JEFFREY BROWN: Margaret Warner takes it from there.
MARGARET WARNER: And with me is Leonard Spector, who is at Monterey Institute of International Studies as deputy chief of its nonproliferation center. He held a similar post at the Department of Energy during the second Clinton administration.
And, welcome, Mr. Spector.
So what's the significance of these reports, if true, that the IAEA has found hundreds of new centrifuges at this Fordow site?
LEONARD SPECTOR, Monterey Institute of International Studies: Well, this a plant that everyone is very nervous about.
It's buried and very difficult to attack because of this. It is in a mountainside, as we heard. The number of units in the plant are going up steadily. And nothing we seem to be doing, such as export controls, interdictions, sanctions, seems to be slowing the program down.
And at this rate, the plant will be completed and fully with 3,000 centrifuges by the end of the year.
MARGARET WARNER: And is that faster than was anticipated?
LEONARD SPECTOR: I think there was some hesitation. Because it looked as if they had all of these empty casings for the centrifuges, and now they are filling them.
Some had thought that they really didn't have that ability. So, that's a very negative development.
MARGARET WARNER: Now, part of the report is also said to say that Iran has particularly stepped up its production of this richer grade of uranium, 20 percent level. What does that tell you?
LEONARD SPECTOR: Well, it is something that makes you nervous because this is a big stepping-stone toward the actual development of weapon-grade uranium, which is about 90 percent enriched.
But the hardest part of the enrichment process in the lower numbers. Once you get to 20 percent, you can move up the ladder very rapidly. And that is a kind of stockpile that they are building and that is making everybody very worried.
MARGARET WARNER: So what does this do, when you heard -- well, we ran a quote from Prime Minister Netanyahu of Israel about we have had these alarming reports. What do you think this does to the calculation of other players involved in this, particularly Israel?
LEONARD SPECTOR: Well, I think Israel is getting very nervous as this plant comes to completion. And it has a reason to be.
And, of course, their initial reaction in a sense is to think about military action. We don't want to see that, certainly, because we have been embroiled in two wars in the region. The country is weary of this. And that is not a direction we want to take. But the pressures of the election here and the pressures from Israel may be very strong and create a new kind of dynamism.
MARGARET WARNER: Explain why the addition of more centrifuges -- I mean, would that advance the timetable by which Iran could -- if they took the political decision to produce a nuclear weapon from all of this, does it advance that timetable?
LEONARD SPECTOR: It would eventually.
In other words, as the stockpile grows of this 20 percent enriched uranium, then they can rapidly upgrade it, and the more centrifuges that they have for that upgrading process, the faster it goes. So we could be talking about a matter of months to get that done, getting the weapon-grade material, whereas now it might take let's say a year or something of that kind.
MARGARET WARNER: So, when people talk about the breakout sort of moment, what are they talking about? Is that the period between when they decide they're going for the weapons and they can actually produce it?
LEONARD SPECTOR: That's right. So they don't want a small stockpile. I think if they have one nuclear weapon, they become a target. If they had a dozen, other people become targets.
So I think what you will see here from the Iranian side is to build up the stockpile of the 20 percent material as rapidly as possible, get the facilities ready for the next stage, which they're doing, and then when the moment is right take the plunge, not yet, but certainly you can see it in the offing.
And they may decide to hold, but hold in a position that will make everybody very, very nervous as long as they are on the verge of proliferating weapons.
MARGARET WARNER: And particularly Israel...
LEONARD SPECTOR: Absolutely.
MARGARET WARNER: You said they don't want to see it get to that point.
Finally, today, also at this meeting between the weapons inspectors, the U.N. weapons inspectors and Iran in Vienna, they were also apparently very focused on trying to access to a whole different site at Parchin. What was that about?
LEONARD SPECTOR: That's the site where Iran claims it was attempting to develop artificial diamonds using an explosive technique that is used in nuclear weapons, which is to crush a sphere or in the case of the artificial diamonds the diamond dust that they are trying to get a different shape.
But they use a spherical tool, or spherical set of explosive lenses to do the job. The individual teaching them learned his trade in the Russian nuclear weapon program, and then supposedly was trying to develop this commercial application.
So what -- the reason the site is so important is that if there are traces of uranium in the residue of whatever is left at the site as they are cleaning it up, it will be the smoking gun, some real hard evidence that this is a nuclear weapon program and not an innocent site, and nor are the other sites innocent.
MARGARET WARNER: And the satellite photos show attempts to clean it up?
LEONARD SPECTOR: Yes. There is now -- the site has been razed, and now there is a tarp over it elevated. And they are doing more cleanup.
But the IAEA has very, very sensitive instruments. And I think the Iranians want to get the job done before they let the IAEA in.
MARGARET WARNER: Well, Leonard Spector of the Monterey Institute, thank you.
LEONARD SPECTOR: Thank you.