Naturally enriched uranium.

I've read that at Oklo mine in Gabon uranium 235 occured natrually at levels of 3%, about what a low enriched reactor needs for fuel. Further, this underwent fission while in the ground with groundwater acting as a moderator. All this happened eons ago, but surprised me anyway.

WI there were other uranium deposits of this purity to be found, could this affect history? Apparently it takes the most enrichment effort to go from 0.7% to 10-20%. Perhaps if the Nazis had access to U235 at this purity could their abortion of a programme actually get somewhere? Or other countries who rely on imported and strictly controlled nuclear technology, could Saddam or others get a HEU bomb if they were starting with U235 at 3% rather than 0.7%?
 

wormyguy

Banned
OTL, the German nuclear program didn't go anywhere because Heisenberg miscalculated, and decided that several tons of U-235 were required for a critical mass. After that, the German nuclear program was mostly disbanded, and mostly just used for research into civilian nuclear power and possibly dirty bombs.
 
Different physical properties of 3% U235 would probably move the parameters enough that Hiesenberg wouldn't make the same mistake, or perhaps recalculate in light of the higher purity.
 
I've read that at Oklo mine in Gabon uranium 235 occured natrually at levels of 3%, about what a low enriched reactor needs for fuel. Further, this underwent fission while in the ground with groundwater acting as a moderator. All this happened eons ago, but surprised me anyway.

WI there were other uranium deposits of this purity to be found, could this affect history? Apparently it takes the most enrichment effort to go from 0.7% to 10-20%. Perhaps if the Nazis had access to U235 at this purity could their abortion of a programme actually get somewhere? Or other countries who rely on imported and strictly controlled nuclear technology, could Saddam or others get a HEU bomb if they were starting with U235 at 3% rather than 0.7%?
U235 decays MUCH faster than U238. The half-life of U238 is 4.5 billion years (approximately the age of the earth), so we still have half of what the earth started with. The half-life of U235 is 700 million years. so we have ~1/64 of what the earth started with. In other words, the amount of U235 goes down by a factor of ~32 over the lifespan of earth. Therefore, if today Uranium were 3%, then when earth was formed the Uranium would have been about 1/2 U235, and it would have been a lot more than just Gabon would have had chain reactions. Maybe even natural explosions.
 
Apparently the reactions happened 2 billion years ago, and over 100,000 year timeframes. But what impressed me was that it happened at all, that uranium in some places was 3% U235, and that by natural means fission reactions occured. I was under the impression that U235 had always been at 0.7%, not that it arrived at this level after billions of years of regular radioactive decay. How does unranium ore form, is it like gold for example where Victorian deposits are 400 million years old but Western Australian deposits are vastly younger? Could a 5% U235 deposit form naturally only a few million years ago and then not fission but decay to 3%?
 
My understanding...

As far as I know, the Uranium we have is all from the formation of Earth. Isotopes are (usually) fairly evenly distributed, but some decays faster. Without a source of new Uranuim 235, the proportions will inevitably slide down, as the 235 decays faster.

(Other elements sometimes have different proportions in different places for a variety of reasons, but U-235 is fiendishly difficult to seperate, and I know of no natural method of seperation. Chemicaly, it acts the same, so that won't do it.)

Helium has different proportions on Earth from in space, since Helium escapes to space, and only He-4 is created. (He-3 is comparitively abundant out there)

So, to have a natural reactor today, you'd need a higher original proportion of U-235, a method of renewal (ASB, I think) or a younger planet.

As for what such a reactor would do--IF it attracts interest in the first place, the fission products could provide hints as to what's going on.
 
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