Geothermal Energy Could Outperform Nuclear Power | Hacker News Reader

Geothermal Energy Could Outperform Nuclear Power

oilprice.com

48 pointsPaulHoule34 comments

So the article doesn't really go into what the innovation is here (from hydraulic fracturing). It's actually just a driling technique invented for fracking called horizontal drilling. Some detail here [1]. A primer on horizontal drilling in fracking is here [2].

Basically, current geothermal designs are built on vertical wells and I believe they are paired (but I'm not 100% sure about this) so you drop water down one, the heated rock boils it into steam and the steam comes out the other to turn a generator and generate electricity.

Detail is light here so I'm speculating that perhaps geothermal hotspots aren't uniform with depth in a lot of places so you can drill horizontally to get more heat generation. Or maybe a geothermal plant can use this to access a wider area of hotspots?

What's not clear to me is how you'd move water (and steam) through horizontal wells. Oil drilling has a whole process for doing this that I don't think applies.

I'm favor of trying whatever this is though. Sure, why not? I still think solar is our future but I'm happy to be wrong.

[1]: https://time.com/6302342/fervo-fracking-technology-geotherma...

[2]: https://oerb.com/environment-innovation/horizontal-drilling-...

The economist has a graphic:

https://www.economist.com/science-and-technology/2024/09/13/...

Archive: https://archive.ph/k1qZ9

It is still two paired wells. But I think the trick is that water can be injected more targeted.

Horizontal drilling is one thing, but also literally fracking - creating fractures in rock underground with high pressure. These fractures vastly increase the surface area of contact between the water and the rock as it flows between the two wells.

Finnish energy company ST1 tried to make a deep heat district heating plant and drilled few over 6km deep wells. They wanted to connect the wells at the bottom but failed to get enough water flowing between wells for profitable operation.

https://www.st1.com/st1s-otaniemi-geothermal-pilot-projects-...

Geothermal energy can be seen as just natural nuclear energy, where the fission reactions are safely isolated deep underground.

Sure, minus fuel processing, disposing of processing waste, transportation of fuel, inspection of the vessel and plant, maintenance of the vessel and plant, storage and/or reprocessing of used fuel rods and transportation of used fuel rods.

I think the OP agrees?

Have we ever thought about building a nuclear reactor underground before? Seems a little insane, but I'm trying to think through the "why" part.

It would be awfully convenient if the way you "store" the nuclear waste is to just leave it in the reactor underground and then build another one!

Immediate problem that comes to mind: Groundwater contamination.

Also it being a pain to build (probably?).

Anybody aware of if anybody has explored this before?

So there are people working on that [1]. It's basically geothermal where the heat is generated by a nuclear reactor. If anything goes wrong, you just bury it. If it's geologically stable, not near a water table and a mile deep, then there's a certain logic to that.

[1]: https://eepower.com/news/underground-energy-how-this-mile-de...

Sounds neat, but isn't like the number 1 most important thing at a reactor keeping it cooled?

You can do that underground in Klei’s Oxygen Not Included — synthesize some supercoolant, run it through an aquatuner, eat up the waste heat with steam turbines, maybe throw a wheezewort someplace for good measure… but I might be missing some steps.

Water is generally used to cool nuclear reactors. And you're heating water so it's kind of a 2-for-1.

You could even have a separate cooling loop with a heat exchange with the water you're boiling to avoid any radioactive containment, I guess?

I don't know what the failure modes for this look like. These are small reactors. Is there enough fuel for it go critical? I would assume not. What happens if there's a containment breach? Will it start releasing radioactive steam?

The whole thing is still at a conceptual stage.

That idea was totally crazy. In order to save on pouring lots of concrete for a containment dome, you dig one mile in bedrock.

