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Handbook of Activation Data Calculated Using EASY-2007
... Activated nuclei that can produce significant radioactivity over a long period of time need to be avoided. The neutron-induced activity after exposure to the first wall of a fusion reactor is shown in Fig. 2 [55]. Although the absorption cross sections do not differ significantly between Nb and other elements shown in Fig. 1, Nb can maintain a much higher radioactivity than other elements after 100 years. ...
... We note that the choice of 1 and 2 MeV is beyond the resonance region (except for Fe) where large variations of the cross sections are present Fig. 2 Simulated activities of 1-kg pure elements induced by deuterium-tritium fusion neutron spectrum after 5 years of exposure in the reactor first wall. Data are taken from the Handbook of activation data calculated using EASY-2007 [55] and enhanced irradiation resistance. Elements of V, Cr, Fe, W and Ta were chosen in Ref. [58] due to their low activation properties. ...
High-entropy alloys greatly expand the alloy design range and offer new possibilities for improving material performance. Based on the worldwide research efforts in the last decade, the excellent mechanical properties and promising radiation and corrosion resistance of this group of materials have been demonstrated. High-entropy alloys with body-centered cubic (BCC) structures, especially refractory high-entropy alloys, are considered as promising materials for high-temperature applications in advanced nuclear reactors. However, the extreme reactor conditions including high temperature, high radiation damage, high stress, and complex corrosive environment require a comprehensive evaluation of the material properties for their actual service in nuclear reactors. This review summarizes the current progress on BCC high-entropy alloys from the aspects of neutron economy and activation, mechanical properties, high-temperature stability, radiation resistance, as well as corrosion resistance. Although the current development of BCC high-entropy alloys for nuclear applications is still at an early stage as the large design space of this group of alloys has not been fully explored, the current research findings provide a good basis for the understanding and prediction of material behaviors with different compositions and microstructures. Further in-depth understanding of the degradation mechanisms and characterization of material properties in response to conditions close to reactor environment are necessary. A critical down-selection of potential candidates is also crucial for further comprehensive evaluation and engineering validation.
... In addition, the brazing alloy compositions were chosen with consideration to the requirement of low activation. Based on the data given in [15] a periodic table of the elements (Fig. 1) was designed. So, in this paper, to solve the problem of joining steel with tungsten for DEMO application, Cu-Ti and Cu-Ge brazing alloys quenched rapidly into ribbon were used, and the preliminary results of their use are presented in [16]. ...
... Periodic table of the elements with residual activity of the elements 100 yr from the end of operation: less than 10 mSv/h; near 10 mSv/h; more than 10 mSv/h (designed based on literature data[15]). ...
The work presents the results of high-temperature brazing of reduced activated ferritic martensitic steel EK-181 with pure tungsten, which is essential for DEMO fusion reactor. To reduce thermal stresses, vanadium interlayer was used. Brazing alloys to be used were rapidly quenched into ribbons Cu-28Ti and Cu-28Sn for EK-181/V, Cu-50Ti for V/W. Microstructure investigations, mechanical and thermocycling test were carried out. It is shown that Cu-28Ti is better to use; however, it is necessary to improve the reliability of V/W seam.
... All constituent elements of the two current refractory high entropy alloys belong to the 4-5-6 elemental palette with high melting points as shown in Figure 1a. The relatively short period of time required for the refractory elements found in the current HEAs (i.e., Hf, W, Ta, Ti, V, and Zr) compared to other elements such as Mo, Nb, and Ni to reach "hands-on" level after irradiation is shown in Figure 1b [34]. X-ray diffraction patterns of Ta-Hf and Ta-W HEAs in as-cast and annealed (at 723 K for 2 h) conditions are shown in Figure 1c,d, respectively. ...
