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A worker's gloved hand holds a plutonium pit at the Rocky Flats production facility, U.S. Department of Energy

Issue Brief


Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. Plutonium, like uranium, is a mix of several isotopes. Plutonium-239 and plutonium-241 are fissile and can sustain a nuclear chain reaction, thus leading to applications in nuclear weapons and nuclear reactors. Material rich in the isotope plutonium-239 is referred to as “weapons-grade plutonium.”

Plutonium is solid under normal conditions and can form compounds with other elements. It is a silvery-gray metal that tarnishes when exposed to air. It has been described as “an element at odds with itself” because it can change its density by as much as 25%; expands when it solidifies; and can be as brittle as glass or as malleable as aluminum. It reacts vigorously with its environment, especially with oxygen, hydrogen, and water. Centers for Disease Control and Prevention, “Radioisotope Brief: Plutonium,” April 4, 2018 [last updated], https://www.cdc.gov/nceh/radiation/emergencies/isotopes/plutonium.htm
Plutonium has a half-life of 24,110 years, and emits alpha particles as its mode of decay. It is extremely dangerous, even in tiny quantities, when inhaled. Once lodged in lung tissue, the alpha particles can kill lung cells, scarring the lungs and leading to further lung disease and cancer. Plutonium can enter the blood stream from the lungs and concentrate in the bones, liver, and spleen, further exposing those organs to alpha particles.

The Manhattan Project developed special technologies as well as special materials to produce nuclear weapons—this included highly enriched uranium (uranium-235) and plutonium. Both are made via different processes that require naturally occurring uranium ore. While plutonium and uranium are key parts of modern nuclear weapons, the first generation used one or the other separately. Historically, the Manhattan Project produced plutonium in quantities useful for the development of the first atomic bombs. The bomb used in the Trinity nuclear test in July 1945, and “Fat Man” bomb that devastated Nagasaki, Japan in August 1945, both contained plutonium cores, while the “Little Boy” bomb detonated on Hiroshima incorporated highly enriched uranium to create a nuclear explosion.

U.S. Department of Energy, Office of Environmental Management, “Closing the Circle on the Splitting of the Atom: The Environmental Legacy of Nuclear Weapons Production in the United States and What the Department of Energy is Doing About It," DOE/EM-0266, January 1996, https://www.energy.gov/sites/default/files/2014/03/f8/Closing_the_Circle_Report.pdf.Because incredible amounts of energy and infrastructure are required to physically separate out Uranium-235 from the majority uranium-238 in nature, scientists sought a way to work-around the trouble of enriching uranium by producing an alternative nuclear material that could be chemically separated for use in bombs. This led to the development of plutonium-239, an element created in nuclear reactor facilities. Basically, low-enriched uranium (consisting of less than 20% uranium-235) is separated into radioactive byproducts, a process that releases neutrons; the neutrons bombard uranium-238 and transform it into plutonium-239. Material rich in plutonium-239 then moves from the reactor to a reprocessing plant that separates it from the uranium and other radioactive byproducts. The plant extracts the uranium and plutonium by dissolving the irradiated uranium in acid, which leaves behind high-level radioactive liquid waste.

U.S. Department of Energy, Office of Environmental Management, “Closing the Circle on the Splitting of the Atom: The Environmental Legacy of Nuclear Weapons Production in the United States and What the Department of Energy is Doing About It," DOE/EM-0266, January 1996, https://www.energy.gov/sites/default/files/2014/03/f8/Closing_the_Circle_Report.pdf.Between 1944 and 1988, the U.S. built and operated plutonium production reactors at Hanford, WA and Savannah River, SC. Within the weapons complex, after uranium from the Fernald plant, OH was coated with aluminum or zirconium metal, it was assembled into reactor fuel and targets. At the Hanford site’s reactors, fuel slugs were inserted into the front face of the reactor where they underwent neutron bombardment, and then were gradually pushed through horizontal channels cut into large cubes of graphite blocks. By contrast, the reactors at Savannah River submerged highly enriched fuel in large tanks of “heavy water” and separated out depleted uranium targets. Regardless of the methodology, reactors converted only a small fraction of uranium in fuel and targets into plutonium during each cycle, thus requiring workers at both sites to process hundreds of thousands of tons of uranium.

