Which statement best captures why zirconium-based alloys are chosen for cladding in LWRs?

• A. They offer excellent high-temperature ductility.
• B. They have very low neutron absorption cross-section and good corrosion resistance in reactor coolant.
• C. They are the most economical material available.
• D. They catalyze fission product decay.

Answer: (B)

The key idea is that cladding in light water reactors must both let neutrons through efficiently and stand up to the harsh reactor coolant environment. Zirconium-based alloys meet these needs because they have a very low neutron absorption (capture) cross-section, so they don’t steal neutrons needed for fission. At the same time, they form a stable, protective oxide layer in hot reactor water, giving excellent corrosion resistance and limiting hydrogen uptake that can embrittle the material. This combination preserves the reactor’s neutron economy and keeps the fuel cladding intact over time. Other options don’t offer this same balance: materials with higher neutron absorption would reduce reactor efficiency, and the stated alternatives don’t capture the essential compatibility with hot water.