Name a common fissionable material used in naval nuclear reactors.

Uranium-235 is a common fissionable material used in naval nuclear reactors due to its favorable properties for sustaining a nuclear chain reaction. It has a relatively low neutron absorption cross-section, allowing for efficient fission when subjected to thermal neutrons, which are the kind typically produced in the reactors. This isotope makes up about 0.7% of natural uranium and is enriched to increase its proportion for use in reactor fuel, making it suitable for the high power and energy density required in naval propulsion systems.

In contrast, Plutonium-238, while also fissionable, is primarily used in radioisotope thermoelectric generators rather than in traditional fission reactors due to its short half-life and the type of applications it serves. Thorium-232 is fertile rather than directly fissionable; it can be converted into the fissile isotope Uranium-233 in a reactor, but it is not used directly as a fuel in naval reactors. Californium-252 is a fissionable material as well, but it is not feasible as a fuel in reactors due to its high radioactivity and the complexity of obtaining and handling it. Thus, Uranium-235 stands out as the most practical and widely utilized fissionable