Examination of Molten Salt Reactor Relevant Elements Using Hydrothermal Synthesis

Abstract

The structural chemistry of elements relevant to the FLiBe molten salt reactor, Th, U, Np, and Zr, including Ce and Nd (as analogues for Pu and Am, respectively), have been examined using hydrothermal synthesis at 200 °C. These reactions serve to model the reaction of molten salts under hydrolysis conditions. The results show that U and Np formed LiAnF 5 , while Ce formed Li 4 CeF 8 . The source of U also controlled the crystal quality, where UO 2 gave small crystals, while UO 3 •2H 2 O gave very large crystals. It is likely that Be incorporation was not observed because of the high solubility of [BeF 4 ] 2− in water. Zr formed a third product, Li 6 BeF 4 ZrF 8 , which features isolated [BeF 4 ] 2− and [ZrF 8 ] 4− units bridged by Li + . Additionally, Li 2 BeF 4 was regularly isolated. When little to no alkali metal was included in the reaction, M 3 F 12 (H 2 O) was isolated for Np, U, and Ce.

Exploring the Oxidation States of Neptunium with Schiff Base Coordination Complexes

“…The solid-state UV/vis/NIR spectrum of Np IV L 2 reveals an intense broad charge transfer band with λ max = 493 nm accounting for the orange coloration of the crystals (Figure ). Several weak absorptions between 500 and 1300 nm are assigned to the Laporte-forbidden 5f → 5f transitions, as observed in other solid-state spectra of Np IV compounds. ,,− Solution-phase UV/vis/NIR in toluene reveals an intense broad band similar to that of other M IV L 2 ( M = Ce , U , Th , Hf , Zr ,) complexes. Despite our best attempts, however, the Laporte forbidden 5f → 5f transitions of Np IV L 2 were not observed in the solution phase, as was the case for U IV L 2 .…”

Expansion of the Na3MIII(Ln/An)6F30 Series: Incorporation of Plutonium into a Highly Robust and Stable Framework

“…The investigators probed the phases beyond their structures by examining the optical properties and conducting a thorough analysis of bonding interactions . This work is critical considering the development of advanced reactor designs, including the molten salt reactor, which might use high‐fluoride content salt eutectics . Recently, Scheibe et al.…”

“…[14] This work is criticalc onsidering the development of advanced reactor designs, including the molten salt reactor, whichm ight use high-fluoridec ontent salt eutectics. [15] Recently,S cheibe et al reported on the synthesis and structures of MAnF 6 •3H 2 O( M= Mn 2 + ,Z n 2 + ;A n= Np 4 + ,P u 4 + ), an ovel series of transition metal actinide fluorides that also represent the first example of at ransition metal-containing plutonium fluoride. [16] In our search for phases containing surrogates that might functiona sh osts for plutonium substitution, we investigated the Na n M(Ln/An) 6 F 30 (n = 3o r4;M= divalent or trivalent metal; Ln = Ce 4 + ,A n= Th 4 + ,U 4 + )s eries as ap otentials tructural candidatef or plutonium inclusion on account of the exceedingly stablen ature of the phases and the ability to incorporate ad iverse range of metalc ations into the structure.…”

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

“…11−13 Molecular dynamic simulations on the molten AF−ThF 4 (A = Li, Na, K) mixtures at different molar percentages and temperatures revealed the dominance of ThF 8 4− and ThF 7 3− , depending on the alkali metals. 14−16 Apparently, there is no report regarding the thorium speciation in molten FLiBe that possesses different properties from those studied before, 17 and the correlation between experimental and theoretical results from vibrational spectroscopic studies has not been validated.…”

“…Recent studies employing extended X-ray absorption fine structure (EXAFS) and nuclear magnetic resonance analyses on the LiF–ThF 4 system described the evolution from free to bridging fluorine between ThF x in the melts rich in ThF 4 . It appears that the coordination number of thorium varies between six and ten, with the dominant species depending on the alkali metal ion in molten fluorides, according to EXAFS analysis. − Molecular dynamic simulations on the molten AF–ThF 4 (A = Li, Na, K) mixtures at different molar percentages and temperatures revealed the dominance of ThF 8 4– and ThF 7 3– , depending on the alkali metals. − Apparently, there is no report regarding the thorium speciation in molten FLiBe that possesses different properties from those studied before, and the correlation between experimental and theoretical results from vibrational spectroscopic studies has not been validated.…”