Model for evolution of crystal defects in UO2 under irradiation up to high burn-ups

The model for dislocations evolution under irradiation conditions in UO2 is developed and implemented in the MFPR code. Being combined with the MFPR set of microscopic equations for the evolution of point defects and their interactions with gas bubbles, a self-consistent consideration of the whole system of point and extended defects in irradiated fuel, including point defects (vacancies, interstitials and gas atoms), as well as extended defects (bubbles, dislocations, vacancy loops and pores), is attained. The MFPR code with the new defect evolution model is successfully validated against steady-irradiation experiments, in which the dislocation density and the bubble concentration and mean size were directly measured as functions of burn-up at ≈1000 K. Being applied to higher temperatures, the code allows mechanistic interpretation of the temperature threshold for the fuel restructuring observed in the rim-zone of high burn-up UO2 fuel.