Uranium vacancy mobility at the sigma 5 symmetric tilt grain boundary in UO2

Uberuaga, Blas P.¹ 

[1] Los Alamos National Laboratory

关键词: BUBBLES;    BURNUP;    DEFECTS;    DIFFUSION;    DISLOCATIONS;    DISTRIBUTION;    FISSION;    FISSION PRODUCTS;    FUEL PINS;    GASES;    GRAIN BOUNDARIES;    IMPURITIES;    KINETICS;    PERFORMANCE;    SEGREGATION;    SWELLING;    TRANSPORT;    URANIUM;    VACANCIES;   

DOI  :  10.2172/1039684
RP-ID  :  LA-UR-12-21065
PID  :  OSTI ID: 1039684
Others  :  TRN: US1202274

美国|英语

来源: SciTech Connect

【 摘 要 】

An important consequence of the fissioning process occurring during burnup is the formation of fission products. These fission products alter the thermo-mechanical properties of the fuel. They also lead to macroscopic changes in the fuel structure, including the formation of bubbles that are connected to swelling of the fuel. Subsequent release of fission gases increase the pressure in the plenum and can cause changes in the properties of the fuel pin itself. It is thus imperative to understand how fission products, and fission gases in particular, behave within the fuel in order to predict the performance of the fuel under operating conditions. Fission gas redistribution within the fuel is governed by mass transport and the presence of sinks such as impurities, dislocations, and grain boundaries. Thus, to understand how the distribution of fission gases evolves in the fuel, we must understand the underlying transport mechanisms, tied to the concentrations and mobilities of defects within the material, and how these gases interact with microstructural features that might act as sinks. Both of these issues have been addressed in previous work under NEAMS. However, once a fission product has reached a sink, such as a grain boundary, its mobility may be different there than in the grain interior and predicting how, for example, bubbles nucleate within grain boundaries necessitates an understanding of how fission gases diffuse within boundaries. That is the goal of the present work. In this report, we describe atomic level simulations of uranium vacancy diffusion in the pressence of a {Sigma}5 symmetric tilt boundary in urania (UO{sub 2}). This boundary was chosen as it is the simplest of the boundaries we considered in previous work on segregation and serves as a starting point for understanding defect mobility at boundaries. We use a combination of molecular statics calculations and kinetic Monte Carlo (kMC) to determine how the mobility of uranium vacancies is altered at this particular grain boundary. Given that the diffusion of fission gases such as Xe are tied to the mobility of uranium vacancies, these results given insight into how fission gas mobility differs at grain boundaries compared to bulk urania.