Fuel failure is a breach of what?

• A. A breach of the fuel rod cladding integrity, releasing fission products into reactor coolant
• B. A rupture of the reactor pressure boundary
• C. A failure of the control rod drive mechanism
• D. A failure to insert control rods

Answer: (A)

Fuel failure means the protective barrier around the fuel pellets—the cladding—has been breached. The cladding is the primary containment that keeps fission products inside the fuel rod. When it fails, those fission products can enter the reactor coolant, which is why fuel failure is defined by a loss of cladding integrity. This is different from a rupture of the reactor pressure boundary, which would involve the outer coolant system boundary and is far more extreme. Problems with the control rod drive mechanism or with inserting control rods affect reactivity control, not the containment of fission products. So the breach in question is the fuel rod cladding integrity.