The U.S. Energy Department has underestimated the potential deadly consequences should plutonium escape Los Alamos National Laboratory, which produces bomb cores for America’s nuclear weapons, a study published Friday by independent scientists found.

The chances of a leak are considered minuscule. But one is possible, especially following a natural disaster like an earthquake. Plutonium could escape from protective work stations inside a building called Plutonium Facility 4, or PF-4, and ignite. Then, if one or more of the building’s safety systems fail, radioactive plutonium particles could enter the outside air and spread through the surrounding communities in a plume of smoke.

The Energy Department, which manages the country’s nuclear weapons production, had previously concluded a so-called loss of containment at the lab could spread about 1 kilogram of plutonium, a radioactive metal, leading to nine cancer deaths on average in the surrounding area. But modeling in the new study, published in Science and Global Security, showed the potential for much worse: Hundreds of people who inhale or ingest particles from a leak could eventually die from cancer, the researchers said.

And in the most serious possibility modeled in the study — if more than 1 kilogram of plutonium escaped — the town of Los Alamos could become unlivable and radioactive particles could spread across state lines. As many as 3,200 people could eventually get cancer, the researchers estimated, leading to about 1,000 deaths. The remediation of land could run up to an estimated $150 billion.

“In the worst case, it would be devastating for Los Alamos and New Mexico,” said Sébastien 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 to independently evaluate the department’s assessment of a potential leak. The journal Science and Global Security is affiliated with Princeton University, where Philippe is also a visiting researcher. The study was funded by the Andrew Carnegie Foundation and the Ploughshares Fund, both of which underwrite 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 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 1 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.

Using wind and precipitation data from every hour of every day of 2022, the researchers modeled 8,760 scenarios of a plutonium leak, tracing the possible trajectory of particles. In some circumstances, the data shows particles would have traveled as far north as central Colorado and as far south as Southern New Mexico.