Analysis: No proof of Iranian nuke weapon

VIENNA -- Nine years ago, the United States invaded Iraq after telling the world that Saddam Hussein had covert programs that could build nuclear arms. Nothing was found. Today, acting on similar fears, Israel is threatening to attack Iran.

Yet, while Iran has the equipment and raw materials to produce the fissile core of a nuclear weapon, there is no evidence that the Islamic republic has taken steps in that direction.

Reports by the UN nuclear agency contain a mix of confirmed data and theories built on outside intelligence. An Associated Press analysis of the published data by the International Atomic Energy Agency and interviews with officials probes key questions on Iran's nuclear ambitions: What can it do and what can't it do now?

Uranium enrichment

Iran's ability to turn uranium into nuclear fuel is at the heart of the confrontation with the West and its allies.

Iran is running nearly 9,000 centrifuges enriching uranium to produce nuclear fuel, a jump from 8,000 a year ago, according to reports and interviews with IAEA officials. From its main enrichment site, Iran has stockpiled at least 5.5 tons of uranium enriched to 3.5 percent levels, the IAEA says. That is a sufficient level to power reactors; uranium enriched to at least 90 percent is needed to produce the material for a bomb.

Iran also has churned out nearly 250 pounds of 20 percent enriched uranium that it says is needed to fuel a medical research reactor in Tehran. In the past three months, Iran has nearly tripled the number of devices producing 20 percent uranium.

Finally, Iran is building a "heavy water" research reactor. The IAEA estimates it could be complete in two to three years, and once in operation, will produce plutonium, another possible pathway to nuclear arms.

Critical mass

Does Iran have enough enriched uranium to move toward the higher-enriched, weapons-grade material? Judging by the amounts noted in the IAEA reports, the answer is yes. But those reports also say there is no indication that Iran has moved beyond the 20 percent threshold. The current known amount of 3.5 percent enriched uranium is enough to be turned into cores for four warheads if further enriched.

Enriching enough of it for a single warhead would take about four months with the available centrifuge equipment, says nuclear proliferation expert David Albright.

The confirmed stockpile of 20 percent enriched uranium is about half the amount needed for a potential warhead. At the current enrichment pace, it would reach the required amount by the end of the year, according to IAEA figures.

But getting enough weapons-grade material is only part of the equation. Albright said any nuclear bomb made in that time frame would be a crude device with no means of delivery. Mounting it on a missile would take "another six months to a year," he said.

Iran's enrichment centrifuges still are nearly all concentrated at the main site in Natanz in central Iran, which is believed to be about 25 feet underground and protected by two concrete walls. But it's shifting some operations to a far more heavily fortified site dug into a mountain south of Tehran. This alone does not violate the UN treaty overseeing the spread of nuclear technology, which allows signatory nations to have enrichment plants. IAEA inspectors have visited the new site.

Bomb design

Highly enriched uranium or plutonium is only part of the workings of a nuclear warhead. Tests need to be conducted on elements such as containment casings and triggers to start the bomb's atom-busting chain reaction. The IAEA has no confirmation of such weapons-related work under way in Iran. But the agency has pressed for access to the Parchin military compound, where it suspects tests occurred in possible simulations of the blasts needed to set off a nuclear chain reaction.

For nearly four years, it has also asked for -- and been denied -- more information based on 1,000 pages of intelligence and open-source documentation that suggests Iran drafted computer models of a nuclear warhead as well as worked on developing a nuclear payload for its Shahab 3 intermediate-range missile, which can reach Israel.