’s spitting out particles like there’s no tommorrow, it will be radioactive as hell but will be short-lived. If it has a very long lifetime, it won’t be very radioactive.

Fresh spent fuel rods are hideously radioactive. They are stored under water for about a year while all the very-short half-life stuff decays away to nothing. The water is hot from the decay heat. After a year they’re cool enough to dispose of. (you could use this decay heat to generate energy, but it is a low density source of heat compared with a chain reaction or burning chemical fuels. The massive precautions needed to handle the rods prevent it from being cost-effective.)

This is where it becomes controversial. How long do the rods have to be isolated from the world before they become safe? Greenpeace and others like to screech tens of thousands of years, but such long-lived isotopes are comparatively non-radioactive, certainly no more so than the uranium was when it was dug up. A discussion in New Scientist a few weeks ago suggested that 500 years is borderline and 1000 years is more than good enough. Jerry Pournelle has long contended that 600 years is fine, and is having a discussion on the subject on his mail pages at the moment.

So one point of view is that the long-lived elements in nuclear waste aren’t really a problem, and there’s no reason why (after 600 years) we shouldn’t mix it with dirt and stick it back in the holes where we mined the uranium in the first place. We should be able to store waste for 600 years safely - we have cities older than that. (And one of them has stood in water on cedar piles for a thousand years. We know how to build stuff. We’re good at it.)

An alternative is to burn the long-lived elements in a fast neutron reactor like the IFR. This will actually create MORE short-lived nuclear waste, but means that the waste will be truly stable after 600 years. The best reason for doing this is that it massively increases the total energy reserve availble from fission, but a percieved advantage in waste disposal is good PR. It also gives us something to do with all that pesky plutonium. (As an aside, I don’t like the IFR design very much. That liquid alkali-metal pool leaves me deeply, deeply unhappy.)

End of nuclear reprocessing hijack:

26

** Why orbits decay, or “what goes up don’t have to come down”**

We’re very used to orbits decaying - Skylab and Mir came down, as do many satellites. Whenever they have engine failures on Star Trek, it’s full panic mode as the Enterprise starts to fall towards the planet.

However, ORBITS DON’T HAVE TO DECAY. Things in orbit around the Earth fall down because of drag from our atmosphere!

Our atmosphere gets thinner as you get higher, but there is no clear demarcation line where “space” begins. We have defined “space” as starting at an altitude of 50 miles so we know who deserves their astronaut badges and who doesn’t, but there is still air there. It may be thinner than in an average lab vacuum on Earth, but it’s there, and it drags at you when you’re whipping through it at 20000 mph.

Put something in orbit at 50 miles and you’re going to be seeing it again shortly. Put something in orbit at 80 miles and it’ll stay up for days. Satellites in Low Earth Orbit stay up for years. Put something good and high and it’ll stay there for as long as you like.

Now, things in orbit around the Sun don’t really decay worth a damn on any sensible time scale - the Sun will have gone out before any planets crash into it.

Galt asked: “how much slower than the earth would something have to be traveling in order for its orbit to decay into the sun?”
There’s a number of answers to this. The simplest one is that it would have to be stationary w.r.t. the Sun - then it’ll go on a terrific screaming straight-line plummet into it. That’s not the most efficient way to do it, however.

If something (say, you in a spacesuit) is in orbit around the Sun and you suddenly lose a big chunk of orbital velocity, you don’t spiral into the Sun. Instead you spiral in to a new, lower orbit. So to end up in the Sun, you have to lose enough orbital velocity for your new, lower orbit to be the same radius as the Sun itself. That way you skim the “surface” and lose the rest of your velocity by drag. In fact, you’d only have to be close enough for the solar atmosphere to start robbing you of velocity at an appreciable rate. I’m much too lazy to do the maths and give you a hard figure!

There is a third way, though. As CalMeacham said, instead of mucking about killing velocity to get a small enough circular orbit to decay into the Sun, you can put yourself into a zany elliptical orbit which’ll clip it. Getting the required velocity change to do this is probably a job for a computer.

As an aside, due to tidal effects, the Moon’s orbit is actually getting higher with time.

