Study on repairing defects in S32101 duplex stainless steel clad plates for spent fuel storage pools in nuclear power plants using underwater local dry laser fillet welding with filler wire

Abstract To address the deficiencies in the fillet welding position of the clad plates in the simulated spent fuel pool, an underwater test platform was designed for local dry laser fillet welding under both normal and high-pressure environments. This study focused on multi-layer and multi-pass (MLMP) welding repairs, specifically examining the local underwater laser dry fillet welding process using filler wire made of duplex stainless steel S32101 for third-generation nuclear power stations in air environment (AE), underwater environment (UE), and high-pressure underwater environment (HPUE). The analysis included the microstructure, ferrite content, phase composition, chemical composition, microhardness, and localized corrosion resistance of the fillet welds across the three environments. The main conclusions are as follows: under HPUE, the grain size is the smallest, the cooling rate is the fastest, and the weld consists of intragranular austenite (IGA), grain boundary austenite (GBA) and widmanstätten austenite (WA); the ferrite content in the heat-affected zone (HAZ) is greater than that in the weld zone, with the highest ferrite content observed in the HPUE; the full width at half maximum (FWHM) of d (110) and γ (111) varies across different environments; the manganese (Mn) content in HPUE is low; the hardness of the weld zone is the highest, followed by the HAZ, while the base metal (BM) exhibits the lowest hardness; and the pitting corrosion resistance in HPUE is the strongest, attributed to the rapid cooling rate and the pressure of nitrogen (N2) gas velocity.