A Nuclear Probe to Explore Earth’s Interior(beyondearthlyskies.blogspot.com)
beyondearthlyskies.blogspot.com
A Nuclear Probe to Explore Earth’s Interior
http://beyondearthlyskies.blogspot.com/2013/09/a-nuclear-probe-to-explore-earths.html
21 comments
> A self-sinking probe is basically a dumb probe measuring less than 100 cm in diameter - a lump of nuclear waste encapsulated in a tungsten sphere and sunk into the ground.
Even more so if you wonder if it couldn't be a way to dispose of waste. Also, if corrosion was an issue, perhaps they could coat it with something?
Even more so if you wonder if it couldn't be a way to dispose of waste. Also, if corrosion was an issue, perhaps they could coat it with something?
Nuclear waste is waste because it doesn't produce enough heat anymore to be useful in production of electricity. So I doubt that spent nuclear fuel would be able to produce 1000C+ temperatures for 30 years to bury itself deep enough.
Nuclear waste is waste because it doesn't contain enough fissile nuclides (i.e. nuclides, which could produce heat in fission). It has almost nothing to do with radioactivity or decay power. Radioactivity just makes it harder to manage.
But you have it right: The decay power density of nuclear waste is quite soon not enough for such a probe.
But you have it right: The decay power density of nuclear waste is quite soon not enough for such a probe.
IANAG, but it probably doesn't need to get 100km under the ground. It only needs to go to the depth at which the nuclear waste stops being a problem.
With a good amount kilometers of rock between the surface and the waste, the danger is already gone. Furthermore, melting the waste and have it move thorugh the mantle will lower its concentration and will over time have the heavy materials fall into the core.
My guess is that the point at which the nuclear waste becomes less problematic than current methods will probably occur quite quickly, just a few kilometers if that. The point at which the tungsten corodes and the waste can be swept away doesn't seem to be that deep either.
With a good amount kilometers of rock between the surface and the waste, the danger is already gone. Furthermore, melting the waste and have it move thorugh the mantle will lower its concentration and will over time have the heavy materials fall into the core.
My guess is that the point at which the nuclear waste becomes less problematic than current methods will probably occur quite quickly, just a few kilometers if that. The point at which the tungsten corodes and the waste can be swept away doesn't seem to be that deep either.
A Caltech professor, David Stevenson, proposed a temperature-resistant probe immersed in a blob of molten iron: Stevenson, David J. Mission to Earth's Core - A Modest Proposal. Nature, 423, 239-240, 2003a. No radioactivity necessary, and the PDF is here: http://mathcs.albion.edu/~mbollman/Honors/ToTheCore!.pdf
What prevents it from cooling down?
A patent for a similar device from back in the 60s:
http://www.google.com/patents/US3115194
Happened to see it while archiving the inventor's papers. :)
Happened to see it while archiving the inventor's papers. :)
What a fascinating proposition. FYI: This blog article is from 2013 and is about scientific papers written in 2008 and 2005. A few minutes of cursory Googling turns up nothing else.
It was actually used as the basis of a Young Adult book in 2005 [1] or a very similar idea. The book uses a large molten ore body created from explosive charges.
[1] https://en.wikipedia.org/wiki/Artemis_Fowl:_The_Opal_Decepti...
[1] https://en.wikipedia.org/wiki/Artemis_Fowl:_The_Opal_Decepti...
"... and they were never heard from again!"
Did this go anywhere? The only papers if find that reference the original ideas (2005 and 2008) mention nuclear waste that melts itself into the Earths core.
Probably not. That's a scary thing to build. Cobalt-60 gammas are hard to shield, and 2000K is really hot. The laws of physics don't forbid building such a thing, but I wouldn't want to be in the same building with it.
Okay, so you have something that's so self-heating that it'll easily melt rock. In fact, it's hot enough that it self-liquifies quickly at STP. Cobalt reacts weakly with oxygen, but you'll still have to be careful with it in air, so you'll have to seal it in something; at 2000K, there are only a few materials with which you can hold and seal it, tungsten being one. Also, it's radioactive, and the tungsten sphere you put it in isn't nearly sufficient to stop the gammas.
So, you get your tungsten sphere all ready to go, let the cobalt liquify itself, pour it into the sphere, and then lower/drop it into a borehole. Better not be any water down there, or it might come back up.
Once you've got it doing it's melting thing and it's really deep at the bottom of a borehole, it probably can't hurt anyone.
I can't imagine a funding agency being ballsy-enough to fund it, and _really_ can't imagine a nuclear regulatory agency being interested in letting you build a source that could get itself so thermally hot.
