Fission gas release in irradiated UO2 fuel at burnup of 45 GWd/t during simulated reactivity initiated accident (RIA) condition

Pulse irradiation simulating reactivity-initiated-accident (RIA) condition was conducted for test rod prepared from fuel irradiated in a commercial reactor and fission gas release behavior from fuel pellet during pulse irradiation was investigated. Optical microscopy (OM) and scanning electron microscopy (SEM) observations and electron probe micro analysis (EPMA) were carried out for the test rod as a part of destructive tests after the pulse irradiation. Fission gas release during pulse irradiation was evaluated by EPMA and puncture test. Xenon depression was observed in the fuel pellet after pulse irradiation at periphery and center region. It is considered that the xenon depression at pellet periphery was due to rim structure formation and fission gas was mainly released from the pellet center region during pulse irradiation. Comparing the fractional fission gas release during pulse irradiation with other results of out-of-pile annealing tests, it was concluded that most fission gas, which was accumulated at grain boundary during base irradiation, was released from the center region of test fuel pellet during pulse irradiation.