Influence of recrystallization on tungsten divertor monoblock under high heat flux

Extremely high heat flux reaching 20 MW·m−2 can be foreseen for the future fusion reactor. Such high heat flux would induce recrystallization of tungsten (W) material, leading to significant strength loss of tungsten material and increment of ductility at high temperature, in particular when the temperature is much higher than its ductile-to-brittle transition temperature (DBTT). In this paper, an International Thermonuclear Experimental Reactor (ITER)-like tungsten divertor monoblock is modeled, and benchmark has been done first to get consistent results with ITER. Then, the monoblock structure has been optimized in order to get a lowest possible temperature and stress during heating and cooling phase separately compared to the baseline structure. Structural analysis of two kinds of states: stress-relieved tungsten and recrystallized tungsten using finite element method has been performed, aiming at finding out the recrystallization impact on the mechanical behavior of tungsten in divertor monoblock under cyclic high heat flux. Damages due to progressive deformation and time-independent fatigue lifetime of these two states of tungsten have been assessed and compared according to criteria The Structural Design Criteria for ITER In-vessel Components. Finally, the impact of different material recrystallization temperature on mechanical behavior has been explored under stationary heat load. The result shows that after recrystallization, thermal stress of tungsten material can be released by the larger plastic deformation compared to the stress-relieved tungsten. However, it is easier for recrystallized tungsten to get damaged due to progressive deformation as well as fatigue under 20 MW·m−2 cyclic heat flux than stress-relieved tungsten because of its relatively lower yield strength and larger plastic strain, which would cause low-cycle strain fatigue. Furthermore, tungsten with lower recrystallization temperature distorts more seriously, and therefore, it can be predicted the cracks would be initiated more easily.