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26 July 1959
A clogged coolant channel resulted in a 30% reactor core meltdown at the Santa Susana Field Laboratory (now known as the Boeing-Rocketdyne Nuclear Facility) in the Simi Hills area of Ventura County, California. Most of the radioactive fission products were trapped, but gasses were vented which resulted in the release of the third greatest amount of radioactive iodine-131 in nuclear history. The incident was largely covered up until a class-action suit was filed by local residents, who successfully sued for $30 million over cancer and thyroid abnormalities contracted due to their proximity to the facility.

2 September 1944
Peter Bragg and Douglas Paul Meigs, two Manhattan Project chemists, were killed when their attempt to unclog a tube in a uranium enrichment device led to an explosion of radioactive uranium hexafluoride gas exploded at the Naval Research Laboratory in Philadelphia, PA. The explosion ruptured nearby steam pipes, leading to a gas and steam combination that bathed the men in a scalding, radioactive, acidic cloud of gas which killed them a short while later.

21 August 1945
Louis Slotin , a physicist, was killed during the final stages of the Manhattan Project undertaken at Los Alamos, New Mexico to develop the first atomic bomb) from a radiation burst released when a critical assembly of fissile material was accidentally brought together by hand. This incident pre-dated remote-control assembly of such components, but the hazards of manual assembly were known at the time (the accident occurred during a procedure known as "tickling the dragon's tail"). A similar incident occurred nine months later (dramatized in the Hollywood movie Fat Man and Little Boy); this time, eight people were exposed, one of whom died days later. Hand-maniuplations of critical assemblies was abandoned only after another accident on 30 December 1958.

2 July 1956
Nine persons were injured when two explosions destroyed a portion of Sylvania Electric Products' Metallurgy Atomic Research Center in Bayside, Queens, New York.

1957
A radiation release at the the Keleket company resulted in a five-month decontamination at a cost of $250,000. A capsule of radium salt (used for calibrating the radiation-measuring devices produced there) burst, contaminating the building for a full five months.

30 December 1958
A nuclear criticality accident occured from a solution in a plutonium recovery operation at Los Alamos Scientific Laboratory in New Mexico. The operator died later of acute radiation sickness. The March, 1961 Journal of Occupational Medicine printed a special supplement devoted to the medical analysis of this accident.

1959
A partial sodium reactor meltdown occurred at the Santa Susana Field Laboratory in Simi Valley Hills, California.

5 October 1966
A sodium cooling system malfunction caused a partial core meltdown at Detroit Edison's Enrico Fermi I demonstration breeder reactor near Detroit, Michigan. Radioactive gases leaked into the containment structures, but radiation was reportedly contained.

1974
Whistleblowers at the Isomedix company in New Jersey reported that radioactive water was flushed down toilets and had contaminated pipes leading to sewers. The same year a worker received a dose of radiation considered lethal, but was saved by prompt hospital treatment.

1982
International Nutronics in Dover, New Jersey, which used radiation baths to purify gems, chemicals, food, and medical supplies, experienced an accident that completely contaminated the plant, forcing its closure. A pump malfunctioned, siphoning water from the baths onto the floor; the water eventually was drained into the sewer system of the heavily populated town of Dover. The NRC wasn't informed of the accident until ten months later -- and then by a whistleblower, not the company. In 1986, the company and one of its top executives were convicted by a federal jury of conspiracy and fraud. Radiation has been detected in the vicinity of the plant, but the NRC claims the levels "aren't hazardous."

1986
The NRC revoked the license of a Radiation Technology, Inc. (RTI) plant in New Jersey for repeated worker safety violations. RTI was cited 32 times for various violations, including throwing radioactive garbage out with the regular trash. The most serious violation was bypassing a safety device to prevent people from entering the irradiation chamber during operation, resulting in a worker receiving a near-lethal dose of radiation.

ca. December 1991
One of four cold fusion cells in a Menlo Park, CA, laboratory exploded while being moved; electrochemist Andrew Riley was killed and three others were injured. The other three cells were buried on site, leading to rumors that a nuclear reaction had taken place. A report concluded that it was a chemical explosion; a mixture of oxygen and deuterium produced by electrolysis ignited when a catalyst was exposed. The Electric Power Research Institute, which spent $2 million on the SRI cold fusion research, suspended support for the work pending the outcome of an investigation