Question

Enlist the nuclear fuels.

Answer 1

Nuclear fuels are materials that can be used to produce energy via nuclear fission. They are typically categorized into two main groups: fissile materials, which can sustain a nuclear chain reaction, and fertile materials, which can be converted into fissile materials.

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Primary Fissile Fuels

These isotopes can undergo fission with low-energy (thermal) neutrons, making them capable of sustaining a chain reaction in most common reactor types.

• Uranium-235 ($^{235}$U)
  * Significance: This is the only naturally occurring fissile isotope. It makes up about 0.72% of natural uranium. Most commercial nuclear reactors require uranium to be "enriched" to increase the concentration of U-235 to 3-5%. It is the most common nuclear fuel in the world.

• Plutonium-239 ($^{239}$Pu)
  * Significance: Plutonium-239 is not found in nature. It is created inside a nuclear reactor when an atom of Uranium-238 absorbs a neutron. It is a highly effective fissile fuel and is the primary fissile component in MOX (Mixed Oxide) fuel and breeder reactors.

• Uranium-233 ($^{233}$U)
  * Significance: Like plutonium, Uranium-233 is not found in nature. It is created from the fertile material Thorium-232. The thorium fuel cycle, which produces U-233, is considered a promising future technology due to the high abundance of thorium.

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Fertile Materials (Precursors to Fuel)

These isotopes are not fissile themselves but can be converted into fissile isotopes after absorbing a neutron. They are essential for "breeding" new fuel.

• Uranium-238 ($^{238}$U)
  Significance: The most abundant isotope of uranium, making up over 99.27% of natural uranium. When it absorbs a neutron, it becomes Plutonium-239. While not fissile with slow neutrons, it is fissionable* with high-energy (fast) neutrons, contributing a significant amount of the power in a typical reactor.

• Thorium-232 ($^{232}$Th)
  * Significance: A naturally abundant element (about 3-4 times more common than uranium). When it absorbs a neutron, it undergoes a series of decays to become the fissile Uranium-233. It is the basis for the thorium fuel cycle.

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Summary Table

| Category | Isotope | Natural/Artificial | How it's Used |
| :--- | :--- | :--- | :--- |
| Fissile | Uranium-235 ($^{235}$U) | Natural | Primary fuel in most light-water reactors. |
| Fissile | Plutonium-239 ($^{239}$Pu) | Artificial | Created from U-238. Used in MOX fuel and breeder reactors. |
| Fissile | Uranium-233 ($^{233}$U) | Artificial | Created from Th-232. Key to the thorium fuel cycle. |
| Fertile | Uranium-238 ($^{238}$U) | Natural | Transmutes into Pu-239. The bulk of natural uranium. |
| Fertile | Thorium-232 ($^{232}$Th) | Natural | Transmutes into U-233. A potential future fuel source. |

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Future & Experimental Fuels (Nuclear Fusion)

While the term "nuclear fuel" almost always refers to fission fuels, materials for nuclear fusion are also technically nuclear fuels. This process, which powers the sun, involves fusing light atoms together.

• Deuterium ($^{2}$H or D): A stable, heavy isotope of hydrogen found in seawater.
• Tritium ($^{3}$H or T): A radioactive isotope of hydrogen that must be produced, often from lithium.

The most promising reaction for future fusion power plants is the Deuterium-Tritium (D-T) reaction, though this technology is still in the experimental stage.