Expert Commentary

How Reliable Are North Korea’s Nukes?

David Wright
Co-Director, Global Security Program, Union of Concerned Scientists

After President Donald Trump’s vow that any threats from North Korea “will be met with fire, fury, and frankly, power the likes of which this world has never seen before,” Pyongyang responded within hours, threatening to strike American military forces based on the U.S. island of Guam.

The war of words came the same day as the Washington Post reported on a recent Defense Intelligence Agency assessment that concluded North Korea now has the capability to put a miniaturized nuclear warhead on a ballistic missile and is in possession of 60 nuclear weapons.  

The Cipher Brief’s Wilson Dizard spoke with David Wright, the co-director of the Global Security Program at the Union of Concerned Scientists, to find out more about the development of the North Korean nuclear program and what we know, and don’t know, about its capabilities.

The Cipher Brief: How did North Korea get this far in its nuclear weapons program? Is there any surprise at the pace at which they developed this technology?

David Wright: Nuclear weapons are fairly old technology, so a lot is known about them, especially first generation weapons. The hardest part is getting the plutonium or the highly enriched uranium (HEU) for them. North Korea had a reactor, sort of a research reactor, that was built with Soviet help back in the 1980s, and that started producing plutonium. In time, and I don’t know the detailed history of this, with help from the Pakistanis, North Korea learned how to do uranium enrichment technology.   By those two routes they basically got fissile material.  Then it’s the matter of figuring out do the high explosives to compress the material and things like that, but then again, those things are relatively well known—it’s fairly old technology.

The other thing that helped them was sometime back in the 1980s, Pakistan apparently got a design of a nuclear warhead, an early nuclear warhead, from China that was fairly simple and relatively easy to make as far as we can understand. People believe that North Korea may have gotten that design from Pakistan. And if that’s true, that also helped them get an idea of exactly how you do this and what goes into actually building it.

TCB:  And then what about missile technology?

Wright: Missiles are pretty old technology. I started following the missile program in the early 90s.  Sometime in the 80s they got short range SCUD missiles.  The Soviet Union had built these short range SCUD missiles, which had about a 300 kilometer range, and a lot of different countries had bought these from the Soviet Union. North Korea got a handful of them from Egypt and started studying how they work and how to make them, and basically worked their way up from there. It’s what a number of countries have done. You start with short range missiles. And then you figure out how to make them lighter, how to make the engines bigger and over time, they developed the engineering capability and expertise to figure out how to build these things themselves, as opposed to having to buy them or buy parts.

So what we saw for a long time is they seemed to be building missiles that appeared to be based on components, like engines, that they got from the Soviet Union when it broke up.  For a long time, we saw them using these different components in different combinations to get longer and longer range missiles.

What we seem to have seen more recently is they’ve been doing more things on their own.  It certainly appears that four or five years ago they must have started putting money into funding the development of a bunch of different kinds of systems, because in the past year and a half, we’ve not only seen a large number of tests, but tests of a lot of different systems. The two-stage solid missile they can launch from underwater and the ground and the longer range missile that was launched earlier this year.  We’ve seen a shorter range missile that they were intending as an anti-ship missile.

What it looks like to me is they sort of cut their teeth on getting components from outside, figured out how to put those together, and then started to fund in a serious way the build up of its aerospace missile engineering capability and the development of a bunch of different systems.

TCB: How effective is North Korea’s arsenal of weapons? How much do we know about their specific limitations and capabilities?

Wright: There are really two parts to that.  One is the nuclear warheads themselves. They’ve conducted five underground nuclear tests. Some of those have not worked so well. But the last one, people think, had a yield of the bomb that the U.S. dropped on Hiroshima. They seem to have a nuclear device that explodes with significant yield. People think they’ve made that small enough to fit on a missile.

Then the question is what do we know about the capability of their missiles.  We’ve seen that missile ranges are getting longer and longer to the point where they can hit the U.S. There’s still a couple of issues. One issue is reliability. We’ve have seen a few successful launches, but these are complicated systems and everything has to work perfectly.  One of the things North Korea doesn’t know is how reliable its systems are, because it hasn’t done enough tests to determine that.  The reason that’s important is, if you are going to use these things, you want to make sure they don’t blow up on the launch pad and spread nuclear material around.

The other thing is, even if you did launch it, these missiles would have very low accuracy. If you aimed at a given point you would be lucky to get within tens of miles of that target point. And what that means is that you’re not going to be using these on a specific target, on a military target.  What you would be shooting at is a very large target, like Los Angeles. In that sense, it’s a threat people worry about because that is a big enough target that you could hit with bad accuracy.

Then the last piece people have talked about is whether they could build a heat shield that would allow it to get down to Earth in one piece. And there is some question if the re-entry vehicle broke up before it hit the ground. But I think there’s not much doubt that they have a working re-entry vehicle, or they will have soon. So that’s the last piece people worry about.

TCB:  How powerful are North Korea’s nuclear weapons, and how many do they have? Do they have thermonuclear capability?

Wright: The question of how many nuclear weapons they have depends on how much plutonium and uranium they’ve been able to make, and people have done estimates of that. The person I always turn to is Sig Hecker who has worked on this. He estimates they have enough material for 15 to 20 weapons currently, and are presumably continuing to make this stuff, so they could add a couple a year.

