" Incredible as it seems, the difference between the subcritical neutron population in a uranium mass, making no fission, and supercritical, making wild, increasing fission, is a very small number of available neutrons out of trillions: all it takes is just one neutron. "

― James Mahaffey , Atomic Accidents: A History of Nuclear Meltdowns and Disasters: From the Ozark Mountains to Fukushima