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A New Mechanistic and Engineering Fission Gas Release Model for a Uranium Dioxide Fuel

A mechanistic and engineering fission gas release model (MEGA) for uranium dioxide (UO2) fuel was developed. It was based upon the diffusional release of fission gases from inside the grain to the grain boundary and the release of fission gases from the grain boundary to the external surface by the interconnection of the fission gas bubbles in the grain boundary. The capability of the MEGA model was validated by a comparison with the fission gas release data base and the sensitivity analyses of the parameters. It was found that the MEGA model correctly predicts the fission gas release in the broad range of fuel burnups up to 98MWd/kgU. Especially, the enhancement of fission gas release in a high-burnup fuel, and the reduction of fission gas release at a high burnup by increasing the UO2 grain size were found to be correctly predicted by the MEGA model without using any artificial factor.