Thorium Reactor History and Oak Ridge Tennessee

Where is Thorium's Commercial Breakthrough?

Why, when thorium has so much to offer, remain only experimental reactors? The answer begins in the 1960s at Oak Ridge National Laboratory, where physicist Alvin Weinberg led a team that developed the molten salt reactor using thorium. Yet, despite its advantages thorium plants have yet to reach commercialisation.

The Thorium Fuel Cycle

Thorium is a naturally occurring, slightly radioactive metal. It's about three times more abundant than uranium — the element used in today's nuclear reactors. More than 99% of naturally occurring uranium is non-fissile. Thorium is a precursor to uranium-233, a fissile material. The thorium fuel cycle begins when thorium-232 absorbs a neutron. This doesn't split the thorium atom; instead, it turns into thorium-233. Thorium-233 has a half-life of about 22 minutes, decaying into protactinium-233, which then turns into uranium-233. This uranium-233 can sustain a nuclear chain reaction and generate energy. This is how a reactor that "breeds" thorium works. This cycling process ensures that nearly all the thorium can be used as fuel, making it a more efficient fuel source than uranium. Unlike uranium, thorium cannot sustain a nuclear chain reaction on its own—it must be converted into uranium-233 first.

Reasons for Delayed Adoption

How politics impeded physics in Tennessee

In 1965, Weinberg's team at Oak Ridge switched on the Molten Salt Reactor Experiment (MSRE), the first reactor to run on uranium-233 made from thorium. It ran until 1969, proving the concept but not achieving full-scale thorium breeding. The Atomic Energy Commission, however, backed a different design. Despite Weinberg's advocacy for his design, he was pushed out of the lab in 1973.

Challenges with Weathering the Neutron Storm

A breeder reactor must withstand an intense neutron flux. Neutrons hitting thorium-232 only convert it to thorium-233; they do not split it. This means thorium fuel must endure prolonged neutron bombardment without degrading, which poses significant engineering challenges. Today, about 0.7% of mined uranium is the fissile isotope uranium-235. In contrast, thorium-232, the isotope that can turn into a fissile material, makes up nearly 100% of natural thorium. This abundance makes thorium an attractive alternative. While thorium has significant potential, its commercial use remains elusive. This is partly due to the engineering challenges of building a reactor that can withstand the intense neutron flux required to convert thorium into a usable fuel. Additionally, the politics of nuclear energy have historically favored uranium-based designs.

Small Modules and Big Promise

Modern thorium reactors often focus on smaller, modular designs. These reactors can be factory-built and transported to sites, reducing construction time and costs. Additionally, thorium reactors can use fuel more efficiently, potentially extending fuel supplies and reducing waste.

What to Expect in Thorium Nuclears

A common misconception is that thorium reactors are cleaner or safer than conventional reactors. In reality, the primary advantage of thorium is its abundance and potential for more efficient fuel use, but it shares similar safety and waste challenges as uranium reactors. To get a start in thorium, look for experimental or demonstration reactors. These small-scale projects often use thorium in innovative ways, such as in molten salt reactors or other advanced designs. Keeping an eye on regulatory developments and policy shifts can also provide insights into the future of thorium reactors, as government support can significantly impact their deployment.