핵융합발전소에서의 텅스텐 기반 합금 초기 연구 (Ab initio study of tungsten-based alloys under fusion power-plant conditions)
본 연구는 텅스텐 합금의 특성을 조사하고, 원자력 융합 조건에서 어떻게 작동하는지의 연구 정보를 제공합니다.
Tungsten (W) is considered a leading candidate for plasma-facing applications in magnetic fusion energy (MFE) devices. The most attractive properties of W for MFE are its high melting point and thermal conductivity, low sputtering yield and low long-term disposal radioactive footprint. These advantages are accompanied unfortunately by very low fracture toughness characterized by brittle trans- and inter-granular failure, which severely restricts its operating temperature window [1]. In recent years, several families of W-based alloys have been explored to overcome the aforementioned limitations of pure W. High-entropy alloys (HEAs) are a promising class of materials with remarkable properties [2], [3], [4], [5]. They were originally conceived in the early 2000s as a blend of five or more elements with individual concentrations between 5 and 35 atomic percent [6]. Interestingly, the composition stability of different HEA phases is strongly correlated with the valence electron concentration from electronic structure analysis [7]. In particular, tungsten-based HEAs (W-HEAs) have shown superior mechanical properties at high temperatures, a superior melting point (above 2873 K), enhanced radiation resistance to heavy ion irradiation, and negligible radiation hardening when compared to pure W [8], [9], [10], [11], [12], [13]. Another attractive option are the so-called tungsten-based “SMART alloys” (W-SAs), where SMART stands for Self-passivating Metal Alloys with Reduced Thermo-oxidation, that can adapt their behavior to the environment [14], [15], [16], [17], [18]. For example, in the event of a loss-of-coolant accident (LOCA) combined with an air ingress, W-SAs containing small amounts of Ti or Y have demonstrated the capability to create stable oxides that prevent their mobilization into the atmosphere. The exposure of W-based plasma-facing materials (PFMs) to high neutron fluxes causes nuclear reactions that can change the nuclide composition over time. The reactions lead to the production of radionuclides, causing a material to become activated, while also producing nuclides of new elements, a process known as transmutation, that can alter material properties. Both activation and transmutation are commonly observed in fields such as nuclear fission, nuclear fusion, astrophysics, nuclear security, and medical research. Since activation can create hazard and transmutation can change material performance, it is vital to carefully understand the nuclear reaction rates. Inventory codes are frequently used to predict the response of materials to a specific neutron irradiation field. Such an approach consists of numerically solving a set of coupled differential equations that describe the rate of change of all possible nuclides and thus evolve the nuclide composition in time [19], [20]. Experimentally, neutron irradiation campaigns at the fast test reactor Joyo [21], [22], [23], [24], [25], [26], the Japan Materials Testing Reactor (JMTR) [25], [26], [27], and the High Flux Isotope Reactor (HFIR) [25], [26], [28], [29], [30], [31] have investigated the microstructural evolution of W and W alloys. Their results indicate, for example, that the impact of transmutant Re and Os on the properties of materials after irradiation is at least as relevant as the displacement damage. Meanwhile, the current lack of experimental reactors and materials testing facilities that fully represent the conditions for making fusion a commercially feasible energy source has motivated multi-scale materials modeling efforts to investigate the irradiation and temperature effects expected in fusion power plants [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50]. These approaches, frequently based on first-principles calculations, have demonstrated their ability to provide quantitative and qualitative predictions of the material behavior in such extreme environments. Despite the recent experimental advances in Joyo, JMTR, and HFIR, and the numerous efforts in the literature to investigate the effects of alloying elements on various properties of W-based materials such as phase stability [51], [52], [53], [54], [55], elastic properties [51], [52], [53], [54], [56], [57], [58], ideal tensile strength [54], [59], ductility [60], radiation defects [12], [52], [61], point defects [51], [61], [62], [63], [64], [65], [66], screw dislocation structures [67], [68], grain boundaries [69], etc., to the best of our knowledge, there is still a lack of understanding on how the thermomechanical behavior of W-based PFMs change due to nuclear transmutation. In this work, we present a novel approach that integrates nuclear science and first-principles DFT electronic structure methods to better understand the neutron irradiation effects in PFMs. In particular, the goal of this study is to investigate how the bulk and mechanical properties of W-based SAs and HEAs evolve over time under neutron irradiation-induced transmutation. Our paper is organized as follows. After this introduction, we provide in Section 2 an overview of the computational methods employed. The results are given in Section 3, which include: (i) the changes in the chemical composition during the course of irradiation due to transmutation; (ii) the calculation of the equilibrium lattice constant, elastic properties, density of states, generalized stacking fault energy, unstable stacking fault energy, gamma surface, and dislocation-based ductility parameter of five W-based candidate materials at the beginning of their operational life; and (iii) the effects of irradiation on these properties. We finalize in Section 4 with a brief discussion and the conclusions in Section 5.
국내외 전문자료
2023-08-31
국내외 전문자료핵융합발전소에서의 텅스텐 기반 합금 초기 연구 (Ab initio study of tungsten-based alloys under fusion power-plant conditions)
- 국가슬로베니아
- 발행기관Jozef stefan institute (요세프 스테판 연구소)
- 원본링크https://www.sciencedirect.com/science/article/pii/S0022311523001903?via%3Dihub
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