Electrochemistry of uranium in LiF–BeF2 melt

On the Structures of Thorium Fluoride and Oxyfluoride Anions in Molten FLiBe and FLiNaK

The structures of thorium fluoride and oxyfluoride ions in molten FLiBe-ThF₄ and FLiNaK-ThF₄ were investigated by Raman spectroscopy and density functional theory calculations. Thorium fluorides are present in the form of ThF₆^2- (O_h) and ThF₇^3- (C_2v) in molten FLiNaK-ThF₄. Similar speciation was identified in FLiBe-ThF₄, and the thorium fluoride anions are in equilibrium with free F^- ions and beryllium fluoride anions, which are responsible for the red shift of the beryllium fluoride bands in the Raman spectra. With the addition of Li₂O into the FLiNaK-ThF₄ and FLiBe-ThF₄ melts, the Th₂OF₁₀^4- anion with a linear Th-O-Th geometry was formed at the expense of thorium fluoride anions. The beryllium fluoride bands in the Raman spectra of FLiBe-ThF₄ exhibit a blue shift upon Th₂OF₁₀^4- formation, which results from the release of free F^- ions that can further react with beryllium fluoride. Insoluble thorium oxides were found in the FLiNaK and FLiBe melts at a Li₂O concentration of 15 mol %, and the Th₂OF₁₀^4- anion is, therefore, a bridge connecting the soluble thorium fluorides and insoluble thorium oxides in molten fluorides.

Effect of the [U(IV)]/[U(III)] ratio on selective chromium corrosion and tellurium intergranular cracking of Hastelloy N alloy in the fuel LiF-BeF2-UF4 salt

Effect of the [U(IV)/U(III)] ratio of fuel salt on selective chromium corrosion and tellurium intergranular cracking (IGC) of Hastelloy N alloy in the LiF-BeF2-UF4 salt mixture was investigated. The chromium corrosion of Hastelloy N alloy is caused by the oxidation of chromium on the alloy surface by reaction with UF4. The tellurium IGC of Hastelloy N alloy is caused by the diffusion of tellurium along the grain boundaries with the formation of unstable tellurides with based metals and alloying additives. Results indicate that the selective chromium corrosion and the tellurium IGC of the Hastelloy N alloy in fuel salt can be controlled by the [U(IV)]/[U(III)] ratio. The tellurium IGC of Hastelloy N alloy exposed in fuel LiF-BeF2-UF4 salt can be avoided. For temperatures up to 760 °C the selective chromium corrosion can be minimized to the acceptable level when the [U(IV)]/[U(III)] ratio of fuel salt is bellow 30–40.

Toward a Greenish Nuclear Fuel Cycle: Ionic Liquids as Solvents for Spent Nuclear Fuel Reprocessing and Other Decontamination Processes for Contaminated Metal Waste

The final disposition of spent nuclear fuel (SNF) is an area that requires innovative solutions. The use of ionic liquids (ILs) has been examined as one means to remediate SNF in a variety of different chemical environments and with different chemical starting materials. The effectiveness of various ILs for SNF reprocessing, as well as the reaction chemistry that occurs in them, is discussed.

Electrochemical investigation of the stable chromium species in molten FLINAK

This work proved the stable valence state of Cr in molten FLINAK is Cr(iii) determined by CV and SWV. The conversion of Cr(ii) to Cr(iii) should be attributed to the formation of the more stable species [CrF₆]³⁻ identified by Raman spectroscopy.