LiF NaF KF Research Articles

Simulation of dissolution of cerium trifluoride in a mixture of LIF–NaF–KF

The study of phase diagrams of multicomponent molten mixtures is traditionally carried out either by experimental measurements or thermodynamic calculations based on known experimental data. Atomistic modeling occupies a significantly smaller share in the methodology, and the capabilities of this approach have been poorly studied. In this work, we simulated the dissolution of cerium trifluoride in the ternary eutectic of lithium, sodium, and potassium fluorides using the molecular dynamics method. A time- and ensemble-scale simulation of the coexisting crystalline phase and melt at several temperatures was carried out. The influence of ensemble size was studied. The rate of dissolution was studied depending on temperature. The asymptote of the dependence agrees well with the experimental liquidus temperature for a given composition. A conclusion is given about the possibility of using molecular dynamics to determine the complete solubility of a melt component.

ELECTROCONDUCTIVITY OF MOLTEN FLiNaK AND FLiNaK–CeF<sub>3</sub>

The eutectic mixture LiF–NaF–KF (FLiNaK) is promising as a carrier salt for molten-salt reactors. Cerium fluoride CeF3 can be considered as a simulant of plutonium fluoride PuF3. In this work, the temperature dependence of the electrical conductivity of the molten ternary eutectic LiF–KF–NaF containing from 0 to 25 mol % cerium fluoride in the temperature range 480–777°C. FliNaK–CeF3 mixtures containing up to 25 mol. % of cerium fluoride were prepared directly in the experimental cell, dropping the required amount of CeF3 into the melt and keeping mixtures of a given composition for 12 h at temperatures exceeding the liquidus temperatures of the studied compositions. The electrolyte resistance was determined from impedance hodographs, which were taken using the Z-1500J impedance meter. A two-electrode cell with Pt electrodes was used. Analysis of the experimental values of the electrical conductivity of double and triple fluoride melts KF–LiF available in the literature; KF–NaF; LiF–NaF–KF shows that our data on the electrical conductivity of the LiF–NaF–KF (FLiNaK) eutectic mixture are consistent with the general trend in electrical conductivity with increasing KF concentration in the melt. A significant decrease in the specific electrical conductivity of the molten system and a slight increase in the activation energy of electrical conductivity with an increase in the concentration of cerium fluoride are shown. The temperature dependences of the electrical conductivity of the molten system were approximated by second-order polynomials. The formation of the \({\text{CeF}}_{6}^{{3 - }}\) complex ion in the melt was confirmed by spectral studies. The Raman spectra of molten FLiNaK and FliNaK–CeF3 mixtures containing 8 and 15 mol. % of cerium fluoride were recorded. With an increase in the concentration of CeF3 in the melt, the amount of \({\text{CeF}}_{6}^{{3 - }}\) complex ions increases, which leads to an increase in the intensity of the observed vibrational bands.

Phase Assemblage of the Li+,Na+,K+||F–,Cl–,Br– Five-Component Reciprocal System and Its LiF–KCl–KBr–NaBr–NaCl Stable Pentatope

The phase assemblage of the Li+,Na+,K+||F–,Cl–,Br– five-component reciprocal system was studied for the first time. The phase tree obtained by partition of the phase assemblage into stable elements is linear. It consists of the following stable elements: the LiF–NaF–KF–KBr–KCl pentatope, LiF–NaBr–NaCl–KCl–KBr–NaF hexatope, and NaCl–KCl–KBr–LiBr–LiCl–LiF–NaBr heptatope, linked by the LiF–NaF–KCl–KBr stable tetrahedron and the LiF–KBr–NaBr–NaCl–KCl square pyramid (pentatope). Phase equilibria in the LiF–KCl–KBr–NaBr–NaCl stable pentatope were studied by differential thermal analysis (DTA). Monovariant phase equilibrium L ⇄ LiF + NaClxBr1 – x + KClyBr1 – y occurs in the pentatope, where NaClxBr1 – x and KClyBr1 – y are continuous solid solutions (css) between NaCl and NaBr, KCl and KBr salt pairs, respectively. The composition of the mixture at point Min◻ 591 and the lowest monovariant equilibrium temperature were determined. A 3D computer model was designed as a projection of the phase assemblage on the LiF–KCl–KBr–NaBr–NaCl pentatope in KOMPAS-3D software. The volumes of crystallizing equilibrium phases were outlined.

