What is a fissile material?

• A. A fuel grade radioactive material which means it is capable of undergoing a nuclear chain reaction.
• B. A non-radioactive material used as a nuclear fuel.
• C. A material that can sustain a chemical reaction but not a nuclear chain reaction.
• D. A radioactive material used only for medical imaging.

Answer: (A)

Fissile material is a radioactive substance that can sustain a nuclear chain reaction when it absorbs a neutron. This means it can fission and release additional neutrons that propagate the reaction, which is why such materials are used as nuclear fuel. The phrase "fuel grade" signals suitability for use in reactors. Examples include uranium-235 and plutonium-239.

This differs from non-radioactive materials, which cannot undergo fission, and from materials that only participate in chemical reactions or are used for medical imaging purposes. Those cannot sustain a nuclear chain reaction, which is the defining property of fissile materials.