Safety issues associated with mobilized activation products in selected APEX designs

In the advanced power extraction (APEX) project, safety and environmental concerns considered up front, as designs evolve, so that the goal of safety and environmental attractiveness is realized. Since the neutron and surface heat loads are higher in APEX designs than those in conventional fusion designs, decay heat and activation are generally higher, presenting an increased challenge when justifying the safety case. Potential first wall materials that can function adequately under higher neutron and heat loads include materials such as tungsten and molybdenum. The activation products of both these materials are radiologically hazardous and mobilizable under accident conditions. We have examined a number of APEX concepts to determine the ability of the design to remove decay heat from the plasma-facing surface during a loss of coolant and air ingress event. In this paper, we concentrate on mobilization of first wall materials during ingress events, and provide guidance to enhance the safety characteristics of APEX designs that utilize tungsten and similar high heat load materials.