Electrochemical impedance spectroscopy analysis of ht9, gr.92 and sic in liquid sodium environment for ucfr application

Abstract

Since HT9, Gr.92 (Ferritic/martensitic steels) and SiC(silicon carbide) are considered as candidates materials of Ultra-long Cycle Fast Reactors (UCFR) which is developed in UNIST (Ulsan National Institute of Science and Technology), their long term behavior (during30 to 60 years of operationtime) is one of issues especially dissolution, chemical reaction with impurities, and mechanical properties. HT-9 and Gr.92 are known as compatible in sodium environmentas cladding materials of SFRs (Sodium-cooled Fast Reactors) because the usual refueling time of SFRsis designed about 18 months. However, UCFR is designed with no-refueling for its whole operation time (30 to 60 years). So, it is very important to investigate the corrosion-related behavior such as surface corrosion rate, carburization, decarburization and mechanical properties for its operation time. However our previous study on mechanical behavior of candidate cladding materials in irradiation environment shows that only SiC can be the candidate of cladding materials among them. Since this result, SiC is also investigatedwith corrosion behavior in sodium environment.To monitor the corrosion behavior of these candidate materialsin sodium environment, Electrochemical Impedance Spectroscopy (EIS) method is first introduced and investigated in this study. Alumina covered HT-9, Gr.92 and SiC will work as working electrode (WE) and two molybdenum rods will work as counter electrode (CE). For the development of reference electrode (RE), solid electrolyte (YSZ, GDC used) based oxygen sensors are under development. And for accelerating the aging time in sodium to simulate long operation time, Time-Temperature superposition method will be adopted with optimized activation energy of each candidate materials.