A potential candidate structural material for molten salt reactor: ODS nickel-based alloy

doi:10.1016/j.jmst.2021.08.071

Abstract

Abstract:

The commercialisation of molten salts reactors (MSRs) is hindered by the lack of structural materials capable of withstanding the corrosive environment therein. To address this problem, we herein prepared 1 wt% Y₂O₃ dispersion-strengthened NiMo-based alloys using powder metallurgy and evaluated their potential as structural materials for MSRs based on their mechanical properties, He swelling behaviour, and molten salt corrosion resistance. In view of the strengthening provided by homogenously dispersed Y₂O₃ particles, all NiMo-Y₂O₃ samples exhibited ultimate tensile strengths and yield strengths exceeding those of the Hastelloy N alloy, a state-of-the-art structural material for MSRs. Moreover, the volume fraction of He bubbles in the NiMo-Y₂O₃ samples (∼0.3%) was lower than that in the Hastelloy N alloy (0.58%), which showed that the introduction of Y₂O₃ nanoparticles effectively inhibited He swelling. All NiMo-Y₂O₃ samples showed excellent resistance to molten salt corrosion (as reflected by the absence of obvious holes therein), thus holding great promise for the development of irradiation- and molten salt corrosion-resistant structural materials for high-temperature MSRs.

Key words: Molten salt reactor, ODS nickel-based alloy, Powder metallurgy, Tensile mechanical properties, Helium swelling resistance, Molten salt corrosion

Cheng Li, Guanhong Lei, Jizhao Liu, Awen Liu, C.L. Ren, Hefei Huang. A potential candidate structural material for molten salt reactor: ODS nickel-based alloy[J]. J. Mater. Sci. Technol., 2022, 109: 129-139.

Figures/Tables 19

Table 1. Notation used to identify pristine, He-ion-irradiated, and corroded samples.

Milling time	Pristine samples^a	Irradiated samples^b	Corroded samples^c
2 h	S₁	S_1-1	S_1-2
4 h	S₂	S_2-1	S_2-2
8 h	S₃	S_3-1	S_3-2
Hastelloy N	Hastelloy N	S_R	S_R

Fig. 1. He concentration and irradiation damage profiles produced using 1-MeV He ions at a dose of 5 × 1016 ions cm-2.

Table 2. Contents of main impurities (ppm) in the molten salt.

Impurity ions	Ni	Mo	Cr	Fe	Mn	Y
FLiNaK	6171.9	3.1	31.6	111.3	14.6	-
FLiNaK after corrosion	2154.4	6.5	35.8	90.7	14.8	0.66

Fig. 2. Schematic illustration of the corrosion test setup.

Fig. 3. Dimensions (mm) of dogbone-shaped tensile specimens.

Fig. 4. XRD patterns of S1, S2, and S3.

Fig. 5. SEM micrographs of (a) S1, (b) S2, and (c) S3.

Fig. 6. Bright-field TEM micrographs of (a) S1, (b) S2, and (c) S3. (d) EDS mapping of S2. (e) HRTEM image of S2. (f) SAED image of S2. (g) The size distribution of Y2O3 precipitates in samples S1, S2 and S3. (h) The number density of Y2O3 precipitates in samples S1, S2 and S3.

Fig. 7. Yield strengths, tensile strengths, and elongations at break of NiMo-Y2O3 alloys and the Hastelloy N alloy [23].

Fig. 8. Fracture surfaces of (a) S1, (b) S2, and (c) S3.

Fig. 9. (a) TEM micrograph of S1-1 covering depths of 0-2500 nm. (b) Under-focus and (c) over-focus images of the area enclosed by the orange box in (a).

Fig. 10. (a), (c), (e) TEM micrographs of He bubbles in the region of 1600-2000 nm in S1-1, S2-1, and S3-1, respectively. (b), (d), (f) are enlarged micrographs of the areas enclosed by orange boxes in (a), (c), (e), respectively.

Fig. 11. The size distribution of helium bubbles in samples S1-1, S2-1 and S3-1.

Fig. 12. The mean diameters and number densities of helium bubbles in samples SR, S1-1, S2-1 and S3-1.

Fig. 13. The volume fraction of helium bubbles in samples SR, S1-1, S2-1 and S3-1.

Fig. 14. SEM micrograph of corroded (a) SR, (b) S1-2, (c) S2-2, and (d) S3-2.

Fig. 15. (a) Typical region of corroded SR. (b) Enlarged micrograph of Zone A. (c) Enlarged micrograph of Zone B. EDS point analysis results of (d) Zone A and (e) Zone B.

Fig. 16. (a) Typical region of S2-2. (b) Enlarged micrograph of Zone A. (c) Enlarged micrograph of Zone B. EDS point analysis results of (d) Zone A and (e) Zone B.

Fig. 17. Cross-sectional elemental distributions of (a) corroded SR, (b) S1-2, (c) S2-2 and (d) S3-2.

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