basic water-cooled uranium-fueled design
The current predominant reactor design did not "take root" because it produced "weapons-grade spent fuel" as stated. The driving force for development of this concept was the nuclear submarine powerplant. The first commercial reactors (and most current reactors) were based on this design. Probably no weapons-grade material has been produced in these plants, but in special-purpose designs whose spent fuel could be removed after fairly short irradiation times.