Bonus Episode: Reactor That Killed... Itself?

There's a kind of nuclear nightmare we all know how to picture. The flash. The mushroom cloud. The sky torn open above a city. It's terrifying, but in a strange way it's comforting. At least you know what to fear. At least it has a face. Morgan Miller: The nightmare I'm about to tell you has no face. No flash, no cloud, no blast wave racing toward a harbor. It happened in a country famous for refusing to fight in anyone's wars, inside a mountain, in a building almost nobody on Earth has ever heard of. Nobody died. Nobody outside the mountain was ever in danger. And somehow, that makes it more unsettling. Because the danger was never the explosion you could see. It was the fire you couldn't. Morgan Miller: This podcast was brought to you by flooftags, visit floof tags dot com for one of a kind laser engraved pet tags. Morgan Miller: This is the story of the Lucens reactor. Morgan Miller: To find it, you would drive through the rolling farmland of the canton of Vaud, past fields and forests and villages that have looked the same for centuries. Nothing about the landscape suggests a nuclear site. The buildings at the surface were low and plain, tucked against the edge of the forest, easy to miss entirely. And that was the point. The real building was underground. Below the grass and the trees, behind hundreds of feet of stone, sat a reactor that almost nobody was allowed to see, running a design almost nobody else was trying. Morgan Miller: Picture Switzerland. Chocolate, watches, railways that run on time. A country so committed to staying out of other people's wars that it turned neutrality into a kind of national art form. But neutrality is not pacifism, and the Swiss have never confused the two. For decades, their defense strategy treated the Alps themselves as a fortress. They called it the Reduit, the redoubt. Tunnels dug through the mountains, bunkers poured into the slopes, bridges and passes wired so they could be dropped into the valleys at a moment's notice. The plan was simple. If anyone ever invaded, the country would retreat into the rock and wait them out. Stone was the armor. The mountain was the answer to everything. Morgan Miller: And here is the part of the story almost no one expects. Within months of the atomic bombs falling on Hiroshima and Nagasaki, the Swiss government quietly set up a commission to study whether Switzerland could build an atomic bomb of its own, and the secret program ran for forty-three years, until it was finally wound down in nineteen eighty-eight. Even the Swiss wanted the bomb. Hold that thought, because it makes what happened in the mountains even stranger. Morgan Miller: In the early nineteen sixties, Switzerland decided to do something audacious in peacetime, not in war. It would design and build a nuclear reactor of its own. Not bought off the shelf, not licensed from the Americans or the French. Swiss engineers, Swiss physics, Swiss pride. A small experimental power station, generating only about six megawatts of electricity from roughly thirty megawatts of heat. It used heavy water to slow its neutrons and carbon dioxide gas to carry the heat away from the core, a combination almost nobody else in the world was even trying. If it worked, Switzerland would own a reactor design it could call entirely its own. Morgan Miller: And in keeping with the Swiss idea of defense, they did not build it on an open field behind a fence. They built it inside a rock cavern. A hole bored into the mountainside, near the town of Lucens, in the canton of Vaud. Almost everywhere else in the world, a reactor's containment was a structure you built around the machine, a dome of concrete and steel. At Lucens, the containment was the mountain itself. That was the whole bet. Whatever went wrong inside would stay inside, held behind millions of tons of stone. No dome could ever fail the way a mountain could not fail. Or so the thinking went. Morgan Miller: Construction began in the spring of nineteen sixty-two. For four years, crews worked inside the cavern, fitting the machine into the rock. In nineteen sixty-six, the chain reaction began for the first time. On the twenty-ninth of January, nineteen sixty-eight, the Lucens reactor was connected to the grid, feeding Swiss-designed power into Swiss homes. It was formally commissioned that May. Barely a year later, the mountain would get to prove itself, in the worst possible way. Morgan Miller: Now, a partial meltdown is not an explosion. There is no bang, no fireball, no drama you could photograph. It is a slow-motion disaster, measured in degrees. Metal that was designed to withstand temperatures far beyond anything normal operation could produce, giving way one degree at a time, in the dark, inside rock. And when uranium metal burns, it does not burn politely. It burns hot, and it keeps burning, feeding