Cecil Kelley criticality accident

A criticality accident occurred on December 30, 1958, at Los Alamos National Laboratory (LANL) in Los Alamos, New Mexico, in the United States. It is one of 60 known criticality events that have occurred globally outside the controlled conditions of a nuclear reactor or test and the third event that took place in 1958, after events on June 16 at the Y-12 Plant and on October 15 at the Vinča Nuclear Institute.

Source: Wikipedia — Cecil Kelley criticality accident (CC BY-SA 4.0)