Molten fluoride salt and liquid metal multistage extraction model

Abstract

A multistage extraction model based on the distribution of actinides and rare earths between two phases of lithium activated bismuth and molten LiF-BeF 2 (66 mole % LiF) has been developed. The model shows that the distribution across the cascade is affected by the concentration of Li in the metal phase, system temperature, flow rates of each phase, and the presence and concentration of other elements in the molten salt phase. Based on the model, it is predicted that an online molten salt coolant purification system could be used to separate both rare earths and actinides from the primary salt coolant in fluoride salt-cooled hightemperature reactors (FHRs). Additionally, the results provide sufficient evidence that this extraction method can separate primarily actinides prior to extraction of other rare earth elements, which would allow for fission products and other reactor poisons to be discarded, while fuel materials (U and Pu) can be recycled back into a reactor system.

Impurities in Primary Coolant Salt of FHRs: Chemistry, Impact, and Removal Methods

“…The superscript I represents the initial condition and represents the total number of elements. Subsequently, the following equation can be obtained…”

“…However, considering the equation is obtained based on the assumption of infinite dilution ( dose not depends the concentration of ), the solution of the equation cannot be applied to calculate the distribution coefficients of concentrated solution. Equation – have been applied to study the separation of actinides and rare earths from LiCl‐KCl using Cd–Li and from LiF–BeF 2 using Bi–Li …”

“…Although most of the thermodynamic data for fission products, actinides, and corrosion products in liquid Bi are available, the thermodynamic data of these elements in the primary salt (LiF–BeF 2 ) are still scarce even there are lots of studies on measurements of these data in salt but using a surrogate salt (LiF–NaF–KF). The apparent potentials of redox couples of U 3+ /U, Pu 3+ /Pu, La 3+ /La, Ce 3+ /Ce, Sm 3+ /Sm, and Li + /Li in the primary salt (FLiBe) were summarized in a previous study . Based on the relationship between the apparent potential and the activity coefficients, the activity coefficients of U 3+ , Pu 3+ , La 3+ , Ce 3+ , and Sm 3+ in the primary salt therefore can be calculated.…”

“…Based on the available data, the multistage extraction of actinides and lanthanides from the primary salt using Bi–Li liquid metal was modeled . The model results showed that the actinides (U and Pu) are first extracted from the primary salt, followed by lanthanides (La, Ce, Sm), and the extraction efficiency depends on parameters of temperature, the counter‐current flow rate of both molten salt and liquid metal, the Li concentration in liquid Bi, and the presence and concentration of other elements in the primary salt.…”

“…Considering that the concentration of actinides in the FHR primary salt is much lower than that in the MSBR, the direct extraction of actinides using Bi–Li liquid–liquid extraction can be the way to remove them from the FHR primary salt. A model recently developed for liquid–liquid extraction has shown the efficiency of the method . Based on the success of actinide separation from molten salt in pyroporcessing, the actinides should be able to be removed by electrochemical separation…”