Cecil Kelley criticality accident
In the annals of nuclear history, few events are as chillingly direct as a criticality accident. These are not reactor meltdowns, but uncontrolled nuclear chain reactions happening outside a reactor core, often in laboratory settings. The Cecil Kelley accident in 1958 stands as a stark reminder of the terrifying power of such an event and its devastating human cost. A hidden, dangerously high concentration of plutonium in a mixing tank led directly to the accidental criticality. The criticality event, though brief, exposed Cecil Kelley to an unimaginably lethal dose of radiation, leading to his agonizing death within 35 hours. The aftermath revealed systemic failures in safety protocols and a disturbing disregard for human dignity, as Kelley's body was treated as an 'experiment of opportunity'.
AI Summary
In the annals of nuclear history, few events are as chillingly direct as a criticality accident. These are not reactor meltdowns, but uncontrolled nuclear chain reactions happening outside a reactor core, often in laboratory settings. The Cecil Kelley accident in 1958 stands as a stark reminder of the terrifying power of such an event and its devastating human cost.
- A hidden, dangerously high concentration of plutonium in a mixing tank led directly to the accidental criticality.
- The criticality event, though brief, exposed Cecil Kelley to an unimaginably lethal dose of radiation, leading to his agonizing death within 35 hours.
- The aftermath revealed systemic failures in safety protocols and a disturbing disregard for human dignity, as Kelley's body was treated as an 'experiment of opportunity'.
The Silent Killer
On December 30, 1958, a terrifying event unfolded at Los Alamos National Laboratory in New Mexico. It was a criticality accident—an uncontrolled nuclear chain reaction—involving plutonium compounds dissolved in liquid chemical reagents.
This wasn't an isolated incident; it was one of 60 known criticality events to have occurred outside the controlled conditions of a nuclear reactor or test, and the third in 1958 alone. But for chemical operator Cecil Kelley, it was a personal tragedy that would claim his life in just 35 agonizing hours.
A Seasoned Operator, a Dangerous Task
Cecil Kelley was a 38-year-old chemical operator, highly experienced with 11 years in the field, over half of which were spent at Los Alamos. One of his routine duties involved operating a large, 1 cubic meter capacity, stainless-steel mixing tank.
This tank was central to the lab's plutonium recovery efforts. It would hold residual plutonium-239, along with various organic solvents and acids in aqueous solution, all intended for reprocessing and reuse. Plutonium itself is a fascinating element—a dense, silvery metal that quickly tarnishes in air and readily dissolves in strong acids.
A Hidden Danger
On the day of the accident, the mixing tank should have contained a very 'lean' concentration of dissolved plutonium—less than 0.1 grams per liter of solution. This was a safe operational level for the bath of nitric acid and organic emulsion.
However, unknown to Kelley, the tank's actual plutonium concentration was nearly 200 times higher than anticipated. This critical error was the result of at least two improper transfers of plutonium waste from undetermined sources, turning a routine task into a deadly one.
Even worse, the plutonium wasn't evenly distributed. The upper layer of the solution held exceptionally high concentrations, amounting to a total of over 3 kilograms of plutonium—a dangerously high amount, hovering precariously close to its critical mass.
The stage was set for disaster. When Kelley switched on the mixer, a vortex began to form in the tank. The denser aqueous layer was forced outward and upward, creating a 'bowl' shape.
The Flash of Blue
As the vortex deepened, the less dense, plutonium-rich layer was drawn toward the vessel's center. For a fissile substance, the optimal shape to become supercritical—meaning a sustained nuclear chain reaction—is a sphere, as it has the least surface area for neutrons to escape.
While not perfectly spherical, the vortex's action thickened the plutonium-rich solution in the center. This, combined with the increased density and neutron reflectivity of the surrounding aqueous layer, inadvertently created the perfect conditions for a chain reaction to ignite.
