The Oklo region has now-exhausted Uranium deposits.
From Wikipedia:
"Some of the mined uranium was found to have a lower concentration of uranium-235 than expected, as if it had already been in a nuclear reactor. When geologists investigated they also found products typical of a reactor. They concluded that the deposit had been in a reactor: a natural nuclear fission reactor, around 1.8 to 1.7 billion years BP – in the Paleoproterozoic Era during Precambrian times, during the Statherian period – and continued for a few hundred thousand years, probably averaging less than 100 kW of thermal power during that time. At that time the natural uranium had a concentration of about 3% 235U and could have reached criticality with natural water as neutron moderator allowed by the special geometry of the deposit."
jvanderbot
100 kW for a few hundred thousand years is basically the best sales pitch for nuclear power I've ever heard. Even of "just" heat output.
Alupis
Its impressive the amount of clean, cheap energy that's been locked away because of fearmongering tales from well before many were even alive.
throw310822
Cheap until it isn't. I wonder what has been the actual cost per kWh of nuclear power in Japan once factored in the price of Fukushima's disaster (between 200 and 600 billion dollars).
keepamovinOP
The cost you cite sounds more like the cost of the earthquake and tsunami, rather than the Daiichi reactor meltdown cost.
Even if it were, in the time limit safety increases, such costs decrease, more so with more development.
More broadly, nuclear looks expensive not because it's unproductive — but because standard asset pricing discounts its most valuable feature: time. Dense, stable power for centuries gives a low net present value due to long-duration-use and high up front cost, but this more a flaw in how future value is discounted in common economic models that punish rather than reward long life.
Agree - there are places that maybe should consider other methods of power generation.
Upper Midwest USA / Middle Canada? probably pretty darn safe.
linotype
Maybe don’t build a nuclear reactor near the ocean in a place famous for tsunamis?
cdaringe
It is natural and reasonable to be of two minds on the matter. Surely that’s not controversial.
jvanderbot
All power generation has tradeoffs. I like nuclear because it can be small, tucked away, generate _lots_ of power, and has few day to day environmental risks. Spent fuel is an issue, but there's very likely a virtuous cycle that will evolve if we start ramping up nukes again. Dry cask storage is no big deal IMHO, and something will likely evolve that either can use spent fuel or can deal with it better.
legitster
Richard Rhodes brought this up in an interview. He made it a point for critics who say nuclear waste can't be safely disposed of through burial. Well, we have pretty good natural evidence that nuclear fission products can remain buried and undisturbed for a pretty long time!
joe_the_user
I don't disagree that nuclear waste can be disposed of safely under good conditions[1].
But I think a fallacy to claim that natural phenomena should inherently be considered "environmentally safe" in human terms. There are coal seam fires that have been going on for centuries and the pollution of these is just as bad as the pollution generated by human created coal mine fires (and that's truly awful, a significant source of carbon pollution).
[1] The problem with nuclear reactors isn't that their pollution couldn't disposed of with ideal methods but that when they run by for-profit corporations, you will always have the company skirting the edge of what's safe 'cause corporations just go bankrupt with catastrophic events and so their risk-reward behavior isn't the risk-reward optima for humanity.
legitster
No one is saying that it's "inherently" safe but there are a lot of people who claim it is inherently unsafe which is clearly untrue.
glompers
> There are coal seam fires that have been going on for centuries and the pollution of these is just as bad as the pollution generated by human created coal mine fires (and that's truly awful, a significant source of carbon pollution).
Has CO2 fire suppression been unsuccessfully attempted in these seams? Since nobody is underground and we know how to inject CO2 into underground deposits at various pressures, it seems like it would be a good candidate. Plus, with rotary steerable drilling, we could come in laterally (from a safe location above ground) to as many depths of injection as necessary.
a11r
These are large coal seams with significant exposure to the atmosphere. See https://en.wikipedia.org/wiki/Jharia_coalfield for an example. That excavator in the picture is not trying to put out the fire, it is just mining coal that happens to be burning. Spray some water, put out the fire and ship it off to customers.
recursivecaveat
Apparently in mines they are sometimes extinguished with nitrogen. For less contained ones, injecting water or mud, while trying to seal off the ground with impermeable clay to halt oxygen and hopefully choke the fumes. Their scope can be huge though, and they generate a lot of energy which can cause subsidence to open up new passages. The Centralia fire in the US is apparently 15km².
rkagerer
I have a question on rotary steerable drilling. I gather we're only talking about a degree or less of deflection on the steering head. But how does the km's long rest of the stack behind the head snake through the curves? Is it like rail cars, with a little bit of angular bend allowed at the connection of each segment?
