Quantitative safety goals for fusion power plants: Rationales and suggestions

"How safe is safe enough?" is a key and fundamental question for any risky engineering and safety goals has been extensively studied in many fields, such as chemical industry, nuclear industry, etc. Fusion reactors are advanced nuclear reactors which are expected to be more attractive in terms of safety and environmental impact, and remarkable progress has been made toward the realization of fusion energy in this regard. However, fusion safety is not guaranteed automatically: accidents could happen with any possible future fusion reactor, potentially resulting in releases of radioactive materials. Meanwhile, there are also safety issues about radioactive wastes and occupational exposure, due to high neutron radiation produced in the reactor. To ensure the safety of fusion reactors from the origin, defining safety goals is very necessary to guide reactor design. In this paper, the evolution of safety goals for nuclear reactors is reviewed and a hierarchical framework for fusion quantitative safety goals is established in the four aspects of occupational radiation exposure, routine releases of radioactive materials, accidents and radwastes, based on the characteristics of fusion reactors from a designer's perspective as well as the experiences from the pressurized water reactor, Generation-IV, and International Thermonuclear Experimental Reactor. These safety goals will provide reference for designers of fusion reactors These safety goals will be helpful to guide the designer of fusion reactors to seek and develop appropriate means to enhance safety.