Reflector performance in reactor physics Reflectivity of a reflector is defined as the fraction of neutrons that, after entering the reflector, are returned (scattered back) into the reactor core. Is this definition correct?

Introduction / Context:
Neutron reflectors surround many reactor cores to reduce neutron leakage, improving economy and flattening the flux. The metric used to describe how effectively a reflector returns neutrons is its reflectivity.

Given Data / Assumptions:

• Reflector is a non-fueled region adjacent to the core.
• Neutrons migrate into the reflector via diffusion.
• Some neutrons scatter back; others are absorbed or escape.

Concept / Approach:

Reflectivity is indeed defined as the fraction of neutrons entering the reflector that return to the core. High-scattering, low-absorption materials (e.g., graphite, heavy water, beryllium) tend to have higher reflectivity. This improves neutron economy by reducing the required fuel loading for criticality or by boosting the effective multiplication factor.

Step-by-Step Solution:

Verification / Alternative check:

Diffusion-theory solutions with reflected boundary conditions show increased flux near the edge and an effective albedo that captures this “return fraction,” consistent with the verbal definition.

Why Other Options Are Wrong:

Limiting correctness to a specific material or fuel enrichment misunderstands that reflectivity is a property/metric applicable to any reflector material.

Common Pitfalls:

Confusing reflectivity with moderator effectiveness; a reflector can also moderate, but its primary role here is to return neutrons, not necessarily slow them to thermal energy.

Final Answer:

Agree