< Inside an underground facility where the U.S. tests nuclear weapons

REGINA BARBER: Hey, Short Wavers, before we get started, a quick little favor to ask. Can you help us shape the future of Short Wave by completing a short, anonymous survey? It's a chance for you to tell us about what you like and don't, and how we can serve you better. It's an awesome responsibility, but I trust you. And we want to hear from everyone, whether you're a day one or brand new listener, just go to npr.org/shortwavesurvey. We'll also put a link in our show notes. Thank you. OK, on to our show. You're listening to Short Wave from NPR.

GEOFF BRUMFIEL: Hey, Gina.

BARBER: Hey, NPR science correspondent Geoff Brumfiel. Why are you darkening my doorstep?

BRUMFIEL: To talk about one of my all-time favorite topics, nuclear weapons testing. And I got a question for you.

BARBER: OK.

BRUMFIEL: When do you think is the last time the US tested a nuclear weapon?

BARBER: I'm going to say possibly in the late '70s.

BRUMFIEL: They actually stopped a lot later than that. They stopped in 1992.

BARBER: Wow.

BRUMFIEL: And they've been pursuing a very different program based on science.

BARBER: OK.

BRUMFIEL: And recently, I got a very, very unusual look at that program and all its facets and sort of how the US continues to verify its nuclear weapons work without having to set any of them off.

BARBER: Are they thinking about testing again?

BRUMFIEL: I would say the official answer is, no, but there is more concern that the US or another country might soon test another nuclear weapon.

BARBER: So today on the show, Geoff takes us on a rare trip to tunnels deep under the Nevada desert where America does science instead of nuclear testing. I'm Regina Barber, and you're listening to Short Wave, the science podcast from NPR.

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BARBER: OK, so let's start with, like, a little history on nuclear testing. Like, how did we get to where we are today, where we're not doing it anymore?

BRUMFIEL: You know, you think of nuclear testing, and it's like a mushroom cloud over the desert. But that was actually just a very brief period that those above-ground tests were happening. It was mostly in the 1950s, and it stopped because of radioactive fallout. The wind was carrying radioactive material much further than expected, and it started showing up on fishing boats, in milk, and baby teeth-- places nobody wanted it. So in 1963, the world's nuclear powers signed a treaty to move testing deep underground. And it kept going that way all the way until the end of the Cold War.

BARBER: Which was what, like, the late 1980s, early 1990s? That's when the Soviet Union collapsed.

BRUMFIEL: Right, right.

BARBER: So why did nuclear testing stop then?

BRUMFIEL: I spoke to Hans Kristensen with the Federation of American Scientists. He tracks nuclear weapons all over the world. And he says there were two big reasons. The first was political.

HANS KRISTENSEN: It was very much an attempt to look around and see, what can we do that makes it clear that we're not just talking about the end of the Cold War; we're serious about it; we're willing to do some things?

BRUMFIEL: But the second reason they could stop testing was actually technical. It was this growing power of supercomputers. They could now take these supercomputers and simulate nuclear testing in silicon.

KRISTENSEN: You didn't need to do nuclear tests to do what you needed to do for the foreseeable future, which is to make sure that the nuclear weapons you have work, and if there's a problem, a glitch, you can fix it.

BARBER: So you could still run tests. They were just on computers, not, like, an actual detonation of a nuke.

BRUMFIEL: Yeah, and that actually takes us to the first stop on this whole nuclear testing road trip.

BARBER: OK.

BRUMFIEL: I traveled out to Lawrence Livermore National Laboratory in California, and I got to see their newest computer, where they do what they call the button-to-boom calculations.

BARBER: The button-to-boom.

BRUMFIEL: It's inside a secure vault. The computer is called El Capitan.

[MACHINES WHIRRING]

TERRI QUINN: He named it after Yosemite. There's a very prominent granite chair, and it's in California.

BRUMFIEL: Terri Quinn oversees high-performance computing at Livermore, and she showed us around. Now, this machine uses advanced processors, similar to those used for generative AI, actually. El Cap can do more than 2 quintillion calculations per second.

