Diplomats and experts will start hammering out the legal and technical details of a nuclear agreement between Iran and six world powers next week in Vienna, the EU diplomatic service announced Thursday.

Foreign ministers from Iran and the group of Britain, China, France, Russia, the United States and Germany agreed on the outlines of the deal on April 2 in Lausanne. In addition, Iran and the group of six still have to draw up a list of Iranian nuclear sites, which experts from the International Atomic Energy Agency, IAEA, will get to visit as part of its probe into alleged nuclear weapons projects.

A senior IAEA delegation returned from a visit to Tehran on Thursday, without any answers on ten new suspected research and development projects identified by the agency in addition to the two that are already being discussed.

DW talked to Robert Kelley, former IAEA director for nuclear inspections in Iraq and now expert for nuclear energy and weapons issues with the Stockholm-based International Peace Research Institute.

DW: The IAEA plays a central role in the nuclear deal reached in Lausanne on April 2. Now, an IAEA delegation under chief inspector Tero Varjoranta, which sought answers to allegations over the possible military use of Irans nuclear program in the past, left Tehran without those answers. What exactly is the IAEA looking for?

Robert Kelley thinks the Iran nuclear deal could be derailed

Robert Kelley: The IAEA is receiving external information, primarily from intelligence agencies in Israel and the United States. And they have written up this information in a report published in November 2011 in which they raise a whole series of allegations that Iran had a nuclear weapons program prior to 2004 and it may have continued past that point. That report concerned things like high explosives and electronic detonators that set off explosives, calculations of neutron multiplication in weapon-type systems. All those things are thrown out as accusations with very little proof or information where the allegations came from.

How credible are those accusations in your eyes?

Many of these accusations I find to be quite incredible. One example: There is a specific type of electrical detonator to set off explosives. It is called an "exploding-bridgewire detonator". And the IAEA says, they have information that Iran has been researching these detonators. IAEA also says in the 2011 report, "these detonators have very few other uses besides nuclear weapons and so we think it is an indicator they research nuclear weapons". But if you go and look up these "exploding-bridgewire detonators" you find out millions of them are manufactured every year. And it is not for nuclear weapons. The IAEA got it exactly wrong.

There are now two and a half months left to hammer out the details of the Lausanne accord. But the devil is usually in the details. This phase is giving various groups critical of the deal time to try to derail the whole negotiation process. Could those allegations be part of an effort to derail the nuclear deal with Iran?

Absolutely yes! It is a poison pill that is included in the deal. People know that the IAEA is going to be unable to reach a decision on these issues because it is beyond their capability. So when the IAEA needs to be satisfied before the sanctions are lifted, history tells you: This will not happen.

I was involved in Iraq for many years - starting in 1991 and ending in 2005. I was a director at IAEA during that time. And one thing that came across very clearly is: The United States would not allow us to say that we were satisfied. But the point is: We were satisfied. There were some very minor points. But we were forced to keep those minor points on the table rather than say we reached a decision. Therefore, I think there is every indication that this could be a game killing activity.

Talking about game killing: The Obama administration just had to give in to the US Congress. The compromise bill will give Congress a voice on the proposed nuclear deal. Is this going to make a final deal more difficult, or is it just a minor distraction, since President Obama could veto any legislation from Congress?

Aerial photograph of Iran's Natanz nuclear facility

I have looked briefly at the text of the bill that they put on the table. I think almost anybody will be able to accept it: the president and Congress, the Republicans and the Democrats. But the poison pill is in there again: It says that the secretary-of-state will ensure, that the IAEA has the tools it needs to resolve this issue. It also says the IAEA will need sufficient access to "suspicious sites" and the ability to follow up allegations. But "suspicious sites" can just go anywhere. It could be your bedroom if somebody says, you are hiding documents there. I know that from Iraq. We got reports all the time from very unreliable sources. But we had to follow them up. And that is the issue with allegations in the congressional language. Because allegations from whom? If I got allegations from the CIA, I might take them more seriously than if it is something on Facebook. You may find somebody posting something on Facebook saying: "I know there is a new centrifuges factory over there behind this mosque". Is the IAEA then obliged to follow that up?

In this age of satellites and super high sensitive detectors, how difficult would it be to effectively hide nuclear activities?

The very best detectors in the world are the IAEA inspectors. If you for some reason offend Iran so much, that they kick the IAEA out, then you are blind. You won´t know anything about what is going on. So one of the things that are good about this new agreement is: The inspectors have access to every aspect of uranium mining, conversion to the right chemicals, chemicals producing uranium hexafluoride in the enrichment plant and things after the enrichment plant. So the inspectors are getting a very good picture of everything Iran is openly doing.

And they are also going to be looking at procurement. The import regime is part of the agreement. That is a very powerful thing. The chances of having a completely clandestine, hidden, secret program becomes much more difficult when you have these things in place. Things like the handling of uranium and plutonium do leave a lot of signatures and detectors can pick them up. Not from space but on the ground. But you can´t detect things like explosives and explosive bridgewire detonators, because they have conventional military uses, they are used in mining, for all kinds of other activities. And you can´t call that a nuclear activity.

Robert Kelley is a veteran of over 35 years in the US Department of Energy nuclear weapons complex, most recently at Los Alamos. He was also seconded by the USDOE to the IAEA where he served twice as a director of the nuclear inspections in Iraq in 1992 and again in 2001. He is now Associated Senior Research Fellow within the SIPRI Nuclear Weapons Project, Arms Control and Non-Proliferation Programme.

Interview: Matthias von Hein