The first question of the vice-presidential debate on Tuesday night was whether the candidates would support or oppose a pre-emptive strike on Iran by Israel. It framed the issue for Gov. Tim Walz and Senator JD Vance as urgent to consider because Tehran has “drastically reduced the time it would take to develop a nuclear weapon,” cutting its acquisition time to “one or two weeks.”
The premise behind the question from Margaret Brennan of CBS News, one of the debate’s moderators, highlights a popular confusion over what it takes to build a usable nuclear bomb.
Nuclear experts said on Wednesday that it would take Iran not weeks to make a nuclear weapon, but months and possibly as long as a year. Ms. Brennan’s question, they added, began the debate on a false note.
“I don’t think there’s a danger that Iran this year is going to start exploding nuclear weapons,” said Houston G. Wood, an emeritus professor of mechanical and aerospace engineering at the University of Virginia. A specialist in atomic centrifuges and other nuclear matters, Dr. Wood estimated that it would take Iran up to a year to devise a weapon once it had enough nuclear fuel.
“It would likely take many months,” said Siegfried S. Hecker, a former director of the Los Alamos weapons laboratory in New Mexico, “not weeks.”
The experts said that the CBS question conflated the time it would most likely take Iran to manufacture a bomb’s worth of highly enriched uranium with the overall process of turning it into a weapon. Once enough uranium metal is produced, it must be carefully machined into the core of an atom bomb, which is then set amid the other parts of a nuclear warhead that would sit atop a missile.
“It takes advanced metallurgy and engineering,” Dr. Hecker, who served as the Los Alamos director from 1986 to 1997, said in an interview. The process is harder than might be expected. The atomic workers, for instance, face health risks because the tiny radioactive particles created during the shaping of nuclear parts could, unless they’re careful, settle in their lungs and spur cancerous growths.
The CBS question, though based on a false premise, seemed appropriate for the moment because Iran fired 180 missiles at Israel on Tuesday night in a dramatic escalation of the conflict between the two countries. Israel has vowed to retaliate, and President Biden said on Wednesday that he would not favor an attack on Iran’s nuclear infrastructure.
The widespread misunderstanding of the state of Iran’s nuclear capabilities stems from the many recent public reports that gave detailed timelines for Iran’s production of fuel for a nuclear bomb. But those reports offer few details on the other steps Iran must complete to build a nuclear weapon, including feats of atomic purification, engineering, manufacture and testing.
The public reports focus on what weapon experts call nuclear breakout — the time it would take a would-be atomic power to acquire a bomb’s worth of atomic fuel. An August report by the Institute for Science and International Security, a private group in Washington that tracks nuclear proliferation, for instance, declared that Iran had developed its fuel-making expertise to the point where it could now “break out quickly, in days.”
The institute’s president, David Albright, did not respond to questions about the group’s Iran timeline.
If Tehran did achieve breakout, it would then face a series of other crucial steps before producing a deliverable nuclear warhead. One would be developing an electronic firing system to set off a group of conventional explosives that compress the nuclear core, starting the chain reaction that emits bursts of atomic energy. In addition, the complete warhead must be tested rigorously to ensure that it can withstand the extraordinary heat and shaking of atmospheric re-entry.
Nuclear experts say the lengthy process also usually culminates with a bomb’s explosive testing underground to make sure the warhead would detonate as expected in war.
A March study by the Congressional Research Service cited federal reports saying that Tehran needed between one and two weeks to produce enough enriched uranium for a single weapon. But that study also cited testimony from Gen. Mark A. Milley, the former chairman of the Joint Chiefs of Staff, that Iran would need “several months to produce an actual nuclear weapon.” And it said that the “U.S. intelligence community assesses that Iran has not resumed work on its weaponization research.”
Finally, the congressional study noted that reports from the International Atomic Energy Agency, the United Nations watchdog that monitors Iran’s nuclear progress, suggested Tehran “does not yet have a viable nuclear weapon design or a suitable explosive detonation system.”
Dr. Wood, the University of Virginia professor, said many additional factors go into assessing the actual threat that Iran’s nuclear program might pose to Israel.
“You don’t want to fire one weapon and then be out of ammunition,” he said in an interview. Iran, Dr. Wood suggested, might want to possess an arsenal of a half dozen or more weapons before it tested one underground or detonated one in war.
The big problem for the councils of war and arms control, he added, is that “having that first one is a game changer.”
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