Little progress was made towards a deal between Iran and the six major powers at talks this week in Iraq.With speculation about a possible Israeli strike still high, one key aspect of a possible conflict with Iran has been little discussed. Michael Adler, an expert on Iran’s nuclear capabilities at the Woodrow Wilson Center here in Washington, discusses the “zone of immunity.”

With all the talk of whether Israel will attack Iran, it is important to understand when Israel might feel it has no other choice but to act. Amos Yadlin, a former Israeli military intelligence chief, wrote in the New York Times that, “an Israeli strike against Iran would be a last resort, if all else failed to persuade Iran to abandon its nuclear weapons program. That moment of decision will occur when Iran is on the verge of shielding its nuclear facilities from a successful attack – what Israel’s leaders have called the ‘zone of immunity’.”

The zone of immunity is most often discussed in relation to Iran’s enrichment of uranium at the
Fordow site in the northwest of the country. Enriched uranium is a strategic material since it can be fuel for a civilian power reactor but also for a bomb. Fordow is still under construction although some centrifuges are installed. The danger for Israel is that it is under a mountain and thus well protected from air strikes.

But there is a little mentioned plutonium dimension to the zone of immunity. This concerns a heavy-water reactor being built in Arak, also in northwest Iran, and expected to come online in 2014. [Eds. note: The IAEA revised the date in a May 25 report, saying the Arak reactor could come online in fall next year.] It is the only reactor currently under construction in Iran and it would be able to produce significant amounts of plutonium. Like uranium, plutonium can be used as the explosive center of an atomic weapon. Reactors meanwhile are not easy to bomb for the simple reason that striking one that is in operation could create a radioactive cloud and a Chernobyl-like phenomenon of spreading, deadly contamination from radiation. Says nuclear expert David Albright: “If any running reactor is attacked, there would be a major release in the radioactive core … If Israel does attack Arak, it will definitely be before it’s running, and it’s quite possible it will happen within the next two years.”

A reactor coming online presents a different dilemma than an impregnable enrichment site. The reactor is above-ground and very easy to spot. It would remain vulnerable to an attack. But hitting a reactor carries the risk of unacceptable collateral damage, namely the radioactive contamination which could threaten civilian populations. Such considerations led Israel to carry out preventive strikes twice in the past – against the Osirik reactor in Iraq in 1981 and against a reactor at Dair Alzour in Syria in 2007.

Arak is Iranian-made, unlike the Russian-built Bushehr power reactor which came online last year. Arak is designed to be a research reactor, one that will produce isotopes used for medical diagnosis. Its uses natural uranium, which is not monitored by the UN watchdog International Atomic Energy Agency (IAEA). This means that its fuel cycle is harder to monitor for proliferation concerns. In addition, it produces plutonium, which can be extracted to make nuclear weapons. This is definitely a proliferation possibility. If a nation such as Israel wanted to move against Arak, the reactor could be attacked, or the heavy water plant near it, which makes the heavy water used in the reactor to moderate the chain reaction. The heavy water plant is already up and running, according to the IAEA.

Plutonium, while little discussed in the international press covering Iran, is still of great concern for countries monitoring the Islamic Republic. One intelligence source reported on a possible channel for Iran to buy plutonium. In a highly detailed account, the source said that an Iranian broker, Seyd Saleh Sadr Addini, had been contacted in 2011 by “criminal elements from CIS (Commonwealth of Independent States, former Soviet republics) countries … with a proposal to secretly sell him plutonium 239,” said to be weapon-grade.

The source said Addini was general manager of the Faraz Armaghan Sanat (FASCO) company at Tabriz in Iran, alleged to be a front for “smuggling prohibited materials to Iran from various countries.”

“It is not clear whether the Iranian broker has already raised the subject with the relevant parties in Iran, but it is known that Iran invests great effort in finding alternative approaches for acquiring plutonium, such as through covert procurement, in addition to producing plutonium itself. This is in order to significantly shorten the timetable for acquiring fissile material for a bomb,” the source said. He said the amount offered for sale was “not known but it is known that the suppliers proposed a number of kilograms at a price of two million dollars per kilogram of plutonium.” About six kilograms of weapon-grade plutonium are needed for a bomb.

The information could not be independently confirmed but is a clear indication of the extent to which a possible plutonium route to the bomb is on the radar of nations which closely watch Iran. For instance, since the fall of communism, there has been worry about the smuggling of fissile material from the former Soviet bloc. The reprocessing of plutonium from spent nuclear fuel is also closely watched.

Iran does not yet have the same mastery of producing plutonium as it does of manufacturing enriched uranium. Arak coming online could change this, however.

The zone of immunity is thus built around two types of fissile material, not just uranium alone.

Michael Adler is a scholar at the Woodrow Wilson International Center for Scholars, writing a book on diplomacy in the Iranian nuclear crisis. Michael covered this extensively for five years while in Vienna, where he reported on the International Atomic Energy Agency.