[HN Gopher] Oklo, the Earth's Two-billion-year-old only Known Na...
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Oklo, the Earth's Two-billion-year-old only Known Natural Nuclear
Reactor (2018)
Author : keepamovin
Score : 155 points
Date : 2025-06-20 09:52 UTC (13 hours ago)
(HTM) web link (www.iaea.org)
(TXT) w3m dump (www.iaea.org)
| wjnc wrote:
| 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.
| danielbln wrote:
| Wikipedia is the best first point of entry, but if you do use
| Claude, just tell it to do web search for you:
| https://claude.ai/share/73e67582-3e03-454b-aa12-e8906bd7b3fd
| croes wrote:
| Why not just do a web search?
| geocrasher wrote:
| 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 wrote:
| 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.
| the_arun wrote:
| 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 wrote:
| 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 wrote:
| What a great metaphor. I'm adopting that immediately, thank
| you.
| pfdietz wrote:
| 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.
| adev_ wrote:
| 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:
|
| https://www.sciencedirect.com/science/article/abs/pii/S00167...
| b800h wrote:
| 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 wrote:
| 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.
| HelloUsername wrote:
| (2018)
|
| https://news.ycombinator.com/item?id=17736262
| Aardwolf wrote:
| > 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?
| BurningFrog wrote:
| 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_ wrote:
| 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.
| BurningFrog wrote:
| Anyone can look it up, yet I was the only one who did.
| CamperBob2 wrote:
| Is it wrong?
| joemi wrote:
| 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.
| philipkglass wrote:
| It's related to how long ago the uranium was formed:
|
| 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.
| lazide wrote:
| 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.
| cryptonector wrote:
| 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.
| mandevil wrote:
| 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.
| kkwteh wrote:
| Maybe it's a remnant from a nuclear ancient civilization.
| julienchastang wrote:
| A civilization (even perhaps extraterrestrial) that possessed
| nuclear energy? Unlikely, but still fun to think about! ;-)
| geocrasher wrote:
| 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 wrote:
| 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 wrote:
| Only to mine it later and re-use it over and over again.
| The 5 billion year long recycling program.
| eabeezxjc wrote:
| Or a remnant of a nuclear war in a riotous time
| airstrike wrote:
| https://en.wikipedia.org/wiki/Silurian_hypothesis
| legitster wrote:
| 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!
| krunck wrote:
| 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 wrote:
| 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.
| joe_the_user wrote:
| 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.
| Manuel_D wrote:
| What are the conditions under which nuclear waste buried a
| mile deep in bedrock will post a risk to society?
| Loughla wrote:
| Burying it in a cheaper place that happens to flood
| occasionally?
| legitster wrote:
| 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.
| bobmcnamara wrote:
| 1) the assumption that because something can be done safely
| it will be done safely
|
| 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)
| roughly wrote:
| 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.
| Terr_ wrote:
| Yeah, if waste management was as viable as proponents
| claim, places like Hanford [0] would _already_ be an
| inactive site with a memorial park on top.
|
| Whether it's technology, economics, or politics, clearly
| the state of the art is deficient because we currently
| _have persistent deficiencies._
|
| [0] https://en.m.wikipedia.org/wiki/Hanford_Site
| Manuel_D wrote:
| It's politics. The US already built a waste site in Yucca
| Mountain, but never bothered to actually use it for
| political reasons.
|
| Digging a shaft half a kilometer into bedrock and sealing
| it is not state of the art.
| Manuel_D wrote:
| 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.
| AtlasBarfed wrote:
| I look forward to your revolutionary nuclear waste
| teleportation device.
| Manuel_D wrote:
| Teleportation? You dig a tunnel underground, put the
| waste there, and fill the tunnel. It's been done before,
| it's not revolutionary engineering: https://en.m.wikipedi
| a.org/wiki/Onkalo_spent_nuclear_fuel_re...
| lukan wrote:
| The point was, you cannot ignore the risks of
| transportation, if you only have some safe spots to burry
| it.
|
| And what you linked is still under construction. We don't
| know yet, if it really works safe long term, or if there
| will be future costs.
| Manuel_D wrote:
| Finland has two other disposal sites in operation since
| the 90s: https://en.m.wikipedia.org/wiki/Deep_geological_
| repository
| lukan wrote:
| Yes, but when we want to store something in the range of
| million years, it is a bit early to say that 30 years are
| sufficient as a ultimate proof that nothing leaks.
|
| Now I believe it can be done safely, but only if
| monitored all the time with good care. But that is
| expensive and humans tend to skimp.
| Manuel_D wrote:
| Again, when you bury uranium half a kilometer deep in an
| area with no aquifer, how will it ever result in
| contamination?
|
| The only real scenarios are deliberate excavation, and a
| meteor impact directly on the waste repository. Neither
| of which are particularly likely scenarios.
| lukan wrote:
| Because the ground is not static. And we are just
| starting to understand what is going on down there. So
| yes, there are sites that remained quite unchanged (like
| with the natural fission reactor), but personally I
| remain sceptical with such statements.
| Manuel_D wrote:
| Half a kilometer isn't particularly deep. There are
| dozens of mines over 2 KM deep:
| https://en.wikipedia.org/wiki/List_of_deepest_mines
|
| Are we supposed to hold off on developing the only
| geographically independent and non-intermittent form of
| clean energy because of some vague nebulous fear that
| waste buried half a kilometer deep in bedrock will come
| back up to the surface and harm people... somehow?
| AnthonyMouse wrote:
| The primary transportation risk is that spent fuel
| contains cesium metal, which is reactive with air and
| water, so if you expose it to air you get a fire.
|
| It seems like a pretty obvious solution to this would be
| to purposely do the reaction under controlled conditions
| before transporting it, so then you're transporting
| stable cesium compounds instead of elemental cesium
| metal.
| lostlogin wrote:
| Regarding 3) and 4): Ground water contamination.
| Manuel_D wrote:
| You can dig in bedrock that has no groundwater.
|
| Furthermore, naturally occurring uranium exists in
| groundwater and needs to be filtered out in places where
| levels exceed safe limits. So it's not like burying waste
| is creating a new problem:
| https://www.kqed.org/stateofhealth/120396/uranium-
| contaminat...
| AtlasBarfed wrote:
| It's kind of the nature of a heavily regulated safety
| industry. The industry comes to resent the safety
| regulations. And therefore they will fail.
|
| 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
| sllabres wrote:
| It's not a mile deep, but I think the depth isn't the
| problem here:
|
| https://en.wikipedia.org/wiki/Asse_II_mine
| Manuel_D wrote:
| This is the one I was referring to, though I guess it's
| just over half a kilometer deep: https://en.m.wikipedia.o
| rg/wiki/Onkalo_spent_nuclear_fuel_re...
|
| The Asse II site used an existing mine to avoid having to
| excavate a new tunnel, which subsequently flooded.
| glompers wrote:
| > 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 wrote:
| 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 wrote:
| 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.
| legitster wrote:
| 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.
| foobarian wrote:
| > 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
| Analemma_ wrote:
| 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 wrote:
| 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?
| teuobk wrote:
| Per NIST[1], the value is 0.7204% +/- 0.0006%, with the
| uncertainty representing one standard deviation.
|
| [1] https://physics.nist.gov/cgi-
| bin/Compositions/stand_alone.pl...
| fnord77 wrote:
| > only known natural nuclear reactor
|
| um, stars?
| preisschild wrote:
| the word "fission" is missing
|
| https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...
| stmw wrote:
| Fun aside - Oklo is also the name of a successful YC company that
| makes a passively-safe nuclear reactor - https://www.oklo.com
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