The deadline for an agreement on Iran’s nuclear program is something of a moving target, but right now negotiators need to wrap things up by June 2015. The five permanent members of the United Nations Security Council — China, France, Russia, the United Kingdom and the United States — along with Germany, have until then to strike a deal with the Islamic republic. If all goes the way the United States hopes, a signed agreement will keep Iran out of the nuclear weapons club.

For now, the two sides are operating under an interim agreement, which rolls back Iran’s stock of enriched uranium and freezes the country’s capability to produce nuclear materials that could be used to make a nuclear bomb. In exchange, Iran can sell its oil more freely and gain access to millions of dollars in frozen assets.

One element that’s fully expected in a long-term arrangement is a limit on the number and kinds of centrifuges Iran can use to enrich uranium. Former CIA deputy director Michael Morell said there’s an irony in that.

"If you are going to have a nuclear weapons program, 5,000 is pretty much the number you need," Morell, now a CBS analyst, said on Charlie Rose. "If you have a power program, you need a lot more. By limiting them to a small number of centrifuges, we are limiting them to the number you need for a weapon."

Morell told PunditFact he said 5,000 because that was lowest number he had heard was in play. The number of centrifuges in place today is a hair over 20,000, and a likely goal is to cut that to about 5,000. But Morell’s basic point struck us as just plain intriguing. We wanted to learn more about this idea that a nuclear power program would require many more centrifuges than you’d need for a bomb -- which by extension means that limiting centrifuge capacity is just one negotiating point out of many.

The consensus among the experts we reached is that Morell is on the money. Matthew Kroenig at Georgetown University told PunditFact the Morell is "is absolutely correct." Ditto for Daryl Kimball of the Arms Control Association and David Albright of the Institute for Science and International Security.

Matthew Bunn at Harvard agreed with his colleagues.

"People think surely you must need a bigger enrichment system to make 90 percent enriched material for bombs than to make 4-5 percent enriched material for power reactors," Bunn said. "But exactly the opposite is true."

Bunn said there are two reasons. First, you need tens of tons of material to fuel a power reactor for a year, but just tens of kilograms to make a bomb. According to the International Atomic Energy Agency , the threshold amount for a bomb is about 25 kilograms of the most highly enriched U-235.

And while yes, it’s harder to make 90 percent enriched uranium (bomb) than 4-5 percent enriched uranium (power), it’s not that much harder, Bunn said.

The toughest part in the process comes when you start with the raw uranium. By the time you’ve brought that to 4-5 percent, "you’ve already done more than 2/3 of the work of going all the way to 90 percent U-235 for weapons," Bunn said. "So the amount of work needed to make bomb material is only a modest amount more per kilogram, and the number of kilograms you need for bombs is 1,000 times less.

Bottom line: Making bombs takes fewer centrifuges. And without a lot of centrifuges, it’s hard to make nuclear power. For the record, some centrifuge models are better than others, so that's also a factor.

Today, Iran has just one nuclear power station, the plant at Bushehr that it bought from the Russians. To keep that facility running, Iran would need to increase its centrifuge capacity ten-fold . A steady supply of fuel from Russia is what keeps Bushehr online.

Centrifuges and a nuclear deal

This fact that bombs require fewer centrifuges than power is a source of frustration for Albright, a physicist with the Institute for Science and International Security.

"I wish it were reversed," he told us. "Then we could easily tell if the program was for weapons."

As the clock clicks down to reach an agreement, the number of centrifuges and their level of sophistication will draw a lot of scrutiny.

Kimball, of the Arms Control Association, said the specific terms on this front will have to resolve a crucial question: "What are Iran’s practical needs, and how do you square that with international concern about the real purpose?"

Ideally, Kimball said, Russia or another nation would continue to supply the fuel, but barring that, the five permanent members of the United Nations Security Council and Germany aim to put on cap on the number of centrifuges for as many years as possible. Allowing about 5,000 would help.

"With that, it would take 12 months for Iran to produce enough material for one bomb," Kimball said. "That would give you enough time to detect that activity."

But Bunn underscored that an agreement would have many moving parts and a key element would be the number of years that Iran agreed to rein in its centrifuge capacity.

"Because the sides have already agreed in the (interim agreement) that after the agreement expires, Iran is to be treated like other parties to the Nuclear Nonproliferation Treaty. That would mean it could build up its enrichment capacity to have enough to fuel Bushehr or even more reactors," Bunn said.

The variables don’t stop there. If Iran ramped up production of fuel for nuclear power, it would need a ready supply of raw ore, which it might need to purchase on the international market.

During his interview with Charlie Rose, Morell warned that the focus on declared centrifuges is misplaced, because he expects that if Iran were to try to build a bomb, it would do so in secret. The only protection against that, Morell said, is unannounced inspections at any place in the country at any time.

Our ruling

Morell said that it takes fewer centrifuges to make bomb-grade nuclear material than it does to supply fuel for a nuclear power plant and argued that the focus on centrifuges can go too far.

That argument aside, experts agreed that Morrell has his facts right. A power plant requires tons of fuel each year. A bomb requires about 25 kilograms of U-235 enriched to the 90 percent level. If an agreement limits Iran to about 9,000 centrifuges, that would be sufficient to produce enough bomb-grade material but would leave Iran well short of the capacity to generate fuel to power nuclear power plants.

We rate Morrell’s claim True.