A neutron tomography study to visualize fluoride salt (FLiNaK) intrusion in nuclear-grade graphite

Manufactured graphite is a preferred material for in-core components of molten salt reactors and fluoride salt-cooled high-temperature reactors, which are in permanent contact with liquid salts. However, owing to the porous nature of nuclear graphite, under certain conditions, molten salts may intrude graphite's pores and affect graphite's properties and functionality. Therefore, a better understanding of molten salt intrusion (distribution across sample cross section and penetration depth) is needed to assess its effects. In this work, we have demonstrated the use of neutron imaging (computed tomography) in the evaluation of salt penetration and distribution of a wide range of graphite grades with diverse microstructures that have been subjected to FLiNaK (LiF–NaF–KF) intrusion at 750 °C and 5 bar pressure for 12 h. Because of the great neutron attenuation contrast from scattering and adsorption between Li (from FLiNaK) and the graphite matrix, we have obtained direct visualization of FLiNaK salt distribution in the salt-impregnated graphites for the first time. Three-dimensional reconstructed images and cross-sectional concentration profiles demonstrate that salt penetration and density distribution are greatly dependent on the microstructural properties of the graphite grade.

КОРРОЗИЯ КОНСТРУКЦИОННЫХ МАТЕРИАЛОВ В РАСПЛАВЛЕННЫХ ФТОРИДАХ ЩЕЛОЧНЫХ МЕТАЛЛОВ

Corrosion processes of candidate materials for MSR were investigated: nickel-chromium-molybdenum alloys of the "Hastelloy" type: C-2000, CrNi65 and steel 12Cr18Ni10Ti, nickel-chromium (Ni80Cr20), nickel-titanium (NITINOL), nickel-copper (Monel 404) in a melt based on LiF–NaF–KF with compositions characteristic of MSR at a temperature of 550 °C. The weight and depth indicators of corrosion of materials are determined.

Erratum to: Sorption of Protactinium, Thorium, and Other Actinides from the LiF–NaF–KF Melt by Activated Carbon

Erratum to: Sorption of Protactinium, Thorium, and Other Actinides from the LiF–NaF–KF Melt by Activated Carbon

Corrosion of Hastelloy‐N and Hastelloy‐G35 from vapors generated from FLiNaK salt with addition of 5% oxygen in argon atmosphere

AbstractThis study investigates the corrosion of Hastelloy‐N and Hastelloy‐G35 alloys in an environment of vapors generated from FLiNaK (LiF–NaF–KF: 46.5–11.5–42.0 mol%) salt in an argon and partial (5%) oxygen at 800°C for 48 h. The result of the experiment showed that Hastelloy‐N and Hastelloy‐G35 experienced corrosion in the salt vapor/oxygen environment, causing an increase in the final weight of the samples. The corroded layer had fluorides and oxygen‐bearing compounds in the Hastelloy‐N samples, and oxide‐containing compounds in the Hastelloy‐G35 samples. The elemental mappings of the surface area, of a line across the surface (line scan) and of a cross‐section of the Hastelloy‐N samples showed Mo‐deficient areas and Mo‐rich areas, which reacted differently with the corrosive environment in the case of Hastelloy‐N samples. On the other hand, the elemental mappings of Hastelloy‐G35 samples showed a significant amount of chromium and iron oxides, as chromium had diffused out to the surface and reacted preferentially with oxygen (rather than fluoride) to form part of the corroded layer.

