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: Fri 18 Dec 2015, 20:09

Talk 4.6: Thermodynamic modeling of the Ni-Te and Fe-Te intermetallic phases

Carl-Magnus Arvhult1, Stéphane Gossé2, Malin Selleby3, Christine Guéneau4
  • 1,3: KTH Royal Institute of Technology, dpt. of Materials Science and Engineering, 10044 Stockholm, Sweden
  • 2,4: CEA, DEN, DANS/DPC/SCCME, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France

Abstract

For the purpose of evaluating the possibility of premature stainless steel cladding failure due to internal corrosion induced by volatile fission products in Gen IV Sodium cooled Fast Reactors, CEA is in cooperation with KTH performing thermodynamic assessments of Metal-Fission Product systems, using the Calphad method, as a contribution to the TAF ID database. The thermodynamic descriptions are the fundamental basis for understanding and modeling the corrosion process, which may possibly be a life-limiting factor of the ASTRID Gen IV prototype reactor design.

In this study, both Fe Te and Ni Te binary systems have been under investigation. In the Fe Te system there are two known intermetallic phases stable at room temperature, the tetragonal β-phase (~Fe1.11Te) and the orthorhombic ε-phase (FeTe2). A high-temperature rhombohedral β’-phase (~Fe1.125Te) has been analysed by high Temperature XRD and has earlier been found as a ternary Fe1.5Ni1.5Te2 phase. This is not stable in the Ni-Te system, where instead another high temperature phase resides with an orthorhombic structure. The NiAs type structure is present in both system as the monoclinic δ-phase (Fe0.75Te), and in the Fe-Te system undergoes a first-order transition into the CdI2 type hexagonal δ’-phase (Fe0.67Te) at increasing Te content; in contrast, this is a second-order transition in the Ni-Te system. In the Ni-Te system this phase extends in composition up to the CdI2 prototype composition whereas in the Fe-Te system the ε-phase becomes stable.

The intermetallic compounds are described using sublattice models representative for the physical ordering of atoms in the crystal structure lattices; vacancy defect sublattice models are used for any phase with published evidence that the heterogeneity in composition is due to partly occupied interstitial metal atom sites in a matrix of Te atoms. There are published indications regarding a possible liquid miscibility gap in the Fe-Te composition range, whereas this is not evident in the Ni-Te system. An ionic associate liquid model ensures the possibility to model this in the Fe-Te system while experiments to attempt the confirmation of this are planned. Results on the thermodynamic modelling of the two binary systems will be presented.