Oklo, the Earth's Two-billion-year-old only Known Natural Nuclear Reactor (2018)

https://www.iaea.org/newscenter/news/meet-oklo-the-earths-two-billion-year-old-only-known-natural-nuclear-reactor

by keepamovin • 1 year ago

208 115 1 year ago

wjnc2• 1 year ago

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• 1 year ago

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• 1 year ago

Why not just do a web search?

the_arun• 1 year ago

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?

lazide2• 1 year ago

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.

pfdietz4• 1 year ago

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_• 1 year ago

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• 1 year ago

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."

jvanderbot3• 1 year ago

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• 1 year ago

Its impressive the amount of clean, cheap energy that's been locked away because of fearmongering tales from well before many were even alive.

HelloUsername• 1 year ago

(2018)

https://news.ycombinator.com/item?id=17736262

Aardwolf• 1 year ago

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?

BurningFrog2• 1 year ago

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_3• 1 year ago

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.

philipkglass• 1 year ago

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.

lazide2• 1 year ago

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• 1 year ago

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• 1 year ago

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?

keepamovin3• 1 year ago

This is excellent. I love your depth of knowledge in this subject. I learned a lot from this clear comment.

mandevil• 1 year ago

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• 1 year ago

Maybe it’s a remnant from a nuclear ancient civilization.

julienchastang• 1 year ago

A civilization (even perhaps extraterrestrial) that possessed nuclear energy? Unlikely, but still fun to think about! ;-)

geocrasher3• 1 year ago

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• 1 year ago

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.

eabeezxjc• 1 year ago

Or a remnant of a nuclear war in a riotous time

airstrike• 1 year ago

https://en.wikipedia.org/wiki/Silurian_hypothesis

legitster3• 1 year ago

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• 1 year ago

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• 1 year ago

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• 1 year ago

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_D16• 1 year ago

What are the conditions under which nuclear waste buried a mile deep in bedrock will post a risk to society?

glompers• 1 year ago

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.

legitster3• 1 year ago

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.

nec4b• 1 year ago

> 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.

datatrashfire• 1 year ago

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.

acidburnNSA2• 1 year ago

The US built WIPP. It's not licensed for commercial waste but it sure is a long term geologic disposal site.

andrewflnr• 1 year ago

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.)

mystified5016• 1 year ago

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.

foobarian• 1 year ago

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_• 1 year ago

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• 1 year ago

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• 1 year ago

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• 1 year ago

only known natural nuclear reactor

um, stars?

preisschild• 1 year ago

the word "fission" is missing

https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...

eapriv• 1 year ago

um, “Earth’s”?

stmw• 1 year ago

Fun aside - Oklo is also the name of a successful YC company that makes a passively-safe nuclear reactor - https://www.oklo.com

keepamovin3• 1 year ago

Then they picked a very clever name.

acidburnNSA2• 1 year ago

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.

Oklo, the Earth's Two-billion-year-old only Known Natural Nuclear Reactor (2018)

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