Two billion years ago, the earth’s geology came together to spontaneously and naturally
form what was essentially a nuclear fission reactor.
It operated stably for about a million years, and its radioactive waste has been safely
contained--again, totally naturally--for millions of years since.
Surely we can learn from this, right?
And also this DEFINITELY sounds like the origin story for an awesome comic book hero, I’m
just saying.
Before we dive into how the heck this happened, let’s do a quick overview of fission.
Nuclear fission happens when a heavy atomic nucleus splits into lighter elements and rogue
particles and releases a LARGE amount of energy . In
addition to the energy, those smaller byproducts are usually lighter atomic nuclei that are
unstable after the fission process and are therefore highly radioactive.
This is where the bulk of nuclear power’s hazardous waste comes from.
Fission also releases stray neutrons, and these neutrons can excite other nearby heavy
nuclei into the fission state, causing a chain reaction that when controlled in a nuclear
power plant, can be harnessed to power our everyday life.
But when left uncontrolled, it can be disastrously destructive.
So when humans make a nuclear reactor we have to work pretty hard to get fission to occur.
First, we’ve gotta have that heavy element to split, which for us is usually uranium.
There are three main kinds--or isotopes--of uranium.
The most common isotope is U-238, and it’s found all over the earth and in our oceans--But
it’s not fissionable by itself because it’s just not unstable enough, so we can’t break
it apart to release that energy we need.
Isotope U-235, however, is unstable enough to be fissionable...but it makes up less than
1% of the naturally occurring uranium in the world.
So when we mine uranium, we have to manually enrich it to contain about 3% U-235 before
we can use it in a nuclear reactor.
But fissionable fuel is just step one--for your power-producing nuclear reactor to be
safe you also need some kind of moderator that will slow down the neutrons enough so
that they don’t cause an uncontrollable reaction.
In most nuclear reactors, we use water for this.
There are also control rods made out of other neutron-absorbing materials like silver, and
water is also be used as a coolant so the whole operation doesn't overheat and go into
meltdown.
So how is it that something we’ve spent decades trying to perfect just magically happened
all by itself in nature?
Well, two billion years ago there was a lot more U-235 than there is now, since it decays
more quickly than U-238.
And in a place called Oklo, Gabon, there was a high enough concentration of U-235 to induce
spontaneous nuclear fission.
Wow.
Presumably there was also enough of a moderator, probably water, to keep the whole thing from
exploding.
AND there weren’t enough neutron absorbing materials around to prevent the fission from
sustaining itself.
This is the only natural nuclear reactor in the world that we know of so far.
But that’s not to say there aren’t others--they may have been subducted or eroded, or maybe
we just haven’t found them!
But this one natural nuclear reactor has been completely mined by humans.
It’s gone now.
That’s how we even know about it in the first place, we went down into the ground
looking for uranium to enrich and came back up and said, ‘Uhhhhh, either someone’s
stolen almost 200 kilograms of uranium-235 or this is a natural nuclear reactor that’s
burned it all off already’.
It’s the latter, in case you haven’t been following along.
But we can learn a lot from Oklo today.
Because again, it operated safely for MILLIONS of years and NONE of its nuclear waste has
leaked or adversely affected ANYTHING!
This is remarkable because uranium fission byproducts can be highly hazardous, and we
struggle to know what to do with that waste.
Cesium is one particularly nasty fission byproduct, and is one of a suite of compounds that could
cause symptoms of radiation poisoning.
Cesium is one of the elements that makes the Chernobyl and Fukushima sites so dangerous.
Researchers recently studying the Oklo mines discovered that the cesium byproducts from
the natural reactor were most likely absorbed and contained by another element that occurred
naturally there called ruthenium.
Ruthenium’s structure allows it to bind to these radioactive elements, kinda like
an atomic hug, making the elements like cesium less radioactive.
Ruthenium itself is too rare for us to use on an industrial scale in taking care of commercial
nuclear power waste.
But this new insight into the world’s natural fission reactor gives researchers hope that
they can find or make something similar to safeguard our modern nuclear waste.
Check out this video here to learn more about radioactive material, and subscribe to Seeker
to keep Seeker to keep up worth all the amazing natural phenomena around the world.
And fun fact, the Oklo reactors isn’t just one reactor-it’s SIX.TEEN. different reactors.
PLUS one nearby.
Mother nature’s an overachiever.
Thanks for watching!