Effect of graphite particles in molten LiF-NaF-KF eutectic salt on corrosion behaviour of GH3535 alloy
Introduction
Molten salt reactors (MSR) are among the six potential generation IV nuclear reactors [[1], [2], [3]]. Molten fluorine salts and Ni-Mo-Cr alloys are considered the most suitable coolants and structural materials for MSR [[4], [5], [6], [7], [8]]. Although Hastelloy-N, a typical representative of a Ni-Mo-Cr alloy developed especially for MSR by Oak Ridge National Laboratory [[9], [10], [11]], has exhibited good performance in molten fluoride salt systems, corrosion remains a significant primary problem, especially when the alloy is co-present in molten salt with graphite as a moderator [[12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23]].
Many laboratory-scale investigations on the mutual compatibility of Hastelloy-N and graphite in molten fluorides have been conducted to imitate material interactions in a practical advanced nuclear reactor environment [[24], [25], [26], [27], [28]]. For reasons of safety and ease of operation, FLiNaK (LiF-NaF-KF: 46.5–11.5–42.0 mol.%) eutectic salts of a very similar corrosion nature have often been used to simulate the corrosion behaviour of fluorides salts in MSR. These studies have focused primarily on the interaction between Hastelloy-N alloy and bulk graphite. However, graphite particles are likely to be washed off from the surface of graphite in the harsh reactor core environment and diffused into molten fluoride salt [29]. Graphite particles entering the molten salt will change the physicochemical properties of molten salt and affect the compatibility of salt and alloy. Thus, evaluating the effect of graphite particles in molten salt on the corrosion of Hastelloy-N alloy is critical from the viewpoint of its use in MSR.
In this study, the corrosion behaviour of GH3535 alloy, which shares the same name with Hastelloy-N alloy in the ASTM code, is systematically investigated in the presence and absence of graphite particles in molten FLiNaK salt at 700.0 °C. The mass loss, morphology, and element distribution on the surface and in the cross-section of GH3535 alloy are characterized in this experiment. Moreover, this paper discusses the mechanism underlying the effect of graphite particles in molten salt on the corrosion behaviour of GH3535 alloy. It provides a few insights into the corrosion control of GH3535 alloy.
Section snippets
Materials
The chemical composition of GH3535 alloy is summarized in Table 1. A GH3535 alloy sheet was cut into 20.0 mm × 10.0 mm × 3.0 mm piece, and a hole was drilled at one end of each sample. Before the corrosion experiment, samples were ground with SiC abrasive paper down to 1500 grit, cleaned with water assisted by sonication, and rinsed with ethanol. The size and weight of each sample were determined using a micro-meter and an electronic balance, respectively, and the precision of the electronic
Weight change
Fig. 1 illustrates the weight change of the corroded GH3535 alloy samples post immersion in molten FLiNaK salt with (Fig. 1(a)) and without (Fig. 1(b)) graphite particles for different durations. All experimental values of mass change were averaged using the data of three specimens in each group of corroded GH3535 alloys. The weight change measured here, especially for the salt with graphite represents two phenomenon, weight loss due to the active dissolution of elements like chromium and the
Conclusion
The effect of graphite particles in molten FLiNaK eutectic salt on the corrosion behaviour of GH3535 alloy was investigated using a static immersion corrosion technique. Regardless of the presence or absence of graphite particles in molten FLiNaK eutectic salt, chromium in GH3535 alloy was selectively dissolved, and its depletion depth increased gradually with the extension of corrosion duration. Different from the results of corrosion in pure FLiNaK molten salt, the introduction of graphite
Author statement
The authors have made substantial contributions to the conception or design of the work, or the acquisition, analysis, or interpretation of data for the work, drafted the work or revised it critically for important intellectual content, and approved the final version to be published.
Declaration of Competing Interest
The authors declare no conflict of interest.
Acknowledgements
This study was supported by the National Key R&D Program of China (2018YFB1501002), Qinghai Major Science and Technology Projects (2017-GX-A3), “Transformational Technologies for Clean Energy and Demonstration” Strategic Priority Research Program of the Chinese Academy of Sciences (XDA21080100), “Thorium Molten Salt Reactor Nuclear Energy System” Strategic Priority Research Program of the Chinese Academy of Sciences (XDA02020000).
References (34)
The advanced high-temperature reactor: high-temperature fuel, liquid salt coolant, liquid-metal-reactor plant
Prog. Nucl. Energy
(2005)- et al.
The molten salt reactor (MSR) in generation IV: overview and perspectives
Prog. Nucl. Energy
(2014) - et al.
Evaluating physical properties of molten salt reactor fluoride mixtures
J. Fluor. Chem.
(2009) - et al.
Current status of knowledge of the fluoride salt (FLiNaK) heat transfer
Nucl. Technol.
(2009) - et al.
An Overview of Liquid Fluoride Salt Heat Transport Systems
(2010) - et al.
Molten fluorides for nuclear applications
Mater. Today
(2010) - et al.
Fluoride salt coolant properties for nuclear reactor applications: a review
Ann. Nucl. Energy
(2017) - et al.
Corrosion behavior of ZrC-SiC composite ceramics in LiF-NaF-KF molten salt at high temperatures
Ceram. Int.
(2015) - et al.
Considerations of alloy N for fluoride salt-cooled high-temperature reactor applications
Proceedings of the ASME Pressure Vessels and Piping Conference
(2011) An Evaluation of the Molten-salt Reactor Experiment Hastelloy N Surveillance Specimens-third Group
(1971)
Development Status and Potential Program for Development of Proliferation-resistant Molten Salt Reactors
Corrosion Phenomena Induced by Molten Salts in Generation IV, Chapter5
Investigation on corrosion behavior of Ni-based alloys in molten fluoride salt using synchrotron radiation techniques
J. Nucl. Mater.
The elemental move characteristic of nickel-based alloy in molten salt corrosion by using nuclear microprobe
Nucl. Instrum. Meth. B
The high-temperature corrosion of hastelloy N alloy (UNS N10003) in molten fluoride salts analysed by STXM, XAS, XRD, SEM, EPMA, TEM/EDS
Corros. Sci.
The influence of temperature gradient on the corrosion of materials in molten fluorides
Corros. Sci.
Long-term corrosion behaviors of hastelloy-N and hastelloy-B3 in moisture-containing molten FLiNaK salt environments
J. Nucl. Mater.
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