The irradiated fuel and targets discharged from production reactors contained hundreds of different radioactive isotopes that had to be separated out from the uranium and plutonium through chemical processes. Due to the lethality of even short-term exposure to these “fission products,” workers had to handle the materials via remote control behind lead-glass shielding and concrete walls. These chemical separation plants operated for recovering plutonium and uranium until the 1980s. U.S. Department of Energy, Office of Environmental Management, “Closing the Circle on the Splitting of the Atom: The Environmental Legacy of Nuclear Weapons Production in the United States and What the Department of Energy is Doing About It," DOE/EM-0266, January 1996, https://www.energy.gov/sites/default/files/2014/03/f8/Closing_the_Circle_Report.pdf.According to the Department of Energy (DOE), reprocessing plants have generated over a hundred million gallons of highly radioactive and hazardous chemical waste (approximately 99% of the total radioactivity left from nuclear weapons production), including long-lived radioactive elements that pose environmental and human health risks for tens of thousands of years. Reprocessing also generated billions of gallons of wastewater. Even though this wastewater contained approximately 1% of the radioactivity and trace amounts of chemicals, it was discharged directly into the ground during the Cold War and has caused widespread contamination.

The national weapons laboratories used plutonium to make and test weapons prototypes and processes. However, the majority of plutonium from processing plants traveled to the Rocky Flats plant in Colorado, where they were machined into warhead components or “pits.” Plutonium metallurgy required workers to use glove boxes equipped with ventilation systems and other safety features. Glove boxes offer a sealed environment and, when necessary, can be filled with inert gas to keep plutonium inside from igniting in air. How monitoring and protection were implemented, regulated, and adhered to or not at Rocky Flats and other facilities in the nuclear weapons complex is an ongoing controversy, with many workers sick from occupational safety hazards from working with plutonium and other hazardous materials. Len Ackland, Making a Real Killing: Rocky Flats and the Nuclear West (Albuquerque, NM: University of New Mexico Press, 1999).Moreover, there were two major known plutonium fires at the Rocky Flats plant in 1957 and 1969 that released radioactive contamination. Lower concentrations of radioactive isotopes were released throughout the operational life of the plant, with winds carrying airborne contamination south and east of the plant into the populated areas northwest of Denver. Reportedly sixty-two pounds of plutonium dust was detected in the ductwork of the ventilation system—enough for multiple nuclear weapons. Weapons production at the Rocky Flats plant was halted after a combined FBI and EPA raid in 1989 and years of protest. Debates are ongoing over the remaining contamination, including unaccounted-for plutonium after the plant’s shutdown.

Securing plutonium and disposal of plutonium waste are central nuclear proliferation and environmental concerns today. Even though the Cold War is considered to be over, plutonium remains a high-risk nuclear material. While reprocessing plants are no longer needed for the extraction of weapons-grade plutonium, and the nuclear materials inside are no longer intended for a nuclear arms race, the DOE is charged with the daunting task of stabilizing facilities, many of which are well over fifty years old, and stabilizing extraordinarily sensitive materials in order to prevent explosions, leaks, further radiation exposures, and potential terrorist attacks.

Plutonium resides at the heart of many controversies and unresolved debates, from human radiation experiments that studied plutonium’s embodied effects without informed consent to downwind/downstream contamination and criticality accidents, from plutonium dangerously left in facility ducts and unaccounted for during site cleanups to vehement disagreements over whether commercial energy reactors should be granted use of the plutonium stockpile. Because reprocessing spent fuel has been illegal in the U.S. since the 1970s due to concerns over proliferation, plutonium remains and will persist as one of the most enduring legacies of the nuclear age on earth.


Ackland, Len. Making a Real Killing: Rocky Flats and the Nuclear West. Albuquerque, NM: University of New Mexico Press, 1999.

Baker, Richard D., Siegfried S. Hecker, and Delbert R. Harbur, "Plutonium: A Wartime Nightmare but a Metallurgist's Dream." Los Alamos Science no. 148 (1983): 150–151. Accessed June 4, 2021.

Centers for Disease Control and Prevention. “Radioisotope Brief: Plutonium.” Last updated April 4, 2018. Accessed June 4, 2021.

Hecker, Siegfried S. “Plutonium and Its Alloys: From Atoms to Microstructure.Los Alamos Science no. 26 (2000): 290-335. Accessed June 4, 2021.

Moore, LeRoy. “Plutonium and People Don’t Mix: The Crisis of Rocky Flats, Colorado’s Defunct Nuclear Bomb Plant.” Rocky Flats Nuclear Guardianship, Rocky Mountain Peace and Justice Center. August 8, 2015. Accessed June 4, 2021.

U.S. Department of Energy, Office of Environmental Management. “Closing the Circle on the Splitting of the Atom: The Environmental Legacy of Nuclear Weapons Production in the United States and What the Department of Energy is Doing About It.” DOE/EM-0266. January 1996. Accessed June 3, 2021.

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