Atomistic simulation of fracture in UO2 under tensile loading

Abstract

Density-functional-theory (DFT) calculations and molecular dynamics simulations were performed to resolve the fracture behavior in UO2 under tensile loading. By molecular dynamics simulation, potential dependence was identified on the existence of transient plastic deformation prior to intergranular fracture in polycrystalline UO2, so we further improved the Morelon interatomic potential based on GGA + U calculations to obtain reliable fracture behavior in UO2. Using the improved potential, the fracture behaviors in polycrystalline and single crystal UO2 under tensile loading were investigated. In polycrystalline UO2, brittle intergranular fracture was observed, and no phase transition was found. In single crystal, Fm3¯m-Pbcn and Fm3¯m-P42/mnm structural transitions were observed under <100> tensile loading. The non-coherent interfaces between Pbcn and P42/mnm phases play a critical role in microcrack formation. Under <110> tensile loading, only Fm3¯m-P42/mnm transition was detected and the interface between Fm3¯m and P42/mnm structures was coherent, so no crack was found until the end of the simulation with strain of 25% in <100> direction.