Was there an untold sense of urgency to Iran talks?

How close was Iran to a bomb?

Energy Secretary Ernest Moniz said Tehran was "maybe three months away" from developing materials for a nuclear weapon before the agreement in April. He did not delineate which materials he was referring to in an interview for the WGBH show Greater Boston.

Questioned about Iran's involvment in Syria or its conviction and imprisonment of Americans such as Washington Post correspondent Jason Rezaian, Moniz said the point of the nuclear accord was to address the "key existential issue" between Iran and the US and its allies: the development of a nuclear weapon. After that agreement, Washington can press on issues he identified as Iran's support for Hezbollah, detention of Americans and "unacceptable language" toward Israel.

Moniz also spoke on climate change, the focus of two upcoming conferences, and the future of nuclear energy in America. He said that in the past year, both the United States and China have made advances in cutting their dependence on fossil fuel; America on a clean power plant initiative and China on a cap-and-trade commitment.

On America's nuclear energy future, the former MIT physicist said it will differ by regions. The Northeast will see a decline, as the Pilgrim Nuclear Power Station in Plymouth, Massachusetts prepares to close in 2019. The Vermont Yankee nuclear plant closed at the end of 2014. The Southeast, however, is seeing five nuclear plants being developed, including plants soon coming into operation in South Carolina and Georgia.

Asked about stress during the many weeks of negotiations with the Iranians, Moniz said he had an advantage in not being a diplomat. He preferred to think of the nuclear talks as a scientist facing a problem. You've got a problem in front of you, Moniz said, you deal with it.

For more on the interview, airing Monday, catch Greater Boston.