Equilibrium distribution of lanthanum, neodymium, and thorium between fluoride salt melts and liquid bismuth

Abstract

The extraction of lanthanum, neodymium, and thorium from 73LiF-27BeF 2 , 78LiF-22ThF 4 , 75LiF-5BeF 2 -20ThF 4 , 15LiF-58NaF-27BeF 2 , and 60LiF-40NaF (mol %) fluoride salt melts into liquid bismuth with admixtures of lithium as a reducing agent was studied at 580-750°C. Equilibrium values of their distribution coefficients were measured. Beryllium as distinct from neodymium and lanthanum almost was not extracted into bismuth from salt beryllium containing compositions. A decrease in the mole fraction of LiF in LiF-BeF 2 melts substantially increased the effectiveness of its purification from lanthanides. The LiF-ThF 4 and LiF-BeF 2 -ThF 4 salt mixtures with comparatively high thorium concentrations (≥20-22 mol %) could not be used for effective separation of lanthanides and thorium in a system for extraction processing of fuel salts.

The molten salt reactor (MSR) in generation IV: Overview and perspectives

“…The main advantages of a two fluid system are a reduced initial fissile inventory and a simplification of fuel salt clean up from both protactinium (Pa removal is not necessary as it is diluted in the blanket salt) and soluble rare earth fission products from the fuel salt in absence of thorium (LeBlanc, 2010). Because thorium and rare earth fission products have similar chemical behavior, (Zagnit'ko and Ignatiev, 2012) the removal of rare earth fission products is greatly simplified without thorium in the core fluid. Rare earth fission products absorb neutrons and reduce the production of new fissile fuel, their concentration in the salt needs thus to be kept low, as they have a large cross section for neutron capture in a thermal neutron spectrum.…”

Molten fluoride salt and liquid metal multistage extraction model

“…All stages are assumed to have a residence time large enough for equilibrium to be reached and electrochemical kinetics are therefore not considered. However, previous experiments and studies show that the time scale for reaching equilibration in a batch system is on the order of a few hours to a couple days [7,8]. This is a significant challenge that will need to be addressed in order for the continuous extraction process described in this paper to be advantageous.…”