Chemical interactions between zirconium and free oxide in molten fluorides

Abstract

The chemical interactions between zirconium and free oxide in FLiNaK melts at different zirconium to oxide (n Zr /n O ) molar ratios were studied by means of a carbothermal-reduction technique (LECO oxide analyzer) and Raman spectroscopy. ZrO 2 precipitates were formed with n Zr /n O # 0.5, while ZrO 2 was converted to Zr 2 OF x 6Àx complexes with n Zr /n O > 0.5. The maximum amount of Zr 2 OF x 6Àx complexes in FLiNaK melts was found to be 0.020 mol kg À1 . With an initial oxide concentration lower than 0.020 mol kg À1 and the required amount of ZrF 4 , the free oxide in FLiNaK melts could be completely converted to Zr 2 OF x 6Àx complexes, which would further prevent the formation of UO 2 precipitates. Fig. 9 The Raman spectra of UO 2 (ref. 38) ore and the bottom precipitates taken from the solidified FLiNaK-UF 4 (0.007 mol kg À1 ) melts at initial oxide ¼ 0.020 mol kg À1 and n Zr /n O ¼ 0. Fig. 8 The solidified FLiNaK melts with initial oxide at 0.020 mol kg À1 and different n Zr /n O ; (a) n Zr /n O ¼ 0; (b) n Zr /n O ¼ 7.0. 40712 | RSC Adv., 2015, 5, 40708-40713This journal is

Probing the ionic structure of FLiNaK–ZrF4 salt mixtures by solid-state NMR

“…Fluoride eutectic salts have been studied extensively as a coolant or a fuel salt for nuclear reactor systems due to their ability to act as an effective heat transfer uid at high temperature and low pressure and based on high radiation ux. [1][2][3][4] Specic to the fuel salt, the concentration of free oxygen dianion O 2À is rigorously regulated to avoid UO 2 [5][6][7] being precipitated. As reported by Oak Ridge National Laboratory (ORNL), the zirconium tetrauoride (ZrF 4 ) can act as the O 2À absorber additive in fuel salts for removing free O 2À and avoiding UO 2 being precipitated.…”

Inhibition effect of ZrF4 on UO2 precipitation in the LiF–BeF2 molten salt

“…Besides,Gibilaro 18 has found that the addition of calcium oxide (CaO) into a ZrF 4 -containing lithium uoride-calcium uoride (LiF-CaF 2 ) salt leads to the formation of a close to equimolar mixture of solid ZrO 2 and ZrO 1.3 F 1.4 . Korenko et al19 and our previous studies7,8,16,20 have used X-ray diffraction (XRD) phase analysis and electrochemical techniques and discovered the ZrO 2 formation when oxide contamination occurs in the ZrF 4 -containing systems (i.e., LiF-NaF-KF-ZrF 4 and LiF-NaF-KF-UF 4 -ZrF 4 ), whereas only UO 2 is observed in the systems without ZrF 4 (i.e., LiF-NaF-KF-UF 4 and LiF-BeF 2 -UF 4 ). These studies demonstrate that O 2À in zirconium-based systems can be reduced by forming Zr(IV) oxide or oxyuorides, preventing the UO 2 precipitation.…”

“…2, which was described in detail in our previous studies. 7,8,16,17,20,21,24 The whole experiment was conducted in a glove box protected by dry argon atmosphere (99.999%), and the oxygen and water contents in the glove box were both strictly controlled below 0.5 ppm.…”

“…through the carbothermal reduction technique, which was in accordance with the work of Mediaas 25,26 and our previous studies. 7,8,16,20 Herein, the result measured by LECO was the total oxide content including O 2À and oxide in oxygenated anions. The oxygenated anions in the melts were determined using ICE ion chromatography (IC, ICS-2100, Dionex Co., Ltd.) with a valve-switching technology.…”

“…Zirconium tetrauoride (ZrF 4 ) may be a good selection, which has a strong affinity toward oxide and is a good oxide getter that can easily capture O 2À to form zirconium oxides (e.g., ZrO 2 ) or zirconium oxy-uoride species (e.g., ZrOF 2 and Zr 2 OF 10 4À ) in the molten uorides. 16,17 In this manner, the combination of U(IV) and O 2À can be effectively avoided. Shen et al 16 have studied the interactions between Zr(IV) and O 2À in lithium uoride-sodium uoridepotassium uoride (LiF-NaF-KF (46.5 : 11.5 : 42 mol%, FLi-NaK)) molten salt and found that different products are formed at different molar ratios of nZr(IV)/nO 2À .…”