Gaseous fission product release has a significant impact on nuclear fuel performance. Diffusion-based fission gas release (FGR) models are well established and well validated under steady-state conditions. However, under transient conditions gaseous fission gas release may be governed by different "burst" mechanisms which are not well captured by fuel performance codes. This benchmark is organised to examine the models for fission gas release during transients representative of anticipated operational occurrences (AOOs). The benchmark will utilise experimental cases which had transient powers high enough to ensure burst FGR, but low enough transient powers and short enough transient durations to ensure that diffusional FGR was minimal.

The objectives of this benchmark include:

• Improve understanding of burst FGR amongst NEA member organisations [in particular in Anticipated Operational Occurrences (AOOs) and Design Basis Accidents (DBAs)].
• Facilitate development of new fuel performance code models, or improvements of existing models, for burst FGR.
• Facilitate improvement in accuracy of FGR predictions and hence reduction in modelling uncertainties, increased margin to fuel performance limits (e.g. rod internal pressure), and increased plant flexibility.

The benchmark will be performed using two cases available in the International Fuel Performance Experiments (IFPE) database: REGATE and HATAC-C2