I'm not an expert on this by any means, but are you sure the reason they don't have nukes is that other countries are stopping them? I had gotten the impression that they definitely have the ability, and haven't done it because they know it will cause a serious escalation in tension for not really a lot of benefit.
When the recent Iran deals were being announced, I read material that said something along the lines of "Iran is 3 months from having a nuke" (breakout). It seemed to be saying, "Iran is holding steady, but could pull the trigger (so to speak) and begin the final 3 months of preparation at any moment". The goal of the nuclear agreement was to keep them perpetually some certain number of months away (or increase it) from having enough material for a bomb.
> The IR-1s installed in the Natanz and Fordow facilities have been performing at an average per unit rate of 0.75 to 1 SWU per year. Using the 1 SWU/year performance of the latest IR-1 model, the breakout time with 9,000 machines using a natural uranium feed would be six to seven months. However, Iran also has substantial stocks of 3.5 percent enriched uranium hexafluoride (UF6) that can be used as an alternative feed, shrinking the breakout time to three months.
http://www.washingtoninstitute.org/policy-analysis/view/iran...
> Mr. Kerry was joined at the talks by Energy Secretary Ernest J. Moniz, who will have to certify to Congress that the deal ensures that Iran will remain at least a year away from being able to produce a weapon’s worth of bomb fuel over the next decade, a complex calculation in which the size of Iran’s stockpile is a major factor.
http://www.nytimes.com/2015/06/02/world/middleeast/irans-nuc...
Now maybe there's far more sabotage than we know about going on, but it sounds like Iran has the ability to accumulate enough material, and is choosing not to. The way this is phrased implies that Iran is halting work toward a bomb.
> The [International Atomic Energy Agency] inspectors, who have had almost daily access to most of Iran’s nuclear production facilities, reported finding no evidence that Iran was racing toward a nuclear weapon, and said Tehran had halted work on facilities that could have given it bomb-making capabilities.