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News Analysis

U.S. Hangs Back as Inspectors Prepare Report on Iran’s Nuclear Program

WASHINGTON — An imminent report by United Nations weapons inspectors includes the strongest evidence yet that Iran has worked in recent years on a kind of sophisticated explosives technology that is primarily used to trigger a nuclear weapon, according to Western officials who have been briefed on the intelligence.

But the case is hardly conclusive. Iran’s restrictions on inspectors have muddied the picture. And however suggestive the evidence about what the International Atomic Energy Agency calls “possible military dimensions” of Iran’s program turns out to be, the only sure bet is that the mix of sleuthing, logic and intuition by nuclear investigators will be endlessly compared with the American intelligence agencies’ huge mistakes in Iraq in 2003.

Just as it was eight years ago, the I.A.E.A., which was conceived as a purely technical organization insulated from politics, is about to be sucked into the political whirlpool about how the world should respond to murky weapons intelligence. Except this time everything is backward: It is the I.A.E.A., which punched holes in the Bush administration’s claims about Iraq’s nuclear progress, that today is escalating the case that Iran has resumed work on bomb-related technology, after years of frustration over questions that have gone unanswered by that government.

For its part, the Obama administration, acutely aware of how what happened in Iraq undercut American credibility, is deliberately taking a back seat, eager to make the conclusions entirely the I.A.E.A.’s, even as it continues to press for more international sanctions against Iran. When the director of the agency, Yukiya Amano, came to the White House 11 days ago to meet top officials of the National Security Council about the coming report, the administration declined to even confirm he had ever walked into the building.

The final touches are still being put on the report and its critical annex, where some of the investigative details will be laid out, which may be released as early as Wednesday. But already Russia and China have sent a diplomatic protest to Mr. Amano, urging him to not to make details of the evidence public.

“Russia and China are of the opinion that such kind of report will only drive Iran into a corner,” they wrote in the note, which was obtained by The New York Times and is a rare instance of those countries commenting jointly.

One of the crucial pieces of intelligence information that officials say the I.A.E.A. is weighing for the report concerns activity at a military base called Parchin. The officials briefed on the intelligence, speaking on condition of anonymity because the report has not yet been released, say the experts identified a structure there that some believe is a testing capsule for what is called an “implosion device.” Such devices use the detonation of a sphere of conventional explosives to create a blast wave that compresses a central ball of nuclear fuel into an incredibly dense mass, starting a chain reaction that ends in a nuclear explosion.

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The Parchin military base in Iran, shown in a 2004 photograph, was cleared in earlier inspections but has drawn new scrutiny.Credit...Institute for Science and International Security, via Agence France-Presse — Getty Images

The report also details how Iran was aided by a Russian scientist who gave lectures in the country. But it was unclear whether he knew he was helping work on a nuclear weapons program.

Iran has admitted in the past that it works on explosives at Parchin, and seven years ago it briefly allowed I.A.E.A. inspectors into the site to look around. But it insisted the work was entirely on conventional weapons, and the inspectors found no evidence to contradict those statements. “We took environmental samples, saw equipment, and didn’t notice any nuclear signatures at that stage,” said Olli Heinonen, the former chief inspector at the agency, who is now at Harvard. “Most of the high-explosive test installations we saw were still under construction.”

But something has changed in the ensuing years. The new Parchin intelligence emerged from a series of satellite photographs, documents, records of equipment sales and interviews with defectors and outside experts whom the Iranians appeared to have consulted. Some of that information came from the United States, Israel and Europe; the agency says it is publishing only information it could confirm.

Such accusations are always risky. Secretary of State Colin L. Powell came to regret the case he made about mobile biological weapons labs and other suspected sites in Iraq, and that is one reason the Obama administration wants the I.A.E.A. to take the lead. It has credibility that Washington does not.

Experts will be examining the I.A.E.A. report to determine whether it contradicts a 2007 National Intelligence Estimate on Iran, published by the Bush administration, which concluded that Tehran suspended intense work on how to design and produce a nuclear weapon in 2003. Since then the report has been widely criticized as flawed. But the question is whether the agency has identified evidence that such work has resumed. News reports published from the agency’s Vienna headquarters and Europe say the I.A.E.A. document will cite evidence that Iran has built a large steel container for testing high explosives applicable to the development of nuclear arms.

Parchin is important because it would be hard for Iran to explain a “peaceful” use for implosion experiments. Weapons based on implosion are considered advanced models compared with the bomb that the United States dropped on Hiroshima. In 2009, senior staff members of the I.A.E.A. warned that Iran had sufficient information to design and build an implosion device.

But implosion is not easy: It requires casting conventional explosives into special shapes that can focus a blast on a nuclear core rather than letting its energies dissipate in many directions. The castings are known as explosive lenses — and their creation was a breakthrough that let the scientists at Los Alamos build the world’s first atom bomb.

“Critical Assembly,” a 1993 history of that World War II project, called the team’s explosive testing full of “ambiguous steps, and numerous failures.” Historians say the canyons of Los Alamos echoed with scores of test explosions.

A correction was made on 
Nov. 9, 2011

An article on Monday about the International Atomic Energy Agency’s findings concerning Iran’s nuclear program misspelled the given name of the agency’s director. He is Yukiya Amano, not Yukia.

How we handle corrections

A version of this article appears in print on  , Section A, Page 4 of the New York edition with the headline: U.S. Hangs Back as Inspectors Prepare Report on Iran’s Nuclear Program. Order Reprints | Today’s Paper | Subscribe

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