The draft document - one of several technical appendices meant to accompany the main text of any deal - has dozens of bracketed text where disagreements remain. Technical cooperation is the least controversial issue at the talks, and the number of brackets suggest the sides have a ways to go not only on that topic but also more contentious disputes with little more than a week until the June 30 deadline for a deal.
With that deadline looming, Iran's top leader, Ayatollah Ali Khamenei, on Tuesday rejected a long-term freeze on nuclear research and supported banning international inspectors from accessing military sites. Khamenei, in comments broadcast on Iranian state television, also said Iran will sign a final deal provided all economic sanctions now on Iran are first lifted, in a sign the Islamic Republic may be toughening its stance ahead of the deadline.
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The West has always held out the prospect of providing Iran peaceful nuclear technology in the nearly decade-long international diplomatic effort designed to reduce Tehran's potential ability to make nuclear weapons. But the scope of the help now being offered in the draft may displease US congressional critics who already argue that Washington has offered too many concessions at the negotiations.
Iran denies any interest in nuclear weapons but is prepared to make concessions in exchange for relief from billions of dollars in economic penalties. Beyond a pact limiting Iran's ability to make a nuclear weapon for at least 10 years, the US and its negotiating partners hope to eliminate any grounds for Iran to argue that it needs to expand programs that could be used to make such arms once an agreement expires.
To that end, the draft, entitled "Civil Nuclear Cooperation," promises to supply Iran with light-water nuclear reactors instead of its nearly completed heavy-water facility at Arak, which would produce enough plutonium for several bombs a year if completed as planned.
Reducing the Arak reactor's plutonium output was one of the main aims of the US and its negotiating partners, along with paring down Iran's ability to produce enriched uranium - like plutonium, a potential pathway to nuclear arms.
Outlining plans to modify that heavy-water reactor, the draft, dated June 19, offers to "establish an international partnership" to rebuild it into a less proliferation-prone facility while leaving Iran in "the leadership role as the project owner and manager."
The eight-page draft also promises "arrangements for the assured supply and removal of nuclear fuel for each reactor provided," and offers help in the "construction and effective operation" of the reactors and related hardware. It also offers to cooperate with Iran in the fields of nuclear safety, nuclear medicine, research, nuclear waste removal and other peaceful applications.
As well, it firms up earlier tentative agreement on what to do with the underground site of Fordo, saying it will be used for isotope production instead of uranium enrichment.
Washington and its allies had long insisted that the facility be repurposed away from enrichment because Fordo is dug deep into a mountain and thought resistant to air strikes - an option neither the US nor Israel has ruled out should talks fail.
But because isotope production uses the same technology as enrichment and can be quickly re-engineered to enriching uranium, the compromise has been criticized by congressional opponents of the deal.
A diplomat familiar with the negotiations said China was ready to help in re-engineering the heavy water reactor at Arak; France in reprocessing nuclear waste, and Britain in the field of nuclear safety and security.
He spoke on the eve of Wednesday's new round of nuclear talks in Vienna and demanded anonymity because he was not authorized to discuss the confidential talks.
Diplomats say the other appendices include ways of dealing with enrichment; limits on Iran's research and development of advanced uranium-enriching centrifuges and ways of making sure Tehran is keeping its commitment to the deal.
Iran has most publicly pushed back on how much leeway the UN's International Atomic Energy Agency would have in monitoring Tehran's nuclear activities. Iran's supreme leader, Ayatollah Ali Khamenei, is rebuffing US demands that the IAEA have access to military sites and nuclear scientists as they keep an eye on Iran's present activities and try to follow up suspicions that the country worked in the past on a nuclear weapon.
But a senior US official who demanded anonymity in exchange for commenting on the talks said Tuesday that the sides are still apart not only on how transparent Iran must be but all other ancillary issues as well. Separately, White House spokesman Josh Earnest suggested the talks could go past June 30.
If a deal "requires us to take a couple of extra days, then we'll do that," he said.
A delay up to July 9 is not a deal-breaker. If Congress receives a deal by then, it has 30 days to review it before President Barack Obama could suspend congressional sanctions.
But postponement beyond that would double the congressional review period to 60 days, giving both Iranian and US opponents more time to work on undermining an agreement.
Earnest indicated that negotiations may continue even if the sides declare they have reached a final deal, in comments that may further embolden congressional critics who say the talks already have gone on too long. He said that even past that point, ongoing "differences of opinion, may require additional negotiations."