Force-Free Helical Reactor. FFHR. is a conceptual design of helical fusion power reactor. Flibe is chosen as the coolant/ breeding material in this reactor mainly because of safety considerations. Two types of structural materials, i.e. ferritic steel and vanadium alloys were closely examined. Compatibility of these materials with Flibe is one of the largest issues for the selection of materials. It has been concluded that both systems using Flibe as coolant are feasible provided that the chemistry of Flibe is appropriately controlled.