Reply #6: I suspect these reactors were extremely transient

[Porcupine]

or extremely low powered. From other posts I've read around here it's clear that a nuclear reactor starts poisoning itself with by products fairly soon after it starts up.

Having some natural ores reach criticality does not mean that they generated the kind of heat and quantities of byproducts that a high powered reactor does today. Also these reactors were in undisturbed bedrock, deep underground, in Africa.

The last I checked there isn't a whole lot of plate tectonic activity in Africa, few volcanoes, no uplift mountain ranges. Yucca mountain is fairly close to an active geothermal area. Now if we could get the Australians to accept all of the worlds nuclear waste then we would be talking. That place is 100% old, dead, rock.

Could somebody find the original article?