From Oklo, the fossil pile, to the four generations of reactors
Nuclear Reactors - Generalities 1. Boilers and Fuel Cycle - Systems - Main Constraints

Two billion years ago, on our rocky planet where the water cycle had become established, a dozen natural nuclear reactors operated in Oklo, in present-day Gabon (figures 14 and 15 ). This phenomenon was made possible by the enrichment of natural uranium, which at the time was greater than 3% (compared to 0.7% today)—that is, close to the industrial enrichment levels of the so-called Generation II light-water nuclear reactors (LWRs) of the 1960s and 1970s. Nature had provided a moderator and “coolant”: the water present in the deposit,...