Pore pressure and swelling in the rim region of LWR high burnup UO2 fuel

Based on measured rim characteristics of LWR high burnup UO2 fuel, the pres sure of rim pores and the additional pellet swelling due to rim formation h ave been modeled. Using the assumption that the number of Xe atoms retained in the rim pores is the same as that which is depleted from the rim matrix , excessive pore pressure is derived as a function of temperature, pellet a verage burnup and pore radius. The rim pores with small radii are calculate d to be highly overpressurized at high burnup. Comparison with experimental data shows that, while the pellet swelling obtained with best-estimate rim width is underpredicted, the one calculated with conservative rim width ag rees well with the measured data for rim burnups between 50 and 65 GWd/tU. On the other hand, the measured swelling at 85 GWd/tU is about in-between t he two calculations. (C) 2001 Elsevier Science B.V. All rights reserved.