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.
Laser surface melting of Ni based superalloys (alloys 600, 690 and 693) was carried out to study the effect of surface modification on the corrosion behaviour in simulated nuclear high level waste (HLW) and chloride medium. Surface characterisation was performed by optical microscopy, scanning electron microscopy and X-ray diffraction. The alloys exhibited cubic crystal system and cellular microstructure. Double loop electrochemical potentiokinetic reactivation test in 0?5M H 2 SO 4 containing 0?0001M KSCN showed a low degree of sensitisation compared to the solution annealed specimens. Laser surface melting resulted in enhancement of corrosion resistance of the alloys in simulated HLW and chloride medium when compared to as received and solution annealed specimens; nevertheless, no discernable difference was found between the laser surface melted alloys 600, 690 and 693 in simulated HLW. However, the laser surface melted alloy 690 showed superior pitting corrosion resistance. The results of the present investigation are discussed in this paper.
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