In any fissile material, a stray neutron can cause an atom to fission, releasing more neutrons. Normally, the effective neutron multiplication factor, known as keff, is kept below 1.0, ensuring any nascent chain reaction quickly dies out.
But when keff exceeds 1.0—even by a tiny fraction—a rapidly accelerating nuclear chain reaction begins. Changes in shape, concentration, and reflectivity can all push a system past this critical threshold.
In a liquid criticality accident, the immense energy released by the chain reaction indirectly causes it to slow or stop. The sudden increase in temperature, thermal expansion, and steam formation physically disperses the fissile material, making it subcritical again. However, sometimes the reaction can surge or restart.
This uncontrolled burst of nuclear energy, an 'excursion,' lasted only 200 microseconds—less than the blink of an eye. Yet, in that fleeting moment, it unleashed a colossal burst of neutrons and gamma radiation.
Fortunately, within about 3 seconds, the mixer dispersed the layers in the tank, making any further excursions impossible. This was a grim mercy, unlike other accidents where subsequent actions triggered additional, smaller bursts of radiation.
"I'm Burning Up!"
Cecil Kelley was standing on a ladder, peering into the mixing tank through a viewing window when the excursion occurred. He witnessed a blinding flash of bright blue light—likely Cherenkov radiation—followed by a dull thud.
The sudden shock either caused him to collapse or knocked him off the ladder. Disoriented, he somehow managed to switch the mixer off and then back on again before stumbling out of the building. His colleagues found him outside, suffering from severe ataxia—uncoordinated muscle movements—and repeatedly crying out, 'I'm burning up! I'm burning up!'
Initially, the possibility of a criticality accident in a mixing tank was considered virtually non-existent. The technicians, therefore, believed Kelley must have been exposed to alpha radiation or the corrosive acid bath, or both. One rushed him to a chemical shower, while the other switched off the mixer.
Within minutes, other staff arrived to find Kelley nearly unconscious. His face was a bright, alarming pink—a clear sign of erythema, or radiation-induced reddening of the skin, a hallmark of acute cutaneous radiation syndrome.
Any accident involving radioactive substances at Los Alamos triggered an immediate investigation by radiation monitoring teams. Even as Kelley was rushed to the emergency room, these specialists began their survey. They first searched for alpha radiation, which would indicate plutonium had escaped the tank, but found none.
Eighteen minutes later, they switched to searching for gamma radiation. To their shock, they found intense gamma readings—tens of rads per hour—near the mixing tank. Such extreme gamma radiation could only be produced by significant amounts of fission products, confirming that the bright flash and Kelley's symptoms were indeed the result of a criticality accident.
A Tragic Decline
For the first hour and forty minutes after the accident, Kelley was incoherent, battling intense waves of vomiting and retching. Then, he briefly stabilized, able to converse normally, and medical staff could take his pulse and draw blood.
The blood sample painted a horrifying picture: Kelley had been exposed to an estimated 9 Gray (Gy) from fast neutrons and 27 Gy from gamma rays, totaling a staggering 36 Gy. To put this in perspective, an exposure of just 4.5 to 5 Gy is considered the median lethal dose (LD50) for humans; 8 Gy is almost certainly fatal (LD99).
Cecil Kelley had received more than seven times the LD50 and at least four times the LD99. Though doctors administered pethidine and morphine to ease his unimaginable pain, his death was tragically inevitable. Within six hours, his lymphocytes—crucial white blood cells—were all but gone.
A bone biopsy performed 24 hours after the incident revealed watery bone marrow, completely devoid of red blood cells. Numerous blood transfusions proved futile. Just 35 hours after his initial exposure, after a final desperate bout of restlessness, agitation, sweating, and an irregular pulse, Cecil Kelley succumbed to heart failure.
Unanswered Questions and Unjust Blame
The investigation into the circumstances of the accident never produced a public explanation for how the mixing tank became filled with such a dangerously high concentration of plutonium. Shockingly, the initial blame was placed squarely on Cecil Kelley himself.
