But other experts say the time is just a few weeks at most. Intense radioactive buildup won't begin at Bushehr until the reactor is turned on after fuel loading is completed on Sept. 5, Iranian officials say.
"I think that the idea of bombing Bushehr – whether in a day or a month – is crazy," he says.
The potential environmental and health impacts of bombing Bushehr after it is operating depends on wind conditions and how much radiation has built up inside the reactor, he says. Long- and short-lived radiation levels would be relatively small until power output reaches perhaps 10 percent or more, Dr. Von Hipple says.
But dangerous levels of radioactivity could be reached in less than a week after Bushehr begins operating, says Edwin Lyman, a nuclear physicist with the Union of Concerned Scientists, who also does not favor bombing.
Radiation will build up significantly in the two-week span after Sept. 5, if Iranians ramp up power to 50 percent as they say they will, he says.
"There will be an enormous quantity of radioactivity even at a fraction of the rated power of the reactor soon after startup," Lyman writes in an e-mail. "Even after a few days at a significant power level, like 20 percent, these [radioactive isotopes] would be numerous enough to be of great concern if released into the environment."
While Von Hipple, Mr. Sokolski, or Dr. Lyman differ on how significant the threat from Bushehr is, all say that the reactor's first year to 18 months – when the first load of nuclear fuel is being irradiated – will be telling. That's where agreement ends.