Constructing a Grain Boundary Sensitization-Embrittlement Map for Type 310S Stainless Steel Fuel Cladding in the Canadian SCWR Concept

The goal of this study is to identify the predominant grain boundary factor (sensitization versus embrittlement) that controls the intergranular stress corrosion cracking (IGSCC) susceptibility of austenitic stainless steel Type 310S exposed to supercritical water (SCW). Pre-treatments involving thermal ageing at high temperature in combination with plastic deformation were applied to induce specific types of grain boundary structure instability such as solute segregation, secondary phase precipitation and dislocation channeling. Each of these structural instabilities was independently assessed in terms of the susceptibility to both grain boundary sensitization and embrittlement in order to construct a 2-D property assessment grid Grain boundary sensitization was assessed using the double loop electrochemical potentiokinetic (DL-EPR) technique. Grain boundary embrittlement was assessed using nano-indentation and nano-scratching techniques. The susceptibility of the various degraded material will be evaluated using slow strain rate testing (SSRT) in 25 MPa SCW at 500°C with 8 ppm dissolved oxygen in an autoclave flow loop (200 mL/min.) facility. This paper presents and discusses the results of our attempt to link the IGSCC susceptibility to a particular grain boundary degradation signature.