Fuel enrichment check: the U-235 content of enriched uranium commonly used in light-water power reactors (e.g., early Tarapur BWR units) is approximately what percent?

Introduction / Context:
Light-water reactors (LWRs)—which include boiling water reactors (BWRs) and pressurised water reactors (PWRs)—use uranium fuel enriched in U-235 beyond its natural abundance (~0.71%). A typical commercial enrichment band balances reactivity, fuel cycle economics, and safety margins.

Given Data / Assumptions:

• LWR class reactors (e.g., Tarapur BWRs) historically used low-enriched uranium (LEU).
• LEU is defined as U-235 enrichment below 20%.
• Question asks for an approximate, representative value.

Concept / Approach:
Most LWR cores operate on fuel enriched to roughly 2–5% U-235. A commonly cited nominal value in introductory questions is about 3%. Heavy-water reactors (e.g., CANDU) can use natural uranium; fast reactors use plutonium-bearing fuel; research reactors may use higher enrichments depending on design and HEU-LEU conversion programs.

Step-by-Step Solution:
Identify reactor type as LWR (BWR at Tarapur).Recall typical U-235 enrichment range (2–5%).Select the closest representative value: ~3%.

Verification / Alternative check:
Vendor data and nuclear engineering texts align on ~3–5% for many LWR designs. Early Indian BWR units similarly operated with LEU in this range, often quoted as about 3% for pedagogy.

Why Other Options Are Wrong:

• 85% and 97%: Highly enriched uranium (HEU), not used in power LWRs.
• 50%: Also HEU; not typical for power generation.
• 20%: Upper bound of LEU definition; not standard for LWR cores.

Common Pitfalls:
Confusing natural uranium (0.71%) with LEU; assuming higher enrichment always means better performance without considering neutron economy and proliferation controls.

Final Answer:
3