Manuel_D
What are the conditions under which nuclear waste buried a mile deep in bedrock will post a risk to society?
bobmcnamara
1) the assumption that because something can be done safely it will be done safely
3) exploding waste barrels due to corner cutting in kitty litter selection exposing surface workers and contaminating the work area - only 1/2 mile down but this type of accident is depth independent https://www.latimes.com/nation/la-na-new-mexico-nuclear-dump...
4) fires
5) lack of a safety culture
6) communicating to future peoples not to mine here
7) long term structural stability and management (ex: Morsleben radioactive waste repository and Schacht Asse II)
Manuel_D
2) I asked about waste buried in the ground, not in transit.
3) if a waste barrel explodes, somehow, underground how does the waste make it's way through a mile of bedrock?
4) Again, how does a fire bring the wast up through a mile of bedrock?
5) This is just a vague statement.
6) So the concern is that future society will forget that this is a waste site, mine a mile deep and retrieve waste, and never figure out that the waste is bad for them? This is rather specific hypothetical that IMO demonstrates just how hard it is for a nuclear waste site to result in contamination.
Just to call it explicitly, because I think this is one of the big points of misunderstanding between pro- and anti-nuclear people (take that as a very rough categorization and not an accusation) -
There is a difference between “something can be done correctly” and “something is likely to be done correctly.” Nuclear advocates I’ve read tend to argue the former - it’s possible to have safe reactors, it’s possible to keep the waste sequestered safely, there’s not a technical reason why nuclear is inherently unsafe. Skeptics tend to be making a different argument - not that it’s not possible to do things safely and correctly, but that in our current late-capitalist milieu, it’s almost impossible that we _will_. It’s not an argument about capability, it’s an argument about will and what happens in bureaucracies, both public and private.
The Asse II site used an existing mine to avoid having to excavate a new tunnel, which subsequently flooded.
Loughla
Burying it in a cheaper place that happens to flood occasionally?
legitster
Insisting on only worst case scenarios is such a bad faith argument. OP specifically asked about deep repositories.
It would be like having a discussion about green energy and insisting that people should assume dams will fail or that blades are going to fly off of turbines.
brians(dead)
[flagged]
BriggyDwiggs42
Can you link me?
nec4b
>> The problem with nuclear reactors isn't that their pollution couldn't disposed of with ideal methods but that when they run by for-profit corporations, you will always have the company skirting the edge of what's safe 'cause corporations just go bankrupt with catastrophic events and so their risk-reward behavior isn't the risk-reward optima for humanity.
Chernobyl was state run.
andrewflnr
From another perspective, its safety lasted almost exactly as long as it took for humans to come around. That window is now closed for future deposits.
(I'm pro-nuclear but that's a hilariously bad argument.)
datatrashfire
Except for Finland nobody has actually created a long term geologic disposal site. Like so many problems, the issue is dominated by political coordination, not physical limits.
acidburnNSA
The US built WIPP. It's not licensed for commercial waste but it sure is a long term geologic disposal site.
mystified5016
It was undisturbed until humans came around and specifically went looking for uranium and dug up the spent reactor fuel.
Which is kind of a problem for future burials because humans exist now and want and know how to find uranium.
The time between humans cracking the atom and the excavation of this nuclear waste is only a few decades. It took less than a hundred years for humans to find this nuclear waste in the ground.
Your argument is not well-founded. Burying nuclear waste for it to be discovered and excavated in less than a century is not nearly long enough.
krunck
This is nonsense. Yep, after 2 billion years this thing is now safe to touch. But that had nothing to do with it's burial.
We at least have pretty good evidence that nuclear fission products can be exposed to groundwater/hydrothermal fluids for a pretty long time.
sliken
Not sure I'd call it safe to touch. Getting with 5cm for an hour gives you as much radiation as a 8 hour flight. I wouldn't want touch it, make jewelry from it, or any substantial near promity. Not to mention if it was "only" a billion years ago it would be MUCH MUCH worse.
wjnc
This article could be so much better: How large are the estimated stores of ore that underwent natural fission? How much energy did it release and over how much time? When? Would this be noticable (and to whom)? So many questions, so little information.
