In researches and developments (R&Ds) on sodium (Na) management technology, the experimental data related to a cold trap and a plugging meter have been accumulated in each country because the impurities such as sodium oxide (Na2O), sodium hydride (NaH) and/or sodium hydroxide (NaOH) in Na coolant accelerate the corrosion on the stainless-steel surface. The cold trap has stainless-steel wire mesh and wall where the saturated impurities are recrystallized to remove the impurity in the Na coolant. Similarly, the plugging meter has stainless-steel orifice where the saturated impurities are recrystallized to measure the saturation concentration (plug temperature).

The recrystallization is common physical chemistry phenomena, in which is dominated by the temperature and the concentration. To date, a phase-field model (PFM) has been developed extensively as a powerful tool to predict microstructure evolution of micro–meso scale. Especially, the PFM has some simulation merits: it can calculate movement of interface without explicit trace of the interface (calculate robustly the large deformation), and this simulation results are known to be consistent with the thermodynamics data. In this study, we developed the simulation models for complex recrystallization of one impurity in Na coolant using the PFM, and confirmed that the simulation results are reasonable for the experimental data with the operating experience. In the simulation results for the one impurity of Na2O or NaH, we concluded that the kinetics of recrystallization was determined by the solubility and/or diffusion behavior in liquid Na.

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