How do breeder reactors produce more fissionable material than they consume?

Breeder reactors produce more fissionable material than they consume by utilizing fertile materials—isotopes that are not themselves readily fissionable but can be transformed into fissile materials through neutron capture and subsequent radioactive decay.12

In a fast breeder reactor, uranium-238 absorbs a neutron to become uranium-239, which then undergoes beta decay to form neptunium-239 and finally the fissionable isotope plutonium-239. Similarly, thermal breeder reactors use thorium-232 as fertile material, which captures a neutron and eventually decays into fissionable uranium-233.132

By converting these abundant fertile isotopes into new fissile fuel while simultaneously generating energy through the fission of existing fuel, the reactor effectively "breeds" more fissionable material than it consumes, thereby extending the available nuclear fuel supply.12