LiF-NiF2 system: high temperature stability study of Li2NiF4(s) and interaction of fuel salts of molten salt reactor with structural material components

• Published in: Journal of solid state electrochemistry Vol. 26; no. 4; pp. 1037 - 1050
• Main Authors: Mukherjee, Sumanta, Dash, Smruti
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-04-2022; Springer Nature B.V
• Subjects: Analytical Chemistry; Characterization and Evaluation of Materials; Chemical potential; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Electrochemistry; Electrolytic cells; Energy Storage; Fluorine; Free energy; Fuels; Heat of formation; High temperature; Homogeneity; Lithium fluoride; Mathematical analysis; Molten salt nuclear reactors; Nickel fluorides; Nuclear fuels; Operating temperature; Original Paper; Phase diagrams; Physical Chemistry; Solid electrolytes; Stability; Ternary systems; Thermodynamics; s; NiF; E.m.f. study; Ternary phase diagram; Li; MSR; Ni-based alloy
• ISSN: 1432-8488; 1433-0768
• DOI: 10.1007/s10008-022-05134-w

High temperature interaction of LiF-NiF
2
system is characterized with the ternary compound, Li
2
NiF
4
(s). The compound has been synthesized by solid state route. Li
2
NiF
4
(s) has been characterized with XRD technique and its micro-homogeneity and surface morphology have been tested with EDS and SEM technique, respectively. In order to study the thermodynamic stability, the Gibbs energy of formation, Δ
f
G°
m
(
T
), of Li
2
NiF
4
(s) has been measured with solid electrolyte galvanic cell technique and its measured Δ
f
G°
m
(
T
) can be expressed as Δ
f
G°
m
(
T
) [Li
2
NiF
4
(s)] / k.J mol
−1
 = (-1902.2 ± 1.1) + (0.3491 ± 0.0016) × (
T
/K). Using the experimental thermodynamic data, ternary phase diagram and fluorine potential diagram of Li-Ni-F
2
system have been calculated in order to study the stability domain and coexisting phases of Li
2
NiF
4
(s) at reactor operating temperature. The stability of Li
2
NiF
4
(s) has also been investigated in the presence of oxygen impurity by calculating chemical potential diagram of Li-Ni-F-O system and ternary phase diagram of LiF-NiF
2
-O
2
system at the same temperature. In the study, interaction of major structural components, Ni, Cr, and Fe, with fuel salt components (ThF
4
and UF
4
) of MSR has also been investigated at different temperatures.