TL;DR -- lots could go wrong.
Okay, so you have something that's so self-heating that it'll easily melt rock. In fact, it's hot enough that it self-liquifies quickly at STP. Cobalt reacts weakly with oxygen, but you'll still have to be careful with it in air, so you'll have to seal it in something; at 2000K, there are only a few materials with which you can hold and seal it, tungsten being one. Also, it's radioactive, and the tungsten sphere you put it in isn't nearly sufficient to stop the gammas.
So, you get your tungsten sphere all ready to go, let the cobalt liquify itself, pour it into the sphere, and then lower/drop it into a borehole. Better not be any water down there, or it might come back up.
Once you've got it doing it's melting thing and it's really deep at the bottom of a borehole, it probably can't hurt anyone.
I can't imagine a funding agency being ballsy-enough to fund it, and _really_ can't imagine a nuclear regulatory agency being interested in letting you build a source that could get itself so thermally hot.
TL;DR -- lots could go wrong.
I spoke too-quickly regarding the radioactive shielding requirements, they're more manageable than I thought [1]. For the 10-cm thick tungsten wall, following [1], it looks like the shielding factor is ~25,000. That's more significant than it sounds, because only the gammas emitted at the surface of the cobalt see that shielding factor. The rest are better shielded, up to factors of 10^11 in the best case (propagating all the way across the sphere).
It's still a spooky thing to assemble, but it does appear that if the shielding is preserved, that it could be done without ridiculous quantities of assembly/launch shielding.
It's still a spooky thing to assemble, but it does appear that if the shielding is preserved, that it could be done without ridiculous quantities of assembly/launch shielding.
It's utterly insane!
A 30cm sphere has a volume of around 1.1 x 10^5 cm^3. Cobalt's density is about 8.9g/cm^3, so we're looking at roughly 10^6 grams of 60Co, or about a ton of the stuff.
60Co puts out 1100 Curies of radiation per gram, so this sphere represents about 1.1 billion Curies. To put this in perspective, a nuclear weapon detonation releases on the order of 1-5 MCuries of fallout: the Chernobyl disaster vented about 200 MCuries into the environment: total contamination left behind by the Soviet nuclear weapons program is estimated at around 3 GCuries.
I am not sanguine about a research experiment that requires assembling multiple Chernobyl's worth of high level gamma emitters in a red-hot capsule, dropping it on the ground, and hoping it stays intact ...
A 30cm sphere has a volume of around 1.1 x 10^5 cm^3. Cobalt's density is about 8.9g/cm^3, so we're looking at roughly 10^6 grams of 60Co, or about a ton of the stuff.
60Co puts out 1100 Curies of radiation per gram, so this sphere represents about 1.1 billion Curies. To put this in perspective, a nuclear weapon detonation releases on the order of 1-5 MCuries of fallout: the Chernobyl disaster vented about 200 MCuries into the environment: total contamination left behind by the Soviet nuclear weapons program is estimated at around 3 GCuries.
I am not sanguine about a research experiment that requires assembling multiple Chernobyl's worth of high level gamma emitters in a red-hot capsule, dropping it on the ground, and hoping it stays intact ...
I imagine the safe way of deploying the thing would be to assemble it on-site, over the bore hole, robotically. Don't have any humans anywhere near the entire operation as long as all of that cobalt is in the same place (deliver it to the site with several delivery missions, each only having a relatively safe amount of cobalt).
(Apparently the cobalt would be inserted into the tungsten sphere as a not-yet-liquid sphere. That would make the multiple deliveries and robotic assembly more difficult, so maybe a liquid-assembly like you suggest could be arranged.)
How the hell do you weld tungsten anyway? Maybe make the sphere in two halves, then spin them up in opposite directions and push them together, to friction weld them?
(Apparently the cobalt would be inserted into the tungsten sphere as a not-yet-liquid sphere. That would make the multiple deliveries and robotic assembly more difficult, so maybe a liquid-assembly like you suggest could be arranged.)
How the hell do you weld tungsten anyway? Maybe make the sphere in two halves, then spin them up in opposite directions and push them together, to friction weld them?
Tungsten is usually sintered with a binder. I'm unaware of any welding techniques that work with it.
For a similar fabrication job, check out the LARES satellite (which is awesome, elegant, and the densest free-falling object in the Solar System):
http://www.esa.int/Our_Activities/Launchers/Launch_vehicles/...
For a similar fabrication job, check out the LARES satellite (which is awesome, elegant, and the densest free-falling object in the Solar System):
http://www.esa.int/Our_Activities/Launchers/Launch_vehicles/...
