The next round of negotiations for a permanent deal on the Iranian nuclear program began with technical discussions in Vienna on March 5 between representatives from Iran and the P5+1 (the United States, Russia, China, UK, and France, plus Germany). Political representatives followed, arriving in Vienna on March 17. After last November’s interim agreement, called the Joint Plan of Action (JPOA), in which the P5+1 agreed to ease sanctions on Iran in exchange for a six-month suspension of much of Iran’s nuclear activity, talks on a permanent settlement began in February.

With the next round of high-level talks now underway, several key issues and potential stumbling blocks will necessarily be part of the negotiations. In January, the Institute for Science and International Security (ISIS) put together a comprehensive proposal for what a final nuclear deal might look like. ISIS’s record is problematic. The organization and its director, former UN weapons inspector David Albright, made repeated warnings about the nature of the supposed Iraqi nuclear program in the lead-up to the Iraq War but later admitted to relying uncritically on information provided by the Bush administration. ISIS is well-regarded in the arms control community for its estimates of Iran’s breakout capacity, though Mark Fitzpatrick of the Non-Proliferation and Disarmament Program of the International Institute of Strategic Studies says that they can be seen as “worst case” scenarios. ISIS’s proposed agreement represents a reasonable opening position for the P5+1 in their negotiations; it is certainly more realistic than, for example, the demands of the American Israel Public Affairs Committee (AIPAC) that Iran “dismantle its nuclear program,” which Iran has said quite clearly is something it will not do.

An examination of the potential complications in a final nuclear accord shows several places where talks could break down. In particular, the amount of uranium enrichment that Iran will be permitted to undertake will be considerably difficult to negotiate, given Iran’s insistence on its enrichment rights and the P5+1’s demands that Iran remain at all times at least six months away from having enough highly enriched uranium to produce a weapon. Similarly, Iran’s proposed heavy water reactor at Arak, which could be used to produce weaponized plutonium, will also require significant compromise on the part of Iran as well as the P5+1. However, external complications may be the greatest threat to reaching a settlement. Iranian and American domestic politics, Israeli opposition to the terms of a deal, and international events such as the ongoing crisis over Ukraine that risk fracturing the P5+1 coalition all could reduce the chances of achieving a diplomatic resolution to the current conflict.

Fuel Crisis

Uranium enrichment and spent fuel reprocessing are perhaps the most important issues to be discussed in negotiations. But they may also be the easiest to manage, since November’s interim agreement actually lays out the parameters of a final compromise. In that agreement, Iran pledged to dilute, or convert to oxide, its entire stock of 20-percent enriched uranium; to limit enrichment to 5 percent and to convert any newly enriched uranium to oxide for the duration of the accord; to halt the installation of new centrifuges at its Natanz and Fordow enrichment facilities (and to build no other enrichment facilities); and not to build any reprocessing facilities that could recover potentially weaponizable plutonium from spent reactor fuel. The 5-percent limit on enrichment is in line with the permanent deal envisioned by ISIS.

The JPOA recognizes that Iran will be permitted a limited enrichment program in a comprehensive agreement and allows it to continue to enrich uranium while talks are ongoing. This represents a significant change in the position of the P5+1, who have previously held to the United Nations Security Council’s demands that Iran suspend all enrichment during negotiations. U.S. Secretary of State John Kerry has continued to insist that the JPOA does not mean that the U.S. now recognizes an Iranian right to enrich. However, U.S. officials seem to be more flexible on this issue off the record, and the JPOA itself describes a “comprehensive” deal that includes a “mutually defined enrichment programme with mutually agreed parameters consistent with practical needs.” It even appears that hardline elements in the U.S. Congress, while still opposed to an Iranian enrichment program in principle, have stopped insisting upon zero enrichment as a condition in any permanent agreement.

For its part, Iran has steadfastly refused to surrender what it believes to be its inalienable right under the Non-Proliferation Treaty to carry out uranium enrichment. But even the hardline Iranian Republican Guard Corps (IRGC) has urged Ayatollah Khamenei to limit enrichment to the 20-percent level required for medical research. A deal that permits Iran to continue to enrich to the low (5-percent) level required for reactor fuel, while providing guarantees of external supplies of 20-percent enriched uranium for medical research purposes, could satisfy all parties to the talks.

