Numerical Simulation On Coupled Ermal-mechanical Behavior And Thermal Fatigue Performance Of First Wall In Fusion Reactor

After years of exploration and development, research of magnetic confinement nuclear fusion is progressed into stage of experimental fusion reactor construction and test. As a key plasma-facing component, the anti-fatigue and anti-thermal-shock performance of first wall of fusion reactor receives widely concerns. According to published literatures, many previous researches were focused on engineering applications; few are concentrated in aspects of material/structure mechanism of fatigue and thermal shock. Due to the fact of enduring both periodic loads of pulse operating mode and transient extreme loads of plasma disruption, the coupled mechanical/thermal responses of material and structure are in the state of very complex. It is of great significance and necessary to research the coupled mechanism of fatigue and thermal-shock and its effects on performance, which will be beneficial to develop the key and new technology of anti-fatigue and anti-thermal-shock performance for the first wall of fusion reactors. In this thesis, a relative complete finite element analysis method based on a full coupled thermal/structural heat transfer equation with consideration of elastic/plastic constitutive relation as well as multiple kinds of thermal physical effects such as melting, solidification, evaporation etc. is established. With this method, the thermal/mechanical response of first wall and its fatigue performance are investigated preliminarily. The results are listed as following:1) The coupled thermal/mechanical response of two typical structure of ITER-like first walls (with different plasma-facing material:one is traditionally Be, the other is functionally graded W-Cu) under the heat shock of1～2GW/m2are computed and compared. It is founded that:heat is mainly deposited on PFM layer, leading to a mechanical irreversible damage of repeated thermal elastic and plastic expansion, contraction and yielding. In view of thermal/mechanical performance, the first wall with Be PFM mitigates the damages from heat shock at most only in PFM layer with cost of whole PFM layer plastic yielding, while the first wall with graded W-Cu PFM is potential of higher heat shock resistance performance, providing its material gradient as well as cooling capacity are well optimized under practical loading conditions.2) Based on thermal/mechanical analysis, the thermo-technical performance optimization on first wall in fusion reactor made by continuous W/Cu graded material with different composition distribution parameter p is analyzed. It is concluded that:under the same steady heat load conditions, the optimized composition distribution parameter p for composition continuous W/Cu graded material is very different with that of previous quasi-continuous W/Cu graded material. A26%reducing in thermal stress is observed for first wall with composition continuous W/Cu graded material, demonstrating a more excellent performance; In the process of heat shock, the damage degree measured by volume fraction of plastic deformation is changing with different composition distribution parameter p, its optimized value is different with that obtained in steady state conditions. In consideration of environment conditions endured by first wall, the optimized value should be chosen to be close to1.2; In general, there is a more prominent advantage for composition continuous W/Cu graded material applied in first wall design of fusion reactor due to its continuous variation of thermal physical properties and mechanical properties.3) With the equation of Manson-Coffin, the fatigue performance of first wall with PFM of Wu-C graded material is analyzed. The results show that the fatigue performance is very different with adoption of different W/Cu graded material. The first wall with material of optimized p has the highest fatigue performance.4) Further analysis shows that the fatigue life time of first wall is decreasing nonlinearly with increase of heat loads magnitude. And the heat shock will greatly reduce the fatigue life time of first wall, even there is no distinguishable damages (crack).