Laser, electron-beam and atomic-hydrogen (no, not crackpot-conspiracy-theory "HHO" atomic hydrogen) welding can work with tungsten, in theory...
Interesting that you mention HHO as crackpot theory.
What I am familiar with are kits to generate HHO gas for hydrogen welding. Mainly, they rely on electrolysis of water and gathering of H2. Of course, the amateur kits have blowback preventers and other tech to prevent gas explosions.
But nothing crackpot. Guess I don't read the cranks documents.
What I am familiar with are kits to generate HHO gas for hydrogen welding. Mainly, they rely on electrolysis of water and gathering of H2. Of course, the amateur kits have blowback preventers and other tech to prevent gas explosions.
But nothing crackpot. Guess I don't read the cranks documents.
I think the name "HHO" itself hints that some amount of bullshit is taking place - the electrolysis units are obviously burning a 2:1 mixture of H2 and O2, not some weird mixture of atomic hydrogen and oxygen or impossible isomer of water. Empirically (via youtube), there is a strong connection between "HHO" promoters and "water-fueled car" and "over-unity generator" fraudsters. Oxyhydrogen torches are pretty awesome - I've used both a small electrolysis unit for jewelry work, and a larger tank-fed torch for working with fused quartz. Amazingly clean and hot flame, with definite niche-applications. However, oxyhydrogen combustion (electrolysis-derived, or otherwise) isn't exactly a revolutionary technology. We've made industrial use of it since the 1860s [1], and the trend has been gradual replacement by other fuels and techniques (TIG, electric arc furnaces, etc) that are more controllable and lack H2's unique shortcomings - eg. hydrogen embrittlement, massive range of explosive concentrations, and incredible ability to diffuse through things.
[1] Faraday's 1861 lecture on platinum-group metals is a great example. Small-scale platinum casting is one of the big uses for oxyhydrogen - the combination of a high melting point and severe carbon embrittlement make H2 ideal for working with platinum.
[1] Faraday's 1861 lecture on platinum-group metals is a great example. Small-scale platinum casting is one of the big uses for oxyhydrogen - the combination of a high melting point and severe carbon embrittlement make H2 ideal for working with platinum.
Atomic hydrogen welding is basically taking a COTS plasma cutter and blowing H2 thru it and welding with it, not welding with H2 but with hydrogen ions. On a scale of hazardous welding technologies, its up there. Possibly the only thing I'd less enjoy doing by hand would be explosive welding or some of the thermite processes. Its not "is there going to be a fire" but "how much damage will the inevitable fire cause vs the cost of alternative fabrication"
On the bright side (oh the pun) during the welding its pretty efficient at preventing weld pool oxidation. On the bad side, if long term hydrogen embrittlement is an issue with the base metal, this is an interesting way to find out. Also you can get some gas porosity problems as the weld bubbles while cooling, exactly CO2 in soda water, although hydrogen is better than the noble gasses (like argon in a plasma cutter)
Burning homemade H2 in a modified acetylene torch like you're talking about is comparatively harmless with the exception that H2 can find leaks that acetylene can't find, although its not that much worse. Oh and the regulator is different because acetylene comes out of a coke bottle solution like CO2 out of soda, but hydrogen comes out of a tank like O2 so the pressures are a bit higher.
On the bright side (oh the pun) during the welding its pretty efficient at preventing weld pool oxidation. On the bad side, if long term hydrogen embrittlement is an issue with the base metal, this is an interesting way to find out. Also you can get some gas porosity problems as the weld bubbles while cooling, exactly CO2 in soda water, although hydrogen is better than the noble gasses (like argon in a plasma cutter)
Burning homemade H2 in a modified acetylene torch like you're talking about is comparatively harmless with the exception that H2 can find leaks that acetylene can't find, although its not that much worse. Oh and the regulator is different because acetylene comes out of a coke bottle solution like CO2 out of soda, but hydrogen comes out of a tank like O2 so the pressures are a bit higher.
"assemble it on-site"
This allows you to transport the Co-60 taking advantage of square-cube law scaling. In summary its a zillion times easier to keep a million Co-60 ball bearings cool and frozen than one big sphere because of surface area.
If you're really bored you can do the thermodynamics calculations for how small a pellet has to be to remain cool enough to touch safely (well, other than the radioactivity) in still room temp air, etc. Or if you're willing to clamp the pellet to a 10 C/W transistor heatsink (that heatsink is about the size of a postage stamp, is if you figure on a hot day your skin can tolerate about 10C temp rise without getting a burn, than that means your pellet has to dump less than a watt or so, of course there's no rule you couldn't use a much better larger heatsink, or a modest cooling fan, or drop it in a barrel of water, etc)
The biggest problem you run into with this kind of stuff is thermal shock from expansion. You might be well advised to find some low coeff of expansion cobalt alloy rather than using the straight up stuff. A straight up sphere, would likely shatter if big enough and the exterior is frozen and the inside is very hot.
