Which of the following is not a naturally occurring nuclear fuel?

Question

Examoogle · Accepted Answer

Plutonium-239

Explanation: Plutonium-239 is an artificial fissile isotope created in nuclear reactors through neutron capture by Uranium-238, whereas Uranium-238 and Thorium-232 are naturally occurring primordial isotopes. Because it does not exist in significant quantities in nature, it is classified as a synthetic nuclear fuel.

Working Principle: Plutonium-239 is produced via the process of fertile-to-fissile conversion. When a nucleus of $^{238}_{92}U$ captures a neutron, it forms $^{239}_{92}U$, which undergoes two successive beta decays to become $^{239}_{94}Pu$. This reaction is represented as: $^{238}_{92}U + ^{1}_{0}n ightarrow ^{239}_{92}U \xrightarrow{\beta^-} ^{239}_{93}Np \xrightarrow{\beta^-} ^{239}_{94}Pu$.

Key Formulas: $^{238}_{92}U + ^{1}_{0}n ightarrow ^{239}_{92}U$; $^{239}_{92}U \xrightarrow{\beta^-} ^{239}_{93}Np + e^- + \bar{
u}_e$; $^{239}_{93}Np \xrightarrow{\beta^-} ^{239}_{94}Pu + e^- + \bar{
u}_e$

Key Points: Uranium-238 is the most abundant natural isotope of uranium (~99.27%).; Thorium-232 is a naturally occurring fertile material that can be converted into U-233.; Plutonium-239 is a fissile material primarily produced in breeder reactors.; The presence of synthetic fuel indicates human intervention in nuclear transmutation.

Advantages: High energy density in breeder reactor cycles.; Utilization of otherwise non-fissile U-238 fertile material.

Disadvantages: High radiotoxicity and proliferation risk.; Requires complex chemical reprocessing to separate from irradiated fuel.

Applications: Nuclear weapon manufacturing.; Mixed Oxide (MOX) fuel for power generation.

Additional Info: Note: Thorium-233 is a highly unstable intermediate decay product; the stable naturally occurring isotope is Thorium-232.. Option A (U-238) is the most abundant natural uranium isotope.. Option B (Thorium-233) is often conflated with Thorium-232; however, both are categorized under natural decay chains.

Answer: C is correct — Plutonium-239 is a synthetic isotope produced via neutron irradiation of Uranium-238 in a nuclear reactor, rather than existing as a naturally occurring element in the earth's crust.

Exam Tip: Always distinguish between 'Fissile' (can sustain chain reaction) and 'Fertile' (can be converted to fissile) materials; U-238 is fertile, while Pu-239 is fissile.

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