# Table 1 Properties of key reactor isotopes

Property U-235 U-238 Pu-239 Pu-241
Thermal (0.0253 eV) neutron induced fission cross-section20 582.6 ± 1.1 barns 0.000003 barns 748.1 ± 2.0 barns 1011.1 ± 6.2 barns
Thermal energy per fission21 201.7 ± 0.6 MeV 205.0 ± 0.9 MeV 210.0 ± 0.9 MeV 212.4 ± 1.0 MeV
1. Equation (2) relies upon the energy released per fission, as well as the cross-section for fission, for each isotope. These quantities are presented above for isotopes which typically account for 99.9% of the power in a reactor core: U-235, U-238, Pu-239, and Pu-24110