Breeder reactors in nuclear engineering: Do special breeder reactors provide a net gain of fissionable (fissile) material over their operating cycle?

Introduction / Context:
Breeder reactors are designed to “breed” more fissile material than they consume by converting fertile isotopes into fissile ones. Understanding this principle is central to fuel-cycle engineering and long-term nuclear resource utilisation.

Given Data / Assumptions:

• Fertile isotopes include U-238 and Th-232.
• Fissile isotopes produced include Pu-239 from U-238 and U-233 from Th-232.
• Net gain means bred fissile mass exceeds fissile mass consumed over a defined period (breeding gain > 0).

Concept / Approach:

In a breeder, excess neutrons from fission are captured by fertile nuclei, transmuting them through beta decay chains into fissile isotopes. Blanket assemblies surrounding the core optimise absorption and recovery of bred material, enabling a breeding ratio ≥ 1.

Step-by-Step Solution:

Verification / Alternative check:

Fast breeder reactors (e.g., sodium-cooled) historically demonstrated breeding ratios above unity. Thermal breeders (thorium–U-233 cycles) can also approach unity with suitable moderators and reprocessing technology.

Why Other Options Are Wrong:

Limiting to fusion is incorrect; breeding is a fission-fuel-cycle concept. Heavy water moderates well but is not a prerequisite for breeding. “Only at zero power” contradicts the need for neutron flux to breed.

Common Pitfalls:

Confusing fissile with fertile; assuming all reactors are breeders; overlooking reprocessing needs to realise the bred fuel in practice.

Final Answer:

True