NATURAL CRACK GROWTH IN BWR SHROUD SUPPORT DISSIMILAR METAL WELD JOINTS

The Boiling Water Reactor (BWR) shroud support dissimilar metal (DM) joints, which are made of Alloy182 nickel based alloy weld material, are susceptible to Intergranular Stress Corrosion Cracking (IGSCC). IGSCC of these weld joints is an industry wide issue that is receiving constant attention from both power plant operators and regulatory agencies. Crack growth due to IGSCC in the shroud support DM weld joints is typically evaluated based on conventional idealized crack shape instead of natural crack shape dictated by the crack tip stress intensity factors calculated along the entire crack front. Due to the complexity in the geometry and stress field at these weld joints, the use of natural crack shape as the crack propagates would provide a more realistic assessment of crack growth and structural integrity of the shroud support dissimilar metal weld joints. This paper describes the simulation of natural crack growth due to IGSCC in the shroud support DM weld joints through the use of advanced finite element fracture mechanics techniques. Typical normal operating stresses including welding residual stresses at these weld joints were considered in the IGSCC crack growth simulation. A comparison of the crack growth results between the use of idealized and natural crack shape was made to assess the impact on the structural integrity of the BWR shroud support DM weld joints.