Degradation of tungsten monoblock divertor under cyclic high heat flux loading

•Degradation of pure W monoblock divertor during high heat loading at 20 MW/m2 was evaluated and crack formation mechanism was discussed.•Macro-crack formation could occur due to complexed low temperature cleavage fracture accompanied by plastic deformation. The degradation behavior of the ITER divertor under the cyclic high heat flux loading has been varied in the previous studies, which would be induced by the intrinsic difference in the thermo-mechanical properties of each pure W material. Therefore, the experimental characterization of the thermo-mechanical properties of the W materials and the numerical structural analysis using these data are necessary to clarify the degradation mechanism and the prediction of the fracture scenario and lifetime. In this study, the degradation behavior of the pure W monoblock divertor mockup during the cyclic high heat flux loading test at 20MW/m2 was evaluated and the macro-crack formation mechanism was discussed based on the structural analysis. The macro-crack formation of the divertor mockup in the present study could occur due to a complexed low temperature cleavage fracture accompanied by the plastic deformation under cyclic loading. The fatigue, especially the low temperature fatigue with plastic deformation, could be a mechanism factor for the macro-crack formation. However, further study considering the thermo-mechanical fatigue and the effect of the low temperature plastic deformation is necessary to quantitatively evaluate the macro-crack formation mechanism by the fatigue.