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. 2023 Jun 29;8(27):24673-24679.
doi: 10.1021/acsomega.3c03448. eCollection 2023 Jul 11.

In-Situ Analysis of Corrosion Products in Molten Salt: X-ray Absorption Reveals Both Ionic and Metallic Species

Sean Fayfar  1 , Guiqiu Zheng  1 , David Sprouster  2   1 , Matthew S J Marshall  3 , Eli Stavitski  4 , Denis Leshchev  4 , Boris Khaykovich  1
Affiliations

In-Situ Analysis of Corrosion Products in Molten Salt: X-ray Absorption Reveals Both Ionic and Metallic Species

Sean Fayfar et al. ACS Omega. .

Abstract

Understanding and controlling the chemical processes between molten salts and alloys is vital for the safe operation of molten-salt nuclear reactors. Corrosion processes in molten salts are highly dependent on the redox potential of the solution that changes with the presence of fission and corrosion processes, and as such, reactor designers develop electrochemical methods to monitor the salt. However, electrochemical techniques rely on the deconvolution of broad peaks, a process that may be imprecise in the presence of multiple species that emerge during reactor operation. Here, we describe in situ measurements of the concentration and chemical state of corrosion products in molten FLiNaK (eutectic mixture of LiF-NaK-KF) by high-resolution X-ray absorption spectroscopy. We placed a NiCr foil in molten FLiNaK and found the presence of both Ni2+ ions and metallic Ni in the melt, which we attribute to the foil disintegration due to Cr dealloying.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Pyrolytic boron nitride cell containing FLiNaK salt and a NiCr foil designed for XAS fluorescence measurements in a furnace. (a) 3D design of the boron nitride cell including two parts. (b) FLiNak salt and NiCr foil loaded into the boron nitride cell. (c) Assembled cell placed in a holder and then into the furnace.
Figure 2
Figure 2
(a) 3D design of the furnace built for XAS, and (b) the furnace installed at the ISS beamline. The BN cell sits in a central chamber of the furnace with small holes for the incoming and transmitted beam. There is a larger window in the furnace for the fluorescence signal. A thermocouple is placed through the top to monitor the temperature within the furnace.
Figure 3
Figure 3
(a) XANES spectra of Ni2+ and Ni foil normalized for comparison. (b) XANES results of the Ni K-edge of FLiNaK with varying concentrations of NiF2. The step size of the XANES measurement corresponds to the concentration of Ni in the sample. The vertical heights are shifted for clarity.
Figure 4
Figure 4
Step size fitting results of XANES spectra. (a) XANES spectra of the Ni K-edge with fits to the pre- and post-edge and the calculated step size. (b) The fits to the spectra with known concentrations of NiF2. (c) Fit correlating the step size with NiF2 concentration.
Figure 5
Figure 5
XANES results of the Ni K-edge of molten FLiNaK at 500 °C over a period of 3.75 h. (a) Two of the spectra analyzed with LCA using a Ni metal spectra and a Ni2+ spectra; the fitting bounds are shown as red vertical lines. (b) The concentration of Ni ions calculated from the XANES step size. (c) The spatial distribution of Ni concentrations postcorrosion at room temperature where 0 mm corresponds to the location of the metal foil.
Figure 6
Figure 6
Results of the Ni K-edge XANES spectra at 650 °C over a period of 5 h. The concentration of Ni ions was calculated from the XANES step size.
See this image and copyright information in PMC

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