VIENNA- The UN nuclear watchdog is expected on Tuesday to close its 12-year investigation into whether Iran had a secret nuclear weapons program, a key step towards normalizing Tehran's international status after a landmark deal with major powers.The International Atomic Energy Agency (IAEA) produced a report earlier this month that strongly suggested Iran did have a nuclear weapons program for years up until 2003, but the international response has been muted, even from the United States, which had long accused Tehran of lying.Iran has always denied plans to develop nuclear weapons.The six major powers - the United States, Russia, China, France, Britain and Germany - are now focused on implementation of the deal struck in July whereby Tehran will restrict its nuclear activities in exchange for a lifting of many of the international sanctions weighing on its economy.With companies from the six powers and other nations lining up to do business in Iran once sanctions are lifted, there has been little opposition to a draft resolution of the IAEA's Board of Governors that would close the investigation of Tehran's past while ensuring the agency can keep policing Iran's activities."Iran will become an agenda at the IAEA Board which we hope focuses on its compliance with the Iran Deal - allowing it to move away from consideration alongside the Syrian and DPRK (North Korean) programs, which it has historically been bracketed with," said one Western diplomat.Supporters of the July deal argue that it gives the IAEA far more intrusive powers to inspect Iran's facilities and to monitor what it is doing, and that it extends the time Tehran would need to build an atom bomb if it chose to do so.Others see the closure of the so-called "possible military dimensions" (PMD) file as absolving Iran too easily of stonewalling the probe into its nuclear past for the sake of pushing ahead with the political deal reached in July."Iran's cooperation was certainly not sufficient to close the overall PMD file," said the Washington-based Institute for Science and Technology, which follows the Iran case closely."GOING SMOOTHLY"But with even habitually strong critics of Iran such as France and the United States backing the deal, diplomats expect the IAEA's 35-member board to back the resolution on Tuesday to procedurally close the PMD file."It all seems to be going smoothly," one diplomat said last week after the draft resolution was submitted by the six powers.Tehran has said it expects the economic sanctions against it to be lifted in January.In terms of ongoing IAEA reports, the Iran file will change from a nuclear proliferation case to updates on the July deal as soon as Tehran has fulfilled its promises, which it expects to have done in January, allowing for sanctions relief.Tuesday's draft resolution also asks the head of the agency to report to the board and the UN Security Council "at any time if the Director General has reasonable grounds to believe there is an issue of concern."