Project 56
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"Project 56" was a series of four safety experiments conducted by exploding the radioactive components of nuclear weapons in the atmosphere at the Nevada Test Site between November of 1955 and January 1956.
Early nuclear weapons were large, and to arm the weapon, a nuclear component, called "the pit", had to be inserted by hand just before (or even during) the flight in the bomber. If an accident occurred before the bomb was armed, the conventional explosives of the weapon would detonate; because the nuclear core had not been installed, there would be no nuclear yield. As nuclear weapons became physically smaller, it became impossible for the pits to be installed except during the final assembly at the factory, known as a "sealed pit" design.
To use an overly simple analogy, early nuclear weapons could be thought of as being like citrus fruit. Just as most citrus fruits have spherical interior sections, so did nuclear weapons of this era. The nuclear core is surrounded by high explosives, intended to implode (evenly compress) the core resulting in a nuclear explosion. Asymmetrical implosion (uneven compression) results in a massive radiation emissions, but no detonation (sometimes called a "nuclear fizzle"). Fat Man was the second nuclear device to use implosion; the first was the device detonated at Trinity Site on 16 July 1945.
There was concern that in an accident (for example, an aircraft crash) one or more of the high explosives sections might detonate, triggering the other sections. While this would lead to an asymmetrical implosion, there would still be widespread, lethal radioactive contamination. New nuclear weapons were designed to be "one point safe" so if there was an explosion even at only one point in the sphere of conventional explosives, there would be no radiation emission. Project 56 was the first series of tests to prove the one point safety of the new designs and to determine the extent of the plutonium dispersal in a non-nuclear detonation. Each of the four tests were conducted in Area 11 of the Nevada Test Site, giving it the name "Plutonium Valley".
