Numerical analysis of recrystallization behaviors for W monoblock under cyclic high heat flux

Abstract

The W/Cu monoblock for divertor target will be exposed to cyclic (∼300 cycles) and extremely high heat flux up to 20 MW/m2 in ITER, which may lead to significant macro cracking and W recrystallization according to existing high heat flux tests. Currently, the degradation of W mechanical properties due to W recrystallization, is regarded as one of the most important factors on cracking formation as well as the lifetime of W components. Therefore, to effectively predict W recrystallization behaviors, a method to simulate the evolution and distribution of W recrystallized fraction during the non-isothermal process was introduced. Coupling with finite element thermal analysis, W recrystallization gradients are successfully obtained. The numerical analysis results show very good agreement with those from existing experiments [1]. Further simulations of different heat flux density (15 MW/m2 − 30 MW/m2) and cyclic number (1–104) with heating time of 5 s, 8 s and 10 s were also carried out. It is found that the shape of the final recrystallized W region is according with the isothermal diagram at the end of the heating stage. In particular, the specific temperature of the corresponding isothermal line can be estimated by heating time and cyclic number. A fitting empirical equation was also given, which can be used to make fast prediction of recrystallization depth by comparing with isothermal diagram for such high heat flux tests. This method underlines the high potential to predict the recrystallization behavior of the W plasma-facing component under complex plasma heat flux in fusion devices.

Keywords

• Recrystallization
• Monoblock
• High heat flux
• Plasma facing component
• Numerical analysis