What Happens Inside A Top-Secret U.S. Nuclear Facility?

The U. S. tested nuclear weapons until the early 1990s. Since then, scientists have been using supercomputers and experiments to simulate nuclear test detonations, without detonating any nukes. But there are signs the world's nuclear powers may be readying to test again: Russia, China and the U. S. are all upgrading their nuclear test sites. NPR science correspondent Geoff Brumfiel https://www.npr.org/people/279612138/geoff-brumfiel was among a small group of journalists allowed to tour an underground laboratory where this research happens. Read more of science correspondent Geoff Brumfiel's reporting here https://www.npr.org/2025/01/29/nx-s1-5276315/atomic-bomb-nuclear-weapons-lab-nevada. Help shape the future of Short Wave by taking our survey: npr.org/shortwavesurvey http://npr.org/shortwavesurvey Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:48Speaker 02

  Hey, Gina.

• 0:49Regina Barber?

  Hey, NPR science correspondent Jeff Bromfield. Why are you darkening my doorstep?

• 0:53Speaker 02

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

• 0:59Regina Barber?

  OK.

• 0:59Speaker 02

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

• 1:05Regina Barber?

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

• 1:08Speaker 02

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

• 1:12Regina Barber?

  Wow.

• 1:13Speaker 02

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

• 1:18Regina Barber?

  OK.

• 1:19Speaker 02

  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.

• 1:33Regina Barber?

  Are they thinking about testing again?

• 1:35Speaker 02

  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.

• 1:49Regina Barber?

  So today on the show, Jeff 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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• 3:38Regina Barber?

  Okay, 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?

• 3:45Speaker 02

  You know, you think a nuclear test, 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.

• 4:20Regina Barber?

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

• 4:26Speaker 02

  Right, right.

• 4:27Regina Barber?

  So why did nuclear testing stop then?

• 4:29Speaker 02

  I spoke to Hans Christiansen 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.

• 4:39Speaker 06

  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.

• 4:49Speaker 02

  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.

• 5:02Speaker 06

  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.

• 5:14Regina Barber?

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

• 5:19Speaker 02

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

• 5:25Regina Barber?

  Okay.

• 5:25Speaker 02

  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.

• 5:35Regina Barber?

  The button to boom.

• 5:36Speaker 02

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

• 5:43Speaker 06

  He named it after Yosemite. There's a very prominent granite there, and it's in California.

• 5:48Speaker 02

  Terry 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 two quintillion calculations per second.

• 6:04Regina Barber?

  Wow.

• 6:05Speaker 02

  That's two exit flops 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.

• 6:20Speaker 06

  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.

• 6:27Speaker 02

  And this is what nuclear testing looks like today.

• 6:30Regina Barber?

  Making sure the weapons we do have work, but using supercomputers, right? Like problem solve, like no more real world tests.

• 6:37Speaker 02

  Not quite.

• 6:38Regina Barber?

  Okay, okay.

• 6:39Speaker 02

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

• 6:47Regina Barber?

  Okay.

• 6:47Speaker 02

  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.

• 7:01Regina Barber?

  Okay.

• 7:02Speaker 02

  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.

• 7:21Speaker 02

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

• 7:28Regina Barber?

  Already it sounds scary.

• 7:33Speaker 02

  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.

• 7:46Speaker 02

  David Funk, who oversees work underground, leads us in.

• 7:50Speaker 06

  How long have we had tunnels now? Oh, so the tunnels first, very well, these were dug in the 80s. So this would have been a test shaft potentially? Yeah, this was designed to be nuclear test location originally. And now we do only subcritical experiments in this location.

• 8:07Speaker 02

  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 ended and the thinking was nuclear testing could end too. It would make the world safer. But fast forward to today and nuclear- Their 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.

• 8:50Speaker 02

  Speaking of which, why do they still work down here?

• 8:53Speaker 06

  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.

• 9:05Speaker 02

  If something goes wrong.

• 9:06Speaker 06

  If something goes wrong, yeah.

• 9:08Speaker 02

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

• 9:14Speaker 06

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

• 9:18Speaker 02

  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.

• 9:25Speaker 06

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

• 9:28Speaker 02

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

• 9:34Speaker 06

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

• 9:38Speaker 02

  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 walk deeper into the tunnel network. Some of the floors are still rocky. They've just been dug.

• 10:04Speaker 02

  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.

• 10:14Speaker 06

  As a reminder, here 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.

• 10:25Speaker 02

  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.

• 10:34Speaker 06

  Watch your step entering.

• 10:35Speaker 02

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

• 10:40Speaker 06

  So that is the Nob Hill vessel. That's it. The actual vessel that we will use, that's a three footer.

• 10:44Speaker 02

  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.

• 11:02Speaker 06

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

• 11:07Regina Barber?

  Okay, so Jeff, 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, right? 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?

• 11:23Speaker 02

  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.

• 11:32Regina Barber?

  Okay, so if it's not scientific, it's not technical, why would America test again?

• 11:38Speaker 02

  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.

• 12:16Regina Barber?

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

• 12:22Speaker 02

  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.

• 12:32Speaker 05

  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.

• 12:42Speaker 02

  And historically, at least, testing's been done in some pretty marginalized communities, places of 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.

• 13:02Speaker 05

  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.

• 13:18Speaker 02

  The US has more than 1,000 nuclear tests under its belt. Now, China only has 45.

• 13:25Regina Barber?

  Oh, wow.

• 13:26Speaker 02

  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 in 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.

• 13:48Regina Barber?

  OK, so Jeff, 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. Nobody, like, no country wants to go first, but if one country tests, the other countries are likely to follow, right?

• 14:06Speaker 02

  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.

• 14:19Regina Barber?

  Jeff Brumfield, thank you so much for bringing us this story.

• 14:23Speaker 02

  You're welcome, Gina. A pleasure to be here.

• 14:29Regina Barber?

  This episode was produced by Rachel Carlson and edited by Burley McCoy. Jeff Brumfield and Tyler Jones checked the facts. Jimmy Keeley was the audio engineer. Pat Donovan is our senior director, and Colin 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.

• 15:11Speaker 03

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