Irans nuclear matrix
Iran says its nuclear program is for peaceful purposes, but the United States, Israel and others have accused Iran of seeking at least the capability to make a nuclear warhead. An overview:
- Irans progress
- Irans facilities
Experts say Iran could be anywhere from six months to two years away from developing a bomb. A look at what would be involved before that could happen:

1. Make weapons-grade uranium
Iran has enough low-enriched uranium that it could quickly enrich to make about four nuclear bombs. To do so, it must either:
-- Retool existing plants to make highly enriched uranium, a move that would be immediately detected by U.N. nuclear inspectors. (Iran is building an enrichment plant deep underground to shield it from attack.)
-- Make weapons-grade uranium in secret. Experts say production would slow and Iran would likely be caught.
2. Assemble components
Iranian scientists are believed to have mastered some, but not all, of the skills needed to assemble a bomb, such as fabricating a core of uranium metal as well as a neutron initiator and an explosive triggering device needed to start a nuclear chain reaction.
3. Pair device with warhead
Iran would face a significant engineering challenge in getting its bomb to fit inside one of its intermediate-range missiles.
4. Test
Experts say Iran would almost certainly have to test its weapon to prove validity of the design.
Iran enriches uranium at the Natanz plant in central Iran and at a site at Fordow buried deep in a mountainous region near the holy city of Qom.

Natanz facility
Operational since 2003, the facility has two main buildings -- about 270,000 square feet -- and contains an estimated 9,000 centrifuges for enriching uranium. The facility is protected by a concrete wall eight feet thick. The roof was hardened in 2004 with reinforced concrete and covered with 72 feet of dirt.
Fordow facility near Qom
Secretly built into the side of a small mountain outside the ancient city of Qom and made public in 2009, the plant is designed to house to 3,000 centrifuges.
Fordow's main enrichment hall is protected by about 300 feet of rock.
SOURCES: Nuclear Threat Initiative; James Martin Center for Nonproliferation Studies; Institute for Science and International Security; GlobalSecurity.org. GRAPHIC - The Washington Post. Published April 12, 2012.