Development of High-Temperature Sodium Loop System for Materials Compatibility Test for Ultra-long Cycle Fast Reactor (UCFR)

Sodium is a candidate for fast reactor coolants that has been believed to have favorable compatibility with structural materials. However, recent studies showed results which need for a more careful attention at this previous belief. For prolonging the service life time of cladding and structural materials in contact with liquid sodium, more detail analysis methods are needed to examine this material compatibility issue with sodium. As a candidate of liquid metals coolants of Ultra-long Cycle Fast Reactor (UCFR), the compatibility of sodium with cladding materials has to be investigated in detail with long term exposure time. It is known that corrosion promotes corrosion in two ways. One is corrosion produced by dissolution of alloy elements into sodium and the other is corrosion produced through a chemical reaction with impurities in sodium, especially dissolved oxygen. The use of the technique of impedance spectroscopy to measure the electrical impedance response of any oxide layers may be a good experimental tool to this monitoring system. The motivation of current study is to investigate the relationship between the electrochemical behaviors of oxide scales on ferritic-martensitic (FM) steel and austenitic steels (as shown in Table I) and their corrosion rates in liquid sodium environment