Fuel cladding selection: which of the following materials is NOT used as a nuclear fuel cladding in power reactors?

Introduction / Context:
Fuel cladding provides the first barrier against fission product release and must combine low neutron absorption with corrosion resistance and mechanical integrity. Distinguishing cladding materials from control-rod absorbers prevents dangerous misconceptions in reactor materials engineering.

Given Data / Assumptions:

• Commercial power reactors historically use zirconium alloys or stainless steels as cladding.
• Advanced concepts explore ceramic composites, but conventional fleet practice is metal cladding.
• Cadmium is known as a strong neutron absorber for control rods and shields.

Concept / Approach:
Zircaloy and zirconium–niobium alloys are standard LWR/PHWR claddings because of low neutron absorption and good corrosion resistance in water. Stainless steel has been used in certain designs historically. Cadmium, by contrast, has a very high thermal neutron capture cross-section and is employed in control rods or as neutron poison—not as cladding surrounding fuel where low absorption is crucial.

Step-by-Step Solution:
List typical cladding: zirconium-based alloys; some designs used stainless steel.Consider ceramics: explored for accident-tolerant cladding but not traditional baseline.Identify cadmium as a neutron absorber material for control rods.Therefore, cadmium is not used as fuel cladding.

Verification / Alternative check:
Material specifications from reactor vendors consistently show zirconium alloys for cladding; cadmium appears in absorber components, confirming the role separation.

Why Other Options Are Wrong:

• Zircaloy and Zr–Nb: Canonical cladding materials.
• Stainless steel: Used in some earlier or specific designs.
• Ceramics: Investigational/advanced concepts; not the “not used” distractor compared to cadmium.

Common Pitfalls:
Assuming any corrosion-resistant metal could serve as cladding without considering neutron absorption; confusing absorber materials with cladding.

Final Answer:
Cadmium