Plasma-material Interactions Problems and Dust Creation and Re-suspension in Case of Accidents in Nuclear Fusion Plants: A New Challenge for Reactors like ITER and DEMO

Given the urgent need to converge on precise guidelines for accident management in nuclear fusion plants, in this paper, the authors will analyze the problem related to the choice of possible candidate materials for the nuclear fusion plants like International Thermonuclear Experimental Reactor (ITER), DEMOnstration power plant (DEMO), or PROTOtype power plant (PROTO). Fusion power is a promising long-term candidate to supply the energy needs of humanity. From the safety point of view, nuclear fusion holds inherent and potential safety advantages over other energy sources. In magnetic confinement devices, the plasma edge and surrounding material surfaces provide a buffer zone between the hightemperature conditions in the plasma core and the normal "terrestrial" environment. The interaction between the plasma edge and the surrounding surfaces profoundly influences the conditions in the plasma core and is the principal key engineering issue. Robust solutions to plasma-material interactions (PMIs) issues are required to realize a commercially attractive fusion reactor. PMIs critically affect tokamak operation in many ways. Erosion by the plasma determines the lifetime of plasma-facing components (PFCs) and generates a source of impurities, which cool and dilute the plasma. Deposition of material onto PFCs alters their surface composition and can lead to long-term accumulation of large in-vessel tritium inventories. Retention and recycling of hydrogen from PFCs affect fueling efficiency, plasma density control, and the density of neutral hydrogen in the plasma boundary, which impacts particle and energy transport. Dusts are currently produced in the existing plants like JET (and will also be in the future ones like ITER, DEMO, and PROTO) by PMIs. Thus, the issues related to the PFCs of the first wall of the nuclear fusion plants area topic that the Quantum Electronics and Plasma Physics Research Group have been studying for more than a decade. Regarding the selection of PFCs, there are two strong school of thoughts that work on fusion plants materials for the first wall: (1) one composed by experts working mainly on nuclear fusion and that are focusing their attention on certain materials (like tungsten, beryllium, carbon, tritium, stainless steel, and other), and (2) the other one composed of experts working mainly on the fission plants that want to demonstrate the "dual-use" characteristics of the "fission materials" for fusion plants applications. In this review paper, the authors will (1) review both the approaches mentioned above comparing the main characteristics of all the proposed and tested materials, (2) analyze the consequences (experimentally revealed and numerically predicted) of PMIs that provokes serious damages to the plants and dangerous consequences like radioactive/toxic dust production, and (3) analyze (also thanks to our experimental activities on STARDUST-Upgrade facility) the risks (for the operators) related to the dust re-suspended in case of accidents. The authors will critically comment each section of the paper together with a detailed state of the art.