Iran has struck a historic deal with the United States and five other world powers (known as the P5+1), agreeing to temporarily halt its nuclear program for six months in exchange for limited and gradual relief of sanctions. Iran agreed to halt its uranium enrichment above 5 percent and the foreign powers agreed to give Iran access to $4.2 billion from oil sales. The six-month period will now give diplomats time to negotiate a more sweeping agreement.

We ask three Stanford scholars to weigh in on the technical and political merits of the agreement. CISAC Senior Fellow, Siegfried Hecker, has been working on Track II diplomacy with Tehran in recent years and was one of a number of Americans who met with Iranian Foreign Minister Javad Zarif and his delegation of diplomats and nuclear scientists after the U.N. General Assembly meeting in New York in September. Iranian-American Abbas Milani is director of Hamid and Christina Moghadam Program in Iranian Studies at Stanford and a contributing editor at The New Republic. Ivanka Barzashka is a CISAC affiliate and a research associate at the Centre for Science and Security Studies, King’s College, London, who specializes in Iran’s nuclear capability.

Just how close did Iran come to being able to build a bomb?

Hecker: Very close, possibly weeks away from making sufficient highly enriched uranium bomb fuel, and six months or so away from building a nuclear weapon. Iran developed the nuclear weapon option under the umbrella of the pursuit of civilian reactor fuel. The technologies for developing reactor fuel and bomb fuel are the same, the difference is in the level of enrichment in Uranium-235: 3 to 5 percent for commercial reactors, as much as 20 percent for research and medical isotope production reactors, compared to roughly 90 percent for weapons. The IAEA reports that Iran has not satisfactorily explained nor given access to work and sites suspected of past nuclear weapons-related activities.

This leads me to conclude that Iran had likely previously done most of the work necessary to build nuclear weapons once it obtained the capacity to produce bomb fuel. Iran’s extensive missile development and testing program also points to Tehran pursuing the option of missile deliverable nuclear weapons.

Does the agreement make it more difficult for Iran to pursue the bomb?

Hecker: Yes, the agreement places temporary limits on the level of enrichment of nuclear material and provides for the conversion or dilution of the highest enriched material (20 percent). It will also temporarily halt Iran installing more or better centrifuges to produce enriched uranium at an increasing rate. Iran has also agreed to temporarily halt construction of the heavy-water reactor in Arak. These steps modestly increase the amount of time it would take Iran to obtain nuclear bomb fuel in a breakout scenario. In addition, increased monitoring of facilities as called for in the agreement will provide us with a better understanding of existing capabilities in known facilities and what may exist in potential covert facilities.

They were very close ... six months or so away from building a nuclear weapon."    - Hecker

Why is Iran’s heavy-water reactor in Arak of such concern?

Hecker: It provides a potential second path to the bomb. Iranian nuclear specialists recently told me in New York that they began to design that reactor 20 years ago to replace the old, small American-provided reactor in Tehran that was being used for medical isotope production and research. Construction is several years behind schedule, but I was told it is close to completion. When complete, it would allow Iran to produce badly needed medical isotopes. But concurrently, the choice of reactor design and power level also means that it will produce enough plutonium to fuel one or two bombs per year if Iran decided to extract the plutonium from the spent reactor fuel. The Iranian specialists told me that they are very keen to find a solution that provides them with the means to make medical isotopes and alleviates international concerns about plutonium production. That’s a worthy goal, but a tall order that was left for the long-term agreement.

What prevented Iran from building the bomb?

Hecker: I believe Iran’s leadership settled for developing the option for the bomb, but has not yet decided to build or demonstrate the bomb. Until recently, it is also likely that Iran did not have sufficient bomb fuel to build the bomb. I believe they now have that capacity; therefore our focus should be on convincing them not to flip the bomb production switch.

Can you envision a long-term agreement that will prevent Iran from building the bomb?

Hecker: Completely getting rid of the bomb option is not possible through military action or sanctions with political pressure. The only chance is through diplomatic means. We need to make it clear to the Iranian regime that they are better off without pursuing the bomb. This will take time. Iran Foreign Minister Zarif told me that even appearing to pursue the bomb is bad for Iran’s nuclear security. Now if we can only get the Iranian leadership to believe that. If Iran wants nuclear energy and relations with the West, I believe we need nuclear integration, not isolation, such as those peaceful programs in South Korea and Japan.

Kerry's video message about the Geneva Talks 

Stepping aside from the leaders and countries involved, what do you think this six-month agreement means to the Iranian people themselves?

Milani: I think in the short run, it has brought them a double sense of joy and relief: joy that war might be averted, and relief that dire days of economic hardships might begin to end and that maybe the country will no longer be a pariah and join the community of nations. But I think there is also some trepidation: Will the interim agreements turn into an enduring policy or will the radicals use the interim sanction relief to get out of the current jam and then resume their policies?

Are you hopeful this is a significant step forward or is it too early to tell?

Milani: I think it is too early to be definitive but my sense is that momentum is building for the successful continuation of the thaw. Policies of the regime in the last years brought the country to the verge of the abyss. One could put a bit of Biblical touch to what President Rouhani himself says: men and women do not live by centrifuges alone. They need bread and freedom.

This is a win for Obama but it also appears to be a huge win for Iranian President Hassan Rouhani. Do you believe he is sincere in his commitment to negotiate and keep the talks on track?

Milani: I think Rouhani is one of the cleverest, most cunning and brutality pragmatic leaders the Islamic Republic has seen. He understands that the status quo is untenable and fashions himself as its potential reforming savior. He needs to make this deal work – one that is acceptable to the West, and the international community and sellable domestically as at least a win-win agreement – if he is to politically accomplish his goals as a disciplined man of great ambitions.

The Israelis are up in arms and Prime Minister Benjamin Netanyahu called the deal “a historic mistake” that gives too much to the Iranians. But shouldn’t they be pleased that Iran has stepped back?

Milani: Many in Israel are up in arms, yet others are confident that the U.S. and EU will pursue their interests while never making a deal that threatens Israel's security. In time I think the second narrative might even dominate Israeli discourse.

Is the deal nothing more than a successful confidence-building exercise?

Barzashka (As told to the Bulletin of the Atomic Scientists on Nov. 25): The agreement, the first in nearly a decade of confrontation over Iran’s nuclear program, is a win for diplomacy and proof that Obama’s strategy of direct engagement with Iran works. Enabled by high-level, face-to-face meetings between Tehran and Washington, the deal was struck despite significant opposition by hardliners in the United States, Iran and Israel.

The P5+1 and Iran adopted tangible, though modest, confidence-building measures that demonstrate both sides are serious about negotiations. The deal reflects reasonable compromises. For example, the P5+1 initially demanded that stockpiled, 20 percent-enriched uranium be shipped out of Iran, but exporting uranium was unacceptable for Tehran. Instead, the two sides agreed that Iran would convert 20-percent enriched uranium hexafluoride to uranium oxide or downblend it to below 5 percent—measures that still buy threat reduction without crossing Iran’s red line.

Finally, the agreement succeeds in building trust by leaving out the hard questions, such as Iran’s right to enrichment, which would be addressed during the next phase of negotiations.