... The creep displacement for Ta-Hf and Ta-W high entropy alloys was roughly half of that of pure W, which may be attributed to the sluggish diffusion and highly distorted lattice structure in HEAs. (a) Refractory elements belonging to the 4-5-6 group/period; (b) time in years required for group 4-5-6 refractory elements to reach "hands-on" level after exposure [34]. X-ray diffraction analysis of (c) HfTaTiVZr (Ta-Hf) and (d) TaTiVWZr (Ta-W) refractory high entropy alloys in as-cast and annealed conditions showing single-phase body-centered cubic (BCC) crystal structure for Ta-Hf and a BCC1 major phase and BCC2 minor phase for Ta-W; backscattered scanning electron microscopy image of (e) Ta-Hf and (f) Ta-W alloys showing equiaxed grains with an average grain size of ~250 μm for Ta-Hf and formation of two phases in Ta-W; insets showing selected area diffraction pattern of the alloys. ...
There is a strong demand for materials with inherently high creep resistance in the harsh environment of next-generation nuclear reactors. High entropy alloys have drawn intense attention in this regard due to their excellent elevated temperature properties and irradiation resistance. Here, the time-dependent plastic deformation behavior of two refractory high entropy alloys was investigated, namely HfTaTiVZr and TaTiVWZr. These alloys are based on reduced activity metals from the 4-5-6 elemental palette that would allow easy post-service recycling after use in nuclear reactors. The creep behavior was investigated using nano-indentation over the temperature range of 298 K to 573 K under static and dynamic loads up to 5 N. Creep stress exponent for HfTaTiVZr and TaTiVWZr was found to be in the range of 20–140 and the activation volume was ~16–20b3, indicating dislocation dominated mechanism. The stress exponent increased with increasing indentation depth due to a higher density of dislocations and their entanglement at larger depth and the exponent decreased with increasing temperature due to thermally activated dislocations. Smaller creep displacement and higher activation energy for the two high entropy alloys indicate superior creep resistance compared to refractory pure metals like tungsten.
... In addition, the brazing alloy compositions were chosen with consideration to the requirement of low activation. Based on the data given in [15] a periodic table of the elements (Fig. 1) was designed. So, in this paper, to solve the problem of joining steel with tungsten for DEMO application, Cu-Ti and Cu-Ge brazing alloys quenched rapidly into ribbon were used, and the preliminary results of their use are presented in [16]. ...
... Periodic table of the elements with residual activity of the elements 100 yr from the end of operation: less than 10 mSv/h; near 10 mSv/h; more than 10 mSv/h (designed based on literature data[15]). ...
The designs of DEMO components require the joining of low-activation steel (for example RUSFER EK-181, EUROFER, etc.) with tungsten. One of the most critical parameters is the thermal expansion mismatch between tungsten and steel, which can lead to the failure of components during use or even after manufacturing.In this paper, high-temperature brazing of EK-181 steel with tungsten was carried out. Pure copper was used for the direct joining of steel with tungsten. Brazing alloys based on copper (Cu–Ge and Cu–Ti) rapidly quenched into ribbon were used with a vanadium interlayer. Brazing was carried out in vacuum furnaces at 1100 °C for 20 min. The structural-phase states of the joints obtained were studied, the microhardness measured, shear strength tests carried out and thermocycling tests performed in the range 700–25 °C.
... Such classes of RHEAs cannot be used as structural materials for nuclear energy or other radioactive fields due to their vulnerability to radiation damage. Moreover, high activation elements take a long time to reach the hands-on standard after the decommissioning of relevant equipment, for example, ~10 4 and ~3 × 10 5 years for Mo and Nb, respectively [19,22]. Low activation elements, such as W, Ta, Ti, V, Zr, Cr, Fe, and Mn [19,21], can fundamentally avoid this problem, because the time required for most low activation elements to reach the "hands-on level" is less than 100 years. ...
