Comparison of the safety and environmental characteristics of refractory alloys under consideration in APEX

High temperature refractory alloys of tungsten, molybdenum and tantalum are under evaluation for use as structural materials in the Advanced Power Ext raction Program (APEX) because of their ability to accommodate high wall lo ading and high temperature coolant. However, such materials tend to have un desirable safety and environmental characteristics relative to conventional reduced-activation fusion materials. These alloys have high decay heat and in some cases their activation results in the production of long-lived iso topes that would disqualify the material from being disposed of as low leve l waste. In addition, some of the alloys have oxides that are very volatile , which could be mobilized in accident scenarios in which air ingress is a concern. In this paper we compare the safety and environmental characterist ics of these alloys with their low activation cousin (vanadium) in terms of decay heat, oxidation driven mobilization in air, and waste management.