| dc.description.abstract | Corrosion related failures pose risk to the integrity of routinely cycled and permanent reactor components long before radiation damage alone adversely impact reactor performance. Compared to Light Water Reactors (LWRs), Molten Salt Reactors (MSRs) have not enjoyed a history of continuous engineering development and refinement. Hastelloy N, a nickel superalloy developed at ORNL explicitly for molten fluoride salt conditions, and 316SS, a widely used austenitic alloy, are among the leading candidates for immediate deployment in MSR systems. Data collected during initial development of Hastelloy N suffered from limitations in available microscopy and spectroscopy techniques, obfuscating the role of radiation damage and mechanical stress in the microstructural evolution of the alloy. 316SS, considered a more economical alternative to the nickel superalloy, is restricted by lower corrosion resistance and strength at high temperature. The present work bridges some of the nuanced gaps in knowledge related to Hastelloy N microstructural evolution, as well as evaluating the feasibility of coating systems for enhanced corrosion resistance for 316SS. Hastelloy N was exposed to light ion irradiation, micromechanical testing, and immersion corrosion using FLiNaK molten salt after either irradiation or static strain mounting using the three-point bending technique. 316SS, either coated using a modified cathodic cage plasma nitriding technique or mounted under static strain, was exposed to heavy ion irradiation. Several evaluation techniques were used including scanning electron microscopy (SEM), electron dispersive x-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and micromechanical pillar compression testing. The results show that, low-dose irradiation and subsequent elemental segregation and embrittlement, as well as tensile mechanical stress loading, have a deleterious effect on the corrosion resistance of Hastelloy N. Nickel coating on 316SS is demonstrated as highly radiation tolerant. Combination of irradiation and the three-point bending technique demonstrates a feasible pathway for further evaluation of alloys and coating systems for MSR applications. | |
