Editing Nuclear weapon design (section)

==Production facilities==
{{Globalize|section|USA|2name=the United States|date=June 2014}}
When two-stage weapons became standard in the early 1950s, weapon design determined the layout of the new, widely dispersed U.S. production facilities, and vice versa.

Because primaries tend to be bulky, especially in diameter, plutonium is the fissile material of choice for pits, with beryllium reflectors. It has a smaller critical mass than uranium. The Rocky Flats plant near Boulder, Colorado, was built in 1952 for pit production and consequently became the plutonium and beryllium fabrication facility.{{Citation needed|date=June 2021}}

The Y-12 plant in [[Oak Ridge, Tennessee|Oak Ridge]], [[Tennessee]], where [[mass spectrometer]]s called [[calutron]]s had enriched uranium for the [[Manhattan Project]], was redesigned to make secondaries. Fissile U-235 makes the best spark plugs because its critical mass is larger, especially in the cylindrical shape of early thermonuclear secondaries. Early experiments used the two fissile materials in combination, as composite Pu-Oy pits and spark plugs, but for mass production, it was easier to let the factories specialize: plutonium pits in primaries, uranium spark plugs and pushers in secondaries.{{Citation needed|date=June 2021}}

Y-12 made lithium-6 deuteride fusion fuel and U-238 parts, the other two ingredients of secondaries.{{Citation needed|date=June 2021}}

The Hanford Site near Richland WA operated Plutonium production nuclear reactors and separations facilities during World War 2 and the Cold War. Nine Plutonium production reactors were built and operated there. The first being the B-Reactor which began operations in September 1944 and the last being the N-Reactor which ceased operations in January 1987.{{Citation needed|date=June 2021}}

The [[Savannah River Site]] in [[Aiken, South Carolina|Aiken]], [[South Carolina]], also built in 1952, operated [[nuclear reactor]]s which converted U-238 into Pu-239 for pits, and converted lithium-6 (produced at Y-12) into tritium for booster gas. Since its reactors were moderated with heavy water, deuterium oxide, it also made deuterium for booster gas and for Y-12 to use in making lithium-6 deuteride.{{Citation needed|date=June 2021}}