Uranium-238
Uranium-238 (U-238) is the most abundant isotope in natural uranium at 99.27%. It is fertile, not fissile, but captures neutrons to breed plutonium-239.
U-238 forms over 94% of spent LWR fuel and is used in breeder reactors. In thermal reactors, it absorbs neutrons without fissioning, contributing to neutron economy. Depleted uranium (mostly U-238) has applications in MOX fuel and shielding. Fast reactors fission U-238 directly.
Why it matters now
U-238 recycling via fast reactors or MOX gains traction amid 2025 uranium supply constraints. It supports fuel efficiency for SMRs targeting data centers.