27

matt, thank you for the run-down. Most informative. If the IFR program is capable of usign up radioactive wastes, it seems a curiousity that no one has continued the research or gone about implementing a facility.

Anyway, thanks for the information.

To the OP, why be so concerned about sending something into the Sun? For all intents and purposes, if we were to send something outward from Sol, either in the plane of the planets or at some tangent, the odds of our (or someone else) running into to again would likely be nil, wouldn’t it?

28

The May 21st issue of “US News and World Report” has an article on page 38 about the “pebble bed” reactor which is supposed to be safer than current reactors, but not as safe as the IFR (which isn’t discussed). The first plant in scheduled to go on-line in South Africa within three years. It doesn’t completely solve the nuclear waste problem, but it does make the waste easier to manage.

29

And, in fact, isn’t the moon’s orbit time getting higher due to the same tidal effects as well? “The higher, the longer, or something like that?”

30

Yes, the larger the semimajor axis (radius) of an orbit, the longer the period. So as the Moon moves away from the Earth, the lunar month is getting longer.

Let me be the first to welcome you to SDMB, tdk! (ASAP, LOL, etc.)

31

What’s this fixation with the Sun? Assuming we wanted to get rid of the stuff by getting it off the Earth, it would be a lot cheaper to simply fire it into Venus, or the Moon, or Jupiter, or just send it out of the Solar System completely.

Those people worried about ‘polluting’ interstellar space have absolutely no grasp of its scale. Aim it in the right direction, and it’s not coming near ANYTHING until the radioactivity is completely gone. And in any event, the universe is composed of things so horrendously powerful as to make anything we could come up with not just trivial, but completely unnoticable on a cosmic scale. Hell, we could convert our entire Solar System into Plutonium and it wouldn’t make a difference. There are single objects out there that are more powerful than billions of suns, and our sun has millions of nuclear explosions going off every second. There are explosions in the universe so immense that they create beautiful structures thousands of light-years across.

But why launch it into space? Every launch would contain more risk than 1000 years of storage. The general attitude seems to be that the stuff is so evil that we have to get it off the planet. Not true. Just don’t go near it. Put it in a stable geological formation, put some big signs around saying “KEEP OUT”, and the job is finished. Or dump it in a subduction zone in the ocean. The deep ocean doesn’t transfer material with the surface - there are volcanic vents that spew thousands of pounds of poisons into the water every minute down there.

There is no engineering reason why we can’t handle waste here on earth safely and responsibly. Turn it into glass, encase it in 2" of steel, and sink THAT into a solid block of concrete. I guarantee you that nothing is getting in or coming out of that, and even if it did, the glassification process prevents the waste from leaching. And even if it did, it’s not going to do anything if it’s 7 miles down. And if you hit the edge of a subduction zone, it’ll eventually be driven over by a plate and recycled deep into the Earth.

The problem of waste is political. You can’t transport the stuff without idiots trying to derail your trains, and politicans can’t get elected by promising lots of convoys of waste rolling through town.

32

Ahh, I think you’re all full of it!!

[sub] seriously though, this has been an informative thread![/sub]

I wonder if any of you really realize the amount of nuclear waste we are talking about. It isn’t as if no one ever considered the possibility of sending the stuff into orbit near or far before. The reason it has never been done is the simple fact there are millions and millions of gallons of the crap!

Back in the 70’s I was anti any thing nuclear. Fortunately, I had a mate who questioned my beliefs and challenged me to check it out.

I started working at the Hanford Nuclear Reservation in the state of Washington in 1979. A dolt surveyor, but due to the nature of the job, I got to witness, first hand nearly all if not all of the “Area”. Hanford Nuclear Reservation is thousands and thousands of acres big! It takes a couple hours just to drive across it. Hanford is the home of 7 or 8 “decommissioned” nuclear reactors from the 40’s.

Decommissioned? each is surrounded by a chain link fence, none are entered as far as I know by anyone, each a hundred or two hundred yards away from the Columbia River. We’re talking hurriedly constructed buildings from the 1940’s, including all the out buildings necessary for their operation at the time.

The buildings are not maintained for historical reasons, they are still there 60 years later because they are still so radioactive that it is not technologically or fiscally feasible to remove them.

