ASSESSMENT OF AUSTENITIC STAINLESS-STEELS

An assessment of stainless steels is performed in order to recommend the most suitable structural material for ITER, to identify areas where additional research and development work is needed for full qualification and licensing of the recommended material, and to estimate the cost of such a research and development programme to be completed within a five year time schedule. After a brief assessment of different stainless steel categories, the choice is narrowed down to austenitic stainless steels, and more precisely to the type 316LN composition retained in Europe for the fusion reactors, and used in four generations of fast breeder reactors in France. Material specifications for the recommended steel are presented, incorporating the most recent research and development results, obtained from work performed in Europe, Japan, and the USA. The available database is presented for the selected steel using the boundary conditions extracted from the most recent report by the Joint Central Team on ITER Outline Design, but also incorporating possible changes that may be made in these conditions either for the initial basic performance phase or for the future extended performance phase. For each evaluated property, whether physical, mechanical or environmental, reference values and their corresponding trend curves are presented and, when applicable, lower bound or upper bound design curves are proposed. Using end-of-life properties of unirradiated materials as the reference design critierion, effects of irradiation are evaluated. If the observed changes remain within the safety margins incorporated in design they are considered acceptable. This is shown to be the case for materials irradiated to doses up to 10 dpa at temperatures either less than 200 degrees C or around 400 degrees C. If the observed changes exceed or appear to exceed the safety margins incorporated in design they are considered inadequate. In this case additional experiments, and when applicable safety margins, are recommended. Areas where clear conclusions cannot be drawn, or where there is a lack of experimental data, are identified and a five year research and development programme is proposed for the establishment of a comprehensive database allowing full qualification and licensing of the recommended steel. The proposed research and development programme includes plans to use existing fast breeder reactors as a low temperature irradiation means to obtain doses greater than the 10 dpa.