A Versatile Approach to Determining the Fission Gas Release Threshold in UO2

Accurately predicting the onset of fission gas release under varying reactor operating conditions is essential for accounting for its effects in nuclear fuel safety qualification. The Vitanza threshold model has historically been used to predict the burnup at which the fission gas release fraction reaches 1% for a given fuel centerline temperature; however, it assumes commercial reactor conditions and neglects athermal fission gas diffusion. This work presents an analytical fission gas release threshold model for UO2 fuel that is a function of burnup and the fuel centerline and surface temperatures and is derived from mechanistic simulations performed using the BISON fuel performance code. The predictive capability of the model is evaluated primarily through Bland–Altman analysis using post-irradiation examination data, indicating improved accuracy and reduced variability in the differences between predicted and measured release thresholds relative to the Vitanza model.