Sorption of Protactinium, Thorium, and Other Actinides from the LiF–NaF–KF Melt by Activated Carbon

The sorption of uranium and thorium fluorides by activated carbon from the eutectic was studied. The sorption isotherms of both fluorides at a temperature of 650°C have a pronounced convex character and are described by the Langmuir equation. Experiments were carried out on the sorption of protactinium by activated carbon AG-3 at 650°С from a melt of alkali metal fluorides LiF–NaF–KF containing thorium and neodymium fluorides. It was found that with an increase in the concentrations of neodymium or thorium fluorides, the value of protactinium sorption diminishes, and in the case of thorium fluoride, the decrease occurs to a greater extent. When protactinium is sorbed by activated carbon with metallic sodium, the sorption enhances by a factor of 20 at the 30% sodium content in the carbon. The separation factors of protactinium from other actinides rise with increasing sodium content in the carbon.

Comparative Analysis of Transmutation in a Burner Reactor Based on the Salts LiF–NaF–KF and LiF–BeF2

Comparative Analysis of Transmutation in a Burner Reactor Based on the Salts LiF–NaF–KF and LiF–BeF2

Insights on the corrosion thermodynamics of chromium in molten LiF-NaF-KF eutectic salts

The thermodynamic stability of chromium in the Cr0, Cr2+, and Cr3+ oxidation states considering various F− ion coordination compounds was investigated in molten LiF–NaF-KF (FLiNaK) eutectic salt. Potential fluoride ion activity (F− and CrF3−) diagrams were constructed to predict the most stable Cr oxidation states as a function of anion activity, solvation state of chromium ions and potential at 600 °C. The Gibbs free energies of these compounds were estimated by utilizing a combined cyclic voltammetry – Nernst theory analysis approach in FLiNaK salt. To verify the constructed diagrams, X-ray diffraction was utilized after exposure of Cr at various applied potentials to determine whether compounds detected in solidified FLiNaK salts agreed with thermodynamic calculations. This work aims to identify key thermodynamic factors that are significant to chromium corrosion for molten salt nuclear reactor applications. The F− stability region spans the entire region where spontaneous corrosion of Cr occurs. Cr may be oxidized to Cr2+ and Cr3+ in the presence HF (due to moisture as an impurity) spontaneously except some conditions of p1/2H2/aHF etc. This situation is not changed qualitatively for various states of solvation between oxidized Cr solute in F− solvent and this aspect is substantially similar for the two cases (pair 1: Cr0/CrF3−/ CrF63−; pair 2: Cr0/CrF42−/CrF52−) considered in this work.

Sorption of NdF3 and ThF4 with Activated Carbons and Zeolites from LiF–NaF–KF Molten Salts

Sorption of NdF3 and ThF4 with Activated Carbons and Zeolites from LiF–NaF–KF Molten Salts

Study on the Mechanism of Failure in the LiF–NaF–KF Molten-Salt-Purifying Processing System

The failure of LiF–NaF–KF molten salt processing engineering was investigated. The results indicate that the failure is related to the blockage of pipes. The mechanism of blockage was studied systemically. The results reveal that the blockage of pipes was attributed to corrosion. UNS 022N01 alloy vessel was corroded in molten salt to form KNiF3 and K2NiF4. The corrosion products were reduced by H2 to form metallic Ni, which is the precipitant in salt. The transfer of precipitant in terminal salt was stopped by incomplete root penetration, which results in one pipe blocked at the welded joint. The corrosion products were reduced by H2 to form metallic Ni and deposited on the inner surface of H2 gas outlet, which resulted in another blocked pipe.

Corrosion Behavior of Candidate Functional Materials for Molten Salts Reactors in LiF–NaF–KF Containing Actinide Fluoride Imitators

Molten fluorides of alkali metals are considered a technological medium for molten salt reactors (MSRs). However, these media are known to be extremely corrosive. The successful implementation of high-temperature technological devices using molten alkali metal fluorides requires the selection of such structural materials that have high corrosion resistance in melts with compositional characteristic of MSRs. In this research, the corrosion behavior of 12Cr18Ni10Ti steel, the alloy Ni60Cr20Mo15, and the alloy Monel 404 (Ni50Cu50) was investigated in the LiF–NaF–KF eutectic melt, containing additions of CeF3 and NdF3 from 0 to 5 wt.% as imitator fluorides of actinides in an inert argon atmosphere at 550 °C for 100 h. Gravimetry, energy-dispersive X-ray (EDX) microanalysis of surfaces and cross-section of samples, and ICP-MS were used to establish the corrosion behavior of the investigated alloys. Corrosion resistance of the studied materials was found to decrease in a row from Monel 404 > Hastelloy C2000 > 12Cr18Ni10Ti. The addition of cerium fluoride into the melt resulted in the additional etching of the alloy surface. The addition of neodymium fluoride resulted in the formation of the point/inter-crystalline corrosion damages in the sample bulk. The samples of steel 12Cr18Ni10Ti were subjected to local cracking corrosion. The austenitic nickel-based alloys suffered specific local corrosion with formation of subsurface voids. Excellent corrosion resistance of the Monel alloy under the test conditions was found.

