Swelling Mechanisms of UO2 Lattices with Defect Ingrowths.

Seçkin D Günay

doi:10.1371/journal.pone.0134500

Abstract

The swelling that occurs in uranium dioxide as a result of radiation-induced defect ingrowth is not fully understood. Experimental and theoretical groups have attempted to explain this phenomenon with various complex theories. In this study, experimental lattice expansion and lattice super saturation were accurately reproduced using a molecular dynamics simulation method. Based on their resemblance to experimental data, the simulation results presented here show that fission induces only oxygen Frenkel pairs while alpha particle irradiation results in both oxygen and uranium Frenkel pair defects. Moreover, in this work, defects are divided into two sub-groups, obstruction type defects and distortion type defects. It is shown that obstruction type Frenkel pairs are responsible for both fission- and alpha-particle-induced lattice swelling. Relative lattice expansion was found to vary linearly with the number of obstruction type uranium Frenkel defects. Additionally, at high concentrations, some of the obstruction type uranium Frenkel pairs formed diatomic and triatomic structures with oxygen ions in their octahedral cages, increasing the slope of the linear dependence.

Highlights

Uranium dioxide (UO2) is primarily used as a nuclear fuel, usually under extreme conditions
The lattice expansion that occurs as a result of alpha particle damage is several orders of magnitude greater than that occurs as a result of fission damage [17]
Comparing calculated relative lattice expansion results with those obtained from experiment indicated that the calculations carried out on oxygen initial Frenkel pair (IFP) corroborated fission experiments and those carried out on uranium IFPs corroborated alpha particle experiments

Summary

Introduction

Uranium dioxide (UO2) is primarily used as a nuclear fuel, usually under extreme conditions. UO2 has been widely studied in order to understand its thermo physical, transport, and defect properties [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. Molecular dynamics simulations of temperature dependent physical properties of UO2 have been used to assist ongoing experiments, which cannot be done because of the required extreme conditions. Such properties include lattice parameter, volume, density, electrical resistivity, and diffusion and they are sensitive to both temperature and irradiation [17,18,19,20,21,22]. Radiation damage to UO2 crystals greatly influences reactor fuel, which in turn degrades performance

Methods

Results

Conclusion