Molecular dynamics study of primary radiation damage in PuO2 and (U0.5Pu0.5)O2

Abstract

In this study, primary radiation damage in PuO2 and (U0.5Pu0.5)O2 is investigated as a function of temperature (300–1500 K) using MD simulations with 5 keV cascade. UO2 data from our previous work are used as reference. The interatomic potential develop by Cooper et al. has been used in this study. Time evolution of cascade generated defects is similar for different directions of primary knock on atom (PKA). Our results shows that the number of defects remaining after the cascade events in PuO2 is higher than that in UO2 at all temperatures. Defect concentration in (U,Pu)O2 is observed to be in between that of the pure oxides. The number of residual defects decreases as the temperature increases and finally tends to approach a plateau at elevated temperatures. The concentration of residual anion defects is considerably higher than that of cations in all oxides, while a decrease in the ratio of anion to cation defects with increasing temperature is observed. At lower temperature, the annihilation efficiency (ξ) of defect follows the trend ξPuO2 < ξUPuO2 < ξUO2. It is reported that both pure and mixed oxide fuels form defect clusters in the residual damage. The fraction of interstitial clusters is higher than the vacancy clusters; however, the size of these clusters is smaller than that of voids.