The Advanced Spent Fuel Conditioning Process (ACP) has been proposed and developed by the Korea Atomic Energy Research Institute (KAERI) to treat oxide spent fuels (SFs) from light water reactors to reduce the volume, heat load, and radiotoxicity of processed SFs. In the ACP, an electrochemical reduction process has been developed, and an electroreducer with a maximum 20 kg/batch scale has been installed in the KAERI ACP facility. In this study, electrochemical reduction runs were carried out with 10 kg/batch of SIMFUEL at 923 K under current controlled conditions.

The electrochemical reduction processes adopted LiCl molten salt as the electrolyte, and initially, 3.0 or 4.9 wt% of Li2O was dissolved to increase the oxygen ion activity in this work. A porous MgO basket was used to contain the powder-type test fuels; the basket and fuels along with a metal conductor as the current lead comprise a packed bed reactor where reduction takes place. During the three runs of reduction, the Li2O concentration was decreased with the applied current, and it was found that Ar bubbling in the bulk phase accelerated the depletion rate. Alkali and alkaline earth metal elements from the test fuels had dissolved and accumulated in the molten salt. The reduced metal was recovered after the runs, and sampled products exhibited >90% reduction yields with respect to their positions in the MgO basket. In addition to the experimental study, a three-dimensional model was developed to analyze respective phases in a reactor by using commercial tools. Streamlines of the fluids, the temperature distribution, and the oxygen partial pressure were obtained for the gas phase in motion, and the potential field calculation was carried out to reveal that most of the potential was applied to the cathode side because of the low electrical conductivities of the constituents.