on the air around it. Morgan Miller: To understand what went wrong, you need to picture the inside of the machine. The core was built around seventy-three vertical channels, long tubes standing side by side. Inside each tube sat the fuel, rods of uranium metal wrapped in a magnesium alloy cladding. Carbon dioxide gas flowed up through every channel, carrying heat away from the fuel and keeping everything at the temperature it was designed to run at. Seventy-three channels. As long as every one of them was flowing, the reactor was happy. Morgan Miller: During an earlier shutdown, something quiet happened inside one of them. Damp air condensed on the magnesium alloy of the fuel elements, and the condensation corroded the metal. Bits of corrosion product broke loose, drifted down into the core, and plugged one of the seventy-three channels solid. Nobody knew. There was no alarm for a blocked channel, no gauge on a panel that said one channel out of seventy-three had gone silent. The reactor sat there, looking perfectly healthy, carrying its one quiet flaw into the next startup. Morgan Miller: On the morning of the twenty-first of January, nineteen sixty-nine, the operators began bringing the reactor back up to power. Carbon dioxide surged through the channels, carrying heat away, exactly as designed. Except in one channel, where there was no flow at all. And inside that channel, the fuel was heating with nowhere for the heat to go. Morgan Miller: The temperature climbed past everything the designers had planned for. The magnesium cladding was built to survive heat far beyond normal operation, but normal operation assumed the coolant was flowing, and in this one channel, it was not. Heat does not negotiate. It does not wait for someone to notice a blocked channel on a panel that has no gauge for it. It simply accumulates, degree by degree, in the dark, until the metal that was supposed to protect the fuel becomes a liquid, and then a memory. Morgan Miller: What happened next was a chain of small catastrophes, each one unlocking the next. Without cooling, the magnesium alloy cladding around the fuel melted. The bare uranium metal inside, exposed and burning hot, caught fire in the carbon dioxide atmosphere. A pressure tube, weakened and overheated, split open. Then a second tube failed beside it. The core partially melted down, and radioactive fission products poured out of the broken machine and into the cavern. Morgan Miller: The cavern itself became the disaster's final shape. The walls, the floor, the machine, every surface inside that rock chamber was coated in contamination that no human sense could register. You could have stood at the cavern's entrance, if anyone had let you near it, and seen nothing wrong at all. Just dark rock and machinery and silence. The danger was a physical fact and completely invisible at the same time. That is the particular cruelty of this kind of accident. It does not announce itself. It simply is, everywhere, all at once, behind stone. Morgan Miller: Let that picture sit with you for a moment. A fire you cannot see, inside solid rock, releasing something no human sense can detect. There is no smoke alarm for fission products. There is no smell, no color, no sound. The operators knew they had lost the core, and they knew they could not go in after it. And the one thing nobody had to do, the thing every other reactor disaster has forced, was evacuate a town. The town was on the other side of a mountain. Morgan Miller: Because here is the part that matters. No one was hurt. Not one person. No radiation ever reached the outside world. Every bit of contamination stayed inside the cavern, inside the rock. The mountain held. The containment worked exactly as it was designed to work. International regulators would later rate the accident a level four on the seven level scale, the same band as the SL one disaster in Idaho, an accident with serious local consequences but no escape beyond the fence. Except at Lucens, the fence was a mountain. Morgan Miller: But the mountain that kept everything in also kept everyone out. The cavern was so contaminated that going back inside to repair the reactor was never practical. You cannot fix what you cannot enter. The tight underground spaces that made the cavern such perfect containment made it a nightmare to work in. Decontaminating the cavern, piece by piece, would have cost more than the little experimental reactor was ever worth. So Switzerland did the only thing left to do. It sealed the cavern. The engineers entombed their own machine. Morgan Miller: Think about the cruelty of that position. The same tight, cramped underground spaces that made the cavern such flawless containment made it a nightmare to work inside. Every cubic meter of rock that protected the valley also blocked the cleanup crews. The engineers had designed themselves out of