Atomic scale modelling of hexagonal structured metallic fission product alloys.

S C Middleburgh,D M King,G R Lumpkin

doi:10.1098/rsos.140292

Abstract

Noble metal particles in the Mo-Pd-Rh-Ru-Tc system have been simulated on the atomic scale using density functional theory techniques for the first time. The composition and behaviour of the epsilon phases are consistent with high-entropy alloys (or multi-principal component alloys)—making the epsilon phase the only hexagonally close packed high-entropy alloy currently described. Configurational entropy effects were considered to predict the stability of the alloys with increasing temperatures. The variation of Mo content was modelled to understand the change in alloy structure and behaviour with fuel burnup (Mo molar content decreases in these alloys as burnup increases). The predicted structures compare extremely well with experimentally ascertained values. Vacancy formation energies and the behaviour of extrinsic defects (including iodine and xenon) in the epsilon phase were also investigated to further understand the impact that the metallic precipitates have on fuel performance.

Highlights

Investigation of fission product behaviour will improve the safe and efficient use of nuclear fuel in both current and future nuclear reactors
In a similar manner to the phase diagrams presented by Kleykamp et al [22,23], a set of epsilon phase compositions were investigated that comprised equimolar amounts of Rh and Pd metals, combined with Ru metal such that the Ru : (Pd,Rh) was approximately 2.33
In a similar manner to past work investigating the stability of the CoCrFeNi high-entropy alloy [32], we investigate the drive for vacancy formation in the epsilon phase

Summary

Introduction

Investigation of fission product behaviour will improve the safe and efficient use of nuclear fuel in both current and future nuclear reactors. The metallic precipitates have had less focus, potentially as a consequence of the scarcity of the elements that make up the precipitates and the deviation in modelling methods (mainly due to their metallic nature). Despite these difficulties, limited work has been.

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Conclusion