The High Risks of Low-Yield Nuclear Weapons

Published Apr 9, 2019

Dr. Lisbeth Gronlund, Co-Director of the Global Security Program at the Union of Concerned Scientists, explains the capabilities of the US nuclear arsenal and why smaller-scale nuclear weapons are just as dangerous as bigger bombs.

In this episode
  • Lisbeth explains why low-yield nuclear weapons are bad news
  • Colleen asks what the nuclear non-proliferation treaty is
  • Lisbeth talks about different types of atomic bombs
  • Colleen and Lisbeth explore what all of this means for global security
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Full transcript

Colleen: Lisbeth, thanks for joining me on the podcast.

Lisbeth: I'm so happy to be here.

Colleen: So, I recently learned from a colleague that the U.S. has developed a new nuclear weapon, a low yield, meaning less powerful, I assume, nuclear weapon. So, what's up with that? I have so many questions about that. But, let's start with the actual weapon. What is it?

Lisbeth: This weapon will go on a missile that's launched from a submarine. And it will replace one of the larger warheads that are on it. So, its explosive power is about 6.5 so-called kilotons. And each...and that's the equivalent of kilotons of high explosive. So, that's the relevant factor. The bombs that destroyed Hiroshima and Nagasaki were about 15 to 20 kilotons, so it's lower than those. It's not definitely not very small.

Colleen: Why create a smaller one?

Lisbeth: Well, the U.S. has small ones. We have had small ones for many, many decades. And in fact, during the Cold War, the U.S. and NATO believed that the Soviet Union had a much more powerful conventional army, and that they could invade Western Europe, and that the U.S. and NATO needed to have something to prevent that from happening. And they believed it was nuclear weapons.

And so, at its peak, the U.S. had about 7,000 nuclear weapons in Europe of all stripes. Nuclear howitzers, nuclear, you know, short-range missiles and bombs. And we no longer have that many, but we still have about 150 bombs in Europe that have low-yield options. So, it is really in the context of kind of a nuclear war-fighting scenario where now, Russia might do something with its conventional forces. And the U.S. and NATO feel that their only option is to respond with a small nuclear weapon.

Colleen: I had not idea that the US was so ready to use nuclear weapons in a conventional war.

Lisbeth: Yes. And, in fact, the U.S. and NATO have annual exercises where they exercise these nuclear options. So the U.S. bombs are at air bases in several countries. And the idea is, they are under U.S. custody, but if they were to be used they would be delivered by NATO pilots using NATO aircraft. So, in essence, the U.S. would kind of hand them over.

Colleen: So what’s new about our strategy under president Trump?

The new thing under the Trump administration is that they want the military to more closely integrate their conventional and nuclear exercises and preparations. And the idea is that the NATO and U.S. forces would then be able to fight, continue to fight if a nuclear weapon had been used.

Colleen: So we don't have...I know we've worked toward getting a no first use policy or I'm not sure what you call it, a treaty, a policy?

Lisbeth: A policy.

Colleen: A policy.

Lisbeth: It would be a policy.

Colleen: And that has been unsuccessful?

Lisbeth: Yes. That has been unsuccessful. Over the years the U.S. has narrowed the countries it would use nuclear weapons against and the reasons. Back in the beginning, it was sort of anything goes, and we considered using nuclear weapons in a conflict. Well, in the Korean War, and all kinds of scenarios. And then leading up to the Nuclear Non-Proliferation Treaty, which is a treaty that most of the signatories don't have nuclear weapons and they promised not to get them.

And five of the signatories have nuclear weapons, it's the U.S., Russia, China, Britain, and France. And they promised to get rid of them. And it occurred to those five that maybe if they still had the option of using nuclear weapons against these countries that didn't have any it would be a disincentive for them to sign the treaty, to say, "I'm never gonna get them," because they might feel like having that option would prevent these five states from targeting them.

And so, leading up to that, and in particular, in years after, the U.S. has made public statements that it will not use nuclear weapons against countries that are in the Non-Proliferation Treaty without nuclear weapons.

Colleen: Did we have to reduce what we have?

