NPR logo

A Chemistry Lesson On Uranium

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript
A Chemistry Lesson On Uranium


A Chemistry Lesson On Uranium

A Chemistry Lesson On Uranium

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript

On Monday, Iran agreed to a nuclear deal that it hopes will deflate the threat of sanctions. The agreement hinges on some technical issues, regarding the type of uranium Iran is allowed to use. Leonard S. Spector, deputy director of the Monterey Institute of International Studies' James Martin Center for Nonproliferation Studies, talks to Robert Siegel for a bit of a chemistry lesson in uranium.


This deal hinges on the distinction between highly-enriched uranium and low-enriched uranium and we could throw in weapons grade highly enriched uranium as well, all of which inspired us to get a lesson about uranium. So we've called upon Leonard Spector of the Monterey Institute of International Studies to help explain it to us. Hi, welcome back.

Mr. LEONARD SPECTOR (Monterey Institute of International Studies): Thank you.

SIEGEL: And, first, do I have it right that when we talk about levels of uranium enrichment, we're describing how much of the uranium is not garden variety U-238, but the much more rare and unstable isotope of uranium U-235?

Mr. SPECTOR: That's correct.

SIEGEL: And if you dug a piece of uranium out of a mine, what would it consist of?

Mr. SPECTOR: Less than one percent, .7 percent of the good stuff.

SIEGEL: The unstable U-235.

Mr. SPECTOR: That is correct.

SIEGEL: And then you could have uranium that has been processed to be, well, what the Iranians have, which is 3.5 percent.

Mr. SPECTOR: Right. That's the level that's used for nuclear power plants around the world, the kind that we have, the French, the Japanese and so forth. And, actually, the one in Iran now that the Russians are supplying fuel for.

SIEGEL: And to go from that piece of uranium that's been dug out of the ground to that, say, level of 3.5 percent enrichment, difficult, very difficult, more difficult than what's to come?

Mr. SPECTOR: It's quite difficult because it's a little bit like compound interest. When you start with a very low amount, it takes a long number of cycles to get up to something worthwhile like 3.5 percent of 5 percent. And then as you move up from that, the compounding starts to work a little bit more in your favor and you can move from 3 percent to, say, 20 percent more easily than that first stage and then up to the weapon quality of 80 or 90 percent even more easily.

SIEGEL: In this case, Iran will send this 3.5 percent enriched uranium into Turkey and they'll receive, I gather, fuel rods that are enriched to just under 20 percent. What do we call those, first of all, in terms of how enriched they are?

Mr. SPECTOR: Well, 20 percent is the threshold for high enriched uranium. And once you're above the threshold, in principle, in theory, you could make a nuclear weapon out of the material. As a practical matter, you want 80 or 90 percent or more enrichment. So what we would be supplying, the West, if this all were to go through, is material that still could not be used for nuclear weapons but which is closer to the weapon quality stuff they may ultimately be seeking.

The goal was to alienate, to get out of the country their low-enriched uranium, so that that material couldn't be upgraded further in country. And that would give us some breathing space. Somewhat higher enriched uranium would come back, but not all at once and it would go right into the reactor. It's made out of fuel plates, which have the uranium embedded in aluminum so it's harder to process.

And the thought was this would create more opportunities for negotiations to occur without the sort of sword of Damacles hanging over your head if they had a stockpile of low-enriched uranium they could make into bomb grade if they chose to.

SIEGEL: So in theory what you're saying is one might take these rods and one might conceivably enrich them further, but in practice if this deal works out as you've described it, that would not be practical and the big supply of uranium would have left the country.

Mr. SPECTOR: That is true as the deal was originally planned when there was no other low-enriched uranium in the country. Now, of course, eight months have passed and theyve produced some more. The original quantity was more or less, you know, 90 percent of what they had, now it's probably closer to 50 percent of what they have.

SIEGEL: Does one use the same equipment - I assume these are centrifuges, to go from naturally occurring uranium to low-enriched uranium, as one would use to go from low-enriched uranium to highly-enriched uranium?

Mr. SPECTOR: You do use the same equipment. In other words, you don't change the nature of the device that does the enriching, but you change the configuration of how you line them all up.

SIEGEL: If in fact there is a lot more uranium that's been enriched in Iran than what under this deal would be shipped to Turkey, would that uranium be naturally inspected nowadays or not?

Mr. SPECTOR: Now it's all under inspection, so that part is to the good. We do fear that there may be clandestine facilities in Iran that we haven't found yet and we are discovering them from time to time. So that's very, very worrying. But the other aspect that's worrying is that although the inspectors are present now, Iran could withdraw from the nuclear non-proliferation treaty and in effect break out.

It would have the three to five percent enriched uranium. As the years go by it'll have more. Some of it may be in the 20 percent range. If they kick the inspectors out and decide they want the bomb, they can move up that ladder quite quickly.

SIEGEL: Leonard Spector, thank you very much for talking with us.

Mr. SPECTOR: Thank you.

SIEGEL: Leonard Spector of the Monterey Institute of International Studies and formerly of the U.S. Department of Energy.

Copyright © 2010 NPR. All rights reserved. Visit our website terms of use and permissions pages at for further information.

NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.