Not all the Uranium extracted from the ore can be used as fuel for plant for carrying out the fission reaction. Natural uranium consists of 99.3% of 23892U and only 0.7% of 23592U. Out of these isotopes, 23592U is used in fission reaction

Materials such as 23392U, 23592U,and 23994Pu are called fissile material or fissionable materials. This material is required to carry out the fission reaction.

Materials such as 23892U and 23290Th which occur in nature are called fertile materials. Fissile materials (23392U, 23994Pu ) can also be artificially be produced using fertile materials.