Atomic-scale effects of chromium-doping on defect behaviour in uranium dioxide fuel Zhexi Guo, Raoul Ngayam-Happy * , Matthias Krack, Andreas Pautz Laboratory for Reactor Physics and Systems Behaviour, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland article info Article history: Received 22 August 2016 Received in revised form 3 February 2017 Accepted 23 February 2017 Available online 2 March 2017 abstract The effects of doping conventional UO 2 fuel with chromium are studied through atomistic simulations using empirical force field methods. We first analyse the stable structures of unirradiated doped fuel by determining the preferred lattice configuration of chromium ions and oxygen vacancies within the matrix. In order to understand the physical effects of the dopants, we investigate the energy change upon inserting isolated defects and Frenkel pairs in the vicinity of chromium. The behaviour of point defects is then studied with collision cascade simulations and relaxation of doped simulation cells containing Frenkel pairs. The defective structures are analysed using an in-house tool named ASTRAM. Results indicate definite effects of chromium-doping on the ease with which defects are formed. Moreover, the extent of Cr effects on the residual damage following a displacement cascade is dependent on the dopant distribution and concentration in the fuel matrix. © 2017 Published by Elsevier B.V. Contents 1. Introduction ...................................................................................................................... 160 2. Computational methodology ........................................................................................................ 161 2.1. The “Morelon-Cr” potential ................................................................................................... 161 2.2. The Cr-UO 2 model systems .................................................................................................... 162 3. Results and discussion ............................................................................................................. 163 3.1. Behaviour of Cr in the lattice and impact on crystal properties ..................................................................... 163 3.2. Effect of Cr on the formation of defects ......................................................................................... 164 3.3. Displacement cascades in the presence of Cr .................................................................................... 165 3.3.1. Systems of realistic Cr concentration ................................................................................... 165 3.3.2. Systems with increased and localised Cr concentrations ................................................................... 167 4. Conclusions ...................................................................................................................... 169 Acknowledgments ............................................................ .................................................... 171 References ........................................................................................................................ 171 1. Introduction Out of the existing nuclear power plants, more than 80% are light water reactors (LWRs) [1] which utilise uranium dioxide (UO 2 ) fuel enriched to 3e5% U-235. Despite promising developments of research into thorium-based fuel and Gen IV fast reactors, an esti- mated 63,404 tonnes of uranium are still required in 2016 for the world's nuclear reactors [2], underlining the importance of uranium-based fuel in the near future. Primary considerations associated with nuclear fuel design are 1) enhancement of fuel burnup for higher power uprates, 2) extension of fuel cycle period to optimise cost, and 3) safety reliability that is usually measured in * Corresponding author. E-mail address: raoul.ngayam-happy@psi.ch (R. Ngayam-Happy). Contents lists available at ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat http://dx.doi.org/10.1016/j.jnucmat.2017.02.043 0022-3115/© 2017 Published by Elsevier B.V. Journal of Nuclear Materials 488 (2017) 160e172