The issue of Iran’s Fordow enrichment facility is more complicated and could pose a challenge for negotiators. Its existence was only disclosed in 2009 after it was discovered by Western intelligence services, possibly in violation of Iran’s obligations under the terms of a 2003 Safeguards Agreement with the International Atomic Energy Agency (IAEA). Its location, deep underground and very close to the holy city of Qom, makes it a particularly difficult target for any military strike, which Iran hawks have argued is evidence of a secret Iranian nuclear weapons program. Iran has repeatedly insisted, as recently as this February, that facilities like Fordow and Arak are “non-negotiable.” Similarly, Iranian President Hassan Rouhani has refused to consider dismantling any of Iran’s centrifuges.

The ISIS proposal envisions that all enrichment activity will be conducted at the Natanz facility only and that Iran will operate substantially fewer centrifuges than it currently has available. The number of active centrifuges that Iran is permitted to operate is likely to be one of the major hurdles in a final agreement. In fact, David Albright, in a paper written for the U.S. Institute of Peace, has called it the “key” to such a deal. He argues that Iran will have to accept an upper limit of roughly 4,000 centrifuges to meet the P5+1’s requirement that Iran’s breakout capacity—that is, the time it would take Iran to produce a nuclear weapon were it to pursue one—be in the 6-12-month range. This could be feasible given that Iran’s only current nuclear plant for electrical power, Bushehr, is to be fueled exclusively by Russian-supplied enriched uranium, and any additional Russian-built power plants will include the same stipulation. But should Iran decide to build its own reactor, a 4,000-centrifuge cap would be inadequate to fuel it. Even though both sides agree that Iran will be permitted some sort of enrichment program, the question of what Iran’s “practical needs” are in this regard still looms large over the ongoing talks.

Heavy Water and Monitoring

The final status of Iran’s proposed heavy water reactor in Arak almost caused talks over the Joint Plan of Action to fall apart, but Iran eventually agreed agreed not to advance development on the reactor for the duration of the JPOA. Heavy water reactors are a concern for anti-proliferation efforts because they are fueled with raw uranium, which (unlike enriched uranium) is unregulated internationally, and because they produce higher quantities of plutonium and tritium, both common weapon components, than light water reactors can. Iran has pledged not to build the facilities needed to reprocess the plutonium produced by the Arak reactor for weapons use, but ISIS has expressed concerns that, if Arak is allowed to come on-line, Iran may simply wait until it has produced enough plutonium for a weapon and then construct such a facility. Whether ISIS is right to be concerned or not, the international community is unlikely to agree to a final deal that does not prevent Arak and its byproducts from being weaponized.

Although Iran pledged to halt construction on Arak in the JPOA, the Iranians are certain to balk at scrapping plans for the reactor altogether; they claim that Arak is necessary as a replacement for their aging and potentially unsafe Tehran Research Reactor, which produces radioisotopes for medical use. The ISIS-proposed comprehensive agreement calls for Arak to be converted to a light water reactor running on lightly enriched uranium. Iran is unlikely to agree to fully convert Arak to a light water facility as the ISIS plan requires; after all, it chose to build it as a heavy water facility for a reason. A compromise may be possible based on a suggestion by Olli Heinonen, former head of safeguards for the IAEA, which would modify Arak’s design to use enriched uranium, but would not convert the reactor to a light-water design. This would actually make it a more efficient research reactor, but one that produces considerably less plutonium and tritium. Also, as Albright, writing for USIP, notes, verifiable removal of spent fuel from the facility to another country (presumably Russia) for disposal may also reduce the risk that Arak poses from a proliferation standpoint. This may be a situation where the P5+1 must take a hard line and insist that Iran demonstrate the peaceful intentions of its nuclear program by significantly altering its plans for Arak in some fashion. While Iran has refused to consider dismantling the Arak facility, it will have to be open to redesigning it in some fashion in order for a final agreement to be reached.