This allows you to transport the Co-60 taking advantage of square-cube law scaling. In summary its a zillion times easier to keep a million Co-60 ball bearings cool and frozen than one big sphere because of surface area.
If you're really bored you can do the thermodynamics calculations for how small a pellet has to be to remain cool enough to touch safely (well, other than the radioactivity) in still room temp air, etc. Or if you're willing to clamp the pellet to a 10 C/W transistor heatsink (that heatsink is about the size of a postage stamp, is if you figure on a hot day your skin can tolerate about 10C temp rise without getting a burn, than that means your pellet has to dump less than a watt or so, of course there's no rule you couldn't use a much better larger heatsink, or a modest cooling fan, or drop it in a barrel of water, etc)
The biggest problem you run into with this kind of stuff is thermal shock from expansion. You might be well advised to find some low coeff of expansion cobalt alloy rather than using the straight up stuff. A straight up sphere, would likely shatter if big enough and the exterior is frozen and the inside is very hot.
The article also suggests using the probe to analyze the composition of other planets. Is that doable? It seems pretty tough to me to carry on a space ship a nuclear probe hot enough to melt rocks.
If we're to the point where we're even considering this, presumably we're in a position to obtain the materials from either local sources, or possibly asteroid sources. This presumes a level of tech much higher than our current one since at our current one we can barely land probes that can drill semi-aimlessly into rocks. (And don't get me wrong, that's a hell of an achievement that gives me the Warm Science Fuzzies that we can pull it off... but it's also a long way from being able to do this sort of probe on other planets.)
If you're going to carry a probe powerful enough to melt rocks on a spaceship, the probe better damn well be nuclear powered. There's no other way to get the energy density to make the launch costs feasible.
I agree that the prob will have to be nuclear powered. What I find risky is to put it on a spaceship.
"Subsequent re-crystallisation of the molten material will generate intense acoustic signals."
Why would it make any noise?
Why would it make any noise?
I imagined to be like ice which does make crackling noises when it freezes due to expansion, except cooling rocks will shrink causing the same. Re-solidifying rock would probably sound louder and the acoustic signature may travel further.
Would this produce a new volcano?
Or would the magma just freeze as it travels through the relatively cool hole?
Or would the magma just freeze as it travels through the relatively cool hole?
My read is that the rock would re-fuse above the probe, so no:
"Heat generated from the decay of radioactive cobalt-60 allows the probe to melt its way into the Earth. The probe is estimated to melt down to a depth of 20 km in ~1 year. As the probe descents deeper, the rate of descent will gradually slow until the probe reaches a depth of 100 km after ~30 years. By melting its way into the Earth, the probe will leave behind a wake of molten material. Subsequent re-crystallisation of the molten material will generate intense acoustic signals."
"Heat generated from the decay of radioactive cobalt-60 allows the probe to melt its way into the Earth. The probe is estimated to melt down to a depth of 20 km in ~1 year. As the probe descents deeper, the rate of descent will gradually slow until the probe reaches a depth of 100 km after ~30 years. By melting its way into the Earth, the probe will leave behind a wake of molten material. Subsequent re-crystallisation of the molten material will generate intense acoustic signals."
This sounds like a more practical version of David J. Stevenson's 2003 earth probe proposal: http://news.nationalgeographic.com/news/2003/05/0514_030514_...
Seems that the technique would also work on Europa to melt its way into the ocean underneath the ice.
But if there really is live down there, how do you then explain to them that you just dropped some nuclear waste into their ocean?
"We have reasons to believe you posses weapons of mass destruction"
Worked fine with all the depleted uranium dropped on Iraq.
Worked fine with all the depleted uranium dropped on Iraq.
Europeans (pun intended) could be much better equipped to retaliate than Iraqis.
It has definitely been suggested: http://en.wikipedia.org/wiki/Cryobot http://www.jpl.nasa.gov/releases/2002/release_2002_6.html
This sounds like a controlled version of the China syndrome. http://en.wikipedia.org/wiki/Nuclear_meltdown#China_Syndrome
> As the probe descents deeper, the rate of descent will gradually slow until the probe reaches a depth of 100 km after ~30 years
The article doesn't mention - why will the probe stop descending?
The article doesn't mention - why will the probe stop descending?
