Chemistry-induced fuel failures are caused by which factor?

• A. Adverse chemical conditions in the coolant
• B. Debris in the coolant
• C. PCI
• D. Thermal fluctuations

Answer: (A)

Chemistry-induced fuel failures come from the coolant environment becoming unfavorable enough to attack the fuel cladding and related materials. When the coolant chemistry is out of spec, corrosion of the zirconium alloy cladding accelerates, oxide scales thicken, and hydrogen can be absorbed into the metal. This hydrogen uptake can embrittle the cladding, reduce its ductility, and make it more prone to cracking under normal stress or during power changes. In short, the chemical state of the coolant directly drives material degradation that can breach the fuel rods and release fission products.

Other factors listed are more about physical or mechanical issues rather than chemistry. Debris in the coolant causes mechanical damage from foreign objects. Pellet-cladding interaction involves thermal and mechanical stresses from fuel pellet swelling against the cladding rather than the chemical environment. Thermal fluctuations cause stress and fatigue through temperature changes, again a mechanical effect rather than chemical degradation.