Geoff Brumfiel

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 U.S. scientists are up to underground.

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 U.S. scientists are up to underground.

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 U.S. scientists are up to underground.

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

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

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

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

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

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

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. You guys are familiar with chest x-rays, right? Scorpius is going to work in the same way. It'll create extremely high-powered x-rays.

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. You guys are familiar with chest x-rays, right? Scorpius is going to work in the same way. It'll create extremely high-powered x-rays.

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. You guys are familiar with chest x-rays, right? Scorpius is going to work in the same way. It'll create extremely high-powered x-rays.

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. Next stop, an experiment that simulates a nuclear weapon.

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. Next stop, an experiment that simulates a nuclear weapon.

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. Next stop, an experiment that simulates a nuclear weapon.

It's called Cygnus, and it's arguably the most secretive scientific project in the U.S. government.

It's called Cygnus, and it's arguably the most secretive scientific project in the U.S. government.

It's called Cygnus, and it's arguably the most secretive scientific project in the U.S. government.

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

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