Production route for plutonium-239 (Pu-239): Which option correctly describes how Pu-239 is produced in nuclear fuel cycles?

Introduction / Context:
Plutonium-239 is a fissile isotope important in both thermal and fast reactor fuel cycles. Understanding its production path is foundational in nuclear engineering and safeguards discussions.

Given Data / Assumptions:

• Starting material: U-238 present in natural and enriched uranium fuel.
• Neutron irradiation occurs during reactor operation.
• Beta decay sequences transmute isotopes.

Concept / Approach:

Under neutron flux, U-238 captures a neutron to become U-239. U-239 is beta-unstable and decays to Np-239, which in turn beta-decays to Pu-239. The produced Pu-239 can fission with thermal neutrons, contributing to reactor power and enabling breeding in specific configurations.

Step-by-Step Solution:

Verification / Alternative check:

Spent fuel assays from light water reactors consistently show generated Pu isotopes from U-238 capture, confirming the pathway.

Why Other Options Are Wrong:

“Artificially” is too vague without the neutron-capture mechanism. Th-232 breeds to U-233, not Pu-239. Pu-239 is not a mined raw material. Fusion breeding concerns tritium, not plutonium.

Common Pitfalls:

Confusing thorium breeding (U-233) with plutonium breeding; assuming plutonium exists naturally in mineable quantities (only trace cosmogenic amounts occur).

Final Answer:

when U-238 is irradiated by neutrons (via U-239 → Np-239 → Pu-239)