In this work, novel high-strength, low-activation Wx(TaVZr)100−x (x = 5, 10, 15, 20, 25) refractory high entropy alloys (RHEAs) were prepared by vacuum arc melting. Their microstructure, compressive mechanical properties, hardness, and fracture morphology were investigated and analyzed. The results show that the RHEAs possess a disordered BCC phase, ordered Laves phase, and Zr-rich HCP phase. Their dendrite structures were observed, and the distribution of dendrites became gradually more dense with an increase in W content. The RHEAs demonstrate high strength and hardness, with these properties being higher than in most reported tungsten-containing RHEAs. For example, the typical W20(TaVZr)80 RHEA has a yield strength of 1985 MPa and a hardness of 636 HV, respectively. The improvement in terms of strength and hardness are mainly due to solid solution strengthening and the increase in dendritic regions. During compression, with the increase in the applied load, the fracture behavior of RHEAs changed from initial intergranular fractures to a mixed mode combining both intergranular and transgranular fractures.
... The brazing alloys' compositions were chosen with consideration to the requirement of reduced activation, i.e. residual activity of the material a hundred years from the end of operation should be no more than 10 −2 Sv/h [15]. Cu residual activation is a bit higher than this -3.39 × 10 −2 Sv/h [16], but has the same power. So Cu was chosen to be the base material as it gives the possibility of making brazing alloys with a low melting point. ...
The conceptual designs of the blanket and the helium-cooled divertor of the DEMO reactor require joining of reduced activation steel (for example RUSFER EK-181, EUROFER, etc.) and tungsten. Significant differences in their physical properties can lead to the generation of the stresses during cooling and, as a result, to the failure of the joint. In this paper, diffusion brazing of RUSFER EK-181 steel with tungsten using a V–4Ti–4Cr interlayer was obtained. Rapidly-quenched ribbon brazing alloys based on copper of various compositions were used. Brazing was carried out in vacuum furnaces at temperatures in the range of 800–1000 °C. The structural-phase states of the joints obtained were studied, the microhardness was measured, and thermocycling tests were performed in the interval of 700 to 25 °C. FEM simulation was used to calculate the optimal thickness of the interlayer.
... Yttrium oxide is an industrially and technologically very useful ceramic material under its several advanced properties: good thermal and chemical stability, high mechanical strength and hardness [1][2][3] . Also yttrium oxide has a wide application in nuclear research because of its low activation due to neutron irradiation [4] . ...
Yttrium oxide thin films were prepared by reactive magnetron sputtering in different deposition condition with various oxygen flow rates. The annealing influence on the yttrium oxide film microstructure is investigated. The oxygen flow shows a hysteresis behavior on the deposition rate. With a low oxygen flow rate, the so called metallic mode process with a high deposition rate (up to 1.4µm/h) was achieved, while with a high oxygen flow rate, the process was considered to be in the poisoned mode with an extremely low deposition rate (around 20nm/h). X-ray diffraction (XRD) results show that the yttrium oxide films that were produced in the metallic mode represent a mixture of different crystal structures including the metastable monoclinic phase and the stable cubic phase, while the poisoned mode products show a dominating monoclinic phase. The thin films prepared in metallic mode have relatively dense structures with less porosity. Annealing at 600 °C for 15h, as a structure stabilizing process, caused a phase transformation that changes the metastable monoclinic phase to stable cubic phase for both poisoned mode and metallic mode. The composition of yttrium oxide thin films changed from nonstoichiometric to stoichiometric together with a lattice parameter variation during annealing process. For the metallic mode deposition however, cracks were formed due to the thermal expansion coefficient difference between thin film and the substrate material which was not seen in poisoned mode deposition. The yttrium oxide thin films that deposited in different modes give various application options as a nuclear material.
Handbook of Fusion Activation Data, Part 1: Elements Hydrogen to Zirconium
- C B A Forty
- R A Forrest
- D J Compton
- C Rayner
2 C. B. A. Forty, R. A. Forrest, D. J. Compton, and C. Rayner, ‘Handbook of Fusion Activation Data, Part 1: Elements Hydrogen to Zirconium’, AEA FUS 180, 1992