Interpretation of the VERCORS 4 and 5 experiments with the MFPR version 1.1 code is presented. MFPR is a mechanistic fission product (FP) release code which treats the main volatile and low volatility FPs. Fuel oxidation was predicted to be low with little impact on volatile FP release. Volatile fission products accumulate mainly in intragranular bubbles before being released. The calculated formation of intergranular bubbles appears too low implying that some changes to the modelling are necessary. Effects of grain growth were investigated as well as sensitivities to some other modelling parameters.