Corrosion Properties of Japanese FBR Materials in Stagnant Pb-Bi at Elevated Temperature
Tomohiro Furukawa, Kazumi Aoto, Japan Nuclear Cycle Development Institute
Georg Mueller, Gustav Schumacher, Alfons Weisenburger, Annette Heinzel, Research Center Karlsruhe, Institute for Pulsed Power and Microwave Technology (IHM), Germany
One of the main problems in the development of advanced heavy liquid metal cooled fast reactor (HLMFR) systems is the compatibility of structural and fuel cladding materials with potential coolants. Lead-bismuth eutectic (LBE) is expected to be one promising candidate material for a coolant of HLMFR in the Feasibility Study on Commercialized Fast Reactor Cycle Systems in Japan. In order to investigate the corrosion resistance of three Japanese materials named FBR grade type 316ss (316FR), high chromium type ferritic steel (12Cr-steel) and oxide dispersion strengthened martensitic type steel (ODS-M), corrosion tests were carried out in stagnant LBE of 500°C to 650°C for 800h and 2,000h under oxygen control at 10-6 weight percent by H2/H2O mixture gas flow. According to thermodynamic calculation, oxide layer is formed on the surface at the oxygen potential, and it was estimated that the base metal is protected from the attack of LBE i.e. solution of metal elements to LBE. After the tests, cross sections of the specimens were observed using scanning electron microscopy with energy dispersive X-ray analyzer (SEM-EDX). It was confirmed that the oxide layers were formed on the surface of all specimens, however, the composition differed with testing temperature. The surface of the specimens tested at 550°C or below was covered with two oxide layers. The main elements of inner layer were Fe, Cr and O, and those of outer layer were Fe and O. Although there were exfoliations at the outer layer, base metals were protected by inner layer. From the results, it was considered that three steel showed satisfying protection behavior at 550°C or below. On the other hand, the surface tested in LBE at 600°C or more was only covered a thin layer, and the elements were the same as those of inner layer tested at no more than 550°C. Most of the oxide on the surface seems to exfoliate into LBE during test period, because the thickness of the layer of the region exposed in LBE was smaller that of the exposed at gas atmosphere at the same oxygen potential. In addition, there were attacks of LBE on singular spots at the surface of three materials. The phenomena were observed after 800h exposure for 316FR and ODS-M, and after 2,000h for 12Cr-steel.