Iran operates a number of facilities that carry out the different steps of the nuclear fuel cycle. This infrastructure includes the mines where Iran extracts natural uranium, the mill that processes uranium ore into a concentrate known as "yellowcake," and the plant that converts this yellowcake into uranium hexafluoride (UF6) gas. This gas is the feedstock for centrifuges that enrich uranium. Iran operates several gas centrifuge plants and accumulates enriched uranium that can be used to manufacture fuel for nuclear reactors or nuclear weapons. It also operates reactors for the purpose of generating electricity and conducting research for medical and industrial applications. Because of the dual-use potential of many of these facilities, however, the international community has long raised concerns that Iran could use this infrastructure and expertise to develop nuclear weapons.

Iran has declared the above facilities to the International Atomic Energy Agency (IAEA), and they have been subject to some form of inspection by the Agency. However, recent developments highlight the importance of accessing facilities that Iran has not declared to the IAEA. In 2018, for example, the IAEA became aware of a site in Turquzabad, near Tehran, that had allegedly been used to store nuclear material and equipment. In 2019, Agency inspectors visited the site, took environmental samples, and detected uranium particles of anthropogenic origin there.

The IAEA subsequently identified three additional undeclared sites where nuclear-related activities might have occurred in the past: Lavisan-Shian, Varamin, and Marivan. Iran ultimately granted the IAEA access to Varamin and Marivan to investigate the possible presence of nuclear material or activity, but such access took months to negotiate. As of April 2023, the Agency had not resolved outstanding issues related to those sites due to a lack of cooperation from Iran. The IAEA decided not to seek access to Lavisan-Shian after determining that there would be no verification value because the site had “undergone extensive sanitization and levelling.”

These incidents echo past access challenges for the Agency: before the implementation of the Joint Comprehensive Plan of Action (JCPOA), the IAEA sought to understand the "possible military dimensions to Iran's nuclear program" but was often thwarted in its investigation by a lack of access to locations and key individuals. In accepting the JCPOA, Iran agreed to allow the IAEA expanded access to monitor nuclear fuel cycle facilities and related activities. However, Iran began curtailing its cooperation with the Agency following the U.S. withdrawal from the JCPOA.

The table below lists Iran’s known and alleged nuclear sites and their purposes, locations, and operating statuses.

[1] In January 2022, Iran informed the IAEA that it planned to produce centrifuge rotor tubes and bellows at Isfahan using the equipment installed at the decommissioned Karaj plant. In April 2022, Iran announced that it had instead moved the equipment to a facility in Natanz.

[2] Iran renamed the IR-40 at Arak (commonly known as the Arak Heavy Water Reactor) as the Khondab Heavy Water Research Reactor in April 2017. The original design of the IR-40 reactor was for a power of 40 megawatts thermal (MWt); the JCPOA requires that the reactor be redesigned with a power not exceeding 20 MWt.

[3] Traces of uranium were discovered on site by IAEA inspectors in 2019 or 2020.

[4] Satellite imagery indicated activity as late as 2013 at the Pilot Uranium Laser Enrichment Plant, prompting the IAEA to visit the facility in March 2014. The JCPOA (Annex I, Section S, Paragraph 81) requires Iran to only enrich uranium using gas centrifuge technology, thereby prohibiting laser enrichment. The IAEA has made no subsequent mention of the Pilot Uranium Laser Enrichment Plant since 2014, suggesting that the facility is inactive.