Fuel choice for BWRs: which nuclear fuel is most commonly used in a boiling water reactor (BWR)?

Introduction / Context:
Boiling water reactors (BWRs) are light-water reactors in which the reactor coolant water boils in the core to produce steam directly for the turbine. Fuel selection affects core design, reactivity control, and refueling strategies. Knowing the standard fuel type is basic industry literacy.

Given Data / Assumptions:

• BWRs use ordinary light water as both coolant and moderator.
• Light-water moderation has higher neutron absorption than heavy water.
• Commercial BWRs operate at large thermal powers with on-cycle boiling.

Concept / Approach:
Because light water absorbs neutrons more than heavy water, achieving criticality with natural uranium is impractical in a BWR. Therefore, BWR cores use low-enriched uranium (LEU), typically 3–5% U-235, assembled into fuel rods and bundles. While plutonium may be present in mixed-oxide (MOX) fuel in some reactors, the main and most common fuel specification remains LEU uranium dioxide.

Step-by-Step Solution:

Verification / Alternative check:
Vendor documentation and operating histories for BWR fleets show widespread use of LEU UO2 fuel, with some plants licensed for partial MOX loads under strict controls.

Why Other Options Are Wrong:

• Natural uranium: feasible with heavy-water moderators, not standard for BWRs.
• Plutonium metal/monazite sand/thorium metal: not the mainstream BWR fuel form or composition.

Common Pitfalls:
Assuming all reactor types can run on natural uranium; confusing BWRs with heavy-water designs like PHWR/CANDU.

Final Answer:
Enriched uranium