Hanford is the home of numerous “Tank Farms”, each consisting of dozens and dozens of tanks, many of which contain more than a million gallons of nuclear waste. Most of the older tanks are single walled, many of them were leaking in the 70’s and 80’s when I was there. All well documented, everyone without answers as to what to do with it. Hanford is also home to some of the most highly contaminated buildings known to man, Purex, the Cunk Plant, Fast Flux Test Reactor, among others. Also home to the N reactor, a nuclear reactor decommissioned in the early 80’s as well as the two in-complete WHoops {Washington Water Power} reactors that were in the process of construction in the 80’s.

Since the 1940’s the USA has spent billions and billions of dollars in an attempt to clean up the area. Most of it has gone to private corporations to study the potential on a cost/plus basis. Sixty some odd years later, what has been done to alleviate SOME of the problems?

None, that I am aware of. All of the problems that existed in 1980, exist today, all eight of the reactors still stand as a monument to technology that we still have no answer for, the million gallon tanks continue to leak their waste into the underground aquifers leading to a huge population center (Portland, Oregon and Vancouver, Washington as well as large cities in between and indirectly to you, where ever you are. It may be that one or more of the million gallon tanks will build up enough heat and pressure to explode into the atmosphere, (there is real concern of this possibility), it may come from the fish you eat from the ocean who spent time in the Columbia River, it could come from the migratory goose you ate at Grandpa’s house for Thanksgiving last year, which happened to stop off at one of the off-limits ponds on the reservation.

It is all well and fine to hear about how wonderful nuclear power is, how clean it is, how cheap it is, how easy it is to shoot the waste into orbit.

If it’s so damn easy, why can’t we take care of the problems we have already created?

Are there answers? Definitely! Are there absolute answers? Absolutely not. There are serious risks related to any power source but until we learn to deal with the problems we already know how to create, we have no business fooling with it anymore.

So I’m curious, what new technology have we come up with in the last twenty or thirty years.

33

Ahh, I think you’re all full of it!!
Gee, thanks.

seriously though, this has been an informative thread!
Great. Maybe you should read it.

I wonder if any of you really realize the amount of nuclear waste we are talking about.
Yes.

It isn’t as if no one ever considered the possibility of sending the stuff into orbit near or far before.
And your point is?

The reason it has never been done is the simple fact there are millions and millions of gallons of the crap!
No it isn’t. The reason it has never been done is the fact that it is not economically sensible or safe for us to send millions and millions of gallons of the crap into space.

Your point is misleading anyway. According to the December 2000 DoE Report to Congress:
http://www.hanford.gov/orp/documents/report_to_congress.PDF
the Hanford liquid waste consists of 57 million gallons (roughly 200000 tonnes) with a total activity of 192 million Curies. 91 million curies is accounted for by cesium 137 which corresponds to about 1000kg of cesium, and 98 million curies is accounted for by strontium 90, which corresponds to about 700kg of strontium. So 98% of the radioactivity is accounted for by 1.7 tonnes of radioactive elements. The vast majority of the waste consists of non-radiative water and sodium salts, contaminated with relatively small quantities of radioactive elements. Not that I’m saying that Hanford isn’t a tremendous problem and an environmental disaster - it is. But people should be aware of what “millions of gallons of waste” actually means.

It is all well and fine to hear about how wonderful nuclear power is, how clean it is, how cheap it is, how easy it is to shoot the waste into orbit.
Read the thread again. Nobody says that waste should be put in orbit, everybody says the opposite. Nobody says that nuclear power is wonderful, clean or cheap either. People have said that the waste disposal problem is more political than practical, and that’s about it.

So I’m curious, what new technology have we come up with in the last twenty or thirty years.

According to the report I linked, they are proposing to reprocess and vitrify the waste before burying it. In the short term, new tanks will be built and the waste transferred into these from the leaking tanks.

34

I’m curious to see the math on this one.

Perhaps, but there are some engineering concerns. You mention an excellent vitrification solution but there is one major drawback…expense. (And yes, cost is an important engineering consideration!) Also, there is no data to guarantee long-term (100s/1000s of years) containment. The geology (or more likely, the hydrogeology) of the burial area can change on that timescale. There’s also worker safety concerns for the whole vitrification/burial process.