I only know (or knew) high school physics, and when entering this in Claude I get an answer but am unable to verify the answer. Claude says 680 kWh gained per 0.03 grams of U-235 lost due to fission. I am left wondering into what the U-235 fizzed into (sorry, pun) and if I should take that into account.
Edit: There we go with modernity. I went to Claude instead of Wikipedia. Wikipedia at least has the answers. Thanks u/b800h. 100kW of heat on average. I can start filling in the blanks now.
adev_
The 'natural reactor' in Oklo has been discovered by some french researcher from the CEA in the 70s.
There is an entire scientific publication on the topic if it interests you:
I wonder why Claude’s answers aren’t equal or better than Wikipedia - assuming Wikipedia is one of the training datasets. Is the temperature causing it to be probabilistic & other sources are carrying more weight?
lazide
You can think of a LLM as a type of lossy compression of knowledge.
With that in mind, is it really surprising that you don’t get the ‘right’ answer out? Any more than if you compress an image with JPEG, a given pixel isn’t the ‘right’ color anymore either?
They’re both close (kinda) at least, which is the point. If you wanted the exact right answer, don’t use lossy compression - it’ll be expensive in other ways though.
ksenzee
What a great metaphor. I’m adopting that immediately, thank you.
I can't speak for users of Claude, but as a user of Perplexity, having an LLM do a web search has uncovered sources I'd never have considered. The only time I use Google anymore is when I know exactly what I'm looking for.
When I'm in research/discovery mode, I use Perplexity. Its search/analysis is a lot slower than a Google search, but saves me time overall and generally gives me solutions that I'd have to spend time sorting through a Google search to find, in less time than it takes to do so.
wjnc
Claude gave a great answer at the link, at least for me. There might be a plus in learning as well since the answer is well structured with a recognizable style. Say, the scientific article above, has a distinct style and really was not high school physics level.
pfdietz
Uranium was very enriched back at the formation of the Earth, so for a given geometry it would have been much more reactive.
However, uranium ores are often formed due to redox processes, since U(VI) is much more soluble than U(IV). So maybe concentrations wouldn't have been as common back before the Great Oxygenation Event about 2.4 Gya. Still, that leaves ~600 Mya between that point and this reactor, which would be not quite one half life of U235.
foobarian
> All natural uranium today contains 0.720% of U-235. If you were to extract it from the Earth’s crust, or from rocks from the moon or in meteorites, that’s what you would find. But that bit of rock from Oklo contained only 0.717%.
Heh. The garbage web software developer me would have just called it good enough
Would be really interesting to know what the error bars on those figures look like
teuobk
Per NIST[1], the value is 0.7204% +/- 0.0006%, with the uncertainty representing one standard deviation.
I think it would've been good enough for the miners too, if not for the fact that nuclear arms control treaties require every gram of U-235 to be accounted for. When they were digging it out of the ground and found it was less enriched than it should've been, this needed to be explained. It has always fascinated me to think that this natural phenomenon could and probably would have remained unknown forever if not for these treaties and agreements.
mannykannot
You have me wondering about that as well. If the uranium was going to be enriched for use in a light-water reactor (I would guess it was), maybe the difference translates into needing more stages of enrichment to reach the required level?
Aardwolf
> All natural uranium today contains 0.720% of U-235.
That's related to the material of our solar system all coming from the same supernova explosion or similar, right? Does this apply to our entire milky way or just the solar system? What if parts collided with material of _other_ origins and some of that is on Earth, then there could be different mixes, right?
philipkglass
It's related to how long ago the uranium was formed:
We can calculate the abundances of U-235 and U-238 at the time the Earth was formed. Knowing further that the production ratio of U-235 to U-238 in a supernova is about 1.65, we can calculate that if all of the uranium now in the solar system were made in a single supernova, this event must have occurred some 6.5 billion years ago.
This 'single stage' is, however, an oversimplification...
