Correct Answer

Concept & PrincipleElectricalPower Generation

Option B

Quick Summary:

Naturally occurring uranium is primarily composed of three isotopes: $U_{238}$ , $U_{235}$ , and $U_{234}$ . The isotope $U_{235}$ is the only naturally occurring fissile material, and it constitutes approximately 0.72% (commonly simplified to 0.7%) of natural uranium by mass.

💡 Explanation

🔢 Key Formulas

$N_{U235} \approx 0.0072 \times N_{total}$ — Atomic fraction of $U_{235}$ in natural uranium.

⚙️ Working Principle

Natural uranium is composed of roughly 99.27% $U_{238}$ , 0.72% $U_{235}$ , and trace amounts of $U_{234}$ . Because $U_{235}$ is the isotope that sustains the chain reaction in nuclear fission reactors, it is often enriched (increasing its concentration to 3–5%) to be used effectively as fuel in Light Water Reactors (LWRs).

📌 Key Points

▸
Natural uranium consists almost entirely of the isotope $U_{238}$ .
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Only $U_{235}$ is fissile, meaning it can sustain a nuclear chain reaction with thermal neutrons.
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Enrichment processes are required for most commercial nuclear reactors to achieve a higher $U_{235}$ concentration.

✅ Advantages

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Natural uranium is abundant in the Earth's crust.
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Used directly in CANDU-type heavy water reactors without enrichment.

❌ Disadvantages / Limitations

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Low concentration of fissile $U_{235}$ necessitates enrichment for light water reactors.
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Requires complex chemical separation/enrichment processes for industrial use.

🛠️ Applications / Uses

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Nuclear power plant fuel cycle.
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Research reactors.
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Nuclear weapon development (highly enriched).

📄 Additional Information

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Standard value: Natural uranium contains ~99.27% $U_{238}$ and ~0.72% $U_{235}$ .
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Option B (0.7) is the standard approximation used in nuclear engineering textbooks.

📊 Diagram / Illustration

✅

B is correct — Naturally available uranium contains approximately 0.72% of the fissile isotope $U_{235}$ .

Core Concepts Used

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Isotopes of Uranium Fissile vs Fertile material Nuclear fuel cycle

💡 EXAM TIP

Always distinguish between natural uranium (0.7% $U_{235}$ ) and low-enriched uranium (3-5% $U_{235}$ ) used in standard light water reactors.

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