NuFuel & MMSNF 2015

First Workshop on Research into Nuclear Fuel in Europe
and Materials Modeling and Simulation for Nuclear Fuels Workshop
Karlsruhe, Germany, November 16th to 18th, 2015

Updated: Tue 08 Dec 2015, 14:27

Poster 3.5: Features of Zr-rich corner of Zr-N-O ternary system by controlled low-pressure oxidation

Do Van Lam, Do Thi Mai Dung, Hisayuki Suematsu and Toru Ogawa
  • Department of Nuclear System Safety Engineering, Nagaoka University of Technology

Abstract

It is well known that in accidents involving LWR fuels with air ingress, the oxidation of zirconium alloys are much faster with larger heat generation. This vigorous oxidation is related to the formation of zirconium nitride and the instability of the ZrO2 layer in the presence of nitrogen [1, 2]. On the other hand, even the reliable ternary phase diagram of Zr-N-O system nor relevant thermodynamic data are still lacking. Due to the existence of the oxynitride phases, the N-rich part of the Zr-N-O ternary system has attracted much attention. But the information on the Zr-rich corner is scarce. We investigated the feature of the Zr rich corner of the Zr-N-O ternary system by oxidation experiments in low oxygen partial pressure conditions. The experiments included both the separated reaction sequence (oxidation of the nitrided Zr) and also the simultaneous reaction sequence (simultaneous nitridation and oxidation of fresh Zr). Low oxygen partial pressure conditions were realized by utilizing REDOX couples of Mo/MoO2 and CuO/Cu2O. After heating, the samples were analysed by XRD, EPMA and laser raman spectroscopy. We found that at a low partial pressure of oxygen the oxidation proceeds both at the surface of ZrN layer and at the interface of Zr(N,O) and α-Zr(O,N). The latter proved to be much faster than the former. Based on the results, the homogeneity ranges of nitride Zr(N,O)~1-x~ and metal α-Zr(O,N) phases will be discussed.

Key words: Zr oxidation, ZrN, Zr-N-O phase diagram.

References:
  1. M. Steinbrück, et al. High-temperature reaction of oxygen-stabilized a-Zr(O) with nitrogen. Journal of Nuclear Materials 447 (2014) 46–5.
  2. Marina Lasserre, et al. Prototypical experiments on air oxidation of Zircaloy–4 at high temperatures. ICONE21–16440, Proceedings of the 2013 21st International Conference on Nuclear Engineering -ICONE21.