Debris-induced clad failure is commonly caused by what scenario?

• A. Foreign materials exclusion (FME) practices failing, debris in loop causing cladding damage
• B. Debris causing chemical corrosion of cladding
• C. Thermal fatigue of the reactor vessel
• D. Boron dilution in the coolant

Answer: (A)

Debris-induced cladding failure comes from physical damage to the fuel rod outer layer caused by debris in the reactor coolant. When Foreign Materials Exclusion practices fail, debris can enter the primary loop and circulate around the fuel assemblies. The debris can rub, gouge, or abrade the cladding as flow moves past it, potentially causing a breach. This mechanical damage path is the direct reason debris in the loop is linked to clad failure, which is why this scenario—debris in the loop following a lapse in FME—best explains the problem.

Chemical corrosion isn’t the primary mechanism here, and thermal fatigue of the reactor vessel or boron dilution of the coolant affect other aspects (structure integrity over time or reactor reactivity, respectively) rather than the direct mechanical damage to cladding caused by debris.