ABSTRACT
Only fissile isotopes can be used directly in nuclear fission for generating power. Fertile isotopes have to be rendered fissile first, before being used to produce nuclear fission. Uranium has two isotopes – fissile isotope 235U with an abundance of about 0.7%, and fertile isotope 238U with an abundance of about 99.3%. Neutron absorption in 238U produces the fissile plutonium isotope, 239Pu. On the other hand, thorium has no fissile isotope, but consists entirely of fertile isotope 232Th which has to be converted to fissile 233U through neutron absorption before being used for nuclear fission. 233U produces the most neutrons per neutron absorption at thermal energies (slow neutrons) and is hence superior to both 235U and 239Pu as nuclear fuel in the common light water thermal reactors.