The really interesting thing is that phrase "the production ratio of U-235 to U-238 in a supernova is about 1.65"; the now-rare U-235 is actually more abundant than U-238 in the fresh debris of a supernova. Prolonged aging has preserved more U-238 (half life 4.47 billion years) than U-235 (half life 0.704 billion years) to the point that U-238 is now much more terrestrially abundant. If Earth had been formed with uranium that rich in U-235, there would have been Oklo events all over the place. Uranium wouldn't need isotopic enrichment to be used as fuel in light water reactors. Nuclear fission would probably have been discovered early in the 19th century, soon after the element itself was recognized, because any substantial quantity dissolved in aqueous solution would have reached criticality.
cryptonector
I read GP's question really as: "did all Uranium on Earth come from the same source?" and your answer implies "yes". I think that's right.
The fact that everywhere we see the same U-235/U-238 ratio or very close (Oklo) strongly implies either a single source (supernova) or that if it was more than one source they were all at roughly the same time (6.5 billion years ago), with the latter seeming [to me] less likely, so a single source at 6.5 billion years ago is what makes sense. Unless there were many supernovae and their remnants mixed quite well in our corner of the galaxy where our sun was born.
kretaceous
I don't understand so bear with me.
If the Uranium came from multiple supernovae, then why is it shocking that earth has different concentrations of U235? Moreover, how is it proof of a past fission reaction?
What if that "part" of U235 came from a separate supernova which is a little older and some more of its U235 had already decayed?
ReaLNero
There were unusual elements characteristic of the decay chain following a fission.
After a U-235 atom undergoes fission, one of the outcomes is it releases Barium and Krypton (and some neutrons), which then eventually decay to stable/semi-stable elements. If one of those stable elements is common in the deposit but otherwise rare naturally, it would point to a nuclear reaction having occurred.
Also note that the U-235 decay chain generally looks different from the decay chain following a fission reaction of U-235.
lazide
It’s interesting to extrapolate that to the early earth - radioactive decay and fission interactions likely play a much larger role than we are able to reliably model. Okla is somewhat unique in that the formation survived for us to dig it up - most from that time would not.
keepamovinOP
This is excellent. I love your depth of knowledge in this subject. I learned a lot from this clear comment.
mandevil
This is just in our little corner of the Milky Way, but not thought to be the result of just one supernova. I last looked into this about a decade ago so I might be behind the times, but at that time the most popular theory was that the cloud that became our Solar System was the result of thousands of supernova scattering and mixing atoms, across both the first two generations of stars (the Sun is considered to be a third-generation star), and that mixing is thought to be an important factor in making it complex enough to have rocky inner planets, gaseous outer planets, etc.
BurningFrog
Grok says: At Earth's formation ~4.5 billion years ago, natural uranium contained approximately 23.2% U-235
These numbers are probably only for the local corner of the galaxy. It depends on when the supernova(s) that created the uranium exploded.
_Algernon_
We all have access to Grok and other AI models, and we will ask it if we want it's bullshit hallucinations. There is no point polluting HN with this trash.
CamperBob2
Is it wrong?
joemi
That's a good question.
In order to know whether or not the AI was wrong, you'd need to do some research. Otherwise it's about as reliable as any "fact" some random person on the internet claims to be true.
_Algernon_
Talk about missing the point. Why should I spend my time fact checking the output of a glorified, stochastic parrot?
CamperBob2
Because your competitors are using it, and they are going to flatten you.
Effective tool use is kind of a big deal.
BurningFrog
Anyone can look it up, yet I was the only one who did.
_Algernon_
You didn't look anything up. You prompted a stochastic parrot.
kkwteh
Maybe it’s a remnant from a nuclear ancient civilization.
geocrasher
Maybe it's a sign of a future time travelling civilization with nuclear power but poor navigation, warped straight into the mantle Earth's crust :D
Gregaros
I thought where you were going with his was "that realized the best way to dispose of their nuclear waste was to dump it in the deep past." I’d read that novel.
geocrasher
Only to mine it later and re-use it over and over again. The 5 billion year long recycling program.
julienchastang
A civilization (even perhaps extraterrestrial) that possessed nuclear energy? Unlikely, but still fun to think about! ;-)
stmw
Fun aside - Oklo is also the name of a successful YC company that makes a passively-safe nuclear reactor - https://www.oklo.com
acidburnNSA
They are certainly financially successful. But they haven't split an atom yet so jury is still out on whether their reactor products work well.
