The Untapped Potential of Thorium
Thorium-232 is far more abundant than uranium-235, which powers most of today’s nuclear reactors. It’s three to four times more common in Earth’s crust, and almost 500 times more abundant when you consider only the fissile uranium we currently use.
Thorium itself isn’t fissile, meaning it can’t start a nuclear chain reaction on its own. But when seeded with a small amount of uranium-235 or plutonium-239, thorium absorbs a neutron, transforms into thorium-233, then decays into uranium-233, a fissile material. This process not only sustains a chain reaction but breeds more fuel than it consumes. That’s the holy grail of nuclear energy: a breeder reactor.
A Second Nuclear Age?
Back in the 1960s, scientists at Oak Ridge National Laboratory successfully ran a molten salt reactor for over 15,000 hours. It used thorium, bred its fuel, and produced 8 MW of heat consistently. But the project was shelved in favor of other nuclear designs, and molten salt technology faded into obscurity. Alvin Weinberg, the physicist who championed thorium, was even fired for his persistence.
Today, that dream is being revived. A startup from Denmark, Copenhagen Atomics, is working to commercialize the breeder reactor Weinberg once envisioned. Their goal? A small modular reactor (SMR) that runs on thorium, fits in a shipping container, and operates safely and autonomously for years.
Compact Reactors with Big Ambitions
Copenhagen Atomics’ reactors are designed to be mass-produced, with the company aiming to build one per day on an assembly line. Each unit is modular, fitting inside a standard 40-foot shipping container, and can be deployed in clusters depending on the desired energy output. The strategy mirrors the scale-and-repeat model of modern manufacturing, avoiding the ballooning costs and delays common in traditional nuclear projects.
This plug-and-play approach means smaller, more flexible nuclear facilities—especially useful in countries with no prior nuclear infrastructure. The company has already signed its first customer: Indonesia, where the reactors will help produce hydrogen and ammonia.
Safe by Design, Not by Luck
One of the most compelling aspects of molten salt reactors is their safety profile. Unlike traditional nuclear reactors that rely on solid fuel rods and high-pressure water cooling, MSRs use liquid fuel and operate at atmospheric pressure. This eliminates the risk of steam explosions and catastrophic meltdowns.
Copenhagen Atomics has also engineered a “freeze plug” system. If the reactor overheats, a plug of frozen salt melts, and the molten fuel drains into a backup tank, stopping the reaction automatically. This “walkaway safety” feature means the reactor can shut down safely even if all human operators vanish—a major win in nuclear engineering.
Tackling Nuclear Waste—and Legacy Waste too
Thorium reactors produce far less long-lived radioactive waste compared to conventional uranium reactors. Traditional nuclear waste can remain hazardous for tens of thousands of years. In contrast, waste from thorium-based systems decays within a few hundred years—short enough to store above ground safely.
Even more impressively, thorium reactors can consume waste from existing uranium reactors. Copenhagen Atomics plans to integrate this capability, making their reactors not just fuel breeders, but also nuclear waste burners—a potential game-changer for long-term waste management.
The Global Race: Denmark vs. China
While Copenhagen Atomics is preparing for a full-scale prototype test in Switzerland in 2026, China has already taken bold steps forward. In 2024, Chinese researchers ran a molten salt reactor using thorium and uranium at full power for ten days. In early 2025, they refueled the reactor without shutting it down—a major milestone.
Both projects are racing toward the same goal: a self-sustaining breeder reactor that produces more fissile fuel than it consumes. If achieved, this would allow each reactor to eventually produce enough fuel to power another, doubling nuclear capacity every decade or two.
Engineering Hurdles Remain
The path isn’t entirely smooth. Molten salt is highly corrosive, especially at the temperatures required (around 700°C). Pumps, pipes, and reactor vessels must withstand not only the chemical assault but also intense radiation. Copenhagen Atomics has developed pumps that levitate moving parts with magnetic bearings to minimize wear. The custom steel alloy used in their reactors is designed to last five years before needing replacement—at which point the entire reactor module can be swapped like a battery.
While this might sound costly, it also allows for faster innovation. “Every five years, you get to upgrade your reactor,” says CEO Thomas Jam Pedersen. “That’s a big step up from 50-year-old technology running in today’s plants.”
A New Business Model for Nuclear Power
Perhaps just as revolutionary as the technology is Copenhagen Atomics’ business model. Instead of selling reactors, they plan to build, operate, and decommission each unit themselves. Customers simply pay for the heat or electricity generated. This hands-off approach could help bring nuclear energy to regions where regulatory or technical hurdles have previously kept it out.
By taking full responsibility for installation and safety, Copenhagen Atomics hopes to make thorium-powered nuclear energy as accessible as solar or wind. And with energy costs projected to drop as low as $20–40 per MWh, the economics could rival or even beat renewables—especially for industries that need constant, high-temperature heat.
The world has long been searching for energy sources that are clean, scalable, safe, and affordable. Thorium-powered molten salt reactors check nearly every box—and in 2025, we’re closer than ever to seeing them in action. While challenges remain, particularly around materials and licensing, momentum is building.
Whether Denmark or China gets there first, one thing is clear: thorium is no longer just a forgotten side story in the nuclear age. It’s poised to be one of its most important chapters.
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