Properties of the LiCl-KCl-Li2O system as operating medium for pyro-chemical reprocessing of spent nuclear fuel

Self Cite

Reduction of ZrO 2 by lithium during electrolysis of LiCl-KCl-Li 2 O melt at 650°C was studied using a set of physicochemical methods of analysis. Influence of ZrO 2 in the space near a molybdenum cathode on the kinetics of the cathode process was established. Possible variations of the electrode reaction associated with the zirconium reduction were proposed. The appearance of ZrO 2 in the cathode space resulted in consumption of reduced lithium and in increase in the potential relaxation time of the molybdenum cathode after cathode polarization. Long-term galvanic impulse electrolysis of LiCl-KCl-Li 2 O melt at 650°C was carried out using the molybdenum cathode which was immersed into the ZrO 2 powder. According to the X-ray fluorescence analysis as well as the method of nuclear reactions the reduction product was presented by the ZrO 2 , Li 2 ZrO 3 , Zr 3 O phases. Additionally, by alloying the reduction product with tin, the ZrO 2 reduction degree to metallic zirconium was estimated, which was close to zero. It was assumed that the main pathway for the appearance of the metallic zirconium in the ZrO 2 reduction product during electrolysis of the LiCl-KCl-Li 2 O melt was direct electroreduction of dissolved zirconium in the melt.

Section: Methodsmentioning

confidence: 99%

Reduction of ZrO₂ during SNF Pyrochemical Reprocessing

Nikolaev

Suzdaltsev

Pavlenko

et al. 2021

Self Cite

“…The Li 2 O concentration in the melt was determined by the pH of an aqueous solution of the electrolyte. 24,27 The amount of passed electricity (Q) is given as a percentage of the theoretical amount of electricity required for a complete ZrO 2 reduction by metallic lithium. As can be seen from Table II, the method used for determining the degree of ZrO 2 reduction, as well as the previously used methods, [8][9][10][11] showed that the samples reduced up to 55%.…”

Section: Resultsmentioning

confidence: 99%

“…[24][25][26] The required amount of Li 2 O was immersed into the electrolyte as a pre-saturated LiCl-Li 2 O melt. 27,28 All procedures were carried out in a dry argon box.…”

Section: Methodsmentioning

confidence: 99%

Reduction of ZrO₂ in LiCl-Li₂O Melt During Electrolysis

Shishkin¹,

Shishkin²,

Nikolaev³

et al. 2022

Reduction of spent nuclear fuel (SNF) components to metals during the electrolysis of the LiCl-Li2O melt at 650°C is extremely important in the framework of the development of fuel reprocessing technology. Here, ZrO2 reduction by lithium during the electrolysis of the LiCl-Li2O melt at 650°C was studied. Cathode processes on a molybdenum substrate in contact with different ZrO2 samples (powder, pressed pellet, dense ceramic) were analyzed using cyclic voltammetry and electrolysis. It was shown that the appearance of ZrO2 near the molybdenum cathode leads to increasing cathode currents and decreasing lithium oxidation current. Both effects indicate the consumption of reduced lithium for the reduction of ZrO2 samples. In order to analyze the reduction products X-ray phase analysis and scanning electron microscopy were used, and to estimate the reduction degree of ZrO2 samples three methods were tested: dissolution of samples in inorganic acid solution, dissolution of samples in EtOAc/Br2 solution, and carbothermal reduction. It was shown that during the electrolysis of dense samples only the lithium zirconate (Li2ZrO3) was formed at their surfaces, whereas the electrolysis of ZrO2 powder samples resulted in the formation of Li2ZrO3, Zr3O, and ZrO phases.

“…After the experiment was finished, the mass of the preliminary washed ZrN powder was 4.95 g. The X-ray diffraction pattern of the ZrN powder after the experiment and washing from salts is demonstrated in a number of works. 39,40 The ZrN behavior in such melts may differ because of formation of complexes, which can impact the Reaction 1 kinetics. For the experimental verification the ZrN powder of 5.01 g was immersed in the LiCl-KCl-PbCl 2 melt with the molar ratio equal to 6 mol/mol at 650°C.…”

Section: Results and Discussion (Experimental Verification)mentioning

confidence: 99%

High Temperature Corrosion of ZrN Powder in Molten LiCl with Additions of PbCl₂, KCl, Li₂O, H₂O, and LiOH

Nikolaev

Suzdaltsev

Zaikov

2019

The chemical resistance of the ZrN powder to molten LiCl with additions of PbCl 2 , KCl, Li 2 O, LiOH, and H 2 O at 650°С have been thermodynamically evaluated and experimentally verified. Using complex physical-chemical methods it has been demonstrated that ZrN exhibits a high resistance to the LiCl-PbCl 2 melts. After long-term exposure of the ZrN powder in these melts the PbCl 2 concentration was not changed and the ZrCl 4 content did not exceed 0.002 wt% in the melt and 0.23 wt% in the sublimates. An increase in temperature or molar ratio of PbCl 2 /ZrN, as well as appearance of the KCl modifying component insignificantly reduces the ZrN resistance to molten LiCl-PbCl 2 . According to the SEM analysis, a structure of the ZrN powder becomes less dense after the exposure in LiCl-PbCl 2 . Almost complete oxidation of the ZrN powder was found after long-term exposure in the LiCl-PbCl 2 melts with Li 2 O and LiOH additions, and only partial oxidation was observed in melts with H 2 O addition. Nevertheless, a high resistance of the ZrN powder to the LiCl-Li 2 O melt was determined.