Increase in density as you get closer to the core.
On top of which gravity is going to lessen as you get to the center of mass, so even a little resistance will eventually become extremely significant...
Only 100 km down, the gravitational acceleration would not be reduced by very much. Assuming the Earth is spherical and has uniform density, the probe would only be below ~3% of the mass and would be less than 2% closer in distance. So the acceleration felt by the probe would only vary by a few percent.
At 100km, the gravitational acceleration is actually higher than at the surface.
http://www.wolframalpha.com/input/?i=gravitational+accelerat...
In fact, it increases until 3500km below the surface (2800km radius).
http://en.wikipedia.org/wiki/Gravity_of_Earth#mediaviewer/Fi...
http://www.wolframalpha.com/input/?i=gravitational+accelerat...
In fact, it increases until 3500km below the surface (2800km radius).
http://en.wikipedia.org/wiki/Gravity_of_Earth#mediaviewer/Fi...
What was that recent speculation based on seismic resonance about there possibly being a large amount of previously un-theorized water, rather than rock, somewhere in the interior?
Why not place the sphere into a pre-made hole so it will make it to the center of the planet faster?
A couple reasons, I'd bet - first, a hole wide enough to fit the probe is pretty unusual, and would be an expensive research project all on its own. Second, the probe near the surface will emit the largest signal, so you get some really good SNR data to calibrate your algorithms against. If you don't understand the signals you're receiving when it's shallow, you won't understand them any better when it's deep - a regime where we have more theories than data. Or maybe something else.
Drop it into a volcano, for example?
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why cant we dispose our nuclear waste in this way?
I don't think most nuclear waste gets nearly hot enough.
If it did, we could just harvest it.
Excellent point. If you have a sphere that can maintain 2000C and melt through rock, toss it into a steam turbine and hook it up to the grid.
if they get to the center they will find the gnomes, which won't end well.
wow this is actually genius cheap and doable can some please forward this to Jeff Bezos?
"transform some of the energy from radioactive decay"
Not so simple. You need a hot source and a cold sink to transform energy. Where's your cold sink? This thing is intended to melt what's around it, and the outside of the probe is not that different in temperature from the inside.
Not so simple. You need a hot source and a cold sink to transform energy. Where's your cold sink? This thing is intended to melt what's around it, and the outside of the probe is not that different in temperature from the inside.
Erm. If it's melting the rock around it, then the rock is your cold sink. By the time the temperature of the rock catches up with the probe, it's already molten anyway.
More specifically: the interior of the probe is 2000F, the surrounding rock melts at 1000F. That's a pretty good temperature gradient right there.
You need a hot source and a cold sink to transform energy.
Only if it's thermal energy. Given the small amount of power needed, they could easily use a betavoltaic generator.
Only if it's thermal energy. Given the small amount of power needed, they could easily use a betavoltaic generator.
Co-60 decays via beta (and then gamma) decay. It's a straightforward matter to convert the beta decay into electrical power.
Is it really that simple? You can't have any active electronics - they would melt.
And the tungsten is touching the cobalt, with no air gap (i.e. to opportunity to harvest power from the electrons returning to the cobalt to neutralize charge).
How would you harvest the electrons?
And the tungsten is touching the cobalt, with no air gap (i.e. to opportunity to harvest power from the electrons returning to the cobalt to neutralize charge).
How would you harvest the electrons?
Of course it's not simple, it's a very challenging project. But in terms of providing electrical power, if it's possible to have electronics that work at all then it would be possible to power them via beta decay. This is already an established technology in the form of "betavoltaics", which have powered existing devices (such as pace makers) in the past.
http://en.wikipedia.org/wiki/Betavoltaics
http://en.wikipedia.org/wiki/Betavoltaics
Tungsten oxidizes in air beginning around 600°C and as the temperature increases, the tungsten oxide layer scales off, exposing underlying metal to further oxidation. (see, for example, http://labfus.ciemat.es/AR/2011/C_004/AM_4x.pdf)
Tungsten is great for high temperature use in vacuum, neutral (the inert gases) or reducing environments (hydrogen, for example). You can use it nearly up to its melting point in those conditions if you aren't too dependent on structural integrity.
In oxidizing environments (air, oxygen, water, halogens, silicates, etc.) it fails quite rapidly. Molten rock is replete with chemical species that react with tungsten at elevated temperatures.
At 2000°C, the tungsten blanket covering the Co60 heat source would be corroded away, I'll guess, within a week of launch on its journey to the center of the earth.
Although it would be incredibly costly, they might have better luck with iridium or rhenium.
Nevertheless, a fun mission to think about.