Effect of Heat Treatment on Corrosion Behavior of Alloy 690 and Alloy 693 in Simulated Nuclear High-Level Waste Medium

Abstract

Nickel-based alloys are being considered as candidate materials for the storage of high-level waste generated from the reprocessing of spent nuclear fuel. In the present investigation, Alloy 690 (UNS N06690) and Alloy 693 (UNS N06693) were assessed using the potentiodynamic anodic polarization technique for the corrosion behavior in the solution-annealed and sensitized conditions, in 3 M nitric acid (HNO3) and simulated high-level waste (HLW) at 25°C and 50°C. From the results of the investigation, it was found that the polarization curves for the solution-annealed specimens were characterized by a long passive range and low passivation current density, at 25°C. Increasing solution temperature to 50°C led to a corresponding increase in corrosion potential as well as passivation current density. The solution-annealed specimen showed improved corrosion resistance compared to the sensitized specimen in both media, for both alloys. Double-loop electrochemical potentiokinetic reactivation (DL-EPR) test was carried out for both solution-annealed and sensitized Alloy 690 and Alloy 693 in 0.5 M sulfuric acid (H2SO4) containing 0.0001 M potassium thiocyanate (KSCN), to measure the degree of sensitization (DOS). Microstructural examination was carried out by optical microscopy and scanning electron microscopy (SEM) after electrolytic etching. The results of the present investigation are discussed in the paper.