Cecil Kelley criticality accident
The Cecil Kelley criticality accident was a criticality accident that took place on December 30, 1958, at the Los Alamos National Laboratory in Los Alamos, New Mexico, in the United States. It is one of only ten such events to ever occur outside of a nuclear reactor, though it was the third such event to take place in 1958 (the others having taken place on 16 June at the Y-12 Plant in Oak Ridge, Tennessee, and on 15 October at the Vinča Nuclear Institute in Vinča, Yugoslavia). The accident involved plutonium compounds dissolved in liquid chemical reagents, and it caused the death of one man – Cecil Kelley, a chemical operator – from severe radiation poisoning within 35 hours.
Context of the accident
Cecil Kelley was a 38-year-old chemical operator with 11 years of experience, more than half of those while at the Los Alamos lab where one of his duties was to operate a large (1,000 liter capacity) stainless steel mixing tank. The tank contained residual radioactive plutonium-239 remaining from other experiments and applications, along with various organic solvents and acids in an aqueous solution for the purpose of recovering it for reuse. In pure form and under normal temperature and pressure conditions, plutonium – a mostly man-made element existing in trace amounts in nature – is a solid silvery metal. However, it tarnishes quickly when exposed to air and readily dissolves in concentrated hydrochloric, hydroiodic and perchloric acids as well as others. On the day of the accident the mixing tank was supposed to contain what nuclear chemists call a "lean" concentration of dissolved plutonium (≤0.1g of plutonium per liter of solution) in a bath of highly corrosive nitric acid and a caustic stabilized aqueous organic emulsion. However, as a result of what were later determined to be at least two "improper transfers" of plutonium waste to the tank (the sources for which were never determined or at least never publicly disclosed), the concentration of plutonium in the mixing tank on this particular occasion was nearly 200 times higher, and was distributed unevenly. The upper layer of solution had especially high concentrations and contained a total of over 3 kg plutonium, and was already close to criticality before Kelley acted. When Kelley switched on the mixer, a vortex began to form. The denser aqueous layer within the tank immediately pushed outward and upward forming a "bowl" and the less dense plutonium-rich layer swirled toward the vessel's center.
Among other ideal characteristics, the ideal shape or "geometry" for any fissile substance to become supercritical is a sphere. While the plutonium-rich solution was not spherical, it did become thicker in the center and this, along with the corresponding increase in density and the neutron reflectivity of the aqueous layer surrounding it, caused the dissolved plutonium to reach and cross the criticality threshold in approximately one second: neutrons within the mixture began to bombard the nuclei of the solution's plutonium atoms with sufficient frequency that these atoms broke apart and released other neutrons in a sustained nuclear chain reaction lasting only 200 microseconds but releasing a huge burst of neutrons and gamma radiation. Such an uncontrolled release of nuclear energy is often referred to as an excursion.
Within three seconds the layers in the mixture had become dispersed and no further excursions were possible.
Events of the excursion
Kelley had been standing on a foot ladder looking at the contents of the mixing tank through a viewing window when the excursion event occurred. Two other technicians working within the laboratory witnessed a bright flash of blue light followed by the sound of a thud. The power burst either caused Kelley to collapse or knocked him off the ladder, and he had fallen to the ground. He arose disoriented, and apparently switched the mixer off and then back on again before running outside of the building. The other technicians found him there in the snow in a state of ataxia and only able to say to them, "I'm burning up! I'm burning up!"
Because the possibility of an excursion taking place in a mixing tank had been considered to be virtually non-existent, the technicians decided that Kelley must have somehow been exposed to either alpha radiation, the acid bath, or both, and one of them took him to a chemical shower while the other switched off the mixer. Additional staff members arrived on the scene within minutes to find Kelley virtually unconscious. The bright pink color of his face indicated erythema brought on by cutaneous radiation syndrome.
