Models for fuel porosity evolution in UO2 under various regimes of reactor operation

•Analysis of experiments and critical assessment of models are presented.•Key models of the mechanistic MFPR code are overviewed and refined.•Development of new models allows notable improvement of the code predictions.

On the base of the additional analysis of experimental observations of porosity behaviour in UO2 fuel irradiated under various conditions of in-pile and out-of-pile tests as well as under normal and abnormal conditions of nuclear reactor operation, the key models of the mechanistic MFPR code are overviewed and refined. Some important modifications of the existing MFPR models and development of new models are presented.