Why is the US ramping up production of plutonium ‘pits’ for nuclear weapons?

On one side of the US – on New York’s Staten Island – the US army corps of engineers began this month to remove the radioactive remnants of Robert Oppenheimer’s Manhattan Project that produced the atomic bombs that ended the second world war.

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Meanwhile, 2,000 miles away, at the Los Alamos national laboratory north of Santa Fe in New Mexico, on the same site that developed and assembled the bombs dropped on Hiroshima and Nagasaki, work is being ramped up to produce plutonium “pits” – spherical shells about the size of bowling balls that are a vital component of warheads in the US nuclear arsenal.

Both in their own way tell the story of the nuclear age, but one is historic housekeeping – in 1939, 1,200 tons of high-grade uranium ore was purchased and transferred from the Belgian Congo to Staten Island, where there are still traces of radioactive contamination – and the other is far more controversial and very current.

Both arrive as concern over a conflict involving the use of nuclear weapons rises.

Increasing geopolitical tensions with Russia and a militarily expansionist China are behind a $1.5tn US effort to modernize the US nuclear arsenal, including tens of billions of dollars to replace ageing, silo-launched Minuteman intercontinental ballistic missiles stationed in Wyoming, Montana and North Dakota with a successor, the Sentinel .

But the prospect of placing new missiles, with potentially more warheads, in the US heartlands is under scrutiny for its logic. “Why plant a $100-billion nuclear ‘kick me’ sign on the country’s breadbasket?” asked the authors of a report in Scientific American this month.

For two decades, the Pentagon and Congress have been concerned about the US ability to produce the cores of nuclear warheads, including the plutonium pits. Since 1989, the US has not been able to produce pits in quantities required to refresh or renew a stockpile of 3,708 warheads (about 1,770 warheads are deployed and 1,938 are held in reserve).

The issue is that plutonium degrades over time, but estimates vary on how quickly or at what point the pits become too soft to be usable. Most are already 40-plus years old, but some studies say they could be good up to 80 years. The Livermore lab in northern California announced in 2012 that it had found “no unexpected aging issues … in plutonium that has been accelerated to an equivalent of ~150 years of age”.

In 2018, the National Nuclear Security Administration (NNSA) produced a plan to meet the defense department’s goal of 80 pits a year by maximizing production lines at Los Alamos and converting a plant near the Savannah River in South Carolina originally built to dispose of 34 tons of cold war-era plutonium deemed unneeded by nuclear weapons programs. But the project was unsuccessful and cancelled in 2020 .

According to the Scientific American report , the first 800 new pits would go to the Sentinel program, and then all 1,900 US submarine-launched missiles would be refreshed. The new warheads would also be shock-resistant, or “insensitive” to accidental detonation that could disperse plutonium.

But there is now no pit-production expertise at the South Carolina facility and cost estimates have already grown from $3.6bn to over $11bn for a third fewer pits. In January, the Government Accounting Office (GAO) warned that the NNSA’s plutonium modernization program had not developed “either a comprehensive schedule or a cost estimate that meets GAO best practices”.

Questions over US nuclear weapons re-entered public conscience with Russian posturing over the use of battlefield nuclear weapons in Ukraine, then the overflight of a Chinese spy balloon close to areas critical to US nuclear deterrence in January.

It’s not just practical obstacles though.

In September, the UN secretary-general, António Guterres, warned that a “worrisome new arms race is brewing. The number of nuclear weapons could rise for the first time in decades.” Over the summer, a biopic of Robert Oppenheimer was released that touched on anxieties the physicist experienced over the development of the nuclear bomb and its use on Japan.

Those anxieties resurfaced in a recent weeks when a since-reprimanded Israeli minister speculated on dropping a nuclear bomb on Gaza, and the deployment of an 18,000-ton Ohio-class nuclear submarine to the Mediterranean.

Last week, the Green party presidential hopeful Jill Stein warned that US leaders were “absolutely” risking the possibility of nuclear war in its support of Israel after sending the sub and missile groups to the region. “We’re not at nuclear war now, but could a nuclear war be triggered? Absolutely. And we’re seeing this become more dangerous every day,” Stein told Newsweek.

People have assumed the probability [of nuclear war] was close to zero, which it isn’t unfortunately

Frank N von Hippel of Princeton University

The US spends about 5% of its military budget on nuclear weapons. Last year, the Biden administration threw its weight behind the sprucing up of the US nuclear arsenal. “Much of the stockpile has aged without comprehensive refurbishment,” it said in a long-awaited nuclear posture review . “At a time of rising nuclear risks, a partial refurbishment strategy no longer serves our interests.”

Frank N von Hippel, a US physicist and co-director of the program on science and global security at Princeton University, says the effort to manufacture new plutonium pits might be justified if a crisis existed.

But without a firm understanding of how long plutonium pits take to degrade, the effort and costs to restart production may be unnecessary.

“Many of us thought the problem on nuclear weapons was over at the end of the cold war. I remember a strategic air command officer saying we were on a glide path. But we’re not on a glide path any more,” Von Hippel said.

Fears of nuclear conflict, with its identifiable symbol of a doomsday mushroom cloud, have largely been replaced by fears over the observable climate crisis, he says, but they may now be returning.

“Nuclear war is a probability thing, and it’s been 80 years, a lifetime, since we had one to deal with one,” Von Hippel says. “So people have assumed the probability was close to zero, which it isn’t unfortunately.”