Lisbeth: No. So the treaty basically, in a way, it sought to codify the status quo. That's really what it did. And there were promises, in particular, of moving towards disarmament, and also providing access to nuclear technology for nuclear power, nuclear reactors and things like that.

Colleen: So, having grown up in in the '70s, I mean, I recall being really scared that nuclear weapons, destroying the planet, was a real thing. And the narrative I remember, and I'm not sure how accurate this is, but I remember thinking that the idea was the Soviet Union would launch a bunch of nuclear weapons at our big cities and destroy many, many people, civilians. And then once they did that, we would send a bunch of nuclear bombs there to destroy them. And to me, it felt very much like the end of the world...

Lisbeth: It could have been.

Colleen: we know it. And so, with that being the way that we were thinking of it, we figured, well nobody's gonna shoot a weapon first because it's gonna be the destruction of the planet, is what I do in my mind I thought we were talking about.

Lisbeth: People call that theory MAD, Mutual Assured Destruction.

Colleen: Right. But these smaller weapons, that feels very troubling to me that...what is the strategy? I mean, you talked about it a little bit a few minutes ago, but doesn' seems like we're making it much more likely that's something will happen.

Lisbeth: Yes. I mean, it lowers the barrier to entry, basically. And the argument, of course, the U.S. military is not gonna say, "Well, this is would be easier for us to begin," but rather that if we don't have these weapons, it will be easier for Russia to begin, because Russia also has small ones.

In fact, so in its arsenal already, the U.S. has bombs that have a variable yield. You can set it before you drop the bomb. On the low-end is 0.3 kilotons, which is 2% of the weapons that destroyed Hiroshima and Nagasaki. So, small on the scale of nuclear weapons.

Then we have the option of 1.5, 5 and 10. And so this new one is 6.5. And the argument the military makes is that if we don't have that 6.5 that Russia will believe that it can use small nuclear weapons because we won't respond so that we need...there will be a gap. There's a gap there. And so, I'm not making this up. It really is as crazy as it sounds.

Colleen: You're describing the look on my face right now.

Lisbeth: Right.

Colleen: So, if I understand this correctly, Russia might use a nuclear weapon of some size?

Lisbeth: Yes.

Colleen: And if we don't have a 6.5 somehow...?

Lisbeth: They are gonna believe that there is a gap that they can "exploit.”

I mean, these are arguments that are very hard to get you...I mean, you know, what do you do except laugh, and that's not very effective. Most weapons, it takes years to develop and then you have to produce them. But this one, unfortunately, it was a really quick deal.

Colleen: This raised another question and that is testing because they've built it but they can't test it. So, how do you even know that it works?

Lisbeth: Right. The U.S. conducted over 1,000 explosives tests until testing was banned. All of those tests were to take a new design and basically, just prove that it worked. Beyond that, trying to understand the reliability of these weapons would take so many tests that that was impossible.

Colleen: So when you say prove that it worked, did they actually blow them up?

Lisbeth: They sure did. Initially, in the atmosphere.

Colleen: Right. I mean, I do know that.

Lisbeth: And then underground. But the part they blew our weapons, most weapons in the world are called hydrogen weapons. Unlike the bombs that were dropped on Hiroshima and Nagasaki, they were atomic weapons.

So they only involved fission, which in this case you could basically break apart plutonium or uranium atoms, and that releases a lot of energy. But if you wanna get a really, really powerful weapon, you have to go beyond that. And you start with this fission process. And then, that in turn, the energy released kicks off a fusion process. It fuses the hydrogen atoms, which is why they're called hydrogen bombs.

Colleen: Okay. You've got a two-part process?

Lisbeth: Two parts, that's right. And people call it the first stage and second stage. And so, as I said, the U.S. currently has hydrogen warheads on the submarines. It happens that they are being refurbished now. So they're all being taken apart and put back together. The factory floor is busy.

Colleen: And this is where a new design comes in? They can take them apart and they don't have to put them back exactly as they came apart.

Lisbeth: Well, that's what they're doing now. That's what they're doing with this weapon. And to make this a less powerful 6.5 weapon, they are basically removing the second stage, in essence. So you don't need to do more testing of the weapon itself. It's very quick. And they are nearing the end of production if they haven't already finished producing it.

