A prerequisite for the reliable operation of lead-fast reactors (LFRs) is the compatibility of the heavy liquid metal (HLM) coolant with the structural/functional steels used to construct these nuclear systems. The primary HLM coolant in the LFR Pilot Plant MYRRHA system is the liquid lead-bismuth eutectic (LBE), while the 316L and DIN 1.4970 austenitic stainless steels are the candidate structural and cladding steels, respectively. One of the undesirable forms of interaction between liquid LBE and austenitic stainless steels is dissolution corrosion. Dissolution corrosion is promoted when steels are exposed to oxygen-poor liquid LBE, since these exposure conditions suppress/decelerate the formation of a protective oxide scale on the steel surface. Dissolution corrosion of austenitic stainless steels is typically characterized by: (a) transfer of the highly-soluble steel alloying elements (Ni, Mn, Cr) into the LBE, (b) LBE penetration into the base steel, and (c) ferritization of the dissolution-affected zone due to the loss of the highly-soluble austenite stabilizers Ni and Mn. For reasons that are not always clear, dissolution corrosion is sometimes locally-accelerated, which can be a serious concern for thin-walled components such as the fuel cladding tubes. Since dissolution corrosion, especially in its locally-accelerated variant, results in the thinning of the affected steel components and the compromise of their mechanical integrity, it is imperative to identify the set of variables that favor dissolution, so as to limit the occurrence of this undesirable liquid metal corrosion phenomenon to an acceptable minimum during reactor operation. This work addresses the main aspects of the dissolution corrosion behavior of 316L and DIN 1.4970 austenitic stainless steels at 500ºC in contact with oxygen-poor ([O] < 10-8 mass%) static LBE. The exposed steel specimens were either cylinders made of different 316L and DIN 1.4970 steel heats, or tubes made of DIN 1.4970 steels with a variable degree of cold working, while the duration of exposure varied between 250 and 3300 h. Since specimens made of different steels/heats were simultaneously exposed in the same LBE bath, this work also compares the dissolution corrosion behavior of simultaneously-exposed steel specimens wherever possible. The exposed 316L steel specimens have been characterized by means of light optical microscopy (LOM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM).
|Title of host publication||Proceedings of the SEARCH/MAXSIMA 2014 International Workshop|
|Editors||J. Pacio, A. Weisenburger, Th. Wetzel|
|Publisher||KIT - Karlsruher Institut für Technologie|
|State||Published - 2014|