their own building. What remained was a slow, painstaking extraction, working in a poisoned cavern to pull the fuel out of a machine that could never run again. Morgan Miller: On the third of March, nineteen sixty-nine, barely six weeks after the accident, the Lucens reactor was shut down for good. It had fed power to the grid for just over thirteen months. Four years of construction inside the mountain. Thirteen months of electricity. And then thirty-four years of cleanup, ending only when the last radioactive waste was finally removed in two thousand and three. Morgan Miller: The cleanup took years. The fuel was taken out and the worst of the waste was dealt with by nineteen seventy-three. But radioactive waste kept being pulled from the site for decades afterward, and the last of it was not removed until two thousand and three. The Swiss regulator did not formally release the site until nineteen ninety-five, more than a quarter of a century after the accident. A reactor that ran on the grid for barely a year was given a tomb in a mountainside. Morgan Miller: And the dream died with it. Switzerland abandoned its home-grown reactor design entirely. Every nuclear plant the country built afterward used the standard light-water design the rest of the world used. The indigenous Swiss reactor, born of Swiss pride and Swiss engineering, ended its life sealed inside Swiss rock, and the idea of a Swiss reactor was never revived. Morgan Miller: It is worth pausing on what that decision really meant. A country had set out to prove it could stand on its own two feet in the most demanding technology of the age. It built the machine, it proved the physics worked, it connected it to the grid. And then one corroded channel, out of seventy-three, in a space no one could reach, ended the entire program. Not the physics. Not the mountain. A little bit of condensation, from a maintenance shutdown, that nobody thought to worry about. That is how fragile the line is between a triumph and a tomb. Morgan Miller: It is worth remembering that the Lucens accident did not end the other Swiss nuclear story, the secret one. Even after the meltdown, even after Switzerland signed the non-proliferation treaty later that same year, the quiet study of the bomb went on for nearly twenty more years, until nineteen eighty-eight. The reactor in the mountain died in nineteen sixty-nine. The program in the shadows outlived it. Morgan Miller: Here is the irony at the heart of this one, and it is a quiet irony, not a loud one. The engineers who built Lucens were not careless. They were careful in a very Swiss way. They looked at the worst thing that could happen and they buried it inside a mountain, and the mountain did exactly what they asked it to do. Nothing escaped. Nobody was harmed. The safety feature worked perfectly. And it was also a death sentence. The very thing that made the accident survivable is what made the mistake permanent. The shield and the grave were the same hole in the mountain. Morgan Miller: And the deeper irony is this. The whole philosophy behind Lucens was that geography could be trusted more than engineering. A concrete dome is a human thing, built by fallible hands, and it can fail the way human things fail. A mountain is not a human thing. It was there before the reactor and it would be there after. So the designers outsourced their safety to geology. But geology does not fix broken fuel channels. Geology does not un-melt a core. The mountain kept its promise perfectly, and the promise was only ever half of what they needed. Morgan Miller: There is something quietly frightening about a disaster with no victims. It teaches the wrong lesson, or the right one, depending on how you look. The lesson of Lucens is not that mountains fail. It is that even when the mountain holds, the fire still happened. The invisible fire, in the dark, in the rock, where no one could watch and no one could help. A machine built to prove a nation's ingenuity, sealed away by the same ingenuity that buried it for safety. Morgan Miller: The mountain is still there, of course. It was there before the reactor, it was there during the fire, and it is there now, holding a sealed cavern that almost nobody will ever enter. The fields above it are still fields. The forest is still forest. Drivers pass through the canton of Vaud and see nothing, suspect nothing. That is the final quiet of this story. Not a ruin you can visit. Not a scar you can point to. Just stone, doing what stone was asked to do, keeping a secret it was never asked to keep. Morgan Miller: That is the horror of it. Not the explosion with a face. The fire without one. Morgan Miller: I'm Morgan Miller, and this has been Nuclear Shadows. Morgan Miller: A big thank-you to floof tags dot com for sponsoring the show. Morgan Miller: Visit our website, nuclear shadows pod dot com, for more information.