About twenty plutonium isotopes have been discovered and described. Except for 244Pu, all these isotopes are artificial isotopes. The main isotopes, which have to be considered in the fuel cycle of all commercial light water reactors, are:
- 238Pu. 238Pu belongs to the group of fertile isotopes. 238Pu decays via alpha decay to 234U with a half-life of 87.7 years. 238Pu generates very high decay heat and has a very high rate of spontaneous fission.
- 239Pu. 239Pu belongs to the group of fissile isotopes. 239Pu decays via alpha decay to 235U with a half-life of 24100 years. This isotope is the principal fissile isotope in use.
- 240Pu. 240Pu belongs to the group of fertile isotopes. 240Pu decays via alpha decay to 236U with a half-life of 6560 years. 240Pu has a very high rate of spontaneous fission and a high radiative capture cross-section for thermal and resonance neutrons.
- 241Pu. 241Pu belongs to the group of fissile isotopes. 241Pu decays via negative beta decay to 241Am with a half-life of 14.3 years. This fissile isotope decays to non-fissile isotope with a high radiative capture cross-section for thermal neutrons. An impact on the reactivity of nuclear fuel is obvious.
- 242Pu. 242Pu belongs to the group of non-fissile isotopes. 242Pu decays via alpha decay to 238U with a half-life of 37300 years. 242Pu has a very high spontaneous fission rate, but its quantity in the irradiated nuclear fuel is relatively low.