Austenitic Stainless Steels for Back End of Nuclear Fuel Cycle

Abstract

Austenitic stainless steels have received much attention in recent years due to their excellent combination of corrosion, mechanical and wear properties. They are finding wide applications in chemical, power, oil, refinery, biomedical, marine sectors and other industries where both good mechanical properties and excellent corrosion and wear resistances are demanded. In the spent nuclear fuel reprocessing plants and waste storage and processing plants involving nitric acid as the main process medium, type 304L stainless steels (SS) are employed as work horse materials for manufacturing more than 90% of the plant components. Though these alloys form a protective Cr2O3 passive film over the surface in nitric acid under plant operating conditions, they undergo various types of corrosion failures in service. Welding and other metallurgical parameters including alloying elements, cold working, heat treatment etc. degrade the performance of the alloy in service. For qualifying the alloy for plant applications, ASTM A262 practice A and C are currently employed, however, long term performance under simulated plant operating conditions is necessary to understand the failure modes and life prediction of components. Today, nitrogen represents an economically, environmentally, attractive and versatile alloying element to steels and stainless steels. The beneficial effect of nitrogen alloying in stainless steels are manifolds, including solid solution strengthening, precipitation effects, phase control and corrosion and wear resistances. Recent years have seen a rapid development of these alloys with improved properties owing to advances in alloy processing technologies. The objective of the lecture is to bring out the various corrosion issues in reprocessing plants, short term laboratory versus long term field corrosion data, modeling for life prediction, effect of redox ions, nitrogen alloying, welding and corrosion damage, etc. and highlight the remedial actions to overcome the shortcomings due to corrosion issues.