Materials and Chemistry for Molten Salt Systems: Corrosion
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Stephen Raiman, University Of Michigan; Kumar Sridharan, University of Wisconsin-Madison; Nathaniel Hoyt, Argonne National Laboratory; Jinsuo Zhang, Virginia Polytechnic Institute and State University; Michael Short, Massachusetts Institute of Technology; Raluca Scarlat, University of California, Berkeley
Monday 8:30 AM
March 15, 2021
Room: RM 49
Location: TMS2021 Virtual
Session Chair: Kumar Sridharan, University of Wisconsin
8:30 AM
Introductory Comments: Materials and Chemistry for Molten Salt Systems: Stephen Raiman1; 1Texas A&M University
Introductory Comments
8:35 AM
Assessment and Qualification of Austenitic Stainless Steel for Use in Molten Salts: George Young1; Micah Hackett1; 1Kairos Power
Kairos Power has developed a fluoride salt-cooled high-temperature reactor which utilizes stainless steel structural components, Flibe salt as its primary coolant, and ‘solar salt’ as an intermediate coolant. Materials performance in the KP-FHR system may be affected by degradation phenomena that are grouped into four broad categories: corrosion, environmentally assisted cracking (EAC), thermal degradation, and irradiation damage. This presentation focuses on recent developments in corrosion and EAC testing. The corrosion tests utilize novel rotating cage loop (RCL) systems which simulate key features of the KP-FHR (temperature, flow rate, dissimilar material contact, cold leg flow, etc.) in a design that is more efficient than conventional pumped loop designs. Similarly, the EAC tests utilize state-of-the-art systems for slow strain rate, fatigue crack growth rate, and constant K stress corrosion cracking tests. Results to date will be presented and the discussion will focus on assessing the performance of safety-related components in the KP-FHR.
9:05 AM
Corrosion Behavior of SS316, Hastelloy X, and Hastelloy N in FLiNaK: Amanda Leong1; Huali Wu1; Jinsuo Zhang1; 1Virginia Tech
Fluoride salts are promising salt coolants for molten salt reactors; therefore, the need to search for a suitable material that is compatible in FLiNaK environments is essential to minimize corrosion. This work addresses the corrosion behavior of SS316, Hast. X, and Hast. N exposed in FLiNaK at 750°C for up to 336 hours. Initial oxidation results show that chromium oxide forms on material surfaces; however, the oxide is chemically unstable as the reaction favors the formed chromium oxide to dissolve into FLiNaK as ions eventually. As chromium migrates from the bulk to the surface, the continuation of chromium dissolution in FLiNaK led to severe depletion as many pits were formed, affecting the material's integrity. The depletion depth of chromium increases significantly with exposure times. The chromium depletion depth of Hast. X was much more profound in comparison to Hast. N, due to its higher chromium concentration from the bulk material.
9:25 AM
Corrosion of 316 Stainless Steel in Molten Chloride Salt Micro Convection Loop: Yafei Wang1; 1University of Wisconsin Madison
Material corrosion is a significant concern for the deployment of molten salt reactor (MSR) which is a generator-IV reactor concept with the great advantages of low-pressure primary system and high-temperature power cycle. Considering the lack of the molten salt corrosion study under flow conditions, the present study performed a corrosion test of 316 stainless steel (316 SS) in a NaCl-MgCl2 molten salt natural convection loop at the temperature of 700 ℃ for 1000 hours. The cross sections of the 316 SS corrosion samples are investigated by material characterization methods including SEM and XRD. Through comparing the 316 SS corrosion samples at different positions of the loop, the corrosion behavior at different temperatures and the thermal driven corrosion mechanism are analyzed. The design and preliminary results of a thin-layer activation analysis system to study corrosion of 316SS in molten salt flow loops in-situ will finally be presented.
