The Department of Energy has downplayed the possible lethal outcomes if plutonium were to escape from Los Alamos National Laboratory in New Mexico, the site responsible for manufacturing cores for U.S. nuclear weapons, according to a study released today by independent researchers.

The odds of such a release remain very low. Yet it could occur, particularly after a natural event such as an earthquake. Plutonium might exit shielded workstations inside a structure known as Plutonium Facility 4, or PF-4, and catch fire. Should one or more safety mechanisms then fail, radioactive particles could reach the open air and travel over nearby communities in a cloud of smoke.

The Energy Department, which oversees nuclear weapons work, had earlier determined that a containment failure at the lab might release roughly one kilogram of plutonium, a radioactive metal, resulting in nine cancer deaths on average in the region. Modeling from the new study, published in Science and Global Security, indicated far greater harm: hundreds of people who breathe in or swallow particles could later die from cancer, the authors stated.

In the most severe case examined, if more than one kilogram of plutonium escaped, the town of Los Alamos could become uninhabitable and particles could cross state lines. As many as 3,200 people might develop cancer, leading to roughly 1,000 deaths. Cleanup costs could reach an estimated 150 billion dollars.

The risks of a leak at Los Alamos

Researchers modeled the spread of radioactive particles that could result from a plutonium leak at the Los Alamos National Laboratory. This map shows the highest amount of radiation estimated for every location among thousands of simulated conditions.

"In the worst case, it would be devastating for Los Alamos and New Mexico," said Sebastien Philippe, an assistant professor of nuclear engineering and engineering physics at the University of Wisconsin-Madison, who led the study. "We find that it could be 10 to 100 times worse" than the government's estimates, he added.

The peer-reviewed study is the first independent review of the department's assessment of a potential leak. The journal Science and Global Security is affiliated with Princeton University, where Dr. Philippe is also a visiting researcher. The study was funded by the Andrew Carnegie Foundation and the Ploughshares Fund, both of which support arms control and nonproliferation research.

The study arrives amid a threat of a global nuclear arms race. China, North Korea and Russia are upgrading or expanding their arsenals. And Iran, at war with the United States and Israel, has a stockpile of enriched uranium. The United States is ramping up its own bomb core production at Los Alamos, where the country's only active plutonium-handling facility is running round-the-clock operations as part of a 1.7 trillion dollar effort to modernize the nation's weapons.

The country already has thousands of bomb cores, each about the size of a grapefruit, made during the Cold War, but the new ones are intended to arm next-generation land-based missiles and submarines. Just one would produce a blast far more powerful than the one at Hiroshima. And while Congress required the production of at least 30 bomb cores per year by 2030, Los Alamos could be called upon to produce up to 80 per year.

The lab sits on a fault system, and the federal government has identified the most consequential risk to be an earthquake that knocks over one of PF-4's thousands of glove boxes, oxygen-free enclosures where workers handle radioactive materials.

Plutonium particles pose little harm if they are not inhaled, similar to radiation from an X-ray. But when inhaled or ingested, those particles can cause damage over years or decades, even altering DNA. Children are the most vulnerable because their cells are still forming.

In a statement, a spokesperson for the National Nuclear Security Administration, an agency within the Energy Department, wrote that PF-4 "has robust safety programs and systems in place to ensure multiple and redundant layers of protection for our workers, the environment and the public." The statement continued: "The facility is one of the safest places in the country to be in the event of a natural disaster."

In 2008, the department publicly released a loss-of-containment scenario written by a government contractor. It concluded that if all of the plutonium estimated to be in the handling facility were engulfed in flames, just over one kilogram would escape outside in a form that could be inhaled, and an average of nine people would eventually die of cancer related to exposure.

For the new study, the researchers reverse-engineered the government's methodology, and replicated a similar fatality average. But then, they recalculated the risks of a leak with additional context and under different assumptions.

Thomas B. Cochran, a former senior scientist at the Natural Resources Defense Council and former adviser to the Energy Department, who was not involved in the study, said the research seemed to offer a "thorough analysis of the issue."

And the scientists chose the best modeling software for the analysis, said Steven Hanna, an expert in meteorology and atmospheric physics who was also not involved with the study. But, he added, they did not account for statistical uncertainty as exhaustively as is possible.

For estimates in its own assessment, the government had used an Energy Department handbook that relied on data from the 1960s through the 1980s, information that predated findings about other containment breaches, the study said.

For example, from 1951 to 1989, hundreds of fires occurred at the Rocky Flats Plant, a federal nuclear facility near Denver that produced bomb cores during the Cold War. A major fire there in 1957 released a large amount of plutonium particles, according to research published after the plant shuttered in the 1990s.

Soil analysis from Rocky Flats show that the size of those particles were roughly one-fifth the size of the particles considered in the government's analysis. Smaller particles can disperse farther, the researchers said, increasing the area contaminated and the number of people exposed. They can also remain in the lungs longer, increasing the risk of cell damage.

In one scenario modeled by the researchers, approximating a lab breach on an October night in 2022, shifting wind patterns could have moved smaller particles across several towns, tribal reservations, Santa Fe and parts of Albuquerque. Up to 210 people could have eventually died from cancer, they estimated.

Things get even more dire should more plutonium escape. Using other data from Rocky Flats, the researchers determined that just over five kilograms of plutonium, quadruple government estimates, could escape Los Alamos. On that October night, as many as 3,200 people could have developed cancer, leading to about 1,000 deaths, not including lab workers or emergency medical workers, the study said.

The researchers also examined the Savannah River Site in Aiken, S.C., which is expected to begin plutonium-pit production in the mid 2030s. The Energy Department estimated in 2020 that a breach there would lead to an average of two long-term cancer fatalities. But the scientists identified a night in May 2022 when wind could have carried the particles northwest beyond a buffer zone and into Georgia, possibly leading to as many as 330 cancer-related deaths.

The plutonium-handling facility was built almost 50 years ago for nuclear research, not production. Now, it is replacing aging infrastructure that has disrupted work at times and spread contamination, a New York Times investigation found last year.

The lab performs its own internal safety analysis, which is not made public. Workers are installing a new fire suppression system, which Rocky Flats did not have. And some, but not all, of the glove boxes at Los Alamos have been made earthquake resistant as part of the renovation.

But one component will not be fully replaced: the ventilation system.

For decades, the Defense Nuclear Facilities Safety Board, a federal watchdog, has recommended the facility upgrade the system so that, in the case of a catastrophe, it could capture tiny plutonium particles before they leak into the environment.

In 2022, the Energy Department said the upgrade was too expensive.

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