Role of compression metallization in UO₂ fission-product energy cascade track: Multiscale electron-phonon analyses

Journal Article · Fri Sep 07 00:00:00 EDT 2018 · Journal of Nuclear Materials

DOI:https://doi.org/10.1016/j.jnucmat.2018.09.005· OSTI ID:1543567

Kim, Woong Kee ^[1]; Melnick, Corey ^[2]; Shim, Ji Hoon ^[1]; Kaviany, Massoud ^[3]

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1. Pohang University of Science and Technology (POSTECH) (Korea, Republic of)
2. University of Michigan, Ann Arbor, MI (United States)
3. Pohang University of Science and Technology (POSTECH) (Korea, Republic of); University of Michigan, Ann Arbor, MI (United States)

While the electronic stoppage of charged fission fragments is relatively well understood, the subsequent energy cascade is not. Recent efforts to investigate this cascade and predict the resulting damage have used a two-temperature model (TTM) of the electronic and phononic systems coupled with a classical molecular dynamics (MD) simulation of the crystal lattice. In order to accurately predict the track radius produced by a fission fragment in UO₂, this model (TTM + MD) requires that UO₂, an insulator, have metallic properties, e.g., a substantial electron thermal conductivity and heat capacity. However, it has been predicted that UO₂ becomes metallic under large pressures, and we perform ab initio (DFT-HSE) simulations to support this prediction. We show that the average U-U bond length decreases within and near the ion track during TTM + MD simulations, supporting the use of volume contraction to model the pressurized UO₂ cell. Additionally, we evaluate the electron, phonon, and electron-phonon coupling properties of UO₂ for variations in the pressure. In particular, we calculate the electronic heat capacity and thermal conductivity, and the electron-phonon energy coupling for use in subsequent TTM + MD simulations. The ab initio parameterized TTM + MD simulations provide a set of the track radii predictions which bracket and include the experimentally observed radii. The accuracy of the ab initio parameterized TTM + MD simulations depends on the pressure and degree of electron-phonon non-equilibrium assumed during the ab initio calculations. We suggest improvements to the current TTM + MD methodology in light of these results. Here we show that the pressure-induced transition of UO₂ from insulator to metal and subsequent energy transfer from the electronic to phononic systems can accurately explain radiation damage during swift, heavy ion stoppage in UO₂. We make some additional observations regarding the accumulation and recombination of damage along the ion track and make comparison to the common SRIM model of ion stoppage and damage accumulation.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC); University of Michigan, Ann Arbor, MI (United States)
• Sponsoring Organization: Korea Institute of Science and Technology; Ministry of Science and ICT; National Research Foundation of Korea (NRF); USDOE Office of Science (SC)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1543567
• Alternate ID(s): OSTI ID: 22752313; OSTI ID: 22814862
• Journal Information: Journal of Nuclear Materials, Journal Name: Journal of Nuclear Materials Journal Issue: C Vol. 511; ISSN 0022-3115
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ab-initio
classical molecular dynamics
compression metallization
electronic stopping
fission product
irradiation
swift heavy ion
two temperature model