These two things occur to me when I hear of Iran's intent to develop nuclear weapons and hiding its development activities.
First: If they tested a nuclear weapon of their own design and manufacture today they'd still be over 60 years behind us not to mention have no means of delivery.
Second: How do you hide nuclear development? 10% of all the electricity generated in the United States during the Second World War went to making the materials that went into the atom bombs detonated during that war. Think about what it takes to hide that sort of power generation and use in light of today's spy satellites. This too may add in understanding how difficult it would be to hide a nuclear program. When you hear about centrifuges being involved in the process its sort of misleading. What they should say is centrifugal compressors are in use. These are very similar to the ones used to maintain the pressure in large gas pipelines all around the country. They are strung together in vast arrays, each compressor being about the size of a motor-home. It takes arrays of tens of thousands of these things to make the bomb materials. That means one continuous building the size of a small town. Witness Oak Ridge Tennessee.
http://www.atomicarchive.com/History/sites/K_25.shtml