9:45 AM
Development of an In-situ Mechanical Test System for Molten Salts: Jake Quincey1; Peter Beck1; Josef Parrington2; Lars Parrington2; Christopher Lamb2; George Young1; Julie Tucker1; Samuel Briggs1; 1Oregon State University; 2Parrington Instruments
Advanced reactor coolants such as molten salts pose unique challenges for test systems designed to study environmentally assisted cracking (EAC). Challenges with in-situ testing include immersing the sample in molten salt while preventing air exposure and providing sample access for real-time load control and monitoring of crack initiation and growth. This work presents scoping work done on an in-situ mechanical test system that addresses these issues and is capable of state-of-the-art, fracture mechanics-based EAC testing in molten salt environments with concurrent electrochemical monitoring. This test system is constructed from stainless steel to minimize dissimilar metal contact, enables electrical isolation of the test sample for potential drop monitoring of crack growth, has feedthroughs allowing electrodes for electrochemical monitoring, and utilizes a novel, pumped ‘cold leg’ to prevent excessive contaminant buildup in the coolant. The key features of the system and initial results from testing in molten FLiNaK salt will be described.
10:05 AM
High-throughput Electrochemical Methods Development to Accelerate Molten Salt Corrosion-resistant Alloy Design: Bonita Goh1; Yafei Wang1; William Doniger1; Phalgun Nelaturu1; Dimitris Papailiopoulos1; Dan Thoma1; Kumar Sridharan1; Adrien Couet1; 1University Of Wisconsin Madison
Following the enthusiastic reception of our work from TMS 2020 in which we presented progress made in developing a miniaturized, high-throughput molten salt corrosion assembly, we present a heuristic algorithm capable of on-the-fly extraction of features of interest from a molten salt cyclic voltammogram. This code is able to rapidly analyze in-situ cyclic voltammetry data acquired by high-throughput electrochemical probing of a grid of 3D printed alloys exposed to individual molten salt environments. In addition, the code is demonstrated to apply the Berzins & Delahay model for inhomogeneous reactions and the Myland & Oldham model for homogeneous reactions to extract analyte concentration values, diffusion coefficient and electron transfer coefficient. The code is validated using cyclic voltammetry data taken from conventional and high throughput electrochemical experiments. This data-acquisition methodology facilitates the contribution towards a Materials Genome Library and development of training and test data sets for machine learning for materials discovery.
10:25 AM
Role of Alloy Chemistry in Governing Corrosion Rates of Candidate Materials for Molten Salt Reactors: Rishi Pillai1; Cory Parker1; Stephen Raiman1; Bruce Pint1; 1Oak Ridge National Laboratory
Selection of optimum materials for structural components in molten salt systems is largely based on extensive and costly experimental evaluation with limited gain in mechanistic understanding of the corrosion processes. Physics-based models to identify critical corrosion mechanisms and predict corrosion behavior of materials as a function of salt chemistry, time and temperature are integral to the success of molten salts powered technologies. The aim of the present work was to evaluate the role of alloying elements (Fe, Cr, Ni, Mn, Si, Al, Ti, Mo, W) in governing corrosion rates of commonly employed structural materials (ferritic and austenitic steels and Ni-base alloys) by performing coupled thermodynamic-kinetic modelling. Element concentrations and phase distributions were obtained by scanning electron microscopy. Phases were identified by energy/wavelength dispersive X-ray spectroscopy and electron backscatter diffraction. The modelling results were validated with experimental data in terms of depth of corrosive attack, element depletion and phase transformations.
10:45 AM
Influence of Corrosion Product Solubility and Dissimilar Materials on Corrosion of Alloys in Molten Salt Environment: Cody Falconer1; William Doniger1; Matthew Weinstein1; Mohamed Elbakhshwan1; Kumar Sridharan1; Adrien Couet1; 1University of Wisconsin - Madison
Corrosion of structural alloys in molten salts is a recognized concern for the development of the Molten Salt Reactors (MSR). In an MSR, different materials will be present in the vicinity of each other in the molten salt environment. In static molten salt tests that are frequently used for evaluating materials corrosion, two factors have an impact on the sample corrosion rate have been investigated. First, the ratio of sample surface area to salt volume which dictates corrosion product saturation in molten salt. As corrosion products build up in the salt, the driving force for further corrosion may be reduced. Second, is the influence of the capsule material which affects the corrosion rate of test samples due to mass transport induced by activity gradients. These two effects will be presented for tests performed in molten FLiNaK salt at 700oC.