Some recent results on stainless steel 316L(N) for a 60 years design life as ASTRID structural material

摘要

Austenitic stainless steel 316L(N) is the prime French candidate material for the vessel and components operating at high temperature in Sodium-cooled Fast Reactor CEA, EDF and AREVA have launched a R&D program to validate that SS 316L(N) meets the specific high level requirements of the ASTRID prototype. One of the main challenges is the material qualification for an extended design life of 60 years. This paper gives an overview on some recent R&D results on three particular domains: welding, long term creep modeling and compatibility with liquid sodium. Based on the industrial knowhow, welding procedures are being developed using SMAW and GTAW processes and several filler materials (with austeno-ferritic and austenitic microstructure). Assessment of the welded joints quality is based on the properties in the as-welded and aged states. Experimental and theoretical work is devoted to understanding and modeling of long term creep. Models are being developed to account for different creep mechanisms activated at intermediate times and long times. A corrosion device has been designed to carry out corrosion tests in controlled purity sodium. Exposure of 316L(N) specimens in sodium at 550°C up to 5000 hours give an insight in the corrosion mechanisms.