Numerical Evaluation on Heat Shock Resistance of Two ITER-Like First Wall Mockups

Abstract

The first wall of fusion reactor is a plasma-facing component and is a key link to maintain the integrity of the structure during thermal shock induced by plasma disruptions. Previous researches on thermal shock resistance of the first wall lacks coupled thermal/mechanical analysis on heat shock process based on practical operating conditions, such as material melting, solidification and even evaporation etc., which is significant to further understand the heat shock damage mechanism of first wall structures. With the aim to lean more detailed mechanical mechanism of thermal shock damage and then to improve the thermal shock resistance performance of first wall design, 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 of 1–2 GW/m² are computed by the finite element method. Special considerations of elastic–plastic deformation, material melting, solidification are included in numerical models and methods. The mechanical response behaviors of different structures and materials under normal servicing operation as well as plasma disruption conditions are analyzed and investigated comparatively. It is concluded that: (1) During the normal servicing operation state, both kinds of first walls manifest a good thermal and mechanical performance. However, the first wall with graded W–Cu material presents a more complex distribution and larger values of interfacial thermal stress and deformation. (2) In high energy shock pulse induced by plasma disruptions, heat is mainly deposited on PFM layer, complex thermal stress change as well as coupled melting and solidification processes in PFM layer are observed, involving a mechanical irreversible damage of repeated thermal elastic and plastic expansion, contraction and yielding. (3) The mechanically irreversible damages for both mock-ups under the thermal shock with H₀ = 1–2 GW/m² are mainly limited in PFM layer, the internal parts of both mock-ups are protected effectively. (4) 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.