Analysis of MOX fuel behavior in Halden reactor by FEMAXI-6 code

Udagawa, Yutaka  ; Suzuki, Motoe; Fuketa, Toyoshi

Capabilities of the FEMAXI-6 code to analyze the behavior of high burnup MOX fuels in LWRs have been evaluated. Detailed power histories and specifications of the MIMAS-MOX fuel rods of IFA-597.4-7 irradiated in the Halden reactor were input, and calculated rod internal pressures and pellet center temperatures were compared with measured data for 0-31 MWd/kgUO. In the period up to 23 MWd/kgUO, the calculated pellet temperatures sufficiently agreed with the measured data and also the calculated rod pressures reproduced the tendency of increase in the measured rod pressures. These results suggest that fission gas release from MOX fuels can be reasonably predicted by diffusion process that is modeled in UO pellet grains. On the other hand, the steep increase in the measured rod pressure observed at 23 MWd/kgUO cannot be reproduced and can be regarded as the result of large amount of gas release, which possibly caused pellet-cladding-gap closure through pellet gas-bubble swelling.