A summary of ‘criticality accidents’, or: the dangers of working with plutonium

I’ve been browsing the ‘criticality accident‘ page on Wikipedia this morning; I found it a year ago and I’ve gone back 2-3 times to find out more about the people and incidents involved. Something about dying in that particular manner disturbs me; but I’m also captivated by the relative ease with which these radioactive materials can kill you, and also by the continued willingness of people to work with them.

If it’s your first time reading about it, check out the Wikipedia info on a sphere of plutonium nicknamed the Demon Core, it became famous after causing separate accidents at Los Alamos and I imagine it’s fairly well known.


A sphere of plutonium surrounded by neutron-reflecting blocks of tungsten carbide. A re-creation of the August 21, 1945 criticality accident at Los Alamos to measure the radiation produced when an extra block was added, making the mass supercritical. Taken from Wikipedia, see link.

There are other Interesting excerpts below; edited for brevity:


Criticality accident — an accidental increase of nuclear chain reactions in enriched uranium or plutonium. This releases a surge of neutron radiation which is highly dangerous to humans.

Occurs when — a critical reaction is achieved unintentionally. Typical criticality accidents cannot reproduce the design conditions of a fission bomb, so nuclear explosions do not occur. Heat released by the nuclear reaction will typically cause the fissile material to expand, so that the nuclear reaction becomes subcritical again within a few seconds.

Since 1945 there have been at least 60 criticality accidents. These have caused at least 21 deaths: seven in the United States, ten in the Soviet Union, two in Japan, one in Argentina, and one in Yugoslavia.

  • On 30 December 1958, the Cecil Kelley criticality accident took place at the Los Alamos National Laboratory. Cecil Kelley, a chemical operator working on plutonium purification, switched on a stirrer on a large mixing tank, which created a vortex in the tank.The plutonium, dissolved in an organic solvent, flowed into the center of the vortex. Due to a procedural error, the mixture contained 3.27 kg of plutonium, which reached criticality for about 200 microseconds. Kelley received 3,900 to 4,900 rads according to later estimates. The other operators reported seeing a flash of light and found Kelley outside, saying “I’m burning up! I’m burning up!” He died 35 hours later.


The vessel in which the accident took place. Taken from Wikipedia, see link.

  • On 10 December 1968, Mayak, a nuclear fuel processing center in central Russia was experimenting with plutonium purification techniques. Two operators were using an “unfavorable geometry vessel in an improvised and unapproved operation as a temporary vessel for storing plutonium organic solution”; in other words, the operators were decanting plutonium solutions into the wrong type of container. After most of the solution had been poured out, there was a flash of light and heat. “Startled, the operator dropped the bottle, ran down the stairs, and from the room.” After the complex had been evacuated, the shift supervisor and radiation control supervisor re-entered the building. The shift supervisor then deceived the radiation control supervisor and entered the room of the incident and possibly attempted to pour the solution down a floor drain, causing a large nuclear reaction that irradiated the shift supervisor with a fatal dose of radiation.


I guess the takeaway is: don’t take a job dissolving plutonium in organic solvent?