An Iranian official said for the first time that Iran may modify a heavy-water reactor near Arak, signaling a willingness to compromise on one of the most contentious issues in efforts to curtail its nuclear program.

“We can do some design change — in other words, make some change in the design in order to produce less plutonium in this reactor and in this way allay the worries and mitigate the concerns,” Ali Akbar Salehi, head of the Atomic Energy Organization of Iran, told Iran’s official English-language Press TV in an interview today.

The uncompleted Arak heavy water reactor was a stumbling block that almost derailed nuclear talks between Iran and other nations last November, when France’s Foreign Minister Laurent Fabius insisted that Iran agree to halt work there before world powers would sign onto a six-month deal to ease some of the sanctions that have hobbled Iran’s economy.

U.S. and European nonproliferation specialists have said they are concerned that Arak could be used to produce plutonium, which can be used to fuel a nuclear weapon as an alternative to highly enriched uranium. Iran says its atomic program is solely for peaceful civilian energy and medical purposes and the Arak reactor is intended to produce isotopes for cancer patients.

“It is a welcome development if Iran is willing to convert the reactor from a heavy water reactor to a light water reactor” that “would pose less of a proliferation threat,” David Albright, a former United Nations weapons inspector and the founder of the Institute for Science and International Security in Washington, said in an interview.

Under an accord signed between Iran and six world powers in Geneva that went into force on Jan. 20, the Persian Gulf state agreed to stop most work on the reactor project for the period of the interim deal.

President Barack Obama has said he rates prospects for achieving a final negotiated settlement at 50-50. Iran’s supreme leader, Ayatollah Ali Khamenei, will be the final decision-maker on Iran’s nuclear program.

Salehi, who served as Iran’s foreign minister from 2010 until last year and previously as his country’s representative to the UN’s International Atomic Energy Agency, was asked by Press TV why Iran needs plutonium in the first place.

Salehi, who has a physics degree from the American University of Beirut and a Ph.D. in nuclear engineering from the Massachusetts Institute of Technology in Cambridge, replied that Iran has “many types of reactors,” just as it has “many types of cars.”

“The heavy-water reactor of Arak is not for the production of plutonium,” he said, calling it a research reactor “for the purpose of producing radio-isotopes and making other tests.”

Referring to Arak, Salehi added, “This reactor will produce about nine kilograms of plutonium, but not weapons-grade plutonium. I want to underline this: not weapons-grade plutonium.”

He also said that Iran doesn’t have the intent or the capacity to extract plutonium from the Arak reactor once it is completed. It would take as long as eight years to do so, “plus you need a reprocessing plant, which we don’t have and we don’t intend to construct,” Salehi said.