Fission gas release in BWR fuel with a burnup of 56 GWd/t during simulated reactivity initiated accident (RIA) condition

A pulse irradiation simulated reactivity initiated accident (RIA) condition was tested for the test rod prepared from a BWR fuel rod with a burnup of 56 GWd/t irradiated in a commercial reactor, and fission gas release during pulse irradiation was investigated based on the result of a rod-puncture test and the electron probe microanalysis of a fuel pellet. The local xenon concentration of a pulse-irradiated pellet decreased compared with that of a base-irradiated pellet in the relative radius range of 0 to approximately 0.8. The decrease in local xenon concentration corresponded to a fractional fission gas release of approximately 11%, and this value was comparable to the rod-puncture test result after pulse irradiation. Considering the microstructural change of the fuel pellet and the amount of gas retained in the grain boundary, it is likely that the fission gas release during pulse irradiation was affected by grain boundary separation, which occurred near the midradius rather than near the peripheral region of the fuel pellet during pulse irradiation.