Simulation of radioactive fission gas release from defective PWR fuel rod using the MFPR/R mechanistic code

A software package was elaborated by coupling the mechanistic code MFPR/R with a recently developed advanced model of mass exchange in defective fuel rods, to simulate the release of radioactive gaseous fission products into the coolant during operation of a thermal reactor. To simulate the oxidation of UO2 fuel, the processes of steam dissociation and radiolysis in the rod free volume were additionally considered. The package was validated by calculating the release of krypton, iodine and xenon isotopes into the coolant from defective rods under irradiation in the pressurized light water loop of the NRX reactor at Chalk River Nuclear Laboratories. It is shown that a reasonable overall agreement between calculations and experiment for noble gas isotopes can be obtained by introducing a single fitting parameter that takes into account uncertainties in the rod geometry and the rate of hydrogen production in the rod free volume.