Meanwhile, the amount of international monitoring that Iran will permit is ultimately the key to a final deal. For the P5+1 to agree to an Iranian enrichment program, or even to its operation of light water reactors (which still produce some plutonium byproduct, albeit not in the quantities that a hard water reactor will), Iran must agree to substantial monitoring for a considerable period of time. In fact the very nature of the Non-Proliferation Treaty, which is intended both to prevent the spread of nuclear weapons and to ensure that signatories retain the right to develop and operate peaceful nuclear programs, depends on a robust monitoring program by the IAEA. Any nuclear deal reached with Iran will be important not just for what it means for the Iranian nuclear program, but for the fact that it will set a precedent for similar deals—i.e., deals that allow some amount of uranium enrichment—in the future. There are questions as to whether Iran will allow intrusive levels of monitoring at all key facilities, particularly at military facilities like Parchin, where Iran has resisted allowing access to inspections but whose inclusion in a verification protocol will undoubtedly be one of the P5+1’s core demands.

Iran has steadfastly maintained that its nuclear intentions are peaceful, but the IAEA has contended that, while it has no evidence that Iran has pursued a nuclear weapon, “more remains to be done” in terms of access and verification before the agency can determine that Iran is only pursuing peaceful nuclear uses. U.S. intelligence suggests that Iran seeks to develop breakout capacity but not to produce an actual bomb. Since breakout capacity depends to a great deal on development of the intangible knowledge and processes needed to produce a weapon, it is virtually impossible for any final agreement to entirely eliminate Iran’s capacity regardless of what physical limits are imposed on its nuclear infrastructure.

ISIS’s proposed agreement envisions that Iran’s infrastructure will be limited such that it remains six months away from being able to produce a bomb, but ensuring that it remains so limited will demand monitoring and verification safeguards (the ISIS proposal deals with the technical aspects of Iran’s nuclear program but does not discuss monitoring requirements). Iran agreed to substantial monitoring and verification requirements in the Joint Plan of Action, although its requirements under the 2003 Additional Protocol, which it agreed to implement but later suspended, remain unfulfilled. The IAEA’s statements suggest that more verification will be required for a final agreement. Will Iran agree to tougher monitoring for a period far longer than the JPOA’s six-month duration?

Further Complications

Even if the P5+1 and Iran are able to reach agreement on what an Iranian nuclear program should look like, this may not be enough to reach an agreement if the parties cannot agree on the conditions under which sanctions against Iran might be lifted. The Obama administration recently suggested that Iran’s ballistic missile program must also be discussed as part of the final settlement, a detail that Iranian Foreign Minister Mohammad Javad Zarif flatly rejected. Iran’s missile program was not part of the JPOA and is not included in ISIS’ proposed accord, and U.S. insistence on its inclusion would seem to risk scuttling the talks.

Then there are the external factors that affect the talks, including the domestic politics in the participating nations, especially in the United States and Iran. However, there is reason for some optimism here; American hardliners have recently lost a key fight over additional sanctions against Iran, and Iranian hardliners actually offered praise—albeit muted—for the JPOA, while President Rouhani has publicly urged those same hardliners not to interfere in the ongoing negotiations. Another potentially complicating factor in these negotiations is the political nature of the P5+1 itself; if those six nations are unable to agree internally, it would obviously threaten a final deal with Iran. This almost happened in November, when French insistence on a tougher deal nearly wrecked talks over what eventually became the JPOA. Conflicts between the United States, European Union, and Russia over Ukraine may make cohesion among the P5+1 even harder to achieve moving forward.

Relations between Iran and Israel also pose challenges in reaching a permanent deal. Israeli Prime Minister Benjamin Netanyahu has warned against allowing any Iranian enrichment program, and Israeli officials have in the past suggested that Israel could attack Iranian nuclear targets on its own initiative. It should be noted that prominent figures in Israel’s national security establishment have intimated that a deal that allows a limited Iranian enrichment program would be acceptable. However, the recent Israeli seizure of what it terms an Iranian arms shipment to militants in Gaza will only strengthen Israel’s concerns about Iranian intentions. Pledges of non-aggression will be a prerequisite for any deal to go through, but are Israel and Iran prepared to reach such a deal with one another?

Although November’s Joint Plan of Action provided cause for optimism, there are still significant challenges to a permanent deal around Iran’s nuclear program. However, there does seem to be a path forward on many of these challenges, provided that both sides are willing to compromise.

Derek Davison is a Washington-based researcher and writer on international affairs and American politics. He is a contributor to Foreign Policy In Focus.