This is now a serious nuclear arsenal that threatens the region and, soon, the continental United States.
- By Jeffrey LewisJeffrey Lewis is director of the East Asia Nonproliferation Program for the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies at Monterey.
Unlike in January, when I was sipping a cocktail at Doris Day’s Cypress Inn, I learned that North Korea had conducted its fifth nuclear test while I was at home. My first thought was: Really, Kim Jong Un? On a school night?
I have three small children. So I did interviews while an unsupervised toddler decorated the television in lotion. I never before understood the intuitive appeal of massive nuclear retaliation until I saw the plasma screen coated in some beurre corps super nourrissant my wife probably imported at great expense from France. Screw you, Kim Jong Un.
So, the bomb. First, the technical details. This is the biggest test ever conducted by North Korea. There are a range of estimates, but everyone agrees this is bigger than the other ones. They just don’t agree about how big and, frankly, I could write an entire column or three just briefly summarizing debates about the best way to estimate the actual size of the explosion based on the seismic signal. I don’t want to write that. You don’t want to read that. Just believe me when I say the explosion is at least 10 kilotons, and probably more than that. About the same size as what the United States dropped on Nagasaki. The important thing is that it is far too large to be anything but successful. And, fortunately, too small to be a staged-thermonuclear weapon. So what is it?
The North Koreans issued a statement making clear that this was a “a demonstration of the toughest will of the WPK and the Korean people to get themselves always ready to retaliate against the enemies if they make provocation as it is part of practical countermeasures to the racket of threat and sanctions against the DPRK kicked up by the U.S.-led hostile forces who have gone desperate in their moves to find fault with the sovereign state’s exercise of the right to self-defence while categorically denying the DPRK’s strategic position as a full-fledged nuclear weapons state.” That’s a real quotation. These guys are colorful.
But perhaps more to the point, North Korea said it had tested a “nuclear warhead that has been standardized to be mounted on strategic ballistic rockets of the Hwasong artillery units of the Strategic Force of the Korean People’s Army.” Hwasong is the name North Korea gives to its ballistic missiles. And that word, standardized, was the same word that Kim Jong Un used when he stood next to a mock-up of a compact nuclear weapon in March. Remember that silly photo op, Kim in glasses and fur hat, grinning widely next to something that looked like a giant disco ball of Armageddon? “The nuclear warheads have been standardized to be fit for ballistic missiles by miniaturizing them,” Kim was paraphrased as saying then, adding, “This can be called true nuclear deterrent.”
I think the North Koreans are saying that they’ve tested the bomb that will arm their missile units. And that’s a big deal. In the past, we’ve treated North Korean nuclear tests as temper tantrums or political demonstrations. There is some of that today, of course. North Korea didn’t just decide to test a new Scud missile during the G-20 summit in China by coincidence. No, the North Koreans have been hopping mad since China failed to shield them from condemnation by the U.N. Security Council following the test of a submarine-launched ballistic missile in early August. So, it’s a missile test to spoil China’s big party, followed by some nuclear fireworks to end this particular cycle of provocation and condemnation. This has happened so many times in the past few years that the governments all know their roles in this sad little drama too well.
But this test isn’t just a political statement. It has a technical purpose. And that purpose is demonstrating the reliability of that “standardized” nuclear warhead to arm the missile force. The fact that the warheads are “standardized” is, I think, intended to convey that they are being produced in quantity, another point made in the statement — that North Korea can now “produce at will and as many as it wants a variety of smaller, lighter and diversified nuclear warheads of higher strike power with a firm hold on the technology for producing and using various fissile materials.”
Notice that reference to various fissile materials. A lot of people have asked whether North Korea has ever stated that it is using highly enriched uranium (HEU) in its nuclear warheads. There you go. They aren’t talking about americium in their smoke detectors.
North Korea is saying that it tested the thing that Kim Jong Un posed with back in March. And that thing isn’t just a nuclear weapon compact enough to arm North Korea’s ballistic missiles, it is a design intended to be produced in fairly large numbers and deployed with the missile units of the Strategic Rocket Forces.
That’s OK, you might be thinking: I’ve read that North Korea has enough plutonium for only a handful of nuclear bombs. Boy, this column is going to upset you.
Let me tell you what I think the North Koreans are testing, and why they are claiming they can produce “as many” nuclear weapons as they want.
Yes, North Korea has stockpiled about 40 kilograms of plutonium, according to various estimates, although North Korea has also said it will continue to produce new plutonium. How many bombs is that? We used to divide the kilograms by 8, because that’s what the International Atomic Energy Agency said. That’s five bombs, then, but that’s also technically silly. It is an unclassified fact that a bomb can be made with as little as 4 kilograms. Divide by four, that’s 10 bombs. North Korea also has an almost totally unknown stockpile of highly enriched uranium. OK, so now you may be thinking that North Korea might have some plutonium bombs and some highly enriched uranium bombs. In that case, you are overlooking an unpleasant technical possibility: composite pits.
Yeah, you can use both in the same bomb. That’s one way to stretch a small supply of plutonium. When Kim Jong Un posed with that bomb in March, he called it a “Korean-style structure of mixed charge … adequate for prompt thermonuclear reaction.” Mixed-charge. Thermonuclear. It’s a bit ambiguous, but I think it is very likely the North Koreans are claiming two things. First, they use composite pits of both Pu and HEU (mixed charge) and they “boost” the yield of the explosion using a gas of hydrogen isotopes (prompt thermonuclear reaction).
That means there might be as little as 2 kilograms of plutonium in each device. And so divide by 2. The existing stockpile of about 40 kilograms of plutonium would be enough for about 20 nuclear weapons, with more on the way. Oh, and don’t forget to add whatever uranium is left over for all those HEU bombs, if they decide to build some of those. Let that sink in.
This is exactly what other countries have done. The 12th Chinese nuclear test, for example, was a test of a nuclear device with a composite pit using 2 kilograms of plutonium. It was also boosted with deuterium-tritium gas. Chinese-style mixed-charge for prompt thermonuclear reaction, you might say. This device produced 15 kilotons of explosive power when it was tested on Nov. 18, 1972. Back then, China was doing the opposite of what North Korea is doing; it was moving from nuclear weapons based on highly enriched uranium to plutonium, while North Korea may be going the other way stretching a supply of plutonium and possibly shifting to an all-HEU stockpile. But the principle is the same.
And, just to be clear: I am not saying that China supplied this design to North Korea — that would be silly, it was more of a science experiment as far as I can tell — but Pyongyang’s nuclear weapons designers are just as likely to have hit on the same idea as their Chinese counterparts 40-odd years ago. The North Koreans know what they are doing. They have now conducted five nuclear tests, which is actually quite a lot. (Oh, by the way, take a look at all the tunneling at the North Korean nuclear test site. They plan a lot more tests.)
That means we don’t really know how big North Korea’s nuclear arsenal is, or will be once the “standardized” warheads are deployed to the missile forces. But its not a small number, and certainly not just a handful. It’s a nuclear force, one that poses a threat to South Korea, Japan, and U.S. forces in the region. And it’s likely to keep growing. If we do nothing, I suspect it will grow in number, grow to threaten the continental United States, and eventually grow to include very powerful staged-thermonuclear weapons. And all this is going to happen sooner that you think. That nuclear weapons program is going to grow quickly — much like the toddler who decorated my television in lotion. Before I know it, he’ll be off to college. I wonder how big Kim Jong Un’s nuclear arsenal will be by then.
Photo credit: SEONGJOON CHO/Bloomberg