ALLOY 59 (UNS N06059): ANOTHER ALTERNATIVE TO ALLOY 22 (UNS N06022) FOR THE RAD-WASTE CONTAINER FOR THE YUCCA MOUNTAIN PROJECT

摘要

The Nuclear Waste Policy Act of 1982 established an objective of Nuclear Waste disposal in a deep geological repository. This act was later amended in 1987, and established Nevada as the only site to be characterized. In 1994 a technical decision was made for a multipurpose container consisting of an outer barrier of carbon steel, alloy 400 or Cu-Ni 70/30 and an inner barrier of alloy 825. Later this concept was modified to use more corrosion resistant alloys for the outer shell of the containers. Since then the corrosion resistance characteristics of alloys 825, 625, C-276 and 22 were compared for this application. The waste package design underwent several iterations with one of the latest concepts consisting of 20 mm thick alloy 22 (UNS N06022) as the outer container barrier. Taking into account that one of the main design features of the containers is the long term thermal stability not only of the base metal but also of the welds after long periods of exposure at elevated temperatures another nickel based alloy, namely alloy 59 (UNS N06059), has to be considered as an equal or even better alternative. This paper presents data on the relatively new but well established alloy 59 (UNS N06059) and on the primary candidate for the rad-waste container alloy 22 (UNS N06022). New results on the mechanical properties, corrosion resistance and thermal stability of welded and unwelded material aged at 200, 300 and 427°C up to 20,000 h is compared for both alloys.