Analysis of high-burnup fuel performance during load-follow operation

In Japan, an objective of the burnup extension of nuclear fuel is to raise the licensing limit of burnup from 39 to 48 GWd/t for pressurized water reactors (PWRs) in the near future. Because of an increasing ratio of nuclear power generation, the necessity of the load-follow operation, which responds flexibly to changing power demands, is more apparent. To evaluate accurately the mechanical integrity of PWR fuel at high burnup during a load-follow operation, the FEMAXI-III code, originally developed for analyses of fuel experiments, was modified, improving submodels to evaluate PWR fuel; the new code was named IRON. The results of verification work on the code using data on PWR fuel covering wide ranges of burnup and linear heat rate show that it has good predictability and, therefore, that the improvement was confirmed as effective.