Even today in the 21st century, nuclear energy is a symbol of a modern age and a complicated technical requirement that only the most ambitious countries can achieve.
But nuclear reactors are fairly simple. You can find them in nature.
In 1975, the international scientific community identified 16 naturally occurring nuclear reactors in Oklo, Africa.
Pictured: Deposits of exhausted nuclear fuel in Oklo. The worker is pointing at them so you know where to look.
With natural nuclear fuel deposits (in this case uranium 235), surrounding neutrons pass trough it fast and without reaction, so the material decays slowly (over 700 million years).
However, in artificial reactors, neutrons are slowed down, causing them to „hit“ the uranium 235, causing high temperatures, which is then easily converted into electrical energy.
With the Oklo sediments, changes in climate and the ground slowly created underground waters around the uranium deposits. And water is pretty good in slowing down neutrons.
Slow neutrons would then bombard the uranium, a nuclear reaction would start up and the entire underground region would heat up. Scalding water would start turning into pressurized steam which would try to escape trough cracks in the earth. After half an hour, all the water would would be gone. Without it, neutrons would again become too fast to react with the uranium and then nuclear reaction would stop. Eventually, new water would collect around the deposits and the entire process would start all over again.
Pictured: Scars of a underground dance of water and radiation. And they say geology isn’t exciting.
The natural reactors in Oklo worked for a couple of hundred thousand years until the uranium depleted. A true wonder of the geologic world.