Analysis: The Continuing Mystery About Iran’s Shadowy Nuclear Weapons Program

William J. Broad and David E. Sanger

March 8, 2015

OVER the course of a dozen years, ever since atomic sleuths from the United Nations began scrutinizing Iran’s nuclear program, hundreds of inspections have uncovered a hidden world of labs and sprawling factories, some ringed by barbed wire and antiaircraft guns, others camouflaged or buried deep underground. Yet despite that progress, Iran has so far managed to evade a central question — whether it knows how to build an atom bomb.

With negotiators from six world powers facing a deadline later this month to cut a basic agreement with Iran on the fate of its nuclear program, much of the public discussion has focused on curtailing Iran’s uranium plants and plutonium complex, its pathways to atomic fuel. In short, the buzz centers on brawn, not brains. But quietly, the United States and its allies are also discussing whether a final deal should compel Tehran to reveal the depth of its atomic knowledge.

That inner debate, as one European official in the midst of the negotiations put it, turns on “whether to force Iran to explain its past” — especially before 2003, when American intelligence officials believe Iran operated a full-scale equivalent of the Manhattan Project — “or whether to focus on the future.”

American officials are vague when pressed on how fully Iran will have to answer questions it has avoided for years from United Nations inspectors with the International Atomic Energy Agency, based in Vienna. To date, Iran has dodged all but one of the agency’s dozen sharp questions on bomb design.

“Iran’s most serious verification shortcoming,” Olli Heinonen, the former chief inspector, now at Harvard, said recently, “remains its unwillingness to address concerns about the past and possibly ongoing military dimensions of its nuclear program.”

Investigators at the I.A.E.A., drawing on intelligence from member states as well as their own investigations, have assembled a secret trove of reports, correspondence, viewgraphs, videos and blueprints that purport to show Iran’s skill in warhead design.

Iran ridicules the material as fake, maintaining that the trove is full of forged documents created by the Central Intelligence Agency or Israel’s Mossad. (The atomic agency’s chief, Yukiya Amano, dismissed that allegation in an interview last summer, saying the inspectors had confirmed the documents by consulting other sources.)

The problem is that the documents, if real, would undercut Iran’s argument that its nuclear ambitions are entirely peaceful, centering on the production of radioisotopes for medicine and electrical power for economic growth.

Expertise in warhead design, as opposed to atomic fuel production, is far more ephemeral and hard to track. It can also be less ambiguous. Some nuclear parts have application only to making weapons, such as neutron spark plugs at the core of some atom bombs. In contrast, uranium can fuel both nuclear arms and reactors that make electricity — it can light cities or annihilate them.

In early 2003, when the inspectors began their investigation, the focus was mainly on whether Iran was building factories that could make fuel for nuclear arms. That agenda made sense because acquiring fuel is the hardest part of the bomb equation. It’s the chokepoint. Moreover, it was relatively easy for the inspectors to monitor the giant factories that Iran was building, such as the plutonium reactor at Arak and the uranium plant at Natanz, its halls roughly half the size of the Pentagon.

Today, the six powers negotiating with Iran — Britain, China, France, Germany, Russia and the United States — still focus overwhelmingly on fuel production. They want Tehran to downsize or disconnect the centrifuges that spin at supersonic speeds to purify uranium. They want the reactor at Arak, still under construction, reconfigured to produce less plutonium, the other bomb fuel. The negotiators want the cutbacks to be large enough and long enough in duration — a decade or more — to ensure that Iran for the near future cannot mount a headlong rush for a bomb, known in the field as breakout.

Even Prime Minister Benjamin Netanyahu of Israel, in his dramatic speech to a joint session of Congress on Tuesday, elevated brawn over brains, saying “nuclear know-how without nuclear infrastructure doesn’t get you very much.” He added, “A pilot without a plane can’t fly.”

True enough. But there are other ways to get fuel, including buying it from the likes of North Korea or on the black market. So the design riddle still lurks in the background, both for breakout and what experts call sneak out.

Iran already knows how to make a rudimentary bomb. So do terrorists and college students. The real question is whether Iran can miniaturize a weapon to fit atop a missile, can make bombs more destructive than the one that turned Hiroshima into a radioactive cinder, and can use precious fuel sparingly enough to build a nuclear arsenal.

The I.A.E.A. inspectors saw hope of getting answers in mid-2007 when they agreed on a “work plan” with Iran meant to shed light on what happened inside the secretive laboratories run by Mohsen Fakhrizadeh, said to be Iran’s atomic mastermind. More than two years later, in late 2009, the plan lay in ruins. Mohamed ElBaradei, then the agency’s director general, said the inquiry had “effectively reached a dead end” because of Iran’s intransigence.

In November 2011, the inspectors stepped up the pressure by publishing a detailed listing of a dozen major fields critical for warhead building, saying their cache indicated that Iran had deeply researched the topics. Iran repeated its disavowal. In August 2013, as tensions mounted, Iran’s new president, Hassan Rouhani, elected on a platform of getting international sanctions lifted, agreed to open negotiations about the overall fate of Iran’s atomic program.

While those talks have dragged on for 18 months, Iran has let inspectors deep inside its production facilities and observed every commitment on cutting back its production of nuclear fuel. But it has continued to stiff-arm the inspectors on the question of suspected “military dimensions,” despite agreeing to another work plan. The Obama administration has said little about that silence.

Last month, the inspectors reported that “Iran has not provided any explanations” for two of the three design questions now on the table. The other nine remain in limbo.

So will Iran have to come clean before the economic sanctions are lifted? American officials won’t say. “It’s the most sensitive topic for the Iranians,” said one former American negotiator. “Is it worth blowing up a potential agreement in the name of forcing a confession?”

One solution, analysts suggest, would be the gradual lifting of sanctions in step with the investigators certifying that Tehran was finally answering their longstanding queries. That is under discussion. But it remains unclear whether the atomic riddle will be resolved. If past is prologue, the West might once again find itself stonewalled.