GENERAL KNOWLEDGE

Detailed explanation-1: -Thorium-232, the only naturally occurring isotope of thorium, is a fissionable material but not a fissile one, meaning that it needs high-energy neutrons to undergo fission-the splitting of atomic nuclei which releases energy that is used for electricity generation.

Detailed explanation-2: -Thorium (Th-232) is not itself fissile and so is not directly usable in a thermal neutron reactor.

Detailed explanation-3: -Uranium-233 (233U or U-233) is a fissile isotope of uranium that is bred from thorium-232 as part of the thorium fuel cycle. Uranium-233 was investigated for use in nuclear weapons and as a reactor fuel.

Detailed explanation-4: -By contrast, the binding energy released by uranium-238 absorbing a thermal neutron is less than the critical energy, so the neutron must possess additional energy for fission to be possible. Consequently, uranium-238 is a fissionable material.

Detailed explanation-5: -A material, which is not itself fissile (fissionable by thermal neutrons), that can be converted into a fissile material by irradiation in a reactor. There are two basic fertile materials: uranium-238 and thorium-232.