We don’t think they have thermonuclear capability. We think they are going beyond a simple uranium or plutonium bomb. And one way you can do that is put material in the core of a sphere of plutonium or uranium, and when the nuclear reaction goes off, that would be fission energy from the plutonium or uranium that would would give you some fusion energy. So we think they’re working on some things like that, but it’s not a true thermonuclear weapon.

There’s been speculation that one of the recent tests, that’s referred to as boosting by putting this small material in the middle, is what one of those tests might have been. It’s tritium or lithium deuteride. It’s the kind of thing you use in a thermonuclear weapon, but when it’s compressed under high temperatures, you get fusion.  It partly adds energy but it also spits out a large number of neutrons, and those neutrons make the fission of the uranium or plutonium more efficient. So you get more fission power out of it as well.

TCB:  What countermeasures are available to South Korea and Japan to defend against conventional and nuclear North Korean attack? How effective are they? 

Wright: I don’t know of anybody talking about counter-measures to conventional artillery on Seoul for example. They’re talking about many hundreds of artillery troops, and other than trying to attack the artillery sites themselves, I don’t know if there is much you can do about that.

In terms of trying to defend against missile attacks, for South Korea, it would be something like the Patriot or THAAD system.  For Japan, it would be the Patriot or the ship-based Aegis system. The problem is that nobody really knows how well those would work against an attack like this.  They haven’t been tested enough or tested under real world conditions. It’s not the kind of thing that either country could trust to deal with the threat.

TCB: What’s a greater risk to the North’s neighbors: their conventional weapons or its nuclear arsenal? What does this mean for policymakers?

Wright: Certainly for Seoul, the artillery attacks are probably the bigger risk. For Tokyo, for example, I think it’s not completely clear. The range there is too far for conventional artillery, so they’d be talking about a missile attack. Then I think you’d be talking about a nuclear warhead or a chemical warhead. The problem is that the missiles are so inaccurate. If you’re shooting inaccurate artillery, but you’re shooting hundreds of thousands of them, it doesn’t really matter if they’re inaccurate.  If you’re shooting a ballistic missile, and you’re only shooting one or two of them, then having a conventional warhead doesn’t make a lot of sense because of the inaccuracy. Then the threat people would worry about for Tokyo is a missile launched with a nuclear weapon or possibly a chemical weapon.

TCB: How does the experience of North Korea help inform other efforts at nuclear non-proliferation from a technical perspective?

Wright: One of the things that this shows is these technologies that used to be cutting edge and hard to produce are getting easier and easier for countries to be able to develop. The big thing for North Korea for nuclear weapons is having a small nuclear reactor that could be used to make plutonium, and then getting help from Pakistan to build an enrichment capability for HEU. One of the things the international community has to do is figure out how to make that harder and harder for countries to do, but it’s very difficult to turn it off entirely.  I think North Korea is an example of a place where people have been trying through sanctions and other sorts of things from going down this path. And yet here we are.

TCB:  So are sanctions ineffective?

Wright: It’s very hard to have sanctions be effective enough to keep a country from being able to develop weapons like this. What I think was really effective in the case of the Iran sanctions was you’ve got a big middle class there, and the sanctions were really hurting the country as a whole and was putting pressure on the government.  It’s less clear to me that sanctions were good enough to really cripple its ability to develop these weapons if they wanted to, and I think that’s what we’ve seen in North Korea.

And when we talk to our Chinese colleagues, when they look at North Korea, they sort of see themselves in the 1960s and 1970s. The world was putting sanctions on them and trying to keep them from developing nuclear weapons, and it sort of reinforced their desire to move forward with these things. They found they could cut corners elsewhere but still make progress on these systems.

I think from a technical point of view, it’s very hard to get sanctions to be effective enough to really stop these things. You can make life difficult for people, you can increase the costs, but I don’t think sanctions are the whole solution.

TCB:  If the North does attack South Korea, Japan or U.S. bases directly, what options does the U.S. have in the region to respond?

Wright: How the U.S. would want to respond depends a lot on what the scenario is. Between having bombers based in Guam that could get there fairly quickly, or having subs that could launch nuclear weapons or conventional cruise missiles, there’s a lot of things that the U.S. could do. It depends a lot on the scenario and what the point of response would be.

TCB: What does the most likely scenario for war look like?

Wright: I think it’s really hard to know. I don’t think Kim Jong-un is crazy. I think he’s despicable, but I don’t think he’s irrational. And for that reason I think he knows that if he launches an attack, it would mean the end of his regime, because there would be a devastating  response from the U.S., one way or another.

I worry less about him deciding at some point to launch an attack out of the blue, as much as there being a crisis situation where tensions are high, there are misunderstandings, there are mistakes, and something gets started. If that’s what you’re talking about, it’s hard to know how that will happen or what the most likely thing to do is.

I think it has to be something North Korea feels like it would be worth launching an attack that would result in a counter attack that would destroy the regime. And it’s hard to know what does that.

The Author is David Wright

Dr. David Wright is the co-director of the Union of Concerned Scientist's Global Security Program.  He is a nationally known expert on the technical aspects of nuclear weapons policy, missile defense systems, missile proliferation, and space weapons. For the past 27 years, Wright has been a primary organizer of the International Summer Symposiums on Science and World Affairs, which fosters cooperation among scientists around the world working on arms control and security issues.

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