Redistribution of Nb and other alloying elements in Nb-doped Zr alloy under high dose ion irradiation

ABSTRACT

To understand the microstructural changes in Nb-doped zirconium alloy cladding at high irradiation doses, the Mitsubishi Developed Alloy (MDA) cladding was ion- irradiated up to 40 dpa at 400^◦C and the distribution of alloying elements was in- vestigated using atom probe tomography (APT) and scanning transmission electron microscopy and energy dispersive X-ray spectroscopy (STEM-EDS). APT analysis revealed two types of Nb nanoclusters with different Nb contents after the ion irradia- tion. The Nb concentration in the matrix decreased significantly with ion irradiation up to 10 dpa and then decreased slowly to 40 dpa. STEM-EDS analysis estimated that the secondary phase precipitates (SPPs) of Zr(Fe,Cr,Nb)2 and Zr(Fe,Cr)2 were formed before the ion irradiation. Although Fe, Cr, and Nb were dissolved from the SPPs during the ion irradiation, these alloying elements still remained in the SPPs after 40 dpa irradiation. Other Fe-Cr nanoclusters, Nb-rich phase, and Fe-rich phase were also formed during the ion irradiation. These radiation-induced precip- itates were observed until after 40 dpa irradiation and were expected to be stable under irradiation conditions.

KEYWORDS:

• Zirconium alloys
• nuclear fuel cladding
• radiation induced precipitate
• nanoclusters
• APT
• STEM-EDS

Acknowledgments

We would like to thank Mitsubishi Heavy Industry Co., Ltd. for providing the fuel cladding tube samples. The ion irradiation for this study was performed under the Shared Use Program of QST Facilities. The authors thank Dr. Norio Ishikawa in the Japan Atomic Energy Agency for assistance with ion irradiation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.