Fracture modes of ITER tungsten divertor monoblock under stationary thermal loads

During the qualification program of the tungsten divertor vertical targets, the tested mock-ups (250 tested tungsten monoblocks in total) successfully demonstrate their thermal performances and structural integrity. However, some of the tested monoblocks, in average 30%, showed macro-cracks in the tungsten. This paper presents the results of 3D elastic-plastic thermo-mechanical analysis of the tungsten monoblock under stationary thermal loads for two cases of tungsten material properties: (1) stress-relieved and (2) recrystallized. The comparison pointed out that the recrystallized tungsten monoblock accumulated more damages at the loaded than stress-relieved tungsten. In addition, recrystallization may lead to early development of cracks on the monoblock either due to progressive deformation or fatigue while the non-recrystallized monoblock has a much smaller probability to develop cracks, as long as the exposed surfaces are free from defects.