عنوان مقاله [English]
One of the factors that changes the UO2 fuel thermal conductivity is the generated porosity in the fuel due to increasing burnup. At high burnups, the structure known as rim region, is created. This is due to the Xe depletion process from the fuel matrix, porosity formation, and fuel grain recrystallization, which in turn change the fuel thermal conductivity. In this paper by the use of existing low temperature high burnup fission gaseous swelling model with the progressive recrystallization for UO2 fuel, the matrix swelling terms are calculated and the evolution of the total volume porosity up to burnup of 120 MWd/kgU is estimated. For the study the effect of porosity formation on the irradiated UO2 thermal conductivity, the HALDEN correlation of the thermal conductivity is selected. Then, a porosity correction factor is developed based on an assumption that the fuel morphology is a three-phase type consisting of the pores, with no contribution to the matrix swelling and large pores due to intergranular bubbles with the contribution to matrix swelling dispersed in the fully dense material, composed of UO2 matrix and solid fission products. The predicted thermal conductivity, based on the present porosity correction factor, demonstrates an additional degradation of 25% due to porosity formation at the burnup levels around 120 MWd/kgU causing an increase in the fuel temperature.
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