Corrosion behaviors of Ni-WC cemented carbide in high temperature molten fluoride salt and vapor

Ni-WC cemented carbides has a series of excellent properties, such as mechanical properties, thermal stability and wear resistance, but its corrosion resistance in molten fluoride salt is unknown. In this work, the corrosion behaviors of a Ni-WC cemented carbide (86.7W-8C-5Ni-0.3Cr wt.%) in molten FLiNaK salt (LiF–NaF–KF: 46.5–11.5–42 mol.%) and salt vapor were investigated by static immersion tests at 700 °C. The microstructure and phase composition of the material after corrosion were characterized by scanning electron microscopy (SEM), electron probe micro-analysis (EPMA) and scanning transmission electron microscopy with energy dispersive spectrometry (STEM/EDS). The results show that in the liquid salt, Ni-rich particles are deposited on the material surface, and Cr from the binder of the specimens is dissolved. The oxidative impurities in the salt vapor induce the formation of flaky Cr2O3 on the material surface. The relatively little corrosion in both salt and vapor indicates that the application of this material in molten fluoride salts environment is promising.

Effect of high temperature molten salt corrosion on the microstructure of a Co-Mo-Cr-Si wear resistant alloy

The corrosion behavior of a novel low Cr content Laves phase strengthened wear-resistant alloy (Co-27.3Mo-2.9Cr-3.1Si) in molten FLiNaK salt (LiF–NaF–KF: 46.5–11.5–42 mol.%) was investigated by static immersion test at 700 °C. The microstructure and phase composition of the alloy after corrosion were characterized by scanning electron microscopy (SEM), electron probe micro-analysis (EPMA) and transmission electron microscopy with energy dispersive spectrometry (TEM/EDS). Results show that the alloy surface exhibit either pitted or roughened morphology after corrosion. The preferential corrosion of the Laves phase contributes to the pitting, whereas the formation of Co 3 Mo particles and Co layers contributes to the roughening. Carburization occurs in both the Laves phase and alloy matrix in the corrosion affected zone, forming Co 3 Mo 3 C carbides of different sizes. In addition, the thermal exposure effect during corrosion causes phase transformation in the entire alloy matrix and form Co 3 Mo stripes. The observed non-uniform corrosion is mainly induced by the trace amount of H 2 O in the salt, and it suggests that the corrosion resistance of the alloy is not satisfying in the test condition. • A novel low Cr content wear-resistant alloy was fabricated and its corrosion behavior in molten fluoride salt was tested. • Complex changes in microstructure induced by molten salt corrosion were characterized by XRD, SEM, TEM, EDS and EPMA methods. • The non-uniform corrosion of the alloy was mainly induced by the trace amount of water presented in the salt.

Investigation of the Corrosion Resistance of Nickel-Molybdenum Alloys in the Eutectic LiF–NaF–KF

Investigation of the Corrosion Resistance of Nickel-Molybdenum Alloys in the Eutectic LiF–NaF–KF

