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DOE OSTI · 3377446

In situ monitoring of lanthanide reactions with oxide species via combined absorption spectroscopy and electrochemical methods

LeCroy, Garrett S. [Idaho National Laboratory] (ORCID:0000000216776191)·Yang, Qiufeng [Idaho National Laboratory]·Gakhar, Ruchi [Idaho National Laboratory] (ORCID:0000000228293533)·Cao, Guoping [Idaho National Laboratory] (ORCID:0000000231774733)
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Abstract

Molten salts for engineering scale applications of spent nuclear fuel pyrochemical processing will inevitably have some level of oxygen impurities which can form insoluble oxide and oxychloride species with fission products. This work demonstrates real-time concentration monitoring of two lanthanide (Ln3+) fission products, Nd3+ and Pr3+, and their reactions with oxygen (O2-) impurities to form insoluble products in LiCl-NaCl-KCl eutectic salt. Combined absorption spectroscopy and electrochemical testing were used to track lanthanide concentrations. O2- impurity levels were controlled by adding Li2O to lanthanide-salt solutions. After the introduction of O2- impurities, Ln3+ concentrations were monitored via time-resolved absorption spectroscopy. Concentrations of both Ln3+ species in solution decreased with time as insoluble products formed. The initial impurity concentration controlled whether insoluble products were predominantly oxychlorides or mixtures of oxychlorides and oxides. However, absorption spectroscopy is limited for weakly absorbing species, such as Pr3+, and under conditions of high impurity concentrations where solutions can be turbid. To circumvent this limitation, the concentrations of Pr3+ were monitored with cyclic voltammetry (CV). Reaction rates and extent of Pr3+ removal from solution as monitored by CV agreed closely with results found from spectroscopic monitoring. This demonstrates that simultaneous electrochemical testing complements the capabilities of absorption spectroscopy to monitor reactions of fission products in molten salts.

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11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRYabsorption spectroscopymolten saltpyroprocessingRaman Spectroscopy

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LeCroy, Garrett S. [Idaho National Laboratory] (ORCID:0000000216776191), Yang, Qiufeng [Idaho National Laboratory], Gakhar, Ruchi [Idaho National Laboratory] (ORCID:0000000228293533), Cao, Guoping [Idaho National Laboratory] (ORCID:0000000231774733). 2025-08-21. In situ monitoring of lanthanide reactions with oxide species via combined absorption spectroscopy and electrochemical methods. https://www.osti.gov/biblio/3377446

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