

A Nuclear Probe to Explore Earth’s Interior - mike_esspe
http://beyondearthlyskies.blogspot.com/2013/09/a-nuclear-probe-to-explore-earths.html

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ridgeguy
The post states that tungsten "...has a low corrosion rate at elevated
temperatures." This is not accurate.

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](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.

~~~
Natsu
> 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?

~~~
gambiting
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.

~~~
tarre
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.

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bediger4000
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](http://mathcs.albion.edu/~mbollman/Honors/ToTheCore!.pdf)

~~~
RachelF
What prevents it from cooling down?

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entangledqubit
A patent for a similar device from back in the 60s:
[http://www.google.com/patents/US3115194](http://www.google.com/patents/US3115194)

Happened to see it while archiving the inventor's papers. :)

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wmeredith
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.

~~~
valarauca1
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...](https://en.wikipedia.org/wiki/Artemis_Fowl:_The_Opal_Deception)

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ChuckMcM
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.

~~~
ISL
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.

~~~
Crito
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?

~~~
ISL
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/...](http://www.esa.int/Our_Activities/Launchers/Launch_vehicles/Vega3/LARES_Laser_Relativity_Satellite)

~~~
msds
Laser, electron-beam and atomic-hydrogen (no, not crackpot-conspiracy-theory
"HHO" atomic hydrogen) welding can work with tungsten, in theory...

~~~
kefka
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.

~~~
msds
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.

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S4M
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.

~~~
jessriedel
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.

~~~
S4M
I agree that the prob will have to be nuclear powered. What I find risky is to
put it on a spaceship.

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rdmcfee
With the accelerating change in the earth's magnetic field it would be
fantastic to drop a few of these bad boys and see what's actually going on
down there.

~~~
gipp
Wouldn't get anywhere near the dynamo, sadly.

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ars
"Subsequent re-crystallisation of the molten material will generate intense
acoustic signals."

Why would it make any noise?

~~~
ejr
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.

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spingsprong
Would this produce a new volcano?

Or would the magma just freeze as it travels through the relatively cool hole?

~~~
dredmorbius
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._ "

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curtis
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_...](http://news.nationalgeographic.com/news/2003/05/0514_030514_earthcore.html)

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cromwellian
Seems that the technique would also work on Europa to melt its way into the
ocean underneath the ice.

~~~
panzi
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?

~~~
rational-future
"We have reasons to believe you posses weapons of mass destruction"

Worked fine with all the depleted uranium dropped on Iraq.

~~~
TeMPOraL
Europeans (pun intended) could be much better equipped to retaliate than
Iraqis.

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gulpahum
This sounds like a controlled version of the China syndrome.
[http://en.wikipedia.org/wiki/Nuclear_meltdown#China_Syndrome](http://en.wikipedia.org/wiki/Nuclear_meltdown#China_Syndrome)

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grecy
> _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?

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toomuchtodo
Increase in density as you get closer to the core.

~~~
TallGuyShort
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...

~~~
privong
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.

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msane
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?

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youaredoomed
Why not place the sphere into a pre-made hole so it will make it to the center
of the planet faster?

~~~
jimmyswimmy
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.

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doctorKrieger
why cant we dispose our nuclear waste in this way?

~~~
mikeash
I don't think most nuclear waste gets nearly hot enough.

~~~
JetSpiegel
If it did, we could just harvest it.

~~~
mikeash
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.

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BorisMelnik
if they get to the center they will find the gnomes, which won't end well.

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3327
wow this is actually genius cheap and doable can some please forward this to
Jeff Bezos?

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ars
"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.

~~~
gipp
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.

~~~
ars
The rock would not work as a cold sink - the cold rock is too far from the
probe. The rock right near the probe is at almost the exact same temperature.

~~~
kijin
And that's exactly why the probe will take 30 years to move 100km. It's going
to be a very slow process.