So now they have this explosive piece that has to go in a warhead, has to go on the missile, has to go on the sub, which takes time and additional training. And so it's not out to sea yet. It is sitting in a warehouse.

Colleen: So Lisbeth, you're a physicist. If were developing or refurbishing this bomb, would you be content without ever testing it that it was going to work and explode and do what it's supposed to do?

Lisbeth: Yes, because the big ones have been tested. And the main thing that you are worried about if you are a weapons designer is the first stage. If you get that right, it's guaranteed the second stage will operate. So, it's really about the first stage.

Colleen: And the first stage, they haven't redesigned it. They're just putting it back together with less...or they've taken stage two off, which is making it...

Lisbeth: For these new weapons. So, there's another plan for a new nuclear weapon in Trump's nuclear posture review, which would entail designing a new weapon. It's off in the future, if it ever happens. But this particular idea was at exactly the right or wrong time, depending on how you looked at it.


Colleen: Uranium or plutonium, which one? Are they the same? Why would you use one over the other?

Lisbeth: No, they're different elements like silver and gold. The need less plutonium. It's a more sophisticated design, which is why countries that are starting out often will use uranium. And so, all of our weapons, the first stage, has a plutonium pit is what they call it, spherical with an opening in the middle. And that is what fissions and then provides the energy for the second stage.

Colleen: What is it when you you mine plutonium?

Lisbeth: You don't mine plutonium. Plutonium does not exist. It is made by humans in nuclear reactors. The first plutonium was produced during World War II as part of the Manhattan Project. And it is produced in all reactors.

Colleen: What do you use to make it?

Lisbeth: You put in uranium, and then there are neutrons that are captured by the uranium and some of it turns into plutonium.

Colleen: And you have to get you have to get the uranium first.

Lisbeth: You have to get the uranium.

Colleen: Where do you get that?

Lisbeth: There's uranium ore, a lot of places.

Colleen: And you can go mine it without any danger? Can you pick it up and...?

Lisbeth: No, there's dust you don't wanna breathe in that has uranium, I mean, I think all mining has problems but it's not...

Colleen: It's not like on "The Simpsons" where it's glowing green.

Lisbeth: No, it is not glowing green.

Colleen: And if you touch it it's going to...

Lisbeth: No, it's not. I mean, you have to take precaution, obviously, but it's not glowing green.

Colleen: Give us a sense of how many nuclear weapons we have right now. I want a picture of what we have, sizes, where they are, are they right ready to go right away or are they in storage somewhere?

Lisbeth: The U.S. has about 1,800 weapons that are ready to go. It has 400 on land-based missiles. Each one is in a silo in the middle of the country.

It has about 1,000 missiles on submarines. And then it also has bombs and air launch cruise missiles, which is just what it sounds like, a cruise missile launched by an airplane. On top of that, it has weapons in storage, same kinds of weapons in storage.

And those are...people call them strategic, which really just means they're long-range. And they would be intended for use in a war with Russia or China. In addition, the U.S. has what are called tactical nuclear weapons, which are short-range. It has about 150 bombs at U.S. air bases in Europe. And it has the same bombs in storage in the U.S. So, all together, about 4,000.

Russia has a comparable number of strategic weapons. They have more we believe. They have more tactical weapons. And all the U.S.-Soviet and U.S.-Russian agreements have only covered deployed strategic, nothing in storage. And there has been no arms control about the shorter-range systems.

Colleen: Yeah, so we've talked about this new low-yield weapon, what else is on the table?

Lisbeth: So, under the Obama administration, he laid out a plan for the next 30 years. And it entailed pretty much refurbishing or replacing every element of our nuclear forces with new ones.

And that goes from the warheads to the missiles to the submarines, and some of those things really do need replacing. For example, submarines operate at great depths. The metal is under tremendous stress. And at some point, it just can't do it anymore. You need new submarines. Other things are much less defensible.

And, really, another question is, the assumption was that the U.S. would have the same level of forces. That 30 years from now, we would still have this many weapons and this many submarines and missiles, and that's shocking actually. That's shocking that the Defense Department is planning to maintain this level of weaponry into the future. And you know, when we produce these new upgraded weapon systems, they then will have a life beyond that. So we are basically putting in place an arsenal that will last for many decades at this scale.

