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Assessing Environmentally Assisted Cracking Of Structural Alloys In Molten Salts

The potential for structural alloys to undergo environmentally assisted cracking in molten salts is relatively unexplored due to their limited industrial application. However, fluoride salts are of prime interest to many advanced reactors including the Kairos Power FHR reactors. Table I summarizes literature studies of EAC in molten fluoride salts. For the ten studies shown, seven are for Ni-Mo-Cr family of alloys (INOR-8 / Hastelloy N or variants) that were used in the Molten Salt Reactor Experiment (MSRE), two studies investigate austenitic stainless steels, and there is one report of EAC in oxygen free high conductivity (OFHC) copper.

Product Number: ED22-17120-SG
Author: George Young, Jake Quincey, Andrew Brittan, Pit Shulze, Stella Tsotsos, Lars Parrington, Josef Parrington, Anne Demma, Micah Hackett, Samuel Briggs and Julie D. Tucker
Publication Date: 2022
$20.00
$20.00
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Molten salt coolants are fundamental to many advanced reactors due to their desirable physical and nuclear properties. However, the potential for environmentally assisted cracking (EAC) of structural alloys in molten salts is relatively unexplored. As part of the effort to license and deploy Fluoride-cooled High-temperature Reactors (FHR), Kairos Power is assessing the EAC resistance of 316H stainless steel in molten FLi2Be4 (Flibe) salt. This paper describes the Kairos Power testing systems and outlines best practices for EAC testing in molten salts. Additionally, it summarizes literature reports of EAC of alloys in fluoride salts and presents results of scoping tests in both molten FLiNaK and Flibe. Slow strain rate testing of 316L/316 stainless steel in unpurified FLiNaK salt shows that under oxidizing conditions and at stresses above yield, sulfur deposition onto the metal causes intergranular cracking, similar to the tellurium embrittlement seen in the Molten Salt Reactor Experiment (MSRE). Comparable tests on 316H stainless steel in Flibe salt show very high ductility and no evidence of EAC. Scoping tests in FLiNaK demonstrate the ability to conduct fracture mechanics based, K-controlled corrosion-fatigue and stress corrosion testing via direct current potential drop.

Molten salt coolants are fundamental to many advanced reactors due to their desirable physical and nuclear properties. However, the potential for environmentally assisted cracking (EAC) of structural alloys in molten salts is relatively unexplored. As part of the effort to license and deploy Fluoride-cooled High-temperature Reactors (FHR), Kairos Power is assessing the EAC resistance of 316H stainless steel in molten FLi2Be4 (Flibe) salt. This paper describes the Kairos Power testing systems and outlines best practices for EAC testing in molten salts. Additionally, it summarizes literature reports of EAC of alloys in fluoride salts and presents results of scoping tests in both molten FLiNaK and Flibe. Slow strain rate testing of 316L/316 stainless steel in unpurified FLiNaK salt shows that under oxidizing conditions and at stresses above yield, sulfur deposition onto the metal causes intergranular cracking, similar to the tellurium embrittlement seen in the Molten Salt Reactor Experiment (MSRE). Comparable tests on 316H stainless steel in Flibe salt show very high ductility and no evidence of EAC. Scoping tests in FLiNaK demonstrate the ability to conduct fracture mechanics based, K-controlled corrosion-fatigue and stress corrosion testing via direct current potential drop.