The nuclear deal between Iran and six world powers will face its first test this weekend. Inspectors from the International Atomic Energy Agency are due to make a long-delayed visit to a nuclear site in Iran where plutonium could be produced.
A nuclear reactor and associated production plant in Arak are a special concern because plutonium can be used in a nuclear bomb. Under last month's accord, Iran promised to allow inspections of its nuclear facilities.
Officials on both sides say they are committed to the nuclear deal, but keeping it on track will be a challenge.
Iranian officials also plan to meet next week with representatives from the United States and other countries to plan the next steps in implementing their deal.
Olli Heinonen, a longtime nuclear inspector, says this is the good news.
"There is now a process in place where the people are talking with each other," he says. "Whether they agree or disagree with each other, that's a different thing. But we got to the process."
The bad news? A deal might not be possible.
The overall concern is that Iran might develop a nuclear bomb.
Two Types Of Fuel
To keep that from happening, international watchdogs have to focus on two elements of a nuclear weapons program. The first is the fuel for a bomb — highly enriched uranium, or plutonium. The second is the design and manufacture of the explosive device itself — the nuclear warhead.
The accord reached in Geneva theoretically limits Iran's production of enriched uranium or plutonium — the fuel part. There's nothing about warhead research, at least not directly.
That's because the agreement leaves weaponization for the International Atomic Energy Agency to deal with. The IAEA has long worried about a possible "military dimension" in Iran's nuclear program. Under the Geneva agreement, Iran agreed to work with the IAEA to resolve "past and present issues of concern."
That, says IAEA Director General Yukiya Amano, includes his agency's concern about possible nuclear weapons research — past and present.
Iran denies it has ever worked on a nuclear weapon, but it has not allowed the kind of inspections that would settle the issue.
An IAEA report last month included a long summary of its unsuccessful efforts to investigate possible explosives experiments in Iran and any work on fuses or detonators.
David Albright, a former IAEA inspector, notes that the agency has also been denied access to an Iranian military base where nuclear weapons work was suspected.
"There [are] other sites the IAEA has identified that are allegedly related to past nuclear weapon activities," he says. "There [are] many people the IAEA has asked to see that they've been unable to interview. There [are] documents they want from Iran."
If Iran is to comply with the terms of the Geneva deal, it will have to satisfy those IAEA demands, besides limiting its fuel enrichment. And those two aspects of the agreement are inseparable. Albright, who is now president of the Institute for Science and International Security, calls attention to another line in the accord.
"Nothing is agreed upon unless everything is agreed upon," he says.
In other words, it's an all-or-nothing agreement: If Iran doesn't come clean about nuclear weapons research, it gets nothing.
What Iran wants most, Albright points out, is permission to continue nuclear enrichment.
"Iran is unlikely to get that at all if it doesn't satisfy the IAEA's concern about past weaponization activities and possibly ongoing ones," he says. "So everything is linked. If one major part of this agreement does not happen, there will be no deal."
But Olli Heinonen, formerly at the IAEA and now at Harvard, doubts that there will be any progress on the weaponization issues for at least six months — and that's not good, he says.
"Time is running, and some of this information will disappear. Then the IAEA task is much more difficult and in certain ways may become impossible," he says.
That's because by then, it may be too late to know what Iran has been up to.