Fast burst reactors were the first fast-spectrum research reactors to reach criticality by using only prompt neutrons with high-enriched uranium as fuel, creating a pulse for microseconds. Among many achievements, fast burst reactors were the first research reactors to demonstrate the ability of thermal expansion to terminate a pulse and to show how this could aid in reactor safety. In addition, fast burst reactors were pivotal in early fission studies including critical mass determination, criticality safety, the study of prompt and delayed neutrons, and much more.

Systems for Nuclear Auxiliary Power (SNAP) was an Atomic Energy Commission program with the goal of producing a portable and dependable power source centered around nuclear technology that could be utilized in land, sea, and space applications. The program aimed to provide a compact reactor—a necessity for space applications—and ran from 1955 until 1973, when it was discontinued.

In March 1949—75 years ago this month—the 25-kilowatt reactor known as Clementine reached full power. As an experimental reactor, it had a rather long and successful run. It was the world’s first fast neutron (high-energy) reactor and operated from initial criticality in 1946 to final shutdown in 1952.