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This American scientist has seen North Korea’s nuclear program up close

How advanced is North Korea's nuclear weapons program? Just ask the few Western experts who have seen glimpses of the program and its evolution, like nuclear scientist Sig Hecker, who has visited seven times and given eye-opening access to their facilities. Science correspondent Miles O’Brien reports on how experts try to access the North’s capabilities.

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  • Judy Woodruff:

    The story we turn to now: How advanced is North Korea's nuclear weapons program? It is a question with heightened urgency, given the escalating rhetoric between the United States and that secretive regime.

    One way to get an answer, visit the nuclear facilities themselves.

    Miles O'Brien recently sat down with one American who did just that.

    It's part of our weekly look at the Leading Edge of science and technology.

  • Miles O’Brien:

    Capricious and erratic as the nation and its leaders may seem, North Korea's march toward nuclear weapons has been steady and successful. Just ask the few Western experts who have seen glimpses of the program and its evolution.

  • Siegfried Hecker:

    I was very much surprised by their capabilities and their competence.

  • Miles O’Brien:

    Nuclear scientist and metallurgist Sig Hecker was surprised that he was invited to North Korea in the first place. After all, he spent most of his career at the birthplace of the atomic bomb, the Los Alamos National Laboratory. He served as its director from 1986 through 1997.

  • Siegfried Hecker:

    The most important thing was, I was just trying to learn as much as possible, and then also trying to figure out, what are they trying to tell me and why are they telling me that?

  • Miles O’Brien:

    His first of seven visits came in 2004.

  • Siegfried Hecker:

    They were going to show us a significant part of their nuclear complex, particularly the plutonium complex. And that — yes, that was just — it was an eye-opener. It was really surprising.

  • Miles O’Brien:

    Plutonium is very rare in nature. The process of making it begins with uranium fission in a nuclear reactor. Hecker visited the reactor the North Koreans use for this purpose.

    He says it looked like Los Alamos in the 1950s, but it was functional. The byproduct of a reactor like this is not weapons-grade plutonium metal. That requires another step of separation from used reactor fuel called reprocessing.

    The North Koreans took Hecker to that facility is well. In a conference room, the director of the program asked Hecker if he'd like to see their product.

  • Siegfried Hecker:

    I said, sure, bring it out. And, lo and behold, they have got this plutonium. Usually, you don't take plutonium into a conference room. But they did.

    And so they brought out this red metal box, and they slid the top off. And I sort of looked in, and there were two glass jars in there. I was still skeptical.

    So, I actually asked them, can I hold the plutonium jar? Plutonium is very, very dense, almost three times as dense as iron. And then, second, it is warm, because it is radioactive. It was both. But I still told them, yes, it looked like plutonium. It felt like plutonium.

    But, in the end, I didn't have any instrumentation. I didn't know.

  • Miles O’Brien:

    The plutonium picture in North Korea is as clear as anything in this opaque world. When a nuclear reactor is operating, it's obvious to anyone who's watching from the outside. And there is no more watched piece of real estate in the world than this nuclear reactor near Yongbyon.

    Physicist and former arms control inspector David Albright has visited North Korea twice. He now spends a great deal of his time poring over open-source satellite imagery of North Korea.

  • David Albright:

    You don't know what's going on inside, but you still can know quite a bit about it and their nuclear reactors. And then you piece that together with other information, you can get a much better picture of how much plutonium they could make.

  • President Bill Clinton:

    I am pleased that the United States and North Korea yesterday reached agreement on the text of a framework document on North Korea's nuclear program.

  • Miles O’Brien:

    In 1994, the U.S. and North Korea signed the so-called agreed framework. It forced Pyongyang to share details of its plutonium production and mothball its reactor.

  • Siegfried Hecker:

    I saw that facility.

  • Miles O’Brien:

    Sig Hecker saw some of the idle equipment on one of his visits. But the Bush administration and North Korea abandoned the agreement after each accused the other of not meeting its terms.

    And U.S. intelligence sources indicated the North was trying to produce highly enriched uranium. It is a required ingredient in the most powerful compact nuclear weapons. The North Korean pursuit of that is a bigger mystery.

  • David Albright:

    The plutonium is known much more finely because North Korea has revealed much more about its plutonium program because of earlier arms control agreements. And there's never been a declaration at all by North Korea on its uranium enrichment program.

  • Miles O’Brien:

    Uranium, mined from rock, must be enriched to be potent enough to make a bomb. A chemical process transforms it into a gas, and it is pumped into a centrifuge. As it spins, the heavier isotope, uranium 238, separates from the lighter weapons-grade uranium 235.

    The shopping list for uranium centrifuges includes high-strength aluminum and specialty steel, very specific, telltale if you know what you're looking for. Albright is always on the prowl for these purchases.

  • David Albright:

    They don't say, oh, this is for a gas centrifuge plant, but when you look at the list of goods, you go, oh, this is for a gas centrifuge plant. And it's to make an addition to the program of a certain size. You can make estimates.

    And so, with that information, you can put a plot together of what they have procured and how many centrifuges they could build.

  • Miles O’Brien:

    Much of this was confirmed during Sig Hecker's last visit to North Korea in 2010. He asked to see their centrifuge facility. He was taken to this building with the big blue roof in the North Korean nuclear center of Yongbyon.

  • Siegfried Hecker:

    And they took us up to the second floor and they had us look down through these big glass observation windows at these two centrifuge halls down below, and it was just — my jaw must have dropped this far, because I just couldn't believe it.

  • Miles O’Brien:

    He saw 2,000 centrifuges arrayed in so-called cascades like this.

    Three years later, that blue roof doubled in size. But unlike a nuclear reactor creating plutonium, the secrets of centrifuge facilities stay under the roof.

    And Hecker and many other experts are convinced there is another centrifuge facility somewhere else in North Korea. So, when it comes to bomb-grade uranium, there is great uncertainty, all of which leads to this bottom line:

  • Siegfried Hecker:

    We made an assessment. So, plutonium, 20 to 40 kilograms, highly enriched uranium, again, great uncertainty, maybe 250 to 500 kilograms, something on that order.

    You put that all together, that's enough of the fissile material, the bomb fuel, for perhaps 25 to 30 bombs.

  • David Albright:

    If you believe in the second centrifuge plant, then you end up with a range of about 20 to 40 nuclear weapons.

  • Miles O’Brien:

    Reading the tea leaves to assess what kinds of weapons the North Koreans have been able to craft from this raw material is also as much art as science.

    More on that in our next report.

    I'm Miles O'Brien for the "PBS NewsHour."

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