Investigation of Novel Nickel-Based Alloys for High Temperature Molten Salt Reactor Structural Applications

Molten chloride and fluoride salt fast reactors (MSR) are under active development because they offer several operational and safety advantages over other types of reactors. Modern designs require structural materials with superior corrosion, creep, thermomechanical fatigue, irradiation damage and Helium bubble and tellurium-induced grain boundary embrittlement resistance to high temperatures of 750-950¡C. Nickel-base alloys generally perform better than all other alloys studied to date, though none yet have the set of properties to meet these demanding conditions. We will report on the development of the next generation of nickel-base alloys based on the Ni-Mo-W-Cr-X system that combine solid solution strengthening with ordered and other precipitates for superior high temperature properties. An ICME approach is combined with a detailed experimental processing, testing, characterization, and modeling program. Results of the alloy design strategy, phase equilibria and transformations and evolution of microstructure and high temperature mechanical properties will be presented. Apart from investigation of several baseline commercial alloys (Haynes 244, Haynes 282, Haynes 214, Haynes 230 and Hastelloy C-276), a few modified NiMoCrW alloys with varying Mo and W contents and with addition of other elements such as Al, Ti and Nb were cast at lab scale. Alloying and aging effects on the microstructure and its correlation to the mechanical properties was investigated using XRD, SEM, S/TEM and APT. The irradiation behavior of selected baseline alloys was studied via heavy Ni+ ion irradiation and corrosion behavior of selected baseline and modified alloys in molten KCl/NaCl/MgCl2 salt at 750¡C for times to 500 hours was studied. Post-test properties and microstructure were characterized by XRD, hardness, SEM and S/TEM. These various results will be presented with a discussion of phase transformations, microstructural, irradiation and corrosion damage mechanisms and the potential of these new alloys for high temperature structural applications.