The Nuclear Science, Technology, and Education for Molten Salt reactors (NuSTEM) Integrated Research Project started in October of 2017 as a collaboration between Texas A&M University, the University of California Berkeley, and the University of Wisconsin – Madison. The NuSTEM project involves five technical mission areas (TM) and one educational mission area: TM 1 Material and Corrosion Science, TM 2 Chemical Sensor Development, TM 3 Modeling, Multiphysics Simulation and Uncertainty Quantification, TM 4 Thermal Hydraulic Science, TM 5 Chlorine-35 9 (n,p) cross-section measurements, and the educational mission area is meant to provide educational tools to prepare young professional to work on the development of molten salt reactors and safety analysis.
At the University of Wisconsin – Madison, we are working on TM 1 Material and Corrosion Science specifically to test and characterize the performance of structural alloys and to further develop the understanding of materials interactions in molten fluoride salt environments. The structural alloy candidate we are most focused on is Hastelloy-N. Hastelloy-N is a nickel based superalloy with high concentrations of molybdenum and low concentrations of chromium originally designed by Oak Ridge National Laboratory in the 1960s specifically for the use in molten salt Reactors. The chromium concentration is kept low because chromium is susceptible to dissolution into the molten salt due to its stability in the form of chromium fluoride, but a certain concentration of chromium is needed in order for the alloy to be protected from oxidation on the air exposed side of the structure.
Long term corrosion experiments of 1000, 2000, and 3000 hours in molten fluoride salt at 700 oC are being planned to test Hastelloy-N’s performance. Additionally proton irradiation of Hastelloy-N and subsequent exposure to molten salt is planned to investigate the effects that pre-irradiation may have on the performance of Hastelloy-N. To further understand materials interactions in molten fluoride salt environments, several corrosion experiments putting dissimilar metals in the same salt solution are planned to investigate how the fluoride salt can facilitate mass transport between dissimilar metals.