Overview
This lecture covers the promise and development of thorium molten salt breeder reactors, focusing on Copenhagen Atomics' efforts to commercialize small, modular, walkaway-safe nuclear reactors for cleaner and more abundant energy.
The Promise of Thorium Reactors
- Thorium reactors can breed more fuel than they consume, making nuclear energy cheaper and more abundant.
- Thorium is ~500 times more abundant than reactor-grade uranium-235.
- Thorium cannot sustain a chain reaction alone, but absorbs a neutron to become uranium-233, which is fissile.
- Self-sustaining breeder reactors could double nuclear capacity every few decades without depleting uranium reserves.
Copenhagen Atomics' Reactor Design
- Their reactors are small modular reactors (SMRs), designed for mass production and easy deployment.
- Each reactor fits in a 40-foot shipping container and operates as a sealed, self-maintaining unit.
- The core uses molten salt (containing thorium and uranium) at high temperatures and atmospheric pressure.
- Their “Onion Core” design uses layers: a molten salt core, heavy water moderator, and a breeding blanket for thorium.
Safety and Waste Management
- MSRs avoid meltdowns by operating at atmospheric pressure and using passive safety features like freeze plugs.
- Gamma radiation from uranium-232 in the fuel makes theft and weaponization difficult.
- Reactor operation and maintenance are fully remote to limit radiation exposure.
- Thorium reactor waste is shorter-lived, requiring only a few hundred years of storage above ground.
- Reactors can use waste from traditional reactors as startup fuel, helping reduce legacy nuclear waste.
Engineering and Commercialization Challenges
- MSRs face material challenges: heat, corrosive salts, neutron bombardment, and intense gamma radiation.
- All reactor components are designed to last at least five years, after which the module is replaced.
- Fuel salt and heavy water are reused, while the module is swapped, enabling regular technology upgrades.
- Regulatory hurdles and licensing are major barriers to deployment.
- First full-scale prototype test planned at Switzerland’s Paul Scherrer Institute in 2026, aiming for commercial operation within a decade.
International Developments
- China has operated a thorium-based molten salt reactor at full power and demonstrated continuous operation, but true self-sustaining breeder reactors remain unproven.
- Copenhagen Atomics’ first customer is Indonesia, targeting direct industrial heat and hydrogen/ammonia production.
Key Terms & Definitions
- Thorium Reactor — A nuclear reactor using thorium-232 to breed fissile uranium-233, enabling more efficient fuel use.
- Molten Salt Reactor (MSR) — A reactor where nuclear fuel is dissolved in hot molten salt, acting as both fuel and coolant.
- Small Modular Reactor (SMR) — A compact, factory-built nuclear reactor designed for modular deployment.
- Breeder Reactor — A reactor that produces more fissile material than it consumes.
- Walkaway Safety — Passive safety feature allowing a reactor to safely shut down without human intervention.
Action Items / Next Steps
- Monitor progress of Copenhagen Atomics’ prototype reactor testing at Paul Scherrer Institute (planned for 2026).
- Review differences between thorium and traditional uranium reactor fuel cycles for next class.
- Prepare questions on molten salt reactor safety mechanisms for discussion.