What I Saw in North Korea and Why it Matters by Siegfried Hecker (Transcript)

Now, it turns out for the uranium-235, you can make a rather simple bomb. And that is you just take two sub-critical hemispheres and you put them in a gun and you shoot them together very rapidly. Okay, when you do that, in essence, if you do it right, that was the Hiroshima device, about 13 or so kilotons, 13,000 ton TNT equivalent. It destroyed a city. One plane, one bomb, destroyed a city. That’s because of this nucleus stuff. When you split the nucleus, you get a factor of millions in the energy gain compared to all the other chemical techniques. And so that’s why nuclear is so special. And not only do you get that in nuclear energy but also you also get it in the bomb if you do it right, or if you do it wrong, depending on your point of view. So this gun assembly works for highly enriched uranium for a bomb that’s typically 80% to 90% enriched. It doesn’t work for plutonium for very good nuclear physics reasons I won’t get into. So for plutonium instead, you have to use what we call the implosion device. And that is, you have a sub-critical mass of plutonium, pack explosives around it like a [soccer pole], you put detonators around and you try to implode it all very symmetrically to drive it to super-criticality and then it blows up, that’s Nagasaki. It takes about six kilograms for the implosion device of plutonium, takes a few tens of kilograms for — in highly enriched plutonium. You can also use the implosion device with highly – use highly enriched uranium in the implosion device but a much simpler way to go, and this would be the nuclear terrorism lecture, would be to use this gun assembly.

So, most countries that have nuclear weapons today actually pursued both of these. And in the United States, we did that in the Manhattan project.

Okay. So with that as the premier, then let me just say that North Korea has mastered the entire plutonium fuel cycle. Fuel cycle, meaning everything from the time you dig it out of the ground, you mine it — and by the way, they have significant quantities of uranium ore in North Korea, none in South Korea but quite a bit in North Korea. So, they know how to mine it, mill it, convert it and then make fuel. The type of reactors that they chose to build that are called gas-cooled graphite moderated reactors. They’re patterned after the ones that the Brits built in the early 1950s, the first one of which was Calder Hall reactor. Turns out the benefits of this type of reactor is you can feed in natural uranium. You don’t have to enrich it a little bit first as you do with light water reactors. So that means the North Koreans, since they did this on their own, I mean they copied the Calder Hall reactor but they did it strictly on their own with no more help at that time from the Soviets, from the Chinese, from nobody. And so, they didn’t need enrichment, they were able to make their own fuel, used metallic fuel for these reactors instead of ceramic fuels because you need a higher uranium density since all you have is seven tenths of a percent of the fissile isotope. And so, they know how to make fuel.

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Second, they built reactors. They finished one, the small one, five mega-watt electric. That’s very small. It doesn’t produce much electricity but it produces one bomb’s worth of plutonium a year if you can extract it. And so, they’ve had that reactor operating since 1986, off and on over the years. They had a 50-megawatt within one or two years of completion when they signed this agreement with the Americans in 1994, that was then halted. And I will tell you later through my visits, I found out it’s dead. It can’t be resurrected. They had a 200-megawatt electric reactor that actually would have produced quite a bit of electricity for North Korea. That was just in the beginning stages of construction. They halted that. That’s also not salvageable today. The back-end, the reprocessing facility, it’s just a complicated chemical engineering facility where you deal with all of this hot nucleus stuff that you’ve heard about related to Japan except, in this type of facility you handle it in hot cells with remote handling where that radioactivity is essentially separated from the workers. They know how to that. They patterned that facility after a facility in Belgium. Again, they built it by themselves. North Koreans are terrific engineers. They built this whole complex then by themselves. So, that’s the Yongbyon nuclear complex.

So, what do they have? It’s sort of the bottom line slide. On the basis of my visits and my discussions with the North Koreans, and on the basis of looking with Google Earth as to whether that there’s a plume coming out of the cooling tower of the Yongyon reactor, we pretty much know how many days it’s operated. We can estimate what power level they operate at and we know what sort of reactor they have, what fuel they put in, and you can calculate how much plutonium they’ve made. So this is actually the part we know the best. And then some of the holes they filled-in in my personal discussions with them. So they have to date 24 to 42 kilograms sort of four to eight bombs worth. So — and they indeed do have the bomb because they exploded two of them, one didn’t work so well. The second one, as far as I’m concerned was successful.

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Now, my view is that — since they’ve had have let’s say, one and a half test, the bombs that they have are most likely primitive bombs. In other words like our Nagasaki bomb which had to be delivered — it was huge 10,000 pounds, had to be delivered by a plane. It’s very difficult to miniaturize these things and it takes nuclear testing, it takes computational capability and I just don’t believe they’ve had the opportunity to get there yet.

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