However, Robert L. Nance, a colleague assigned to recover the remaining plutonium from the tank, discovered a crucial clue. He found that the solvent in the tank was not as potent as expected, possibly degraded by extended radiation exposure. This degradation could have caused plutonium to build up to a higher concentration. Nance's report, however, was never approved for publication.
A darker side to the aftermath emerged: although Kelley had neither ingested nor inhaled plutonium during the accident, like many laboratory technicians at Los Alamos, he had been exposed to minute airborne plutonium particles over the years. His tragic accident was, disturbingly, viewed as an 'experiment of opportunity'.
Meticulous records were kept of every moment of Kelley's life from the accident until his death, and subsequently, during his autopsy. His organs were retained for pathological examination, and their plutonium levels analyzed. These results were considered invaluable for understanding the effects of radiation exposure in a population during a nuclear attack—data they believed impossible to obtain any other way.
The bone marrow biopsy, for instance, was performed under the guise of determining if Kelley was a candidate for a bone marrow transplant. Yet, with his death inevitable, an actual transplant was never seriously considered. His body was a research subject.
Article
Cecil Kelley criticality accident
A criticality accident occurred on December 30, 1958, at Los Alamos National Laboratory (LANL) in Los Alamos, New Mexico, in the United States. It is one of 60 known criticality events that have occurred globally outside the controlled conditions of a nuclear reactor or test and the third event that took place in 1958, after events on June 16 at the Y-12 Plant and on October 15 at the Vinča Nuclear Institute. The accident involved plutonium compounds dissolved in liquid chemical reagents; within 35 hours, it killed chemical operator Cecil Kelley by severe radiation poisoning.
Context of the accident
Cecil Kelley criticality accident
Diagram of the criticality accident
Cecil Kelley was a 38-year-old chemical operator with 11 years of experience; he had spent more than half of this time at LANL, where one of his duties was to operate a large, 1 m3 capacity, stainless-steel mixing tank. The tank contained residual plutonium-239 (239Pu) from other experiments and applications, along with various organic solvents and acids in aqueous solution for the purpose of recovery and reuse. In pure form and under normal temperature and pressure, plutonium is a solid, silvery metal. It tarnishes quickly when exposed to air and readily dissolves in concentrated hydrochloric, hydroiodic, perchloric, and other acids. On the day of the accident, the mixing tank was supposed to contain a "lean" concentration of dissolved plutonium (≤ 0.1 g of plutonium per liter of solution) in a bath of highly corrosive nitric acid and a caustic, stabilized, aqueous, organic emulsion; however, the concentration of plutonium in the mixing tank was in fact nearly 200 times higher than Kelley anticipated, as a result of at least two improper transfers of plutonium waste to the tank from undetermined sources. Also, the plutonium was distributed unevenly, with the upper layer of solution containing especially high concentrations, amounting to a total of >3 kg of plutonium, dangerously close to criticality. When Kelley switched on the mixer, a vortex began to form. The denser aqueous layer within the tank was forced outward and upward forming a "bowl", and the less dense, plutonium-rich layer was drawn toward the vessel's center.
The excursion
Cecil Kelley criticality accident
The optimal shape for any fissile substance to become supercritical is the shape of least surface area—a sphere. Although the plutonium-rich solution was not spherical, the vortex made it thicker in the center; this, along with the increase in density and neutron reflectivity of the aqueous layer surrounding it, caused the fissile material in the mixer to become supercritical after approximately one second.
A randomly occurring neutron in any assembly occasionally strikes a fissile nucleus, causing it to fission and liberate more than one neutron. Normally, the effective neutron multiplication factor (the average number of secondary neutrons provoked by one neutron) is intentionally kept far less than 1.0, so that each incipient nuclear chain reaction cannot accelerate; it dies out very quickly. Changes of shape, concentration, neutron reflectivity, and other factors can increase the neutron multiplication factor. As soon as the neutron multiplication factor exceeds 1.0, one of the next random neutrons starts a rapidly growing nuclear chain reaction. In a liquid criticality accident, the energy released by the chain reaction indirectly slows or stops the chain reaction (due to increasing temperature, increasing volume due to thermal expansion and steam formation, and other factors). Sometimes the reaction rate increases again or restarts.