BARBER: Wow.

BRUMFIEL: That's 2 exaflops for those in the supercomputing game. And its only job is to calculate, you know, a nuclear weapons detonation. It used to be it might take them a week to do a calculation on how a weapon would detonate.

QUINN: Now they can get it back by the end of the day or within hours. I mean, that is game changing, especially in this world where we have to move faster.

BRUMFIEL: And this is what nuclear testing looks like today.

BARBER: Making sure the weapons we do have work, but using supercomputers, right? Like, problem solved. Like, no more real-world tests.

BRUMFIEL: Not quite.

BARBER: OK, OK. Oh, no.

BRUMFIEL: As you know, Gina, any good computer model still needs some real-world data to make sure it's grounded in reality.

BARBER: OK.

BRUMFIEL: And so, you know, nuclear weapons scientists have continued to collect data. They're doing experiments in the same tunnels underground where they used to set up their nuclear weapons tests.

BARBER: OK.

BRUMFIEL: Now, this is not a place many journalists get to go. But I asked and asked and asked very nicely. And eventually, I and a few other journalists made it to Nevada, where they do this testing. We stepped onto an old mining elevator.

DAVID FUNK: All right. Watch your step getting onto the cage.

BRUMFIEL: And the elevator just drops into pitch blackness, nearly 1,000 feet underground. Here's what it was like at the bottom.

BARBER: Already, it sounds scary.

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BRUMFIEL: There's a long corridor that's been carved out of an ancient lake bed. Pipes along the walls carry air, water, and power. Workers in hard hats are everywhere. David Funk, who oversees work underground, leads us in. How long have we had tunnels down here?

FUNK: Oh, so the tunnel is the first-- well, these were dug in the '80s.

BRUMFIEL: So this would have been a test shaft, potentially.

FUNK: Yeah, this was designed to be nuclear tests location, originally, and now we do only subcritical experiments in this location.

BRUMFIEL: Subcritical experiments-- that means experiments that simulate conditions inside a nuclear weapon without triggering a nuclear chain reaction. That runaway chain reaction is what gives a nuke its incredible power. These tunnels were originally built to contain nuclear explosions. Then in 1992, the US officially stopped all testing. The Cold War had ended, and the thinking was nuclear testing could end, too. It would make the world safer. But fast forward to today, and nuclear weapons are back on the front pages. Same goes for nuclear testing. China, Russia, and America are all upgrading their test sites. And that's why we're here to see what US scientists are up to underground. Speaking of which, why do they still work down here?

FUNK: We do this because it is secure, right? So we can control the environment. And we also are concerned about a potential breach of the vessel. And so we want to do it in an environment that's controlled and we don't lose any of the plutonium into the environment.

BRUMFIEL: If something goes wrong,

FUNK: If something goes wrong. Yeah.

BRUMFIEL: We arrive at our first stop, a long, empty corridor that's just been dug out for a new experiment.

FUNK: So this is where the Scorpius machine is going to reside.

BRUMFIEL: The Scorpius machine. It kind of feels like you're in a James Bond movie. Funk explains it's actually a giant X-ray machine.

FUNK: You guys are familiar with chest X-rays, right?

BRUMFIEL: Scorpius is going to work in the same way. It'll create extremely high-powered X-rays.

FUNK: And the reason is we need higher energy X-rays to be able to look through plutonium.

BRUMFIEL: Plutonium from America's nuclear weapons. Much of it was made decades ago, and it's getting old. The X-rays are used to take a look inside to see how well the plutonium would work if detonated. Scorpius will cost $2 billion to build down here. We walked deeper into the tunnel network. Some of the floors are still rocky. They've just been dug.

[RADIO CHATTER]

BRUMFIEL: Next stop, an experiment that simulates a nuclear weapon. It's called Cygnus, and it's, arguably, the most secretive scientific project in the US government.

TIM BELLER: As a reminder, [INAUDIBLE] going into, no cell phones. Any Bluetooth devices, smart watches, smart rings-- if you have them, they need to go in the locker over here.