Electrodeposition of Tungsten from Molten KF–KCl–WO3 and CsF–CsCl–WO3

Introduction Tungsten metal is known for its robustness, especially high melting and boiling points and hardness. However, its hardness and brittleness make it difficult to work. Thus, electrodeposition of flat and dense tungsten films is worth investigating. There are a number of reports on the electrodepositon of tungsten from high temperature molten salts such as fluorides [1], chlorides [2], oxides [3], etc. It is known that dense and coherent tungsten deposits are more easily obtained from molten fluorides compared to molten chlorides. One drawback of typical fluoride melts like LiF–NaF–KF is difficulty in removing the adhered molten salts by water washing because LiF and NaF have limited solubility to water [4]. Although good tungsten deposits can be electrodeposited from molten oxides [3], the operation temperature tends to be very high, typically over 1123 K.From this background, we proposed new electrolyte baths, molten KF–KCl [5,6] and CsF–CsCl. Since all the components salts of KF, KCl, CsF and CsCl have large solubility to water [4], solidified salts on deposited films can be easily removed by water washing. Results & Discussion First, electrodeposition of tungsten was investigated in eutectic KF–KCl melt to which WO3 was added at 923 K. Cyclic voltammograms at copper and gold electrodes indicated the deposition of tungsten metal at more negative potential than 1.55 V vs. K+/K. The effects of electrolysis conditions on the morphology of deposits were studied by changing the cathodic current density from 12.5 to100 mA cm−2. As shown in Fig.1(a), a dense tungsten film with a thickness of approximately 20 µm was obtained on a copper substrate electrode at 12.5 mA cm−2 for 120 min. From the Raman spectra of molten KF–KCl and molten KF–KCl–WO3 at 923 K, the coordination structure of W(VI) complex ion was indicated to be fac-[WO3F3]3−.Secondly, eutectic CsF–CsCl melt was used to lower the operation temperature. After adding 2.0 mol% of WO3, the electrodeposition was investigated using copper and gold electrodes at 823–923K. As shown in Fig.1(b), a flat and dense tungsten film was obtained by galvanostatic electrolysis at 12.5 mA cm−2 for 120 min at 873 K. Acknowledgement This study is supported by Sumitomo Electric Industries, Ltd. The present address of Kouji Yasuda is Graduate School of Engineering, Kyoto University.

Corrosion behavior of a wear resistant Co-Mo-Cr-Si alloy in molten fluoride salts

Evaluating the corrosion performances of wear resistant alloys is important for designing the molten salt-wetted bearings and valves in molten salt reactors. In this study, the corrosion behavior of wear-resistant Tribaloy T-400 alloy (Co-29Mo-8.5Cr-2.8Si) in molten FLiNaK salt (LiF–NaF–KF: 46.5–11.5–42 mol.%), with and without the presence of UNS N10003 alloy, were investigated through static immersion tests at 650 °C. After 400 h corrosion, T-400 alloy showed greater weight loss than UNS N10003 alloy, and the presence of UNS N10003 alloy further increased the weight loss of T-400 alloy. Electron microscopic and salt chemistry analyses showed that Cr and Co were selectively dissolved from T-400 alloy matrix after corrosion, resulting in a porous structure. On the other hand, the Laves phase precipitates were hardly corroded but showed signs of carbide formation on the surface. In addition, when tested with UNS N10003 alloy, some of the Co dissolved from T-400 alloy transferred to the surface of UNS N10003 alloy, hence promoted the corrosion of T-400 alloy. The results have indicated that even T-400 alloy has a relatively low Cr content among high temperature wear-resistant hardfacing alloys, its corrosion resistance is still inadequate in a typical molten salt reactor environment where UNS N10003 alloy and graphite are also present.

Corrosion of Ceramic and Carbon-Based Materials in FLiNaK

Corrosion resistance of ceramic and carbon materials was studied in molten salt systems based on LiF–NaF–KF mixture in the temperature range 550–750°C. The rates of corrosion of silicon nitride, boron nitride, carbon-carbon composites, and high density graphite in the fluoride electrolyte were determined. The mechanisms of materials degradation after the contact with molten FLiNaK are proposed, and the effect of the salt media and the temperature on the mechanical properties of ceramic and carbon materials is considered.

Corrosion of Metallic Materials in the Molten FLiNaK

Corrosion resistance of molybdenum, tantalum, and nickel-based alloys was studied in molten salt systems based on LiF–NaF–KF mixture in the temperature range 550–750°C. The rates of corrosion of these materials were determined, the nature of the degradation of the surface of materials established, and the effect of the salt medium and temperature on the corrosive properties of metals and nickel-based alloys considered.