An uncontrolled release of nuclear energy is referred to as a criticality accident or an excursion. This excursion lasted only 200 microseconds, but it released a huge burst of neutrons and gamma radiation before it stopped. Within 3 seconds, the mixer had dispersed the layers in the mixture, which fortuitously made further excursions impossible, unlike the 1964 Wood River Junction criticality accident, in which subsequent actions provoked two additional smaller excursions.
Immediate consequences
Cecil Kelley criticality accident
Kelley was standing on a ladder looking at the contents of the mixing tank through a viewing window when the excursion occurred. Two other technicians working in the laboratory witnessed a bright flash of blue light followed by a thud. The 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 out of the building. The other technicians found Kelley outdoors in a state of ataxia (uncoordinated muscle movement) and repeating the phrase, "I'm burning up! I'm burning up!"
Because the possibility of an excursion 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. Other staff members arrived at 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 examining the mixing room with radiation detectors capable of assessing the alpha radiation from escaped plutonium. Alpha activity would have been widespread if any of the plutonium mixture had escaped the tank, but none was found. Eighteen minutes later, the team began searching for gamma radiation, and were surprised to find intense gamma radiation near the mixing tank, on the order of tens of rads per hour. Such intense gamma radiation could only be produced by significant amounts of fission product; this, plus the otherwise inexplicable flash of light reported by the other two technicians, confirmed that a criticality accident had occurred.
Kelley's clinical course
Cecil Kelley criticality accident
For the first hour and forty minutes after the accident, Kelley was incoherent, and went through waves of intense vomiting and retching. He then stabilized, was once again able to converse normally, and was able to have his pulse taken and his blood drawn. The blood sample indicated that Kelley had been exposed to about 9 Gy from fast neutrons and 27 Gy from gamma rays—a total of 36 Gy. For an adult human, exposure to 2 Gy from an unfocused radiation source such as an excursion will cause radiation sickness but is not definitely lethal; about 4.5 to 5 Gy is the LD50, or median lethal dose; 8 Gy is the LD99. Kelley had received more than 7 times the LD50 and at least 4 times the LD99. Although the medical staff in the emergency room took steps to ease his pain with pethidine and morphine, previous research on radiation exposure in animals indicated Kelley's death was inevitable. Within six hours his lymphocytes were all but gone. A bone biopsy 24 hours after the incident produced bone marrow that was watery and contained no red blood cells. Numerous blood transfusions had no lasting helpful effect: Only 35 hours after his initial exposure and after a final bout of intense restlessness, agitation, sweating, becoming ashen-skinned, and having an irregular pulse, Kelley died of heart failure.
Implications
Cecil Kelley criticality accident
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.
Robert L. Nance, a colleague of Kelley, was the chemist assigned to recover the remaining plutonium in the tank. This task revealed to him that the solvent in the tank was not as potent as expected (possibly broken down by extended exposure to radiation), so there may have been a buildup to a higher concentration for that reason. The report prepared by Nance was not approved to be published.
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 pathological examination 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 inevitable, and an actual transplant was not seriously considered.
Court case
Cecil Kelley criticality accident
Kelley's death left a widow, Doris Kelley, and two children, then ages 8 years and 18 months. Doris was not notified while he was still alive that her husband had been irradiated, and only learned of his death from the laboratory authority when representatives 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 Doris received was a lifetime-level position working for the lab itself at near-poverty levels, until she had to retire for health reasons.
In 1996, Doris Kelley and her daughter, Katie Kelley-Mareau, filed a lawsuit against 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 Lushbaugh and others performed many more in later years at Los Alamos. During a deposition for the case, Lushbaugh, when asked who gave him the authority to take eight pounds (3.6 kilograms) 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.