uranium containing the mixture of isotopes occurring in nature; uranium whose content in uranium 235 is less than the normal; thorium; any of the foregoing in the form of metal, alloy, chemical compound or concentrate;
Nuclear fission fuels are classified as fertile or fissile by the behaviour or their nuclei in fission reactions. The fertile fuels are those whose nuclei, if they react with a neutron, will be likely to capture it and undergo transmutation into the nuclei of fissile fuels. Uranium-238 is them most commonly used fertile fuel. It decays on absorption of a neutron and loss of a beta-particle into plutonium-239.