Any accident at Los Alamos involving a radioactive substance requires an immediate investigation by a team of radiation monitoring staff. Even before Kelley was taken to an emergency room, these staff members began an examination of the mixing room with radiation detectors capable of assessing the alpha radiation indicative of plutonium decay. This radiation should have been widespread if any of the plutonium mixture had escaped the tank. Nothing unusual was initially found. Eighteen minutes later, however, the team began searching for gamma radiation – they unexpectedly found this kind of radiation in abundance near the mixing tank, on the order of tens of rads per hour. Such intense gamma radiation could only have been produced during an excursion; this, combined with the otherwise inexplicable flash of light reported by the other two technicians, was sufficient to identify the event as a criticality accident.
Kelley's clinical course
For the first hour and forty minutes following the accident Kelley had been incoherent, and had gone through waves of intense vomiting and retching. He then stabilized, was able to once again converse normally, and was able to have his pulse taken and his blood drawn. The blood draw indicated that Kelley had been exposed to approximately 9 Gy from fast neutrons and 27 Gy from gamma rays, for a total of 36 Gy. For an adult human, exposure to 2 Gy from a spherical (unfocused) radiation source such as an excursion will cause radiation sickness but is not considered definitely lethal; 2.4–3.4 Gy is the median lethal dose; a dose of 5 Gy is almost always deadly. Kelley had received more than seven times the adult human lethal dose. Although the medical staff in the emergency room took steps to ease his pain with Demerol and morphine, previous research on radiation exposure in animals indicated Kelley's death would be inevitable. Within six hours his lymphocytes were all but gone. A bone biopsy performed 24 hours after the incident produced bone marrow that was watery and contained no red blood cells. Numerous intravenous blood transfusions had no lasting helpful effect: 35 hours following his initial exposure and after a final bout of intense restlessness, agitation, sweating, becoming ashen-skinned, and having an irregular pulse, Cecil Kelley died of heart failure.
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An investigation into the circumstances of the accident never resulted in a public explanation of how the mixing tank became filled with such a high concentration of plutonium—initially the blame was placed on Kelley himself. Although Kelley had neither ingested nor inhaled any plutonium during the accident, he, like many laboratory technicians at Los Alamos, had been exposed to minute particles of airborne plutonium over the course of several years. An event such as this was therefore considered an "experiment of opportunity." Careful records were kept of every moment of Kelley's life from accident through death and onto the autopsy table. His organs were kept for pathologic exam and their plutonium levels analyzed. The results of these tissue analyses were considered fundamental to understanding what would happen to a population during a nuclear attack and impossible to obtain any other way. Although the bone marrow biopsy of Kelley's sternum was performed under the premise that the physicians wished to determine if he were a candidate for a bone marrow transplant, Kelley's death was of such certainty that an actual transplant was never seriously considered.
Mr. Kelley's death left a widow, Doris Kelley, and two children, then ages eight years and 18 months. Mrs. Kelley did not receive notification while he was still alive that her husband had been irradiated, and only learned of his death from the laboratory authority when it visited her at her home shortly afterward. Assuring her verbally that they would provide her with financial compensation for her husband's death, they convinced her not to file any lawsuits against the laboratory. Despite such assurances, the only compensation Mrs. Kelley received was a lifetime level position working for the lab itself at near-poverty levels, until health reasons caused her to retire.
In 1996, Mrs. Kelley and her daughter, Katie Kelley-Mareau, filed a lawsuit against Dr. Clarence Lushbaugh, the pathologist who performed the autopsy on Cecil Kelley. The case alleged the misconduct of doctors, the hospital, and the administration of Los Alamos in removing organs from the deceased without consent from next-of-kin over a span of many years (1958–1980). Kelley's autopsy was the first instance of this type of post-mortem analysis, but there were many more performed by Dr. Lushbaugh and others in later years at Los Alamos. During a deposition for the case, Dr. Lushbaugh, when asked who gave him the authority to take 8 pounds of organs and tissue from Kelley's body, said, "God gave me permission." The class action suit was settled by the defendants for about $9.5 million in 2002 and an additional $800,000 in 2007. None of the defendants admitted any wrongdoing.
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- Doris E. Kelley, et al. v Regents of the University of California, et al, settled (Santa Fe County District Court, New Mexico 1996). SF-96-2430. This case was settled by all defendants.
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- See Stewart Settlement, the second of 2 settlements in this case.