Speaker
Description
Following the decision by ITER in its new baseline to replace beryllium with tungsten in the first wall, the fabrication of large-area curved plasma-facing tungsten components has attracted growing attention. Low-cost, high-efficiency manufacturing of tungsten (W) first wall structures for breeding blankets holds significant importance for future large-scale tokamak fusion experimental reactors. Among various coating processes, thermal-spray-based tungsten coating techniques have regained research interest after years of limited activity. Over the past five years, our laboratory has been dedicated to studying and improving the detonation spraying process to produce tungsten coatings suitable for ITER first wall applications.
This report systematically introduces a coating-based tungsten/steel first wall structure developed in our laboratory, along with a series of studies on its high-heat-flux performance and post-treatment modifications. The process begins with depositing a pure tungsten coating onto a steel substrate, which exhibits excellent comprehensive properties including high density, purity, bonding strength, hardness, and thermal shock resistance. Subsequently, a high-purity, high-density iron (Fe) interlayer is deposited between the tungsten coating and the steel substrate to further enhance performance under high heat flux (HHF) conditions. The key thermomechanical properties of both the tungsten and iron coating materials have been thoroughly characterized.
Based on this characterization, finite element analysis was used to optimize the thicknesses of the tungsten and iron coatings in the W/Fe/steel first wall structure, ensuring optimal performance under steady-state HHF conditions. Following optimization, a first wall module with the refined thickness design was fabricated and successfully tested under 1,000 cycles of 1 MW/m² HHF loading as well as under prolonged steady-state HHF conditions.
Furthermore, systematic research was conducted on heat treatment to improve the performance of the tungsten coatings. For example, annealing was found to enhance the crack initiation resistance of the as-sprayed tungsten coating but reduce its crack propagation resistance, whereas recrystallization treatment resulted in a stable equiaxed grain structure, comprehensively improving crack resistance.
Together, these advances demonstrate that the detonation spraying method is a viable and efficient approach for manufacturing and in-situ repairing tungsten/steel first wall structures for breeding blankets, offering notable advantages in both effectiveness and performance.