On the Corrosion Performance of Monel 400 in Molten LiCl-Li 2 O-Li at 923 K
- PDF / 2,645,205 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 4 Downloads / 127 Views
INTRODUCTION
THE pyrometallurgical method of reprocessing metallic fuel developed by Argonne National Laboratory offers an advanced method for closing the nuclear fuel cycle.[1] To integrate the used oxide fuels from light water reactors into a pyroprocessing-based fuel cycle, it is necessary to reduce the actinide oxides to metallic form prior to the electrorefining operation. Currently, electrolytic reduction in a LiCl-Li2O electrolyte at 923K (650°C) is the preferred method for actinide oxide reduction, using a process developed by Argonne National Laboratory.[2–5] The reduction of the actinide oxides in LiCl-Li2O is complicated due to the close reduction potentials of the actinide oxides and Li2O. Li2O has a reduction potential 70mV more negative than UO2, which is in theory a large enough difference to allow for the reduction of U without deposition of Li on the cathode. However, in practice it is necessary to provide significant overpotential for UO2 reduction in order to decrease processing time and increase reduction yields, which leads to the cell potential being beyond the potential for Li+ reduction.[6–11] This causes Li to be reduced on the
WILLIAM PHILLIPS and AUGUSTUS MERWIN, are with the Materials Science and Engineering, University of Nevada, Reno, Reno, NV 89557. DEV CHIDAMBARAM is with the Materials Science and Engineering, University of Nevada and also with the Nevada Institute for Sustainability, University of Nevada, Reno. Contact mail: [email protected] Manuscript submitted 18 January 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
cathode surface, which then acts as an additional reduction pathway for the actinides. Consequently, the reduction proceeds through both electrochemical and chemical reduction routes. Due to the solubility of Li in LiCl, a portion of the metallic Li on the cathode surface dissolves into the molten solution, forming a tertiary LiCl-Li2O-Li electrolyte.[12–17] The solubility limit for the dissolution of Li in LiCl-Li2O is not well defined due to the combined effects of physical dissolution and colloidal suspension of Li as the nanocluster, Li8.[18] An understanding of the degradation mechanisms that engineering materials undergo while in contact with the complex and variable solution chemistry present during the electrolytic reduction of used nuclear fuel is of considerable importance to the development of this process.[19–22] The study of high-temperature corrosion in various molten salts is an active research area.[23–25] Previous research conducted by our group has shown that the chromium oxide-based surface films of the engineering alloys stainless steel 316, Inconel 625, and Inconel 718, suffer degradation upon exposure to molten LiCl-Li2O-Li solutions where the weight fraction of Li is above 0.6 pct.[26,27] It is hypothesized that this is due to a transition from corrosion governed by the activity of the O2- anion to an effect similar to liquid metal based attack which occurs when the concentration of metallic Li is beyond the limit of physical dissolution. Consequently, t
Data Loading...