But one thing that everyone missed when the story came out was what was so special about 1 mile. Why not half a mile or 1.5 miles? The neat thing (which they did not bother to publicize) was that the pressure in a pressurized water reactor is exactly the pressure at the bottom of a column of water one mile high. So you do not need pumps for your reactors. You just let your water fall to the reactor, the reactor heats it and sends it back. It's quite elegant. Of course, the remaining engineering details are left to the reader. For example, what happens if some valve breaks 1 mile deep underground?

dimensionally it's hugely advantageous. a 1600-meter-thick containment dome (to use modern units rather than medieval ones) would be 17 billion cubic meters of concrete, which would cost about 700 billion dollars, at the price of 40 dollars per cubic meter i happened to see in the newspaper today. but a 300-mm-diameter hole 1600 meters into the bedrock only requires breaking up 110 cubic meters of bedrock. all things being equal, that's about 150 million times easier

(in practice people skimp on the containment instead of trying to build trillion-dollar containment domes)

as for water pressure, you can design pwrs to work over a significant range of water pressures

Reactors have to be refueled periodically. This might be much more difficult if the reactor is deep underground, or at least it might complicate the design. Unless the design and construction can be simple enough that it's cheaper to make a new one than refuel an existing one.

The plan for old HI nuclear material in USSR in a decommissioned plant was to "settle in place" for a hundred year (after that its mostly MI/LI that you can glass easily). If you have enough space, the "return to green" that is the goal in France (10-30% of the lifetime costs depending on who you listen to) is too expensive for little benefits.

Doesn't most geothermal heat come from radioactive decay and gravitational potential energy of the planet as it formed, rather than reactions involving multiple particles? I'd have agreed if you'd said "radioactive substances" rather than "fission reactions".

Natural radioactive decay is also an example of fission - just not a fission chain reaction (… except when it is! https://en.m.wikipedia.org/wiki/Oklo )

In like fashion, we can see wind, solar, and hydro as just natural nuclear energy, where the fusion reaction is safely isolated at eight light-minutes' distance through space.

We can see fossil fuel as nuclear energy, as the molecular bonds we break were formed by said fusion reactor millions of years ago

Oh, well, that is a clever twist! Light of the ancient sun, indeed.

The claim here is that 80% of it is nuclear and the other 20% heat comes from gravitational accretion

https://petrowiki.spe.org/Geothermal_energy

Doesn't seem like a particularly helpful or practical way of categorizing fuel sources. Would you then place wind as a subset of solar, and solar as a subset of nuclear?

I've read here(HN) in the past that fracking hotspots caused "earthquakes" somewhere in europe, is it debunked or non issue?

In addition I've read/heard that Ormat which manages/builds many such small plants that they pump a different fluid(not water) in the pipe to extract the heat to create power [as opposed to what is stated in the article and in comments here] https://patents.google.com/patent/CN101142377B/en

basel. induced seismicity also happened in south korea. the industry claims it's under control

It is true, Not only in europe, it happen in the US and in Asia too. It is a "non issue" in the sense that it won't trigger a catastrophic seism, as long as houses are mostly well built, the risks are minimal.

This might be a stupid question … but would harnessing geothermal somehow be akin to allowing a hot ember to cool to room temp? Would we do the same to the core? I guess not since it’s radioactive and giving off heat I guess?

It’s not a stupid question. In most threads on geothermal energy this does come up and a lot of other people have answered it though.

The short answer is that there is so much heat in the massive amount of melted rocks and metal under our feet that we could never possibly cause any sort of significant cooling of the earth.

Awesome! Then I’m onboard. Let’s do it! god knows we need the power — let’s hope it doesn’t all go to AI or to mine bitcoins

Don't worry: Jevons' paradox assures us that once the power becomes cheap enough, some application even more frivolous than bitcoin mining will be invented to consume it.

I'm waiting for replicators.

Perhaps the problem could be different. Wouldn't the energy gathered from renewable sources otherwise be used by nature? At which point will the amount we capture be large enough to impact sognificantly the ecosystem?

In theory yes, over a geological timescale. In practice, it would be like worrying about the sun expanding and engulfing the earth, when it reaches its red giant phase, when you are installing solar panels.

Nuclear is probably more expensive than renewable energy with storage. Geothermal will likely be limited to favorable locations or to harvest low quality heat for heating building (or district heating).

somehow this article, written apparently by an llm deepfake, doesn't mention either induced seismicity or the enormous drop in the price of solar energy over the last year. outperforming nuclear power, an economically nonviable energy source, is necessary but not sufficient to reach economic viability; we'll need cheaper heat engines for that

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