Relationship Between Fuel Reliability and I-131/I-133 in the Primary Coolant of CPR1000 PWRs

The production and release of fission products in fuel rods and the primary coolant have been simulated by the kinetic model during the normal operation of a pressurized water reactor. The typical ratio of I-131/I-133 in the primary coolant has been theoretically estimated at the equilibrium conditions for intact fuels and fuel failure with small or large defects, respectively. The radiochemical data in the primary loops have been gathered and compiled from thirty-six cycles in the operating CPR1000 PWR units. The statistical results show that the predictions made by the model and the statistical results in the operating CPR1000 PWR units are qualitatively in agreement for both intact fuel and fuel failure. It also indicates that the conventional threshold I-131/I-133 ≥ 0.1 for fuel failure may cause misjudgment due to the overlap of distributions, and I-131/I-133 ≥ 0.15 can distinguish 98% operation date for intact fuel rods and 94% operation data for fuel failure.