Thorium-232
Thorium-232 (Th-232) is the primary isotope of thorium, comprising nearly 100% of natural thorium. It is fertile and breeds fissile uranium-233 via neutron capture.
Th-232 decays to protactinium-233 then U-233, which fissions like U-235 but with fewer long-lived waste products. Thorium resources exceed uranium by 3-4 times. It requires a driver fissile material to initiate the cycle in reactors.
Why it matters now
Thorium cycles attract investment for waste reduction in 2025-2026 SMRs. Pilot projects address HALEU bottlenecks by leveraging abundant Th-232.