Compatibility of High Ni, Fe-Cr Alloys In Li and In Li Containing Traces of LiH

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Liquid lithium is considered as a candidate material for tritium breeding and reactor coolant applications in many magnetic fusion reactor concepts. Austenitic stainless steels of the type AISI 316 are envisaged on a priority base as containment materials in the first generation of reactors and for this reason their compatibility in static and flowing lithium has been extensively investigated. In a previous work, we have studied the behaviour of samples of AISI 316 and 304 in the presence of pure lithium and in lithium containing traces of LiH (1). The mechanism of corrosion is mostly influenced by the preferential dissolution of Ni with subsequent destabilization of the austenitic structure and the presence of 40 ppm H in Li seemed to exert a beneficial effect on the extent of the corrosion layer. Following this study we have examined the behaviour of Cr-Mn austenitic stainless steels (in the same experimental conditions) which may be an interesting alternative to the classical Ni-Cr steels (2). Also in this case, the presence of traces of hydrogen seemed beneficial. We thought that it would be of interest to extend the study to high Ni, Fe-Cr alloys such as Incoloy 800, Incoloy 825, Uranus B6 and to Ni-Cr alloys such as Inconel 600 and 601. These materials are engineering alloys extensively studied, which on account of their good mechanical properties have occasionally been considered for possible use as containment materials for Li in fusion reactors. Their corrosion resistance in liquid Li is not foreseen to be excellent on the basis of what was found for lower Ni containing stainless steels. This is confirmed by some Russian works on nickel and cobalt base alloys mentioned by Bates (3). The same author has studied, in static tests, alloys containing 45 – 47% Ni as RA-333 and Hastelloy X at 1163 K working in an argon atmosphere containing 0.15% N2 and with 1200 ppm of N2 in Li. He found a severe corrosion. Other authors have studied alloy 800 and alloy 600 in pure static Li (4,5) stating that between 773 and 973 K they corroded significantly after 1000 hrs, but that the corrosion of alloy 600 could be inhibited when 5 w% Al was added to Li. We have carried out our tests at 873 K.