Oxidation and hydrogen uptake in zirconium, Zircaloy-2 and Zircaloy-4: Computational thermodynamics and ab initio calculations Michael V. Glazoff a,⇑ , Akira Tokuhiro b , Sergey N. Rashkeev a , Piyush Sabharwall a a Idaho National Laboratory, MS 3710, Idaho Falls, ID 83415-3710, United States b University of Idaho, CAES, Idaho Falls, ID 83401, United States graphical abstract The ‘‘checker board’’ configuration for O atoms in octahedral interstitials. Zr atoms are shown in cyan, O in the first layer – in red, O in the second layer – in pink. Four non-equivalent groups of interstitials are indicated by numbers and yellow arrows. The formation of such ‘‘suboxide’’ ordered atomic structures was shown to slow down the uptake of hydrogen by different zirconium nuclear components. article info Article history: Received 30 April 2013 Accepted 18 September 2013 Available online 28 September 2013 abstract Zirconium-based alloys Zircaloy-2 and Zircaloy-4 are widely used in nuclear industry as cladding mate- rials for BWRs and PWRs, respectively. Over more than 60 years these materials displayed a very good combination of properties such as low neutron absorption, creep behavior, stress-corrosion cracking resistance, reduced hydrogen uptake, corrosion, and/or oxidation, especially in the case of Zircaloy-4 [1–3]. However, over the last couple of years energetic efforts were undertaken to improve their oxida- tion resistance during off-normal temperature excursions, as well as to further improve upon the already achieved levels of mechanical behavior and reduced hydrogen uptake [1–3]. In order to facilitate the development of such novel materials, it is very important to achieve not only engineering control, but also scientific understanding of the underlying material degradation mechanisms, both in working con- ditions and in storage of spent nuclear fuel. This paper strives to contribute to these efforts by constructing the thermodynamic models of both alloys, constructing of the respective phase diagrams, and oxidation mechanisms. A special emphasis was placed upon the role of zirconium suboxides [4] in hydrogen uptake reduction and the atomic mech- anisms of oxidation. To that end, computational thermodynamics calculations were conducted concur- rently with first-principles atomistic modeling. Published by Elsevier B.V. 0022-3115/$ - see front matter Published by Elsevier B.V. http://dx.doi.org/10.1016/j.jnucmat.2013.09.038 ⇑ Corresponding author. Tel.: +1 2085268937. E-mail address: michael.glazoff@inl.gov (M.V. Glazoff). Journal of Nuclear Materials 444 (2014) 65–75 Contents lists available at ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat