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Comment by nonrandomstring | Hacker News Reader

Many are keen to point out that we live in proximity of a giant fusion reactor and ought to be smart enough to harness its output.

But it took me a long time to appreciate something odder; We're living on a giant fission reactor [1]. The Earth's core isn't hot because it just hasn't cooled down in the icy void of space. It's actively producing heat. Our gravity acts upon the heavy elements, which sink through the molten iron and silicon, to the core, where they become fissile.

[1] https://blogs.scientificamerican.com/observations/nuclear-fi...

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Not a fission reactor. Just a radiothermal generator. It's not critical.

This article doesn't say anything surprising; the news is that these guys calculated how much heat is produced.

Ok I just read a bit more and apparently there are some fringe geophysicists who think it really is more like a reactor. I didn't know that.

There were actual "natural" fission reactors in the crust in central Africa some time ago[1] .. the broader region provided the bulk of the ore for the Cold War production of weapons grade ore.

[1] https://en.wikipedia.org/wiki/Oklo_Mine

Nature used up the best ore billions of years ago. We did get radiation-resistant microbes in exchange.

The news here, specifically, is that:

> Enter Quaise, which “is developing technology to blast rock with microwaves to potentially drill the deepest holes on Earth.

ie. there's a new, untried at extremes, bore drilling technique.

The calculation of heat production from earths core isn't new here, and nor, sadly, is any demonstration of a bore hole at a 10 mile depth.

They do acknowledge the deepest convential borehole so far was 7.6 mile (at some considerable effort at no small expense).

Mostly.

https://en.m.wikipedia.org/wiki/Natural_nuclear_fission_reac...

When I asked a physicist about this, he said it's mostly conjecture. You can't really prove it because we can't actually visit the Earth's core.

Yes, I'm aware how the neutrino velocity measurement supposedly confirms it. But I don't think the scientific community has accepted it at large.

Radiothermal heating of planetary cores is established scientific fact. It's not a fission reactor because there's no chain reaction, just a lot of unstable elements in one place. Some details are controversial, but not the basics. (I have a geochemistry PhD)

Ok I just read a bit more and apparently there are some fringe geophysicists who think it really is more like a reactor. I didn't know that.

Yes, I think that is the where the debate is over the exact nature of things. Fission happens spontaneously, even the bismuth in Pepto Bismol has a bit of a fission going on, slowly decaying into thallium.

²⁰⁹Bi decay to ²⁰⁵Tl is alpha decay — the bismuth nucleus splits into an alpha particle (helium) and a thallium nucleus. I think you’d be hard pressed to find a nuclear physicist or engineer who calls that “fission”.

Here’s the Wikipedia article on fission. It’s a rather different process:

https://en.m.wikipedia.org/wiki/Nuclear_fission

Can you link to what you are reading? I am a nuclear engineer, I suspect they are using a very loose definition of critical, one that would imply the entire universe itself is critical.

Maybe the fault is with me for using the word "reactor" a bit loosely.

I don't think anyone knows for sure what is going on down there.

My theory is that it's both critical and quiescent, with a violent dynamic at play. Gravity will concentrate the heaviest and least stable elements as you'd expect. As that happens pockets of dense matter in close neutron proximity will approach critical and heat billions of tons of matter which then convects outwards, dispersing the mixture. Think of a lava lamp.

Geochemists say uranium concentrates in the crust, for chemical reasons -- which is, in fact, where we find it.

are there estimates for how much heat is produced this way? any other way? (solar magnetic field interaction?) how much is the residual heat dissipation?

edit: ah, just read the title of the link posted in the top level comment. apparently it's "half of the heat" :)

Yes. Alpha decay in particular is also the source of essentially all helium on earth, and the reason helium is captured from gas wells.

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