Colleen: And what would you like to see?

Lisbeth: I would like to see the U.S. reduce its arsenal. Ideally, hand-in-hand with Russia. But I don't think that's necessary. Under Obama, the Joint Chiefs decided that the U.S. could, in fact, reduce its arsenal independent of what Russia did, but they wanted to do so with Russia and that did not come to pass.

But there's no reason that U.S. security requires it to have the same number of weapons that Russia does. Really, all you need is to have some weapons that Russia could not possibly destroy, which the U.S. could then retaliate with and that would be more than enough to prevent Russia, if it had such an inclination, from attacking the U.S. with nuclear weapons.

Colleen: So I did a little digging in the history books to learn about the START treaty. So that stands for strategic arms reduction treaty, and it was signed in 1991 and ultimately reduced nuclear weapons between the US and Soviet Union by 80%. It expired in 2009 then in 2010 the US and Russia agreed to a replacement, known as the new START treaty. So what’s that?

Lisbeth: So the U.S. and Russia signed a treaty, New START, which limits their numbers of deployed long-range weapons. And it went into effect in 2011, and will expire in early 2021, and can be extended for another 5 years. So, this is a treaty that Trump has been grumbling about. It puts identical limits on these two countries.

The military is very keen on not just this treaty but treaties because there's verification, and they get to know what Russia's doing. And they find that very valuable. And former Secretary of Defense Mattis, among others, has really made the case for arms control agreements like that. So it reduced the arsenals by about a third relative to what they had been.

Colleen: So, let's start with the actual weapon. What is it?

Lisbeth: It will be based on a missile on a submarine. It will be called the W76-2, and the "-2" is because the W76-1 is the regular, so-to-speak, higher-yield weapon. So, it's a modification of an existing warhead and it'll just be much less powerful.

Colleen: So, the W76, how powerful is that?

Lisbeth: It is 100 kilotons. And the W76-2 will be about 6.5.

Colleen: Do you know, are there a lot of, or are there any women weapons developers?

Lisbeth: Yes. Actually, I was at a meeting that I helped organize a couple of years ago, and one of the...there were several weapons designers. And one of them was a relatively young woman, which, you know...and she and the others do their work because they believe it will make the U.S. more secure. And they should believe that. It would be awful if they didn't.

Colleen: I was just curious though because I was thinking about women in science, in your field, and it just made me wonder if you've been the lone woman out there a lot.

Lisbeth: Well, it's interesting. When I was in graduate school, the average graduate department had about 5% women among their graduate students. I went to Cornell because it had 15%. It's one of the reasons I went there. The number has crept up over the last many years.. But there's definitely a's a minority.

And I think that the same holds true for weapons designers. I mean, they're not that many. The U.S. has maybe a few dozen of the people who really are designing the weapons. There's lots of other stuff that is required for a nuclear weapon. There are thousands of components, but the nuclear part, they are probably a few dozen people who do that work. And I don't know for sure whether she was the only one but there can't be many. There can't be many. And that's true more generally when you are in technical fields related to national security. It is...

Colleen: I imagine you've probably found yourself as the only woman on panels, at conferences, or at meetings or at...

Lisbeth: There are not very many people outside of the government who have a technical background who work on these issues.

Of the, say, two dozen people who have permanent jobs in this field, there are two. I'm one and my colleague, Laura Grego, was the other.

Colleen: So, did I hear this right? You and Laura are the two non-governmental physicists that...

Lisbeth: Women...

Colleen: Women.

Lisbeth: ...that had jobs.

Colleen: That's fascinating. I had no idea. And I know both of you.

Well Lisbeth, thanks so much for coming over to talk to me about nuclear weapons and these new low-yield nuclear weapons. I’m not feeling super happy about them, but I’m glad that you gave me a little bit of perspective on it.

Lisbeth: I’m so glad to have joined you.

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This Week in Science History: Katy Love
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Executive producer: Rich Hayes
Host: Colleen MacDonald

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