From Wikipedia:
"Some of the mined uranium was found to have a lower concentration of uranium-235 than expected, as if it had already been in a nuclear reactor. When geologists investigated they also found products typical of a reactor. They concluded that the deposit had been in a reactor: a natural nuclear fission reactor, around 1.8 to 1.7 billion years BP – in the Paleoproterozoic Era during Precambrian times, during the Statherian period – and continued for a few hundred thousand years, probably averaging less than 100 kW of thermal power during that time. At that time the natural uranium had a concentration of about 3% 235U and could have reached criticality with natural water as neutron moderator allowed by the special geometry of the deposit."
Even if it were, in the time limit safety increases, such costs decrease, more so with more development.
More broadly, nuclear looks expensive not because it's unproductive — but because standard asset pricing discounts its most valuable feature: time. Dense, stable power for centuries gives a low net present value due to long-duration-use and high up front cost, but this more a flaw in how future value is discounted in common economic models that punish rather than reward long life.
Upper Midwest USA / Middle Canada? probably pretty darn safe.
But I think a fallacy to claim that natural phenomena should inherently be considered "environmentally safe" in human terms. There are coal seam fires that have been going on for centuries and the pollution of these is just as bad as the pollution generated by human created coal mine fires (and that's truly awful, a significant source of carbon pollution).
[1] The problem with nuclear reactors isn't that their pollution couldn't disposed of with ideal methods but that when they run by for-profit corporations, you will always have the company skirting the edge of what's safe 'cause corporations just go bankrupt with catastrophic events and so their risk-reward behavior isn't the risk-reward optima for humanity.
Has CO2 fire suppression been unsuccessfully attempted in these seams? Since nobody is underground and we know how to inject CO2 into underground deposits at various pressures, it seems like it would be a good candidate. Plus, with rotary steerable drilling, we could come in laterally (from a safe location above ground) to as many depths of injection as necessary.
2) transportation to the site: https://static.ewg.org/files/nuclearwaste/plumes/national.pd...
3) exploding waste barrels due to corner cutting in kitty litter selection exposing surface workers and contaminating the work area - only 1/2 mile down but this type of accident is depth independent https://www.latimes.com/nation/la-na-new-mexico-nuclear-dump...
4) fires
5) lack of a safety culture
6) communicating to future peoples not to mine here
7) long term structural stability and management (ex: Morsleben radioactive waste repository and Schacht Asse II)
3) if a waste barrel explodes, somehow, underground how does the waste make it's way through a mile of bedrock?
4) Again, how does a fire bring the wast up through a mile of bedrock?
5) This is just a vague statement.
6) So the concern is that future society will forget that this is a waste site, mine a mile deep and retrieve waste, and never figure out that the waste is bad for them? This is rather specific hypothetical that IMO demonstrates just how hard it is for a nuclear waste site to result in contamination.
There is a difference between “something can be done correctly” and “something is likely to be done correctly.” Nuclear advocates I’ve read tend to argue the former - it’s possible to have safe reactors, it’s possible to keep the waste sequestered safely, there’s not a technical reason why nuclear is inherently unsafe. Skeptics tend to be making a different argument - not that it’s not possible to do things safely and correctly, but that in our current late-capitalist milieu, it’s almost impossible that we _will_. It’s not an argument about capability, it’s an argument about will and what happens in bureaucracies, both public and private.
It's not even a a matter of mundane human error when executing procedures over and over again.
It's that the entire managerial pyramid gradually and slowly erodes
https://en.wikipedia.org/wiki/Asse_II_mine
The Asse II site used an existing mine to avoid having to excavate a new tunnel, which subsequently flooded.
It would be like having a discussion about green energy and insisting that people should assume dams will fail or that blades are going to fly off of turbines.
Chernobyl was state run.
(I'm pro-nuclear but that's a hilariously bad argument.)
Which is kind of a problem for future burials because humans exist now and want and know how to find uranium.
The time between humans cracking the atom and the excavation of this nuclear waste is only a few decades. It took less than a hundred years for humans to find this nuclear waste in the ground.
Your argument is not well-founded. Burying nuclear waste for it to be discovered and excavated in less than a century is not nearly long enough.
