EXPERIENCE WITH QUALIFICATION OF METAL MATRIX COMPOSITES USED AS FIXED NEUTRON ABSORBERS

Since Transnuclear first introduced the use of boron carbide / aluminum metal matrix composites (MMCs) in the TN-68 storage and transport cask, other cask designers have begun to use these materials, and new suppliers have entered the market. The interest of the US regulator in how these materials are qualified for use is demonstrated by the ASTM work item WK936 which was initiated by US NRC staff members. MMCs lack a long history of large-scale manufacturing, and there are no widely-accepted standard specifications for manufacturing and inspecting them. Thus, it becomes necessary to develop methods for demonstrating that the material is suitable for its intended use, that it will perform in its working environment for the design lifetime, and that the manufacturing methods will be consistent. Initial efforts at materials qualification, the qualification of Boralyn® by Transnuclear (the designer), and the qualification of Metamic® by the Reynolds Corp. (the supplier) were quite extensive and correspondingly expensive. Because changes to manufacturing processes might require re-testing, and because that re-testing could be prohibitively expensive, such qualification programs could become an impediment to product development. Therefore, for its current license applications, Transnuclear has developed a more focused approach to MMC qualification along the lines of the WK936 work item. This approach requires collaboration of the supplier and the designer – the supplier cannot know all of the design requirements for the material, and the designer cannot know all of the appropriate controls to supply a consistent product. The first such license application to be approved is the NUHOMS® HD, USNRC CoC 1030. This paper examines the concepts behind this approach, and the practical implementation experience qualifying Alcan MMC for use in the NUHOMS® HD canister.