But overall, I’d lean toward vitrification before launching. At least until our space program becomes experienced enough and cheap enough to make it a more viable option.

35

I’ll probably get this all wrong, 'cause it’s been about 20 years since I took astronomy in college, but here goes:

If you want to hit the sun, you have to kill the orbital velocity of Earth that our Plutonium carries with it at launch, or at least a good chunk of it.

The Earth’s orbital velocity is about 30 km/s.

Objects in orbit around the Earth are going roughly 8 km/s relative to the Earth.

To leave the Earth permanently, you need to attain escape velocity relative to the Earth’s motion, or about 11.2 km/s. So, the Delta-V you need to leave Earth completely once you’re in orbit is only about 3 km/s.

To leave the solar system completely, you need to reach escape velocity for the Sun, about 16 km/s.

So, once you’re in orbit, you only need about 8 km/s of delta-V to leave the Solar System completely, which is about the same as what you needed to get into orbit in the first place. But to go the other way and kill your velocity relative to the Sun so you fall straight into it, you need you’d need a Delta-V of about 22 km/s, or almost 3 times as much.

That’s the simple math. Beyond that, you get into transfer orbits, gravitational slingshots, eccentric orbits to take you close enough to the sun to shed velocity through atmospheric braking, etc. How that all shakes out is beyond me. But if you’re going the other way, let me quote Robert Heinlein: “Once you are in orbit, you are halfway to anywhere in our Galaxy.”

If you’ve got lots of time.

36

The benefits of blasting our wastes away from Earth (to where doesn’t really matter) don’t seem to be worth the risks.
Given that, should we start making even more? We can, with great effort and expense, do something about the stuff we already have. But if we re-open the door to fission type reactors the resulting waste will, within 50-100 years, make what we have now seem like a drop in the ocean.
Do we need more power that badly?
I don’t know, but the whole waste thing makes me nervous. Plus the slight danger of catastrophic accident.
Peace,
mangeorge

37

The resulting waste doesn’t have to be that amount. One of the problems with the way things are done today is that the high-level waste (spent fuel rods) is mixed with low-level waste (contaminated gloves, water, tools, you name it). The low-level waste isn’t nearly as dangerous, and it makes up the vast bulk of the waste produced.

Canada sells a Breeder reactor that recycles spent fuel rods. It also has a feature that its moderator is also the coolant. If you have a coolant leak, the reactor shuts down automatically. Pretty safe design, and there’s never been an accident in one that I know of.

38

Besides the obvious dangers, what is keeping us from developing a nuclear powered shuttle? Could this solve the economic problem of launches? Just wondering.

39

Well, basically there are two kinds of nuclear rockets: NERVA and Orion (there are a couple more theoretical possibilities, but we’re not going to build them in this century, no matter the size of the R&D program).

NERVA heats hydrogen (the best reaction mass) by means of energy generated by nuclear fission. You can get a high specific impulse (I[sub]sp[/sub], essentially the exhaust velocity) but a low thrust; a shuttle with a NERVA engine could never take off using that engine.

Orion is politely called a “pulsed nuclear drive”: you set off a small fission or fusion bomb under the ship. Having the ship remain in one piece is left as an exercise for the student (the problem has been worked on; however, any such ship would almost certainly be outlawed by the 1967 Outer Space Treaty, so nothing beyond “proof-of-concept” has been done in this area). Orion could be built with a whacking great thrust, but the radioactivity of the launch area would be <major understatement>a problem</major understatement>. Circumstances under which that could be tolerated (as opposed to the alternative) can be imagined; routine launch of nuclear waste into the sun, however, is not one of them.

As pointed out others in this thread, disposing of nuclear waste by launching is very nearly a textbook example of overkill. There are better and cheaper ways of handling it.

40

With the Space Shuttle disaster, how far has a nuclear propulsion system for space exploration been pushed back?

I don’t see any such craft (as mentioned in the link below) ever launching into space during my lifetime.

http://www.space.com/news/budget_nasa_030203.html