We at least have pretty good evidence that nuclear fission products can be exposed to groundwater/hydrothermal fluids for a pretty long time.
I only know (or knew) high school physics, and when entering this in Claude I get an answer but am unable to verify the answer. Claude says 680 kWh gained per 0.03 grams of U-235 lost due to fission. I am left wondering into what the U-235 fizzed into (sorry, pun) and if I should take that into account.
Edit: There we go with modernity. I went to Claude instead of Wikipedia. Wikipedia at least has the answers. Thanks u/b800h. 100kW of heat on average. I can start filling in the blanks now.
There is an entire scientific publication on the topic if it interests you:
https://www.sciencedirect.com/science/article/abs/pii/S00167...
With that in mind, is it really surprising that you don’t get the ‘right’ answer out? Any more than if you compress an image with JPEG, a given pixel isn’t the ‘right’ color anymore either?
They’re both close (kinda) at least, which is the point. If you wanted the exact right answer, don’t use lossy compression - it’ll be expensive in other ways though.
When I'm in research/discovery mode, I use Perplexity. Its search/analysis is a lot slower than a Google search, but saves me time overall and generally gives me solutions that I'd have to spend time sorting through a Google search to find, in less time than it takes to do so.
However, uranium ores are often formed due to redox processes, since U(VI) is much more soluble than U(IV). So maybe concentrations wouldn't have been as common back before the Great Oxygenation Event about 2.4 Gya. Still, that leaves ~600 Mya between that point and this reactor, which would be not quite one half life of U235.
Heh. The garbage web software developer me would have just called it good enough
Would be really interesting to know what the error bars on those figures look like
[1] https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl...
That's related to the material of our solar system all coming from the same supernova explosion or similar, right? Does this apply to our entire milky way or just the solar system? What if parts collided with material of _other_ origins and some of that is on Earth, then there could be different mixes, right?
https://world-nuclear.org/information-library/nuclear-fuel-c...
We can calculate the abundances of U-235 and U-238 at the time the Earth was formed. Knowing further that the production ratio of U-235 to U-238 in a supernova is about 1.65, we can calculate that if all of the uranium now in the solar system were made in a single supernova, this event must have occurred some 6.5 billion years ago.
This 'single stage' is, however, an oversimplification...
The really interesting thing is that phrase "the production ratio of U-235 to U-238 in a supernova is about 1.65"; the now-rare U-235 is actually more abundant than U-238 in the fresh debris of a supernova. Prolonged aging has preserved more U-238 (half life 4.47 billion years) than U-235 (half life 0.704 billion years) to the point that U-238 is now much more terrestrially abundant. If Earth had been formed with uranium that rich in U-235, there would have been Oklo events all over the place. Uranium wouldn't need isotopic enrichment to be used as fuel in light water reactors. Nuclear fission would probably have been discovered early in the 19th century, soon after the element itself was recognized, because any substantial quantity dissolved in aqueous solution would have reached criticality.
The fact that everywhere we see the same U-235/U-238 ratio or very close (Oklo) strongly implies either a single source (supernova) or that if it was more than one source they were all at roughly the same time (6.5 billion years ago), with the latter seeming [to me] less likely, so a single source at 6.5 billion years ago is what makes sense. Unless there were many supernovae and their remnants mixed quite well in our corner of the galaxy where our sun was born.
If the Uranium came from multiple supernovae, then why is it shocking that earth has different concentrations of U235? Moreover, how is it proof of a past fission reaction?
What if that "part" of U235 came from a separate supernova which is a little older and some more of its U235 had already decayed?
After a U-235 atom undergoes fission, one of the outcomes is it releases Barium and Krypton (and some neutrons), which then eventually decay to stable/semi-stable elements. If one of those stable elements is common in the deposit but otherwise rare naturally, it would point to a nuclear reaction having occurred.
Also note that the U-235 decay chain generally looks different from the decay chain following a fission reaction of U-235.
These numbers are probably only for the local corner of the galaxy. It depends on when the supernova(s) that created the uranium exploded.
In order to know whether or not the AI was wrong, you'd need to do some research. Otherwise it's about as reliable as any "fact" some random person on the internet claims to be true.
Effective tool use is kind of a big deal.
https://www.hackerneue.com/item?id=17736262
um, stars?
https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...