Molecular Dynamics Simulation of Fission Fragment Damage in Nuclear Fuel and Surrogate Material
- PDF / 549,927 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 97 Downloads / 185 Views
Molecular Dynamics Simulation of Fission Fragment Damage in Nuclear Fuel and Surrogate Material Ram Devanathan1 1 Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland WA, 99352, U.S.A. ABSTRACT We have performed classical molecular dynamics simulations of swift heavy ion damage, typical of fission fragments, in nuclear fuel (UO2) for energy deposition per unit length of 3.9 keV/nm. We did not observe amorphization. The damage mainly consisted of isolated point defects. Only about 1% of the displacements occur on the uranium sublattice. Oxygen Frenkel pairs are an order of magnitude more numerous than uranium Frenkel pairs in the primary damage state. In contrast, previous results show that the ratio of Frenkel pairs on the two sublattices is close to the stoichiometric ratio in ceria. These differences in the primary damage state may lead to differences in radiation response of UO2 and CeO2. INTRODUCTION Nuclear energy produces reliable baseload electricity with a high capacity factor and without the emissions associated with the burning of fossil fuels. In the United States, nuclear energy accounts for about 20% of electricity generation and is vital to energy security, electric grid stability, and economic competitiveness. In a nuclear reactor, uranium dioxide (UO2) fuel undergoes fission that results in two fission fragments each with mass of ~100 amu and energy of ~100 MeV. As these swift heavy ions slow down, they damage the periodic atomic arrangement in the fuel. The accumulation of such damage results in voids, gas bubbles, precipitates, swelling, and cracks that can affect the thermal conductivity and mechanical integrity of the fuel pellet. To advance the use of nuclear energy, it is essential to understand the performance of nuclear fuel under normal reactor operation, accident scenarios, and long term spent fuel storage. Fission fragment damage in nuclear fuel has been extensively studied [1-5], but there remain gaps in our understanding of key mechanisms due to the transient nature of the energetic processes and the challenge of experimentally characterizing radioactive materials. Experimental studies have used ceria (CeO2) as a surrogate material to understand the behavior of UO2 without radiological concerns [6]. In addition, modeling and simulation have been used to illuminate fundamental mechanisms of damage accumulation and microstructural evolution in nuclear fuel [7, 8]. The present work uses molecular dynamics (MD) simulations of thermal spikes to study atomic-level damage accumulation mechanisms in UO2 and compares the findings to previous simulation results for CeO2. DETAILS OF THE SIMULATION We performed MD simulations with the DL_POLY4 computer code [9] with the Basak potential [10] for UO2 and Sayle potential [11] for CeO2 and smoothly splined these potentials to the repulsive Ziegler-Biersack-Littmark potential [12] at distances shorter than 0.1 nm. The ion
Downloaded from https:/www.cambridge.org/core. University of Arizona, on 10 Apr 2017 at 01:30:02, subj
Data Loading...
