The following is the Sept. 19, 2018 Congressional Research Service report, Iran’s Nuclear Program: Status.
From the report:
Iran’s nuclear program began during the 1950s. The United States has expressed concern since the mid-1970s that Tehran might develop nuclear weapons. Iran’s construction of gas centrifuge uranium enrichment facilities is currently the main source of proliferation concern. Gas centrifuges can produce both low-enriched uranium (LEU), which can be used in nuclear power...
https://news.usni.org/2018/09/23/report-congress-status-irans-nuclear-programs