The United States nuclear program has, since its inception, suffered from a number of accidents of varying forms, ranging from single-casualty research experiments (such as that of Louis Slotin during the Manhattan Project), to the nuclear fallout dispersion of the "Castle Bravo" shot in 1954, to the accidental dropping of nuclear weapons from aircraft ("broken arrows"). How close any of these accidents came to being "major" nuclear disasters is a matter of technical and scholarly debate and interpretation.
Weapons accidentally dropped by the United States include incidents near Atlantic City, New Jersey (1957), Savannah, Georgia (1958) (see Tybee Bomb), Goldsboro, North Carolina (1961), off the coast of Okinawa (1965), in the sea near Palomares, Spain (1966, see 1966 Palomares B-52 crash), and near Thule Air Base, Greenland (1968) (see 1968 Thule Air Base B-52 crash). In some of these cases (such as Palomares), the explosive system of the fission weapon discharged, but did not trigger a nuclear chain reaction (safety features prevent this from easily happening), but did disperse hazardous nuclear materials across wide areas, necessitating expensive cleanup endeavors. Eleven American nuclear warheads are thought to be lost and unrecovered, primarily in submarine accidents.
The nuclear testing program resulted in a number of cases of fallout dispersion onto populated areas. The most significant of these was the Castle Bravo test, which spread radioactive ash over an area of over one hundred miles, including a number of populated islands. The populations of the islands were evacuated but not before suffering radiation burns. They would later suffer long-term effects, such as birth defects and increased cancer risk. There were also instances during the nuclear testing program in which soldiers were exposed to overly high levels of radiation, which grew into a major scandal in the 1970s and 1980s, as many soldiers later suffered from what were claimed to be diseases caused by their exposures.
Many of the former nuclear facilities (see next section) produced significant environmental damages during their years of activity, and since the 1990s have been Superfund sites of cleanup and environmental remediation. The Radiation Exposure Compensation Act of 1990 allows for U.S. citizens exposed to radiation or other health risks through the U.S. nuclear program to file for compensation and damages.
Nuclear weapons and the United States - Wikipedia, the free encyclopedia
Check this site for more nuclear accidents in US. Countless...
http://www.cdi.org/Issues/NukeAccidents/Accidents.htm