What is Primary Water Stress Corrosion Cracking (PWSCC) and where is it most often observed in LWRs?

• A. Intergranular cracking of nickel-based alloys in the reactor primary coolant, commonly in welds and bends of the primary circuit.
• B. Surface cracking due to chemical attack on cladding.
• C. Transgranular cracking in steel.
• D. Pitting corrosion on stainless steel.

Answer: (A)

PWSCC is cracking that occurs in susceptible nickel-based alloys when they are under tensile stress in the high-temperature, high-purity water of the reactor’s primary coolant. The cracks propagate along grain boundaries (intergranular mode) rather than through the grains themselves. In light water reactors, this type of cracking most often shows up in components of the reactor coolant system made of nickel-based alloys and in areas with high tensile stresses, especially welds and bends of the primary circuit where residual stresses are present.

Other options describe different phenomena: surface chemical attack on cladding is not PWSCC; transgranular cracking in steel is a different material and cracking mode; pitting on stainless steel is a separate corrosion mechanism.