BRUMFIEL: Cygnus is a smaller version of Scorpius. It fires X-rays at plutonium that's inside a spherical steel container about the size of a mini fridge.

BELLER: Watch your step entering.

BRUMFIEL: Tim Beller is directing the next test, code named Nob Hill.

BELLER: So that is the Nob Hill vessel. That's the actual vessel that we will use. That's the three-footer.

BRUMFIEL: In a few months inside this vessel, scientists will blow up a tiny quantity of plutonium using chemical explosives. It's designed to simulate a nuclear detonation. But again, this test will be subcritical. The US government says there will not be a runaway nuclear chain reaction.

BELLER: Whatever rules they set, I ensure they happen here in Nevada.

BARBER: OK, so, Geoff, this gives like a real sense of what it was like to visit those tunnels and, like Tim Beller said, is that the US is following these rules. But you mentioned there might be, like, a return to testing. Is that because scientists need to do, like, another test they couldn't do with these supercomputers?

BELLER: No, actually it isn't. In fact, you know, I heard, again and again from nuclear weapons scientists on this trip-- there is no technical need to test right now.

BARBER: OK, so if it's not scientific, it's not technical, why would America test again?

BRUMFIEL: We'd start testing again for exactly the same reason we stopped testing, and that's politics. Nuclear weapons have a new role in the world. You know, Russia is developing some wild, new nuclear weapons designs. China is expanding its nuclear arsenal. And into all of this comes the Trump administration. Now, Project 2025, which is sort of a conservative blueprint for the government-- it says the US should be ready to test another nuclear weapon if it needs to. Trump's former national security advisor has gone further. He's written that the US should test another nuclear weapon.

BARBER: OK, so if the US did resume underground testing, what would be the consequences of that?

BRUMFIEL: First things first, we should say underground testing is safer than atmospheric testing, but that doesn't mean it's totally safe. Here's Jamie Kwong with the Carnegie Endowment for International Peace.

JAMIE KWONG: Underground tests can also have environmental and humanitarian impacts. You know, they're obviously not as severe as the atmospheric impacts, but they're still possible.

BRUMFIEL: And historically, at least, testing has been done in some pretty marginalized communities, places in rural Nevada, rural Mississippi, the Aleutian Islands. These are communities where the population just doesn't have that much political power. But there's also another way in which the resumption of nuclear testing could hurt the US strategically.

KWONG: The US has a technical advantage locked in by this moratorium on nuclear testing. Because it undertook so many more tests during this Cold War period, it has loads of historical legacy data.

BRUMFIEL: The US has more than a thousand nuclear tests under its belt. Now, China only has 45.

BARBER: Oh, wow.

BRUMFIEL: So if global testing resumes, China's going to learn a lot more from test 46 than the US will from its next test. But I should say, like, you know, this isn't all up to Trump and the Trump administration and America. China or Russia could decide it was time to do an underground test. And if they did, the US would be under a lot of pressure to test as well.

BARBER: OK. So, Geoff, I can see now that we could be at this precipice of a return to nuclear testing because we're at this, like, very unstable moment right now in the world of nobody-- like, no country wants to go first. But if one country tests, the other countries are likely to follow, right?

BRUMFIEL: That's exactly it. And you know, if testing happens, arms control experts worry it's going to spark new kinds of research into other nuclear weapons. And those weapons will get built, and we'll be right back in the middle of a nuclear arms race.

BARBER: Geoff Brumfiel, thank you so much for bringing us this story.

BRUMFIEL: You're welcome, Gina. Pleasure to be here.

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BARBER: This episode was produced by Rachel Carlson and edited by Berly McCoy. Geoff Brumfiel and Tyler Jones checked the facts. Jimmy Keeley was the audio engineer. Beth Donovan is our Senior Director, and Collin Campbell is our Senior Vice President of Podcasting Strategy. I'm Regina Barber. Thank you for listening to Short Wave, the science podcast from NPR.

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